Electrochemical determination of guanine and adenine by CdS microspheres modified electrode and evaluation of damage to DNA purine bases by UV radiation.

Sensitive electrochemical sensor based on a composite of novel pearl-like CdS microspheres and chitosan (CdS-CHIT/GCE) was constructed and characterized using cyclic voltammetry. Single-stranded (ssDNA) and double-stranded (dsDNA) deoxyribonuleic acid were electrochemically adsorbed onto CdS-CHIT/GCE and a significant difference in electrochemical impedance spectra of the ssDNA/CdS-CHIT/GCE and dsDNA/CdS-CHIT/GCE electrodes was found. Electrocatalytic properties of CdS allowed to use the CdS-CHIT/GCE successfully for the trace determination of simple guanine and adenine with nanomolar detection limits by differential pulse voltammetry (DPV). Moreover, damage to the DNA purine bases, guanine and adenine, liberated in previously hydrolyzed calf thymus dsDNA, caused by UV-B, UV-C, and visible light was evaluated. While only minor changes in anodic DPV response of guanine and adenine could be seen after 60 min exposition to UV-B and visible light, total degradation of DNA bases was observed after 20 min exposure to UV-C. A great potential of the CdS microspheres used as the interface at the nucleic acid based biosensors was demonstrated.