A portable microcontroller-enabled spectroscopy sensor module for the fluorometric detection of Cr(vi) and ascorbic acid, utilizing banana peel-derived carbon quantum dots as versatile nanoprobes†

Highly luminescent carbon quantum dots were produced from banana peels (BP-CQDs) using a facile one-step method without the incorporation of chemicals. BP-CQDs were comprehensively characterized using techniques like TEM, FT-IR, XRD, and XPS analyses. The synthesized BP-CQDs exhibited outstanding optical characteristics, displaying a vibrant green color under UV light and a quantum yield of 41%. These properties enabled them to function as effective on–off fluorescent nanoprobes for the precise and sensitive detection of hazardous Cr(VI) concentrations below regulatory limits, leveraging the inner filter effect (IFE) and a static quenching mechanism. The detection limit is calculated to be in the nanomolar range i.e., 60.5 nM. Consequently, the BP-CQDs + Cr(VI) system also acted as a selective off–on sensor for the reductant ascorbic acid (AA) with 86 nM limit of detection. This effect was due to AA's reduction of Cr(VI) to Cr(III) species, which eliminated the IFE and restored the fluorescence of the BP-CQDs. Moreover, efforts have been undertaken to create a low-cost, portable electronic device utilizing spectroscopy sensors to detect heavy metal pollutant concentrations in the test samples. The experimental results affirm the effectiveness of the portable electronic device as a detector for Cr(VI) in test samples. This study sets the groundwork for creating carbon quantum dots (CQDs) with enhanced properties by using banana peels as a biowaste precursor to detect the concentrations of Cr(VI) and AA.