Surface modification of TiO2 for photoelectrochemical DNA biosensors

Abstract

A photoelectrochemical (PEC) DNA biosensor is developed using surface-modified TiO₂ nanoparticles (NPs) as a sensitive transducer. Different catecholates and gallates are used as sensitizers for TiO₂ NPs. The molecules are adsorbed on TiO₂ via the catecholate type bonding mechanism to enhance light absorption in the visible range. The adsorbed molecules act as charge transfer mediators and enhance photocurrent. Despite the similar bonding mechanism of the molecules, the TiO₂ NPs exhibit significant differences in photocurrent. The modified TiO₂ films showed photocurrent increase in the order: 3,4-dihydroxy-L-phenylalanine < 2,3,4-trihydroxybenzoic acid < 3,4-dihydroxybenzoic acid < 2,3,4-trihydroxybenzaldehyde < 3,4-dihydroxyphenylacetic acid < 3,4-dihydroxybenzaldehyde < caffeic acid. Testing results provide an insight into the influence of the structure and properties of the organic molecules on their adsorption and photocurrents of modified TiO₂ films. The TiO₂ NPs modified with caffeic acid are used for the fabrication of PEC DNA biosensor by forming photoelectrodes and immobilizing probe single-stranded DNA on their surface. The caffeic acid-modified TiO₂-based photoelectrodes offer the required signal magnitude to distinguish between complementary and non-complementary DNA sequences in the 100 nM–1 pM DNA concentration range and with a limit of detection of 1.38 pM, paving the way towards PEC DNA sensing.