Portable hydrogel-embedded molecularly imprinted polymer/nitrogen-doped graphene quantum dot fluorescent sensor for selective of D-proline in biofluids

We developed a fluorescence sensing platform based on nitrogen-doped graphene quantum dots (N-GQDs) integrated with a molecularly imprinted polymer (MIP) and encapsulated in an alginate hydrogel matrix (N-GQDs@MIP@hydrogel) for the rapid and selective detection of d -proline in saliva and human serum using a portable fluorometer. The N-GQDs@MIP composite was synthesized via sol–gel polymerization and characterized by transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FT-IR), confirming the formation of an imprinted polymer layer on the N-GQDs surface. Encapsulating the core-shell particles in the hydrogel improves dispersion stability and prevents N-GQDs@MIP aggregation, enabling a ready-to-use sensing platform. Adding d -proline enhances fluorescence resulting from synergistic contributions from the inhibition of photoinduced electron transfer (PET-off) and aggregation-induced emission (AIE). The sensor exhibited two linear ranges of 0.01–1.00 mM (r² = 0.9918) and 1.00–15.00 mM (r² = 0.9162), with limits of detection of 0.0045 and 0.0273 mM, respectively, and limits of quantification of 0.0149 and 0.0902 mM. The platform demonstrates reliable performance in saliva and human serum, highlighting its potential as a portable, low-cost, and non-invasive tool for point-of-care screening of gastric cancer biomarkers.