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Page 2 of 21 Tang et al. Soft Sci. 2025, 5, 11 https://dx.doi.org/10.20517/ss.2024.62

INTRODUCTION
The miniaturization and integration of electronic devices have spurred the swift evolution of implantable
[1-3]
and wearable electronics . Those electronics are promising tools for detecting or monitoring various
signals for healthcare and environment awareness because of their potential for sensing applications. The
performance of sensors can be achieved by their intrinsic awesome characteristics such as their sensitivity
and wide detecting range. However, their novelty and comprehensive performance can be accomplished by
the combination of material science, energy efficiency, and integration with cutting-edge technologies. Self-
powered technologies including triboelectric, piezoelectric, photovoltaic, and thermoelectric (TE) sensors
have made significant strides, offering strategies for eliminating the need for external power sources and
[4-6]
frequent battery replacement . Among them, TE materials and conversion systems are increasingly
recognized for their distinct advantages over traditional power conversion methods, particularly in their
silent operation, simplicity of design, and exceptional reliability. These systems have the potential to
efficiently detect the heat fluctuations generated from various sources, such as industrial processes, vehicle
exhaust systems, and even human body heat, and convert them into usable electrical energy without the
need for complex mechanical parts, which can inherently increase their reliability [7-10] . Unlike triboelectric
and piezoelectric sensors, TE sensors do not need mechanical motion and external force to operate and can
function with a steadier and more consistent energy source - namely, a temperature gradient. Photovoltaic
sensors convert light into electricity and are ideal for environments with ample light. However, they
perform poorly in low-light conditions, whereas TE sensors can operate effectively with a steadier energy
source [4-6,11] . Therefore, due to the capabilities of TE materials in thermal-electrical signal conversion, TE
techniques have been explored for advanced application in biosensing [12,13] .

Among the myriad scenarios, physiological signals monitoring for healthcare use stands out as a pivotal
application for biosensors. Particularly, sensor technology has evolved from basic detection mechanisms to
sophisticated, multifunctional devices capable of real-time health monitoring and environmental
sensing [14-18] . With the surging development of sensor hardware and wearable sensors, biosensors could
realize high-precision and highly comfortable monitoring [19-21] . Moreover, the combination of the internet of
things (IoT) with wearable biosensors enables continuous and remote monitoring . By perceiving
[22]
physiological signals, analyzing data with algorithms, and even triggering alarms in extreme conditions,
these biosensors could be used to inform healthcare decisions and improve patient care . Recent progress
[15]
of multi-channel sensors could track various human health parameters, allowing for a more comprehensive
understanding of the users . Additionally, the TE technique also offers a novel solution for continuous
[23]
monitoring, providing energy for the sensors without occasionally replacing the power supply. Hence,
[24]
detecting human signals is a promising issue for the application of biosensors .
In environmental monitoring, TE sensors are being used to detect changes in temperature and humidity,
which are pivotal for assessing ambient conditions [14,16] . These sensors are particularly crucial in fire
monitoring applications where early detection can be a matter of life and property safety [25,26] . Recent
advancements in TE technology have enabled the development of self-powered, rapid-response fire warning
systems that utilize the temperature gradients present during a fire event to generate an electrical signal,
thereby enhancing detection efficiency and reliability.

The flexibility of these sensors is crucial for comfortable, long-term wear, and it is achieved using materials
such as polyimide (PI) substrates and thin-film TE materials such as Bi Te . However, their application in
[27]
2
3
wearable sensors can be limited by mechanical brittleness and suboptimal performance under flexible