Smartphone-Integrated Fluorescence Sensing Platform for Specific Detection of Methamphetamine Using a Fe,Zn@PEI-CDs Fluorescent Probe.

Considering the growing global abuse of methamphetamine (MA) and its related public health and social consequences, developing rapid and sensitive point-of-care testing (POCT) methods for forensic applications has attracted increasing attention. This study developed an iron- and zinc-doped carbon dots (Fe,Zn@PEI-CDs)-based smartphone-integrated fluorescent sensor using a simple one-pot hydrothermal synthetic procedure. The fluorescence intensity of the Fe,Zn@PEI-CDs at 360/452 nm (excitation wavelength/emission wavelength) was significantly increased upon exposure to MA through an aggregation-induced emission (AIE) mechanism. The sensor displayed excellent linearity (R2 = 0.991) over the 60- to 600-μg/mL range. Irradiation with 365-nm ultraviolet light resulted in a distinct fluorescence color transition from light blue to dark blue. The values of the red (R), green (G), and blue (B) channels for the captured images were determined by a smartphone-installed color picker application, and a grayscale analysis model was then constructed for visually detecting MA, yielding a limit of detection of 14.61 μg/mL. The proposed method was validated using urine samples, displaying recovery values ranging from 98.37% to 103.34% with relative standard deviations of less than 3.0%. These results provide a reliable method for detecting MA and offer a new solution for the rapid analysis of illicit drugs.