Tubular Au-TTF solid contact layer synthesized in a microfluidic device improving electrochemical behaviors of paper-based potassium potentiometric sensors

Tetrathiafulvalene (TTF) based charge-transfer compounds are ideal as a transducer layer for a solid-contact ion-selective electrode (SC-ISE), because of their excellent ionic conductivity and high capacitance. Since nanomaterials with tailored geometries exhibit unique shape-dependent properties and subsequent utilization of them for the fabrication of electrochemical devices is of significant interest. Gold-TTF (Au-TTF) with different morphologies such as flower-like, sheet-like, long wire and tubular with different length, were synthesized by microfluidics-dictated synthesis in a fast, simple and continuous procedure. The electrochemical performance of synthesized Au-TTF hybrid crystals was characterized by cyclic voltammetric, electrochemical impedance and constant-current chronopotentiometric measurement. The results demonstrate that long-tubular-like Au-TTF crystal is best suitable for ISE due to its great stability, high capacitance and co-existence of TTF/TTF+ providing a stable interphase potential. Then paper-based potentiometric potassium sensors were fabricated based on flower-like and long-tubular-like Au-TTF hybrid crystal as transducer layer of ISE and reference electrode. Compared to paper-based sensor with flower-like Au-TTF as transducer layer, paper-based sensor with long-tubular-like Au-TTF as transducer layer exhibits a much better Nernstian response with a slop of 57.64 ± 0.09 mV/dec and a lower detection limit of 2.75 × 10−6 M. Furthermore, the fabricated potentiometric sensor requires only 5 μL samples to test and displays little water-layer, good anti-interference, and great reproducibility and selectivity.