Selective detection of clinically relevant Gram-negative bacteria using a colistin-functionalized ISFET biosensor

Rapid and selective detection of Gram-negative bacteria is important for clinical diagnosis and for monitoring environmental and food-related samples. In this study, we developed a label-free ISFET sensor based on a p-type silicon/SiO₂ platform modified with ZnO and colistin for the detection of Gram-negative bacteria. The sensor was evaluated against several Gram-negative species, including Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, Salmonella enterica serovar Enteritidis, Klebsiella oxytoca, and Klebsiella pneumoniae, with the Gram-positive species Staphylococcus aureus and Enterococcus faecium used as negative controls. The device showed measurable changes in drain-source current upon bacterial binding, and the standard curves indicated a low detection limit and a linear response within the tested concentration range. The calculated limits of detection were approximately 137 CFU/mL for E. coli, 169 CFU/mL for A. baumannii, 188 CFU/mL for S. enterica, 218 CFU/mL for K. oxytoca, 235 CFU/mL for K. pneumoniae, and 289 CFU/mL for P. aeruginosa. The sensor stability was also assessed over 14 days in the E. coli assay. In addition, real-sample experiments in commercial bottled drinking water and human urine spiked with E. coli showed good agreement with PBS measurements, with a recovery of 101.13% ± 3.08% and an RSD of 3.05% in bottled water. These results indicate that the proposed platform has potential for selective detection of Gram-negative bacteria under controlled laboratory conditions and in tested real matrices.