Recyclable nanoparticles based on a boronic acid–diol complex for the real-time monitoring of imprinting, molecular recognition and copper ion detection

Molecularly imprinted polymers (MIPs) have now become one of the most remarkable materials in the field of molecular recognition. Although many efforts have been made to study the process and mechanism of molecular imprinting, it has not been possible to monitor the interactions between the template and the growing polymer chains under real-time experimental conditions. The behavior of the template-monomer complex during the whole polymerization process has remained largely unknown. In this work, we introduce a fluorescence technique that allows monitoring of the template-functional monomer complex during an actual imprinting process, as well as the real-time signaling of template binding and dissociation from the imprinted polymer. For the first proof-of-principle, we select Alizarin Red S (ARS) and 4-vinylphenylboronic acid as the template and functional monomer, respectively, to synthesize MIP particles via precipitation polymerization. As the formation of the template-functional monomer complex leads to strong fluorescence emission, it allows the status of the template binding to be monitored throughout the whole reaction process in real time. Using the same fluorescence technique, the kinetics of template binding and dissociation can be studied directly without particle separation. The hydrophilic MIP particles can be used as a scavenger to remove ARS from water. In addition, the MIP particles can be used as a recyclable sensor to detect Cu ions. As the Cu ion forms a stable complex with ARS, it causes ARS to dissociate from the MIP nanoparticles, leading to effective fluorescence quenching. The non-separation analytical method based on fluorescence measurement provides a convenient means to study molecular imprinting reactions and the kinetics of molecular recognition using imprinted polymers. The recyclable nanoparticle sensor allows toxic Cu ions to be detected directly in water in the range of 0.1-100 μM with a recovery of 84-95%.