Recent advances in pristine/heterojunction bismuth
tungstate-based (photo)electrochemical sensing
strategies

Amira Nahdi, Salah Kouass, Hamdi Ben Halima, Nicole Jaffrezic-Renault

► To cite this version:

Amira Nahdi, Salah Kouass, Hamdi Ben Halima, Nicole Jaffrezic-Renault. Recent advances in pristine/heterojunction bismuth tungstate-based (photo)electrochemical sensing strategies. Microchemical Journal, 2025, 216, pp.114566. 10.1016/j.microc.2025.114566. hal-05185217

HAL Id: hal-05185217

https://hal.science/hal-05185217v1

Submitted on 25 Jul 2025

**HAL** is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire **HAL**, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
Review Article

Recent advances in pristine/heterojunction bismuth tungstate-based
(photo)electrochemical sensing strategies

Amira Nahdi<sup>a</sup>, Salah Kouass<sup>a</sup>, Hamdi Ben Halima<sup>b</sup>, Nicole Jaffrezic-Renault<sup>b,*</sup>

ARTICLE INFO

Keywords:

Bi₂WO₆

Heterojunction

Hole-trapping agent

Photoelectrochemical sensor

Photoelectrochemical biosensor

A B S T R A C T

Photoelectrochemical (PEC) sensors, which combine photocatalytic and electrochemical properties, have become a novel analytical tool. A PEC sensor's notable benefits include in-situ analyses, easy construction, portability, exceptional sensitivity, and cost-effectiveness. This review article presents bismuth tungstate-based electrochemical and photoelectrochemical sensors. Electrochemical sensors include pristine Bi₂WO₆-based sensors and rGO-Bi₂WO₆ composite-based sensors. Photoelectrochemical sensors are divided into five sections: pristine Bi₂WO₆-based sensors, Bi₂WO₆ heterojunction-based sensors, Bi₂WO₆ heterojunction-based sensors with hole-trapping agent, Bi₂WO₆ heterojunction-based label-free biosensors, and Bi₂WO₆ heterojunction-based sandwich-biosensors. Different heterojunctions have been obtained by associating narrow bandgap semiconductors (WO₃, CuS, Fe₂O₃, Bi₂S₃, Ag₂S, BiOBr, CuS, MoS₂, CdS), conductive carbon materials (g-C₃N₄, RGO), metallic nanoparticles (Au,Ag), or conductive polymers (polypyrrole, polydopamine) with Bi₂WO₆ crystals. Many sensors and biosensors provide a signal-on detection, whereas some sensors and biosensors, associated with a hole-trapping agent (ascorbic acid, hydrogen peroxide, sulfate), lead to a signal-off detection. Many molecules of health interest (metabolites, biomarkers, drugs) and a few pollutants have been detected with low detection limits. Additionally, the challenges for further large-scale applications of Bi₂WO₆-based sensors in the fields of health and environmental control are analyzed.

# 1. Introduction

Combining the photocatalytic and electrochemical methods, the photoelectrochemical (PEC) sensors are now novel analytical tools [1]. An affordable, green technique, this advanced method utilizing semiconductors shows promise for oxidizing a wide range of organic molecules [2–4]. The PEC sensor’s notable benefits include in-situ analyses, easy construction, portability, exceptional sensitivity, and cost-effectiveness [5]. The photoactivity of the semiconductor determines its sensitivity in the presence of the target [6–8]. Photon-active semiconductor material with visible absorptivity plays a critical role in the detection and remediation process [9,10]. PEC detection has a lot of advantages over other detection methods. As this method is based on different energy forms at input (light) and output (electricity), PEC detection, in general, is more sensitive than conventional electrochemistry and chemiluminescence [11]. PEC detection takes advantage of the high energy of the photogenerated charges and allows electrochemical reactions to be carried out at lower electrochemical potentials [12,13].

In addition, PEC instrumentation is less expensive and easier to minia-
turize compared with spectroscopic detection technologies, which
generally involve more sophisticated equipment [14,15]. The key point
is the choice of the photoactive semiconductor material [16,17]. It
should absorb light in a large wavelength range, be stable in function,
and present a large surface area with a large density of active sites
[18,19].

Bi₂WO₆ is an appealing semiconducting oxide that has found extensive use in the domains of sensors and photocatalysis [20]. As part of the generic formula Bi₂A n⁻₁BnO₃n⁺₁, this material is part of the Aurivillius phases family (n = 1), where A = K, Na, Bi, Pb, Ba, Sr, Ca, and B = Fe, W, Mo, Ta, Nb, Ti [21]. Fig. 1 shows the schematic structure of the Bi₂WO₆. Perovskite-like (WO₄) n 2n⁻ layers and alternating (Bi₂O₂) n 2n⁺ layers make up its orthorhombic structures [22,23].

Bismuth tungstate (Bi₂WO₆), a semiconductor oxide, presents several
physical and chemical properties, including ferroelectric [24,25], pho-
toluminescence [26], nonlinear dielectric induction [27], photocatalysis
[28,29], and others. Bi₂WO₆ presents good light absorption properties in

<footnote><sup>a</sup> LMTA, National Institute of Research and Physico-chemical Analysis (INRAP), Sidi Thabet, 2020 Tunis, Tunisia</footnote>

<footnote><sup>b</sup> UTINAM Institute, UMR CNRS 6213, Marie and Louis Pasteur University, 25030 Besançon, France</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: nicole.jaffrezic-renault@univ-fcomte.fr (N. Jaffrezic-Renault).</footnote>
<figure><img src="image_2.png" /><figcaption>Fig. 1. Structure of Bi₂WO₆. From [23] with permission.</figcaption></figure>

the visible range, due to its narrow band gap (2.69 eV) [30]. Because of its stable physicochemical characteristics, [31–33] Bi₂WO₆ offers a variety of benefits, including a direct band gap, quick charge separation, longer carrier separation lifetimes, and longer carrier transport distances. However, there are significant obstacles to further enhancing its electrochemical performance, including the limited light absorption efficiency of pure Bi₂WO₆ and poor electron transfer efficiency. To enhance the separation of electron(e⁻)-hole(h⁺) pairs and reduce needless carrier recombination effects, scientists have adjusted the physical shape and controlled the chemical composition. Large specific surface area and porous structures can improve the interaction between materials and organic compounds. As a result, scientists have created a range of Bi₂WO₆ morphologies, including single-crystal-like [34], helix-like [35], 3D microspherical [36], and 3D flower-like Bi₂WO₆ [37]. Of these three-dimensional structures, the flower-shaped Bi₂WO₆ has a huge surface area and a remarkable ability to separate charge carriers produced by photolysis. The primary areas of concentration for composition tuning include heterostructures [38], element doping [39], noble metal loading [40], and so forth. Nevertheless, the absorption edge of pristine Bi₂WO₆ is around 450 nm [41], and it presents a wide band gap that limits solar energy harvesting. Moreover, its photo-conversion efficiency is limited due to numerous charge recombinations [42]. As shown in this review article, two main ways were adopted to enhance the photoelectrochemical response of pristine Bi₂WO₆: building a heterojunction by the association of two or more semiconductors and adding a hole-trapping agent.

Seven recent reviews (2023–2024) deal with the photocatalytic properties of bismuth tungstate [43–49]. A review of photo-electrochemical architectures for biosensing was published in 2018 [11] in which a few semiconductors were cited (CdTe, CdS, PbS, WS₂, ZnO). To date, no review has been published about the electrochemical and photoelectrochemical applications of Bi₂WO₆. This review article presents Bi₂WO₆-based electrochemical and photoelectrochemical sensors. Electrochemical sensors include pristine Bi₂WO₆-based sensors and rGO-Bi₂WO₆ composite-based sensors. Photoelectrochemical sensors are divided into pristine Bi₂WO₆-based sensors, Bi₂WO₆ heterojunction-based sensors, Bi₂WO₆ heterojunction-based sensors with hole-

trapping agents, Bi₂WO₆ heterojunction-based label-free biosensors, and Bi₂WO₆ heterojunction-based sandwich-biosensors. Detected targets are in two main fields: health (vitamins, neurological molecules, metabolites, biomarkers, drugs), and the environment (estrogens, heavy metals, pesticides) Tables 1 and 2.

## 2. Methods for the synthesis and characterization of Bi₂WO₆

The physical structure and form of Bi₂WO₆ are intimately related to its dimensional morphology. It is important to understand the influence of diverse synthesis techniques and morphologies on Bi₂WO₆, as they significantly affect its characteristics and properties [35].

### 2.1. Hydrothermal/solvothermal method

Hydrothermal synthesis is one of the methods used to synthesize Bi₂WO₆ [50–52]. The reaction between bismuth and tungsten precursors in an aqueous solution at high pressure and temperature is promoted by either using an autoclave or a sealed container. Through this method, the size, shape, and crystal structure of the particles can be precisely controlled, leading to improved characteristics and the creation of Bi₂WO₆. It should be highlighted, nonetheless, that in comparison to other methods, this approach needs more specialized equipment and more prolonged reaction times. The solvothermal method, a further option, is comparable to the hydrothermal approach [53]. Adjusting variables such as reaction temperature, time, precursor concentration, and pH enables control over the crystal structure of Bi₂WO₆ particles and their shape and size. However, longer processes and more specialized equipment are required for the solvothermal approach.

### 2.2. Sol-gel synthesis

The sol-gel process allows the regulation of composition, homogeneity, and purity, and it provides the ability to incorporate dopants. It is imperative to realize that this procedure is notably complex, involving several stages. Both gel formation and the next thermal treatment require longer processing periods. [54,55].

### 2.3. Solid-state technique

This easy and economical approach involves the high-temperature solid-state reaction between tungsten oxide (WO₃) and bismuth oxide (Bi₂O₃) [56]. Nevertheless, applying high temperatures may alter the crystal structure and cause larger crystals to form particle aggregation. This may therefore have an impact on the material’s optical, electrical, and catalytic characteristics in addition to its possible uses [57,58].

### 2.4. Microwave irradiation process

In summary, a reaction mixture containing precursors for tungsten and bismuth is heated using microwave radiation [59]. There are many benefits to this method, including quick heating and quicker reaction times. Furthermore, in comparison to traditional techniques, it yields better phase purity and increased crystallinity. A few disadvantages should be taken into account. This method’s capacity to scale up for mass production is constrained. Carefully adjusting the reaction parameters is essential to avoid the development of localized hotspots.

### 2.5. Other synthesis methods

The ion-exchange method [60], co-precipitation method [61], electro-spinning method [62,63], ultrasonic spray pyrolysis [64], ultrasonic chemical method [65], sucrose template method [66], and so on are some of the other formation methods of Bi₂WO₆ that have been reported to date.
<table><caption>**Table 1**
Bi₂WO₆ based electrochemical sensors</caption><thead><tr><th>Modified electrode</th><th>Analyte</th><th>Technique</th><th>Linear range</th><th>Detection Limit (LOD)</th><th>Reference</th></tr></thead><tbody><tr><td colspan="6"><strong>Pristine Bi₂WO₆-based electrochemical sensors</strong></td></tr><tr><td>Bi₂WO₆ (hollow spheres)/GCE</td><td>Riboflavin</td><td>DPV</td><td>0.03–457 µM</td><td>3.65 nM</td><td>[50]</td></tr><tr><td>Nafion/HRP/3D-Bi₂WO₆/GCE</td><td>H₂O₂</td><td>Amperometry</td><td>0.5 to 250 µM</td><td>180 nM</td><td>[73]</td></tr><tr><td>Bi₂WO₆ (nanosheets)/GCE</td><td>Sudan I</td><td>DPV</td><td>0.02–114.6 µM</td><td>2 nM</td><td>[74]</td></tr><tr><td>Bi₂WO₆ (nanoplates)/CPE</td><td>Diethylstilbestrol</td><td></td><td>50–2100 nM</td><td>15 nM</td><td>[75]</td></tr><tr><td></td><td>Bisphenol A</td><td></td><td>70–1300 nM</td><td>20 nM</td><td></td></tr><tr><td colspan="6"><strong>Bi₂WO₆-rGO composite-based electrochemical sensors</strong></td></tr><tr><td>Bi₂WO₆ (nanospheres)/rGOS/GCE</td><td>4-Nitroquinoline N-oxide</td><td>Amperometry</td><td>0.025–718 µM</td><td>6.11 nM</td><td>[76]</td></tr><tr><td>Bi₂WO₆ (flower-shaped microspheres)/rGO/GCE</td><td>Artemisinin</td><td>DPV</td><td></td><td>10 nM</td><td>[77]</td></tr><tr><td>Bi₂WO₆ (flowers)@GNRs (nanoribbons)/SPCE</td><td>Hydroquinone (HQ)</td><td>DPV</td><td>0.021–1550 µM</td><td>7.51 nM</td><td>[78]</td></tr><tr><td></td><td>Catechol (CC)</td><td></td><td>0.021–1550 µM</td><td>5.31 nM</td><td></td></tr><tr><td colspan="6"><strong>Bi₂WO₆ composite-based electrochemical biosensor</strong></td></tr><tr><td>Bi₂WO₆/Bi₂S₂/FTP</td><td>SARS-CoV-2 (COVID-19)</td><td>DPV of H₂O₂</td><td>0.01–1.00 pg.mL⁻¹</td><td>3.0 fg.mL⁻¹</td><td>[79]</td></tr><tr><td>g-C₃N₄/Au/WO₃ labeled secondary antibody</td><td>Sandwich immunosensors</td><td></td><td></td><td></td><td></td></tr></tbody></table>

<table><caption>**Table 2**
Bi₂WO₆-based photoelectrochemical sensors.</caption><thead><tr><th>Modified electrode</th><th>Analyte</th><th>Technique</th><th>Linear range, Sensitivity</th><th>Limit of Detection (LOD)</th><th>Refs</th></tr></thead><tbody><tr><td colspan="6"><strong>Pristine Bi₂WO₆-based photoelectrochemical sensors</strong></td></tr><tr><td>Bi₂WO₆-V (nanocrystal with O-vacancies)</td><td>H₂O₂</td><td>chromoamperometry</td><td>1.5–2.2 mM (0.14 mA/mM)</td><td>500 nM</td><td>[81]</td></tr><tr><td>Br-terminated 2D Bi₂WO₆ nanosheets/GCE</td><td>Sulfamethoxazole</td><td>DPV</td><td>22 mM–230 mM</td><td>3560 nM</td><td>[82]</td></tr><tr><td>3D biconcave-shaped Bi₂WO₆/Al/aluminum foil</td><td>Nicotine</td><td>Amperometry</td><td>0–40 µM</td><td>13 nM</td><td>[83]</td></tr><tr><td colspan="6"><strong>Bi₂WO₆ heterojunction-based photoelectrochemical sensors</strong></td></tr><tr><td>CoTAPc-GO/Cu doped-Bi₂WO₆/ITO</td><td>Dopamine</td><td>PEC</td><td>0.05–5.0 µM</td><td>72 nM</td><td>[40]</td></tr><tr><td>Bi₂WO₆/TiO₂-Ag</td><td>Dopamine</td><td>PEC (CV)</td><td>0.1782 mA/cm²</td><td></td><td>[84]</td></tr><tr><td>Bi₂WO₆@g-C₃N₄/FTO</td><td>Dopamine</td><td>PEC</td><td>0.1–10 µM</td><td>28 nM</td><td>[85]</td></tr><tr><td>Bi₂WO₆/WO₃/g-C₃N₄/GCE</td><td>Dopamine</td><td>PEC (DPV)</td><td>10 µM–120 µM</td><td>10 nM</td><td>[86]</td></tr><tr><td>Bi₂WO₆ nanosheets/TiO₂ NTAs/Ti</td><td>Glucose</td><td>PEC</td><td>0–2500 µM</td><td>4300 µM</td><td>[87]</td></tr><tr><td>Flower-like hallow Bi₂WO₆/RGO/ITO</td><td>Diethylstilbestrol</td><td>PEC</td><td>0.1–1200 pM</td><td>0.06 pM</td><td>[88]</td></tr><tr><td>Bi–CuS decorated Bi₂WO₆/ITO</td><td>Paracetamol</td><td>PEC</td><td>0.01–60 mM</td><td>2.12 nM</td><td>[89]</td></tr><tr><td>α-Fe₂O₃ decorated Bi₂WO₆/FTO</td><td>Tetracycline</td><td>PEC</td><td></td><td>300 nM</td><td>[90]</td></tr><tr><td>N-GQDs decorated Bi₂WO₆/ITO</td><td>Pentachlorphenol</td><td>PEC</td><td>0.2 pM – 1000 pM</td><td>0.06 pM</td><td>[91]</td></tr><tr><td colspan="6"><strong>Bi₂WO₆ heterojunction-based photoelectrochemical sensors with hole-trapping agent</strong></td></tr><tr><td>Flakes of Bi₂S₃ on flower core Bi₂WO₆/FTO+ SO₄ (hole-trapping agent)</td><td>Ofloxacin</td><td>PEC<br>(decrease of photocurrent)</td><td>1 µM – 100 µM</td><td>906 nM</td><td>[92]</td></tr><tr><td>Bi₂S₃/Bi₂WO₆ nanosheets/FTO + AA (hole-trapping agent)</td><td>Azomycin</td><td>PEC<br>(decrease of photocurrent)</td><td>0.1–500 µM</td><td>24 nM</td><td>[93]</td></tr><tr><td colspan="6"><strong>Bi₂WO₆ heterojunction-based label-free biosensors</strong></td></tr><tr><td>TiO₂@hallow macrospheres Bi₂WO₆/Ag₂S/ITO + AA (hole-trapping agent)</td><td>SARS-COV-2</td><td>PEC</td><td>0.001–50 ng/mL</td><td>0.38 pg/mL</td><td>[94]</td></tr><tr><td>Bi₂WO₆/BiOBr/ITO + AA (hole-trapping agent)</td><td>Prostate-specific antigen (PSA)</td><td>PEC signal-off detection</td><td>0.001–50 ng/mL</td><td>0.084 pg/mL</td><td>[95]</td></tr><tr><td>rGO-BWO/FTO</td><td>MicroRNA</td><td>PEC</td><td>1.0 fM–1.0 nM</td><td>0.47 fM</td><td>[96]</td></tr><tr><td>Au/Ag₂S/rare-earth doped Bi₂WO₆/ITO + AA</td><td>Vibrio parahaemolyticus</td><td>PEC</td><td>3.2 × 10²–3.2 × 10⁸ CFU/mL</td><td>40 CFU/mL</td><td>[97]</td></tr><tr><td>rGO-Bi₂WO₆/Au/FTO + AA</td><td>Kanamycin</td><td>PEC</td><td>1 pM–5 nM</td><td>0.78 pM</td><td>[98]</td></tr><tr><td>CuS/MoS₂/Bi₂WO₆/ITO + AA</td><td>Pb²⁺</td><td>PEC</td><td>0.01–50 µM</td><td>3.3 nM</td><td>[99]</td></tr><tr><td>Bi₂WO₆-rGO/ITO</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td colspan="6"><strong>Bi₂WO₆ heterojunction-based sandwich-biosensors</strong></td></tr><tr><td>polypyrrole@Bi₂WO₆/ITO + ALP labeled Ab2</td><td>Creatinine kinase MB</td><td>PEC</td><td>0.5–2000 ng/mL</td><td>0.16 ng/mL</td><td>[101]</td></tr><tr><td>Bi₂WO₆/CdS:Mn/ITO + NaYF₄:Yb, Tm labeled Ab2</td><td>Procalcitonin</td><td>PEC (DPV)</td><td>0.5 pg/mL–100 ng/mL</td><td>0.13 ng/mL</td><td>[102]</td></tr><tr><td>Ag₂S on flower like Bi₂WO₆/ITO + GO/PDA labeled Ab2</td><td>NT-pro BNP</td><td>PEC</td><td>0.1 pg/mL–100 ng/mL</td><td>0.03 pg/mL</td><td>[103]</td></tr><tr><td>Bi₂WO₆/CdS/ITO + Mn:CdSe labeled Ab2</td><td>Amyloid beta (Aβ)</td><td>PEC</td><td>0.2 pg/mL–50 ng/mL</td><td>0.068 pg/mL</td><td>[104]</td></tr></tbody></table>
## 2.6. Characterization methods

Using X-ray powder diffraction (XRD), the various phases of the produced Bi₂WO₆ can be distinguished [67]. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used to examine the various morphological features of the manufactured Bi₂WO₆ [54]. Surface area analysis (BET) is used to measure the surface area of the produced Bi₂WO₆ [68]. Vibration modes can be determined in connection to molecular dynamics using Raman spectroscopy [69]. Moreover, X-ray photoelectron spectroscopy (XPS) [70] and Fourier-transform infrared spectroscopy (FTIR) [71] are used to determine the surface chemical groups of the produced Bi₂WO₆. Impedance spectroscopy is used to find the frequency-dependent conductivity spectra [72].

# 3. Bi₂WO₆-based electrochemical sensors

Bi₂WO₆ materials are valuable for sensor development. Two types of electrochemical sensors are described: pristine Bi₂WO₆-based and Bi₂WO₆-rGO composite-based ones. rGO-based composite presents the advantages of improving the stability of the nanomaterials and their electrocatalytic properties, and providing new active sites.

## 3.1. Pristine Bi₂WO₆-based electrochemical sensors

### 3.1.1. Molecules of health interest

- Vitamin B2 (Riboflavin)

Vitamins are organic substances that are necessary for the regular functioning of our body's metabolic rate; their deficiency causes a variety of illnesses. Amalraj et al. [50] synthesized Bi₂WO₆, with the assistance of PVP and NaOH, for GCE functionalization, and DPV was used to monitor the electro-oxidation and reduction of riboflavin. The tested concentration range was 0.03–457 µM, while the LOD and sensitivity were 3.65 nM and 1.14 µA µM⁻¹ cm⁻², respectively, in reduction and in oxidation, 8.9 nM and 0.95 µA µM⁻¹ cm⁻², respectively.

- Hydrogen peroxide

Using a simple hydrothermal process, three-dimensional flower-shaped Bi₂WO₆ microspheres are created by Liu and al [73], which are then utilized to create an enzyme-free sensor for H₂O₂ detection. The Nafion/HRP/3D-Bi₂WO₆/GCE sensor has a broad linear range for H₂O₂ measurements, ranging from 0.5 to 250 µM, and a low LOD of 0.18 µM.

### 3.1.2. Environmental pollutants

- Sudan I

Synthetic azo dye Sudan I (1-phenylazo-2-naphthol) is frequently used to color industrial products; it can then be found in industrial effluents [74]. The electrochemical determination of Sudan I was conducted using the as-synthesized Bi₂WO₆ nanosheets to modify a GCE surface. Using DPV procedures, a broad linear range of 0.02 to 114.6 µM was obtained, with a good sensitivity (3.0563 µA µM⁻¹) and a low LOD (2 nM) (S/N = 3) [74].

- Diethylstilbestrol and bisphenol A

Diethylstilbestrol has been widely used as a growth promoter in animal feed, and bisphenol A for the industrial production of epoxy resins. They are both environmental estrogens. For the sensitive and simultaneous detection of diethylstilbestrol (DES) and bisphenol A (BPA), Bi₂WO₆ nanoplates were introduced in a CPE. With a LOD of 15 nM for DES and 20 nM for BPA, the Bi₂WO₆/CPE displayed wide linear

ranges of 50–2100 nM and 70–1300 nM, respectively. [75].

## 3.2. Bi₂WO₆-rGO composite-based electrochemical sensors

### 3.2.1. Molecules of health interest

- 4-Nitroquinoline N-oxide (4-NQO)

4-Nitroquinoline N-oxide, or 4-NQO, produced from cancer tumorigenic cells, is used as a biomarker [80]. Muthumariyappan et al. present the sonochemical design of novel Bi₂WO₆ Nanospheres coupled with reduced graphene oxide (Bi₂WO₆/rGOS) nanocomposite. The GCE, modified with Bi₂WO₆/rGOS nanocomposite, exhibited good electrocatalytic activity with a nanomolar detection limit of 6.11 nM. Additionally, a good recovery was obtained in human blood and urine samples [76].

- Artemisinin

Artemisinin is an antibiotic used for the treatment of malaria. The developed bismuth tungstate-treated rGO was shown to have a LOD of 10 nM. Compared to other antibiotics, a high selectivity for artemisinin is observed [77].

### 3.2.2. Environmental pollutant

- Dihydroxybenzene isomers (catechol and hydroquinone)

Dihydroxybenzene isomers, including hydroquinone (HQ) and catechol (CC), are extensively utilized in manufacturing medications, colors, cosmetics, and insecticides. Better electrocatalytic activity was shown by the Bi₂WO₆@GNRs (graphene nanoribbons) composite-modified SPCE in the redox reactions of HQ and CC. The Bi₂WO₆@GNRs integrated sensor showed LODs of 5.31 nM and 7.24 nM, for CC and HQ respectively. The composite-modified electrode's enhanced electrocatalytic capacity is demonstrated by its much larger specific surface area, excellent interface conductivity, and readily accessible catalytic sites [78].

## 3.3. Bi₂WO₆ composite-based electrochemical biosensor

### 3.3.1. Molecules of health interest

- Coronavirus pneumonia (COVID-19)

A sandwich-type electrochemical SARS-CoV-2 (COVID-19) nucleocapsid protein immunosensor was developed by Karaman et al. [79], based on bismuth tungstate/bismuth sulfide composite (Bi₂WO₆/Bi₂S₃) for electrode modification and graphitic carbon nitride sheet decorated with gold nanoparticles (Au NPs) and tungsten trioxide sphere (g-C₃N₄/Au/WO₃) as signal amplification (Fig. 2). The electrochemical detection of H₂O₂ increased in the presence of the labeled secondary antibody, after the capture of SARS-CoV-2 nucleocapsid protein (SARS-CoV-2 NP). SARS-CoV-2 NP was successfully detected in a tiny saliva sample (100.0 µL) in 30 mins, with a LOD of 3.00 fg mL⁻¹.

# 4. Photoelectrochemical sensors

## 4.1. Pristine Bi₂WO₆-based photoelectrochemical sensors

### 4.1.1. Molecules of health interest

- Hydrogen peroxide (H₂O₂)

When highly active natural or consumable water is improperly treated, pollutants like hydrogen peroxide (H₂O₂) are frequently
<figure><img src="image_3.png" /><figcaption>**Fig. 2.** Scheme of the fabrication steps of the electrochemical SARS-CoV-2 immunosensor. Ag: SARS-CoV-2 nucleocapsid protein (Ag); Bi₂WO₆; AuNPs.</figcaption></figure>

released into the environment. Accurate and quick detection of H₂O₂ is difficult due to its wide concentration range and short half-life time under various sample circumstances [105]. Tong et al. [81] presented a photoelectrochemical (PEC) sensor for H₂O₂ detection using Bi₂WO₆ nanocrystal with abundant oxygen vacancy (Bi₂WO₆-V). When exposed to visible light, the Bi₂WO₆-V PEC sensor's H₂O₂ LOD is 0.5 µM, which is ten times higher than without light. This PEC sensor presents a good selectivity, a high reaction time, and a detection range from 1.5 µM to 230 mM.

- Antibiotic: sulfamethoxazole

Hu and colleagues (2021) have used two-dimensional (2D) Bi₂WO₆ nanosheets to detect the antibiotic sulfamethoxazole (SMX) [82]. Under light irradiation, the ultrathin 2D Bi₂WO₆ nanosheet electrode exhibits a remarkable photochemical regenerative ability and efficient detection capabilities. 3.56 µM was the detection limit. The Br-terminated 2D Bi₂WO₆ nanosheet electrode's narrower semicircle suggests lower resistance compared to the O-terminated bulk Bi₂WO₆ electrode. All of the findings demonstrate that Br-terminated 2D Bi₂WO₆ nanosheets exhibit superior photogenerated carrier separation behavior than O-terminated bulk Bi₂WO₆. The hydrophilic characteristic of Bi₂WO₆'s surface is well-regulated by adding bromine, which is in situ generated by the surface ligand exchange process [82].

- Nicotine

For photoelectrochemical nicotine detection in human sweat and cigarette samples, Veeralingam et al. [83] present a single-step hydrothermal synthesis of three-dimensional (3D) biconcave-shaped Bi₂WO₆ nanostructures. When exposed to nicotine, the manufactured sensor showed a broad linear range of 50 nM - 100 µM and a sensitivity of 56.97 ± 2 µM⁻¹, with a LOD of 13 nM in the presence of UV light and 26 nM without light.

## 4.2. Bi₂WO₆ heterojunction-based photoelectrochemical sensors

### 4.2.1. Molecules of health interest

- Neurotransmitter: dopamine

Since 2019, three studies have focused on using Bi₂WO₆ for the electrochemical detection of dopamine (DA). Jinyun Peng and colleagues (2019) [40] developed a novel sensor for the photo-electrochemical detection of DA, based on the CoTAPc-GO (Cobalt

Tetraaminophthalocyanine functionalized Graphene Oxide)/Cu doped Bi₂WO₆/ITO electrode. The LOD was 0.072 µmol L⁻¹ (S/N = 3) under ideal conditions. The photocurrent response signals demonstrated a good linear relationship with the DA concentrations in two concentration ranges of 0.05–5.0 µmol L⁻¹ and 5.0–250.0 µmol L⁻¹. Fig. 3A presents a schematic illustration of the PEC mechanism for the determination of DA.

In another study, Kavinkumar et al. (2021) synthesized a Bi₂WO₆/TiO₂-Ag (BWTA) ternary composite to detect DA photoelectrochemically [84] (Fig. 3B). A high redox current response was observed for the BWTA2.0 specimen at 0.1782 mA/cm².

Wu et al. (2023) [85] developed a simple, inexpensive cathodic photoelectrochemical (PEC) sensor based on Bi₂WO₆@g-C₃N₄ (BWO-0.1CN) to detect DA [85]. The linear ranges have a sensitive LOD of 0.28 µM and are 0.1–10 µM and 10–250 µM. The potential method for selective DA detection on the Bi₂WO₆@g-C₃N₄/FTO electrode is depicted in Fig. 3C.

The design of a triphasic composite material Bi₂WO₆/WO₃/g-C₃N₄ (BWWCN) introduces a novel approach to enhance photo-electrochemical sensor performance. It was applied to the photo-electrochemical detection of dopamine, on a GCE [86] (Fig. 3D). The dopamine photoelectrochemical sensor also presents a large linear detection range (0.01-110 µM) and a low LOD of 0.01 µM. Additionally, it presents remarkable stability and reproducibility, making it possible to measure dopamine in saliva with a satisfactory recovery.

The detection of dopamine was obtained with four different configurations (Fig. 3):

A) CoTAPc-GO (Cobalt Tetraaminophthalocyanine Functionalized Graphene Oxide)/Cu doped Bi₂WO₆ [40]. A LOD of 0.072 µM was obtained.

B) Bi₂WO₆/TiO₂-Ag [84]. A sensitivity of 0.1782 mA/cm² was obtained.

C) Bi₂WO₆/g-C₃N₄ [85]. A LOD of 0.28 µM was obtained.

D) Bi₂WO₆/WO₃/g-C₃N₄ [86]. A LOD of 0.01 µM was obtained.

For all configurations, the current increases when the concentration of dopamine increases. The lower detection limit is obtained with the composite Bi₂WO₆//WO₃/g-C₃N₄. The proposed mechanism represents the processes of photo-excited electron-hole separation in a double Z scheme system, as schematically illustrated in Fig. 3D. Exposure to visible light can cause WO₃, g-C₃N₄, and Bi₂WO₆ to form photo-generated electron/hole pairs because of their band gaps of roughly 2.77, 2.97, and 2.79 eV, respectively. Under visible light, the photo-induced electrons on the CB of WO₃ (0.54) can instantly be moved with the holes on the VB of Bi₂WO₆ (1.77), whereas the excited electrons held in the CB of Bi₂WO₆ (−1.04 eV) prefer to recombine with the holes
<figure><img src="image_4.png" /><figcaption>Fig. 3. Schematic illustrations of the PEC mechanism for determination of DA (A) From [40]. (B) from [84] with permission. (C) from [85]; (D) from [86].</figcaption></figure>

kept on the VB of g-C₃N₄ (1.10 eV). Afterward, it is possible to transfer the remaining electrons in the g-C₃N₄ CB to the GCE substrate. The oxidation process is carried out simultaneously by the VB of WO₃'s remaining holes. Because holes on the VB of WO₃ (+3.51 eV) have a higher oxidation potential and electrons on the CB of g-C₃N₄ (-1.66 eV) have a substantially larger reduction potential, which may hinder the recombination process. The ternary nanocomposite exhibits increased photo-electrochemical activity due to electron-hole pairs being separated from one another and accumulating in various locations. The developed double Z-scheme system facilitates electron-hole pair separation, which improves PEC performance in the Bi₂WO₆/WO₃/g-C₃N₄ modified photo-electrode. Compared to configuration 3C (Bi₂WO₆/g-C₃N₄), the presence of WO₃ increases the concentration of holes for dopamine oxidation. Configuration A is a rather good configuration, whereas configuration B is not favorable due to the large TiO₂ bandgap.

- Metabolite: glucose

For the photoelectrochemical detection of glucose, Pang et al. prepared Bi₂WO₆/TiO₂ NTAs sensor. The obtained sensor presents a detection sensitivity of 0.244 µA mM⁻¹, a linear range of 0 to 2500 µM, and a LOD of 4.3 µM [87]. The improvement in photoelectrochemical performance is not due to the change in optical absorption brought about by Bi₂WO₆ deposition on TiO₂ nanotubes. The photocurrent produced by the electron transfer from TiO₂ to the Ti substrate is reduced by the electron transfer from the CB of TiO₂ to the CB of

Bi₂WO₆. The holes on the Bi₂WO₆ nanosheets that were transferred from TiO₂ had a high activity in the direct oxidation of organics and a low activity in the formation of • OH radicals [87].

- Synthetic estrogen: diethylstilbestrol (DES)

Diethylstilbestrol is a synthetic estrogen, used as a growth promoter for livestock production. Cai et al. [88] produced flower-like hollow Bi₂WO₆ (FHBWO) nanoparticles, which were then grown in situ on the surface of reduced graphene oxide (RGO) to construct a 3D structural FHBWO/RGO composite, using a one-pot hydrothermal technique, for the detection of diethylstilbestrol (DES). Compared to pristine Bi₂WO₆, the produced nanocomposites exhibited much higher photoactivity. The addition of RGO substantially accelerated electron transfer, and the photocurrent was boosted nine times. The adsorbed DES molecules onto the FHBWO/RGO surface significantly impede the electron-transfer character and cause the recombination of photogenerated holes and electrons, which reduces the photocurrent. The PEC sensor presents a detection range of 0.1 pM to 1200 pM with a LOD of 0.06 pM. Fig. 4 presents the schematic mechanism of the PEC sensor based on FHBWO/RGO 0.35 composite for DES detection.

- Anti-inflammatory drug: paracetamol

Paracetamol (PA) is a non-steroidal anti-inflammatory drug, mainly used to treat headaches, arthritis, osteoarthritis, and other diseases. Li
<figure><img src="image_5.png" /><figcaption>Fig. 4. Schematic mechanism of DES detection with the PEC sensor. From [88] with permission.</figcaption></figure>

et al. [89] created a Bi–CuS/Bi₂WO₆ ternary nanocomposite and used it to create a unique PA PEC sensing platform. The photocurrent increases linearly with PA concentration between 0.01 and 60 mM, with a 2.12 nM LOD. In the potential mechanism for the detection of PA, CuS and Bi₂WO₆ were reported to have respective band gaps of 2.18 and 2.82 eV. In addition, the CuS had higher conduction band (CB) and valence band (VB) locations than the Bi₂WO₆. When exposed to radiation, CuS nanoparticles can be excited, causing the formation of holes (h⁺) and electrons (e⁻). Because of its advantageous conductivity and SPR effect, bimetal (Bi) can be used as an electron conductor or as a component to enhance PEC activity. Since their CB energy levels differ, the photo-generated electrons then quickly go to Bi₂WO₆. Those isolated holes on Bi₂WO₆ VB penetrate CuS to oxidize PA.

- Antibiotic: tetracycline

Tetracyclines (TCs) are antibiotics used to treat infections in animals, and humans. Adhikari et al. presented a heterojunction photoelectrode that combined the wet chemical synthesis of Bi₂WO₆ with the atomic layer deposition (ALD) approach to generate a layer of Fe₂O₃ to detect tetracycline [90]. At an external bias of 0.6 V, the performance of 15-nm Fe₂O₃–Bi₂WO₆ heterojunction is 4.3 µA/cm², 3.6 times greater than that of pure Bi₂WO₆ (1.2 µA/cm²). The antibiotic was detected with a 0.3 µM LOD.

### 4.2.2. Environmental pollutants

- Pesticide: pentachlorophenol

Any chemical or organism used to manage, get rid of, repel, or lessen the effects of a pest is referred to as a pesticide. The main issue with them is their buildup in the food chain because they are the most used items in the agri-food sector. The Maximum Residual Limits (MRLs) permitted by law in the European Union are 0.5 µg/L for the total and 0.1 µg/L for each pesticide [106]. As a result, from water and soil to human bodies, they must be closely regulated and observed in the food chain.

Combining the benefits of Bi₂WO₆ with nitrogen-doped graphene quantum dots (NGQDs), Hao et al. used the solvothermal approach to create NGQDs decorated Bi₂WO₆ (Bi₂WO₆/N-GQDs) for the photo-electrochemical detection of pentachlorophenol (PCP) [91]. Under ideal circumstances, the as-obtained Bi₂WO₆/N-GQDs hybrid materials showed exceptional photocurrent responsiveness, six times higher than pure Bi₂WO₆ NPs. This suggested PEC sensor showed a low LOD of 0.06 pM and a broad detection range of 0.2 pM to 1000 pM. The schematic diagram of the PEC sensor for PCP detection based on Bi₂WO₆/N-GQD hybrid materials is similar to that of the PEC sensor for diethylstilbestrol (DES) (Fig. 4).

## 4.3. Bi₂WO₆ heterojunction-based sensors with hole-trapping agent

### 4.3.1. Molecules of health interest

- Antibiotic: ofloxacin

Ofloxacin is a fluoroquinolone antibiotic. Adhikari et al. [92] investigated a new sensor, the Bi₂S₃/Bi₂WO₆/FTO modified electrode, which demonstrated a high performance for ofloxacin detection over a broad linear range of 1 µM to 100 µM, with a LOD of 0.906 µM. As a result, 10 wt% Bi₂S₃/Bi₂WO₆/FTO shows ofloxacin oxidation under applied bias to linearly determine this antibiotic. The effective charge separation is achieved by quenching electron-hole pair recombination by heterojunction creation between Bi₂S₃ and Bi₂WO₆. The transient photocurrent responses of Bi₂S₃/Bi₂WO₆/FTO, in the presence of 0.5 M Na₂SO₄ (hole-trapping agent), with the successive addition of different molar concentrations of the antibiotic, decreased linearly as a function of the concentration logarithm.

### 4.3.2. Azomycin

Azomycin is an emerging antibiotic against protozoan infections. Based on the Bi₂S₃/Bi₂WO₆ heterostructure, Yu et al. [93] created a superb PEC sensor that uses ascorbic acid (AA) as a hole-trapping agent to detect azomycin. The distribution of Bi₂S₃ on the Bi₂WO₆ nanosheets
significantly raises the specific surface area and active sites by preventing the nanosheets from grouping to create a hierarchical structure. Moreover, the coupling effect between Bi₂S₃ and Bi₂WO₆ creates a heterojunction, which modifies Bi₂WO₆'s electronic structure, narrows its band gap, and substantially promotes charge transfer, boosting the number of photogenerated electron-hole pairs. By inhibiting photocarrier recombination, the hole-trapping compound AA greatly raises the PEC sensor's detection sensitivity. The steric hindrance effect of the adsorbed azomycin may quench the photocurrent intensity of the Bi₂S₃/Bi₂WO₆ heterostructure, and this intensity diminishes as the concentration of azomycin increases. The LOD was 0.024 µM.

## 4.4. Bi₂WO₆ heterojunction-based label-free biosensors

### 4.4.1. Molecules of health interest

- Coronavirus pneumonia (COVID-19)

A global pandemic arose from the 2019 coronavirus illness (COVID-19), called Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-COV-2). It is therefore crucial to diagnose SARS-COV-2 early to stop the disease from spreading severely. A PEC immunosensor based on TiO₂@Bi₂WO₆@Ag₂S composite material was successfully constructed by Chang and coworkers to detect SARS-COV-2 [94]. TiO₂ and Bi₂WO₆ created heterojunctions in this system, which improved visible light absorption. Furthermore, TiO₂@Bi₂WO₆ hollow microspheres were sensitized with Ag₂S to successfully increase the photocurrent responsiveness by inhibiting e⁻/h + recombination. The obtained PEC immunosensor showed a low LOD of 0.38 pg/mL and a linear range from 1 pg/mL to 50 ng/mL. In addition to offering a unique, workable way to detect SARS-COV-2, this sensor's high sensitivity, superior selectivity, repeatability, and stability also gave a fresh approach for the construction of other pathogen sensors. Ascorbic acid (AA) was used as a hole-trapping agent, preventing the composite material's electron-hole recombination while the charges are being transported. The SARS-COV-2 NP antibody's specific binding to the antigen, due to its large volume, can hinder the electron transfer between AA and Ag₂S. which decreases the electrodes' photocurrent and increases the impedance. The photocurrent intensity gradually dropped as the concentration of SARS-COV-2 NP antigen increased. For comparison, a smartphone-based electrochemical immunoassay [107] gave a seven times higher limit of detection.

- Prostate-specific antigen (PSA)

One of the most prevalent malignancies worldwide is prostate cancer, and death can be significantly decreased with early detection. Chang and al [95] constructed a new label-free photoelectrochemical (PEC) immunosensor based on Bi₂WO₆/BiOBr nanocomposite materials for the detection of prostate-specific antigen (PSA) in human serum. The PEC immunosensor presents a detection range between 1 pg/mL and 50 ng/mL, a LOD of 0.084 pg/mL, and good selectivity, repeatability, and stability. To maintain the stability of the photocurrent signal in the interim, AA serves as a good electron donor by preventing the recombination of photogenerated holes. The PSA antibody's particular binding to PSA decreases the photoactive material's ability to transfer holes to donor molecules; it therefore increases the impedance. The photocurrent gradually becomes less intense as the PSA concentration rises. PSA was detected using a photoelectrochemical aptasensor based on AuNPs/graphene nanohybrids and CdS quantum dots/TiO₂, with a LOD of 0.52 pg/mL [108]. A signal-on detection photoelectrochemical PSA immunosensor based RGO/BiFeO₃ nanohybrids allowed PSA detection with a LOD of 0.31 pg/mL [109].

- MicroRNA

Gong et al. [96] created a novel, universal CRISPR/Cas12a-driven PEC sensor for the detection of microRNA-21 (miR-21). The photo-active material used is reduced graphene oxide anchored to Bi₂WO₆ (rGO-BWO), coupled with a target-triggered catalytic hairpin assembly (CHA). MiR-21 was used as an activator in conjunction with two programmable hairpin DNA modules for CHA isothermal amplification. The target-triggered CHA circuit products were introduced into the Cas12a-crRNA duplex to initiate the CRISPR/Cas12a nuclease's trans cleavage capacity in the presence of miR-21. This process accompanied the digestion of the single-stranded DNA (ssDNA)-encoded magnetic bead (MB) labeled with alkaline phosphatase (ALP) via the activated CRISPR system. ALPs being separated from the magnetic beads, they boosted the production of ascorbic acid (AA), which raised the rGO-BWO-modified electrode's photocurrent. The photocurrent value was favorably connected with the AA level, and the AA level was linearly correlated with the target concentrations. The CRISPR-based PEC sensing device demonstrated satisfactory photocurrent responses toward miR-21 at a LOD of 0.47 fM and a dynamic range of 1.0 fM to 1.0 nM under ideal conditions.

- Vibrio parahaemolyticus

Of all foodborne pathogens, Vibrio parahaemolyticus, a gram-negative halophilic bacterium found in estuarine and marine environments, can cause a variety of serious diseases in humans and animals. Hou et al. [97] employed a layer-by-layer self-assembly technique to build the PEC aptamer sensor for detecting vibrio parahaemolyticus. Ag₂S and rare-earth doped Bi₂WO₆ (BWO-1) are coupled as a very effective photo-active material. A wide linear range from 3.2 × 10² CFU/mL to 3.2 × 10⁸ CFU/mL and a LOD of 40 CFU/mL were obtained. Visible light easily excites Bi₂WO₆ and Ag₂S. In the process, electron-hole pairs may be produced. Aptamer acts as a capture probe via its affinity binding to Vibrio parahaemolyticus, and this capture leads to a decrease in the photocurrent.

- Antibiotic: Kanamycin

To determine the antibiotic Kanamycin, Zeng et al. [98] successfully developed an enhanced PEC bioanalysis platform by connecting rGO-Bi₂WO₆-Au (rGO-BWO-Au) with a branched hybridization chain reaction (t-bHCR) for signal amplification. Two clear benefits of this approach over conventional PEC bioanalysis techniques should be highlighted. Most importantly, the t-bHCR allowed for the short-term generation of an exponentially amplified hyper-branched assembly with multiple CuS NPs included from the molecular recognition event. Second, using a multistep electron-transfer (MET) method, the ternary nanocomposite rGO-BWO-Au with cascade energy level (BWO → rGO → Au) may easily inhibit the charge recombination. The formation of a hyper-branched structure further lessened the generation of photocurrent by obstructing the transmission of ascorbic acid and blocking the light irradiation to the surface of rGO-BWO-Au. The PEC sensor presents a linear range of 1 pM to 5 nM and a LOD down to 0.78 pM.

- Anti-inflammatory drug: Diclofenac

Diclofenac, a non-steroidal, anti-inflammatory drug, is used for the treatment of osteoarthritis, non-articular rheumatism, etc. He et al. [99] created a new PEC aptamer sensor for diclofenac (DCF) detection, based on CuS/MoS₂/Bi₂WO₆ nanocomposite. The PEC sensor's photocurrent response surpasses the detection limit and linearity of conventionally modified electrodes and functions across a wide linear range of 0.1–500 nM with a LOD of 0.03 nM; it is based on the CS/CuS/MoS₂/Bi₂WO₆ heterostructure. Since the UV and visible light source energy could be absorbed by the CuS/MoS₂/Bi₂WO₆–5 % composite, the electron transfer rate might have been significantly increased in the absence of DCF. An electron donor, ascorbic acid, absorbs holes in the
semiconductor material, lowering the material's rate of electron-hole recombination, and increasing the photocurrent signal. The DCF-aptamer complexes on the sensor interface introduce a steric barrier for ascorbic acid diffusion, resulting in a drop in photocurrent.

### 4.4.2. Environmental pollutants

- Heavy metal ions: Pb²⁺

Since heavy metals are widely distributed in the environment, they have the potential to bioaccumulate and cause major health problems in people, including kidney and heart disease. The principal hazardous heavy metals were formerly thought to be lead (Pb²⁺) and cadmium (Cd²⁺) ions. Chen and coworkers successfully produced Bi₂WO₆-rGO NCs using a simple hydrothermal treatment procedure [100] for the preparation of a new PEC aptasensor platform for Pb²⁺. The addition of rGO increases the capacity to capture visible light while also facilitating better electron transport and separating photogenerated electron-hole pairs. K⁺-stabilized G-quadruplex DNAzyme was immobilized onto Bi₂WO₆ rGO/ITO. This DNAzyme presents a good catalytic capability to facilitate the oxidation of 4-chloro-1-naphthol by H₂O₂. The produced benzo-4-chloro hexadienone was insoluble and insulating; it settled on

the electrode and caused a decrease in photocurrent. This obtained aptasensor demonstrated a low LOD of 0.0033 µM and a wide detection range from 0.01 µM to 50 µM.

## 4.5. Bi₂WO₆ heterojunction-based sandwich-biosensors

### 4.5.1. Molecules of health interest

- Creatine kinase-MB (CK-MB)

The improved organic-inorganic heterojunction of poly-pyrrole@Bi₂WO₆ (PPy@Bi₂WO₆) was developed by Zhu et al. [101] and used in the sensitive PEC immunoassay of CK-MB. The system demonstrated acceptable analytical performance in the immunoassay through the alkaline phosphatase (ALP)-induced BCP amplification. The photocurrent gradually decreased along with increased CK-MB concentrations from 0.5 to 2000 ng/mL, and a LOD of 0.16 ng/mL was obtained.

- Biomarker: procalcitonin

Procalcitonin (PCT), a biomarker of severe inflammation, is a calcitonin propeptide (116 aminoacids). Wang et al. [102] developed a

<figure><img src="image_6.png" /><figcaption>**Fig. 5.** (A) Schematic mechanism of PEC detection of procalcitonin. From [102] with permission. (B) Schematic mechanism of PEC detection of beta amyloid. From [104] with permission.</figcaption></figure>
sandwich-type PEC immunosensor for the detection of procalcitonin (PCT), based on the signal amplification effect of a rare-earth-doped up-conversion material, NaYF₄:Yb,Tm, and the sensitization of Mn²⁺ doped CdS (CdS:Mn) for a heterojunction with Bi₂WO₆. Ascorbic acid was used for hole capture, and its concentration was optimized. NaYF₄:Yb,Tm is associated with the secondary antibody and enhances the photocurrent response (Fig. 5A). The developed immunosensor for PCT detection offers a linear range of 0.5 pg/mL - 100 ng/mL and a LOD of 0.13 pg/mL.

- Biomarker: Amino-terminal pro-B-type natriuretic peptide (NT-pro BNP)

The amino-terminal pro-B-type natriuretic peptide, or NT-pro BNP, is a biomarker for heart failure diagnosis and prognosis. Qian et al. [103] created a sandwich-type PEC immune-sensing platform to detect NT-pro BNP, based on flower-like Bi₂WO₆/Ag₂S nanoparticles (F-Bi₂WO₆/Ag₂S). A cascade-like band-edge level between Ag₂S and F-Bi₂WO₆ successfully increased the photocurrent, in the presence of ascorbic acid as a hole-trapping agent. The goal of the conjugated GO/polydopamine (PDA) secondary antibody was then to increase the signal, since GO's impressive conductivity sped up the electron transfer while PDA's ability, as an electron donor, allowed it to sweep the holes and prevent photogenerated electron-hole pairs from recombining. The quantity of GO/PDA conjugates increased the photocurrent, and this rise was positively correlated with the NT-pro BNP. With a LOD of 0.03 pg/mL (S/N = 3), the suggested sandwich-type PEC immunosensor demonstrated the desired linear relationship for NT-pro BNP under ideal experimental conditions, ranging from 0.1 pg/mL to 100 ng/mL.

- Beta amyloid (Aβ)

Alzheimer's disease (AD), the most prevalent form of dementia among the elderly, is a chronic degenerative illness of the central nervous system. Abnormal beta amyloid (Aβ (1-42)) peptide aggregates in the brain are a major factor in the development of Alzheimer's disease (AD) [110]. Based on the sensitization of Mn:CdSe to Bi₂WO₆/CdS, a novel competitive-type photoelectrochemical sensor was successfully developed by Xu and coworkers [104] for Aβ detection. The immunosensor demonstrated a broad linear range of 0.2 pg/mL–50 ng/mL, with a LOD of 0.068 pg/mL, demonstrating great sensitivity to Aβ detection. The resulting immunosensor also has good stability and acceptable repeatability for the quantitative detection of Aβ. The photogenerated electrons might transfer to the conduction band (CB) of CdS and then to the CB of Bi₂WO₆ because the band energy levels of Mn:CdSe and CdSe match (Fig. 5B). In the meantime, ascorbic acid could mix with photo-generated holes to prevent the recombination of photogenerated electrons and holes, leading to an increase in photocurrent signals.

## 5. Summary and prospects

In this review, we sum up the recent developments of nanostructured Bi₂WO₆ in electrochemical and photoelectrochemical sensors and biosensors. It was used as pristine or as a composite, forming a heterojunction with narrow bandgap semiconductors. Different morphological Bi₂WO₆ crystals have been successfully prepared on a large scale by various methods. Continuous breakthroughs in the controllable fabrication and modification methods of nanostructured Bi₂WO₆ have enabled different sizes, shapes, surface areas, light absorption ranges, and energy band structures to be obtained. Different heterojunctions were obtained by associating narrow bandgap semiconductors (WO₃, CuS, Fe₂O₃, Bi₂S₃, Ag₂S, BiOBr, CuS, MoS₂, CdS), conductive carbon materials (g-C₃N₄, RGO), metallic nanoparticles (Au, Ag) or conductive polymers (polypyrrole, polydopamine) with Bi₂WO₆ crystals. Sensors and biosensors present a signal-on detection, whereas when the target molecule is not electroactive, sensors and biosensors, associated with a hole-trapping agent (ascorbic acid, hydrogen peroxide,

sulfate), lead to a signal-off detection. Recently, CRISPR-Cas12a-based photoelectrochemical biosensors have been published in this area [111,112]. On the other hand, Bi₂WO₆ heterojunction-based sandwich-biosensors, associated with a hole-trapping agent, lead to a signal-on detection.

Many molecules of health interest (metabolites, biomarkers, drugs) and a few pollutants were detected with low detection limits. Recently, similar research has been carried out [113,114]. The most sensitive configuration is the Bi₂WO₆ heterojunction-based sandwich biosensor, the secondary antibody being linked with complementary nanomaterials, allowing the signal-on detection of biomarkers with detection limits in the femtogram per mL range.

However, research into the optimization of the photocatalytic properties of different dimensional nanostructured Bi₂WO₆ and their association with different nanomaterials (semiconductors, carbon materials, metals, polymers) is still in its infancy. A further comprehensive exploration of the factors governing the photocatalytic activity is needed and should be modeled by theoretical chemistry, as in recent works [115,116].

For future commercial applications, the synthesis procedure of nanostructured Bi₂WO₆ and the heterojunctions needs to be simplified. Overall, Bi₂WO₆-based nanomaterials are generally considered to be non-toxic [117]. The cytotoxicity and genotoxicity of Bi₂WO₆-based photocatalysts were evaluated using Allium cepa [118], and no cytotoxicity or genotoxicity was shown in the tested system. These findings suggest that Bi₂WO₆-based photocatalysts have a low potential for causing harm. Nevertheless, it is important to note that Bi₂WO₆-based materials can generate reactive oxygen species and free radicals during their photocatalytic processes, which can potentially cause cellular toxicity [119]. It is then crucial to conduct comprehensive biosafety studies to assess the potential risks associated with the use of Bi₂WO₆-based nanomaterials.

This review will open a wider path by summarizing all the tested combinations with Bi₂WO₆, which gives lower detection limits for the photoelectrochemical detection of molecules of health interest and some pollutants. Despite their advantages, challenges remain regarding the long-term stability, standardization, and field deployment of Bi₂WO₆-based photoelectrochemical sensors. Ongoing research should focus on enhancing sensor robustness, developing scalable fabrication techniques, and integrating these systems into existing monitoring infrastructure.

To fully realize the potential of Bi₂WO₆ nanoparticles in photoelectrochemical sensors, collaborative efforts among academia, industry, and regulatory agencies are crucial. Additionally, considerations such as scalability and cost-effectiveness are key to the practical implementation and widespread adoption of Bi₂WO₆-based sensors for environment and health applications.

## CRediT authorship contribution statement

**Amira Nahdi:** Writing – original draft. **Salah Kouass:** Conceptualization. **Hamdi Ben Halima:** Writing – original draft. **Nicole Jaffrezic-Renault:** Writing – review & editing.

## Funding

University of Tunis Carthage is acknowledged for A. Nahdi's traineeship grant.

## Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Nicole JAFFREZIC-RENAULT reports equipment, drugs, or supplies was provided by University of Franche-Comté. The other authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.

## Data availability

Data will be made available on request.

## References

[1] N. Hao, X. Zhang, Z. Zhou, J. Qian, Q. Liu, S. Chen, Y. Zhang, K. Wang, Three-dimensional nitrogen-doped graphene porous hydrogen fabricated biosensing platform with enhanced photoelectrochemical performance, Sens. Actuators B 250 (2017) 476-483, https://doi.org/10.1016/j.snb.2017.05.003.

[2] X. Chen, L. Liu, F. Huang, Black titanium dioxide (TiO 2) nanomaterials, Chem. Soc. Rev. 44 (7) (2015) 1861-1885, https://doi.org/10.1039/C4CS00330F.

[3] S.P. Vattikuti, P.A.K. Reddy, N. Bandaru, J. Shim, C. Byon, Hydrothermally synthesized highly dispersed Na₂Ti₃O₇ nanotubes and their photocatalytic degradation and H 2 evolution activity under UV and simulated solar light irradiation, Korean J. Chem. Eng. 35 (2018) 1019-1025, https://doi.org/10.1007/s11814-017-0355-z.

[4] T. Li, T. Sun, T.B. Aftab, D. Li, Photocatalytic degradation of methylene blue in aqueous solution using ceramite coated with micro-Cu₂O under visible-light irradiation, Korean J. Chem. Eng. 34 (2017) 1199-1207, https://doi.org/10.1007/s11814-017-0014-4.

[5] J. Gong, T. Fang, D. Peng, A. Li, L. Zhang, A highly sensitive photoelectrochemical detection of perfluorooctanoic acid with molecularly imprinted polymer-functionalized nanoarchitected hybrid of AgI-BiOI composite, Biosens. Bioelectron. 73 (2015) 256-263, https://doi.org/10.1016/j.bios.2015.06.008.

[6] J. Shu, D. Tang, Recent advances in photoelectrochemical sensing: from engineered photoactive materials to sensing devices and detection modes, Anal. Chem. 92 (2020) 363-377, https://doi.org/10.1021/acs.analchem.9b04199.

[7] Q. Zhou, D. Tang, Recent advances in photoelectrochemical biosensors for analysis of mycotoxins in food, TrAC Trends Anal. Chem. (2020) 115814, https://doi.org/10.1016/j.trac.2020.115814.

[8] P. Yan, L. Xu, D. Jiang, H. Li, J. Xia, Q. Zhang, M. Hua, H. Li, Photoelectrochemical monitoring of ciprofloxacin based on metallic Bi self-doping BiOBr nanocomposites, Electrochim. Acta 259 (2018) 873-881, https://doi.org/10.1016/j.electacta.2017.11.026.

[9] J. Shu, D. Tang, Current advances in quantum-dots-based Photoelectrochemical immunoassays, Chem. Asian J. 12 (2017) 2780-2789, https://doi.org/10.1002/asia.201701229.

[10] J. Qin, Z. Yu, D. Wu, M. Li, D. Tang, Target-induced oxygen vacancy on the etching WO₃ photoanode for in-situ amplified photoelectrochemical immunoassay, Biosens. Bioelectron. 279 (2025) 117405, https://doi.org/10.1016/j.bios.2025.117405.

[11] W. Tu, Z. Wang, Z. Dai, Selective photoelectrochemical architectures for biosensing: design, mechanism and responsibility, TrAC Trends Anal. Chem. 105 (2018) 470-483, https://doi.org/10.1016/j.trac.2018.06.007.

[12] H. Wang, J. Tang, X. Wan, X. Wang, Y. Zeng, X. Liu, D. Tang, Mechanism exploration of the Photoelectrochemical immunoassay for the integration of radical generation with self-quenching, Anal. Chem. 96 (2024) 15503-15510, https://doi.org/10.1021/acs.analchem.4c04050.

[13] Z. Yu, J. Tang, C. Zeng, Y. Gao, D. Wu, Y. Zeng, X. Liu, D. Tang, Shaping the future of neurotransmitter sensor: tailored CdS nanostructures for state-of-the-art self-powered Photoelectrochemical device, ACS Sens. 9 (2024) 2684-2694, https://doi.org/10.1021/acssensors.4c00621.

[14] Y. Gao, J. Tang, Q. Zhou, Z. Yu, D. Wu, D. Tang, Excited-state intramolecular proton transfer-driven photon-gating for photoelectrochemical sensing of CO-releasing molecule-3, Anal. Chem. 96 (2024) 5014-5021, https://doi.org/10.1021/acs.analchem.4c00324.

[15] L. Lu, R. Zeng, Q. Lin, X. Huang, D. Tang, Cation exchange reaction-mediated photothermal and polarity-switchable photoelectrochemical dual-readout biosensor, Anal. Chem. 95 (2023) 16335-16342, https://doi.org/10.1021/acs.analchem.3c03573.

[16] Y. Gao, Z. Yu, L. Huang, Y. Zeng, X. Liu, D. Tang, Photoinduced electron transfer modulated photoelectric signal: towards organic small molecule-based photoelectrochemical platform for formaldehyde detection, Anal. Chem. 95 (2023) 9130-9137, https://doi.org/10.1021/acs.analchem.3c01690.

[17] R. Zeng, J. Xu, T. Liang, M. Li, D. Tang, Photocurrent-polarity-switching photoelectrochemical biosensor for switching spatial distance electroactive tags, ACS Sens. 8 (2023) 317-325, https://doi.org/10.1021/acssensors.2c02314.

[18] Y. Gao, M. Li, Y. Zeng, X. Liu, Tunable competitive absorption-induced signal-on photoelectrochemical immunoassay for cardiac troponin I based on Z-scheme metal-organic framework heterojunction, Anal. Chem. 94 (2022) 13582-13589, https://doi.org/10.1021/acs.analchem.2c03263.

[19] L. Huang, G. Cai, R. Zeng, Z. Yu, D. Tang, Contactless photoelectrochemical biosensor based on ultraviolet-assisted gas sensing interface of 3D-SnS2 nanosheets: from mechanism reveal to practical application, Anal. Chem. 94 (2022) 9487-9495, https://doi.org/10.1021/acs.analchem.2c02010.

[20] H. Wang, D. Tang, X. Wang, X. Wan, D. Tang, Surface plasmon resonance-enhanced photoelectrochemical immunoassay with cu-doped porous Bi₂WO₆

nanosheets, Talanta 273 (2024) 125863, https://doi.org/10.1016/j.talanta.2024.125863.

[21] Y. Li, J. Liu, X. Huang, Synthesis and visible-light photocatalytic property of Bi₂WO₆ hierarchical octahedron-like structures, Nanoscale Res. Lett. 3 (2008) 365-371, https://doi.org/10.1007/s11671-008-9168-7.

[22] X. Liu, S. Gu, Y. Zhao, G. Zhou, W. Li, BiVO₄, Bi₂WO₆ and Bi₂MoO₆ photocatalysis: a brief review, J. Mater. Sci. Technol. 56 (2020) 45-68, https://doi.org/10.1016/j.jmst.2020.04.023.

[23] N. Kim, R.N. Vannier, C.P., Grey detecting different oxygen-ion jump pathways in Bi₂WO₆ with 1-and 2-dimensional 170 MAS NMR spectroscopy, Chem. Mater. 17 (8) (2005) 1952-1958, https://doi.org/10.1021/cm048388a.

[24] T. Chen, L. Liu, C. Hu, H. Huang, Recent advances on Bi₂WO₆-based photocatalysts for environmental and energy applications, Chinese J. Catal. 42 (9) (2021) 1413-1438, https://doi.org/10.1016/S1872-2067(20)63769-X.

[25] X. Er, Y. Zhang, Y. Yin, C. Wang, H. Wang, J. Zhang, Q. Zhan, Atomic structure of domain and defect in layered-perovskite Bi₂WO₆ thin films, Mater Charact 154 (2019) 395-399, https://doi.org/10.1016/j.matchar.2019.06.022.

[26] M. Mansourian, S. Alamdari, Fabrication and investigation on luminescence properties of Bi₂WO₆ microfibers via stretching process, Progr. Phys. Appl. Mater. 3 (1) (2023) 29-33.

[27] D. Wang, Y. Zhen, G. Xue, F. Fu, X. Liu, D. Li, Synthesis of mesoporous Bi₂WO₆ architectures and their gas sensitivity to ethanol, J. Mater. Chem. C 1 (26) (2013) 4153-4162, https://doi.org/10.1039/c3c30189c.

[28] S. Wang, H. Yang, Z. Yi, X. Wang, Enhanced photocatalytic performance by hybridization of Bi₂WO₆ nanoparticles with honeycomb-like carbon skeleton, J. Environ. Manage. 248 (2019) 109341, https://doi.org/10.1016/j.jenvman.2019.109341.

[29] X. Zou, Y. Dong, C. Yuan, H. Ge, J. Ke, Y. Cui, Zn₂SnO₄ QDs decorated Bi₂WO₆ nanoplates for improved visible-light-driven photocatalytic removal of gaseous contaminants, J. Taiwan Inst. Chem. Eng. 96 (2019) 390-399, https://doi.org/10.1016/j.jtice.2018.12.005.

[30] Z. Zhu, Y. Ren, Q. Li, H. Liu, H. Weng, One-pot electrodeposition synthesis of Bi₂WO₆/graphene composites for photocatalytic applications under visible light irradiation, Ceram. Int. 44 (3) (2018) 3511-3516, https://doi.org/10.1016/j.ceramint.2017.11.132.

[31] J. Zhang, L. Huang, H. Jin, Y. Sun, X. Ma, E. Zhang, H. Wang, Z. Kong, J. Xi, Z. Ji, Constructing two-dimensional MoS₂/Bi₂WO₆ core-shell heterostructure as carriers transfer channel for enhancing photocatalytic activity, Mater. Res. Bull. 85 (2017) 140-146, https://doi.org/10.1016/j.materresbull.2016.09.013.

[32] C. Li, G. Chen, J. Sun, Y. Feng, J. Liu, H. Dong, Ultrathin nanoflakes constructed erythrocyte-like Bi₂WO₆ hierarchical architecture via anionic self-regulation strategy for improving photocatalytic activity and gas-sensing property, Appl. Catal. Environ. 163 (2015) 415-423, https://doi.org/10.1016/j.apcatb.2014.07.060.

[33] Z. Zhang, W. Wang, L. Wang, S. Sun, Enhancement of visible-light photocatalysis by coupling with narrow-band-gap semiconductor: a case study on Bi₂S₃/Bi₂WO₆, ACS Appl. Mater. Interfaces 4 (2) (2012) 593-597, https://doi.org/10.1021/am2017199.

[34] C. Li, G. Chen, J. Sun, J. Rao, Z. Han, Y. Hu, Y. Zhou, A novel mesoporous single-crystal-like Bi₂WO₆ with enhanced photocatalytic activity for pollutants degradation and oxygen production, ACS Appl. Mater. Interfaces 7 (46) (2015) 25716-25724, https://doi.org/10.1021/acsami.5b06995.

[35] L. Zhang, W. Wang, L. Zhou, H. Xu, Bi₂WO₆ nano- and microstructures: shape control and associated visible-light-driven photocatalytic activities, Small 3 (9) (2007) 1618-1625, https://doi.org/10.1002/smll.200700043.

[36] L. Zhang, W. Wang, Z. Chen, L. Zhou, H. Xu, W. Zhu, Fabrication of flower-like Bi₂WO₆ superstructures as high performance visible-light driven photocatalyst, J. Mater. Chem. 17 (24) (2007) 2526-2532, https://doi.org/10.1039/b616460a.

[37] S. Qi, R. Zhang, Y. Zhang, X. Liu, H. Xu, Preparation and photocatalytic properties of Bi₂WO₆/g-C₃N₄, Inorg. Chem. Commun. 132 (2021) 108761, https://doi.org/10.1016/j.inocoche.2021.108761.

[38] J. Liu, T. Wang, Q. Nie, L. Hu, Y. Cui, Z. Tan, H. Yu, One-step synthesis of metallic Bi deposited Bi₂WO₆ nanoclusters for enhanced photocatalytic performance: an experimental and DFT study, Appl. Surf. Sci. 559 (2021) 149970, https://doi.org/10.1016/j.apsusc.2021.149970.

[39] L. Liu, J. Liu, K. Sun, J. Wan, F. Fu, J. Fan, Novel phosphorus-doped Bi₂WO₆ monolayer with oxygen vacancies for superior photocatalytic water detoxication and nitrogen fixation performance, Chem. Eng. J. 411 (2021) 128629, https://doi.org/10.1016/j.cej.2021.128629.

[40] J. Peng, W. Zhuge, Y. Liu, C. Zhang, W. Yang, Y. Huang, Photoelectrochemical dopamine sensor based on cu-doped Bi₂WO₆ micro-flowers sensitized cobalt tetraaminophthalocyanine functionalized graphene oxide, J. Electrochem. Soc. 166 (15) (2019) B1612, https://doi.org/10.1149/2.1051915jes.

[41] Z.J. Zhang, W.Z. Wang, M. Shang, W.Z. Yin, Low-temperature combustion synthesis of Bi₂WO₆ nanoparticles as a visible-light-driven photocatalyst, J. Hazard. Mater. 177 (2010) 1013-1018, https://doi.org/10.1016/j.jhazmat.2010.01.020.

[42] G.J. Dong, H.Y. Hu, I. Wang, Y.J. Zhang, Y.P. Bi, Remarkable enhancement on photoelectrochemical water splitting derived from well-crystallized Bi₂WO₆ and Co(OH)₂ with tunable oxidation state, J. Catal. 366 (2018) 258-265, https://doi.org/10.1016/j.jcat.2018.08.010.

[43] A. Elaouni, M. El Ouardi, A. BaQais, M. Arab, M. Saadi, H.A. Ahsaine, Bismuth tungstate Bi₂WO₆: a review on structural, photophysical and photocatalytic properties, RSC Adv. 13 (2023) 17476-17494, https://doi.org/10.1039/D3RA01987J.
[44] S.A. Deshmukh, S. Suresh, D.V. Bhuse, S.U. Raut, M.V.B. Reddy, S. Ravichandran, Review on strategies for the design and synthesis of flower-like Bi₂WO₆ and BiOX (X=-F, cl, Br, I) composites for photocatalytic environmental remediation, ChemistrySelect 9 (2024) e202401038, https://doi.org/10.1002/sict.202401038.

[45] W. Mao, X.W. Shen, L.X. Zhang, Y. Liu, Z.H. Liu, Y.T. Guan, A review on Bi₂WO₆-based photocatalysts synthesis, modification, and applications in environmental remediation, life medical, and clean energy, F.S.E. 18 (2024) 86, https://doi.org/10.1007/s11783-024-1846-x.

[46] Y.J. Zhang, H.J. Yu, R.Q. Zhai, J. Zhang, C.P. Gao, K.Z. Qi, L. Yang, Q. Ma, Recent progress in photocatalytic degradation of water pollution by bismuth tungstate, Molecules 28 (2023) 8011, https://doi.org/10.3390/molecules28428011.

[47] X. Linghu, Y. Shu, L.A. Liu, Y. Zhao, J.W. Zhang, Z. Chen, D. Shan, B.Q. Wang, Hydro/solvothermally synthesized bismuth tungstate nanocatalysts for enhanced photocatalytic degradation of dyes, antibiotics, and bacteria in wastewater: a review, J.W.P.E. 54 (2023) 103994, https://doi.org/10.1016/j.jwpe.2023.103994.

[48] B. Li, X.J. Liu, H.W. Zhu, H.P. Guan, R.T. Guo, A review on Bi₂WO₆-based materials for photocatalytic CO₂ reduction, Small 20 (2024) e2406074, https://doi.org/10.1002/smll.202406074.

[49] P.L. Meena, A.J. Surela, Polyaniline based binary nanocomposite heterostructures with semiconductor photocatalysts for photocatalytic improvement, J. Mol. Liq. 412 (2024) Oct 22 (2024) 125828, https://doi.org/10.1016/j.molliq.2024.125828.

[50] A.J.J. Amalraj, S.F. Wang, An effective morphology controlled hydrothermal synthesis of Bi₂WO₆ and its application in riboflavin electrochemical sensor, Colloids Surf. A Physicochem. Eng. Asp. 648 (2022) 129183, https://doi.org/10.1016/j.colSURFA.2022.129183.

[51] W. Guo, L. Jian, X. Wang, W. Zeng, Hydrothermal synthesis of Ni-doped hydrangea-like Bi₂WO₆ and the enhanced gas sensing property to n-butanol, Sens. Actuators B 357 (2022) 131396, https://doi.org/10.1016/j.snb.2022.131396.

[52] H. Zheng, W. Guo, S. Li, R. Yin, Q. Wu, X. Feng, N. Ren, J.S. Chang, Surfactant (CTAB) assisted flower-like Bi₂WO₆ through hydrothermal method: unintentional bromide ion doping and photocatalytic activity, Catal. Commun. 88 (2017) 68-72, https://doi.org/10.1016/j.catcom.2016.09.030.

[53] Y.Q. Wang, C. Yang, L.H. Gan, Preparation of direct Z-scheme Bi₂WO₆/TiO₂ heterojunction by one-step solvothermal method and enhancement mechanism of photocatalytic H₂ production, Int. J. Hydrogen Energy 48 (51) (2023) 19372-19384, https://doi.org/10.1016/j.ijhydene.2023.01.372.

[54] G. Zhang, F. Lü, M. Li, J. Yang, X. Zhang, B. Huang, Synthesis of nanometer Bi₂WO₆ synthesized by sol-gel method and its visible-light photocatalytic activity for degradation of 4BS, J. Phys. Chem. Solid 71 (4) (2010) 579-582, https://doi.org/10.1016/j.jpcs.2009.12.041.

[55] Z. Lin, Z. Yang, J. Huang, Hierarchical Bi₂WO₆/TiO₂-nanotube composites derived from natural cellulose for visible-light photocatalytic treatment of pollutants, Beilstein J. Nanotechnol. 13 (1) (2022) 745-762, https://doi.org/10.3762/bjnano.13.66.

[56] M. Shang, W. Wang, L. Zhang, S. Sun, L. Wang, L. Zhou, 3D Bi₂WO₆/TiO₂ hierarchical heterostructure: controllable synthesis and enhanced visible photocatalytic degradation performances, J. Phys. Chem. C 113 (33) (2009) 14727-14731, https://doi.org/10.1021/jp9045808.

[57] C. Wu, J. Zhong, J. Xie, D. Wang, Y. Shi, Q. Chen, H. Yan, J. Zhu, Enhanced visible-light-driven photocatalytic properties of acceptor dopant Nb⁵⁺ modified Bi₂WO₆ by tailoring the morphology from 3D hierarchical microspheres to 2D nanosheets, Appl. Surf. Sci. 484 (2019) 112-123, https://doi.org/10.1016/j.apsusc.2019.04.065.

[58] T. Zeng, X. Yu, S. Hui, Z. Zhou, X. Dong, Structural and electrical properties of Bi₂WO₆ piezoceramics prepared by solid state reaction method, Mater. Res. Bull. 68 (2015) 271-275, https://doi.org/10.1016/j.materresbull.2015.04.004.

[59] X.F. Cao, L. Zhang, X.T. Chen, Z.L. Xue, Microwave-assisted solution-phase preparation of flower-like Bi₂WO₆ and its visible-light-driven photocatalytic properties, CrystEngComm 13 (1) (2011) 306-311, https://doi.org/10.1039/C0CE00031K.

[60] F. Xu, C. Xu, H. Chen, D. Wu, Z. Gao, X. Ma, Q. Zhang, K. Jiang, The synthesis of Bi₂S₃/2D-Bi₂WO₆ composite materials with enhanced photocatalytic activities, J. Alloys Compd. 780 (2019) 634-642, https://doi.org/10.1016/j.jallcom.2018.11.397.

[61] S.O. Alfaro, A. Martínez-De La Cruz, Synthesis, characterization and visible-light photocatalytic properties of Bi₂WO₆ and Bi₂W₂O₉ obtained by co-precipitation method, Appl. Catal. Gen. 383 (1-2) (2010) 128-133, https://doi.org/10.1016/j.apcata.2010.05.034.

[62] M. Shang, W. Wang, J. Ren, S. Sun, L. Wang, L. Zhang, A practical visible-light-driven Bi₂WO₆ nanofibrous mat prepared by electrospinning, J. Mater. Chem. 19 (34) (2009) 6213-6218, https://doi.org/10.1039/b907849e.

[63] G. Zhao, S. Liu, Q. Lu, F. Xu, H. Sun, Fabrication of electrospun Bi₂WO₆ nanobelts with enhanced visible photocatalytic degradation activity, J. Alloys Compd. 578 (2013) 12-16, https://doi.org/10.1016/j.jallcom.2013.05.022.

[64] Y. Huang, Z. Ai, W. Ho, M. Chen, S. Lee, Ultrasonic spray pyrolysis synthesis of porous Bi₂WO₆ microspheres and their visible-light-induced photocatalytic removal of NO, J. Phys. Chem. C 114 (14) (2010) 6342-6349, https://doi.org/10.1021/jp912201h.

[65] V. Nithya, R.K. Selvan, D. Kalpana, L. Vasylechko, C. Sanjeeviraja, Synthesis of Bi₂WO₆ nanoparticles and its electrochemical properties in different electrolytes for pseudocapacitor electrodes, Electrochim. Acta 109 (2013) 720-731, https://doi.org/10.1016/j.electacta.2013.07.138.

[66] S.M. Zawiri, R. Yahya, A. Hassan, H.E. Mahmud, M.N. Daud, Structural and optical characterization of metal tungstates (MWO 4; M= Ni, Ba, Bi) synthesized by a sucrose-templated method, Chem. Cent. J. 7 (2013) 1-10, https://doi.org/10.1186/1752-153X-7-80.

[67] S. Luo, Y. Noguchi, M. Miyayama, T. Kudo, Rietveld analysis and dielectric properties of Bi₂WO₆-Bi₄TiO₃ ferroelectric system, Mater. Res. Bull. 36 (3-4) (2001) 531-540, https://doi.org/10.1016/S0025-5408(01)00516-53.

[68] F. Rabanimehr, M. Farhadian, A.R.S. Nazar, M. Moghadam, Fabrication of Z-scheme Bi₂WO₆/CNT/TiO₂ heterostructure with enhanced cephalexin photodegradation: optimization and reaction mechanism, J. Mol. Liq. 339 (2021) 116728, https://doi.org/10.1016/j.molliq.2021.116728.

[69] M.H. Selvi, P.R. Vanga, M. Ashok, Photocatalytic application of Bi₂WO₆ nanolites structure for effective degradation of methylene blue, Optik 173 (2018) 227-234, https://doi.org/10.1016/j.ijleo.2018.08.027.

[70] L. Wu, J. Bi, Z. Li, X. Wang, X. Fu, Rapid preparation of Bi₂WO₆ photocatalyst with nanosheet morphology via microwave-assisted solvothermal synthesis, Catal. Today 131 (1-4) (2008) 15-20, https://doi.org/10.1016/j.cattod.2007.10.089.

[71] C.I. Yu, W. Fang, L.H. Zhu, W.Q. Zhou, Q.Z. Fan, Preparation, characterization and photocatalytic performance of heterostructured AgCl/Bi₂WO₆ microspheres, Chin. J. Catal. 36 (7) (2015) 987-993, https://doi.org/10.1016/S1872-2067(15)06849-X.

[72] Y. Wu, W. Xu, F. Jiang, S. Liu, Y. Li, S. Wang, Z. Xu, Y. Li, Enhancement of bismuth tungstate perovskite photoelectrochemical performance using elemental co-doping and construction of ternary heterojunction for sensitive detection of trenbolone, Bioelectrochemistry 163 (2025) 108887, https://doi.org/10.1016/j.bioelectrochem.2024.108887.

[73] H. Liu, K. Guo, C. Duan, X. Chen, Z. Zhu, A novel biosensor based on the direct electrochemistry of horseradish peroxidase immobilized in the three-dimensional flower-like Bi₂WO₆ microspheres, Mater. Sci. Eng. C Mater. Biol. Appl. 64 (2016) 243-248, https://doi.org/10.1016/j.msec.2016.03.079.

[74] V. Vinothkumar, A. Sangili, S.M. Chen, T.W. Chen, M. Abinaya, V. Sethupathi, Voltammetric determination of Sudan I by using Bi₂WO₆ nanosheets modified glassy carbon electrode, Int. J. Electrochem. Sci. 15 (3) (2020) 2414-2429, https://doi.org/10.20964/2020.03.08.

[75] L. Peng, S. Dong, H. Xie, G. Gu, Z. He, J. Lu, T. Huang, Sensitive simultaneous determination of diethylstilbestrol and bisphenol A based on Bi₂WO₆ nanolites modified carbon paste electrode, J. Electroanal. Chem. 726 (2014) 15-20, https://doi.org/10.1016/j.jelechem.2014.05.008.

[76] A. Muthumariyappan, U. Rajaji, S.M. Chen, T.W. Chen, Y.L. Li, R.J. Ramalingam, One-pot sonochemical synthesis of Bi₂WO₆ nanospheres with multilayer reduced graphene nanosheets modified electrode as rapid electrochemical sensing platform for high sensitive detection of oxidative stress biomarker in biological sample, Ultrason. Sonochem. 57 (2019) 233-241, https://doi.org/10.1016/j.ultronch.2019.04.011.

[77] T. Tarabi, Y. Javed, M.M. Sajid, A. Rakha, A. Munawar, N.A. Shad, H. Munir, A. Riaz, A. Jilani, Ultrasensitive and rapid detection of artemisinin based on bismuth tungstate dressed rGO nanocomposite, Mater. Chem. Phys. 290 (2022) 126547, https://doi.org/10.1016/j matchemphys.2022.126547.

[78] U. Rajaji, M. Govindasamy, S.M. Chen, T.W. Chen, X. Liu, S. Chinnapaiyan, Microwave-assisted synthesis of Bi₂WO₆ flowers decorated graphene nanoribbon composite for electrocatalytic sensing of hazardous dihydroxybenzene isomers, Compos. Part B Eng. 152 (2018) 220-230, https://doi.org/10.1016/j.compositesb.2018.07.003.

[79] C. Karaman, B.B. Yola, O. Karaman, N. Atar, I. Polat, M.L. Yola, Sensitive sandwich-type electrochemical SARS-CoV-2 nucleocapsid protein immunosensor, Mikrochim. Acta 188 (12) (2021) 425, https://doi.org/10.1007/s00604-021-05092-5.

[80] Y.C. Fann, C.A. Metosh-Dickey, G.W. Winston, A. Sygula, D. Ramakrishna Rao, M. B. Kadiiska, R.P. Mason, Enzymatic and nonenzymatic production of free radicals from the carcinogens 4-nitroquinoline N-oxide and 4-hydroxylquinoline N-oxide, Chem. Res. Toxicol. 12 (5) (1999) 450-458, https://doi.org/10.1021/tx980238p.

[81] M. Tong, N. Zhang, Z. Tan, L. Chi, K. Zhang, B. Chen, F. Hu, C. Guo, Oxygen vacancy-rich Bi₂WO₆ nanocrystals for fast and wide-range photoelectrochemical sensing of hydrogen peroxide, Microchem. J. 190 (2023) 108618, https://doi.org/10.1016/j.microc.2023.108618.

[82] S. Hu, Q. Fei, Y. Li, B. Wang, Y. Yu, Br-terminated 2D Bi₂WO₆ nanosheets as a sensitive light-regenerated electrochemical sensor for detecting sulfamethoxazole antibiotic, Surf Interfaces 25 (2021) 101302, https://doi.org/10.1016/j.surfin.2021.101302.

[83] S. Veeralingam, S. Badhulika, Biconcave Bi₂WO₆ nanoparticles for UV light-activated detection of nicotine in human sweat and cigarette samples, ACS Appl. Nano Mater. 3 (12) (2020) 12250-12259, https://doi.org/10.1021/acsnanm.0c02731.

[84] V. Kavinkumar, A. Verma, K. Uma, S. Moscow, K. Jothivenkatachalam, Y.P. Fu, Plasmonic metallic silver induced Bi₂WO₆/TiO₂ ternary junction towards the photocatalytic, electrochemical OER/HER, antibacterial and sensing applications, Appl. Surf. Sci. 569 (2021) 150918, https://doi.org/10.1016/j.apsusc.2021.150918.

[85] Z. Wu, Y. Su, F. Han, Z. Liang, D. Han, D. Qin, L. Niu, Bi₂WO₆@g-C₃N₄ heterostructure for cathodic photoelectrochemical dopamine sensor, Chemosensors 11 (7) (2023) 404, https://doi.org/10.3390/chemosensors11070404.

[86] A. Nahdi, F. Touati, H. Ben Halima, K. Salah, N. Jaffrezic-Renault, Bi₂WO₆/WO₃/g-C₃N₄ ternary nanocomposite-modified glassy carbon electrode for sensitive photo-electrochemical detection of dopamine. Mater. Chem. Phys. (Submitted).
[87] Y. Pang, G. Xu, X. Zhang, J. Lv, K. Shi, P. Zhai, Q. Xue, X. Wang, Y. Wu, Photoelectrochemical properties and the detection mechanism of Bi₂WO₆ nanosheet modified TiO₂ nanotube arrays, Dalton Trans. 44 (40) (2015) 17784-17794, https://doi.org/10.1039/C5DT02973B.

[88] C. Cai, C. Wang, Q. Zhang, Q. Guo, W. Luo, B. Wang, Y. Wang, L. Zhou, M. Wang, One-pot hydrothermal synthesis of three-dimensional flower-like hollow Bi₂WO₆/ reduced graphene oxide hybrid for sensitive photoelectrochemical detection of diethylstilbestrol, Mater. Lett. 259 (2020) 126851, https://doi.org/10.1016/j. matlet.2019.126851.

[89] Y. Li, X. Yu, R. Li, F. Zhao, G. Liu, X. Wang, Selective and sensitive visible-light-prompt photoelectrochemical sensor of paracetamol based on Bi(2)WO(6) modified with Bi and copper sulfide, RSC Adv. 11 (5) (2021) 2884-2891, https:// doi.org/10.1039/D0RA08599E.

[90] S. Adhikari, S. Selvaraj, D.H. Kim, Construction of heterojunction photoelectrode via atomic layer deposition of Fe₂O₃ on Bi₂WO₆ for highly efficient photoelectrochemical sensing and degradation of tetracycline, Appl. Catal. Environ. 244 (2019) 11-24, https://doi.org/10.1016/j.apcatb.2018.11.043.

[91] N. Hao, S. Chen, J. Qian, Y. Zhang, Q. Liu, X. Zhang, K. Wang, A sensitive photoelectrochemical (PEC) platform fabricated with nitrogen-doped graphene quantum dots decorated Bi₂WO₆ for detection of pentachlorophenol, J. Electroanal. Chem. 801 (2017) 410-415, https://doi.org/10.1016/j. jelechem.2017.08.025.

[92] S. Adhikari, D.H. Kim, Synthesis of Bi₂S₃/Bi₂WO₆ hierarchical microstructures for enhanced visible light driven photocatalytic degradation and photoelectrochemical sensing of ofloxacin, Chem. Eng. J. 354 (2018) 692-705, https://doi.org/10.1016/j.cej.2018.08.087.

[93] Z. Yu, F. Zhu, T. Chen, J. Li, Q. Feng, F. Yang, X. Zhang, Sensitive photoelectrochemical detection of azomycin on Bi₂S₃/Bi₂WO₆ heterojunction using ascorbic acid as a hole-trapping agent, J Photochem Photobiol A Chem 440 (2023) 114637, https://doi.org/10.1016/j.jphotochem.2023.114637.

[94] H. Chang, M. Jiang, Q. Zhu, A. Liu, Y. Wu, C. Li, X. Ji, L. Gong, S. Li, Z. Chen, L. Kong, L. Han, A novel photoelectrochemical immunosensor based on TiO(2) @Bi(2)WO(6) hollow microspheres and Ag(2)S for sensitive detection of SARS-CoV-2 nucleocapsid protein, Microchem. J. 182 (2022) 107866, https://doi.org/ 10.1016/j.microc.2022.107866.

[95] H. Chang, Q. Zhu, Y. Wu, A. Liu, M. Jiang, C. Li, H. Li, L. Kong, Z. Chen, F. Sang, A sensitive label-free biosensor based on Ag(2)S-sensitive Bi(2)WO(6)/BiOBr heterojunction for photoelectrochemical immunoassay of prostate specific antigen, Talanta 257 (2023) 124343, https://doi.org/10.1016/j. talanta.2023.124343.

[96] H. Gong, X. Hu, R. Zeng, Y. Li, J. Xu, M. Li, D. Tang, CRISPR/Cas12a-based photoelectrochemical sensing of microRNA on reduced graphene oxide-anchored Bi₂WO₆ coupling with catalytic hairpin assembly, Sens. Actuators B 369 (2022) 132307, https://doi.org/10.1016/j.snb.2022.132307.

[97] Y. Hou, L. Zhu, H. Hao, Z. Zhang, C. Ding, G. Zhang, J. Bi, S. Yan, G. Liu, H. Hou, A novel photoelectrochemical aptamer sensor based on rare-earth doped Bi₂WO₆ and Ag₂S for the rapid detection of Vibrio parahaemolyticus, Microchem. J. 165 (2021) 106132, https://doi.org/10.1016/j.microc.2021.106132.

[98] R. Zeng, L. Zhang, L. Su, Z. Luo, Q. Zhou, D. Tang, Photoelectrochemical bioanalysis of antibiotics on rGO-Bi(2)WO(6)-Au based on branched hybridization chain reaction, Biosens. Bioelectron. 133 (2019) 100-106, https:// doi.org/10.1016/j.bios.2019.02.067.

[99] Y. He, H. Gao, J. Liu, A visible-light-active CuS/MoS(2)/Bi(2)WO(6) aptamer sensitively detects the non-steroidal anti-inflammatory drug diclofenac, Nanomaterials (Basel) 12 (16) (2022) 2834, https://doi.org/10.3390/ nano12162834.

[100] S. Chen, H. Nan, X. Zhang, Y. Yan, Z. Zhou, Y. Zhang, K. Wang, One-step hydrothermal treatment to fabricate Bi(2)WO(6)-reduced graphene oxide nanocomposites for enhanced visible light photoelectrochemical performance, J. Mater. Chem. B 5 (20) (2017) 3718-3727, https://doi.org/10.1039/ C6TB02493A.

[101] L.B. Zhu, L. Lu, H.Y. Wang, G.C. Fan, Y. Chen, J.D. Zhang, W.W. Zhao, Enhanced organic-inorganic heterojunction of polypyrrole@Bi(2)WO(6): fabrication and application for sensitive photoelectrochemical immunoassay of creatine kinase-MB, Biosens. Bioelectron. 140 (2019) 111349, https://doi.org/10.1016/j. bios.2019.111349.

[102] H. Wang, M. Wang, H. Chi, S. Zhang, Y. Wang, D. Wu, Q. Wei, Sandwich-type photoelectrochemical immunosensor for procalcitonin detection based on Mn²⁺ doped CdS sensitized Bi₂WO₆ and signal amplification of NaYF₄:Yb, Tm

upconversion nanomaterial, Anal. Chim. Acta 1188 (2021) 339190, https://doi. org/10.1016/j.aca.2021.339190.

[103] Y. Qian, J. Feng, D. Fan, Y. Zhang, X. Kuang, H. Wang, Q. Wei, H. Ju, A sandwich-type photoelectrochemical immunosensor for NT-pro BNP detection based on F-Bi (2)WO(6)/Ag(2)S and GO/PDA for signal amplification, Biosens. Bioelectron. 131 (2019) 299-306, https://doi.org/10.1016/j.bios.2019.02.029.

[104] R. Xu, D. Wei, B. Du, W. Cao, D. Fan, Y. Zhang, Q. Wei, H. Ju, A photoelectrochemical sensor for highly sensitive detection of amyloid beta based on sensitization of Mn:CdSe to Bi(2)WO(6)/CdS, Biosens. Bioelectron. 122 (2018) 37-42, https://doi.org/10.1016/j.bios.2018.09.030.

[105] T. Kakeshpour, B. Metaferia, R.N. Zare, A. Bax, Quantitative detection of hydrogen peroxide in rain, air, exhaled breath, and biological fluids by NMR spectroscopy, Proc. Natl. Acad. Sci. 119 (8) (2022) e2121542119, https://doi. org/10.1073/pnas.2121542119.

[106] G. Bellisai, G. Bernasconi, A. Brancato, L.C. Cabrera, I. Castellan, L. Ferreira, G. Giner, L. Greco, S. Jarrah, et al., Targeted review of maximum residues levels (MRLs) for indoxacarb, EFSA J. 20 (8) (2022) e07527, https://doi.org/10.2903/j. efsa.2022.7527.

[107] R. Zeng, M. Qiu, Q. Wan, Z. Huang, X. Liu, D. Tang, D. Knopp, Smartphone-based electrochemical immunoassay for point-of-care detection of SARS-CoV-2 nucleocapsid protein, Anal. Chem. 94 (2022) 15155-15161, https://doi.org/ 10.1021/acs.analchem.2c03606.

[108] G. Cai, Z. Yu, R. Ren, D. Tang, Exciton-plasmon interaction between AuNPs/ graphene nanohybrids and CdS quantum Dots/TiO₂ for photoelectrochemical aptasensing of prostate-specific antigen, ACS Sens. 3 (2018) 632-639, https://doi. org/10.1021/acssensors.7b00899.

[109] Q. Zhou, Y. Lin, K. Zhang, M. Lin, D. Tang, Reduced graphene oxide/BiFeO₃ nanohybrids-based signal-on photoelectrochemical sensing system for prostate-specific antigen detection coupling with magnetic microfluidic device, Biosens. Bioelectron. 101 (2018) 146-152, https://doi.org/10.1016/j.bios.2017.10.027.

[110] N. Andreasen, C. Hesse, P. Davidsson, L. Minthon, A. Wallin, B. Winblad, H. Vanderstichele, E. Vanmechelen, K. Blennow, Cerebrospinal fluid β-amyloid (1-42) in Alzheimer disease: differences between early-and late-onset Alzheimer disease and stability during the course of disease, Arch. Neurol. 56 (6) (1999) 673-680.

[111] R. Zeng, J. Xu, L. Lu, Q. Lin, X. Hunag, L. Huang, M. Li, D. Tang, Photoelectrochemical bioanalysis of microRNA on yolk-in-shell Au@CdS based on the catalytic hairpin assembly-mediated CRISPR-Cas12a system, Chem. Commun. 58 (2022) 7562-7565, https://doi.org/10.1039/D2CC02821B.

[112] Y. Li, R. Zeng, W. Wang, J. Xu, H. Gong, L. Li, M. Li, D. Tang, Size-controlled engineering photoelectrochemical biosensor for human Papillomavirus-16 based on CRISPR-Cas12a-induced disassembly of Z-scheme heterojunctions, ACS Sens. 7 (2022) 1593-1601, https://doi.org/10.1021/acssensors.2c06911.

[113] Y. Gao, Y. Zeng, X. Liu, D. Tang, Liposome-mediated in situ formation of type-I heterojunction for amplified photoelectrochemical immunoassay, Anal. Chem. 94 (2022) 4859-4865, https://doi.org/10.1021/acs.analchem.2c00283.

[114] Z. Yu, H. Gong, Y. Li, J. Xu, J. Zhang, Y. Zeng, X. Liu, D. Tang, Chemiluminescence-derived self-powered photoelectrochemical immunoassay for detecting a low-abundance disease-related protein, Anal. Chem. 93 (2021) 13389-13397, https://doi.org/10.1021/acs.analchem.1c03344.

[115] Z. Liu, H. Gong, J. Xu, Y. Li, Y. Zeng, X. Liu, D. Tang, Exploiting photoelectric activities and piezoelectric properties of NaNbO₃ semiconductors for point-of-care immunoassay, Anal. Chem. 94 (2022) 3418-3426, https://doi.org/10.1021/ acs.analchem.2c00066.

[116] R. Zeng, H. Gong, Y. Li, Y. Li, W. Lin, D. Tang, D. Knopp, CRISPR-Cas12a-derived Photoelectrochemical biosensor for point-of-care diagnosis of nucleic acid, Anal. Chem. 94 (2022) 7442-7448, https://doi.org/10.1021/acs.analchem.2c01373.

[117] Q. Li, L. Wang, J. Song, L. Zhang, C. Shao, H. Li, H. Zhang, Facile synthesis of hierarchical S-scheme In2S3/Bi2WO6 heterostructures with enhanced photocatalytic activity, J. Environ. Chem. Eng. 11 (2023) 109832, https://doi. org/10.1016/j.jece.2023.109832.

[118] V. Subhiksha, M.K. Okla, I.A. Alaraidh, A. Mohebaldin, W. Soufan, M.A. Abdel-Maksoud, R.F. Abdelaziz, A.M. Thomas, L.L. Raju, S.S. Khan, A prominent dual heterojunction framed CuWO4/Bi2WO6/MnS ternary NCs for para-chlorophenol degradation, Cr(VI) reduction & toxicity studies, Chemosphere 302 (2022) 134802, https://doi.org/10.1016/j.chemosphere.2022.134802.

[119] H. Yi, L. Qin, D. Huang, G. Zeng, C. Lai, X. Liu, B. Li, H. Wang, C. Zhou, F. Huang, S. Liu, X. Guo, Nano-structured bismuth tungstate with controlled morphology: fabrication, modification, environmental application and mechanism insight, Chem. Eng. J. 358 (2019) 480-496, https://doi.org/10.1016/j.cej.2018.10.036.