Solvent-induced modulation of the chemical sensing performance of gold nanoparticle film chemiresistors

The analyte sensitivity of a chemical sensor is commonly tuned by the type of chemical recognition element. Here, it is shown that the solvent also plays a critical role in the sensing performance of thiol-capped gold nanoparticle film chemiresistors. Both the resistance change and speed of response of the chemiresistor can be optimised by adjusting the composition of methanol and water used for detection of the pesticide permethrin. It is shown that the resistance change is governed by the partitioning of the analyte between the thiol coating of the gold nanoparticles and the solvent. The partition coefficient, log P, has a strong influence on the response magnitude and is directly correlated to the response time. By varying the solvent, the log P of extremely high partitioning analytes such as permethrin in water can be lowered, and a much larger resistance change can be obtained in a shorter time period (5 min). A theoretical model is developed that correlates the experimental findings to changes in analyte partition coefficient with solvent type and composition. The results have significant implications for the design of chemical sensors and solvent conditions that can offer an enhanced signal within a practical timeframe.