Carbon Dot-Infused Molecularly Imprinted Polymer for the Template-Specific Optical Sensing of Sialic Acid and Glucose and Its Integration with a Smartphone Device for On-Site Detection

This work proposes a selective fluorescence sensing platform that uses carbon dots (CDs) embedded in molecularly imprinted polymers (MIPs) to detect physiologically relevant biomarkers, such as glucose and sialic acid. Pristine CDs were synthesized via pyrolysis using galactose as the carbon source. To improve fluorescence stability and prevent leaching in aqueous environments, CDs were encased in a silica shell with APTES using the Stöber method. CDs@MIP were then synthesized by integrating silica-coated CDs into the MIP matrix. Based on the template molecule employed during the synthesis, two types of CDs@MIP, namely, G-MIP (glucose-MIP) and SA-MIP (sialic acid-MIP), were produced. The resultant polymers, G-MIP and SA-MIP, displayed a fluorescence turn-on mechanism with enhanced selectivity and sensitivity for glucose and sialic acid, respectively. Detection limits of 0.0657 ppm (0.365 μM) for glucose and 0.0962 ppm (0.311 μM) for SA were obtained. This enabled the detection of analytes in the micromolar range required for most physiological applications. The mechanism of fluorescence enhancement during the analyte interaction was attributed to hydrogen bonding with CDs, which was verified using FTIR spectroscopy, fluorescence lifetime measurements, and computational studies. In the current study, the turn-on fluorescence of CDs, together with the specialized identification capability of MIPs, provided a powerful platform for selective biosensing that has been incorporated into portable smartphone-based detection systems.