Ultrasensitive and direct detection of DNA and whole E. coli cell at cholesterol gold nanoparticle composite film electrode.

Lipid membrane containing cholesterol gold nanoparticle and cationic, neutral and anionic lipid was prepared on gold electrode using mixed monolayer cushion for ultrasensitive electrochemical label-free DNA and unprocessed whole E. coli bacterial cell detection in the presence of K₃[Fe(CN)₆]/K₄[Fe(CN)₆] in physiological buffer. Cholesterol and gold nanoparticles interactions were characterized by dynamic light scattering (DLS) technique, cyclic voltammetry (CV), electrochemical impedance (EIS), Fourier infrared transform (FTIR) and transmission electron microscope (TEM) techniques. Insulation property of mixed monolayer towards K₃[Fe(CN)₆]/K₄[Fe(CN)₆] is influenced by the presence of lipid–gold nanoparticles. DNA hybridization studies indicate higher discrimination efficiency (75 ± 3%) between the unhybridized ssDNA and hybridized dsDNA for the binary cationic/cationic lipid–gold composite compared to the discrimination efficiencies 20 ± 3% and 5% noticed for other composite membranes cationic/anionic, cationic/neutral and anionic/neutral membranes constructed on thiol monolayer cushion. The sensor showed a wide linear range from 10^–9 to 10^–19 M with lowest detection limit (LOD) of 10^–19 M and limit of quantification (LOQ) 10^–17 M. E. coli DNA was used as a model system. For cross-reactivity validation, Staphylococcus, Enterococcus and E. coli were isolated and used for the direct and selective sensing of whole E. coli cell at 10⁶ CFU/mL by label-free impedance technique. [ABSTRACT FROM AUTHOR]