Development of Electrochemical and Optical Based Biosensors

During recent years, rapid and highly selective determination of nucleic acid (in particularly, DNA) has gained much importance in the field of disease diagnostics, gene analysis, tissue matching, forensic and environmental protection. Various techniques have been employed for DNA detection like fluorescence, surface plasmon resonance (SPR), quartz crystal microbalance (QCM), piezoelectric, electroluminiscene, and electro-chemical. Among all these techniques, electro chemical and SPR based biosensors for nucleic acid detection have attracted researchers worldwide due to their high sensitivity, low detection limit, fast response time, wide detection range, good reliability, easy handling and portability. DNA based biosensors rely on the immobilization of a single-stranded oligonucleotide probe onto a surface to recognize by hybridization its complementary target sequence. The probes are typically short oligonucleotides that are capable of hybridizing with specific and unique regions of the target nucleotide sequence.  Due to formation of double helical structure between complementary strands, a change in current or SPR angle could be easily observed.

In the present study, an effort has been made towards the development of ZnO matrix based biosensors for the detection of Meningitidis using electrochemical (Amperometric) and SPR techniques. The surface plasmon modes have been excited at the ZnO-gold interface in the Kretschmann configuration using a right angled BK7 glass prism (n_p =1.517) with the help of a laboratory assembled system. The shift in SPR reflectance curve for increasing concentration of target DNA ranging from 10 to180 ng/μl were recorded which shows the promising application of SPR technique towards biosensing. The Sensitivity of the ZnO thin film using SPR is found to be about 0.031°/(ng/μl) with the minimum detection limit of 5 ng/μl.

Zinc oxide nanostructures possessing flower-like morphology have been synthesized onto platinized silicon substrate by simple and economical hydrothermal method. The electrochemical sensing response behaviour of the DNA bioelectrode (ssth-DNA/ ZNF/Pt/Si) has been studied by both differential pulse voltammetric (DPV) as well as impedimetric techniques. The fabricated DNA biosensor can quantify wide range of the complementary targets sth-DNA in the range 5–240 ng/μl with good linearity (R=0.98), high sensitivity (168.64μAng/μl/cm²) and low detection limit of about 5ng/μl.