Preparation of hybrid particles of Ag nanoparticles and eggshell calcium carbonate and their antimicrobial efficiency against beef-extracted bacteria

Abstract

In this study, hybrid particles of AgNPs-loaded eggshell calcium carbonate (AgNPs/eCaCO₃) were prepared by co-precipitating the eggshell in the presence of freshly prepared AgNPs with a particle size of 10-30 nm. The hybrid particles were comparatively precipitated at 25°C and 35°C using poly (sodium 4-styrenesulfonate) as a polyelectrolyte. The AgNPs/eCaCO₃ particles prepared at 25°C had a spherical morphology with a mean diameter of 3.56 µm, and Brunauer-Emmett-Teller (BET) surface area of 85.08 m² g^-1. On the other hand, the particles prepared at 35°C had a broader size distribution with a mean diameter of 3.19 µm, and a BET surface area of 79.25 m² g^-1. AgNPs-loaded commercial calcium carbonate particles (AgNPs/CaCO₃) comparatively prepared at 35°C were perfectly spherical with a mean diameter of 5.61 µm. At preparing temperature of 25°C, the hybrid particles contain AgNPs of 0.78 wt% for AgNPs/eCaCO₃ and 3.20 wt% for AgNPs/CaCO₃. The AgNPs/eCaCO₃ and AgNPs/CaCO₃ particles exhibited the same efficiency against bacteria extracted from beef with an average inhibition zone diameter of 7-10 mm according to the modified Kirby-Bauer disc diffusion assay depending on their concentration and beef source. Freshly prepared silver colloids showed comparatively poorer antimicrobial efficiency.

Keywords: antimicrobial agent; co-precipitation; eggshell calcium carbonate; food packaging; silver loaded eggshell calcium carbonate; silver nanoparticles.

Figure 1.

The antibacterial mechanism of silver nanoparticles (AgNPs) [8].

Figure 2.

The image of freshly prepared silver colloids (silver colloids at 0 h) (a) and SEM micrographs of AgNPs obtained from the silver colloids at 0 h with a magnification of 50k× (a1) and 50k× (a2). The image of silver colloids at 24 h (b) and SEM micrographs of AgNPs obtained from the silver colloids at 24 h with a magnification of 10k× (b1) and 100k× (b2).

Figure 3.

TEM micrograph (a), high-angle annular dark-field imaging (HAADF) (b), Silver (Ag) EDS image mapping (c), Sodium (Na) EDS image mapping (d), Oxygen (O) EDS image mapping (e), Silicon (Si) EDS image mapping (f) and EDX spectrum (g) of AgNPs obtained from freshly prepared silver colloids, and the hydrodynamic size distribution curves of (h) and AgNPs obtained from (i) freshly prepared silver colloids.

Figure 4.

TGA curves (a) and DTGA curves (b) of ground eggshells and precipitate eCaCO₃ prepared at 35°C.

Figure 5.

SEM micrographs with magnification of 1k× (a) and 5k× (b), and a particle size distribution curve (c) of precipitated eCaCO₃ particles prepared at 35°C, and XRD patterns of the precipitated eCaCO₃ particles and ground eggshells (d).

Figure 6.

TEM micrograph (a), high-angle annular dark-field imaging (HAADF) (b), calcium (Ca) EDS image mapping (c), oxygen (O) EDS image mapping (d), sulfur (S) EDS image mapping (e) and EDX spectrum (f) of precipitated eCaCO₃ particles prepared at 35°C.

Figure 7.

SEM micrographs with magnification of 1k× (a) and 10k× (b), a particle size distribution curve (c) and an XRD pattern (d) of AgNPs/eCaCO₃ particles prepared at 35°C. SEM micrographs with magnification of 1k× (e) and 5k× (f), a particle size distribution curve (g) and an XRD pattern (h) of AgNPs/eCaCO₃ particles prepared at 25°C.

Figure 8.

TEM micrograph (a), high-angle annular dark-field imaging (HAADF) (b), silver (Ag) EDS image mapping (c), calcium (Ca) EDS image mapping (d), oxygen (O) EDS image mapping (e), sulfur (S) EDS image mapping (f) and EDX spectrum (g) of AgNPs/eCaCO₃ particles prepared at 25°C.

Figure 9.

SEM micrographs with magnification of 500× (a) and 5k× (b), a particle size distribution curve (c) and an XRD pattern (d) for AgNPs/CaCO₃ particles prepared at 25°C.

Figure 10.

TEM micrograph (a), high-angle annular dark-field imaging (HAADF) (b), silver (Ag) EDS image mapping (c), calcium (Ca) EDS image mapping (d), oxygen (O) EDS image mapping (e), sulfur (S) EDS image mapping (f) and EDX spectrum (g) of AgNPs/CaCO₃ particles.

Figure 11.

Antimicrobial activity against bacteria extracted from unpacked raw beef from a local fresh market. The discs were impregnated with precipitated eCaCO₃ (a), freshly prepared silver colloids (b), AgNPs/eCaCO₃ (c), and AgNPs/CaCO₃ (d), at concentrations of 500 mg ml⁻¹ (a), 250 mg ml⁻¹ (b), and 125 mg ml⁻¹ (c).

Figure 12.

Antimicrobial activity against bacteria extracted from vacuum-packed beef (‘MAX BEEF’ brand). The discs were impregnated with precipitated eCaCO₃ (a), freshly prepared silver colloids (b), AgNPs/eCaCO₃ (c), and AgNPs/CaCO₃ (d), at concentrations of 500 mg ml⁻¹ (a), 250 mg ml⁻¹ (b) and 125 mg ml⁻¹ (c).