A general protein aptasensing strategy based on untemplated nucleic acid elongation and the use of fluorescent copper nanoparticles: Application to the detection of thrombin and the vascular endothelial growth factor

The authors describe an aptamer-based detection scheme that is based on untemplated nucleic acid elongation and the use of copper nanoparticles (CuNPs) as a fluorescent probe. An aptamer without any other auxiliary sequence and label is required only which makes the method rather convenient. Under the catalysis of terminal deoxynucleotidyl transferase (TdT), the single-stranded aptamer is elongated without template. By using dTTPs as the substrate, long linear poly T can be produced, and these can act as templates for the synthesis of CuNPs which display red (617 nm) fluorescence under 349 nm photoexcitation. In the presence of the analyte, the TdT-catalyzed production of poly T is blocked, and this results in suppressed fluorescence. The strategy was successfully applied to the determination of the proteins thrombin and vascular endothelial growth factor 165. Only three steps are involved in the whole assay. This aptamer-based assay is believed to have a wide scope in that it may be applied to the analysis of many other proteins if the corresponding aptamers are available.