One-step homogeneous micro-orifice resistance immunoassay for detection of chlorpyrifos in orange samples

• A one-step homogeneous method without separation-washing cycles for bioanalysis was developed. • Polystyrene microsphere probe was integrated with particle counting micro-orifice resistance technology for chlorpyrifos detection. • The sensitivity and accuracy of this assay is improved without any signal amplification. • The sensor provides a sensitive and washing-free tool for detection of pesticide. In this work, a one-step homogeneous micro-orifice resistance immunoassay has been proposed for chlorpyrifos detection by integrating functionalized polystyrene (PS) microsphere probes with particle counting technology. The particle counter is highly sensitive and accurate for detecting the state of PS microspheres, where the particles of different states exhibit significant differences in resistance. The state of the functionalized PS microspheres is altered from dispersed to aggregated during the antigen-antibody recognition. Based on the degree of aggregation of the functionalized PS microsphere probes, chlorpyrifos can be quantitatively detected through the competitive immune response between PS antibodies and PS complete antigens. This one-step homogeneous micro-orifice resistance immunoassay simplified the procedures and greatly increased the sensitivity of detection, which has been successfully applied to detect chlorpyrifos in orange samples within 0.5 h, with the detection limit of 0.058 ng/mL.