In situ amplified chemiluminescent detection of DNA and immunoassay of IgG using special-shaped gold nanoparticles as label

Background: Au(III) catalyzed luminol chemiluminescence (CL) is classic in luminescence analysis. Recently, spherical gold nanoparticles (Au-NPs) were found displaying far stronger catalytic activity on luminol CL than that of Au(III). Some methods based on Au-NPs probes have been developed for DNA detection or immunoassay. However, more complicated labeling or stripping procedures are often inescapable in these protocols. Methods: We synthesized specially shaped, irregular gold nanoparticles (IGNPs) and found their catalytic efficiency on luminol CL to be 100-fold greater than that of spherical Au-NPs. Using the IGNPs-functionalized DNA oligomers and the IGNPs-modified anti-IgG as in situ chemiluminescent probes, we established sandwich-type analytic methods for rapid, simple, selective, and sensitive sequence-specific DNA detection and for human plasma IgG immunoassay, respectively. We used 12 clinical human plasma samples to examine the precision and accuracy of the proposed method for IgG content determination. Results: Calibration curves for the oligonucleotide [Delta I = 15.73 + 27.55 (DNA) X 10(10) (mol/L); R-2 = 0.9936] and IgG [Delta I = 48.84 + 30.23 (IgG) X 10(10) (mol/L); R-2 = 0.9964] show good correlation, demonstrating the linear response over the concentrations tested (0.04-10 nmol/L for DNA, 0.05-10 nmol/L for IgG). The limit of detection, calculated based on 50 mu L of a solution of calibrators, was 13 pmol/L for DNA and 17 pmol/L for IgG, with a signal-to-noise ratio of 3. We obtained good intra-and interassay reproducibility. The IgG contents in 12 human plasma samples obtained by the proposed method are identical with the data of clinical laboratory. Conclusions: We developed a simple and sensitive method for in situ amplified chemiluminescence detection of sequence-specific DNA and immunoassay of IgG by use of highly active, specially shaped, irregular gold nanoparticles (IGNPs) as label and confirmed by clinical samples test. This method has many desirable features including rapid detection, selectivity, and little required instrumentation. This new protocol may be quite promising, with potentially broad applications for clinical immunoassays and DNA hybridization analysis. (c) 2006 American Association for Clinical Chemistry.