Medical H₂S sensing with gold and platinum surface modified ZnO nanowire ChemFETs

Over the past decade, numerous publications highlighted the medical role of hydrogen sulfide (H₂S) for therapeutic applications and early diagnostics, traced in medical breath analysis e.g. with the “electronic nose” approach. It was shown that abnormal endogenous H₂S concentration levels in exhaled breath samples can be linked to airway inflammation in asthma patients, and hence H₂S functions as a potent biomarker.

In this work, we investigate the catalytic effects of gold (Au) and platinum (Pt) nanoparticle layer deposition on highly sensitive zinc oxide (ZnO) nanowires (NW) used for selective H₂S detection in the sub-ppm region. High quality pristine ZnO NWs are grown by high temperature chemical vapor deposition (CVD) and vapor liquid solid growth (VLS) on silicon with a thin Au layer acting as a growth catalyst. The surface modification of pristine ZnO NWs was modified by systematical magnetron sputtering of discontinuous Au and Pt nanoparticle layers of 1 – 6 nm thickness. Resistive gas sensors based on the gas sensing mechanism of a chemical field effect transistor (ChemFET) with open gate, which is formed by hundreds of parallel aligned pristine, Au modified or Pt modified ZnO NWs, were measured towards H₂S diluted in dry nitrogen (N₂) or in dry synthetic air at room temperature. Gas sensing results allow for a first understanding of largely improved signal-to-noise ratio and response due to the catalytic effects of metal deposition on ZnO NW surface. Controlled application of optimized ZnO NW growth and metal catalyst deposition show a clear enhancement of response towards 1 ppm H₂S from initial 15 % with pristine ZnO to 5000 % with ZnO after 5 nm Au deposition and hence greatly lower the limit of detection.