# Cellulose and Vanadium Plasmonic Sensor to Measure Ni\({}^{2+}\) Ions
###### Abstract  
A novel vanadium-cellulose composite thin film-based on angular interrogation surface plasmon resonance (SPR) sensor for ppb-level detection of Ni(II) ion was developed. Experimental results show that the sensor has a linear response to the Ni(II) ion concentrations in the range of 2-50 ppb with a determination coefficient (R\({}^{2}\)) of 0.9910. This SPR sensor can attain a maximum sensitivity (0.068\({}^{\circ}\) ppb\({}^{-1}\)), binding affinity constant (1.819 \(\times\) 10\({}^{6}\) M\({}^{-1}\)), detection accuracy (0.3034 degree\({}^{-1}\)), and signal-to-noise-ratio (0.0276) for Ni(II) ion detection. The optical properties of thin-film targeting Ni(II) ions in different concentrations were obtained by fitting the SPR reflectance curves using the WinSpall program. All in all, the proposed Au/MPA/V-CNCs-CTA thin-film-based surface plasmon resonance sensor exhibits better sensing performance than the previous film-based sensor and demonstrates a wide and promising technology candidate for environmental monitoring applications in the future. v 2021 26 March 2021  
sive, \(>\)20 ug/L [17; 18; 19]. The nickel-ion quantification at low concentrations thus became increasingly important. Several standard techniques have been developed over the years for measuring the total nickel amounts include atomic absorption spectroscopy, inductively coupled plasma spectrometry, anodic stripping voltammetry, and X-ray fluorescence spectroscopy [20; 21; 22; 23]. Overall, these existing methods have their advantages as having very highly sensitive and good accuracy; nevertheless, they have some limitations, such as time-consuming, expensive equipment, and the requirement of complex operation [24; 25; 26; 27; 28]. Hence, the detection of nickel using a very simple and high-sensitive method is of utmost demand. Recently, a very sensitive fluorescence sensor composed of a magnetic core-amino silica shell-fluorescein was successfully applied for the selective and sensitive nanomolar detection of nickel ions [22]. Another fluorescence method-based on imidazole-modified carbon dots with a detection limit of 0.93 mM [29]. A new strategy using a colorimetric sensor in both solution and paper-based membrane for the Ni ions determination was developed, resulting in the detection limit of 36 nM and 83 nM, respectively [30]. To date, only two techniques, fluorescence and colorimetric, are being investigated, yet they require a rather complicated operating process. Optical sensors offer clear advantages when compared to other methods such as easy handling, rapid analysis without pre-sampling, and high sensitivity of small analytes [31; 32; 33; 34; 35]. Surface plasmon resonance sensors stand out as attractive to detect nickel sensitively since nickel ions normally occur at very low-levels in the environment. Several reports have indicated the detection of nickel ion in this technique; however, many of them are not sensitive to detecting trace level concentrations in an aqueous solution. In recent studies, [PERSON] et al. (2019) successfully reported the modification of SPR sensors using graphene/nanocrystalline cellulose for nickel ions detection, but the detection limit of the sensor is only achieved at 0.01 ppm with low sensitivity [36]. Then, there is a growing demand for the development of surface plasmon resonance with enhanced sensitivity and detection limits. The basis of this is an SPR sensor dependent on measuring any increment of resonance angle related to the change of the refractive index at the sensor surface. At this point, it is desirable to modify the sensor surface with other novel materials to enhance the sensing properties. To date, cellulose nanocrystals (CNCs) derived from natural renewable resources meet the requirement of being good alternative sensor elements [37; 38; 39]. They possess desirable mechanical and chemical characteristics, such as high surface area, high tensile strength, high stiffness, and lack of apparent toxicity [40; 41; 42; 43; 44].