Magnetic relaxation switching biosensor via polydopamine nanoparticle mediated click chemistry for detection of chlorpyrifos

Abstract

Traditional magnetic relaxation switching (MRS) biosensors suffer from poor sensitivity and unsatisfactory stability. In this study, a polydopamine (PDA) nanoparticles (NPs)-Cu2+ chelate complex mediated signal conversion system and a Cu+-catalyzed click chemistry triggered magnetic signal amplification system were evaluated and dynamically integrated into an MRS biosensor. Owing to abundant functional groups and a large surface area, PDA NPs enabled the absorption of a large amount of Cu2+ ions by chelation. The residual Cu2+ ions can be reduced with sodium ascorbate to Cu+, which could initiate the click reaction between azide-functionalized magnetic NPs (MNPs) and alkyne-functionalized MNPs that resulted in the production of aggregated nanoclusters. The transverse relaxation time (T2) depends on the degree of aggregation of MNPs; T2 is expressed as the magnetic signal readout. In addition, PDA NPs can be easily conjugated with antibodies by mixing, thus providing a straightforward bridge that integrates the immunoassay and magnetic signal readout. Combined with the high capacity of PDA NPs for chelating Cu2+ and high efficiency of click reaction for changing the T2 signals, the PDA-MRS biosensor enables the detection of chlorpyrifos with a limit of detection of 0.084 ng/mL, providing 22-fold enhancement than traditional enzyme-linked immunosorbent assay (1.86 ng/mL). This demonstrates its great potential for the detection of hazardous chemical molecules in a complex sample matrix.