Haptoglobin-Conjugated Gold Nanoclusters as a Nanoantibiotic to Combat Bacteremia

Abstract

Gold nanoclusters have revealed great potential as nanoantibiotics due to their superior chemical and physical characteristics. In this study, a peptide with 83 amino acids derived from haptoglobin was utilized as a surface ligand to synthesize gold nanoclusters via a facile hydrothermal approach. Characterization of the structural and optical properties demonstrated the successful synthesis of derived haptoglobin-conjugated gold nanoclusters. The spherical derived haptoglobin-conjugated gold nanoclusters exhibited a (111) plane of cubic gold and an ultra-small size of 3.6 ± 0.1 nm. The optical properties such as ultraviolet-visible absorption spectra, X-ray photoelectron spectroscopy spectra, fluorescence spectra, and Fourier transform infrared spectra also validated the successful conjugation between the derived haptoglobin peptide and the gold nanoclusters surface. The antibacterial activity, reactive oxygen species production, and antibacterial mechanisms of derived haptoglobin-conjugated gold nanoclusters were confirmed by culturing the bacterium Escherichia coli with hemoglobin to simulate bacteremia. The surface ligand of the derived haptoglobin peptide of derived haptoglobin-conjugated gold nanoclusters was able to conjugate with hemoglobin to inhibit the growth of Escherichia coli. The derived haptoglobin-conjugated gold nanoclusters with an ultra-small size also induced reactive oxygen species production, which resulted in the death of Escherichia coli. The superior antibacterial activity of derived haptoglobin-conjugated gold nanoclusters can be attributed to the synergistic effect of the surface ligand of the derived haptoglobin peptide and the ultra-small size. Our work demonstrated derived haptoglobin-conjugated gold nanoclusters as a promising nanoantibiotic for combating bacteremia.

Keywords: antibacterial activity; bacteremia; gold nanoclusters; haptoglobin; hemoglobin; nanoantibiotics; reactive oxygen species.

Figure 1

(a) TEM image of the derived haptoglobin peptide-conjugated gold nanoclusters (d-Hp-AuNCs), (b) HR-TEM image of d-Hp-AuNCs, (c) Histogram of the size distributions of d-Hp-AuNCs and the Gaussian fitting curve, and (d) EDX analysis of d-Hp-AuNCs.

Figure 2

(a) UV-Vis absorption spectrum of the derived haptoglobin peptide-conjugated gold nanoclusters (d-Hp-AuNCs), (b) XPS spectra of d-Hp-AuNCs (black line), simulated spectrum of Au ⁴F_7/2 (red line), and simulated spectrum of Au ⁴F_5/2 (blue line). (c) Fluorescence spectrum of the derived Hp peptide (black line) and d-Hp-AuNCs (red line).

Figure 3

FTIR spectra of the derived haptoglobin (Hp) peptide and derived Hp-conjugated gold nanoclusters (d-Hp-AuNCs).

Figure 4

Growth curves of Escherichia coli incubated with various solutions, including (i) E. coli, (ii) E. coli + hemoglobin (Hb), (iii) E. coli + Hb + kanamycin, (iv) E. coli + Hb + derived haptoglobin (d-Hp), and (v) E. coli + Hb + d-Hp-gold nanoclusters (AuNCs). The results are presented as the mean ± SD of n = 4 independent experiments. Asterisks indicate significant differences (*** p < 0.001). *** p < 0.001 compared to E. coli.

Figure 5

Photographs of the growth of Escherichia coli in five different bacterial solutions, including (i) E. coli, (ii) E. coli + hemoglobin (Hb), (iii) E. coli + Hb + kanamycin, (iv) E. coli + Hb + derived haptoglobin (d-Hp), and (v) E. coli + Hb + d-Hp-gold nanoclusters (AuNCs).

Figure 6

ROS levels measured with various solutions, including (i) Escherichia coli, (ii) E. coli + hemoglobin (Hb), (iii) E. coli + Hb + derived haptoglobin (d-Hp), and (iv) E. coli + Hb + d-Hp-gold nanoclusters (AuNCs). For the control, the ROS level of E. coli was set to 1.0. The results are presented as the mean ± SD of n = 4 independent experiments. Asterisks indicate significant differences (*** p < 0.001). *** p < 0.001 compared to E. coli.