Biological sample-compatible Au nanoparticle-containing fluorescent molecularly imprinted polymer microspheres by combining RAFT polymerization and Au–thiol chemistry

The development of biological sample-compatible fluorescent molecularly imprinted polymers (MIPs) with more functions and/or improved performance is of great importance for various bioanalytical and biomedical applications, but remains challenging. Herein, we report on a versatile strategy for preparing well-defined hydrophilic gold (Au) nanoparticle (AuNP)-containing fluorescent MIP microspheres capable of directly optosensing folic acid (FA) in undiluted urine samples and study of the effect of the incorporated AuNPs on their optosensing sensitivity. Such advanced functional fluorescent MIP particles were readily prepared by combining RAFT polymerization (including RAFT precipitation polymerization and surface-initiated RAFT polymerization) and Au-thiol chemistry [including successive attachment of AuNPs and a thiol-terminated poly(2-hydroxyethyl methacrylate) onto MIP particles after aminolysis of their surface dithioester into thiol groups]. They showed "turn-on" fluorescence and high optosensing selectivity and sensitivity toward FA in the undiluted urine sample (detection limit = 0.088 μM). They also exhibited outstanding photostability and reusability and could directly quantify FA in another undiluted urine sample with good recoveries (96.3-101.6%) and high accuracy (RSD = 0.6-3.1%), even in the presence of several interferents. Unfortunately, the incorporated AuNPs did not improve the optosensing sensitivity of AuNP-containing fluorescent MIPs. Nevertheless, introducing AuNPs onto the surfaces of fluorescent MIPs not only provides an effective new way for grafting with hydrophilic polymer brushes, but it also can endow them with certain new functions [e.g., surface-enhanced Raman scattering (SERS)], thus making them highly promising as both efficient optosensors and potential SERS sensors for rapid FA detection in applications such as clinical diagnostics and food analyses.