(50e) A Colorimetric Humidity Sensor Based on Ionic-Liquid-like Materials for the Monitoring of Food and Pharmaceuticals

We have synthesized, characterized, and developed a low-toxicity irreversible peak humidity sensor which requires only a smartphone for accurate analysis for applications in food and drug packaging.  Using supported ionic-liquid membrane (SILM)-inspired methodologies, we have developed a sensor similar to pH paper, with the sensor changing color according to the surrounding environment; its response depending on the environment’s relative humidity. This response can be easily quantified with a standard CMOS smartphone camera.  The humidity indicator is prepared by casting minute amount of low toxicity reagents on a non-toxic substrate, which could be used for highly compact sensor applications in end consumer products. The sensing material consists mainly of a new borate liquid matrix, which acts as a humidity absorbent at a certain humidity level. An oxygen sensitive color indicator then translates the moisture level of the matrix into a color development, giving distinct color saturation for a humidity level in a single sensing element.  In this work, we use sodium borohydride both as a reducing agent and in-situ generator of borates, then use DenimBlu30 to translate chemical changes into a visual change from a yellow to blue color.  The borate-redox dye based humidity sensor was successfully prepared and systematic characterizations, namely Fourier transform infrared spectroscopy, differential scanning calorimetry, and imaging methods, were performed to gain insight on composition, sensor stability, and reactivity.  Test results indicated that this new sensing material can detect a relative humidity in the range of 5-100% in an irreversible manner with good reproducibility and high accuracy, and also be undamaged by temperature exposures to be expected with food and drug products.  This low cost, highly sensitive, and easy-to-use humidity indicator can be made the size of a pH indicator strip, which offers a low cost, safe, and easily packaged sensor to monitor humidity levels in pharmaceutical and food packaging.