Rapidly colorimetric detection of caffeine in beverages by silver nanoparticle sensors coupled with magnetic molecularly imprinted polymeric microspheres

Excessively intaking caffeine can harm human health, and it is imperative to develop a rapid method to identify caffeine for food safety. The magnetic molecularly imprinted polymeric microspheres (MMIPs) were prepared to pretreat samples before silver nanoparticles (AgNPs) colorimetric detection of caffeine. Using Fe3O4 as supporting core, mesoporous SiO2 as intermediate shell, alpha-methylacrylic acid as functional monomer and caffeine as template, the prepared MMIPs were characterised by transmission electron microscopy, Fourier transform infrared spectroscopy and vibrating sample magnetometer. Adsorption process followed Langmuir adsorption isotherm with maximum adsorption capacity at 38.8 mg g(-1) under 298 K. The MMIPs extract caffeine from beverages, then the AgNPs colorimetric method rapidly screened and semi-quantified caffeine >= 5 mg L-1 by naked eye, and accurately quantified caffeine ranging 0.1-5 mg L-1 by UV-vis spectroscopy at 393 nm, which were consistent with HPLC analytical results. Thus, this method might be used to rapidly enrich and analyse caffeine in beverages.