Inkjet-Printed Wearable E-nose with Liquid-Phase Ligand-Exchanged Quantum Dots for Human-Centered Gas/Odor Monitoring

The development of next-generation wearable electronic nose (e-nose) systems for real-time environmental monitoring requires miniaturized gas sensor arrays with high sensitivity and low-power operation. Current limitations persist in the incompatibility between conventional sensing material deposition methods and MEMS microheater architectures. Here, we present an intelligent wristwatch-formatted e-nose system, integrating a printable quantum dot (QD) sensor array fabricated using an optimized colloidal quantum dot (CQD) ink formulation and a precision inkjet printing strategy. We engineered metal cation-surrounded quantum dots (MCSQDs) via liquid-phase ligand exchange with transition metal chlorides (FeCl3, CoCl2, NiCl2, CuCl2), achieving tailored surface functionalities and enhanced gas discrimination capabilities. The engineered MCSQD inks demonstrated exceptional colloidal stability and seamless MEMS microheater integration, enabling gas sensors with parts-per-billion-level detection limits (4 ppb ethanol). A 16-unit sensor array was embedded into a wearable platform incorporating cloud-based neural network processing. System validation achieved 100% classification accuracy in indoor odor recognition tests using a fully connected neural network (FCNN), while field tests at a transportation hub demonstrated reliable monitoring of Total Volatile Organic Compounds (TVOC), NO2, SO2, and CO with <15% deviation from the reference sensors. This work establishes a viable manufacturing framework bridging quantum-confined material engineering to IoT-enabled artificial olfaction, paving the way for scalable production of QD gas sensor array-based e-noses.