G-Quadruplex-Functionalized Gold Nanoparticles for a Real-Time Biomolecule Sensor with On-Demand Tunable Properties

G-quadruplex (G4) DNA-functionalized gold nanoparticles (AuNPs) were fabricated for a new sensing platform for a biomolecule, thrombin. Thrombin-binding aptamer (TBA), which forms a highly ordered G4 structure, was immobilized on AuNPs. The particles were induced to aggregate by binding of thrombin to G4 DNA. Thrombin was thus detected by the color change of the colloidal system from red to purple-blue. The aggregation was not due to the bridging between the particles through thrombin but to the reduction in steric repulsion attributable to the mobility and flexibility of G4 DNA. The change in the colloidal stability was quick and the bathochromic peak shift varied with the concentration of thrombin. The sensor showed a high specificity to the thrombin target over major proteins in human serum. The detection sensitivity and analytical performance were successfully tuned for an on-demand sensor with a linearity of 10.0-40.0 nM. The limits of detection and of quantification were 3.6 and 10.7 nM, respectively.