Palladium Nanoparticles Grafted onto Phytochemical Functionalized Biochar: A Sustainable Nanozyme for Colorimetric Sensing of Glucose and Glutathione

Abstract

The devising and development of numerous enzyme mimics, particularly nanoparticles and nanomaterials (nanozymes), have been sparked by the inherent limitations imposed by natural enzymes. Peroxidase is one of the enzymes that is extensively utilized in commercial, medical, and biological applications because of its outstanding substrate selectivity. Herein, we present palladium nanoparticles grafted on Artocarpus heterophyllus (jackfruit) seed-derived biochar (BC-AHE@Pd) as a novel nanozyme to imitate peroxidase activity en route to the rapid and colorimetric detection of H₂O₂, exploiting o-phenylenediamine as a peroxidase substrate. The biogenically generated BC-AHE@Pd nanocatalyst was synthesized utilizing Artocarpus heterophyllus seed extract as the reducing agent for nanoparticle formation, while the residue became the source for biochar. Various analytical techniques like FT-IR, GC-MS, FE-SEM, EDS, TEM, SAED pattern, p-XRD, and ICP-OES, were used to characterize the BC-AHE@Pd nanocatalyst. The intrinsic peroxidase-like activity of the BC-AHE@Pd nanocatalyst was extended as a prospective nanosensor for the estimation of the biomolecules glucose and glutathione. Moreover, the BC-AHE@Pd nanocatalyst showed recyclability up to three recycles without any significant loss in activity.

Keywords: BC-AHE@Pd; H2O2 sensing; biochar; glucose; glutathione; nanozyme.

Scheme 1

Synthesis of Pd NPs dispersed on functionalized BC derived from Artocarpus heterophyllus seeds (BC-AHE@Pd).

Figure 1

UV–visible spectra of AHE: (a) fresh and (b) after synthesis of BC-AHE@Pd.

Figure 2

FT-IR spectra of: (a) BC and (b) BC-AHE@Pd.

Figure 3

p-XRD pattern of (a) BC and (b) BC-AHE@Pd.

Figure 4

FE-SEM images of: (a) BC and (b,c) BC-AHE@Pd.

Figure 5

EDS spectra of: (a) BC, (b) BC-AHE@Pd NPs, and (c) elemental mapping of BC-AHE@Pd.

Figure 6

HR-TEM images of: (a) BC and (b,c) BC-AHE@Pd [inset c: d-spacing of Pd NPs].

Scheme 2

The peroxidase-like activity of BC-AHE@ Pd in sensing of H₂O₂ using OPD.

Scheme 3

The radical mechanism of peroxidase-like activity of BC-AHE@ Pd.

Figure 7

(a) Change in color of solution at time 0 and 3 min for the peroxidase-like activity of BC-AHE@Pd nanocatalyst, (b) time-dependent absorption spectrum of oxidation of OPD by H₂O₂ using BC-AHE@Pd NPs, and (c) plot of absorbance versus time under various reaction conditions of peroxidase-like activity of BC-AHE@Pd nanocatalyst (BC-AHE@Pd denoted as CAT).

Figure 8

Percent relative activity for the peroxidase-like activity of BC-AHE@Pd with varying (a) pH, (b) catalyst loading, (c) OPD concentration, and (d) H₂O₂ concentration.

Figure 9

Steady-state kinetics and Lineweaver–Burke plot for the peroxidase-like activity of BC-AHE@Pd for: (a,b) H₂O₂ (with 83.33 μM OPD and 0.013–0.12 M H₂O₂) and (c,d) OPD (with 33.33 mM H₂O₂ and 0.033–0.266 mM OPD).

Figure 10

(a) Recyclability of BC-AHE@Pd in the oxidation of OPD with H₂O₂ and (b) FE-SEM image of the three-times recycled BC-AHE@Pd.

Scheme 4

Schematic illustration of the colorimetric detection of glucose using BC-AHE@Pd.

Figure 11

(a) The change in absorbance with different concentrations of glucose and (b) relationship between % relative activity and concentration of glucose (inset: linear relationship plot of glucose).

Scheme 5

Schematic illustration for the colorimetric detection of glutathione using BC-AHE@Pd.

Figure 12

(a) The change in absorbance with different concentrations of glutathione and (b) relationship between % relative activity and concentration of glutathione (inset: linear relationship plot of glutathione).