Seedless One-Pot Synthesis of Colloidal InAs Quantum Dots Enabling a High-Accuracy Photoplethysmography Oximeter

Near-infrared (NIR) wavelengths offer a powerful approach for non-invasive physiological monitoring due to the deep tissue penetration and ability to detect various endogenous molecules such as hemoglobin species, water, and lipids. Herein, we demonstrate a high-speed, non-contact photoplethysmography (PPG) system based on indium arsenide (InAs) colloidal quantum dots (CQDs). To this end, a seedless injection-based one-pot method was devised to synthesize monodisperse NIR InAs CQDs. This scalable approach enables precise bandgap tuning from 1.53 to 1.09 eV, aligning with the absorption spectra of hemoglobin and oxyhemoglobin. Furthermore, the proposed CQD-based PPG system is integrated into a real-time acquisition platform. Exercise-induced desaturation tests show that the CQD-based PPG system exhibits consistent oxygen saturation rate (SpO₂) trends compared to commercial oximeters, exhibiting a considerable agreement of 99.76% (SpO₂ range: 90%-92%). The system also shows reliable operation with a bandwidth up to 2.5 kHz under multi-lock-in detection.