Publication date: 15th December 2025
Recent advances in nanotechnology and diagnostic systems have increased interest in high-
resolution, non-invasive biosensing. Photoplethysmogram (PPG) sensors are widely used for
physiological monitoring; however, silicon-based devices are fundamentally limited at wavelengths
above 1100 nm, making it difficult to detect signals in the near-infrared region. As a result, infrared-
active and non-toxic materials with tunable bandgaps have become important candidates for next-
generation biosensors.
In this work, we investigate group III–V quantum dots, such as InAs and InSb, as near-infrared
optoelectronic materials. These materials offer narrow bandgaps and avoid toxic elements like Pb and
Hg. We synthesized InAs colloidal quantum dots (CQDs) using a seedless, one-pot method, which
simplifies the conventional synthesis process. By controlling the injection rate and reaction time, InAs
CQDs with low oxidation and optical properties comparable to those of conventionally synthesized
CQDs were obtained. The bandgap could be tuned in the near-infrared range of 1.1–1.5 eV through
monomer flux control.
An InAs CQD-based photodetector was fabricated and showed performance similar to that of
conventional InAs CQD devices. Using this photodetector, we built a real-time PPG system for
oxygen saturation measurement. Blood-mimicking samples were prepared using hemoglobin powder
and phosphate-buffered saline (PBS), covering the typical adult oxygen saturation range with 1%
intervals. The measured signals showed fluctuations consistent with reference values. Fingertip
measurements further confirmed that the signal trends from the InAs CQD-based PPG sensor closely
matched those from a commercial medical device.
In addition to biomedical sensing, the infrared sensitivity and quantum confinement of InAs CQDs
make them relevant to future quantum technologies. These properties suggest that InAs CQD-based
devices could be extended to quantum sensing and near-infrared quantum communication platforms.
This work was supported by the Korea Research Institute of Standards and Science (KRISS, KRISS-GP2025-0001), and in part by the National Information Society Agency (NIA) grant by the Korea government (MSIT) (No. 2100-2132-313) and the National Research Foundation of Korea (NRF) (MSIT, NRF2021R1C1C1010434).
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