Abstract
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In this study, Gram flour-derived carbon quantum dots (GFCQDs) were synthesized via a sustainable microwave-assisted approach and explored as dual-mode fluorescent sensor for fluoroquinolones and tetracyclines. GFCQDs exhibited blue fluorescence under UV light and exhibited excitation-dependent emission behaviour, displaying different fluorescence colour upon varying excitation wavelength. Notably, GFCQDs demonstrated remarkable acid stability and long-term storage stability. These GFCQDs show a distinctive dual response: fluorescence enhancement accompanied by a slight bathochromic shift for fluoroquinolones, and fluorescence quenching for tetracyclines. Mechanistic investigations revealed that tetracycline detection is governed by inner filter effect (IFE), whereas ciprofloxacin detection is mediated through hydrogen bond-based interactions. Notably, GFCQDs enabled selective visual detection of tetracycline through calcium -assisted fluorescence colour transition from blue to green and demonstrated effective ciprofloxacin detection in mixed antibiotic pools. The practical utility of GFCQDs was validated in real matrices including milk, tap water, food samples and pharmaceutical formulations, with recovery rates 97%-99%. Furthermore, GFCQDs were fabricated into portable-cellulose paper strips for convenient on-site and off-site antibiotic screening. GFCQDs also successfully demonstrated intracellular tetracycline sensing via blue fluorescence turn-off response in Bacillus subtilis.
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