electrochemical sensors and nanogenerators will be discussed as wearable devices have

seen substantial growth in the past few years. Wearable sensors are those devices, which

can be worn on the body of the user while performing user-based diagnostics. Wearable

sensors monitor levels of physiologically important molecules like glucose, dopamine,

adrenaline, sodium, and potassium levels in sweat, biomarkers for various diseases, and

foreign substances like ethanol and opioids, etc. [3]. To power such wearable sensors, a

compact and flexible power source is needed. Most of the conventional wearable sensors

are powered by batteries that limit their sustainability. Nanogenerators harness the me­

chanical motions of humans to generate electricity, which makes them a sustainable al­

ternative to batteries. Moreover, these nanogenerators can be used for power generation

and self-powered sensing. For instance, triboelectric nanogenerators can scavenge the

mechanical energy of human pulse to generate electricity, which can be used to monitor

human health conditions.

14.2 MOFs as Sensing Materials

The use of MOFs has been reported extensively for electrochemical sensor applications as

both in environmental and physiological sensors [4]. On the environmental front, MOFs

have been used for the detection of pesticides and antibiotics in water bodies. Li et al.

constructed an electrochemical sensor composed of Cu MOF for the simultaneous de­

tection of hydroquinone and catechol in contaminated water. They were able to achieve a

detection limit of 590 nM and 3.30 nM [5]. Fang et al. reported a nanocomposite of Zr

(IV)–based MOF (NH2-UiO-66) and reduced graphene oxide (rGO) for the detection of

ciprofloxacin (Cip) in water [6]. This electrode combined the large surface area of MOF

and the high electrical conductivity of graphene. Anodic stripping voltammetry was used

for the detection of Cip and the limit of detection (LOD) achieved was 6.67 nM. The Cip

was able to form complexes with Cu²⁺ and the anode stripping voltammetry sensed Cip

by the deposition of Cu on the NH2-UiO-66/rGO composite. A Fe3O4@MIL-100(Fe) was

used for the detection of chlorogenic acid [7]. A LOD of 50 nM was achieved using this

material. The existence of unsaturated iron centers and a large number of complex or­

ganic chains led this material to possess a large density of redox-active sites, large pore

volume, and water stability. Recently, Zhao et al. have reported conductive two-

dimensional (2D) MOFs as sensors for the detection of paraquat [8]. This MOF was based

on 2,3,7,18,12,13-hexahydroxyl truxene and copper ions. The MOF was synthesized by a

liquid-liquid interfacial reaction. The limit of detection achieved was 41 nM.

The use of MOFs has been used for the detection of physiologically important mole­

cules also. Gao et al. have reviewed the use of MOFs for sensing neurotransmitters such

as dopamine, acetylcholine, tyrosine, and histamine in detail [9]. Li et al. reported the use

of MOF carbon nanotube composites for the sensitive detection of ascorbic acid [10]. The

MOF used in this study was Zn-based nitroimidazole MOF. The MOF was used as

the redox mediator owing to the presence of oxidizing nitro groups on the frameworks.

The LOD achieved was 1.03 µM. A Cu-hemin MOF was reported, which possessed

peroxidase-like bioactivity and good electrical conductivity [11]. This MOF was used for

the detection of peroxide with LOD of 0.019 µM. The electrical conductivity of the Cu-

hemin MOFs was greatly enhanced when it was combined with CS-rGO. Duan et al.

reported a molecularly imprinted electrochemical sensor for the ultra-trace detection of

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Bioelectronics