Electrochemical sensor based on immobilization of single stranded deoxyribonucleic acid on Pt electrode surface by avidin-biotin system

An electrochemical sensor for detection of specific deoxyribonucleic acid (DNA) sequences based on ssDNA-modified Pt electrode by avidin-biotin has been developed. The method is simple, convenient, reagent-saving and practicale for DNA studies. The experimental steps are as follows: ( i) avidin was immobilized on the Pt electrode surface via direct adsorption, ( ii) biotinylated ssDNA was modified onto the electrode surface by avidin-biotin system, ( iii) the ssDNA-electrode was immersed into 2 mL of the 2 x saline-sodium citrate (SSC) buffer containing complementary DNA, and the hybridization reaction was carried out at certain temperature, (iv) the electrode was immersed into a Co (phen)(3)(3+) solution (5mmol/L Tris-HCI + 5 mmol/L NaCl pH7. 05 and detected voltammetrically. The immobilized probes were specific for most inserted sequences in genetically modified food: the promoter 35 S or the terminator NOS. The sensor signal dependent on external conditions (pH, temperature, the time of hybridization and immobilization) were studied for clarification of their effect on the assay and to find the optimum condition for measurements. The results showed that it was better for avidin to be adsorbed onto the electrode surface twice, 50 minutes every time and the optimum conditions of hybridization reaction were pH 7.0, 50 degrees C, 60 min. Under optimum conditions, the sensor's output signals present primely a relation of linearity with the concentration of complementary DNA sequences between 7.0 x 10(-8) mol/L and 2.3 x 10(-7) mol/L. The linear equation of probe 35 S was y = 1.16x + 0.137, and the correlation coefficient was 0.9996. The sensor can be reused over 6 times by electrode regeneration.