Hybrid ZnO nanostructures modified graphite electrode as an efficient urea sensor for environmental pollution monitoring.

Herein, we propose a facile electrochemical sensing platform for urea detection using pencil graphite electrode modified nanocomposites of CuO/ZnO and Fe2O3/ZnO. The detection of urea is essential to monitor for identifying its pollution in the water, at the soil surface and in diagnosing urea cycle disorder related diseases. Therefore, an effective, accurate, cost-effective method of diagnosis is urgently needed. Nanostructured metal oxides have the potential ability to detect molecules even at trace level and to explore this, the present work is formulated with Cu and Fe based ZnO nanocomposites for enhancing the sensing performance towards electrochemical sensing of urea. The sensing responses were confirmed from the increase in oxidation current with respect to the concentration of urea. The results show that Fe2O3/ZnO coated graphite electrode has a higher response against urea compared to ZnO and CuO/ZnO. The cyclic voltammetry studies also validate urea sensing of Fe-ZnO in the linear range of 0.8 µg/mL to 4 µg/mL, with the detection limit of 2.5 µg/mL. This suggests that the cost-effective pencil graphite electrode modified Fe2O3/ZnO can be utilized as a promising analytical tool for urea sensing.

Green synthesis of white light emitting carbon quantum dots: Fabrication of white fluorescent film and optical sensor applications.

In this work, we have reported on the facile synthesis of white light-emitting carbon quantum dots (CQD) from corncob by hydrothermal method. This CQD has a broad emission from 380 nm to 650 nm with high photoluminescence intensity even after three months of shelf-life and stable at variable pH conditions. The presence of Si and N impurities in the biomass gives a greater advantage in producing white light emission with high quantum yield (54%) and enhanced lifetime at ambient conditions. The CQD is highly sensitive towards DNA, paracetamol, Pb2+, Cu2+, Fe3+, and Cr3+ fluorescence sensing and signifies its application as a multi-modal fluorescence sensor. The results of optical sensitivity calculated from the linear range of 1-10 ng/mL, 0.10-0.30 mg/mL, 2.5446 ng/mL, 0.0694 mg/mL, 0.3103-1.5515 µM/mL, 0.4299-4.7293 µM/mL, 1.3010 µM/mL and 0.05-2.5 µM/mL. The limit of detection is 2.5446 ng/mL, 0.0694 mg/mL, 0.8641 µM/mL, 1.2454 µM/mL, 1.3010 µM/m, 0.8550 µM/mL and 2.8562 µM/mL, respectively. And also, the relative standard deviation values of 2.30%, 4.46%, 1.79%, 1.84%, 0.26%, 1.23% and 0.35% are evidences its possibility of development towards potential optical sensor applications. Flexible white light-emitting sheets were fabricated from the CQD, illuminates uniform brightness, and has good color reproducibility and higher stability under various UV light excitation.