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Xi et al. Soft Sci 2023;3:26 https://dx.doi.org/10.20517/ss.2023.13 Page 11 of 34

Nanomaterials
Nanomaterials are a kind of material with a size of a nanometer, which usually refers to materials with a size
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of fewer than 100 nanometers in at least one dimension . They play an increasingly important role in the
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development of self-powered wearable sensors . They provide a series of characteristics that can be used
to improve the performance and function of these devices . Nanomaterials can be used to improve the
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sensitivity, selectivity, and response time of the sensor, thus improving the sensing ability of the self-
powered wearable sensor. Nanowires, nanoparticles, or nanorods can greatly improve the output capacity to
improve [108,109] . As shown in Figure 3F, Roy et al. proposed to peel palladium thiophosphate by mechanical
shear force . The key parameters of the equipment, such as light response and response and recovery
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time, can be controlled by externally applied voltage and analyte concentration. A frequency-dependent
selective acetone sensor with ultra-fast response and recovery time of less than one second. As shown in
Figure 3G, Singh et al. developed a CeO /CdS TENG. It can realize the high sensitivity and selective Zi-
2
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powered sensing of carbon dioxide . Different nanomaterials were analyzed and characterized, and it was
found that type II heterojunction was formed in CeO and CdS. The sensor had a fast response speed (the
2
minimum response time and recovery time are 1,835 and 835 ms, respectively) and ultra-high sensitivity
(displayed as 30 when the resistance sensor displays 3.96). As shown in Figure 3H, Pan et al. used the
electrospinning technology to produce new polyvinylidene fluoride (PVDF)/Ag nanoparticles/MXene
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composite nanofibers . Due to their material characteristics, they have high piezoelectric properties. This
material shows excellent stability and excellent output performance, enabling it to be used for human
energy collection and power supply for LED.

Metal oxide nanomaterials have a wide range of applications in sensors, mainly due to their unique physical
and chemical properties, which can improve the sensitivity, selectivity, and response speed of sensors. In
IoT sensors, metal oxide nanomaterials can be used to manufacture various types of sensors, such as gas
etc.
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sensors, temperature sensors, humidity sensors, pressure sensors, . Taking gas sensors as an example,
metal oxide nanomaterials can be used to manufacture sensors that can detect harmful gases, such as carbon
dioxide, carbon monoxide, and ammonia. In addition, metal oxide nanomaterials can also be used to
manufacture highly sensitive and selective biosensors for detecting biological molecules such as bacteria,
viruses, and cancer cells.

Stretchable soft materials
In the previous chapters, the role of flexible materials was mentioned. Compared to flexible materials,
stretchable materials have better stretchability and broader applications. These materials play an important
role in self-powered wearable IoT sensors because these materials are able to maintain their electrical
properties when the sensor is stretched or bent, allowing the sensor to continue to function and generate
electricity when it is moved and deformed. The sensors can adapt to the user’s body shape and activity level
and continue to function normally under conditions such as deformation, twisting, and stretching.
Moreover, stretchable materials adapt to the contours of the body and allow a full range of motion. This
makes them ideal for use in wearable sensors that need to be worn for extended periods of time. One key
advantage of stretchable materials is their durability and reliability. They can withstand repeated stretching
and deformation without breaking or losing their properties. This makes them ideal for use in wearable
sensors that need to withstand the wear and tear of everyday use. Additionally, stretchable materials can be
designed with a range of sensing properties, such as pressure sensing, strain sensing, and temperature
sensing. This versatility allows for the creation of sensors capable of detecting various physiological signals
and environmental factors, making them ideal for health monitoring and environmental sensing
applications. While Guo et al. demonstrated a stretchable sensor , the way it achieves stretchability is not
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through stretchable materials but rather through stretchable structures. They designed a snake-shaped