3.2. Binding of Hb and Tbz
Recently, functionalized magnetic nanoparticles have been used in
drug delivery. We have identified interactions of several drugs with
proteins on functionalized Fe3O4 nanoparticles in previous studies [18,
21]. In this study, GPTS modified Fe3O4 magnetic nanoparticles were
synthesized for hemoglobin binding as shown in Scheme 1. Epoxy
groups on the surface of the modified nanoparticle allowed the covalent
binding of the protein to\NH2 at the edge. For this purpose, Hb was
mixed with GPTS modified Fe3O4 magnetic nanoparticles in
20 mM × Tris–HCl (pH 7.4) buffer for 2 h. Then, the binding amount
of the protein to GPTS–SPIONs was determined by using the intrinsic
fluorescence of Hb at 280 nm and 342 nm of excitation and emission
wavelengths (Fig. 4). The intrinsic fluorescence of protein comes from
tryptophan and tyrosine residues in the structure of protein [22,23].
The inset of Fig. 4 shows the change in the intrinsic fluorescence of Hb
as a function of the protein concentration (pH 7.4). The binding amount
of Hb was calculated via its regression equation (y = 2612.8x + 31.921)
with a correlation coefficient of 0.99, where y is the fluorescence intensity
and x is the Hb concentration (mg mL−1
). To test the amount of Hb
immobilized on GPTS–SPIONs, the immobilization of Hb was carried out
with the GPTS–SPION amounts varying between 2.5 and 25 mg. According
to Fig. 5, the amount of immobilized Hb was increased with anincreasing amount of GPTS–SPIONs. The result showed that 3.58 μg of
Hb was immobilized to the 25 mg of GPTS modified SPIONs in Tris–
HCl buffer (20 mM, pH 7.4).
Tbz is a fluorescent molecule which has an emission spectrum at
299 nm and 358 nm of excitation and emission wavelengths (Fig. 6).
The regression equation was also given (y = 478.92x + 15.316, r =
0.99) at a concentration range of 0.1–1 × 10−6 M in the inset of Fig. 6.
This fluorescent property allowed monitoring the binding of Tbz to Hb
immobilized GPTS–SPIONs. The results showed that the binding of Tbz
decreases with an increase in temperatures as shown in Table 1.