Poster V17 - Impedance and Chemiresistor Based Sensor Array Devices for Identifying VOCs in Human Breath and Environmental Passive Detection

Introduction: Environmental exposure assessment and monitoring in terms of determining quantity, frequency, and duration, plays a critical part in ensuring occupational safety. This can be achieved through passive detection or biomonitoring. Biomonitoring is an approach that quantifies and verifies that exposure and uptake of agents has taken place through measurement of chemical agents and their metabolites present in blood, urine, hair, or exhaled breath. Whereas passive ambient detection monitors the magnitude and presence of chemical agents in an environment. Taken together these approaches can detect hazardous vapors, such as organophosphates (OP) and aromatic hydrocarbons (AHC) present in an environment and quantify the level of individual exposure. Occupational exposures to OP and AHC can lead to both acute and chronic health outcomes leading significant morbidity and even death. There exists a need to develop point-of-care technologies that effectively monitor occupational and environmental exposure using both passive detection and biomonitoring approaches. The current work presents a chemiresistor monitoring device comprised of paper-based nanostructured sensor arrays with printed functionalized metal nanoparticle sensing arrays capable of high sensitivity detection of OP and AHC. This sensor can be deployed as both a passive detection and biomonitoring device. The sensor quantifies the presence of agents in an environment and is capable of detecting and quantifying exposure consequences from human breath samples.

Materials and

Methods: The paper-based nanostructured sensor arrays were fabricated by inkjet or screen printing of conductive nanoinks on paper substrates of different porosity as the interdigitated microelectrode-patterned fibrous substrates and assembling nanocomposite thin films as the nano filaments on the patterned substrates. The correlation of the thin film thickness and the assembling parameters was determined by atomic force microscopy, showing good controllability in the range of 100 to 3000 nm, which was also assessed with the electrical resistance of the thin films in the range of 1 kilohm to 100 megaohm. The nanostructured sensor array device was interfaced with an integrated microelectronic board and coupled with auto sampling channels for data acquisition and with a wireless circuit board for data output. The data were processed by pattern recognition algorithm/software. Different pattern recognition techniques, such as ensemble learning and deep learning, were used to enhance the identification.

Results, Conclusions, and Discussions: There were two closely related application areas of our investigations of the nanostructured sensing arrays, to include the detection of chemical agents in an environment, and quantifying exposure consequences from human breaths. The morphological (e.g., size, composition, shape, etc.) parameters were optimized by controlled synthesis of metal and alloy nanoparticles (e.g., Au, Ag, AuCu, AgCu, etc.) and structural combination of surface capping molecules with different functional groups (e.g., carboxylic acid, amine, hydroxyl, and benzyl, etc.) for different VOCs with structural moieties of the targeted AHCs and OPs.
The arrays were evaluated first by testing the sensing films in terms of their responses to some of the common VOCs (e.g., benzene, toluene, xylene, alcohol, hexane, water, etc.) in air, which are related to the targeted VOCs (OPs and AHCs). The response sensitivities demonstrated synergies between interaction structural properties (hydrophobicity/hydrophilicity, polar/non-polar, aromatic/aliphatic, porous/non-porous, electrostatic-bonding, hydrogen-bonding, ligand coordination, etc.) and electrical conductivity properties (conductive, non-conductive, and semiconductive moieties). The effective PCA separation of different gases and VOCs, including CO and CO2, binary mixtures of benzene and toluene, and alcohols of different chain lengths and isomers, demonstrated the capabilities of the nanocomposite array for the targeted application. The sensor arrays were also evaluated by testing human breath samples with and without simulated lung cancer specific and non-specific VOCs and breath samples with and without lung cancer. Simulations of a sensor array in response to air containing VOCs such as benzene, toluene, styrene, o-xylene, dimethyl ether, 1,3-pentadiene, methyl hydrazine, ethanol, ethyl benzene, and 2-ethyl-4-methyl-1-pentanol (lung cancer specific VOC) shows excellent separation and recognition. Excellent separation and recognition capabilities have also been demonstrated by experimental measurements of the sensor arrays with human breaths with and without spiked lung cancer specific VOCs and human breaths with and without lung cancer.
In conclusion, the nanostructured sensor arrays have demonstrated the capability for detection and quantification of VOCs in air and human breaths. The integration of the sensor array devices with the microelectronics hardware and coupling with AI-driven data analytics have shown promises for further expansion to the targeted applications, which is part of our on-going investigation.

Acknowledgements (Optional): Disclaimer
The opinions and assertions expressed herein are those of the author(s) and do not reflect the official policy or position of the Uniformed Services University of the Health Sciences or the Department of Defense.