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Page 14 of 38 Wei et al. Soft Sci 2023;3:17 https://dx.doi.org/10.20517/ss.2023.09

chemiresistive sensing, as shown below.

Electrochemical sensing is the most studied and widely-applied type of chemical signal sensing textiles. This
is due to its simplicity, reliability, and direct conversion of analyte concentrations to potential or current
signals. There are two main types of these multimodal electrochemical sensors, which are standard
electrochemical sensors and organic electrochemical transistors (OECTs).

Based on the measurement of electrode potential or current, the standard electrochemical sensors collect
concentration information according to the Nernst relationship between analyte concentration and
electrochemical potential or current, convert chemical signals into electrical signals, and then submit them
to the readout circuit for amplification and further processing. If different electrodes capable of measuring
multiple signals are integrated into the same textile, multimodal chemical sensing can be realized. For
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example, a textile-based bimodal sensing textile was fabricated for in-situ analysis of Na and K
concentrations in human sweat simultaneously (as shown in Figure 7A) . The chemical sensing ranges of
[162]
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the device covered the typical Na and K concentrations in human perspiration during the whole course of
a physical workout, providing an effective indicator for hydration status and a potential diagnostic tool for
electrolyte imbalance.
Going a step further, a higher-integrated multimodal electrochemical sensing textile with five
analyte-detecting channels was reported (as shown in Figure 7B) . Coaxial structured sensing fibers and
[163]
their corresponding fiber-based reference electrodes were made by coating different active functional
materials onto CNT fibers, respectively. By weaving together all the functionalized fibers into an ordinary
fabric, a conformable and breathable integrated multimodal electrochemical fabric detecting a variety of
physiological chemicals (namely glucose, Na , K , Ca , and pH) was developed, which can be used to collect
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synthetic information of component concentrations in human sweat.
Apart from standard-type electrochemical sensors, another alternative realization of electrochemical sensing
is an OECT-based sensor. OECT is a kind of dual-functional device that simultaneously collects and
amplifies electrochemical signals, simplifying the subsequent signal processing circuits . When it comes to
[169]
multimodal sensing, a promising textile-based sensor is a bimodal sensing fabric produced by integrating
two OECT devices on a single fabric cloth for selectively monitoring ions and adrenaline molecules in
[167]
human sweat (as shown in Figure 7C) . Each OECT device featured a metallic gate and a conductive
fiber-based channel. When an appropriate gate voltage was applied, the Ag-gate participated in the redox
reaction involving Cl in the electrolyte, whereas the Pt-gate surface underwent the oxidation reaction of
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adrenaline, which ultimately enabled analyte-concentration-dependent OECT channel currents in both
devices. Due to the mechanism difference between the two devices, the Ag-gate OECT and Pt-gate OECT
were sensitive and selective to ions and adrenaline molecules, respectively. This combined OECT sensor
could be applied to evaluate hydration state and psychological status (by evaluating adrenaline level) in a
non-invasive way, which is of great application value in personal healthcare management.

Optochemical sensing converts the concentration signals of chemical substances into corresponding optical
signals, such as chromatic or spectral changes [165,166] . Such sensors often have simple structures and low
manufacturing costs. Multimodal sensors can be easily fabricated by combining multiple optochemical
sensing units on one textile substrate. A noteworthy example is a thread/fabric-based microfluidic multi-
sensing band functioning in a method of a colorimetric assay, which could be used to detect pH, Cl and
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glucose concentrations in sweat , as is shown in Figure 7D. After colorimetric treatment, hydrophilic
[165]
threads, working as sweat-transporting channels as well as sweat storage sites, were embroidered into a