By-products contribute substantially toward industrial pollution. However, it is possible to turn by-products into valuable items by using appropriate management systems. Industrial pollution is not always from harmful, toxic ingredients, or heavy metals, but it can also result from ecofriendly products. For example, in the silk industry, water pollution occurs when wastewater from the degumming process runs out through drains. Worldwide, it is estimated that 400,000 tons of dry cocoons produce 50,000 tons of sericin each year. However, sericin is mostly discarded in silk processing wastewater and results in a high chemical oxygen demand (COD) and biological oxygen demand (BOD) levels in the degumming wastewater (Zhaorigetu et al., 2003). Therefore, the recovery and reuse of discarded sericinis is beneficial because of its economic, social, and environmental advantages.
Silk sericin is a type of water-soluble globular protein derived from the silkworm Bombyx mori, and it represents a family of proteins whose molecular mass ranges from 10 to 310 kDa (Altman et al., 2003; Freddi et al., 2003; Mondal et al., 2007; Padamwar & Pawar, 2004; Wu et al., 2007). Silk sericin has many unique properties, including biodegradability, nontoxicity, oxidation resistance, antimicrobial activity, ultra violet (UV) resistance, and moisture absorption (Voegeli, Meier & Blust, 1993; Zhaorigetu et al., 2003; Wu et al., 2007;). The physico-chemical properties of molecules are responsible for numerous applications in biomedicine and are influenced by the extraction method and silkworm lineage, which can lead to variations in the molecular weight and amino acid concentration of sericin. Aramwit et al. (2014) showed that silk sericin has been widely used in biomaterial applications due to its biocompatibility, biodegradability, and anti-oxidative and bioactive activities. The presence of highly hydrophobic amino acids and their antioxidant potential makes it possible for sericin to be applied in the food and cosmetic industry. Zhaorigetu et al. (2003) found that sericin exerts inhibitory activity on ultraviolet-radiation-induced acute damage and tumor promotion by reducing oxidative stress in the skin of hairless mice (Zhaorigetu et al., 2003). In our study, sericin is considered as a new kind of valuable protein source (Kato et al., 1998). Silk sericin membranes are good bandage materials and their film has adequate flexibility and tensile strength. Due to its substantial biocompatibility and infection resistant nature, it is a novel wound coagulant material. Additionally, its flexibility and water absorption properties enable its use as a smooth cure for defects in the skin and do not cause any peeling of the skin under regeneration when detached from the skin (Shelton & Johnson, 1925).Watanabe et al. (2003) mentioned that sericin can be used as a raw material for making contact lenses: oxygen permeable membranes comprising fibroin and sericin with 10–16% water are used for making contact lenses and as artificial skin (Sasaki, 2000). Masahiro et al. (2000) reported that the consumption of sericin enhances the bioavailability of Zn, Fe, Mg, and Ca in rats, and suggested that sericin is a valuable natural ingredient for the food industry (Sasaki et al., 2000). Recently, sericin has been used as a reducing and stabilizing agent in the synthesis of metal nanoparticles (Voegeli, R, Meier, J, Blust, 1993). The primary requirement of the synthesis of metal nanoparticles (NPs) is reducing the biological agents and other constituents present in the cells acting as stabilizing and capping agents, so there is no need to add capping and stabilizing agents from outside ( Prakasham et al., 2012; Naveed Ul Haq et al., 2017; Lv et al., 2019). He et al. (2017) developed a novel, simple, one-step biosynthesis method to prepare a sericin-silver nanoparticle composite in situ in solution. Sericin served as the reductant of silver ion, the dispersant and stabilizer of the prepared sericin-silver nanoparticle composite (He et al., 2017). Tahir et al. (2020) evaluated the antibacterial activity of sericin-conjugated silver NPs synthesized using sericin as a reducing and capping agent (Tahir et al., 2020). Aramwit et al. (Aramwit et al., 2014) synthesized silk sericin (SS)-capped silver nanoparticles (AgNPs) under alkaline conditions (pH 11) using SS as a reducing and stabilizing agent instead of toxic chemicals. Most relevant studies stated that SS-capped AgNPs have substantial potential for use as antibacterials. For this reason, our interest has grown to extract SS from the cocoon of a very popular B. mori variety “Rajshahi Silk” and to introduce a green synthesis approach for the extraction of AgNPs in an aqueous neutral condition. The green synthesis of silver nanoparticles is primarily concerned with the selection of solvent medium, reducing agent, and nontoxic substances for stability (Nahar et al., 2021; Raveendran et al., 2003). In this context, it is essential to mention that the synthesis of silver nanoparticles using biological systems makes nanoparticles more biocompatible and environmentally benign.
In the present work, silver nanoparticles were synthesized using a simple, effective, and ecofriendly method using silk sericin. Silk sericin solution was extracted from B. mori silk cocoons and used as a reducing and stabilizing agent. The synthesized silver nanoparticles (AgNPs) were characterized using UV-visible spectroscopy, Fourier-transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Additionally, we explored the antibacterial activity of biosynthesized silver nanoparticles (AgNPs) against Multi drug resistant Escherichia coli and Pseudomonas aeruginosa.