A Dual QCM Integrated with a Heater and Temperature Sensor for the Detection of VOCs from Human Skin

This work introduces a dual quartz crystal microbalance (QCM) platform for non-invasive detection of skin-emitted volatile organic compounds (VOCs). Two QCMs, integrated with a heater and temperature sensor on a single quartz substrate, enable optimized preconditioning. One QCM was coated with a metal-organic framework (MOF) for sensing, while the other served as a reference. The effect of electrode spacing (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1-3 ~\text{mm}$</tex>) was examined, revealing that only the 3 mm configuration maintained signal integrity in skin trials (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{n}=3$</tex>). Incorporating a Peltier heater improved stability, reducing frequency deviation from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\pm 5 ~\text{Hz}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\pm 1 ~\text{Hz}$</tex>. The system combines simplified fabrication, selective coating, optimized spacing, and thermal control for precise VOC detection.