In the present study, vitamin B6 cofactor
pyridoxal
5′-phosphate (PLP)-conjugated yellow-emitting polymeric nanoparticles
(NPs) were synthesized, characterized, and applied for the sensing
of metal ions. The branched polyethyleneimine (PEI) was cross-linked
by adding formaldehyde and self-aggregated to form the cyan-blue-emitting
PEIF NPs. The covalent conjugation of PLP over the surface of PEIF
NPs via forming an imine linkage between the −NH2 group present over PEIF and the −CHO group of PLP formed
the yellow-emitting PEIFPLP NPs. The spectroscopic (ultraviolet–visible
(UV–vis), fluorescence, Fourier-transform infrared (FTIR),
and X-ray photoelectron spectroscopy (XPS)) and high-resolution transmission
electron microscopy (HRTEM) analyses were performed to characterize
the PEIFPLP NPs. The PEIFPLP NPs showed good photostability, and the
fluorescence emission at 552 nm (λex = 450 nm) was
stable over a wide pH range from 2 to 12. In the metal ions’
sensing experiments, the fluorescence emission of PEIFPLP NPs was
quenched by Cu(II) and Fe(II) among the other examined metal ions
such as Ca(II), Mg(II), Cd(II), Mn(II), Co(II), Ni(II), Zn(II), Fe(III),
Pt(II), Pb(II), Cr(III), Hg(II), Al(III), and Cu(I). The static quenching
occurred due to the electron transfer from the excited PEIFPLP NPs
to the partially filled d-orbital of Cu(II) and Fe(II). The PEIFPLP
NPs showed good linearity between 2.4 × 10–6 to 1.9 × 10–5 and 7.4 × 10–6 to 2.2 × 10–5 M with a nanomolar detection
limit of 17 and 31 nM for Cu(II) and Fe(II), respectively. Further,
the analytical applicability of the developed PEIFPLP NPs was validated
by quantifying Cu(II) and Fe(II) ions in fruits, vegetables, and environmental
water samples.
