Multiplexed soft candy-based sensor for salivary conductivity diagnostics with uneven wetting detection capability

The wetting conundrum in soft candy-based sensors for salivary electrical conductivity diagnostics was solved in this study. Instead of using ill-suited conventional wetting strategies that require modification of the sensor surface, simple time multiplexing was achieved using four measurement points across the sensor surface and taking four 30 s measurements sequentially between these points. Using 0.01, 0.1, and 0.2 M phosphate-buffered saline, both qualitative and quantitative distinctions between uneven and complete wetting were made via wetting signature comparison. The soft candy-based sensor exhibits a limit of detection of 0.01 M (206 mu S/cm). Although it demonstrates a lower performance than a commercially available conductivity tester, it is adequate for chronic kidney disease diagnosis. In the human lick test, it yielded human saliva conductivity of-3535 mu S/ cm, which is consistent with that measured by conductivity tester and that reported in literature. More importantly, the previously established wetting signatures are also relevant to human saliva. The sensor could also be further licked to achieve complete wetting and proper measurements without being discarded.