# Advances in Wearable Smart Chemical Sensors for Health Monitoring
## 2 Wearable Chemical Sensors Based on Different Working Principles
### Wearable Chemical Sensors Based on Triboelectric Nanogenerators
\begin{table}
\begin{tabular}{c c c} \hline
**Type of Sensor** & **Advantages** & **Disadvantages** \\ \hline \multirow{2}{*}{PENGs} & Rapid response rate Durable & Durability concerns Lack of \\  & construction Compact design & environmental resilience \\ \hline \multirow{2}{*}{Solar Cells} & Renewable energy source & Weather sensitivity Inadequate \\  & Modular design & energy storage solutions \\ \hline \multirow{2}{*}{Thermal Energy} & Eco-friendly technology Abundant & Efficiency constraints The impact \\  & energy harvesting & oftemperature variability \\ \hline \multirow{2}{*}{Energy Storage Devices} & \multirow{2}{*}{Integrated energy storage Flexibility} & Low energy density issues Frequent \\  & & \\ \end{tabular}
\end{table} 
Table 1: _Cont._Figure 2: Wearable chemical sensors based on triboelectric nanogenerators. (**a**) Schematic of the fabrication process and crosslinking structure of cellulose-derived PDES-based ion-conductive elastomers. (**b**) Toughness of the elastomer. (**c**) Digital photograph of the elastomer undergoing stretching at \(-20\)\({}^{\circ}\)C. (**d**) Digital photographs of elastomers immersed in different solvents. (**e**) Strain transducer for monitoring wrist movement. (**f**) Strain sensor for monitoring finger movement. (**g**) Schematic of a self-powered ethanol system driven by NP-TENGs. (**h**) Relationship between output voltage and current and load resistance of NP\(-\)TENGs. (**i**) Relationship between output power density and load resistance of NP\(-\)TENGs. (**j**) Motion monitoring application of flexible NP\(-\)TENG in the human elbow. (**k**) Motion monitoring application of flexible NP-TENG in the human foot. (**l**) Fabrication of S\(-\)TENG devices impregnated with CNTs followed by chemical polymerization and assembly of wearable modified textiles into wearable TENG devices. (**m**) I-V curves of textile-modified samples with polypyrrole (W\(-\)PPy), CNTs (W\(-\)CNT) and CNT\(-\)polypyrrole (W\(-\)CNT+PPy). (**n**) Inhibition of _S. aureus_ by pure and modified textiles (cotton/W\(-\)CNT/W\(-\)CNT+PPy/W\(-\)PPy) in Petri dishes in the absence of an external field. The spread of autonomous ethanol detectors is essential in sectors like farming and chemical manufacturing. [PERSON] et al. [63] introduced a TENG (NP\(-\)TENG) that utilized \(\beta\)-Ni(OH)\({}_{2}\)/MXene gas-responsive composites and \(\beta\)-Ni(OH)\({}_{2}\)@PVDF. The preparation process and working schematic are shown in Figure 2g. NP-TENG employs \(\beta-\)Ni(OH)\({}_{2}\) as a superior additive to boost the efficiency of TENGs. As the external resistor value increases, the peak-to-peak value of the open-circuit voltage rises from 0 to 427.95 V, as shown in Figure 2h, i, while the short-circuit current drops from 11 uA to 0 uA. The power density reaches its peak (482.9 mW/m)\({}^{2}\)) at a load resistance of 132 M\(\Omega\). Doping with MXene enhances the charge transfer in the gas-sensitive response of \(\beta-\)Ni(OH)\({}_{2}\), allowing for the wide-ranging and highly sensitive detection of ethanol gas under room temperature and high humidity conditions. Moreover, linking the NP-TENG to the elbow joint of the body can transmit the usual voltage signals produced by the elbow motion, while attaching the NP-TENG to the bottom of a shoe can detect two distinct body motion conditions, jogging and running, instantly, as shown in Figure 2j, k. Expanding the scope of TENG usage for autonomous gas sensors is the focus of this project. [PERSON] et al. [40] introduced friction nanogenerators that were created using altered cotton along with conductive and antimicrobial substances in a separate project, aiming to power a self-sufficient device for electric antimicrobial treatment. Figure 2l shows the process of fabricating W\(-\)TENG. After impregnation with carbon nanotubes, wearable modified textiles were chemically polymerized and assembled in wearable TENG devices.