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.