Gelatin as a new humidity sensing material: Characterization and limitations

Abstract

The goal of this work is to assert the utility of collagen and its denatured counterpart gelatin as cost-effective alternatives to existing sensing layers comprised of polymers. Rather than producing a material that will need to be discarded or recycled, collagen, as a by-product of the meat and leather industry, could be repurposed. This work examines the feasibility of using collagen as a sensing layer. Planar electrodes were patterned with lift-off process to work with the natural characteristics of gelatin by utilizing metal vapor deposition, spin coating, and photolithography. Characterization methods have also been optimized through the creation of specialized humidity chambers that isolate specific characteristics such as response time, accuracy, and hysteresis. Collagen-based sensors are found to have a sensitivity to moisture in the range of 0.065 pF/%RH. Diffusion characteristics were also analyzed with the diffusion coefficient found to be 2.5 × 10−5 cm2/s. Absorption and desorption times were found to be 20 seconds and 8 seconds, respectively. Hysteresis present in the data is attributed to temperature cross-sensitivity. Ultimately, the utility of collagen as a dielectric sensing material is, in part, due to its fibrous macrostructures as well its hydrophilic sites along the peptide chains. Gelatin was patterned between and below interdigitated copper electrodes and tested as a relative humidity sensor. This work shows that gelatin, which is inexpensive, widely available, and easy to process, can be an effective dielectric sensing polymer for capacitive-type relative humidity sensors.

Multivariable Sensors for Ubiquitous Monitoring of Gases in the Era of Internet of Things and Industrial Internet

“…Dielectric polymers exhibit gas-sensing mechanisms such as dispersion, polarizability, dipolarity, basicity, acidity, and hydrogen-bonding interactions . In single-output sensors, measurements are performed with capacitance readout , unless these polymers are formulated with conducting nanoparticles to measure the change in sensor conductivity . Such sensors have known insufficient selectivity; thus, they have been assembled into classic sensor arrays. , Several reviews analyze performance of dielectric polymers in gas sensing. , …”

Capacitive humidity and dew-point sensing: Influence of wetting of surface-attached polymer monolayers on the sensor response

“…When a linear fit is applied for this lower humidity range, the slope of the fit can be considered as the sensor's sensitivity. For the sensor coated with a PDMAA monolayer a sensitivity of around 10 pF/%RH in this humidity range is obtained, which is at least 20 times higher than other polymer coated sensors with a comparable setup reported in the literature [10,13,[22][23][24][25].…”

Multifunctional Flexible Organic Transistors with a High-k/Natural Protein Bilayer Gate Dielectric for Circuit and Sensing Applications

“…At a higher humidity level, capacitance density across the MIM (ITO/HfO 2 /gelatin/Au) structure increases due to the higher electrical permittivity of water in comparison to gelatin and contributes to higher charge accumulation in the channel. 56 From the results, it can be observed that the current in gelatin device reaches to saturation very sharply just after exposure to humidity; similarly, during the desorption process it returns to the initial stage in considerably low time interval, which makes it suitable for highly sensitive humidity sensors. To investigate the practical utility of the device, a continuous breath rate monitoring was demonstrated with help of changes in the humidity levels of breath during exhaling and inhaling.…”