Nirmalya Tripathy

Chemical and biological sensors based on metal oxide nanostructures

Unique and fascinating features of metal oxide nanostructures (MONs) have attracted considerable attention in recent years because without much effort, the MONs can be grown in many different nanoscale forms, thus allowing various novel devices of chemical and biological sensing to be fabricated. To improve the sensors performance by tailoring the properties of MONs through engineering of morphology, particle size, effective surface area, functionality, adsorption capability and electron-transfer properties have been extensively explored. This feature article collates the various MONs and their potential applications in the chemical and biological sensors for clinical and non-clinical applications.

Wide Linear-Range Detecting Nonenzymatic Glucose Biosensor Based on CuO Nanoparticles Inkjet-Printed on Electrodes

Inkjet-printed copper oxide nanoparticles (CuO NPs) on silver electrodes were used to fabricate the nonenzymatic glucose biosensor. The inkjet-printed CuO NPs electrodes produced high and reproducible sensitivity of 2762.5 μAm M(-1) cm(-2) at an applied potential of +0.60 V with the wide linear-detecting range of 0.05-18.45 mM and the detection limit of ~0.5 μM (S/N = 3). The long-term stability and reproducibility of sensor in glucose electro-oxidation resulted from the chemical stability of CuO NPs and pore-like structure formed on Ag surface, which prevented the CuO NPs from conglomeration and the interference of oxygen in the air. Significantly, the effect of interfering species, such as AA, UA, and DA were negligible, whereas sugar derivatives (lactose, fructose, and mannose) show insignificant interference. Finally, the electrode was applied to analyze glucose concentration in human serum samples.

High-performance cholesterol sensor based on the solution-gated field effect transistor fabricated with ZnO nanorods

A high-performance cholesterol sensor based on solution-gated field-effect-transistor (FET) was fabricated by using the vertically aligned ZnO nanorods (ZnO NRs) grown selectively on pre-patterned substrate in solution. The structural characterization showed that the as-grown ZnO NRs are vertically aligned, high purity single crystalline. The active layer of ZnO NRs between source and drain electrodes was immobilized with cholesterol oxidase (ChOx) enzyme. The performance of the fabricated FET sensor has been examined with the cholesterol solutions with and without electroactive species, the human serum (H4522), and the freshly drawn blood sample. The FET sensor provided a real-time response towards a wide range of cholesterol concentration (0.001-45 mM) with high sensitivity (10 μA cm(-2) mM(-1)) and selectivity.

Time-Dependent Control of Hole-Opening Degree of Porous ZnO Hollow Microspheres

Well-designed, monodispersed porous ZnO hollow microspheres with controlled hole-opening were successfully synthesized by a facile two-step solution route at low temperature. The hollow microspheres having average diameter of 3-4 μm showed time-dependent hole-opening, i.e. 4-100% for 15-75 min. The hole-opening percentage increases linearly with time until complete opening. The ZnO hollow microspheres also exhibited a high surface area (34 m(2) g(-1)), a large pore volume (0.19 cm(3) g(-1)) and an average pore diameter of 3.8 nm. A plausible growth mechanism for the formation of ZnO hollow microspheres was also proposed.

A comprehensive in vitro and in vivo study of ZnO nanoparticles toxicity

Nowadays, the exploration of zinc oxide nanoparticles (ZnO NPs) based products is booming in the various directions of bio-nanomedicine and other consumer products, but the comprehensive toxicological impact posed by ZnO NPs still remains unclear. The present study systematically investigates and correlates the toxicity evaluation of ZnO NPs in RAW 264.7 murine macrophages (in vitro) and male ICR mice (in vivo) by two different administration routes, i.e. g.i. and i.p. at different doses. The in vitro studies showed a slight rise in intracellular reactive oxygen species level (ROS), NF-κB transcription factor expression (TF) and NPs uptake at higher dose, indicating the non-toxic nature of ZnO NPs below 100 μg mL-1 doses. The in vivo results demonstrate a slight gain in body weight (BW), reduction in the organ weight, mild to severe pathological alteration in the organs depending upon NP dosage and mode of administration routes. The histopathological investigation suggests that the liver, kidney, lung, spleen, and pancreas may be the target organs for ZnO NPs according to the administration routes. Serum biochemistry assay shows an elevation in the GPT and ALP level, suggesting liver dysfunction. To our knowledge, this is the first study to report the toxic effects of ZnO NPs through i.p. administration. Further, the present work will offer a deeper understanding regarding the toxicology and in vivo behaviours of ZnO NPs in mice depending upon the various administration routes.

Effect of ZnO nanoparticles aggregation on the toxicity in RAW 264.7 murine macrophage

Nanostructured zinc oxide (ZnO) has received much attention due to its biological and medical applications, where detailed knowledge about particle sizing, aggregation propensity and its related hazards are crucial. Herein, the aggregation propensity and dissolution behavior of ZnO nanoparticles in aqueous medium (PBS) were studied as a function of concentration and further correlated with its toxicity in RAW 264.7 murine macrophages. Fast formation of smaller aggregates having high dissolution rate was observed at low concentration ZnO (LC-ZnO). Compared to high concentration ZnO (HC-ZnO) aggregates, the LC-ZnO aggregates were highly pronounced in terms of reactive oxygen species generation and exerting cell apoptosis, ascribed to the secondary size effect, size-dependent cellular uptake and ion solubility. This study outlines the nanoparticle concentration as a key factor in scaling its aggregation, dissolution tendency and also emphasizes the accounting of ingested nanomaterials long-term fate inside the cells.

Solution Process Synthesis of High Aspect Ratio ZnO Nanorods on Electrode Surface for Sensitive Electrochemical Detection of Uric Acid

This study demonstrates a highly stable, selective and sensitive uric acid (UA) biosensor based on high aspect ratio zinc oxide nanorods (ZNRs) vertical grown on electrode surface via a simple one-step low temperature solution route. Uricase enzyme was immobilized on the ZNRs followed by Nafion covering to fabricate UA sensing electrodes (Nafion/Uricase-ZNRs/Ag). The fabricated electrodes showed enhanced performance with attractive analytical response, such as a high sensitivity of 239.67 μA cm−2 mM−1 in wide-linear range (0.01–4.56 mM), rapid response time (~3 s), low detection limit (5 nM), and low value of apparent Michaelis-Menten constant (Kmapp, 0.025 mM). In addition, selectivity, reproducibility and long-term storage stability of biosensor was also demonstrated. These results can be attributed to the high aspect ratio of vertically grown ZNRs which provides high surface area leading to enhanced enzyme immobilization, high electrocatalytic activity, and direct electron transfer during electrochemical detection of UA. We expect that this biosensor platform will be advantageous to fabricate ultrasensitive, robust, low-cost sensing device for numerous analyte detection.

Highly stable hydrazine chemical sensor based on vertically-aligned ZnO nanorods grown on electrode

Herein, we report a binder-free, stable, and high-performance hydrazine chemical sensor based on vertically aligned zinc oxide nanorods (ZnO NRs), grown on silver (Ag) electrode via low-temperature solution route. The morphological characterizations showed that the NRs were grown vertically in high density and possess good crystallinity. The as-fabricated hydrazine chemical sensors showed an excellent sensitivity of 105.5 μAμM-1cm-2, a linear range up to 98.6μM, and low detection limit of 0.005μM. It also showed better long-term stability, good reproducibility and selectivity. Furthermore, the fabricated electrodes were evaluated for hydrazine detection in water samples. We found the approach of directly growing nanostructures as a key factor for enhanced sensing performance of our electrodes, which effectively transfers electron from ZnO NRs to conductive Ag electrode. Thus it holds future prospective applications as binder-free, cost-effective, and stable sensing devices fabrication.

Ammonium ion detection in solution using vertically grown ZnO nanorod based field-effect transistor

Vertically aligned ZnO nanorods were directly grown on a seeded glass substrate between a pre-deposited source–drain to fabricate a field-effect transistor (FET) based ammonium ion sensor. Controlled growth of aligned nanorods provided a well-defined large surface area for the detection of ammonium ions in solution.

Outstanding Antibiofilm Features of Quanta-CuO Film on Glass Surface

Intelligently designed surface nanoarchitecture provides defined control over the behavior of cells and biomolecules at the solid-liquid interface. In this study, CuO quantum dots (quanta-CuO; ∼3-5 nm) were synthesized by a simple, low-temperature solution process and further formulated as paint to construct quanta-CuO thin film on glass. Surface morphological characterizations of the as-coated glass surface reveal a uniform film thickness (∼120 ± 10 nm) with homogeneous distribution of quanta-CuO. The antibiofilm assay showed a very high contact bacteria-killing capacity of as-coated quanta-CuO glass surfaces toward Staphylococcus aureus and Escherichia coli. This efficient antibacterial/antibiofilm activity was ascribed to the intracellular reactive oxygen species (ROS) generated by the quanta-CuO attached to the bacterial cells, which leads to an oxidative assault and finally results in bacterial cell death. Although there is a significant debate regarding the CuO nanostructures antibacterial mode of action, we propose both contact killing and/or copper ion release killing mechanisms for the antibiofilm activity of quanta-CuO paint. Moreover, synergism of quanta-CuO with conventional antibiotics was also found to further enhance the antibacterial efficacy of commonly used antibiotics. Collectively, this state-of-the-art design of quanta-CuO coated glass can be envisioned as promising candidates for various biomedical and environmental device coatings.