Fig. 1 UV-Vis absorption spectra
and SEM (A), X-ray diffraction (B), FTIR spectra (C) and silver ion
release concentration (concentration of AgNPs is 10 mg/L) (D) of AgNPs.
Peroxidase-like activity of AgNPs
The peroxidase-like activity of the AgNPs nanozyme was assessed by
monitoring the oxidation of TMB by H2O2.
As shown in Fig. 2, several solutions containing different components
were subjected to using UV/visible absorption spectroscopy measurements.
The solutions containing TMB (a), TMB+ R12-AgNPs (b) and TMB+ C-AgNPs
(c) showed no peak at 652 nm associated with ox-TMB absorption. In the
case of both groups of TMB + C-AgNPs +
H2O2 (d) and TMB +
H2O2 (e), the TMB oxidation products
appeared slightly blue with weak adsorption bonds at 652 nm, signifying
the limited catalytic potential for C-AgNPs and a slow oxidation of TMB
in the presence of H2O2, respectively.
In contrast, the combinations of R12-AgNPs + TMB +
H2O2 (f) exhibited a strong blue color
with the highest absorbance at 652 nm (Fig. 2),
which indicated the
peroxidase-like catalytic activity of R12-AgNPs (Eq. 3). However, the
catalytic mechanism remains unclear. Sun et al. deactivated the hydroxy
groups, carboxylic groups, or ketonic carbonyl groups on purpose and
assessed the catalytic activities of these derivatives of graphene
quantum dots (GQD). Their findings suggested that the –C=O groups
served as the catalytically active sites, while the O=C–O– groups
acted as substrate-binding sites [42]. It can therefore be inferred
that the peroxidase-like activity of R12-AgNPs may be attributed to the
presence of the additional functional groups on their surface (Fig. 1C).