Temperature sensing with high spatial and temporal resolution is crucial in many industries, including industrial manufacturing, environmental monitoring, and healthcare monitoring. Because of their benefits of remote detection, minimum intrusion, tolerance to electromagnetic interference, and high resolution, optical-based sensors are appealing for temperature monitoring in biological diagnostics.
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Luminous intensity, wavelength, peak breadth, and/or decay duration can all be used as optical sensing modalities. The upconversion mechanism reduces biological autofluorescence, improves tissue penetration, and produces observable and capturable visible light signals, making it a more acceptable tool for biological sensing.
A team of scientists including Dr. He Ding of Beijing Institute of Technology’s School of Optics and Photonics, Prof. Xing Sheng of Tsinghua University’s Department of Electronic Engineering, and co-workers created an optoelectronic NIR-to-visible upconversion device that is based on devised semiconductor heterostructures, displaying a linear response, rapid dynamics, and low excitation power in a new paper published in Light Science & Application.
The optoelectronic upconversion device’s temperature-dependent photoluminescence properties are extensively explored, and its capacity for thermal sensing is proven.
The suggested temperature sensing strategy relies on a fully integrated optoelectronic upconversion device (Figure 1a), which consists of a low-bandgap gallium arsenide (GaAs) based double junction photodiode and a large-bandgap indium gallium phosphide (InGaP) based light-emitting diode (LED) arranged in series.
The device structure, which was formed on a GaAs substrate with a sacrificial interlayer is a cross-sectional scanning electron microscopy (SEM) image. The lithographically specified and epitaxially released microscale devices (size ~300×300 μm2) achieve efficient NIR-to-visible upconversion with a linear response and rapid dynamics.
(a) Circuit diagram and (b) Scanning electron microscopic (SEM) image of the optoelectronic upconversion design, including an InGaP red LED and a GaAs double junction photodiode with serial connection. (c) Schematic diagram of the upconversion device for temperature sensing. Image Credit: He Ding, Guoqing Lv, Xue Cai, Junyu Chen, Ziyi Cheng, Yanxiu Peng, Guo Tang, Zhao Shi, Yang Xie, Xin Fu, Lan Yin, Jian Yang, Yongtian Wang, Xing Sheng.
The red emission of the optoelectronic upconversion device is followed by a decreasing intensity and a redshift of the emission peak from 625 nm to 637 nm with rising temperature under near-infrared light stimulation in the wavelength range of 770–830 nm.
An intensity-temperature sensitivity of ~1.5% °C-1 and a spectrum-temperature sensitivity of ~0.18 nm °C-1 were calculated based on synergic factors attributed to materials properties and structure design.
The scientists propose many uses for such a robust optoelectronic upconversion optical thermometer:
Through a large-area device array of the optoelectronic upconversion devices, we can perform spatially resolved thermal sensing (Figure 3a). For example, we use air guns to generate hot airflow that blows on the sample, disturbs, and eventually extinguishes the upconversion emission. According to the relationship between emission intensity and temperature, we can obtain the spatial distribution and real-time changes of temperature.
He Ding, Beijing Engineering Research Center of Mixed Reality and Advanced Display, School of Optics and Photonics, Beijing Institute of Technology
Xing Sheng from Tsinghua University stated, “The upconversion device can be released from the grown substrate and further integrated with fiber optics to form light-guided thermal sensors. Complementary with tethered electrical sensors, such an optical-based technique is more suitable for use in environments with strong electromagnetic interferences, and in particular, capable of obtaining signals during magnetic resonance imaging (MRI).”
“Such a fiber-coupled, portable system can be conveniently applied for biomedical applications, for example, monitoring the exhalation behavior closed to the mouth of human and deep tissue with the implantation in the mouse brain, as a proof-of-concept demonstration (Figures 3b and 3c),” added Sheng.
“The MRI-compatible, implantable sensors combined with fiber optics offer both research and clinical significance, with a potential for localized temperature monitoring in the deep body. These materials and device concepts establish a power tool set with vast applications in the environment and healthcare,” Xing Sheng concluded and predicted.
Ding, H., et al. (2022) An Optoelectronic thermometer based on microscale infrared-to-visible conversion devices. Light Science & Application. doi.org/10.1038/s41377-022-00825-5.