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Tang et al. Soft Sci. 2025, 5, 11 https://dx.doi.org/10.20517/ss.2024.62 Page 15 of 21

sensing applications. This system is designed to operate within the realm of human applications, offering
enhanced precision in fire detection before ignition. The SWCNT/P3HT composite, integrated with a
circuit microcontroller and a message transmission system, forms an intelligent fire source sensing device. It
has been observed that the synergistic effect of light and heat significantly amplifies the output voltage and
response time of the composite under concurrent stimuli, surpassing the performance under heating alone.
This advancement is crucial for the accurate identification of fire sources and the initiation of alarm
systems, which can be adjusted to detect fire hazards effectively. This system employs a sensing module that
communicates with a mobile phone and a relay system, as illustrated in Figure 6D, accomplishing the
accurate identification of fire sources and effective detection of fire hazards . Jiang et al. presented a
[108]
multifunctional ionic hydrogel [flame-retardant ionic hydrogel (HTIG)] with high thermopower for
intelligent fire protection. This novel material, synthesized through free-radical polymerization, exhibits
exceptional properties such as high thermopower (up to 3.35 mV·K ) based on Soret effect, sensitive fire
-1
warning and strain sensing capabilities, and outstanding flame retardancy. The HTIG demonstrates a rapid
response to fire, triggering an alarm in approximately six seconds and generating a voltage exceeding
100 mV upon exposure to flames. This rapid response time is critical for early fire detection and can greatly
assist in evacuation and firefighting efforts. Moreover, the HTIG significantly enhances the fire safety of
materials it is applied to, such as increasing the limiting oxygen index (LOI) of wood from 27% to over 80%,
indicating a substantial improvement in flame resistance. In addition to its outstanding fire protection
capabilities, the HTIG also shows great self-adhesive properties, which allows it to apply to various
[109]
substrates .
Chemical sensors (chem-sensors) are another popular application for environmental sensing. Based on TE
effect, self-powered chem-sensors are a promising candidate for pollutant detection. For example,
Tsao et al. have developed a novel self-powered mercury ion (Hg ) nanosensor, harnessing the TE effect
2+
[110]
and chemical transformation mechanism for the detection of mercury ions . Experiments have revealed
that the output voltages of the TE nanosensor increased linearly as the concentration of Hg ions in the
2+
water samples varied from 0 to 10 nM and 100 nM, indicating the sensor’s capability to distinguish even
2+
small concentrations of Hg ions from the presence of various other species in environmental samples.
CONCLUSION AND OUTLOOK
As the field of TE-based sensors for health and environmental monitoring continues to evolve, it is clear
that significant strides have been made in recent years. However, there are several areas that require further
attention and innovation to fully realize the potential of these technologies. The performance of TE sensors
is intrinsically linked to the properties of the materials used. Hence, future research would continuously
focus on the development of novel materials with enhanced TE ZT. One key challenge that biosensors face
is their biocompatibility, which is influenced by the selection of materials (such as their natural abundance
and non-toxicity) and structural design. Any changes in those parameters would degrade the performance
of TE material. For some wearable sensors, the choice of substrate is particularly important, as they are
directly attached to the user’s skin. Polymers films including Polyethylene Terephthalate (PET),
Polyethylene naphthalate (PEN), Polyimide (PI), and Polydimethylsiloxane (PDMS) are often utilized as the
substrates for biosensors due to their biocompatibility and their biocompatibility and other key properties
[111]
are summarized by Jia et al. . Similarly, the biocompatibility of hydrogel-based sensors also matters. For
current research, it is significant to choose the target material according to their particular application
scenarios.

Meanwhile, the sensitivity, precision, fast response, and high sensing range of biosensors are desired.
However, there are unavoidable trade-offs between those properties, which require further optimization