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Page 16 of 38 Wei et al. Soft Sci 2023;3:17 https://dx.doi.org/10.20517/ss.2023.09

In addition to the colorimetric assay method, a novel optochemical sensing mechanism combining thread/
fabric-based microfluidic device and surface-enhanced Raman scattering (SERS) technology was reported,
allowing simultaneous detection of glucose and lactate concentrations in human sweat with high
[166]
accuracy . A textile-based microfluidic device was made by embroidering mercerized cotton thread into a
hydrophobic cotton fabric to build the sensing site, with a viscose thread attached to serve as a microfluidic
channel. To detect certain biomolecules, SERS tags targeting glucose and lactate were deposited onto two
as-prepared microfluidic devices (as shown in Figure 7E). After human sweat was absorbed and chemical
reactions occurred between sweat analytes and SERS tags, the devices were used to measure Raman spectra.
The concentrations of the analytes were then correlated to the characteristics of the Raman spectra. These
relationships can be generalized as exponential functions for further analysis.

The textile chemical sensor can also be realized based on the principle that the resistance of the sensor
changes due to its interaction with chemical substances. An example of multimodal textile chemical sensors
that operate according to the chemiresistive principle is a face mask integrated with three fiber sensors with
different sensing functions [Figure 7F] . Flexible nylon fiber substrates were wrapped with different types
[168]
of CNT-based functional materials to produce sensing fibers whose resistances were sensitive to certain
types of chemical concentrations in the air. Combining these sensing fibers into a face mask, three different
gas signals can be detected and distinguished by monitoring resistance changes, realizing multimodal
sensing to poisonous gases from the environment.

Hybrid signal sensing
As shown in the previous sections, wearable textile sensors can realize multimodal sensing of physical
signals, physiological signals, and chemical signals, providing users with a great variety of valuable
information, including human motions, physiological or health status, and environmental variables. On this
basis, wearable device designers further organically integrate these signals to provide simultaneous
monitoring of physical and physiological signals realized on the fabric platform [55,170-173] or multimodal
acquisition of physical and chemical signals [174,175] . Hybrid signal sensing is enabled by integrating multiple
types of fabric sensors on a single sensing textile or arranging sensors at different locations on the human
body. While outputting information in different dimensions, these mixed-signal textile sensors also have the
advantages of comfort, breathability, and biocompatibility, which are inherent in fabric-based sensors, thus
enabling broad prospects in future wearable applications.

Physical/physiological-type hybrid sensing textile combining physical signals and physiological signals is
ideal for the evaluation of overall body conditions in exercise or resting state. For instance, a fabric pressure
sensor with high sensitivity based on rGO decorated carbonized cellulose fabric (CCF@RGO) was created
[170]
for multimodal detection of bending motion and pulse signals . As shown in Figure 8A, the CCF@RGO
material was obtained by a high-temperature reduction process. Two stacked layers of this material could be
sandwiched between Ecoflex layers to form an eco-friendly pressure sensor with high performance. The
inserted diagrams respectively show that the sensor could be used to detect joint bending angles and
measure pulse signals. Therefore, by arranging the pressure sensors on different positions of the human
body, multimodal sensing of physical signals and physiological signals could be realized, thus providing
comprehensive information of body status during physical movements.

Another noteworthy example is a bimodal fabric sensor that can simultaneously detect physical and
physiological signals on the same sensor unit (as shown in Figure 8B) . A nylon-coated graphene/
[171]
Fe (MoO ) /TPU-based micro/nano-porous fiber was manufactured and woven into a fabric. The core
2
4 3
porous fiber in the fabric was used as a thermal resistance sensor to measure temperature, while the whole