Immobilization of aptamer-modified gold nanoparticles on BiOCl nanosheets: Tunable peroxidase-like activity by protein recognition.

A self-assembled nanocomposite is prepared from an aqueous mixture of aptamer-modified gold nanoparticles (Apt-Au NPs), bismuth ions and chloride ions. The Apt-Au NPs are immobilized on bismuth oxychloride (BiOCl) nanosheets in situ to form Apt-Au NPs/BiOCl nanocomposites. The as-prepared nanocomposites exhibit high peroxidase-like activity for the catalytic conversion of Amplex Red (AR) to fluorescent resorufin in the presence of H2O2. The catalytic activity of Apt-Au NPs/BiOCl nanocomposites is at least 90-fold higher than that of Apt-Au NPs or BiOCl nanosheets, revealing synergistic effects on their activity. The catalytic activity of Apt-Au NPs/BiOCl nanocomposites is suppressed by vascular endothelial growth factor-A165 (VEGF-A165) molecules that specifically interact with the aptamer units (Del-5-1 and v7t-1) on the nanocomposite surface. The AR/H2O2-Apt-Au NPs/BiOCl nanocomposites probe shows high selectivity (>1000-fold over other proteins) and sensitivity (detection limit ~0.5nM) for the detection of VEGF-A165. Furthermore, the probe is employed for the detection of VEGF isoforms and for the study of interactions between VEGF and VEGF receptors. The practicality of this simple, rapid, cost-effective probe is validated by the analysis of VEGF-A165 in cell culture media, showing its great potential for the analysis of VEGF in biological samples.