Dynamic gas sensing with blue μLED-activated SnO2 nanoparticles: A real-time tunable detection platform

Micro-light-emitting diodes (μLEDs) have garnered significant interest as light sources for gas sensors due to their advantages, such as room temperature operation and low power consumption. However, despite these benefits, challenges remain, including a limited range of detectable gases and slow response times.

To address this, a research team including Inkyu Park from the Korea Advanced Institute of Science and Technology (KAIST), Sang-Wan Ryu from Chonnam National University, and Ho Won Jang from Seoul National University, developed a blue μLED-integrated gas sensor array based on SnO₂ nanoparticles (NPs). This array exhibits excellent sensitivity, tunable selectivity, and rapid detection with microwatt-level power consumption.

Using the finite-difference time-domain (FDTD) method, Inkyu Park and colleagues simulated the light absorption of SnO₂ nanoparticles under varying light intensities. By assuming a densely packed spherical structure of SnO₂ NPs, they obtained simulated absorption distributions along the z-axis under light intensities of 50, 200, and 500 mW cm^-2. At lower light intensities, the lowest layer of SnO₂ NPs was fully activated and reacted with NO₂. Since the number of photogenerated carriers was far less than the molar quantity of NO₂, all carriers reacted with NO₂ molecules. As the light intensity increased, more layers of SnO₂ NPs became activated, leading to a greater number of NO₂ molecules reacting. Once the activated layers matched the thickness of the sensor’s electrode, the sensor’s response peaked. However, when the activation depth of SnO₂ NPs exceeded the electrode thickness due to excessive light intensity, the sensor’s response diminished. Upon introducing NO₂, most molecules reacted with SnO₂ NPs on the top layer, resulting in increased resistance in the upper layers, with the lower layers experiencing only a slight increase. Consequently, the majority of the current passed through the lower layers, which had lower resistance, leading to a reduced sensor response. Across these stages, the response curve exhibited a volcano-like pattern with respect to light intensity, highlighting the synergistic effects of the SnO₂ material properties and sensor device architecture on gas-sensing performance.

Furthermore, the gas-sensing performance of Au-SnO₂ NPs, Pd-SnO₂ NPs, and Pt-SnO₂ NPs towards NO₂ was studied under light exposure. Compared to SnO2 NPs, the response to 5 ppm of NO₂ decreased for Au-SnO₂ NPs, Pd-SnO₂ NPs, and Pt-SnO₂ NPs, with Pt-SnO₂ NPs showing the most significant reduction. When the reducing gases NH₃, CO, H₂, C₂H₅OH, and CH₃COCH₃ were tested under blue light, all sensors displayed distinct selectivity patterns. Polarization diagrams of SnO₂ NPs, Au-SnO₂ NPs, Pd-SnO₂ NPs, and Pt-SnO₂ NPs toward the reducing gases revealed that SnO₂ NPs showed moderate responses to NH₃, CO, and C₂H₅OH, while Au-SnO₂ NPs exhibited high sensitivity and selectivity to C₂H₅OH. Pd-SnO₂ NPs responded well to H₂, and Pt-SnO₂ NPs displayed strong responses to various gases, particularly NH₃. In summary, noble-metal-modified SnO₂ NP-based gas sensor arrays demonstrated the ability to distinguish a wide variety of gases under light illumination. This work is expected to advance μLED-based gas sensors, expanding the range of detectable gases and contributing to healthier living environments.