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Li et al. Soft Sci. 2025, 5, 13 https://dx.doi.org/10.20517/ss.2024.60 Page 5 of 11

the fibrous temperature sensor clearly demonstrated the core-shell structure that comprises a sensing core
and a protective layer [Figure 1B]. Through this impregnation plant, the fibrous temperature sensors could
be fabricated on a large scale with a high degree of automation [Figure 1C]. Moreover, they could be
stitched and embroidered using a commercial sewing machine [Figure 1D].

The sensing mechanism of the fibrous temperature sensor is intricately linked to the temperature-
dependent conductive behavior of the ionic liquid, 1-ethyl-3-methylimidazolium bis
(trifluoromethanesulfonyl) imide salt. This behavior is governed by the Vogel-Tammann-Fulcher (VTF)
law, which describes the temperature dependence of the viscosity and the ionic conductivity of the
liquid [35-37] . As the temperature increases, the ionic mobility within the liquid also increases due to the
decreased viscosity. This enhanced mobility allows ions to move more freely, leading to an increase in
conductivity. The VTF law captures this non-Arrhenius temperature dependence of conductivity, where the
conductivity does not increase linearly with temperature but rather follows a more complex exponential
relationship. This change in conductivity is directly measured by the sensor, providing a means to correlate
resistance changes with temperature fluctuations. In order to study the electrical characteristics of the
developed fibrous temperature sensors, The I-V characteristic curves of the fibrous temperature sensor at
different temperatures were measured. Under a fixed voltage of 10 V, the current exhibited a increase from
0.185 μA at 0 °C to 2.526 μA at 100 °C [Figure 2A]. The resistance of fibrous sensors decreased gradually
with increased temperature from 0 to 100 °C, exhibiting a notable negative temperature coefficient behavior
in Figure 2B. The response time and recovery time of the fibrous temperature sensor were also investigated
and measured by a conventional method. The results are shown in Figure 2C. The response time and
recovery time of the sensor were calculated to be 6 and 8 s, respectively, which showed that the temperature
sensor has a rapid response to temperature variations and is beneficial for real-time skin temperature
monitoring. To achieve an effective measurement of human body temperature, the response curve of the
fibrous temperature sensor from 25 to 40 °C was investigated in detail. The heating and cooling curves
between 25 and 40 °C were measured for the fibrous temperature sensor [Figure 2D]. The results indicated
that the sensor display high resilience during the heating and cooling process. As shown in Figure 2E, the
fibrous temperature sensor exhibited good linearity and high sensitivity (|ΔR|/R /ΔT = 2.61%/°C), indicating
0
that the sensor’s resistance change is proportional to the temperature variation within the tested range of 25
to 40 °C. This linear relationship is crucial for the accurate and reliable monitoring of body temperature, as
it enables the sensor to provide precise temperature readings based on the measured resistance changes.
Compared to the existing fibrous temperature sensors, the temperature sensor we prepared has excellent
temperature sensing performance with the highest sensitivity in temperatures ranging from 25 to 40 °C [
Figure 2F and Supplementary Table 1].

Subsequently, the resistance of the fibrous temperature sensor to external interference, including pressing,
bending, twisting, pH, and humidity, was investigated. The temperature response of the sensor was
examined under a range of compressive forces from 0 to 10 N. This was done to simulate the effects of
mechanical stress that the sensor might encounter in practical applications. The results showed that the
fibrous temperature sensor maintains its original performance across the entire range of applied forces,
demonstrating its robustness under mechanical stress [Figure 3A]. We also assess the sensor’s temperature
detection capabilities under different bending angles varying from 0° to 360° at room temperature. This test
was crucial to evaluate the sensor’s flexibility and durability. The evaluations confirmed that the fibrous
temperature sensor can withstand severe bending without affecting its detection results, highlighting its
flexibility and reliability [Figure 3B]. Moreover, the sensor was twisted to varying degrees, and its resistance
was monitored throughout the process. The results show that the fibrous temperature sensor can withstand
twisting without compromising its temperature-sensing capabilities [Supplementary Figure 1A].