Nanomaterials constitute novel and interesting matrices for enzyme immobilization. While their high surface to volume ratio is an obvious advantage, their Brownian motion can impact the behavior of enzymes immobilized on these matrices. Carbon nanotubes, superparamagnetic nanoparticles, and mesoporous materials constitute some important classes of matrices. Such immobilized enzyme systems have been used in both aqueous and low water media for biocatalysis and resolution of racemates. This overview examines the behavior of enzymes immobilized on nanomaterials and discusses the results reported with such biocatalyst preparations.

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Ferulic acid (FA) is a widely distributed hydroxycinnamic acid found in various cereals and fruits exhibiting potent antioxidant and anticancer activities. However, due to low solubility and permeability, its availability to biological systems is limited. Non-toxic chitosan-tripolyphosphate pentasodium (CS-TPP) nanoparticles (NPs) are used to load sparingly soluble molecules and drugs, increasing their bioavailability. In the present work, we have encapsulated FA into the CS-TPP NPs to increase its potential as a therapeutic agent. Different concentrations of FA were tested to obtain optimum sized FA-loaded CS-TPP nanoparticles (FA/CS-TPP NPs) by ionic gelation method. Nanoparticles were characterized by scanning electron microscopy, Fourier transformation infrared spectroscopy (FTIR), thermogravimetric analyses and evaluated for their anticancer activity against ME-180 human cervical cancer cell lines. The FTIR spectra confirmed the encapsulation of FA and thermal analysis depicted its degradation profile. A concentration-dependent relationship between FA encapsulation efficiency and FA/ CS-TPP NPs diameter was observed. Smooth and spherical FA-loaded cytocompatible nanoparticles with an average diameter of 125 nm were obtained at 40 lM FA conc. The cytotoxicity of 40 lM FA/CS-TPP NPs against ME-180 cervical cancer cell lines was found to be higher as compared to 40 lM native FA. Apoptotic morphological changes as cytoplasmic remnants and damaged wrinkled cells in ME-180 cells were visualized using scanning electron microscopic and fluorescent microscopic techniques. Data concluded that chitosan enveloped FA nanoparticles could be exploited as an excellent therapeutic drug against cancer cells proliferation.

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The synthesis of glucose-mediated Ag–γ-Fe2O3 nanocomposites in aqueous medium, exhibiting catalytic activity for 4-nitrophenol reduction to 4-aminophenol following the Langmuir–Hinshelwood mechanism at lower [Ag] (μM) (0.3, SPLAg; 6.4, SPHAg), is reported.

The coating of chitosan on γ-Fe 2 O 3 (IO) nanoparticles (NPs) produces the biocompatible nanohybrids (CIO) with enhanced functionalities and optical features associated with a reduction in the average size of IO nanoclusters from 11.3 to 9.3 nm as was estimated by transmission electron microscopy (TEM). The effective capping by chitosan was shown by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), TEM, and Brunauer−Emmett−Teller (BET) analyses. The in situ generation of Ag on the surface of CIO displays characteristic surface plasmonic resonance band resulting in a further decrease in the average size of IO nanoclusters in these binary nanohybrids (CIOMAg) to 8.1 nm involving supramolecular binding through IO and chitosan functionalities. The identification of the phases of iron oxide and Ag NPs and the effective capping of chitosan in binary nanohybrids have been analyzed by XRD, AFM, FESEM, and infrared (IR) analyses. The phase of iron oxide and the presence of Ag NPs in the binary nanohybrids are evidently revealed by X-ray photoelectron spectroscopy (XPS) analysis and also supported by Raman spectroscopy. The interactions among IO, chitosan, and Ag moieties in the binary nanohybrids have been analyzed by IR and XPS. These binary nanohybrids demonstrated superparamagnetic behavior with relatively higher saturation magnetization (72.5−75.5 emu/g) at room temperature compared to those of CIO (69.2 emu/g), which provides an important feature for their catalytic, SERS, and biomedical applications. As-synthesized binary nanohybrids exhibited fairly high catalytic efficiency for the reduction of methyl orange even at low Ag concentration (30 nM) and could be recycled up to ten cycles without any loss of efficiency. It demonstrated the antibacterial activity for model bacteria E. coli with MIC and MBC at 1.1 and 4.2 μg/mL Ag, respectively, and SERS activity for model dye p-ATP with a detection limit at 10 pM, evidently suggesting their environmental and biomedical potential.

The formation of binary nanohybrids consisting of environmentally benign components, γ-Fe 2 O 3 , chitosan (CS), and Ag (Ag-γ-Fe 2 O 3 @CS) (CSIOAg), containing very low concentration of Ag NPs (≤1.2 μM), has been reported. In the as-synthesized nanohybrids, the presence of γ-Fe 2 O 3 (8.5 ± 0.8 nm) and Ag (5.9 ± 0.5 nm) are revealed by optical, XRD, TEM, and XPS analyses, and their presence in cubic phase is determined by XRD and SAED measurements. The catalytic activity of CSIOAg has been analyzed by performing the reduction of certain toxic dyes. Under all kinetic conditions, the reaction is attended by an induction period, which is reduced upon increasing [Ag] and [Dye] in a specific concentration range, as well as temperature, suggesting restructuring of the surface prior to reduction. In case of methyl orange (MO), the reduction results in its cleavage to produce N , N -dimethyl-1,4-phenylenediamine and sodium sulfanilate in a significantly higher (>97%) yield in a bimolecular reaction between MO and BH 4 – . The duration of induction period is regularly decreased and the rate of reduction ( k app ) increases linearly with increasing Ag in the wide concentration range (0.03–2.4 μM). The reduction takes place with a second-order rate constant of 2.7 × 10 4 dm 3 mol –1 s –1 , which is >3.5-fold higher than that in the absence of chitosan (IOAg) under identical experimental conditions. The kinetics of reduction of MO is controlled by the nature and extent of its adsorption on the catalyst surface. The weaker binding between MO and Ag catalyst only allows its effective reduction. The XPS analysis of CSIOAg and IOAg containing the same amount of Ag (1.2 μM) showed its higher amount on the surface of CSIOAg (0.12%) as compared to that of IOAg (0.09%). Detailed kinetic analysis of MO reduction, performed under pseudo-kinetic conditions for both the nanohybrids revealed them to follow Langmuir–Hinshelwood kinetic model and exhibited the recyclability up to 10 cycles with fairly high reaction efficiency and TOF, suggesting it to be a sustainable green nanosystem.

In SAED diffraction patterns, shown in Figure 2 (a″) and (b″), there is an error in the scale bar. The corrected figures are shown below: