Colorimetric Humidity Sensor Based on Liquid Composite Materials for the Monitoring of Food and Pharmaceuticals

Abstract

Using supported ionic-liquid membrane (SILM)-inspired methodologies, we have synthesized, characterized, and developed a humidity sensor by coating a liquid composite material on a hygroscopic and porous substrate. Similar to pH paper, the sensor responds to the environment's relative humidity and changes color accordingly. The humidity indicator is prepared by casting few microliters of low toxicity reagents on a non-toxic substrate. The sensing material is a newly synthesized liquid composite, which comprises a hygroscopic medium for environmental humidity capture, and a color indicator, which translates the humidity level into a distinct color change. Sodium borohydride was used to form a liquid composite medium and DenimBlu30 dye was used as a redox indicator. The liquid composite medium provides a hygroscopic response to relative humidity, and DenimBlu30 translates the chemical changes into a visual change from a yellow to blue color. The borate-redox dye based humidity sensor was prepared, then Fourier Transform Infrared Spectroscopy, Differential Scanning Calorimetry, and image analysis methods were used to characterize chemical composition, optimize synthesis, and gain insight into sensor reactivity. Test results indicated that this new sensing material can detect relative humidity in the range of 5-100% in an irreversible manner with good reproducibility and high accuracy. The sensor is a low cost, highly sensitive, and easy-to-use humidity indicator. More importantly, it can be easily packaged with products to monitor humidity levels in pharmaceutical and food packaging.

Thermochemical Humidity Detection in Harsh or Non-Steady Environments

“…In previous works, we have developed disposable humidity sensors based on color change detection for product monitoring [17]. In this work, we demonstrate the utility of a thermal method for humidity detection, utilizing two approaches, consisting of a surface hydrophilically tuned to produce an exo- or endothermic reaction in response to humidity:

A thermistor-based chemical sensor, which consists of a surface-treated thermistor, enabling an inexpensive and robust contact method with an accurate low-thermal mass thermistor starting at less than $3 in bulk and simple data-acquisition circuitry, which can be insulated from harsh environments.

A thermographic humidity sensor, which utilizes a thermal camera to image a simple disposable sensing element, enabling a non-contact method of transducing humidity signal.

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The Orange Side of Disperse Red 1: Humidity‐Driven Color Switching in Supramolecular Azo‐Polymer Materials Based on Reversible Dye Aggregation

“…Humidity detection, and the quest for low‐cost facile humidity‐sensitive indicator materials is of great industrial interest for many fields, including semiconductor processing, food transport and storage, and the pharmaceutical industry in particular, among a wide range of other humidity‐sensitive products areas, from production through consumption. In recent years, great effort has been spent on developing sensitive and accurate humidity sensors, but of equal utility and importance from the point of the view of transporting and storing humidity‐sensitive goods, is development of simple binary “moisture memory” packaging materials that would trigger a readout above a threshold of water content experienced, and keep the memory of this critical over‐exposure to humidity in any stage of transport or storage prior to receiving the good. Conventional humidity‐responsive materials are typically based on observing electrical signals, but ideal humidity‐detection materials for a broad range of applications might be based on simple clear optical readout with no power supply, i.e., a clear color change observed by the naked eye of any untrained observer, since it does not require any extra instrumentation or interpretation.…”

“…Similar clear readout materials sensitive to humidity however, have proven more challenging to easily and cheaply implement. Clear visible changes have already been demonstrated by embedding photonic crystal materials in hydrogels that swell upon exposure to humidity, or the selective swelling of one block in a block co‐polymer, or by borate‐redox dyes, or by metal nanoparticles, whose plasmon resonance wavelength changes according to the dielectric constant of the surrounding medium. But still an achievement remains elusive of a facile “moisture memory” material based on cheap, robust, green, recyclable, and simple materials that can operate independently of readout assistance .…”

“…Humidity detection, and the quest for low-cost facile humidity-sensitive indicator materials is of great industrial interest for many fields, including semiconductor processing, food transport and storage, [1] and the pharmaceutical industry in particular, [2] among a wide range of other humidity-sensitive products areas, from production through consumption. In recent years, great effort has been spent on developing sensitive and accurate humidity sensors, [3][4][5][6][7][8] but of equal utility and importance from the point of the view of transporting and storing humiditysensitive goods, is development of simple binary "moisture Humidity detection, and the quest for low-cost facile humidity-sensitive indicator materials is of great interest for many fields, including semi-conductor processing, food transport and storage, and pharmaceuticals. Ideal humidity-detection materials for a these applications might be based on simple clear optical readout with no power supply, i.e.…”

Hydrothermal synthesis of Co–ZnO nanowire array and its application as piezo-driven self-powered humidity sensor with high sensitivity and repeatability

“…[1][2][3] These devices can monitor the environmental moisture for human comfort. [1][2][3] These devices can monitor the environmental moisture for human comfort.…”