BAPTA-based potentiometric polymer sensor: towards sensing inflammations and infections

Potentiometric ion sensors represent a significant subgroup of electrochemical sensors. In this study, we have developed a potentiometric sensor using an electrically conductive copolymer of 2,2'-bithiophene (BT) and 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) for the selective detection of Ca²⁺ ions in extracellular interstitial fluids. The integration of BAPTA with its highly selective calcium chelating properties into a polymer matrix via electrochemical polymerization results in a sensitive conductive polymer layer that effectively detects the presence of calcium ions. This sensor aims at the early detection of inflammation or infection around implants because local calcium concentration is strongly elevated in interstitial fluid in such pathologies. The potentiometric study proves the incorporation of BAPTA into the polymer matrix was successful and its potential decreased upon calcium binding demonstrating the Nernstian behavior with a slope of approximately 20 ± 0.3 mV per decade in the concentration range from 0.1 mM to 1 mM. Moreover, the selectivity coefficient of -0.4 was measured by SSM and calculated from the Nicolsky-Eisenmann equation, which indicates selectivity towards Ca²⁺ ions with respect to Mg²⁺ ions.