Ultrasensitive and miniaturized ion sensors using ionically imprinted nanostructured films

The detection of ions is essential for a wide range of applications including biomedical diagnosis, and environmental monitoring among others. However, current ion sensors are based on thick sensing films (∼100 µm), requiring time-consuming preparations, and they have a limit to their sensitivity of 59 mV.Log [C]⁻¹. Consequently, these sensors cannot be applied for high-precision applications that require high sensitivity and reduced dimensions. Furthermore, the research of anion sensors is hampered given the limited availability of molecular receptors or ionophores with acceptable performances. In this work, we overcome these limitations using a 300 nm thick sensing film based on nanoporous ion-imprinted core-shell silica/gold grafted onto a 50 nm gold film. The sensing films were highly selective towards chloride ions, compared to other anions such as nitrate, sulphate and carbonate. Moreover, this nanostructured film exhibited over 3-fold higher sensitivity (-186.4 mV.Log [C]⁻¹) towards chloride ions compared to commercial devices. This breakthrough has led to the fabrication of the smallest and most sensitive reported anion sensor working on open circuit potentiometry, with an exceptional selectivity towards chloride ions that could be used for the measurement of chloride ions in human serum.