bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbon Nanotube Microelectrode Assembly for Electrochemical Sensors
Authors: Alvarez Noe , Miller Sydney , Buschbeck Elke , Gupta Pankaj , Gupta Vandna , Ruhunage Chethani
Published: May 2020

Assembling carbon nanotubes (CNTs) into macroscopic materials allows multiple applications that take advantage of their unique physical properties. Specifically, the synthesis, fiber assembly, polymer coating and application of CNTs as microelectrodes in electrochemical detection and quantification of heavy metals and neurotransmitters will be presented. CNT microelectrodes has been found to detect subnanomolar concentrations of Pb, Hg, Cd and Cu simultaneously. Excellent limits of detection of neurotransmitters (in the range of ~10-11M) such as dopamine (DA), serotonin (5-HT), epinephrine (Epn) and nor-epinephrine (Nor-epn) have been observed when using voltammetric techniques. As a proof of practical application, microelectrodes have been tested in real time DA release from culture rat pheochromocytoma (PC12) cells upon concentrate K+stimulation. In addition, the microelectrodes have been tested for recordings and stimulations of neuron electrical activity that is a topic of great interest in neuroscience. Multiple neurological disorders can benefit from a microelectrode that is flexible, chemically inert, electrically conducting, and preferentially transfers electrons via capacitive charge-injection. We compare the electron transfer capabilities among CNT fiber, noble metals Au and Ag wire microelectrodes when connected biological tissue. The recording ability of microelectrodes is demonstrated through Electroretinography (ERG) on Sarcophaga bullata fly eyes (Fig 1, left), where light stimulation generates potential changes that were detected by our microelectrodes. Stimulation is demonstrated through Au wire and carbon nanotube fiber implants in Madagascar hissing cockroach (Gromphadorhina portentosa) antennas (Fig 1, right)to control their locomotion directions. Interface Impedance, charge injection capacity and electrical conductivity of CNT microelectrodes demonstrates their potential in neuroscience applications.
WITHDRAWN: Room Temperature Operable Semiconducting Metal Oxide Chemi-Resistive NO2 Gas Sensor
Authors: Vijjapu Mani Teja , Surya Sandeep , Yuvaraja Saravanan , Salama Khaled Nabil
Published: May 2020

This abstract has been withdrawn at the request of the authors.
Investigation on Gas Sensing Properties and SVM Training of Perovskite Metal Oxide LaFeO3 Microsphere
Authors: Meng Fanli , Qin Wenbo , Zhang Hua , Yuan Zhenyu
Published: May 2020

Perovskite oxides have attracted extensive attention due to their excellent photoelectric properties in recent years. In this paper, LaFeO3 (LFO) perovskite microsphere were synthesized by simple hydrothermal synthesis with iron nitrate and lanthanum nitrate as metal sources and citric acid as complexing agent. The microstructure and crystal structure of perovskite nanomaterials were characterized by SEM and XRD. The LaFeO3 perovskite type gas sensor was manufactured and its gas-sensitive characteristics were studied. The results show that LaFeO3 sensor has good gas-sensitive performance to ethanol whose response reaches about 15 at 250℃, and has excellent selectivity and recovery ability. In addition, in the concentration gradient test, the support vector machine in mathematical theory was used for training and recognition, and the result shows that the recognition rate could reach 100%.

Figure 1
A Comparative Study of Fabricating IrOx Electrodes By Cyclic Thermal Oxidation and High Temperature Carbonate Oxidation
Authors: Huang Feifei , Bi Peng , Wang Qingrui , Zou Yang , Wang Weipeng , Wu Jiangshun , Jin Ying
Published: May 2020

IrOx electrodes were fabricated by cyclic thermal heating and water quenching (H&Q) process and high temperature carbonate oxidation, respectively. By examining the E-pH relationship, response rate, potential drift behavior of the fabricated electrodes, the electrodes prepared by H&Q process seemed to show better comprehensive performance. Characterization tests such as scanning electron microscopy (SEM), X-ray photoelectron spectrum (XPS), electrochemical impedance spectrum (EIS), etc. were used to characterize the fabricated IrOx electrodes and find out the reason for the better performance of the electrodes prepared by H&Q process. Morphology tests show that the H&Q electrode show a relative multi-layer structure, which could provide larger surface area for the H+ response process. At the meantime, combining the XPS and EIS test etc., more effective response composition, smaller response reaction of surface IrOx film could account for the better performance of the IrOx electrode.
Developing an Ion-Selective Electrode Membrane Sensor to Detect Lead Levels in Drinking Water
Authors: Delestre Jordan , Wang Po-Yen , Tang Xiaochao
Published: May 2020

Lead contamination in drinking water is often a close-to-home contamination caused by corroded lead service pipes connecting households to main lines or lead-based pluming within the households. This is particularly evident in houses built prior to 1986 when the United States Environmental Protection Agency (EPA) amended the Safe Drinking Water Act (SDWA) to prohibit the use of any lead-based pipe. Despite the legally established action limit of lead level of 15 parts-per-billion (ppb) in drinking water, incidents with disastrous consequences have occurred repeatedly (e.g. water crisis in Flint, Michigan). The objective of this research is to develop a polymeric ion-selective electrode (ISE) for the detection of lead levels at the EPA action level, or 10-9 molar concentration (M). Primarily, various ratios of sodium tetraphenylborate, resin powder, and lead-selective ionophore were considered and investigated to accomplish this goal. Two commercially available ionophores (Dibenzo-18-Crown-6 and Tert-Butylcalix(4)Arene-Tetrakis) were investigated as well as a synthesized poly (AN-co-HSA) copolyaniline ionophore. The commercially available ionophores were able to consistently achieve a limit of detection (LOD) of 10-6 M when used for the ISE electrode while the synthesized ionophore showed a less consistent LOD between 10-6 M and 10-9 M.
Photoelectrochemical Bioanalyte Sensor Based on Engineered One-Dimensional Nanostructured Oxide
Authors: Siavash Moakhar Roozbeh , Flynn Elizabeth , Mahshid Sahar Sadat , Mahshid Sara
Published: May 2020

Photoelectrochemical (PEC) non-enzymatic sensing systems are beneficial for the detection of low concentrations of biological molecules. Among different potential nanostructured materials, one dimensional TiO2 and ZnO nanorods are promising semi-conductor which can be successfully applied in many photoelectrochemical applications, mainly due to their photoactive properties, and long-term stability. In spite of their advantages, the wide band gap of 1D TiO2 and ZnO along with their high recombination rate confine their applications dramatically. These properties, prevent 1D TiO2 and ZnO from absorbing visible light; therefore, the semiconductor is only photoactive in the UV range. Here, we describe novel non-enzymatic sunlight-driven PEC sensors based on a modified 1D TiO2 nanorod array with cocatalyst and 1D ZnO core-shell structure for the aim of improved PEC non-enzymatic detection of glucose and H2O2, respectively. The 1D TiO2 and ZnO nanorods array were prepared through facile hydrothermal at and electrodeposition methods, respectively. The modified electrodes were characterized through FESEM, HRTEM, XRD, and UV-vis spectroscopy. The novel 1D TiO2 and 1D ZnO@TiO2 core shell electrodes exhibited enhanced PEC sensing properties with a low limit of detection and a high sensitivity, over a linear range of 0.1 – 1000 nM of glucose and 1 pM-100 mM of H2O2 in PBS. Additionally, the sensor displayed high selectivity, high stability, and high reproducibility. Overall, our engineered PEC sensor demonstrated ultrasensitive detection of glucose and H2O2 and a capable platform for continued development into the field of PEC non-enzymatic sensors.
Solid-State pH Sensors: Comparison of Sensing Performance of IrO2, Rh2O3 and Co3O4
Authors: Ryu Heejeong , Dong Qiuchen , Li Baikun , Lei Yu
Published: May 2020

Due to the importance of pH values for the control of water quality and chemical reactions, pH meter has been employed as a routine instrument in research laboratories and various industrial sectors to probe the acidity or alkalinity of aqueous solutions. Up to date, the most widely used pH sensor is conventional glass-type electrode which typically suffers from the disadvantage of the brittleness. Ion-sensitive field-effect transistor and optical pH sensors are also developed with improved durability, however, they have high power consumption concern and are not suitable for some specific applications. Therefore, solid-state pH sensor, which shares the similar detecting principle (electromotive force between sensing and reference electrodes) as conventional glass-type pH sensor, gradually becomes the trends in the development of pH sensor due to its durability, low cost and small size. In this study, nanostructured metal oxides from group 9 metals were synthesized and characterized, and then systematically investigated in solid-state pH sensing. The performance of different metal oxide-based solid-state pH sensors was compared through pH titration.
(Invited) Electrochemical Detection of Gases and Explosives in Ionic Liquids in Different Humidity Environments
Authors: Silvester Debbie S. , Lee Junqiao , Doblinger Simon , Hay Catherine
Published: May 2020

Amperometric gas sensors (AGSs) are widely used due to their many advantages, such as low-cost, portability, durability, wide linear range, high sensitivity and high selectivity [1]. They are available commercially from a number of companies [2], and can detect a range of redox-active gases. The sensor devices typically employ a water/sulfuric acid mixture as the electrolyte in contact with three electrodes, covered by a gas-permeable membrane. Room temperature ionic liquids (RTILs) have strong potential for use as alternative ‘designer solvents’ in membrane-free AGSs [3], which would solve the existing technological problems of commercial AGSs, including the slow diffusion through the membrane and solvent evaporation. Their non-volatility would enable the membrane to be dispensed with, and the entire sensor to be miniaturised to provide optimal functionality over a much wider range of ambient conditions and with a longer lifespan. This allows and encourages innovative designs, with the potential for gas sensors to move from single, finite devices to more sophisticated systems that exploit recent advances in portable electronics and computing.

In this talk, I will discuss some of the challenges facing ionic-liquid based sensors, such as solvent leakage, sensitivity to moisture and accumulation of electrogenerated products, and how we can innovatively design electrode materials and electrolytes to overcome these challenges. In particular, I will show that the choice of ionic liquid is crucial in high humidity gas environments, due to the structuring and layering of the ions in the electrical double layer [4]. I will also discuss the possibility to detect explosive compounds in RTILs, and polymer-RTIL mixtures [5]. Overall, it is clear that RTILs show tremendous promise as electrolytes in sensors, but more understanding of their long-term operation and utility in real environments is still needed.

References

[1] Stetter JR, Li J, Amperometric Gas Sensors – A Review Chem. Rev.
2008, 108, 352–366.

[2] Xiong L, Compton RG, Amperometric Gas detection: A Review Int. J. Electrochem. Sci., 2014, 9, 7152–7181

[3] Buzzeo MC, Hardacre C, Compton RG Anal. Chem. 2004, 76, 4583–4588.

[4] Doblinger S, Lee J, Silvester DS J. Phys. Chem. C
2019, 123, 10727−10737.

[5] Yu H, Lee J, Lewis SW, Silvester DS Anal. Chem.
2017, 89, 4729–4736.

Figure 1
pH Micro-Sensor from Modified Pt SECM Microelectrode for Local pH Measurement While Chromium Electrodeposition
Authors: Dasque Ariane , Gressier Marie , Taberna Pierre-Louis , Menu Marie-Joelle
Published: May 2020

In this work, it will be presented the chromium electrodeposition mechanisms with the use of a Scanning ElectroChemical Microscopy (SECM) micro-electrode. Among several factors, the pH is key to achieve even a metallic deposit. pH buffers and complexing agents are often used for this purpose [1] but in the vicinity of the electrode, at the electrode/electrolyte interface, strong variations are highly likely to occur. To this respect, since pH is a key parameter, a pH micro-electrode is intended to be developed to scan the pH gradient upon the electrodeposition of chromium. The first part of this work is so devoted to the pH micro-electrode realization from a platinum microelectrode on which iridium oxide is deposited. Iridium oxide has been reported to be suitable for local pH sensing [2-4]. Different parameters have been studied such as IrOx thickness and thermal treatment. The addition of Nafion has been assessed as well to achieve a tradeoff between fast response time, good selectivity and good stability [5]. An optimized IrOx micro-electrode has been obtained and used as SECM micro-electrode to get the evolution of the pH at the electrode/electrolyte interface upon electrodeposition. Different micro-electrode diameters have been used to improve the resolution. These results are promising and will allow going further to the development of chromium electrodeposition electrolyte helping to select the different complexing agents.

[1] D. Del Pianta et al. Determination of the chromium(III) reduction mechanism during chromium electroplating. Electrochimica Acta (2018) 234-241.

[2] H. A. Elsen et al. Effects of electrodeposition conditions and protocol on the properties of iridium oxide pH sensors electrodes. J. Electrochem Soc. 156 (2009).

[3] C. S. Santos et al. Fabrication and use od dual-function iridium oxide coated gold SECM tips. An application to pH monitoring above copper electrode surface during nitrate reduction. Electroanalysis 28 (2016) 1441-1447.

[4] Z. Zhu et al. A fabrication of iridium oxide film pH micro-sensor on Pt ultramicroelectrode and its application on in-situ pH distribution of 316 stainless steel corrosion at open circuit potential. Sensors and Actuators B 25 (2018) 1974-1982.

[5] I. G. Borislav et al. Thin-film IrOx pH microelectrode for microfluidic-based microsystems. Biosensors and Bioelectronics 21 (2005) 248-256.
New Insight into Gas Sensing Properties of SnO2 and Cu2o/CuO Based Gas Sensors By Near Ambient Pressure XPS
Authors: Vorokhta Mykhailo , Hozak Pavel , Khalakhan Ivan , Vrnata Martin , Lančok Ján , Matolín Vladimír
Published: May 2020

This study presents an investigation of the sensing properties of SnO2 and Cu2O/CuO based nanostructured chemiresistors, n-type and p-type semiconductors, respectively. The chemiresistors were used for the detection of ethanol and nitrogen dioxide, reducing and oxidizing agents, respectively. To unravel the chemical processes connected with gas detection, an in-situ approach was applied. This approach was based on near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) combined with simultaneous monitoring of sensor responses. The in-situ measurements were performed during exposure to the analytes at a total pressure of 0.05 – 1.05 mbar and 200 – 300 °C, and were correlated with chemiresistor response measurements carried out at a standard pressure and under an ambient atmosphere. The study enabled assessment of the relationship between the chemistry of surface processes on the sensitive layers and the "integral" response of the sensor devices and presented a complex view on the gas sensing mechanism and chemiresistors functionality.

Figure 1
Simple Electrochemical Method for the Quantification of Chlorite in Aqueous and Non-Aqueous Media
Authors: Rudolph Michael , Schneider Sebastian , Fischer Christian , Terfort Andreas
Published: May 2020

Chlorine-based disinfection technologies are most widely used to limit waterborne diseases and pathogenic organisms. Such disinfectants either are strong oxidants or species that generate oxidants as by-products. Especially for the use of chlorine dioxide as disinfecting agent the quantification of formed chlorite, likewise crucial for the regulatory issues of bleaching products [1,2], is of importance for the analysis of drinking water and process wastewater streams [2,3].

A robust differential pulse voltammetry (DPV) method for the quantification of chlorite (ClO2
-) down to the sub-ppm range has been developed. By using an electrolyte based on an ionic liquid (IL), both, aqueous and non-aqueous samples, could be employed. It was demonstrated that neither the other chlorooxo anions (hypochlorite OCl-, chlorate ClO3
- , or perchlorate ClO4
-) nor chloride interfere with the method. Different working electrode materials and ionic liquids were evaluated, of which the combination of glassy carbon with N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)azanide – based on the work of Hossain et al [4] – turned out to be the most suitable one. To demonstrate the feasibility of the method, a broad range of samples were investigated on their chlorite content, such as commercial disinfectants, bleaches, chlorinating agents, organic acid chlorides, as well as products of the Pinnick reaction, for which chlorite is used as a reagent.

[1] J. K. Skelly, J. Soc. Dyers Colourists, 76 (1960), 469-479.

[2] N. Oke, S. Singh, A. Garg, Water Sci Technol., 76 (2017), 2367-2379.

[3] J. N. Myers, W. H. Steinecker, Z. D. Sandlin, James A. Cox, G. Gordon, G. E. Pacey, Talanta, 94 (2012), 227-231.

[4] M. M. Hossain, E. Hosseini Bab Anari, L. Aldous, Electrochem. Comm., 34 (2013), 331-334.

Figure 1
Sub-ppb Sensing Level Hydrogen Sulphide at Room Temperature Using Doped Indium Oxide Gas Sensors
Authors: Al Shboul Ahmad , Izquierdo Ricardo
Published: May 2020

Hydrogen sulfide (H2S) is a highly corrosive, harmful, and toxic gas. Whereas 130 ppb is the threshold for maximum safety exposure level. Thus, it has become mandatory to develop highly sensitive sensors operating at room temperature to detect low levels of H2S. Sensors based on electrochemical measurement principles, semiconducting metal oxides or p–n heterojunctions have showed promising results to detect H2S gas. To date, drawbacks have boon reported due to their extended response times, high operating temperatures, limited selectivity to the gas and/or sensitivity to humidity changes. Efforts have been made to develop sensors based on metal oxides operable at room-temperature for H2S detection.

Here, we describe novel flexible H2S gas sensors based on optimized composite mixture of indium oxide (In2O3), copper acetate (CuAc), graphite (Gt) and polystyrene (PS). While we employed Gt in sensor’s structure to reduce sensor’s resistance to ~ 0.5 MΩ, we used PS and enhance sensor’s integrity as well as the adhesiveness of the sensing layer on the top of carbon electrodes. Whereas we applied In2O3 as the active material in sensors due to its promising performance to detect ~ 100 ppb gas concentration. We used CuAc as activator when it converts to the form of copper sulfide (CuS) due to its high conductivity (10 S/cm). Hypothetically, upon exposing sensors to the H2S gas, In2O3 converts spontaneously to the metallic form In2S3 (eq.1). Alternately, CuAc plays two critical roles in the sensor composition. First, CuS formation drops sensor’s resistance significantly due its high conductivity (eq.2). At this point, In2S3 and CuS can form a continues metallic layer, thus it increases sensor’s conductivity. Second, CuS may play a similar role as same as noble metals, which can cause the formation the structure of noble-doped metal oxide and ease oxygen molecules adsorption/ionization on sensor’s surface (eq.3,4). This may facilitate oxidizing and/or adsorption H2S on the sensor’s surface (eq.5,6), which consists of releasing electrons to sensors and reduce sensors resistance dramatically. The developed sensors have showed high selectivity toward H2S gas, high sensitivity to H2S concentration of less than 100 ppb, fast detection time less than 60 seconds, and high resistivity to humidity changes.

Figure 1
Development of a Selective Mixed-Potential Ammonia Sensor for Automotive Exhausts
Authors: Nematbakhsh Abkenar Gita , Viricelle Jean-Paul , Rieu Mathilde , Breuil Philippe
Published: May 2020

One of the most effective technologies in decreasing large-scale NOx emission produced by diesel engine vehicles is Urea-SCR (selective catalytic reduction) system. In order to prevent inducing excessive ammonia to the environment, an NH3 sensor is required at the exit of this system [1, 2]. In this study, highly selective ammonia sensors were developed to detect ammonia emissions from automotive exhaust.

The sensors were fabricated with 8-YSZ electrolyte, a platinum reference electrode and a working electrode of Au-V2O5 (mass ratio 85/15), screen-printed on an alumina substrate. A platinum resistor was printed at the backside of the support to control the sensor temperature. The measured sensor’ response (ΔV) is the potential difference between reference and working electrodes. Figure 1 shows the responses of two identical sensors to 100 ppm CO, NO2, NO and 20 ppm of NH3 at four different temperatures. It can be seen that the sensors respond to all gases at lower temperatures while by increasing temperature to 600°C, the selectivity to NH3 is greatly improved. The selectivity of sensors was also confirmed by testing other possible interfering gases: no responses were observed for 20ppm of hydrogen and 100ppm of a hydrocarbon mixture.

The stability of such sensors was studied at 550°C and 600°C. Since the sensors show no long-term stability at 600°C (electrode degradation), but remain stable at 550 °C, investigations were made to decrease the working temperature while maintaining selectivity. After testing different mass percentages of V2O5 in working electrode, we observed that by increasing this value to 50%, the working temperature of selective ammonia sensors could be decreased to 550°C with stable responses.

Further investigations will be performed in order to gain deeper insight in sensing mechanism of V2O5 based working electrodes, which governs the sensor’s performance.

References

[1] K. Shimizu, I. Chinzei, et al. "Doped-vanadium oxides as sensing materials for high temperature operative selective ammonia gas sensors," Sensors and Actuators B, 141, 2009, pp. 410-416.

[2] M. Van Nieuwstadt, I. Dpadhyay, et al. "Control of Urea SCR Systems for US Diesel Applications" in IFP Energies Nouvelles International Conference, Dearborn, USA, 2011, pp. 655-665.

Figure 1
Nanoporous-Based Sensors for Impedance Spectroscopy-Based Detection of Gaseous Pollutants
Authors: Schindelholz Mara , Small Leo J. , Henkelis Susan , Krumhansl James , Nenoff Tina M
Published: May 2020

The advanced in situ detection of gaseous pollutants (e.g. NOx and SOx) is of great interest in many applications, such as the automotive and coal industries. Here, we leverage the previous successful development of impedance spectroscopy-based sensors for the detection of gaseous I2 to develop a novel sensor for the detection of these gaseous pollutants. During initial development of an I2 sensor, a metal-organic framework (MOF ZIF-8) material was utilized as an adsorbent layer deposited onto Pt interdigitated electrodes. The MOF was demonstrated to selectively adsorb I2, irreversibly, from a complex gas stream with a (>105x) change in measured impedance across the electrodes1. Further studies aimed at developing a robust sensor examined other materials, including zeolites2 and additional MOFs. It was demonstrated that utilizing MFM-300(X) (X= Al, Fe, In or Sc metal center) active materials enabled a reversible electrical response via gas adsorption/desorption3. The current work is focused on exploring these same nanoporous phases (MOFs, zeolites, etc.) for the real-time detection of NOx and SOx. The down-selection of candidate materials from bulk synthesis and gas selectivity testing will be discussed. Methods for deposition of these materials onto the Pt interdigitated electrodes and initial sensor performance during controlled gas exposures will be presented.

Acknowledgements

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

References

1) Small, L.J and Nenoff, T.M., ACS Appl. Mater. Interfaces, 2017, 9 (51), 44649-44655.

2) Small, L.J.; Krumhansl, J.L.; Rademacher, D.X.; Nenoff, T.M. Micro. Meso. Mater., 2019, 280, 82-87.

3) Small, L.J.; Hill, R. C.; Krumhansl, J. L.; Schindelholz, M. E.; Chen, Z.; Chapman, K.W.; Zhang, X.; Yang, S.; Schroder, M.; Nenoff, T.M., ACS Applied Materials and Interfaces, 2019, 11(31), 27982-27988.
Optical Defects Engineering of Metal Oxide Nanosheets Toward Exceptional Chemiresistor
Authors: Kim Dong-Ha , Cha Jun-Hwe , Choi Sung-Yool , Kim Il-Doo
Published: May 2020

Metal oxide nanosheets (NSs) exhibit intriguing physicochemical properties such as high specific surface area, high fraction of reaction sites, thus leading to promising performance in various applications including energy storage, catalysis, and gas sensing. [1] Beyond the 2D metal oxide NSs, defect engineering and/or control of non-stoichiometry, that is, control of metal or oxygen vacancies, are a few of the powerful strategies to generate abundant active sites to enhance gas sensing performance. [2] Precise control of the heat treatment, ramping rate control or reducing heat treatment as examples, is an effective way to generate the oxygen vacancies, but is time-consuming which requires high thermal-budget. Building-up of hetero-junctions is another powerful method to boost up the sensing performance. [3] However, it has been a challenge to prepare thin-layered heterogeneous metal oxide NSs with abundant active defect sites.

An optical engineering to generate controllable oxygen vacancies and new crystal phases on various metal oxide nanosheets (NSs) is introduced via graphene oxide (GO) templating route followed by intense pulsed light (IPL) irradiation. Negatively charged GO flakes and metal ions readily self-assemble to form GO@M (where M = Sn2+, Co2+, Ti4+, and Zn2+) and polycrystalline metal oxide NSs, such as SnO2, Co3O4, TiO2, and ZnO, are successfully synthesized after calcination. Upon a few flashes of IPL irradiation (< 20 ms), a rapid increase in temperature (1200 °C) has induced evolution of defect sites and new crystal phases. As a representative, optically treated Pt-SnO2 NSs showed unparalleled formaldehyde (HCHO) response, excellent selectivity, low detection limit (100 ppb), and fast response speed (< 10 s) assisted by the synergistic effects of the Pt catalysts, numerous oxygen vacancies, and hetero-junctions formed by flash-induced partial reduction of n-type SnO2 to p-type SnO. This defects engineering method could greatly strengthen the design of various heterogeneous metal oxide NSs and their potential application toward various fields with the optimal customized physicochemical properties.

References

[1] Peng, L. et al. Holey two-dimensional transition metal oxide nanosheets for efficient energy storage. Nat. Comm.
8, 15139 (2017)

[2] Yuan, H. et al. ZnO nanosheets abundant in oxygen vacancies derived from metal-organic frameworks for ppb-level gas sensing. Adv. Mater.
31, 1807161 (2019)

[3] Miller, D. R. et al. Nanoscale metal oxide-based heterojunctions for gas sensing: a review. Sens. Actuators. B.
204, 250-272 (2014)
Flexible Ion-Selective Ca2+ and pH Microsensors to Study Biofilm/Biomaterials Interface in Real-Time
Authors: Koley Dipankar
Published: May 2020

Solid-state potentiometric sensors have an inherent advantage of miniaturization. We developed a 125 µm diameter solid-state fast response ion-selective pH and Ca2+ wire-sensors. These flexible microsensors were applied to quantify the real-time change in pH and Ca2+ concentration at hard-to-reach biofilm-biomaterials interface while live biofilms were growing on the Ca2+ releasing smart biomaterials. These smart biomaterials or substrates used in these studies were bioactive glass (BAG) containing resin dental composites that are capable of releasing metal ions (Ca2+) at pH less than 5.5.

The newly developed solid-state pH microsensors showed a near-Nernstian response (50 mV/pH) with a fast response time of <500 ms. Similarly, the solid-state Ca2+ microsensors showed a near-Nernstian slope of 28 mV/log[Ca2+] with a linear range of 10 µM to 1 mM along-with response time of less than 0.5 s. Both the pH and Ca2+sensors were then used inside a micro incubator set-up to quantify the real-time pH change at the biofilm-biomaterials interface due to bacterial (S. mutans) metabolism and the corresponding Ca2+ release from the (BAG) containing resins. Our systematic study showed that the lactic acid produced by Streptococcus mutans (Sm) biofilm when exposed to 30 mM sucrose, in BHI/MOPS media at 37°C, caused a pH shift from 7.0 to 5.7 at the biofilm-biomaterial interface. Recent findings of the effect of Ca2+ ions on bacterial growth and metabolism on different compositions of BAG-resin composites will be presented in the conference.

This work is supported by the National Institute of Dental and Craniofacial Research (NIDCR) (Grant # R01DE027999).
Hydrogen Sulfide Detection for Medical Breath Analysis with Surface Functionalized ZnO Nanowires
Authors: Kaiser Angelika , Torres Erick , Mauritz Tanja , Liu Yujia , Huber Florian , Herr Ulrich , Thonke Klaus
Published: May 2020

Over the past decade, the medical role of hydrogen sulfide (H2S) for therapeutic applications and diagnostics was extensively investigated and revealed the importance of H2S for medical breath analysis.

It was suggested that decreased production of the endogenous gaseous mediator H2S in tissues of the human respiratory system can be interpreted as an early detection biomarker for inflammatory diseases like asthma etc. In order to detect the H2S concentration levels of interest, a reliable selective device sensitive to H2S in the very low parts per billion (ppb) range is needed.

The main goal of our project is the development of such a highly sensitive, reproducible and reliable H2S gas sensor, acting as a future integrated component of a multiple-sensor array in an “electronic nose” type device for medical applications or for detecting trace concentrations in chemical industry.

We present here a planar resistive gas sensor design based on the gas sensing mechanism of a chemical field effect transistor (ChemFET) made from very high quality zinc oxide (ZnO) nanowires (NW) with gas sensitive open gate. The open gate operates as a transducer between adsorption/desorption of the ambient target gas and a measurable resistivity change in the NWs. This resistivity change results from the band bending effect of metal oxide surface exposed to different gas atmospheres and is analyzed by current-time (I-t) measurements.

To improve the selectivity of our ZnO NW sensor towards a certain target gas, we investigated the impact of surface modification by addition of catalytic metal layers on the detection limit of our ZnO NWs towards H2S. In particular, we studied the chemical affinity between gold (Au) and sulfur (S) which leads to catalytic effects between the sputtered gold nanoparticle layer and the target gas H2S. Accordingly, H2S molecules are expected to adsorb more efficiently on Au modified ZnO NWs and drastically improve the overall sensor performance towards H2S. Our modified ChemFETs showed higher signal-to-noise ratio (SNR), improved sensitivity, faster response time, and an exceptionally low detection limit of less than 10 ppb for H2S diluted in synthetic air at room temperature.
Single Atom Catalysts-Anchored Carbon Nitride: Dual Sensitisation and Morphological Control of Metal Oxide Nanofibers
Authors: Shin Hamin , Kim Dong-Ha , Kim Il-Doo
Published: May 2020

Reducing the size of noble metal catalysts is one of the key goals in designing catalytic systems with maximum efficiency. Sensitisation of metal oxides with noble metals in a form of single-atoms or a few-atoms-cluster is hence of great interest in various fields including photocatalysis and catalytic conversions [1][2]. With this respect, we employed single atom-anchored shredded carbon nitride nanosheets (Pt-MCN) as a catalyst that can work as both dual-sensitizer and a morphological modifier of tin oxide nanofibers (SnO2 NF). Through electrospinning followed by a calcination process, it is possible to synthesize metal oxide nanofibers uniformly functionalized with Pt-MCN. Thermally stable carbon nitride survives through the calcination step and forms heterojunctions with tin oxide, hence acts as a dual-sensitizer together with the atomic scale Pt, and at the same time, induces the formation of peculiar nano-fiber-in-tubes (FIT) instead of nanofibers. Atomic scale Pt strongly bound on MCN experiences only a minor degree of agglomeration even after calcination, and the majority remains in singly dispersed state, as confirmed by HAADF-STEM analysis. This structure demonstrates an excellent sensing performance toward formaldehyde gas, and in particular, showing an extremely low experimentally determined limit of detection (LOD = 50 ppb).
Ultra-High-Sensitive Detection Using Pulse-Heating of MEMS-Type Oxide Semiconductor Gas Sensor: (2) Detection of Ethanol in Ppb Level By Introducing Oxygen Supplier
Authors: Shimanoe Kengo , Hiroyama Yuki , Suematsu Koichi , Watanabe Ken
Published: May 2020

As mentioned in previous presentation, gas sensor using pulse-heating of MEMS-type Pd-SnO2 could show ultra-high-sensitive (UHS) detection in ppt level to toluene. However, toluene is easy to oxidize on Pd-SnO2 because of aromatic compound. In order to apply the UHS sensor using MEMS-type for aliphatic compounds such as alcohol, the sensing layer needs some modifications because of improvement of oxidation. So we have investigated for UHS sensing to ethanol by using a composite material that consists of the perovskite-type oxide (Ba0.9La0.1FeO3-σ) and SnO2 nanoparticles. SnO2 powder was prepared through a hydrothermal treatment (1) and perovskite type oxide powder was prepared though an amorphous malic acid complex method. The powder mixed perovskite oxide and SnO2 particles was evaluated for the gas sensing properties in ethanol gas by using same apparatus as toluene detection. The obtained results indicated that perovskite type oxide added SnO2 nanoparticles exhibits higher sensor response to C2H5OH than that of pure SnO2, as shown in Fig. 1. In addition, the introducing of the pre-heating before measurement was effective for the sensor response as same as the case of toluene detection. It seems that the perovskite-type oxide plays a role of oxygen supplier to avoid the situation of oxygen absent or that the perovskite-type oxide works as a partial oxidation catalyst.

References

(1) K. Suematsu, Y. Shin, Z. Hua, K. Yoshida, M. Yuasa, T. Kida, K. Shimanoe, ACS Appl. Mater., 6, 5319−5326 (2014).

(2) K. Suematsu, W. Harano, T. Oyama, Y. Shin, K. Watanabe, K. Shimanoe, Anal. Chem., 90(19), 11219-11223 (2018).

Figure 1
Electrochemical Sensors for on-Site Detection of Toxic Metal Ions in Environmental Water Systems
Authors: Hosseini Narouei Farideh , Livernois Leah , Wajdan Zahid , Memon Najma , Andreescu Daniel , Andreescu Silvana
Published: May 2020

Easy to use devices for the rapid detection of toxic metal ions in drinking water is essential for improving monitoring, identification and management of water resources. In 2014, over 100,000 residents of Flint, Michigan, were exposed to high levels of lead in their drinking water, leading to serious environmental and health issues. The problem faced by Flint is a perfect example of the need for a portable device for on-site detection system that can sense the presence of high concentrations of toxic metal ions in the environment in natural pH with no sample pretreatment. In this work, an easy to use method for metal ion detection in natural water samples was developed. Preconcentration of ions at the electrode surface was achieved by optimizing a nanostructured layer consisting of gold nanoparticles and a conductive polymer, which improved detection sensitivity and selectivity withing limits that cover the EPA levels for metal ion exposure. The method was demonstrated for the detection of As, Pb and Hg in natural waters, using anodic stripping voltammetry (ASV). Several parameters were optimized in order to achieve the highest detection sensitivity, including pH, ionic strength and deposition time. Local water samples were tested for heavy metal ion content and validated using lab-based methods, including atomic absorption spectroscopy (AAS) and ICP-MS. This methodology was applied onto the surface of low-cost screen-printed electrodes which are easy to use and portable.
Ppb-Level of Ammonia Sensor on Reduced-Graphene Oxide Nanocomposite By the Supercritical Fluid Technique
Authors: Syu Wei-Jie , Wang Shih-Han , Chen Bo-Rong
Published: May 2020

Ammonia is an important indicator for the environment quality and agriculture safety applications. Besides, various medical reports have indicated that exhaled ammonia gas is considered to be a non-invasive biomarker of liver and kidney diseases. The exhaled ammonia gas concentration for healthy human is in the range of 200-2000 ppb [1], and for the environmental quality evaluation it should be lower than 50 ppb [2]. Due to the low concentration and the complicate sample gases, it is important to develop a highly sensitive and selective ammonia sensor. Several materials such as metal oxide, conducting polymer and carbon nanomaterials have been extensively examined for ammonia gas sensing. In this study, tungsten oxide and polyaniline was incorporated into easily functionalized reduced graphene in supercritical fluid to form a p-type nanocomposite. Metallic nanocatalyst was doped to enhance the sensitivity and selectivity. Ammonia was adsorbed onto the sensing membrane and then oxidized at room-temperature. Therefore, the resistance of sensing membrane increased with ammonia concentration. The sensor could detect the ammonia concentration in the range from 0 to 100 ppm at room temperature. The sensitivity was enhanced 4 times by the nanocatalyst, and the lower detection limit was 50 ppb. The effect of interference gases, including nitric oxide (NO), carbon monoxide (CO), carbon dioxide (CO2), sulfur dioxide (SO2) has been evaluated as well, and all the cross-talk was less than 10%. Furthermore, ammonia gas is highly water soluble, the sensing resistance could shift significantly with humidity, especially in higher humid atmosphere. In order to solve the problem, the electrode surface was designed to be more hydrophobic. After surface modification, the humidity effect decreased. The sensing mechanism of electrode and effect of humidity was also investigated. The experimental result suggested that the catalyst doped nanocomposite had high sensitivity, stability and selectivity for low concentration ammonia sensing at room temperature. A room temperature operated ppb-level ammonia sensor could be valuable solution for exhaled gas or environmental quality monitoring.

[1] S. Abdulla, J. Dhakshinamoorthy, V. Mohan, D. V. Ponnuvelu, V. K. Kallidaikuruchi, L. M. Thalakkotil, B. Pullithadathil. J. Breath Res. 13 (2019) 046005; doi: https://doi.org/10.1088/1752-7163/ab278b

[2] M. Insaustia, R. Timmis, R. Kinnersley , M. C. Rufino. Sci. Total Environ. (2019) 135124； doi: https://doi.org/10.1016/j.scitotenv.2019.135124.
Electrochemical Microbial Sensor for Rapid Detection and Quantification of Total Bacterial Count
Authors: Ramanujam Ashwin , Carroll Ronan K. , Lacerda Carla M. R. , Botte Gerardine G.
Published: May 2020

Early and online detection of pathogens in the agricultural sector is vital in terms of crop protection as well as economy. Within this context, an electrochemical microbial sensor with a locally formed electrocatalyst was used for rapid detection of gram-negative and gram-positive bacteria in a suspension of bacteria in water. Initially, the background signals of each bacterial species in water were determined. Following this, the current response from the sensor was used to detect total bacterial concentration of a suspension containing both types of bacteria. Escherichia coli and Staphylococcus aureus were used as the model bacteria for these experiments. These bacteria had the ability to hinder the reduction reaction occurring at the electrode surface, leading to a drop in the current. Concentrations ranging from 102 to 108 cfu/ml were detected by this sensor. By monitoring the total bacterial concentration of washed water online, this sensor could be of great use anywhere along the food chain, starting from crop production until the marketing of food.
Electrochemical Detection Using Nanoporous Structures
Authors: Jiang Junhua , Wang Congjian
Published: May 2020

Nanoporous electrodes are a unique class of nanostructured electrodes for promising electrochemical sensor applications because of a range of important attributes which include but are not limited to: high surface area, interesting catalytic properties, fast mass transport and low Ohmic resistance drops, potentially low cost and good fouling tolerance [1, 2]. In addition to the conventional concept of enlarged surface area, nanoporous structures provide a unique environment for reactive molecules. Once a reactant molecule enters a nanopore, the probability of interaction between the nanoporous electrode surface and the molecule is increased compared with that on a flat electrode. The molecule involved in a sluggish electrochemical reaction can enter deep into the nanopore, leading to longer penetration depth. Consequently, the heterogeneous charge transfer gets facilitated and the amperometric response of sluggish faradaic reactions can be selectively enhanced. This will selective amperometric detection, in which the selectivity and sensitivity could be tuned by the depth, shape, and interconnectivity of the nanopores. In addition, the nanoporous structures resulted nano-confinement effects can prevent reactive intermediates from escaping back to the bulk solution. Expedited by the rapid advance of nanomaterial engineering and manipulating technology, nanoporous electrodes will be a strong impetus to a wide range of emerging areas such as in-situ and remote monitoring and controls [3, 4].

In this presentation, we will introduce the structural effects of nanoporous materials including discriminative electrokinetics, the nano-confinement effect and electrical double layer overlapping, the fabrication nanoporous microelectrodes, the characterization of their porous structures, and their nanopore-induced enhanced electrochemical responses to several interesting molecules such as nitrate, nitrite, and chlorides.

References

[1] F. Nicholas and C. Knospe, Fabrication and characterization of nanoporous gold electrodes for sensor applications, Adv. Eng. Mater., 21, 1800857 (2019).

[2] Z. Li, et al., Confinement effects on an electron transfer reaction in nanoporous carbon electrodes, J. Phys. Chem. Lett.,
8, 1925 (2017).

[3] K. Fu and P. Bohn, Nanopore electrochemistry: a Nexus for molecular control of electron transfer reactions, ACS Cent. Sci.,
4, 20 (2018).

[4] H. Qiu, X. Li, H. Xu, H. Zhang, Y. Wang, Nanoporous metal as a platform for electrochemical and optical sensing, J. Mater. Chem. C, 2014, 2, 9788 (2014).
Application of Gold Nanoparticles with 1,6-Hexanedithiol Modified Screen-Printed Carbon Electrode As a Sensor for Determination of Arsenic in Environmental Samples
Authors: Etorki Abdunnaser Mohamed , Elraies Mahmoud Abdelsamed , Awin Labib Ali , Elhabbat Mahsen , Shaban Ibrahim
Published: May 2020

The development of electrochemical nano sensor was described for the detection of total arsenic in groundwater, soil, food and honey samples based on the formation of gold nanoparticles. Screen printed carbon electrodes were modified with gold nanoparticles and linked with 1,6-hexanedithiol self-assembled monolayers. The electrodeposition of Au nanoparticles was applied in 10 mL of the solution that totally cover the screen-printed carbon electrode while applying a constant potential of -0.4 V (vs Ag within SPCE) for 600 sec. Cyclic voltammetry was used to characterize the gold nanoparticles before and after modified with 1,6-hexanedithiol self-assembled monolayers on screen printed carbon electrode (Figure 1). Square wave anodic stripping voltammetry with multi point standard addition method was examined for the detection of As(III) and As(V) on Au NPs-1,6-hexanedithiol modified screen printed carbon electrode under optimized conditions. As(III) and As(V) was firstly, deposited for 60 seconds by the reduction of arsenic in buffer solution: (citric acid, sodium chloride and ascorbic acid pH 2.0), followed by As stripping between -0.20 and 0.35 V at the following parameters: scan rate: 100 mV s-1, frequency: 60 Hz, amplitude: 0.025 V and increment: 5.0 mV. it was found that Au- NPs with 1,6-hexanedithiol modified screen-printed carbon electrode had a highest anodic stripping peak current at 0.201V. The limit of detection value for arsenic was identified to be 1.7 ng ml-1. Also, the electrochemical nanosensor showed excellent reproducibility and high stability. The developed method was successfully applied to detect total arsenic in ground water, soil and wastewater samples.

Figure 1
Portable Sensors for Rapid Assessment of Phosphate Level in Eutrophic Waters
Authors: Mustafa Fatima , Andreescu Silvana
Published: May 2020

Portable, easy-to use sensors for in situ detection of water pollutants is of great importance. This presentation will describe the development of a paper-based sensor to determine phosphate levels in eutrophic water bodies. Although phosphorus (P)–based fertilizers are essential for sustaining agricultural food production, the oversupply of P leads to water eutrophication which has severe consequences on the environment and human health. To achieve the objective to develop effective management tools for assessing water eutrophication, we develop sensors that can be used to screen the affected areas and quantify the levels of phosphate in situ. The sensor incorporates nanomaterials with P-specific binding properties deposited on cellulosic paper. This presentation will discuss assembly of the sensing materials on cellulosic paper, the recognition mechanism and the performance characteristics of the system for phosphate detection. The developed sensor is easy to use, portable and can provide rapid and selective onsite detection for monitoring nutrient content in eutrophic water