bovine serum albumin (BSA) [12]. This sensor was based on AuNPs@NH2-MIL-125 (Ti)-

graphene composite in which the MOF was prepared by a rapid ultrasonic method. The

3D porous framework, which was obtained not only provided a highly conducting

MOF due to the presence of Au NPs but also provided a large surface area due to the

presence of MOFs. The electrode under optimal conditions provided a low detection limit

of 4.147 × 10⁻¹⁹ g/mL. This electrode was used for the detection of BSA in milk samples

also. A porphyrin encapsulated HKUST-1 (Cu) was reported by Ling et al. and this

composite can catalyze o-phenylenediamine to 2,2’-diamonoazobenzene, which was then

conjugated with streptavidin as a recognition element [13]. Upon the addition of target

DNA, the stem of the hairpin DNA was unfolded to form a structure with the strepta­

vidin. This activated DNA was then able to bind to the recognition element to greatly

enhance the activity of peroxidase towards o-phenylenediamine oxidation in the presence

of peroxide. This report presented a versatile “signal on” sensor with a detection limit of

0.48 fM. Recently a dopamine sensor was reported by Kang et al. who used hemin doped

HKUST-1 rGO composite as a redox mediator for the detection of dopamine with a LOD of

3.27 nM [14]. The presence of rGO combined with the HKUST-1 was reported to enhance

the electrocatalytic activity of the material towards dopamine oxidation. Gumilar et al.

reported the use of MOFs based on benzene dicarboxylic acid (BDC) with hierarchical 3D

morphologies composed of 2D nanosheets and nanoplates [15]. Multiple metal ions were

used for constructing the MOF like Cu, Mn, Ni, and Zr. The constructed MOFs were used

for electrochemical glucose sensing with a LOD of 6.68 µM. In keeping with the demands of

recent times, MOFs have also been used for the detection of viruses [16].

Despite the immense potential of this material, which has been proved through a mul­

titude of papers reporting lab-scale detection, very limited efforts have been successful in

achieving the application of these materials for nanogenerators and wearable sensors.

14.3 MOFs for Nanogenerators

The design of wearable sensors necessitates an energy source for the functioning of these

devices and these energy sources comprise batteries, solar cells, biofuel cells, super­

capacitors, and nanogenerators [17]. A composite of fuel cells and supercapacitors known

as super capacitive biofuel cells have also been used for various applications [18].

Although these devices are very attractive options for powering wearable sensors, they

do not form a part of the nanogenerator family, which forms the crux of this book

chapter. Nanogenerators are energy-harvesting devices that generate electricity from

mechanical or thermal energy from our surroundings. Wang et al. demonstrated the

working piezoelectric zinc oxide nanogenerator in 2006 for the first time [19]. Later,

different nanogenerators were developed based on triboelectricity, thermoelectricity,

pyroelectric, etc. While piezoelectric nanogenerators (PENG) and triboelectric nanogen­

erators (TENG) function on converting mechanical energy into electricity, the pyroelectric

nanogenerators convert thermal energy into electricity. A typical example of the scale of

energy availability during human motion was reported by Yang et al. who were able to

light 40 LEDs by using a self-powered backpack that integrated these nanogenerators

[20]. This shows that highly sustainable and eco-friendly power generation devices could

be built if nanogenerators are employed for power generation. These nanogenerators

offer ideal power sources for converting ambient energy to a useful form.

Advancements in MOFs Based Nanogenerators

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