Biomolecular hybrid of poly(3-thiophene acetic acid) and double stranded DNA: optical and conductivity properties

Abstract

A new biomolecular hybrid of poly(3-thiophene acetic acid) (PTAA) and double stranded deoxyribonucleic acid (ds-DNA) is prepared. The transmission electron microscopy (TEM) images exhibit fibrillar network morphology making a nanostructured self-assembly of PTAA-DNA hybrid. The confocal fluorescence image of PTAA shows green fluorescence exhibiting agglomeration in the pure state but the spreading of green fluorescence over the network superstructure in the hybrids indicating the immobilization of PTAA on DNA surfaces. Fourier transform infrared (FTIR) spectra indicate hydrogen bonding between -COOH groups of PTAA and P=O groups of Na-DNA. Circular dichroism (CD) spectra denote that DNA conformation remains unaltered during hybrid preparation. A blue shift of the π-π∗ absorption peak of PTAA in the hybrid solutions occurs with aging time. The photoluminescence intensity in the hybrid solution increases with a concomitant blue shift of the emission peak with aging time, and it is faster with increased DNA concentration. Possible reasons of different optical behavior are discussed in the light of duplex and triplex hybrid formation. Dynamic light scattering study indicates an increased particle size of PTAA with addition of DNA favoring the hybrid particles to remain in solution. The dc-conductivity of the hybrids decreases from that of PTAA with an increase of Na-DNA concentration, and the current (I)-voltage (V) curves indicate a semiconducting nature of the hybrids.