In this study, a PoL/RGO material was successfully synthesized and employed to modify the working electrode for determining MPB in medication products through voltammetric techniques. The structure of the nanocomposite was characterized by UV–vis and FT-IR spectrum and its application to the MPB electrochemical detection was tested by the CV and DPV techniques. In the result, the modified PoL-RGO/GCE electrode exhibited a superior response toward MPB by applying the DPV method, compares to using the bare GCE, with a limit of detection (LOD), a limit of quantification (LOQ) is 0.20 μM and 0.70 μM, respectively and the concentration ranging from 1 to 200 μM. In addition, the repeatability (RSD of 2.2, 1.6, 1.4 for 5, 50 and 100 μM MPB, respectively), and the reproducibility (RSD of 4.7%) of the technique were examined as well. This illustrates the performance of the electrochemical sensor was statistically investigated by the CV and DPV methods demonstrating accuracy comparable to other analytical methods as well as indicating that MPB can be determined in cosmetics with high recovery ranging from 97% to 104.3%.

https://iopscience.iop.org/article/10.1149/2754-2726/ac8aa7/pdf

Detection of Methylparaben in Cosmetics by Poly L–Lysine/Reduced Graphene Oxide-Based Sensor

A double layered nanosheet structure of NiO over ZnO incorporated on Micro electro mechanical system (MEMS) device consisting of heater electrodes and sensing electrodes were investigated for gas sensing characteristics of Ammonia (NH 3 ) gas. This process was achieved by combining 2 different deposition processes which are hydrothermal for ZnO and sputtering for NiO. From the synthesized samples, a series of different structural and morphological properties were analyzed such as X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM) and Energy dispersive spectroscopy (EDS). Sensing properties of ammonia gas are investigated with two different thicknesses of NiO and at different temperatures in order to find the best possible sensing response properties. The inspection of NiO/ZnO loaded samples sensing properties with ammonia gas ranging from 2.25 ppm to 18 ppm, revealed that 20 nm thickness of NiO with ZnO at 35 °C is the optimal sensing condition for the study. 18 ppm of ammonia gas recorded 55.8% sensing response at 35 °C with a response time of 8 s. Selectivity of the NiO/ZnO sensor is tested with 6 different gases such as CO, H 2 , H 2 S, NO 2 , SO 2 and NH 3 , sensor demonstrated good selectivity for ammonia gas and showed excellent repeatability property. 

Low-Temperature Ammonia Gas Sensor Based on NiO/ZnO Heterojunction Nanosheet on MEMS Devices


 An ultrasensitive and rapid electrochemical detection of trace Hg(II) sensor was developed. The significantly amplified electrochemical signals were caused by the high specific surface area of the electrochemical sensor. Scanning electron microscopy showed that the gold nanospikes were 200-300 nm in length and 50 nm in diameter. The electrochemical properties of sensor were characterized by square wave voltammetry. Experimental parameters were optimized using square wave stripping voltammetry. The linear range of sensor for Hg(II) is 3×10-10 mol l-1 ~ 7×10-7 mol l-1 and the limit of detection is 1×10-10 mol l-1. Hg(II) was successfully quantified in river water and cosmetics. The original Hg(II) in loose powder, sunblock, and whitening lotion using the high ratio surface area electrochemical sensor determination were found to be 2.234, 2.056, and 2.347 mg kg-1, respectively. The results are within the range of standard values, the RSD are 1.7 %, 1.5 %, and 2.1 %, respectively. The HRSA Au electrode sensor displays high sensitivity, excellent stability, reproducibility, and is more convenient than ICP-MS and AFS verification methods. We look forward to the possibility that the HRSA Au electrode sensor can be used for real-time monitoring of mercury ions in water and cosmetics in the future.

Detection of Trace Hg(II) in Cosmetics and Aqueous Solution by a Gold Nanospikes Electrochemical Sensor

This paper presents our work towards improving the reliability of high-sensitivity pH sensor based on the top-gate effect in an amorphous indium-gallium-zinc oxide thin-film transistor (a-InGaZnO TFT) and its application to the sensing of a sodium ion and a potassium ion. Here, we propose an extended-gate a-InGaZnO TFT pH sensor with an atomic layer deposition (ALD)-AlO x /sputtered-TaO x layered top-gate insulator and a Ti extended-gate electrode. We discuss our primary results for the extended-gate a-InGaZnO TFT pH sensor, including its pH sensitivity and ability to respond to a pH change of 0.001. The extended-gate a-InGaZnO TFT pH sensor resulted in over Nernstian pH sensitivity of 625 mV/pH. The pH sensor indicated the possibility of detecting a pH change of 0.001 with some signal processing techniques. Furthermore, we demonstrated the sensing of a sodium ion and a potassium ion with a-InGaZnO TFT and an ion-sensitive extended-gate electrode. The sensors indicated a clear response to the concentration changes of sodium and potassium ions with a sensitivity of 1030 mV/decade and 866 mV/decade, respectively. These results demonstrate that our extended-gate structure has the potential to detect with high sensitivity concentration changes in various ions just by replacing the extended-gate electrode with various ion-sensitive membranes. 

Demonstration of Extended-Gate Structure for Ion Sensors based on Amorphous Indium-Gallium-Zinc Oxide Thin-Film Transistors


 Hydrogen is regarded as a secondary energy carrier derived from hydrogen evolution reactions. To ensure safety when utilizing this hazardous gas, hydrogen gas sensors with rapid response and recovery times, high sensor sensitivity, and stability are essential. A high surface-to-volume ratio with complete adsorption and desorption of ions renders WS2 a promising candidate for hydrogen gas sensor applications. This study introduces a novel high-performance hydrogen gas sensor based on a metal sulfide-platinum (WS2-Pt) composite. The WS2-Pt composite was successfully synthesized using a solution-based process and spin-coating techniques. WS2-Pt nanostructures were densely distributed on a gallium nitride/sapphire substrate, and a hydrogen sensing device was fabricated. The metal sulfide/platinum composite demonstrated ultra-fast sensor response of approximately 3 seconds toward 500 ppm hydrogen with a satisfactory sensor sensitivity. The response rate was notably encouraging. This research represents the first attempt in the sensor domain to enhance the performance of hydrogen sensing devices using metal sulfide/Pt active layers.

WS2-Pt Nanostructure-Based Composite for Hydrogen Gas Sensing with Ultra-Fast Response and Recovery Rates

This study investigates the use of DC sputtering, physical vapor deposition as a facile method for creating ultralow loading, Au/C electrodes for use in the detection of As (III) in water. The sputtered nanofilm electrodes on carbon papers, substantially reduces the amount of Au consumed per electrode, <10 μg cm−2, compared to use of wire, foil, or screen-printed electrodes. Linear stripping voltammetry (LSV) was chosen for analytical simplicity and ease of automation. Electrodes using Au nanoparticles supported on Vulcan XC 72 R carbon were also investigated but were not viable for LSV analysis due to capacitive current charging of the high surface area carbon. The DC sputtered, Au nanofilm electrodes were used to create calibration curves for concentrations of As (III) between 5 and 50 μg l−1 and the standard addition method was used in a surface water sample with 5.5 μg l−1 total As. Peak areas plotted against concentration displayed strong linear correlation with meaningful detection below the USEPA maximum contaminant level (MCL) of 10 μg l−1. To our knowledge, this is the first study which utilizes the facile and mass manufacturable DC sputtering method to produce As (III) sensing electrodes. The results of this study have implications for the development of single use, low-cost nanofilm electrodes for field As (III) electroanalysis. 

Jackson Jr. Ndenkeh

Papers

DC Sputtered Ultralow Loading Gold Nanofilm Electrodes for Detection of As (III) in Water