Photoelectrochemical detection of chromium (VI) using layered MoS2 modified BiOI

A novel "turn-off" photoelectrochemical aptasensing platform for selective detection of tobramycin based on the Ti3C2-MoS2/BiOI heterojunction

Tobramycin (TOB), as a widely used antibiotic, poses severe unpredictable risks to ecology and health. In this study, a novel photoelectrochemical (PEC) adapter sensor, based on its "turn-off" PEC mode, was constructed for TOB detection. This visible-light-driven photoelectrochemical (PEC) aptasensor was successfully developed for TOB detection using Ti3C2-MoS2/BiOI and TOB aptamer probes. When TOB was captured by probes anchored on the modified electrode, a decreased photocurrent was also noted due to steric hindrance and this further hindered electron transfer. Under optimal conditions, 0.001 ng mL-1 to 40 ng mL-1 of TOB could be identified, with the detection limit being as low as 0.5 pg mL-1. At the same time, actual samples were also explored. Finally, the proposed sensor exhibited high specificity, satisfactory detectability and great reproducibility, thereby providing a novel approach for the detection of pollutants.

Unbiased and Signal-Weakening Photoelectrochemical Hexavalent Chromium Sensing via a CuO Film Photocathode

Photoelectrochemical (PEC) sensors show great potential for the detection of heavy metal ions because of their low background noise, high sensitivity, and ease of integration. However, the detection limit is relatively high for hexavalent chromium (Cr(VI)) monitoring in addition to the requirement of an external bias. Herein, a CuO film is readily synthesized as the photoactive material via reactive sputtering and thermal annealing in the construction of a PEC sensing photocathode for Cr(VI) monitoring. A different mechanism (i.e., Signal-Weakening PEC sensing) is confirmed by examining the electrochemical impedance and photocurrent response of different CuO film photoelectrodes prepared with the same conditions in contact with various solutions containing concentration-varying Cr(VI) for different durations. The detection of Cr(VI) is successfully achieved with the Signal-Weakening PEC response; a drop of photocathode signal with an increasing Cr(VI) concentration from the steric hindrance effect of the in situ formed Cr(OH)₃ precipitates. The photocurrent of the optimized CuO film photocathode linearly declines as the concentration of Cr(VI) increases from 0.08 to 20 µM, with a detection limit down to 2.8 nM (Signal/Noise = 3) and a fitted sensitivity of 4.22 µA·μM^-1. Moreover, this proposed sensing route shows operation simplicity, satisfactory selectivity, and reproducibility.

Ecological effects, remediation, distribution, and sensing techniques of chromium

Chromium is detected in most ecosystems due to the increased anthropogenic activities in addition to that developed from natural pollution. Chromium contamination in the food chain results due to its persistent and non-degradable nature. The release of chromium in the ecosystem accretes and thereafter impacts different life forms, including humans, aquatic and terrestrial organisms. Leaching of chromium into the ground and surface water triggers several health ailments, such as dermatitis, eczematous skin, allergic reactions, mucous and skin membrane ulcerations, allergic asthmatic reactions, bronchial carcinoma and gastroenteritis. Physiological and biological treatments for the removal of chromium have been discussed in depth in the present communication. Adsorption and biological treatment methods are proven to be alternatives to chemical removal techniques in terms of cost-effectiveness and low sludge formation. Chromium sensing is an alternative approach for regular monitoring of chromium in different water bodies. This review intended to explore different classes of sensors for chromium monitoring. However, the spectrochemical methods are more sensitive in chromium ions sensing than electrochemical methods. Future study should focus on miniaturization for portability and on-site measurements without requiring a large instrument provides a good aspect for future research.

Application of Polydopamine Functionalized Zinc Oxide for Glucose Biosensor Design

Zinc oxide (ZnO) nanostructures are widely used in optical sensors and biosensors. Functionalization of these nanostructures with polymers enables optical properties of ZnO to be tailored. Polydopamine (PDA) is a highly biocompatible polymer, which can be used as a versatile coating suitable for application in sensor and biosensor design. In this research, we have grown ZnO-based nanorods on the surface of ITO-modified glass-plated optically transparent electrodes (glass/ITO). Then the deposition of the PDA polymer layer on the surface of ZnO nanorods was performed from an aqueous PDA solution in such a way glass/ITO/ZnO-PDA structure was formed. The ZnO-PDA composite was characterized by SEM, TEM, and FTIR spectroscopy. Then glucose oxidase (GOx) was immobilized using crosslinking by glutaraldehyde on the surface of the ZnO-PDA composite, and glass/ITO/ZnO-PDA/GOx-based biosensing structure was designed. This structure was applied for the photo-electrochemical determination of glucose (Glc) in aqueous solutions. Photo-electrochemical determination of glucose by cyclic voltammetry and amperometry has been performed by glass/ITO/ZnO-PDA/GOx-based biosensor. Here reported modification/functionalization of ZnO nanorods with PDA enhances the photo-electrochemical performance of ZnO nanorods, which is well suited for the design of photo-electrochemical sensors and biosensors.

Enhanced the photoelectrochemical performance of Bi2XO6 (X = W, Mo) for detecting hexavalent chromium by modification of CuS

In this work, Bi₂XO₆ (X = W, Mo) are synthesized at different temperatures. The results of tests find the optimal temperatures of Bi₂WO₆ and Bi₂MoO₆ are 180 and 160°C (BW-180, BM-160). Then, BW-180 and BM-160 are further compounded with different contents of CuS. The results of photoelectrochemical (PEC) tests show that CuS can improve the PEC performance of semiconductor materials, and it has better performance when CuS mass fraction is 5%. These maybe the photoelectron potentials generated by CuS/Bi₂XO₆ (X = Mo, W) heterojunction reduce the combination of photogenerated electrons and holes. When the PEC sensor based on 5%-CuS/BW-180 detects Cr(VI), it has a linear range of 1-80 μmol/L with detection limit of 0.95 μmol/L, while the PEC sensor based on 5%-CuS/BM-160 detects Cr(VI) has a linear range of 0.5-230 μmol/L and a detection limit of 0.12 μmol/L. Thus, 5%-CuS/Bi₂XO₆ has potential application in hexavalent chromium detection.

Visible light-driven photoelectrochemical ampicillin aptasensor based on an artificial Z-scheme constructed from Ru(bpy)32+-sensitized BiOI microspheres

Dye sensitization is an alternative strategy to improve photoelectric activity of semiconductors and, particularly, to enhance the activity towards visible light domain. Herein, an artificial Z-scheme bipyridine ruthenium (Ru(bpy)32+) sensitizing narrow-gap bismuth oxy-iodide (BiOI) microspheres was constructed by a simple electrostatic interaction strategy for the first time. The electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) analysis showed that this design of such Z-scheme structure was helpful to enhance the interfacial charge transfer and improve the photoelectric conversion efficiency. In addition, due to the sensitization of Ru(bpy)32+, the band gap was narrowed from 1.8 eV of BiOI microspheres to 1.3 eV of BiOI/Ru(bpy)32+ microspheres, leading to improve the utilization of visible light. So that, the photocurrent of the resulted BiOI/Ru(bpy)32+ was 13.0 times that of pure BiOI microspheres. In view of the outstanding photoelectrochemical (PEC) performance of BiOI/Ru(bpy)32+ and the high specificity of the aptamer, the PEC aptasensor for ampicillin (AMP) merits the excellent detection performance including a broad linear ranging from 1 × 10-7 nM to 100 nM as well as a low detection limit of 3.3 × 10-8 nM (S/N = 3). This work not only provides a novel way to construct and design highly efficient photoactive materials for PEC detection, but also broadens the application of Z-scheme in the field of sensing.

Recent Advances in Electrochemical Monitoring of Chromium

The extensive use of chromium by several industries conducts to the discharge of an immense quantity of its various forms in the environment which affects drastically the ecological and biological lives especially in the case of hexavalent chromium. Electrochemical sensors and biosensors are useful devices for chromium determination. In the last five years, several sensors based on the modification of electrode surface by different nanomaterials (fluorine tin oxide, titanium dioxide, carbon nanomaterials, metallic nanoparticles and nanocomposite) and biosensors with different biorecognition elements (microbial fuel cell, bacteria, enzyme, DNA) were employed for chromium monitoring. Herein, recent advances related to the use of electrochemical approaches for measurement of trivalent and hexavalent chromium from 2015 to 2020 are reported. A discussion of both chromium species detections and speciation studies is provided.