A novel sensitive immunoassay by nucleic acid barcode dot and its application in the detection of prostate-specific antigen.

BACKGROUND The sensitivity and selectivity of traditional methods limits ultramicro detection of proteins. Bio-barcode amplification detection methods based on nanotechnology enables ultramicro detection of protein. However, bio-barcode amplification detection depends on the oligonucleotides being fixed on a glass chip. It also requires specialized equipment, which limits its application. We introduce a nano-nucleic acid barcode dot detection technology to determine ultramicro concentrations of protein. The method is simple, quick and accurate. METHODS Magnetic probe (IgG-M) and dual-labeled gold nanoparticle bio-probe (IgG-Au-DNA) were prepared. Protein was captured using a sandwich assay technique and magnetic separation was used. The DNA barcode was released with dithiothreitol (DTT) and detected directly without the requirement for polymerase chain reaction (PCR). Serum prostate-specific antigen (PSA) from 135 patients was detected with this method and compared with enzyme linked immunosorbent assay (ELISA) and radioimmunoassay (RIA). RESULTS Each IgG-Au-DNA could be covered with 138+/-47 oligonucleotides and 11+/-3 antibodies. The IgG-M could bind 118 mug of antibody per mg. The sensitivity of nano-nucleic acid barcode dot detection technology might allow detection of 1 fg/mL. There were no significant differences in serum PSA from 135 patients when comparing the three methods (compared with ELISA, r=0.950; and with RIA, r=0.967). CONCLUSIONS The nucleic acid barcode dot method does not require special equipment or complex procedures, but its detection limit is 2-3 orders of magnitude lower than ELISA.