Photocatalytic probing of DNA sequence by using TiO2/dopamine-DNA triads

A method to control charge transfer reaction in DNA using hybrid nanometer-sized TiO2 nanoparticles was developed. In this system extended charge separation reflects the sequence of DNA and was measured using metallic silver deposition or by photocurrent response. Light-induced extended charge separation in these systems was found to be dependent on the DNA-bridge length and sequence. The yield of photocatalytic deposition of silver was studied in systems having GG accepting sites imbedded in AT runs at varying distances from the TiO2 nanoparticle surface. Weak distance dependence of charge separation indicative of a hole hopping through mediating adenine (A) sites was found. The quantum yield of silver deposition in the system having a GG accepting site placed 8.5 Å from the nanoparticle surface was found to be Φ = 0.70 (70%) and Φ = 0.56 (56%) for (A)n and (AT)n/2 bridge, respectively. Hole injection to GG trapping sites as far as 70 Å from a nanoparticle surface in the absence of G hopping sites was measured. Introduction of G hopping sites increased the efficiency of hole injection. The efficiency of photocatalytic deposition of metallic silver was found to be sensitive to the presence of a single nucleobase mismatch in the DNA sequence.