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22 Biofunctionalized Nanomaterials for Sensing and Bioremediation of Pollutants

22.3.1

Covalent Functionalization

Covalent biofunctionalization enables the binding of various biomolecules to

nanoparticles through covalent bonds. Covalent attachment of nanoparticles and

biomolecule prevents random reaction between interacting molecules, minimizes

steric interference, provides stability from environmental hindrances, and supports

biorthogonality and reversibility. Generally, the covalent linkage is mediated

by an active group of nanoparticle and biomaterial; the subsidiary functional

groups like carboxyl, amine, and thiol form covalent attachment by ester, amide,

and disulfide linkage, respectively. Plentiful studies were done to determine the

appropriate functional group for both a particular nanoparticle and a biomolecule

to be conjugated. Chemical selectivity and their conjugation-related findings by

Massey and Algar [1], covalent binding using carbodiimide coupling by Kamra et al.

[2], “click” chemistry-based functionalization by Poonthiyil et al. [3], “SpyTag”

and “SpyCatcher” by Reddington and Howarth [4], and supramolecular interac-

tion of nanoparticles and molecules by Steed and Gale [5] are some of the great

demonstrations in understanding vital insight of covalent binding of molecules

with nanoparticles. The most popular approaches of covalent functionalization of

enzymes, DNA, RNA, small ligands, proteins, peptides, oligonucleotides, and differ-

ent nanoparticles are made using glutaraldehyde, organofunctional alkoxysilanes,

N-hydroxysuccinimide, and 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide

chemistry.

22.3.2

Non-Covalent Functionalization

Non-covalent interactions are formed by π–π interaction, van der Waals forces,

electron sharing ligand system, hydrogen bonding, or enfolding of polymers. While

the strength of non-covalent forces is lower than that of covalent bonding, the

broad application’s resulting impact is comparable. The non-covalent binding

provides reversibility and kinetic freedom to binding molecules and some level

of resistance toward the minute disturbance. These interactions are ideal for

developing various sensors as they are very responsive to change in physical or

chemical stimuli. Non-covalent interaction does not disturb the sp² carbon net-

work like covalent functionalization. This non-covalent binding property helps in

gaining novel usability without affecting the inherent property of nanoparticles and

biomolecules. As compared to other binding techniques, non-covalent interaction

can generate biofunctionalized nanoparticles with enhanced catalytic efficiency,

bioavailability, sensing capability, dispersion efficiency, and biocompatibility. Dif-

ferent bio-nano composite has been reported, which have been fabricated through

non-covalent interaction involving polylactic acid and various forms of nanofillers.

Some successful examples of the research based on non-covalent functionalization

of nanoparticles include non-covalently attached protein nanoparticles using

avidin–biotin assembly by Aubin-Tam and Hamad-Schifferli [6], binding of redox

enzyme–protein complex using non-covalent binding by Diaz, Care, and Sunna [7],