De Novo Development of a Universal Biosensing Platform by Rapid Direct Native Protein Modification

General Gel-sol Method to Synthesize Various Highly Fluorescent Nanoclusters and Assay of Nuclease with the Near Infrared-emitting Gold Nanoclusters

A general egg white gel-sol strategy for fabrication of highly fluorescent Au, Ag, Cu, and Pt nanoclusters (NCs) and the first example of using Au NCs for assay of nuclease activity and inhibition were described. The Au NCs enabled bright red fluorescence, and the other Ag, Cu, and Pt NCs have highly blue emission. The red-emitting Au NCs were further applied in assay of S1 nuclease activity and inhibition. Free hemin efficiently quenches the emission of Au NCs by photoinduced electron transfer due to the formation of Au NCs-hemin conjugates. However, G-quadruplex/hemin exerts negligible effect on its fluorescence due to no Au NCs-hemin conjugate formed. There are stronger electrostatic repulsion effects between both negatively charged G-quadruplex and Au NCs. Therefore, a novel G-quadruplex/hemin-based Au NCs fluorescent sensor for S1 nuclease was designed. A known G-rich oligonucleotide (ODN) serves as not only substrate for S1 nuclease but also for the construction of G-quadruplex/hemin. The G-rich ODN is hydrolyzed into fragments by S1 nuclease resulting in no G-quadruplex/hemin formation. Therefore, the free hemin quenches Au NCs fluorescence remarkably and the assay of S1 nuclease activity and inhibition has accomplished. Both the fluorescent NCs syntheses and the detection of S1 nuclease are facile and efficient.