Serological determination of Helicobacter pylori infection using sandwiched and enzymatically amplified piezoelectric biosensor

A sandwiched and enzymatically amplified piezoelectric immunosensor is presented for Helicobacter pylori antibody detection. AT-cut quartz crystals (10MHz) were used as reaction carrier, onto which recombinant H. pylori antigens were immobilized to capture the associated antibodies. Since the antibody titer in naturally infected patient sera is very low, direct patient serum incubation resulted in less significant positive signals when compared with the negative background. To increase the positive signal and reduce the negative background, serum incubation was followed by the application of anti-h (anti-human) IgG or anti-h IgG conjugates. The specific recognition of anti-h IgG to the bound IgG antibodies led to a sandwiched immunocomplex and the further frequency decrease. Since the binding of the secondary antibody were only observed when patient sera were H. pylori positive, the total frequency changes (caused by serum and secondary antibody) for the positives became more significant than those of the negatives. The resulting positive to negative ratio was increased to 4.1-5.0 depending on different conjugates used. When enzyme (HRP or AP) conjugated antibodies had been used, the sandwiched complexes were exposed to associated substrates. The enzymatically amplified deposition of the converted color products onto sensor surface led to significant enhancement in the sensitivity. By means of this strategy, human serum could be detected as positive in the dilution of 1/100.