Surface Blocking-Based\nPotentiometric Biosensor for\nDetection of E. coli ATCC 15597 Using\nPhage MS2 as a Receptor

Nowadays, using a potentiometric ion sensor to achieve\ndetection\nof biological analytes is still a big challenge, since these analytes\nusually do not yield a measurable ion signal. To address this challenge,\na simple and robust potentiometric sensing protocol based on a delayed\nNernstian response is proposed for the label-free detection of biological\nanalytes. The proposed sensor platform is composed of two layers:\nthe surface recognition layer and the indicator-ion-selective electrode\n(ISE) membrane layer. It is based on a surface blocking mechanism\nin which the surface recognition interactions between the surface\nrecognition element and the target can impede the diffusion of the\nindicator ion from the aqueous phase to the sensing membrane phase\nto reach the final Nernstian-response equilibrium, thus resulting\nin a delayed potential change. Such a potential change could be used\nto measure the concentration of a biological target in the sample.\nThus, a sensing system was designed by using phage MS2, its host bacterium Escherichia coli ATCC 15597(abbreviated as <i>E. coli</i> H), and a solid-contact butyrylcholine ISE as a\nsurface recognition element, a target, and an indicator electrode,\nrespectively. This new concept offers a simple, sensitive, and extremely\nselective potentiometric method for detection of E.\ncoli H with a detection limit of 100 CFU mL<sup>–1</sup>. It can be expected that the present approach may pave the way to\nusing ISEs to detect various important nonionic biological targets\nin clinical and environmental applications.