Effect of Nucleic Acids on Oxidation and Photoluminescence of Porous Silicon

In this work, porous silicon surface was modified by aqueous solutions of nucleic acids and the effect of such modification on the porous silicon photoluminescence was studied. The treatment of porous silicon with the nucleic acid solutions was found to cause an increase in the photoluminescence intensity, the change being greater with DNA rather than RNA (homopolymer poly(A)). By means of infrared spectroscopy, it was found that the number of Si-O bonds at the silicon surface after treatment by nucleic acid solutions is much higher than that after treatment by distilled water. It is found that the porous silicon photoluminescence weakly depends on the concentration of the molecular oxygen in the DNA solution. At the same time, illumination of the DNA-treated porous silicon samples by the visible light enhances the porous silicon photoluminescence intensity. Nucleic acid stimulated increase in the porous silicon photoluminescence is attributed to thinning of the silicon skeleton, which, according to the quantum-size model of photoluminescence, leads to a radiative transition probability increase. The thinning could be related to enhancement of dissolution and, to a greater extent, to oxidation of porous silicon in aqueous solution by the nucleic acids. The effect of nucleic acids in aqueous solutions on the porous silicon modification was assumed to be twofold. Firstly, nucleic acids, being polyanions in aqueous solutions, can enhance the corrosion of porous silicon by water. Secondly, an increased concentration of reactive oxygen species is generated in aqueous solutions of nucleic acids under visible light illumination. The latter is supposed to be the main reason of porous silicon oxidation. The results of the work can be useful for the development of PS-based biosensors.