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.