Label-free impedimetric detection of Listeria monocytogenes based on poly-5-carboxy indole modified ssDNA probe

Listeria monocytogenes is a life threatening pathogenic bacteria concerned with human health. The accurate and rapid detection of L. monocytogenes is required for preventing of listeriosis. In this study, DNA sensing probe based on conducting polymer poly-5-carboxy indole (5C Pin) was developed for the detection of L. monocytogenes hlyA gene responsible for pathogenicity. The probe sequences (24 mer ssDNA) were covalently immobilized on 5C Pin via N-(3-dimethylaminopropyl)-N′-ethylcarbodiimidehydrochloride (EDC) and N-hydroxysuccinimide (NHS). The probe having ssDNA was further hybridized with the target DNA sequence. Electrochemical impedance spectroscopic study was carried out to determine the extent of DNA hybridization over the probe. Significant change was observed in the impedance spectra before and after hybridization of ssDNA immobilized over the probe with the target DNA. RCT (charge transfer resistance) was estimated from the Nyquist plot (impedance plot) for target DNA (hlyA gene) in the solution. RCT vs. logarithmic concentrations of the target (genomic) DNA plot showed a linear range (1 × 10−4 to 1 × 10−12 M) in case hybridization was performed under optimized conditions. The method proposed, is simple, free from any label, and highly sensitive for the detection of L. monocytogenes in environmental and clinical samples.