Colorimetric detection of platelet-derived growth factors through competitive interactions between proteins and functional gold nanoparticles

We have developed a colorimetric assay-using aptamer modified 13-nm gold nanoparticles (Apt-Au NPs) and fibrinogen adsorbed Au NPs (Fib-Au NPs, 56nm)-for the highly selective and sensitive detection of platelet-derived growth factors (PDGF). Apt-Au NPs and Fib-Au NPs act as recognition and reporting units, respectively. PDGF-binding-aptamer (Apt _PDGF) and 29-base-long thrombin-binding-aptamer (Apt _thr29) are conjugated with Au NPs to prepare functional Apt-Au NPs (Apt _PDGF/Apt _thr29-Au NPs) for specific interaction with PDGF and thrombin, respectively. Thrombin interacts with Fib-Au NPs in solutions to catalyze the formation of insoluble fibrillar fibrin-Au NPs agglutinates through the polymerization of the unconjugated and conjugated fibrinogen. The activity of thrombin is suppressed once it interacts with the Apt _PDGF/Apt _thr29-Au NPs. The suppression decreases due to steric effects through the specific interaction of PDGF with Apt _PDGF, occurring on the surfaces of Apt _PDGF/Apt _thr29-Au NPs. Under optimal conditions [Apt _PDGF/Apt _thr29-Au NPs (25pM), thrombin (400pM) and Fib-Au NPs (30pM)], the Apt _PDGF/Apt _thr29-Au NPs/Fib-Au NPs probe responds linearly to PDGF over the concentration range of 0.5-20nM with a correlation coefficient of 0.96. The limit of detection (LOD, signal-to-noise ratio=3) for each of the three PDGF isoforms is 0.3nM in the presence of bovine serum albumin at 100μM. When using the Apt _PDGF/Apt _thr29-Au NPs as selectors for the enrichment of PDGF and for the removal of interferences from cell media, the LOD for PDGF provided by this probe is 35pM. The present probe reveals that the concentration of PDGF in the three cell media is 230 (±20)pM, showing its advantages of simplicity, sensitivity, and specificity.