Abstract
We demonstrate the selective detection of hydrogen sulfide at breath concentration levels under humid airflow, using a self-validating 64-channel sensor array based on semiconducting single-walled carbon nanotubes (sc-SWCNTs). The reproducible sensor fabrication process is based on a multiplexed and controlled dielectrophoretic deposition of sc-SWCNTs. The sensing area is functionalized with gold nanoparticles to address the detection at room temperature by exploiting the affinity between gold and sulfur atoms of the gas. Sensing devices functionalized with an optimized distribution of nanoparticles show a sensitivity of 0.122%/part per billion (ppb) and a calculated limit of detection (LOD) of 3 ppb. Beyond the self-validation, our sensors show increased stability and higher response levels compared to some commercially available electrochemical sensors. The cross-sensitivity to breath gases NH3 and NO is addressed demonstrating the high selectivity to H2S. Finally, mathematical models of sensors’ electrical characteristics and sensing responses are developed to enhance the differentiation capabilities of the platform to be used in breath analysis applications.
Highlights
During the last decade, the potential of exhaled breath analysis as a non-invasive and cost-effective alternative for precise disease identification and health monitoring has been intensively considered [1,2,3,4,5,6]
Each device consists of 64 individual sensors grouped in 4 quadrants of 16 sensors each with a common source/working electrode used for dielectrophoretic deposition of sc-SWCNTs (Fig. 1(d)), electrochemical deposition of AuNP (Fig. 1(e)), and the measurement of the output characteristics (Fig. 1(f))
Its simplicity, good reproducibility, cost-effectiveness, and more importantly, the efficient individualization of carbon nanotubes (CNTs) between electrodes make DEP the most attractive alternative for the fabrication of CNT-based gas sensors compared to other solution processing methods like drop-casting [23, 30] and self-assembly monolayer (SAM) assisted deposition [40, 41]
Summary
The potential of exhaled breath analysis as a non-invasive and cost-effective alternative for precise disease identification and health monitoring has been intensively considered [1,2,3,4,5,6]. Human breath contains over 3,500 components [7, 8] including N2, O2, CO2, and volatile organic compounds (VOCs), presenting a great challenge for sensing technologies in terms of sensitivity, selectivity, and response time. Additional features in terms of stability, reproducibility, and fast response time are critical characteristics that, together with the miniaturization possibilities offered by micro- and nanofabrication technologies, can lead to the development of robust diagnostic devices with a portable and comfortable maneuver In this context, the implementation of nanomaterials, and especially 1D materials such as carbon nanotubes (CNTs) [23] or silicon nanowires [24, 25] has boosted the sensitivity of gas sensors in low power consumption formats. The sensing response of both functionalized and non-functionalized sensors to low ppb concentrations of H2S, NH3, and NO was systematically studied under the same conditions and mathematically modeled toward the improvement of a predictive approach and enhanced target gas differentiation capability
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