**5. Silver nanoparticles incorporated cotton fabrics**

The current interest is to development of efficient, non-toxic, durable and cost effective antibacterial finishing textiles with increased application in medical, healthcare, hygienic products as well as protective textiles materials. However the ability of cotton fibres to absorb large amount of moisture makes them more prone to microbial attack under certain conditions of humidity and temperature. Cotton may act as a nutrient, becoming suitable medium for bacterial and fungal growth (Rosemary, 2006). Therefore, cotton fibres are treated with numerous chemicals to get better antibacterial cotton textiles. Among the various antibacterial agents, silver nanoparticles have shown strong inhibitory and antibacterial activity, has no negative effect on the human body (Gao, 2008). These particles can be incorporated in several kinds of materials such as clothes. These clothes with silver nanoparticles are sterile and can be used to prevent or to minimize infection with pathogenic bacteria. Nowadays, metal based topical dressings have been widely used as a treatment for infections in burns, open wounds, and chronic ulcers (Panyala, 2008). Incorporation of silver naoparticles was carried out by physical means, before being used; cotton fabrics were washed, sterilized and dried. These were submerged in an Erlenmeyer flask containing silver nanoparticles and agitated at 600 rpm for 24 hrs and dried at 70º C followed by curing at 150 º C. The schematic representation of the formation of silver nanoparticles on cotton fabrics is presented in Scheme 1.

Scheme 1. Incorporation of silver nanoparticles on cotton fabrics (G.Thirumurugan, 2011).

bilayer. The phenomenon causes deenergization of the membrane and consequently cell death (Dibrov, 2002). Shahverdi et al., 2007 studied the combined effect of silver nanoparticles with different antibiotics against S.aureus and E.coli using the disk diffusion method. The antibacterial activities of penicillin G, amoxicillin, erythromycin, clindamycin,

The current interest is to development of efficient, non-toxic, durable and cost effective antibacterial finishing textiles with increased application in medical, healthcare, hygienic products as well as protective textiles materials. However the ability of cotton fibres to absorb large amount of moisture makes them more prone to microbial attack under certain conditions of humidity and temperature. Cotton may act as a nutrient, becoming suitable medium for bacterial and fungal growth (Rosemary, 2006). Therefore, cotton fibres are treated with numerous chemicals to get better antibacterial cotton textiles. Among the various antibacterial agents, silver nanoparticles have shown strong inhibitory and antibacterial activity, has no negative effect on the human body (Gao, 2008). These particles can be incorporated in several kinds of materials such as clothes. These clothes with silver nanoparticles are sterile and can be used to prevent or to minimize infection with pathogenic bacteria. Nowadays, metal based topical dressings have been widely used as a treatment for infections in burns, open wounds, and chronic ulcers (Panyala, 2008). Incorporation of silver naoparticles was carried out by physical means, before being used; cotton fabrics were washed, sterilized and dried. These were submerged in an Erlenmeyer flask containing silver nanoparticles and agitated at 600 rpm for 24 hrs and dried at 70º C followed by curing at 150 º C. The schematic representation of the formation of silver

Scheme 1. Incorporation of silver nanoparticles on cotton fabrics (G.Thirumurugan, 2011).

and vancomycin increased in the presence of Ag-NPs against both test strains.

**5. Silver nanoparticles incorporated cotton fabrics** 

nanoparticles on cotton fabrics is presented in Scheme 1.

The antibacterial properties and the toxicity of metals to micro-organisms is well known, thus, now a days, silver is used in different kinds of formulations like surface coating agents, wound dressing, etc., (Shahverdi, 2007). The silver dressings make use of delivery systems that release silver in different concentrations. But different factors like the distribution of silver in the dressing, its chemical and physical form, affinity of dressing to moisture also inuence the killing of micro organisms (Lansdown, 2002). In this direction, metal nanocomposite bres were prepared containing silver nanoparticles incorporated inside the fabric but from the scanning electron microscopic study it was concluded that the silver nanoparticles incorporated in the sheath part of fabrics possessed signicant antibacterial property compared to the fabrics incorporated with silver nanoparticles in the core part (Chopra, 2007). Similar results were obtained by using silver nanoparticles on polyester nonwovens. It is also reported that silver nanoparticles coated textile fabrics possess antibacterialactivity against S.aureus (Shahverdi, 2007).

#### **6. Silver nanoparticles in antibacterial drug delivery**

Drug delivery system provide useful adjuncts for therapeutics including drugs, nucleic acids and proteins, with variety or roles like improving poor solubility, enhancing invivo stability, optimizing the biodistribution and pharmacokinetics of drugs. In recent years, interest has been stimulated by capability of the metal nanoparticles like AgNPs to bind a wide range of organic molecules, their low toxicity, and their strong and tunable optical absorption. This has resulted in a broad array of studies in which silver nanoparticles have played a role as drug and vaccine carriers into target cells or specic tissues. Furthermore, the unique chemical, physical, and photo-physical properties of silver nanoparticles can be exploited in innovative ways to control the transport and controlled release of pharmaceutical compounds (Skirtach, 2006). Generally, this has been achieved by modifying the surface of the silver nanoparticles so that they can bind to the specic targeting drugs or other biomolecules. But direct conjucation of metal nanoparticle with drugs also possible, it has been shown that conjugates of metal nanoparticles with antibiotics provide promising results in the treatment of intracellular infections (Skirtach, 2006). The conjugation of silver nanoparticles in antibiotic can increase the effectiveness of drug delivery to target some cases. Generally, exact dose is required to kill the pathogens but the amount of antibiotic used in therapy is much higher than the actual dose required. The excess amount of antibiotic can cause adverse effects. Therefore, this conjugation of antibiotic with silver nanopaticles would be helpful to improve antibiotic efficacy. Silver nanoparticles can be directly conjugated with antibiotics or other drug molecules via ionic or covalent bonding, or by physical absorption. For example, Drug has been conjugated to silver nanoparticles [Figure 4]. The cytotoxic effect of free drug is about seven times lower than that of drug conjugated silver nanoparticles. Saha et al., 2007, conjugated directly different type of antibiotic to nonfunctionalized spherical metal nanoparticles, conjugated form showed greater degree of antibacterial activity with stability than free antibiotics. However, the conjugated form showed some aggregation after conjugation, a situation that other workers consider very deleterious. Therefore, it is likely that modication of the surface of the metal nanoparticles to prevent aggregation would improve the efficacy of such drug delivery systems further.

Surface chemistry of nanomaterial plays an important role, to improve the stability of metal nanoparticles and prevent their aggregation during the conjugation process between biomolecules and nanoparticles. Compared with other drug release materials, the unique

Silver Nanoparticles: Real Antibacterial Bullets 417

In addition to the surface chemistry of SNPs, their physical properties could be exploited for delivery applications (Asadishad, 2010). The release of a drug from silver nanoparticles could proceed via internal stimuli (pH or glutathione mediated) or also via external stimuli with the application of light. Silver nanoparticles of various shapes can undergo a strong plasmon resonance with light; therefore light induced plasmonic heating may be exploited to release a chemical payload which had been attached to the silver nanoparticles. This may be provided an interesting approach to deliver pharmaceutical compound directly into the cytoplasm or nucleus of target cells. Due to optical properties silver nanoparticles, light sensitive molecule can be attached onto silver nanoparticles in which SNPs serves as a substrate. In this case, light sensitive and fully reversible conformation-changing molecule had been attached onto the silver naoparticles (Jain, 2007). The conformation has been changed from a closed form to an open form when it is irradiated by UV light and the process can be reversed by the application of visible light or heat. This light mediated metal nanoparticle conjugate system could be very effective in the controlled release to treat selected conditions (Jain, 2007). Cheng, 2008, prepared the microcapsules via layer-by-layer technique to encapsulate fluoresceinlabeled dextran. The capsule-shells were doped with metal nanoparticles, which response against near infra red (NIR) light. FITC-dextran released upon laser (1064) treatment due

to rupture of the shell [Figure 6].

**7. Conclusion** 

Fig. 6. Light- mediated drug release (G.Thirumurugan, 2011).

Increasing awareness towards green chemistry and biological processes has led to a desire to develop an environment-friendly approach for the synthesis of non toxic nanoparticles. Unlike other processes in physical and chemical methods, which involve hazardous chemicals, microbial biosynthesis of nanoparticles is cost-effective and eco friendly approach. Therefore, microbes regarded as potential bio factories for nanoparticles synthesis and serves as a new generation anti bacterial agent with their unique chemical and physical properties. The silver nanoparticle have also found diverse applications in the form of wound dressings, coating medical devices, silver nanoparticles impregnated textile fabrics,

surface plasmonic properties of the silver particles make it possible to observe the drug release process in living cells by surface enhanced Raman scattering (SERS) method. Jing Yang et al., 2009, found that silver nanoparticles can be used to control the release of drug in living cells. The reason may be that silver nanoparticles can hold the surrounding drug molecules to its surface until a monolayer is formed. The way drug absorbing on the silver surfaces plays an important role in their drug delivery effect in living cells. Figure 5, depicts the SERS spectra of drug in (a) solution and (b) living cells and viability of cells treated with different concentrations of drug and silver nanoparticles. (a) Pure drug; (b) Drug and silver nanoparticle complex; (c) pure silver nanoparticles.

Fig. 4. Cytotoxic effect of drug conjugated silver nanoparticles (G.Thirumurugan, 2011).

Fig. 5. Left side shows SERS spectra of drug in (a) solution and (b) living cells and right side shows viability of cells treated with different concentrations of drug and silver nanoparticles. (a) Pure drug; (b) Drug and silver nanoparticle complex; (c) pure silver nanoparticles.

surface plasmonic properties of the silver particles make it possible to observe the drug release process in living cells by surface enhanced Raman scattering (SERS) method. Jing Yang et al., 2009, found that silver nanoparticles can be used to control the release of drug in living cells. The reason may be that silver nanoparticles can hold the surrounding drug molecules to its surface until a monolayer is formed. The way drug absorbing on the silver surfaces plays an important role in their drug delivery effect in living cells. Figure 5, depicts the SERS spectra of drug in (a) solution and (b) living cells and viability of cells treated with different concentrations of drug and silver nanoparticles. (a) Pure drug; (b) Drug and silver

Fig. 4. Cytotoxic effect of drug conjugated silver nanoparticles (G.Thirumurugan, 2011).

Fig. 5. Left side shows SERS spectra of drug in (a) solution and (b) living cells and right side

shows viability of cells treated with different concentrations of drug and silver nanoparticles. (a) Pure drug; (b) Drug and silver nanoparticle complex; (c) pure silver

nanoparticles.

nanoparticle complex; (c) pure silver nanoparticles.

In addition to the surface chemistry of SNPs, their physical properties could be exploited for delivery applications (Asadishad, 2010). The release of a drug from silver nanoparticles could proceed via internal stimuli (pH or glutathione mediated) or also via external stimuli with the application of light. Silver nanoparticles of various shapes can undergo a strong plasmon resonance with light; therefore light induced plasmonic heating may be exploited to release a chemical payload which had been attached to the silver nanoparticles. This may be provided an interesting approach to deliver pharmaceutical compound directly into the cytoplasm or nucleus of target cells. Due to optical properties silver nanoparticles, light sensitive molecule can be attached onto silver nanoparticles in which SNPs serves as a substrate. In this case, light sensitive and fully reversible conformation-changing molecule had been attached onto the silver naoparticles (Jain, 2007). The conformation has been changed from a closed form to an open form when it is irradiated by UV light and the process can be reversed by the application of visible light or heat. This light mediated metal nanoparticle conjugate system could be very effective in the controlled release to treat selected conditions (Jain, 2007). Cheng, 2008, prepared the microcapsules via layer-by-layer technique to encapsulate fluoresceinlabeled dextran. The capsule-shells were doped with metal nanoparticles, which response against near infra red (NIR) light. FITC-dextran released upon laser (1064) treatment due to rupture of the shell [Figure 6].

Fig. 6. Light- mediated drug release (G.Thirumurugan, 2011).
