Facile synthesis of carbon dots via pyrolysis and their application in photocatalytic degradation of rhodamine B (RhB).

Carbon Quantum dot (CQDs) is one of the newest materials in carbon-based nanomaterials. It is pertinent to study the synthesis and the application of these carbon dots. Here we have studied the effect of precursor on the optical, morphological, and photocatalytic properties of CQDs. We have synthesized CQDs using pyrolysis method using the precursors citric acid, urea, polyethyleneimine. We have synthesized two samples: CQD-S1; synthesized using urea and polyethyleneimine, and CQD-S2; synthesized using citric acid and polyethyleneimine. In optical properties study two distinct peaks have been obtained at 243 nm and 345 nm for CQD-S1, and at 265 nm and 335 nm for CQD-S2. In fluorescence study, the maximum emission was found at excitation wavelength of 340 nm for CQD-S1 and at excitation wavelength of 350 nm for CQD-S2. In morphological studies, Transmission Electron Microscope (TEM) revealed particle size of sample CQD-S1 and CQD-S2 were 1.91 nm and 1.61 nm, respectively. EDX confirmed the elemental composition in both samples. The rhodamine B (RhB) dye degradation percentages in dark and under visible and UV light were found to 6, 13, and 98.4% respectively for CQD-S1. Similarly, dye degradation for CQD-S2 were 7, 11, and 99.63%, respectively. Effective degradation of photocatalysis performed under UV-light within 100 min using mineralization process.

Rapid and label-free detection of Aflatoxin-B1viamicrofluidic electrochemical biosensor based on manganese (III) oxide (Mn3O4) synthesized by co-precipitation route at room temperature.

Aflatoxin B1 (AFB1) is the most toxic mycotoxin, naturally occurring in food items, and it causes several types of lethal diseases. Therefore, a rapid and convenient detection method for AFB1 is the first step toward overcoming the effect of AFB1. The current work presents the development of an efficient microfluidic electrochemical-based biosensor using tri-manganese tetroxide nanoparticles (Mn3O4nps) for AFB1 detection. The Mn3O4nps were synthesized at room temperature through the co-precipitation route. Its phase purity, structural and morphological studies have been characterized through x-ray diffraction, Raman spectroscopy, energy-dispersive x-ray, Fourier transform infrared spectroscopy and transmission electron microscopy. The mask-less UV-lithography was carried out to fabricate the three-electrode chip and microfluidic channel of the microfluidic electrochemical biosensing system. The designed microfluidic immunosensor (BSA/Ab-AFB1/Mn3O4/ITO) was fabricated using the three-electrode chip, microfluidic channel in poly-dimethyl siloxane. The fabricated sensor exhibited the 3.4µA ml ng-1cm-2sensitivity and had the lowest lower detection limit of 0.295 pg ml-1with the detection range of 1 pg ml-1to 300 ng ml-1. Additionally, the spiked study was also performed with this immunoelectrode and a recovery rate was obtained of 108.2%.

Graphene Quantum Dot-Based Optical Sensing Platform for Aflatoxin B1 Detection via the Resonance Energy Transfer Phenomenon.

An optical sensing platform for the detection of an important mycotoxin, aflatoxin B1 (AFB1), in the absence of a bioactive environment is explored. In this work, a fluorescence-based sensing technique was designed by combining graphene quantum dots (GQDs) and AFB1 via fluorescence quenching, where AFB1 acts as the quencher of GQD fluorescence. GQDs were synthesized through a single-step hydrothermal reaction from the leaves of "curry tree" (Murraya Koenigii) at 200 °C. The fluorescent GQDs were quenched by AFB1 (quencher), which itself is detecting the analyte. Hence, this study reports the direct sensing of the mycotoxin AFB1 without the involvement of inhibitors or biological entities. The possible mode of quenching is the nonradiative resonance energy transfer between the GQDs and the AFB1 molecules. This innovative sensor could detect AFB1 in the range from 5 to 800 ng mL-1 with a detection limit of 0.158 ng mL-1. The interferent study was also carried out in the presence of different mycotoxins and carbohydrates (d-fructose, cellulose, and starch), which demonstrated the high selectivity and robustness of the sensor in the complex sample matrix. The recovery percentage of the spiked samples was also calculated to be up to 106.8%. Thus, this study reports the first GQD based optical sensor for AFB1.

Non-enzymatic and rapid detection of glucose on PVA-CuO thin film using ARDUINO UNO based capacitance measurement unit.

Glucose measurement is one of the essential health monitoring practices for maintaining blood sugar levels. Here, we have fabricated a highly specific capacitive nano-sensor for non-enzymatic glucose detection. Capacitance measurements were carried out on polyvinyl alcohol capped copper oxide (PVA-CuO) thin films on indium tin oxide (ITO) coated glass using ARDUINO UNO. The capacitance study shows a decrease in capacitance with an increase in glucose concentrations. The applicability in real samples was performed by studying the glucose in the presence of fetal bovine serum. Most commonly found interfering agents were used for interference studies, which confirmed the capacitive nano-sensor specificity. The system was further checked for repeatability up to six readings and reproducibility up to 5 chips. The shelf-life study showed stability for four weeks of a chip. These studies indicate that this capacitance-based measurement unit can be used for reliable, rapid, and non-enzymatic detection of glucose in real sample.

Dimanganese trioxide (Mn2O3) based label-free electrochemical biosensor for detection of Aflatoxin-B1.

This work presents, a manganese oxide nanoparticles (Mn2O3nps) based electrochemical immunosensor for the detection of Aflatoxin-B1 (AFB1). X-ray diffrraction spectroscopy study confirms the purely synthesized Mn2O3nps with an average crystallite size of 31.5 nm. Transmission electron microscopy study confirms average particle size of 45 nm. To fabricate an electrochemical biosensor, a thin film of Mn2O3nps was fabricated onto indium tin oxide (ITO) surface using electrophoretic technique. Such fabricated thin film was utilized to immobilize antibodies (Anti-AFB1) for the selective detection of AFB1 using differential pulse voltammetry technique. Prior to perform sensing, bovine serum albumin (BSA) was utilized to block the uncovered sites on the Anti-AFB1/Mn2O3/ITO immunoelectrode surface. The response of BSA/Anti-AFB1/Mn2O3/ITO immunoelectrode was measured as a function of AFB1 in a linear detection range of 1 pg mL-1 to 10 µg mL-1 and sensor showed highest sensitivity of 2.044 µA mL ng-1cm-2 with lower detection limit of 0.54 pg mL-1. A spiked sample response of corn extract was studied in the linear range of 1 pg mL-1 to 10 µg mL-1 and immunoelectrode (BSA/Anti-AFB1/Mn2O3/ITO) showed recovery rate of 98.6 %.

Studies on carbon-quantum-dot-embedded iron oxide nanoparticles and their electrochemical response.

A report on the synthesis of carbon-quantum-dot-embedded iron oxide nanoparticles (CQD@Fe3O4NPs) and their improved electrochemical studies is presented. Fe3O4NPs and CQD@Fe3O4NPs were synthesized by the wet-chemical co-precipitation method. X-ray diffraction measurements exhibited pure cubic phase with Fd3m space group in Fe3O4NPs and CQD@Fe3O4NPs. Fourier-transform infrared spectroscopy measurements confirmed the functionalization of Fe3O4NPs with CQDs. Dynamic light scattering measurements revealed a hydrodynamic radius of 520 nm and 319 nm for Fe3O4NPs and CQD@Fe3O4NPs, respectively. Moreover, zeta potential measurements showed positively charged Fe3O4NPs and negatively charged CQD@Fe3O4NPs. High-resolution transmission electron microscopy measurements showed nearly spherical structure with an average size of around 7 nm for Fe3O4 in both samples, whereas CQDs were nearly 2 nm in size in CQD@Fe3O4NPs. A biocompatibility study showed that CQD@Fe3O4NPs were more biocompatible than the bare Fe3O4NPs. CQD@Fe3O4NPs were then dispersed in chitosan (CHIT) solution, and drop-casted onto an indium tin oxide (ITO) glass substrate for further study. Atomic force microscopy results showed improved surface roughness of the CQD@Fe3O4-CHIT/ITO electrode, providing a better biosensing platform. The electrochemical response studies of CQD@Fe3O4-CHIT/ITO also showed enhanced electrochemical signal compared to Fe3O4-CHIT/ITO electrodes. Thus, a CQD@Fe3O4-CHIT/ITO electrode was used for the detection of vitamin D2 (10-100 ng ml-1) using a differential pulse voltammetry technique. The sensitivity and limit of detection were obtained as 0.069 µA ng-1 ml cm-2 and 2.46 ng ml-1, respectively.