A Smartphone-Based Fluorescent Platform Utilizing Salicylaldehyde-Modified Silicon Nanoparticles for Rapid Detection of Perfluorooctanoic Acid

Perfluorooctanoic acid (PFOA) poses a threat to ecosystems and human health via aquatic environments, which makes detecting toxic PFOA in contaminated water increasingly crucial. This study presents a new PFOA detection system that uses a combination of photogenerated electron transfer (PET) and excited-state intramolecular proton transfer (ESIPT). The system uses salicylaldehyde (SA) to modify fluorescent silicon nanoparticles (F-SiNPs), creating F-SiNPs/SA. Interestingly, pristine F-SiNPs exhibited no response to PFOA prior to SA functionalization. This might be because SA reacts with surface amino groups via a Schiff base reaction, eliminating their quenching effect and enabling sensitive PFOA detection with a limit of detection as low as 0.42 ppb. The system demonstrated a strong linear response, high selectivity, resistance to interference, and high recovery rates in spiked environmental water samples. We also integrated the probe into gel- and paper-based platforms combined with smartphone-based RGB fluorescence detection to expand its potential applications. This provides an efficient and reliable method for on-site PFOA monitoring.