22.3 Binding Techniques for Biofunctionalization of Nanoparticles

347

supramolecular assembly using host–guest interaction by Ma and Zhao [8], binding

of carbohydrate–protein–nanoparticle by Penadés, Davis, and Seeberger [9], binding

of nanoparticles to biomolecules using hydrophobic–hydrophilic interaction by

Chen and Jiang [10], binding using “dock and lock” mechanism by Gong et al.

[11], DNA nanoparticle functionalization by Seeman [12], and self-assembly of

high-affinity protein to nanoparticles by Gurunatha et al. [13].

22.3.3

Encapsulation

Nanoencapsulation is a method of entrapment of nanoparticles, which can be

in any form, i.e. solid, liquid, or gas, inside another shell or matrix made up

of different materials. The particles entrapped in a shell are also referred to as

core/active nanoparticle, which have the conjugated active ingredients. The outer

shell provides selective interaction of nanoparticles with the environment of the

application. It can be fabricated in such a way that the shell remains throughout

the application, or there is a breakdown of the outer shell in response to a stimulus

like pH/temperature change or any enzymatic activity. Several types of material

could be used for shell fabrication. Enclosing matrices are chosen on the basis

of essential properties required for the desired use. Some protein-encapsulating

matrices include albumin, gelatine, lecithin, and legumin. Polysaccharide-based

matrices include starch, alginates, chitosan, dextrin, and gums. There are numer-

ous more examples of matrices used for the encapsulation of nanoparticles like

liposomes, biopolymers, micelles, metal/polymeric/emulsion nanoparticles, den-

drimers, organogels, or various other kinds of functionalized/non-functionalized

nanoparticles. Nanoencapsulation can be done by chemical, physicochemical, or

physico-mechanical technique. The chemical technique follows synthesis through

nucleation and growth, incorporating the building blocks. Encapsulation involving

suspension, emulsion, precipitation, sol–gel, and polymerization are some of the

methods used in chemical encapsulation of nanomaterials. Compared to other

techniques, the chemical technique provides uniform size, high purity, and good

chemical homogeneity. The physicochemical encapsulation technique is based on

both physical and chemical synthesis procedures. Physicochemical encapsulation

includes phase inversion nanoencapsulation, coacervation and phase separation,

inclusion complexes, solid lipid nanoparticles, layer-by-layer deposition, and con-

trolled encapsulation. The physico-mechanical process of encapsulation exploits the

physical properties of nanoparticles and mechanical instrumentation for the entrap-

ment of nanoparticles. Some techniques for physico-mechanical encapsulation

include spray drying, electro-encapsulation, and solvent extraction/evaporation.

Enhanced pollution-degrading capabilities were seen in a comparative study where

alginate polymer-encapsulated nano-zero-valent iron (nZVI) was used. The native

technique was able to remove 43–56% of the pollutant, while 50–75% polycyclic

aromatic hydrocarbons (PAHs) removal was seen using encapsulated nZVI. Encap-

sulation also helps in protecting enzyme-conjugated nanoparticles from protease

attack.