Silver Nanoparticles-Chitosan Nanocomposites: A Comparative Study Regarding Different Chemical Syntheses Procedures and Their Antibacterial Effect

Abstract

Nanocomposites based on silver nanoparticles and chitosan present important advantages for medical applications, showing over time their role in antibacterial evaluation. This work presents the comparative study of two chemical synthesis procedures of nanocomposites, based on trisodium citrate dihydrate and sodium hydroxide, using various chitosan concentrations for a complex investigation. The nanocomposites were characterized by AFM and DLS regarding their dimensions, while FT-IR and UV-VIS spectrometry were used for the optical properties and to reveal the binding of silver nanoparticles with chitosan. Their antibacterial effect was determined using a disk diffusion method on two bacteria strains, E. coli and S. aureus. The results indicate that, when using both methods, the nanocomposites obtained were below 100 nm, yet the antibacterial effect proved to be stronger for the nanocomposites obtained using sodium hydroxide. Furthermore, the antibacterial effect can be related to the nanocomposites' sizes, since the smallest dimension nanocomposites exhibited the best bacterial growth inhibition on both bacteria strains we tested and for both types of silver nanocomposites.

Keywords: AFM; DLS; FT-IR; UV–VIS; antibacterial effect; chemical synthesis; chitosan; nanocomposite; particle sizing; silver nanoparticles.

Figure 1

Chemical reductions in AgNPs-CH composites using two different agents.

Figure 2

The PS calculated of a DLS time series (dots) and the Lorentzian line that best described the PS (continuous red line).

Figure 3

The topography of a region of the sample, illustrating a group of AgNPs-CH.

Figure 4

The plot of four profiles extracted over different AgNP-TSC-CH0.9 from the scanned sample, located in different regions of the sample.

Figure 5

The boxplot of the diameters assessed as the height of the profile peaks extracted over 37 NPs from over each of the six samples. The boxplots correspond, from left to right, to AgNP-TSC-CH0.3, AgNP-TSC-CH0.6, AgNP-TSC-CH0.9, AgNP-NaOH-CH0.3, AgNP-NaOH-CH0.6, AgNP-NaOH-CH0.9.

Figure 6

The absorption spectra of the AgNPs-TSC-CH. The red line stands for the AgNP-TSC-CH0.3 spectrum, the blue line for AgNP-TSC-CH0.6 and the purple line for AgNP-TSC-CH0.9.

Figure 7

The absorption spectra of the AgNPs-NaOH-CH. The red line stands for the AgNP-NaOH-CH0.3 spectrum, the blue line for AgNP-NaOH-CH0.6 and the purple line for AgNP-NaOH-CH0.9.

Figure 8

The FT-IR absorption spectra of the chitosan and AgNPs-CH with 0.9% chitosan concentration. The black line stands for chitosan 0.9%, the red line AgNP-TSC-CH0.9 and the blue line for AgNP-NaOH-CH0.9.

Figure 9

The zoomed FT-IR absorption spectra of the chitosan and AgNPs-CH with 0.9% chitosan concentration covering the wavelength interval 850–1700 cm⁻¹. The black line stands for chitosan 0.9%, the red line AgNP-TSC-CH0.9 and the blue line for AgNP-NaOH-CH0.9.

Figure 10

The FT-IR absorption spectra of the chitosan and AgNPs-CH with 0.9 chitosan concentration covering the wavelength interval 400–850 cm⁻¹. The black line stands for chitosan 0.9%, the red line AgNP-TSC-CH0.9 and the blue line for AgNP-NaOH-CH0.9.

Figure 11

Antibacterial test for reagents used in reactions (controls): TSC 1%, NaOH 0.1 M, CH 0.3% using E. coli and S. aureus strains.

Figure 12

Antibacterial test using E. coli and S. aureus strain for AgNP-TSC-CH0.3, AgNP-TSC-CH0.6 and AgNP-TSC-CH0.9.

Figure 13

Antibacterial test using E. coli and S. aureus strain for AgNP-NaOH-CH0.3, AgNP-NaOH-CH0.6 and AgNP-NaOH-CH0.9.