Synergy of Ionic and Dipolar Effects by Molecular Design for pH Sensing beyond the Nernstian Limit

Knowledge of interfacial interactions between analytes and functionalized sensor surfaces, from where the signal originates, is key to the development and application of electronic sensors. The present work explores the tunability of pH sensitivity by the synergy of surface charge and molecular dipole moment induced by interfacial proton interactions. This synergy is demonstrated on a silicon-nanoribbon field-effect transistor (SiNR-FET) by functionalizing the sensor surface with properly designed chromophore molecules. The chromophore molecules can interact with protons and lead to appreciable changes in interface dipole moment as well as in surface charge state. In addition, the dipole moment can be tuned not only by the substituent on the chromophore but also by the anion in the electrolyte interacting with the protonated chromophore. By designing surface molecules to enhance the surface dipole moment upon protonation, an above-Nernstian pH sensitivity is achieved on the SiNR-FET sensor. This finding may bring an innovative strategy for tailoring the sensitivity of the SiNR-FET-based pH sensor toward a wide range of applications.