stability over several sensing cycles and a very minute change in the sensing response

observed after being stored for 3 weeks without loss of sensor properties. The authors

proposed the possibility of developing similar other sensors by changing the type of MOF

material specific to a particular analyte and this sensing modality can be used to develop

smart textiles and safety suits for the personnel working in laboratories and vulnerable

industries.

Recently, flexible wearable pressure sensors have received remarkable research interest

towards different applications such as wearable electronic skins, disease diagnostics,

human-machine interfaces, touchable displays, and artificial intelligence [43]. The sensing

mechanisms in wearable pressure sensors include capacitive, piezoresistive, piezoelectric,

and triboelectric effects. Among these sensing mechanisms, wearable piezoresistive

pressure sensors have attracted researchers owing to their simple device assembly, reli­

able piezoelectric effect, and relatively low energy consumption [44]. Considering the

high specific surface area, mechanical and thermal stability, and permanent porous

structure, MOFs have been considered as promising candidates for flexible piezoresistive

sensors to deliver excellent sensing performance with the enhanced sensing response

time and sensitivity [45].

A wearable, sensitive, and breathable pressure sensor has been made by Wang et al. by

sandwiching the interconnected nanocomposites of carbonized metal-organic framework

(C-MOF) and polyaniline nanofiber (PANIF) on a polyurethane (PU) sponge between

the breathable fabric and the fabric patterned with an interdigitated conductive electrode

(Figure 14.3(a–c)) [44]. The developed sensor has been denoted asa C-MOF/PANIF@PU

pressure sensor and it exhibited a broad sensing range of up to 60 kPa, high sensitivity of

158.26 kPa⁻¹, a fast response/recovery time of 22 ms/20 ms, and outstanding repeatability

over 15,000 cycles. The sensing mechanism is based on tunable changes in the contact re­

sistance between the interdigitated electrode-coated fabric and the C-MOF/PANIF@PU

under external pressure, which causes a change in current. The deformation of C-MOF/

PANIF@PU provides more conductive paths between the C-MOF/PANIF@PU and the

interdigitated electrodes, resulting in increased current. When the pressure is unloaded,

both the interdigitated electrodes and the C-MOF/PANIF@PU sponge return to their ori­

ginal shapes, which leads to a reduction in current and sensor response. The compressive

deformation of the three-dimensional (3D) C-MOF/PANIF@PU could be obtained under

external pressure, resulting in more contact and conductive paths between the C-MOF/

PANIF@PU and the interdigitated electrodes. This led to increased current and improved

sensing performance. This pressure sensor could be employed to monitor both tiny human

activities such as blood pulse and large human motions such as finger bending and finger

pressing. The authors have already developed E-skins, which were successfully assembled

from the pressure sensor arrays for detecting various tactile signals and to map spatial

pressure distribution (Figure 14.3(d–g)). The authors proposed that this pressure sensor can

be connected with a wireless transmitter for wireless sensing. Overall, this approach opens

the possibility of assembling wearable breathable pressure sensors for potential versatile

applications in clinical diagnosis and personal healthcare monitoring with high sensitivity

and reproducibility, wireless, and broad-range performance.

For continuous monitoring of analytes from a human body (e.g., glucose level in sweat),

it is highly recommended that the materials should have high stretchability and out­

standing electrochemical performance. MOFs synthesized by metal nodes and organic

ligands, display excellent mechanical flexibility along with ultrahigh specific surface area,

and highly accessible active sites, which can be considered as excellent materials for

potential application in stretchable wearable sensors. Towards this aspect, a flexible

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