Biogenic Silver Nanoparticles/Mg-Al Layered Double Hydroxides with Peroxidase-like Activity for Mercury Detection and Antibacterial Activity

Abstract

Over the past decade, the attention of researchers has been drawn to materials with enzyme-like properties to substitute natural enzymes. The ability of nanomaterials to mimic enzymes makes them excellent enzyme mimics; nevertheless, there is a wide berth for improving their activity and providing a platform to heighten their potential. Herein, we report a green and facile route for Tectona grandis leaves extract-assisted synthesis of silver nanoparticles (Ag NPs) decorated on Mg-Al layered double hydroxides (Mg-Al-OH@TGLE-AgNPs) as a nanocatalyst. The Mg-Al-OH@TGLE-AgNPs nanocatalyst was well characterized, and the average crystallite size of the Ag NPs was found to be 7.92 nm. The peroxidase-like activity in the oxidation of o-phenylenediamine in the presence of H₂O₂ was found to be an intrinsic property of the Mg-Al-OH@TGLE-AgNPs nanocatalyst. In addition, the use of the Mg-Al-OH@TGLE-AgNPs nanocatalyst was extended towards the quantification of Hg²⁺ ions which showed a wide linearity in the concentration range of 80-400 μM with a limit of detection of 0.2 nM. Additionally, the synergistic medicinal property of Ag NPs and the phytochemicals present in the Tectona grandis leaves extract demonstrated notable antibacterial activity for the Mg-Al-OH@TGLE-AgNPs nanocatalyst against Gram-negative Escherichia coli and Gram-positive Bacillus cereus.

Keywords: Hg2+ detection; Mg-Al layered double hydroxides; Tectona grandis; antibacterial activity; peroxidase-like activity; silver nanoparticles.

Scheme 1

Synthesis of Mg-Al-OH-supported Ag NPs by the effective biogenic reduction in Tectona grandis leaf extract.

Figure 1

UV-Vis spectra of TGLE (a) Fresh and (b) After preparation of Mg-Al-OH@TGLE-AgNPs nanocatalyst.

Figure 2

FT-IR spectra of (a) Mg-Al-OH and (b) Mg-Al-OH@TGLE-AgNPs nanocatalyst.

Figure 3

FE-SEM images of (a) Mg-Al-OH and (b) Mg-Al-OH@TGLE-AgNPs nanocatalyst.

Figure 4

(a) EDS spectrum and (b) Elemental mapping of Mg-Al-OH@TGLE-AgNPs nanocatalyst.

Figure 5

p-XRD pattern of (a) Mg-Al-OH and (b) Mg-Al-OH@TGLE-AgNPs nanocatalyst.

Figure 6

TG/DTA curves of (a) Mg-Al-OH and (b) Mg-Al-OH@TGLE-AgNPs nanocatalyst.

Scheme 2

The peroxidase-like activity of Mg-Al-OH@TGLE-AgNPs nanocatalyst in the sensing of H₂O₂ using OPD as the peroxidase substrate.

Figure 7

(a) Change in color in H₂O₂ sensing using Mg-Al-OH@TGLE-AgNPs nanocatalyst and OPD at time intervals of 0 and 6 min, (b) Absorption spectra with respect to time for the oxidation of OPD by H₂O₂ using Mg-Al-OH@TGLE-AgNPs nanocatalyst (1.24 wt% Ag) and (c) Plot of absorbance versus time at various reaction conditions.

Figure 8

Comparison of the % of relative activity for the peroxidase-like activity of Mg-Al-OH@TGLE-AgNPs nanocatalyst with respect to (a) pH, (b) Nanocatalyst loading, concentration of (c) OPD and (d) H₂O₂.

Figure 9

The steady-state kinetics assay and double-reciprocal plot (average of triplicate studies) for the peroxidase-like activity of the Mg-Al-OH@TGLE-AgNPs nanocatalyst for (a,b) H₂O₂ (with 0.1 mM OPD and 0–0.04 M H₂O₂) and (c,d) OPD (with 0.04 M H₂O₂ and 0–0.1 mM OPD).

Scheme 3

Schematic illustration of the colorimetric assay for mercury detection using Mg-Al-OH@TGLE-AgNPs nanocatalyst.

Figure 10

(a) Absorption spectra of oxOPD with varying Hg²⁺ concentration (Inset: Plot of change in absorbance versus concentration) and (b) % relative activity with varying Hg²⁺ concentration (Inset: linear relationship between absorbance and concentration).

Figure 11

Photographs showing the antibacterial activity of (a,c) Mg-Al-OH and (b,d) Mg-Al-OH@TGLE-AgNPs nanocatalyst against (a,b) E. coli and (c,d) B. cereus.