Fe3+-mediated fluorescence switching of biomass-derived carbon dots integrated with PVA microneedles for smartphone-assisted determination of ascorbic acid in fruits and vegetables.

Abstract

Rapid and accurate determination of ascorbic acid (AA) is important for evaluating the nutritional quality of fresh produce. In this study, biomass-derived carbon dots (CDs) were synthesized from pomelo peel in a green deep eutectic solvent, and Fe3+ was subsequently coordinated with the CDs to construct an off-on fluorescent probe based on Fe3+-induced quenching and AA-triggered fluorescence recovery. The probe was incorporated into a polyvinyl alcohol (PVA) microneedle (MN) patch to enable localized sampling and in situ sensing in fruits and vegetables. Fluorescence images were acquired using a smartphone, and multidimensional RGB-derived features were analyzed using LightGBM for quantitative prediction. The platform exhibited a linear response to AA over 0-10 mM (R2 = 0.9979) with a limit of detection of 0.2 μM, while the direct sampling, fluorescence sensing, and smartphone readout could be completed within 10 min. In real produce samples, the microneedle measurements showed good agreement with the reference method, supporting the potential of this portable platform for on-site AA quantification.