  The development of an aptamer-based impedimetric sensor for typing of
bacteria (AIST-B) is presented. Highly specific DNA aptamers to Salmonella
enteritidis were selected via Cell-SELEX technique. Twelve rounds of selection
were performed; each comprises a positive selection step against S. enteritidis
and a negative selection step against a mixture of related pathogens, including
Salmonella typhimurium, Escherichia coli, Staphylococcus aureus, Pseudomonas
aeruginosa, and Citrobacter freundii to ensure the species-specificity of the
selected aptamers. After sequencing of the pool showing the highest binding
affinity to S. enteritidis, a DNA aptamer sequence of high affinity to the
bacteria was integrated into an impedimetric sensor via self-assembly onto a
gold nanoparticles-modified screen-printed carbon electrode (GNPs-SPCE).
Remarkably, this aptasensor is highly selective and can successfully detect S.
enteritidis down to 600 CFU 1/mL (equivalent to 18 CFU in 30 \muL assay volume)
in 10 minutes and distinguish it from other salmonella species, including S.
typhimurium and S. choleraesuis. This report is envisaged to open a new venue
for the aptamer-based typing of a variety of microorganisms using a rapid,
economic, label-free electrochemical platform.
