Green synthesis of silver nanoparticles using Eulophia herbacea (Lindl.) tuber extract and evaluation of its biological and catalytic activity

Research Article Green synthesis of silver nanoparticles using Eulophia herbacea (Lindl.) tuber extract and evaluation of its biological and catalytic activity Jayashri S. Pawar1 · Ravindra H. Patil1 Received: 11 September 2019 / Accepted: 4 December 2019 / Published online: 9 December 2019 © Springer Nature Switzerland AG 2019 Abstract The present work is a report on phytosynthesis of silver nanoparticles (AgNPs) carried out using an aqueous extract of the tuber of Eulophia herbacea Lindl. (Orchidaceae) and evaluation of its antimicrobial and catalytic potential. The extract efficiently reduced aqueous silver ions and generated stable and bioactive nanoparticles. The maximum reduction of gNO3 was incubated with 2% w/v extract for 5 h. The biosynthesized AgNPs exhibited AgNO3 was achieved when 1 mM A surface plasma resonance at 447 nm. The zeta potential was − 15 mV. Scanning electron microscopy study showed that the average particle size of the AgNPs was 11.70 ± 2.43 nm and that they were non-agglomerated. An Energy Dispersive X-ray study provided support for the presence of elemental silver. X-ray diffraction studies confirmed that the AgNPs were crystalline and had a face-centered cubic geometry. The AgNPs showed excellent antibacterial and antifungal activity against common human pathogens. This activity was comparable with that of standard antibiotics. The catalytic potential of the AgNPs was studied through the reduction of methylene blue and congo red. The results showed that the AgNPs synthesized using the present method are biologically and catalytically active. Keywords Eulophia herbacea · Silver nanoparticles · Antimicrobial activity · Antifungal activity · Synergistic effect · Dye reduction 1 Introduction There is growing interest in greener synthesis of metal nanoparticles. Plant extracts have been used for nanoparticles synthesis as the process involved is simple, eco-friendly and cost-effective. Moreover, this process is reproducible and easily scaled up [1]. In comparison with microbial synthesis, phytosynthesis is rapid. It does not require aseptic conditions, and it yields stable nanoparticles [2, 3]. Indian traditional systems of medicine recommend the use of medicinal and aromatic plants for curing various human illnesses. Plant extracts containing phytoconstituents are biologically and pharmacologically active. Plant metabolites are known to be excellent reducing and capping agents that can be used to synthesize nanoparticles effectively within a short time [4–6]. The tubers of Curcuma longa [4, 7], sweet potato [8], Dioscorea bulbifera, Dioscorea batatas, Dioscorea oppositifolia, etc. are rich with different reducing and capping agents that generate stable metal nanoparticles [9–11]. Silver is known for its antimicrobial and medicinal properties [12, 13]. However, the antimicrobial effect of silver ions and its salts is limited and of short duration. These limitations can be overcome by using silver nanoforms, which are inert, stable and act as antimicrobial agents effectively [9, 14, 15]. Numerous mechanisms are involved in the microbicidal effect of silver nanoparticles (AgNPs) [16]: (a) AgNPs produce structural changes in the cell membrane by deposition on it * Ravindra H. Patil, ; Jayashri S. Pawar, | 1Department of Microbiology and Biotechnology, R. C. Patel Arts, Commerce and Science College, District Dhule, Shirpur, Maharashtra 425 405, India. SN Applied Sciences (2020) 2:52 | https://doi.org/10.1007/s42452-019-1846-9 Vol.:(0123456789) Research Article SN Applied Sciences (2020) 2:52 | https://doi.org/10.1007/s42452-019-1846-9 [17]; (b) AgNPs form free radicals [18]; (c) AgNPs release silver ions [19], which can interact with and inactivate the thiol groups of several active enzymes [20]; (d) Ag is a soft acid, whereas cells are considered as soft bases (soft acids react with soft bases) [21]; (e) AgNPs destroy the DNA of cells as DNA consist of sulfur and phosphorus, which are considered soft bases. AgNPs modulate signal transduction in bacteria [22]. Moreover, in combination with AgNPs, antibiotics have increased bactericidal effect [9, 23]. Organic synthetic dyes are widely used in the textile, paper, paint, plastic and pharma industries are pollutants that are harmful to the environment [24]. Biosynthesized nanoparticles can degrade organic dyes effectively [25–28]. In the current work, we are for the first time, reporting the bioreduction capability of E. herbacea tuber extract for biosynthesis of AgNPs. Eulophia herbacea Lindl. (family Orchidaceae) is also known as kukkadkand or kutrikand [29]. It is terrestrial herb with fleshy subglobose tubers. Qualitative phytochemical tests have shown that carbohydrates, amino acids, mucilage, tannins, steroids and triterpenoids present in the tubers [30]. A decoction of the tuber has been used in the treatment of spermatorrhoea and urinary complaints and to provide relief during menses [31]. Traditionally, the tubers of the plant have been used in the treatment of tumors of the scrofulous glands of the neck and cardiac problems. They have also been used as an aphrodisiac and an appetizer. They possess antioxidant effects [32]. The tubers contain glucomannan (50–60%), which is responsible for their hypolipidemic and hypoglycemic activity [33, 34]. The tubers of Eulophia herbacea are used to make salep, a well-known Turkish drink [35, 36]. However, to the best of our knowledge, no reports are available on AgNPs biosynthesis potential of E. herbacea tubers. Many researcher reported plant-mediated biosynthesis of metal nanoparticles, but lacking attention towards mechanistic approach. In this study, the phytoconstituents of tuber extract responsible for biosynthesis were quantified. Moreover, the present method of AgNPs synthesis is simple, rapid, cost-effective and can be operated at room temperature. The process parameters for AgNP biosynthesis were optimized. The AgNPs were characterized using UV–visible spectrophotometry, FT-IR spectroscopy, XRD, EDX and SEM. The AgNPs were evaluated for their antimicrobial (antibacterial and antifungal) and catalytic activity (dye reduction activity). 2 Materials and methods 2.1 Materials The silver nitrate (AgNO3), sodium borohydride (NaBH4), methylene blue (MB), congo red (CR) and solvents used Vol:.(1234567890) were of analytical grade and were obtained from SD Fine Chemicals, Mumbai, and Loba, Mumbai. All the solutions and reagents were prepared using double-distilled water. The microorganisms used to study the antimicrobial activity, such as Staphylococcus aureus (NCIM-2079), Escherichia coli (NCIM-2065), Bacillus subtilis (NCIM-2063) and Pseudomonas aeuroginosa (NCIM-2200), and the fungi Aspergillus niger (NCIM-1196) and Fusarium moniliforme (NFCCI2949) were obtained from the culture depository of the Department of Microbiology, R. C. Patel Arts, Commerce and Science College, Shirpur, Maharashtra, India. 2.2 Methods 2.2.1 Plant mater (...truncated)