A Metal–Insulator–Metal Humidity Sensor Using Albumin–WO₃ Composites for Enhanced Responses

The growing demand for precise healthcare monitoring has fueled advancements in humidity sensor technology, which is crucial for applications in meteorology, environmental monitoring, industrial control, agriculture, and biomedical devices. In the biomedical realm, humidity sensors play a vital role in point-of-care testing devices for detecting respiratory conditions, such as bronchitis, asthma, and pneumonia. This study presents a two-terminal metal–insulator–metal (MIM) device utilizing a composite of chicken egg albumin and tungsten trioxide (WO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>) as the active hygroscopic film, with aluminum and copper as the bottom and top electrodes, respectively. Albumin, a biocompatible and hydrophilic protein, efficiently absorbs moisture, while WO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoparticles, known for their excellent electrical conductivity, enhance the device's sensitivity to humidity changes. Experimental results demonstrate that increasing the WO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> content in the composite film from 0% to 50% significantly improves the sensor's performance. Specifically, the maximum current response to humidity increased up to 15 times for pure albumin, 17.3 times for the albumin–WO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (25%) nanocomposite, and 21 times for the albumin–WO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (50%) nanocomposite, as the relative humidity varied from 20% to 95%. This work highlights the potential of albumin–WO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> composites for diverse applications in environmental monitoring, healthcare, and industrial processes.