Seedless Synthesis of Colloidal III-V Quantum Dots for Infrared Non-Invasive Biomonitoring

Due to the development of nanotechnology and diagnostic systems, the demand for self-diagnosis and various bio-recognition in a high-resolution has significantly increased. Photoplethysmogram(PPG) sensor is a reperesentative technology for non-invasive bio-monitoring in this period. Although the absorption limitation of silicon, is restricted to detect various substances over 1100nm. To overcome this problem, the development of infrared materials is a common topic of recent research, especially focusing on non-toxic and bandgap tunable materials for bio-sensing.
In this study, we used group III-V quantum dots(e.g. InAs, InSb), which have recently gained attention as near-infrared optoelectronic materials due to their narrow bulk bandgap and the lack of toxic elements such as PB and Hg. To this end, we utilized a seedless synthesis method of InAs colloidal quantum dot(CQD) that simplifies the conventional synthesis process. By controlling the injection rate and time, we achieve a similar quality and low oxidation rate of InAs CQD compared to conventionally synthesized CQD in one-pot condition. This approach allows facile tuning of the bandgap at a NIR wavelength of 1.5-1.1 eV with monomer flux. Furthermore, we fabricated a photodetector using InAs CQDs and demonstrated that the proposed photodetector performs comparable to conventional InAs CQD PD.
Finally, we developed a simple and highly accurate real-time PPG signal monitoring platform for oxygen saturation. The samples were analyzed within a typical adult range at 1% intervals, revealing saturation signals fluctuate comparable to the calculated reference line. For the accuracy of detection, we compared a commecial medical device and our PPG sensor. As a result, the signal fluctuation of CQD PPG sensor was clearly matched with the commercial deveice. This demonstrated that the seedless InAs CQD photodetector has comparable performance to conventional PPG and promising method to expand the real-time healthcare monitoring platform.