Digital immunoassay of a prostate-specific antigen using gold nanorods and magnetic nanoparticles
Herein, a digital immunoassay was developed by counting highly confined gold nanorod (AuNR) probes with the aid of magnetic nanoparticles (MNPs). MNPs were conjugated with capture antibodies to concentrate the target analytes. AuNRs were conjugated with a mixture of the detection antibody and randomly selected DNA, where the detection antibody was applied to signal the target binding event and DNA was applied to provide sufficient negative charges. The bicomponent AuNR probes in the target-mediated immunocomplexes were eluted and confined onto a positively charged glass slide on the basis of electrostatic attraction for accurate counting. The combination of the magnetic concentration of the target analytes and the confinement of the DNA/antibody AuNR probes results in improved detection efficiency; a good linear range from 0.01 to 10 pg mL−1 and a detection limit of 8 fg mL−1 (∼226 aM) were achieved for the detection of prostate-specific antigen (PSA). The proposed method offers the simultaneous advantages of high sensitivity, digital quantification accuracy, lack of requirement for signal or target amplification, wide dose response curve and low detection cost; thus, it shows good potential in practical applications.