wide linear range of 50 nM to 15 μM. The same research group used an improved

wet spinning technology for the production of reduced graphene oxide/polyurethane

(rGO/PU) fiber followed by coating conductive Ag glue and as-synthesized Ni-Co MOF

nanosheets on the fiber towards developing a stretchable fiber working electrode [47].

The excellent electrocatalytic activity of the developed Ni-Co MOF/Ag/rGO/PU fiber

electrode resulted in enhanced electrochemical performance compared to rGO/PU and

Ag/rGO/PU fiber electrodes towards glucose detection with a low detection limit of

3.28 μM. In addition, Ni-Co MOF/Ag/rGO/PU fiber electrode showed promising elec­

trochemical performance even under mechanical deformation, which demonstrates its

high stretchability. Moreover, they made a wearable nonenzymatic sweat glucose sensor

by suturing the Ni-Co MOF/Ag/rGO/PU fiber electrode as a working electrode along

with Pt wire as a counter electrode and Ag/AgCl fiber as a reference electrode on an

absorbent fabric and fixed on a stretchable PDMS substrate. Overall, the results showed

that the Ni-Co MOF/Ag/rGO/PU fiber-based wearable sensor can be used for the ac­

curate and reliable continuous glucose monitoring from sweat.

The major challenge in employing MOFs for the fabrication of electronic devices is their

poor conductivity. To overcome this, one option is to use transition metal dichalcogenides

(TMDs), which are 2D materials with interesting electronic, chemical, and mechanical

properties for developing a composite material. In this method, MoS2 acts as an active site

for electron exchange and transport owing to its excellent electron mobility. Towards this

aspect, a MOF-MoS2 based flexible, low-cost chemiresistive device as a respiration sensor

has been developed for sleep apnea monitoring [48]. Here, a highly porous HKUST-1

MOF and a conducting MoS2 have been combined for the fabrication of an electronic

sensor on flexible paper support. MOFs can absorb a greater amount of water molecules

exhaled from breath. The HKUST-1 MOF was synthesized by reacting benzene tri­

carboxlyate with copper nitrate. The developed sensor could detect various kinds of

breaths such as normal, deep, fast, slow, and hydrated breath with a fast response time of

just ~0.38 s and outstanding stability for a month without any loss in the performance. In

addition, they proposed a probable mechanism and fabricated a smartphone-based

prototype for real-time applications.

Recently, self-powered wearable piezoelectric sensors have gained much attention in

biomedical monitoring applications, in which the mechanical force is converted into elec­

trical energy. A novel wearable piezoelectric sensor has been developed for arterial pulse

monitoring based on a poly(vinylidene fluoride) (PVDF) nanofibrous membrane containing

microporous zirconium-based MOFs [37]. The PVDF-MOF composite has been attached to

the radial artery at normal body conditions and the piezoelectric output of the sensor was

evaluated. The results revealed an improved output voltage (568 ± 76 mV) with a sensitivity

of 0.118 V/N and this value is highest among flexible energy convertors reported so far.

This work explores a new way to develop flexible and lightweight MOF-based piezoelectric

nanofibrous sensors for self-powered wearable human pulse monitoring systems.

Recently, flexible and sensitive pressure sensors are also of extensive interest in

healthcare monitoring and artificial intelligence. In this context, Roy et al. reported a

combination of porous MOF and PVDF to form a ferroelectret film towards the fabrica­

tion of mechanical energy harvester [38]. As mentioned in the previous secton, the MOF-

PVDF ferroelectret film has been used as an ultra-sensitive pressure sensor with

mechano-sensitivity of 8.52 V/kPa within 1 kPa pressure range. This composite ferroe­

lectret film can be used to detect different physiological signals such as coughing, pro­

nunciation, and gulping behavior which plays a significant role in influenza and chronic

obstructive pulmonary disease-related symptoms. In addition, it can be used for tracking

Advancements in MOFs Based Nanogenerators

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