Portable, smartphone-assisted turn-on fluorescence sensor based on green-synthesized beetroot-derived carbon dots for alpha-cypermethrin monitoring in field samples

Abstract

Conventional detection of α-cypermethrin (α-CYP), a widely used pyrethroid insecticide, often requires costly laboratory instrumentation, limiting its suitability for rapid, on-site monitoring. Here, we present, for the first time, a green, low-cost, and portable fluorescence sensing platform based on carbon dots (CDs) synthesized from red beetroot via a microwave digestion system. The CDs exhibited a strong green emission (λ_ex 347 nm, λ_em 450 nm) and displayed a unique turn-on fluorescence response to α-CYP, attributed to hydrophobic interactions and aggregation-induced emission enhancement (AIEE), as confirmed by solvent-dependent fluorescence studies, concentration studies, and TEM analysis. Under optimized pH and reaction conditions, the probe achieved a limit of detection (LOD) of 0.55 µmol L⁻¹ and a limit of quantitation (LOQ) of 1.68 µmol L⁻¹. The method demonstrated high selectivity against other common pesticides, with recoveries of 92–98% and relative standard deviations (RSDs) below 3.5% in spiked orange samples. Its integration with a smartphone RGB analysis application enabled field-deployable quantification, achieving an LOD of 0.71 µmol L⁻¹ for on-site measurements. This work introduces a sustainable sensing strategy that combines green nanomaterials, smartphone-based analysis, and field validation, offering a practical solution for rapid pesticide detection in food safety and environmental monitoring.