Herbal Extract-Induced Silver Nanoparticles For Antibacterial Cotton Fabric

Silver nitrate crystal [Mw. 169.87] was obtained from S.D. Fine Chemicals ltd. Bacterial cultures of E. coli and S. aureus were procured from NCIM Pune. Chitosan was procured from SRL chemicals in Kanpur. Eucalyptus corymbia leaves were collected locally.

Twenty grams of dried leaves of eucalyptus corymbia were soaked in 200 ml of distilled water, followed by boiling for 30 minutes, and finally filtered twice to get the desired extract. 0.16987 g of AgNO₃ salt was dissolved in 1000 ml distilled water to get a 1mM solution. The herbal extract was added to AgNO₃ solution at pH 9 to get a 1:4 ratio (herbal extract: Ag salt solution) followed by continuous stirring for 24 hrs at 120 rpm. Then the solution was centrifuged at 12000 rpm in a REMI PR-24 centrifuge. The sediment was washed two times with distilled water and again centrifuged each time. The nanoparticles obtained were dried in an oven at 60°C, from which we got dried nanopowder, which was further characterized.

The nanoparticles [H-AgNPs] were applied to scoured cotton fabric. Before applying H-AgNPs on the cotton fabric, the fabric was scoured again. These biosynthesized nanoparticles were applied to the cotton fabric by the pad-dry-cure technique, followed by curing at 120°C for 3 minutes.

A Horiba Particle Size analyzer (ZX100) was used to analyse the particle size distribution, where distilled and deionized water was used as a dispersing agent working on the principle of dynamic light scattering. UV-visible spectra of H-AgNPs were recorded using Motras Scientific Instruments-UV plus UV Visible spectroscopy. An FTIR instrument was used to characterize the functional group in the nanoparticle solution in the transmittance mode. The spectra of FTIR were recorded at a wavenumber from 500 to 4000 (cm^-1). Surface characterization of the nanoparticles was carried out by means of a Field Emission Scanning Electron Microscope NOVA NANOSEM 450 at 10 KV electron voltage. An Energy Dispersive X-ray (EDX) detector was integrated with the X-ray to obtain the chemical composition. A crystallographic study was performed by means of Panalytical Xpert XRD.

The antibacterial efficiency of the treated samples was quantitatively estimated as per the AATCC100 -2004 method. And this was calculated using the following equation: 1 R=X−YX×100 \[R=\frac{X-Y}{X}\times 100\] Where, R is the treated fabric’s bacterial reduction % (antimicrobial efficiency), X (CFUs) is the number of bacteria present in the untreated fabric after inoculation for 24 hours, and Y (CFUs) is the number of bacteria present in the treated fabric after inoculation for 24 hours.

Dynamic Light Scattering (DLS) is the most versatile technique used to identify the size of nanoparticles, which is obtained using a Horiba particle size analyzer (nanoParticaSZ-100V2). The nanoparticle analysis suggests that the Z-average value of nanoparticles is 62.7 nm. The particle size distribution follows a Gaussian distribution, as shown in Fig.1. The narrow distribution of AgNPs shows less variability and a uniform size. It also validated the effective reduction potential of Eucalyptus plant leaf extract.

Fig. 1.

UV-visible spectral analysis is an intense absorption analysis because of the surface plasmon excitation of conduction electrons in metals; silver as metal was used here. In Fig. 2, herbal extract containing Ag-NPs was analyzed in the 290-800 nm range. Silver nanoparticles show a maximum absorption band in the 390-430 nm range due to surface plasmon vibrations of conducting electrons on the silver metal [21, 22].

Fig. 2.

FTIR analysis of silver nanoparticles containing herbal extract was conducted to prove its role as a reducing agent and capping agent, as well as the presence of several functional groups. In Fig.3, FTIR results are used to establish the presence of functional groups of Eucalyptus corymbia leaf extract responsible for silver particle reduction to Nanoparticles (Ag⁺ to Ag⁰). The stretching of a bonded hydroxyl group from the phenol and or alcohol group is shown by a band between 3257 and 3382 cm^-1, while the stretching of –C=C- stretch from alkenes is confirmed by the absorbance peak at 1652 cm^-1, which verifies the presence of alkanols in alkaloids, flavones, and tannins in Eucalyptus corymbia leaf extract [23]. The absorbance at 2123 cm^-1 confirms the presence of the alkyne group, which has a phyto nature. The FTIR results of this study suggest that the reduction of silver into nanoparticles is guided by (-C=C) and (-OH) hydroxyl groups of Eucalyptus corymbia leaf extract [24, 25].

Fig. 3.

The aqueous suspension of silver nanoparticles was placed onto clean aluminium foil, allowing the water to evaporate entirely in an oven. Thus, SEM samples of the solution were created.

After that, a specific sample was placed on electrical stubs. Before scanning, all of the samples were gold-coated. FESEM images are shown in Fig 4. The silver nanoparticles are visible, and the particle size distribution is also relatively narrow, which indicates the effective reduction potential of eucalyptus plant extract as an Ag-reducing agent.

Fig. 4.

It is clear from Fig 4, that the uniformity of Ag-NPs is significantly high. A 62 nm particle size of very high activity was achieved. The particle agglomeration is also visible, confirming these nanoparticles’ high reactivity. Maximum particles are found in a dumbbell shape, which again verifies the reduction potential of leaf extract.

An energy-dispersive X-ray spectrophotometer exploits the photon nature of light. Because a single photon’s energy is only enough to create a quantifiable voltage pulse X-ray in the X-ray range, the output of an ultralow noise preamplifier coupled to the low noise is a statistical estimate of the corresponding quantum energy. A comprehensive representation of the X-ray spectrum is built up practically simultaneously by digitally recording and counting many such pulses in a so-called Multi-Channel Analyzer. The digital quantum counting technique makes the energy dispersive spectrometry technique possible. The EDS approach is quite dependable. The EDX technique can examine microstructures in SEM for their elemental composition in greater depth. The elements and their concentrations are calculated reasonably and accurately because this is a non-destructive study. In an SEM, EDS (EDX) determines the material’s elemental composition.

In Fig. 5 the EDX data indicate the presence of silver nanoparticles. The nanoparticles were kept on aluminium foil during characterization by EDX. The weight % of silver nanoparticles (AgL) was found to be 63.54% with an atomic share of 30.36%, as shown in Table 1.

Fig. 5.

The X-ray diffraction data ignored the presence of any impurity among the silver nanoparticles, which proves the reduction potential of natural plant Eucalyptus extract.

The full width at half-maximum (FWHM) data was used in Debye-Scherrer’s equation (2) to estimate the crystalline dimension of the silver nanoparticles. 2 D=0.9λβCOSθ $$D = {{{\bf{0}}.{\bf{9}}\,{\bf{\lambda }}} \over {{\bf{\beta }}\,{\bf{COS\theta }}}}$$ Where D represents the nanoparticle’s mean diameter, λ the wavelength of X-ray radiation, and β denotes the full angular width at half-maximum of the XRD peak at the diffraction angle θ. In Fig. 6, the X-ray diffraction of silver nanoparticles shows prominent peaks at 38.12, 44.26, 64.42, and 77.39 degrees.

Fig. 6.

These peaks indicate the (111), (200), (220), and (311) planes of silver nanoparticles. The XRD pattern of the nanoparticles fits the face-centred cubic (FCC) crystal structure as given in the X-pert X-ray library file JCPDS no. 89-3722. It is mentioned in Table 2 that various planes of silver nanoparticles have different sizes, indicating that the particles do not have a spherical shape. Various planes have different sizes in nanometers. Plane 111 has an average crystalline size (diameter equivalent) of 11.42 nm, plane 200 - 6.82 nm, 220 - 10.65 nm, and plane 311 - 10.53 nm. These planes showed a lattice constant of 4.10 Å and a cell volume of 68.92 Å, as similarly observed by some other researchers [26,27, 28].

The antimicrobial efficiency of all samples was evaluated using the AATCC 100-2004 standard against E. coli, a gram-negative bacteria, and S. aureus, a gram positive bacteria. The following equation was used to calculate the percentage of microbial reduction R: 3 R=X−YX×100 \[R=\frac{X-Y}{X}\times 100\] where X (CFUs) is the number of microbiological colonies on untreated fabrics after 24 hours of inoculation, while Y (CFUs) is the number of microbial colonies on treated fabrics after 24 h of inoculation. The antimicrobial potential of fabrics treated with silver nanoparticle and with silver nanoparticles along with chitosan is given in Table 3.

Antimicrobial reduction against E. coli, a gram-negative bacteria, is shown in Fig. 7. A sample treated with 100 ppm nanoparticles reduced the bacterial growth by 67%, which then was found to be 38.5% after ten launderings. The silver nanoparticle concentration on the treated samples was increased to 300 ppm; and the bacteria reduction reached 84%, which remained active to reduce bacterial growth by up to 45.2% after ten launderings. The antimicrobial recipe was modified by adding 0.5% and 1% chitosan. The bacterial reduction was enhanced from 82.5% to 93.2% with 0.5% chitosan and silver nanoparticles with 100, 200, and 300 ppm. The antimicrobial potential was reduced by 71.2% to 82.4% after ten launderings, respectively, which indicates the remarkable durability of silver nanoparticles on the cotton fabric surface.

Fig. 7.

It can safely be said that chitosan works as a coupling agent between cotton cellulose and silver nanoparticles, as shown in Fig.8.

Fig. 8.

The cotton fabric was first treated with chitosan to provide an active site for the adsorption of silver nanoparticles to be coupled with the cotton fabric surface, which has plenty of hydroxyl groups due to the availability of cellulose in cotton fibre as similarly explained by Xu et al., (2019). The herbal extract-capped silver nanoparticles are coupled with the hydroxyl group present in the cellobiose unit of the cotton fibre, as shown in Fig. 8.

As the chitosan content increased from 0.5% to 1%, the antimicrobial potential of silver nanoparticle treated cotton fabrics was further enhanced by 91.8, 94.6, and 97.8% in the case of 100, 200, and 300 ppm silver nanoparticles.

Figure 9 shows that as the antimicrobial efficacy was measured against S. aureus, gram-positive bacteria, the bacterial reduction percentage was quite close to E. coli bacterial reduction data. As the samples were treated with 100, 200, and 300 ppm silver nanoparticles, bacterial reduction was found to be 64.2, 72.4, and 79.6%, respectively, and after the 10th laundry wash, it remained at 35.0, 38.2, and 42.6 %, respectively. When this treatment was done with 0.5% chitosan, bacterial reduction was found to be 78.0, 81.3, and 87.0%, respectively, and it remained at 70.8, 75.4, and 81.3% after the 10th laundry wash. Again when this treatment (with 100, 200, and 300 ppm AgNPs) was done along with 1% chitosan, the bacterial reduction was found to be 88.1, 91.2, and 94.8%, respectively, and remained at 80.0, 83.7, and 89.5% after the 10th laundry wash.

Fig. 9.