A room-temperature gas sensor based on 2D Ni-Co-Zn ternary oxide nanoflakes for selective and sensitive ammonia detection.

While most of the reports on NH3 gas sensors are either based on metal oxide composites with other 2D materials, polymers or noble metals or involve multi-step-based synthesis routes, this work is the first report on a pristine ternary metal oxide, 2D NiCo2ZnO4 nanoflake based room-temperature (RT) NH3 gas sensor. The 2D NiCo2ZnO4 nanoflakes were prepared by a one-step hydrothermal method. FESEM and TEM images displayed micro-flower like morphologies, containing vertically aligned interwoven porous 2D nanoflakes, whereas XPS and XRD data confirmed the successful growth of this ternary metal-oxide. This sensor revealed a good response, repeatability, linearity (R2 = 0.9976), a low detection limit of 3.024 ppb, and a response time of 74.84 s with excellent selectivity towards NH3 over six other VOCs. This improved performance of the sensor is ascribed to its large specific surface area (127.647 m2 g-1) resulting from the 2D nanoflake like structure, good electronic conductivity, variable valence states and abundant surface-active oxygen of NiCo2ZnO4. Thus, this highly selective 2D NiCo2ZnO4 based RT NH3 gas sensor can be an attractive solution for the fabrication of next-generation NH3 gas sensors.

Development and Analytical Evaluation of a Point-of-Care Electrochemical Biosensor for Rapid and Accurate SARS-CoV-2 Detection.

The COVID-19 pandemic has underscored the critical need for rapid and accurate screening and diagnostic methods for potential respiratory viruses. Existing COVID-19 diagnostic approaches face limitations either in terms of turnaround time or accuracy. In this study, we present an electrochemical biosensor that offers nearly instantaneous and precise SARS-CoV-2 detection, suitable for point-of-care and environmental monitoring applications. The biosensor employs a stapled hACE-2 N-terminal alpha helix peptide to functionalize an in situ grown polypyrrole conductive polymer on a nitrocellulose membrane backbone through a chemical process. We assessed the biosensor's analytical performance using heat-inactivated omicron and delta variants of the SARS-CoV-2 virus in artificial saliva (AS) and nasal swab (NS) samples diluted in a strong ionic solution, as well as clinical specimens with known Ct values. Virus identification was achieved through electrochemical impedance spectroscopy (EIS) and frequency analyses. The assay demonstrated a limit of detection (LoD) of 40 TCID50/mL, with 95% sensitivity and 100% specificity. Notably, the biosensor exhibited no cross-reactivity when tested against the influenza virus. The entire testing process using the biosensor takes less than a minute. In summary, our biosensor exhibits promising potential in the battle against pandemic respiratory viruses, offering a platform for the development of rapid, compact, portable, and point-of-care devices capable of multiplexing various viruses. The biosensor has the capacity to significantly bolster our readiness and response to future viral outbreaks.

Amplification of ammonia sensing performance through gate induced carrier modulation in Cur-rGO Silk-FET.

Uncontrolled human and industrial activities lead to the increase in demand for selective gas sensors for detection of poisonous gases in our environment. Conventional resistive gas sensors suffer from predetermined sensitivity and poor selectivity among gases. This paper demonstrates curcumin reduced graphene oxide-silk field effect transistor for selective and sensitive detection of ammonia in air. The sensing layer was characterized by X-ray diffraction, FESEM and HRTEM to confirm its structural and morphological features. Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy was carried out to analyze the functional moieties present in the sensing layer. Curcumin reduced graphene oxide introduces sufficient hydroxyl groups in the sensing layer to provide high degree of selectivity towards ammonia vapors. The performance of the sensor device was evaluated at positive, negative and zero gate voltage. Carrier modulation in the channel through gate electrostatics revealed that the minority carriers (electrons) in p-type reduced graphene oxide plays a pivotal role in enhancement of sensitivity of the sensor device. The sensor response was enhanced to 634% for 50 ppm ammonia at 0.6 V gate voltage compared to 23.2% and 39.3% at 0 V and - 3 V respectively. The sensor exhibited faster response and recovery at 0.6 V owing to higher mobility of electrons and quick charge transfer mechanism. The sensor exhibited satisfactory humidity resistant characteristics and high stability. Hence, curcumin reduced graphene oxide-silk field effect transistor device with proper gate bias elucidates excellent ammonia detection and may be a potential candidate for future room temperature, low power, portable gas detection system.

Efficient Hydrogen Evolution via 1T-MoS2 /Chlorophyll-a Heterostructure: Way Toward Metal Free Green Catalyst.

Electrocatalytic hydrogen evolution reaction (HER) is regarded as a sustainable and green way for H2 generation, which faces a great challenge in designing highly active, stable electrocatalysts to replace the state-of-art noble metal-platinum catalysts. 1T MoS2 is highly promising in this regard, but the synthesis and stability of this is a particularly pressing task. Here, a phase engineering strategy has been proposed to achieve a stable, high-percentage (88%) 1T MoS2 /chlorophyll-a hetero-nanostructure, through a photo-induced donation of anti-bonding electrons from chlorophyll-a (CHL-a) highest occupied molecular orbital to 2H MoS2 lowest unoccupied molecular orbital. The resultant catalyst has abundant binding sites provided by the coordination of magnesium atom in the CHL-a macro-cycle, featuring higher binding strength and low Gibbs-free energy. This metal-free heterostructure exhibits excellent stability via band renormalization of Mo 4d orbital which creates the pseudogap-like structure by lifting the degeneracy of projected density of state with 4S in 1T MoS2 . It shows extremely low overpotential, toward the acidic HER (68 mV at the current density of 10 mA cm-2 ), very close to the Pt/C catalyst (53 mV). The high electrochemical-surface-area and electrochemical turnover frequency support enhanced active sites along with near zero Gibbs free energy. Such a surface-reconstruction strategy provides a new avenue toward the production of efficient non-noble-metal-catalysts for the HER with the aim of green-hydrogen production.

Reduced Graphene Oxide Nanosheets for Selective Picomolar Detection of Bovine Serum Albumin.

In this paper, ultra-low level selective detection of bovine serum albumin (BSA) has been demonstrated, based on chemically derived graphene i.e., reduced graphene oxide (RGO) nanosheets. The working principle of the sensor is based upon change in conductance of the RGO nanosheets with different concentration of BSA. The change in conductance is based on the charge transfer between BSA and functional groups of RGO. The morphological and structural characterizations of RGO nanosheets were carried out by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Raman spectroscopy is performed to further validate the interaction between RGO sensing layer and BSA molecules. Electrical impedance spectroscopy is performed to observe the impedance variation when BSA interacts with RGO. The sensor device exhibits sensitivity of 10 nA/pM. The lower limit of detection (LOD) of the sensor is found to be 1 pM and response time around 35 s, confirming very high sensitivity for BSA. All electrical (current-voltage) measurements were carried out at 2 V bias for low power operation. The sensor exhibits highest sensitivity at 30 °C and for RGO thickness ~4 nm. The RGO based sensor device is selective towards BSA when compared to proteins like L-Histidine, HSA, BHB and Biotin. Our results suggest that RGO based devices are promising for low-cost, portable and real time detection of BSA at room temperature.

Glassy carbon microneedles-new transdermal drug delivery device derived from a scalable C-MEMS process.

Because carbon is the basic element of all life forms and has been successfully applied as a material for medical applications, it is desirable to investigate carbon for drug delivery applications, as well. In this work, we report the fabrication of a hollow carbon microneedle array with flow channels using a conventional carbon-microelectromechanical system (C-MEMS) process. This process utilizes the scalable and irreversible step of pyrolysis, where prepatterned SU-8 microneedles (precursor) are converted to glassy carbon structures in an inert atmosphere at high temperature (900 °C) while retaining their original shape upon shrinkage. Once converted to glassy carbon, the microneedles inherit the unique properties of hardness, biocompatibility, and thermal and chemical resistance associated with this material. A comparative study of hardness and Young's modulus for carbon microneedles and SU-8 microneedles was performed to evaluate the increased strength of the microneedles induced by the C-MEMS process steps. Structural shrinkage of the carbon microneedles upon pyrolysis was observed and estimated. Material characterizations including energy-dispersive X-ray spectroscopy (EDX) and Raman spectroscopy were carried out to estimate the atomic percentage of carbon in the microneedle structure and its crystalline nature, respectively. Our investigations confirm that the microneedles are glassy in nature. Compression and bending tests were also performed to determine the maximum forces that the carbon microneedles can withstand, and it was found that these forces were approximately two orders of magnitude higher than the resistive forces presented by skin. A microneedle array was inserted into mouse skin multiple times and was successfully removed without the breakage of any microneedles.

Conjugation of Bovine Serum Albumin With ZnO Nanosphere-A Novel Approach for Ultra-Low Level Mercury Ion Detection.

Solution-processed bovine serum albumin conjugated with ZnO nanosphere (BCZ) have been synthesized for ultra-low level mercury ion detection. Simple drop casting technique was adopted to fabricate such a mercury ion (Hg2+) detection scheme. Morphological and optical characterization of the BCZ was performed by Transmission Electron Microscopy (TEM), UV-Vis and Fluorescence spectroscopic technique prior to device fabrication. The working principle of the BCZ device for Hg2+ detection depends upon the variation of conductance with various concentration of Hg2+. An extensive study was carried out to investigate the effect of Hg2+ upon transport properties of BCZ. The ultra-low level of Hg2+ sensing was performed using this electrical detection technique. More importantly, this proposed BCZ based detection technique is found to be simple, inexpensive and very fast in responding (response time  âˆ¼ 2.5 s) to heavy metal ion with a limit of detection (LOD) 0.03 fg/ml (S/ [Formula: see text]3).

Ultra-Low Level Detection of L-Histidine Using Solution-Processed ZnO Nanorod on Flexible Substrate.

This work demonstrates a novel label free and sensitive approach for the detection of L-histidine. This is a simple and reliable method for ultra-low level detection of L-histidine. All solution processed synthesizing technique was utilized to develop such type of detection scheme. Silicon substrate was replaced by normal transparent sheet to make it more facile and cost-effective detection technique. Fabricated device for L-histidine detection works upon the variation of current through the ZnO nanorod with L-histidine concentration. Operation principle strongly depends upon the electron charge transfer between metal cation and L-histidine inside the chelating complex. Morphological, structural and optical characterization of solution processed synthesized ZnO nanorod (ZnO NR) was carried out prior to sensor device fabrication. Our sensor device exhibits the sensitivity around 0.86 nA/fM and lower limit of detection (LOD) ∼ 0.1 fM(S/N=3).

Synthesis of ZnO nanosphere for picomolar level detection of bovine serum albumin.

In this paper, we demonstrate an electrical detection technique based on solution processed zinc oxide nanosphere for ultra-low level detection of bovine serum albumin (BSA). Our sensor device works on the basis of the variation of conductance of the ZnO nanosphere with different concentration of BSA. The morphological and structural characterizations of ZnO nanosphere were carried out by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Circular dichroism (CD) spectroscopy was performed to investigate the chemical interaction between the BSA and zinc oxide nanosphere. Optical detection was performed using absorbance and Fourier transform infrared spectroscopy (FTIR) studies. Our device exhibits sensitivity 0.126 nA/pM, lower limit of detection (LOD) 10 pM and the fast response time around 5 s, confirming the highest sensitivity for BSA detection achieved so far. Sensing mechanism is governed on the basis of the charge transfer phenomenon between BSA and ZnO. All measurements were carried out at 1 V bias for low power operation.