Bactericide gold decorated mulberry fibers for therapeutic and non-therapeutic tenacities

In this study an approach was made to efficaciously synthesize gold decorated mulberry fibers by a facetious dip coating procedure. Assortments of inorganic compounds are being employed to impart antimicrobial properties to fabrics and textiles. Earlier workers have used gold as coloring agent for cotton and yarn etc. Herein, for the first time an attempt was made to liftoff a progressive textile conjured of gold and mulberry fibers which will be exploited for fabrication of antimicrobial stuffs for diverse medical and non-medical uses. The morphology, physicochemical and antibacterial characteristics of gold decorated mulberry fibers were scanned via X-ray diffraction (XRD), Scanning electron microscope (SEM), Electron probe microanalysis (EPMA), Fourier transform infrared (FTIR) and antibacterial testing. The average size of gold particles was between 1.9 and 3 μm. The even distribution of Au on mulberry fibers was corroborated by SEM, and the results of XRD and FTIR analysis confirmed integration of nanogold in mulberry. The XRD data of Au blended fibers revealed no change in peak location, implying that gold coating has no effect on mulberry fiber structure. Gold decorated mulberry has a little higher intensity and a slight change in peak position toward higher wavenumber, which could be related to functionalization or interaction of gold particles with mulberry fibers. These gold incapacitated mulberry fibers shown out antibacterial activity against illustrative bacterium E. coli. Thus our study provides optimistic indications to pick up mulberry fibers decked with nanogold as prime material for fabrication of forthcoming antimicrobial materials for therapeutic and non-therapeutic tenacities.


Introduction
Apart from the number of versatile applications, the nanotechnology has a pervasive application in textile fields, specifically in technical textiles, finishing, and dyeing procedures. Till date various textiles scrutinized include natural fibers (cotton, silk, and wool), synthetic fibers such as polyester, nylon and semi-synthetic i.e. viscose as well as several common blends of natural and synthetic fibers. Some specific research investigations established that treating fabrics abridged the materials resistive characteristics. Additionally, studies also depicted that treated natural silk fabrics can also be utilized to sense ethanol vapor. Thus, making treated silk fabrics a potential chemical sensor [1]. The exploitation of nanoparticles or nanocomposites is reasonably safer choice, introducing novel extents for antibacterial research. In this direction, noble metals such as gold, silver, palladium, platinum and copper have extensively been explored for amalgamation of stable colloids which are beneficial in diverse fields such as optoelectronics, catalysis, photothermal as well as a great source of remedy [2] and biological labelling [3].

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Among numerous metal nanoparticles, gold nanoparticles (Au-NPs) have been considered an imperative field of investigation owing to their unique and intense plasmon resonance in visible range and their applications in biomedical fields.
Furthermore, many researchers synthesized Au-NPs having numerous colors and have been utilized for the purpose of dyeing cotton fabrics and dyed materials defined color fastening property when uncovered to many stress situations [4]. In a research study, the innovative use of Au-NPs with different particle sizes and colors as a stable colorfast colorants on wool and cotton fibers for utilization in high quality fabrics and textiles for high quality fashions [5] has been exposed. Similarly, another investigation signifies a preliminary path for coloring and bio-functionalization of numerous fabrics with green technologies, consequently, ought to uncluttered novel paths for revolution in textile and garment segments of industries [6]. In addition to aforementioned applications, various nations such as India, China and Egypt are using Au to cure various ailments such as smallpox, syphilis, skin ulcers, or measles [7] from ancient times.
Mulberry (Morus alba) frequently utilized as silkworm diet, is also being used as palatable foodstuffs. Alternatively, dietary mulberry leaf possess a lot of pharmacological properties for instance, antimicrobial, antioxidant anti-inflammatory activity against atherosclerosis and Diabetes mellitus, neuroprotective role and L-3,4-dihydroxyphenylalanine oxidase inhibition and antityrosinase activity [8]. Besides, it possesses unique nutritional properties encompassing proteins, phenolics, flavonoids and anthocyanins that augments its implication as functional tonic [9]. More to point, the polyphenols enclosed in mulberry leaves have also demonstrated capability to impede cancer cell propagation [10]. Nevertheless, various food grade mulberry products such as teas, powders, and tablets etc. are already commercially accessible in many countries particularly in Japan [11]. Conclusively, Genus Morus (mulberry) comprises of more than 150 species and Morus alba L. is most prevailing one [12] and mulberry leaves are rich in aforementioned metabolites. Hanji, a derivative of mulberry, typically instigated from Asian states is natural fiber which is being cast-off as paper traditionally. This Hanji yarns own outstanding chattels viz; competence over quick freshening of moisture and sweat, antimicrobial, deodorization, facile coloring capability, as well as biodegradable and retains its unique shape after tedious laundering [13,14]. Encouraged by these stimulating properties, in present research mulberry fibers were utilized for preparation of Au doped mulberry with objective to prepare competent new antibacterial fabrics. The Au-NPs have recently attracted increasing attention due to unique qualities such as hue and shade variation, UV protection, antimicrobial properties, higher biocompatibility and several researchers are focusing on using them in textile and garment production [15]. The Au decorated fabric material possesses incredible potential to reduce intrinsic odors of unclean fabrics due to presence of bacteria. Motivated by the versatile assets of Au and mulberry, present study involves synthesis and characterization of Au-NPs decorated mulberry fibers and evaluating anti-bacterial effect against E. coli. The E. coli was selected as it is most studied and well understood organism in world owing to its adaptability and simplicity of handling. Besides, this organism causes diarrhea, urinary tract infections, meningitis, peritonitis, septicemia, bacterial pneumonia among other illnesses. Moreover, E. coli occur as enterotoxigenic, enteropathogenic, enteroinvasive, verotoxigenic, enterohemorrhagic and enteroaggregative [16]. So far, there is no report on synthesis of Au-NPs decorated mulberry fibers. This research aimed to fabricate Au decked mulberry fibers. The morphological and physicochemical properties of Au coated mulberry fibers were investigated using XRD, SEM, EPMA, FTIR. A precise plausible antibacterial mechanism was also proposed. SEM revealed even distribution of Au on mulberry fibers, XRD and FTIR confirmed incorporation of nanogold in mulberry. Hence, as-synthesized material may be employed for fabrication of antibacterial textiles, garments, antiodor fabric, craft goods, for UV protection, biomedical materials which can be used in infection prone stuffs as well as for non-medical purposes.

Synthesis of Au-decorated mulberry fibers
The gold precursor HAuCl 4 .3H 2 O (≥ 99.9%) and sodium borohydride were purchased from Sigma-Aldrich, USA. All other regents utilized for this research were of analytical standard. The traditional Hanji yarn was obtained from Jirisan Hanji Co. Ltd., South Korea. The mulberry bark derivative Hanji fibers were censored into pieces computing roughly 1 × 1 cm, were engrossed into aqueous suspension of Au salt (10% w/v) having 20 ml of sodium borohydride (0.02 M) for about 30 min. Then eroded with tap water quite a few times to eliminate unsettled ingredients. Afterwards, Au-decorated Mulberry fibers were shriveled at 80 °C under vacuum overnight. The proportion of Au with respect to Hanji was calculated as such: %immobilized = (w − w 0 )/w 0 × 100. Herein "w" designated quantity of Au decorated mulberry fibers and "w 0" was volume of unadorned Hanji.

Physicochemical categorization
XRD was done to confirm the crystalline structure of samples. XRD investigates of unalloyed mulberry fibers and Au decorated fibers were shown on Rigaku D/MAX-2500 V/ PV with Cu-Kα radiation (40 kV and 200 mA) at a velocity of 4°/min over 2θ range of 10°-70°. The SEM furnished EDX was conceded by Field emission scanning electron microscope (S4800, Hitachi) to detect superficial features and chemical conformation of unalloyed mulberry and Au decorated samples. The fiber diameter was measured directly from SEM images. Whereas the distribution of elements was measured using EPMA. Fourier transform infrared spectroscopy (FTIR, Thermo Scientific ATR) was executed in transmittance mode from 400 to 4000 cm −1 range. The change in chemical structure of fiber mats was investigated by FTIR spectroscopy.

Evaluation of bactericide effect of Au-decorated mulberry fibers
The lyophilized Escherichia coli was obtained from American Type Culture Collection (ATCC 52,922). The inoculant consisted of approximately about 1 × 10 6 CFU/mL. The bactericide activity of Au-decorated mulberry fibers was estimated against ubiquitous E. coli by means of an optical density approach [17]. Roughly, one cm of unalloyed fibers and Au-decorated mulberry fibers were submerged into flask encompassing renewed overnight E. coli culture. The culture nutrients comprise of tryptone soya appropriately supplemented with 0.6% yeast extract. Primarily stationary phase of E. coli was sustained on agar and freshly established bacterial cells were inoculated into nutrient broth. Succeeding inoculation, the mulberry samples (unalloyed and Au-decorated mulberry) were sited in incubator at 37 °C and rpm-150 of rotary shaker. The E. coli culture and wholesome liquid broth were also established separately to be used as control samples. In a usual medium the bacterial propagation was administered by OD with help of UV-visible spectrophotometer (UV-2550, Shimadzu, Japan), till OD touched 0.1 at 600 nm at a gap of 3 h (entire growth phase persisted for 15 h).

Results and discussion
The Fig. 1 indicated XRD spectra of unalloyed fibers and Au incapacitated mulberry fibers. In XRD spectrum of pure mulberry fibers, prominent diffraction peak at 22.7 point out the occurrence of cellulose I category [18] (Fig. 1a). Conversely, in XRD spectrum of Au decorated mulberry fibers, the crests at 38.18°, 44.44° and 64.65° allocated to (111), (200) and (220) planes one-to-one, which approves the materialization of cubic face centered crystal arrangement (JCPDS-89-3697) of Au NPs on the crest of mulberry fibers (Fig. 1b). The XRD pattern of Au blended fibers demonstrated no change in peak position, indicating that Au coating does not affect the structure of mulberry fibers. A slight increase in the peaks intensity is observed for alloyed fibers in comparison to mulberry fibers, suggesting its improved crystalline structures [19].
Additionally, the general morphology and scattering of blended samples was labelled by SEM at low and high resolutions (Fig. 2). Unalloyed mulberry fibers disclosed (Fig. 2a) a smooth peripheral plane inclosing a width of   (Fig. 2b). The typical dimension of Au particles was around 1.9-3 μm. The SEM image of blended sample is in support with the EPMA and EDS analysis; shows the successful deposition of the Au on the surface of mulberry fibers.
The Fig. 3 indicated the elemental mapping spectra of Au decorated mulberry. The tints symbolize the region supplemented with C, O and Au in Au decorated mulberry. Even dissemination and detection of C, O and Au established the animation of Au in mulberry fibers.
In addition, the EDS exploration of Au decorated mulberry fibers was appraised to conclude the pureness and its chemical configuration (Fig. 4). Yet again EDS spectra established that the Au decorated mulberry fibers were encompassed of Au, C and O; not an iota of additional elemental impurity was recognized. The elemental composition of Au in composite was about 8% by weight (Fig. 4). Figure 5 described the FT-IR spectra of mulberry and Au decorated mulberry. The integration band at 3332 and 2913 cm −1 is associated to the O-H and C-H stretching approach. The group at 1640 cm −1 is allocated to C = C stretching vibration. The band at 1030 cm −1 corresponds to C-O-C expansion. These bands are similar to that of cellulose type I [20]. The absorption peaks of Au decorated mulberry is presenting a bit advanced intensity and little shift in peaks position towards larger wavenumber which may be due to functionalization or interaction of Au particles with mulberry fibers [21].
The antibacterial competency of Au decorated mulberry and unalloyed fibers (afore of supplementation with Au) were evaluated quantitatively by means of turbidity intensities. The outcomes were indicated in Fig. 6.
The bacteriostatic impact of unalloyed fibers and Au decorated mulberry fibers indicated that both the samples retain antibacterial property. However, the untreated E. coli logarithmic period protracted from 3 to 9 h (Fig. 6). As revealed in Fig. 6, the unalloyed mulberry revealed reasonable antibacterial activity against E. coli. Conversely, antibacterial effect of Au decorated mulberry fibers was superior than unalloyed mulberry. In particular observable distinction in inhibition of bacterial expansion has been observed from 3 to 15 h of time. Very recently, a plethora of applications of biologically derived Au NPs have been reported [22]. The Au NPs are capable to impede bacterial development by conferring themselves onto bacterial cell surface owing to their surface changes (Scheme 1). Various probable mechanisms of bactericide effect has been proposed such as modification of surface releases reactive oxygen species which result protein distortion, DNA damage as well as mitochondrial dysfunction and lastly end up to cell demise [23]. Similarly an investigation has reported preparation of Au-NPs using Mentha piperita and their outstanding antibacterial effect against E. coli [24]. Another study re-counted synthesis of Au-NPs using Commelina nudiflora and these NPs were very active against Salmonella typhi and Enterococcus faecalis [25]. Additionally, Abdel-Raouf et al. described preparation of Au-NPs consuming Galaxaura elongate and were found exceptionally potent when tested for their antibacterial activity against a number of Gram positive and Gram negative bacteria [26]. Furthermore, the nanogold colloids of diverse dimensions have been utilized to dye natural fibers as well as textiles for improving wash and light fastness [15]. Nevertheless, hitherto there is no report about the antimicrobial activity of Au decorated mulberry fibers. To paramount of our acquaintance it is an original effort to examine bactericide impact of as synthesized Au-NPs which enjoy the usage as an innovative upcoming textile material. However, the exact mechanism of action is uncertain but earlier literature report suggests that Au NPs exhibit their antibacterial activity primarily through two mechanisms: the first is to collapse membrane potential by blocking ATPase activities, lowering ATP level; second is to prevent ribosomal subunit from binding t-RNA. Au NPs improve chemotaxis in early stages of reaction. The mechanism of action of Au NPs actually did not include a reactive oxygen species (ROS) related mechanism, which is cause of cellular death by majority of bactericidal antibiotics and nanomaterials. The low toxicity of Au NPs to mammalian cells may be explained in part by their ROS-independent mechanism of action [27]. In another study, Au NPs have been reported to be capable of traversing diverse structures of S. pneumoniae and reaching cytoplasm, where inclusion bodies of Au NPs have been detected [28]. The various targets of action may aid Au NPs in their fight against multiple drug resistant bacteria. Convincingly, the use of Au NPs in Antibacterial test results of culture (black color), unalloyed mulberry (red color) and Au decorated mulberry fibers (light green). Considerable variance in bacteriostatic effect with unalloyed mulberry and Au decorated mulberry fibers was visualized. Results are articulated in triplicate and the outcomes are specified as mean ± SD (n = 3) Scheme 1 Probable bacteriostatic mechanism of Au decorated mulberry fibers treatment of bacterial infections has emerged as a viable option; nevertheless, the mechanism responsible for bacterial cell lysis remains unknown. Detailed investigations under in vivo conditions are obligatory.

Conclusion
At present plentiful antimicrobial systems are accessible for textile groundwork appropriate to impede growth of microbes. The detrimental amassing of micro-foulers is immense problematic situation. Thus an outstanding antifouling material is need of hour to control biofouling and protect the textile/fabrics from undesirable stink. Moreover, refining wash and light fastness of colorant natural fibers/textiles will be an additional advantage. Regarding these aforementioned properties, the nanogold had recognized to be an excellent material. Credibly, the present study described the fabrication and characterization of Au decorated mulberry fibers quaffed with excellent bactericide properties which can be employed as antimicrobial textiles for therapeutic and non-medical usage. However, for extensive utilization and commercialization of Au-decorated mulberry extensive research is obligatory on biofabrication procedures having discrete sizes and shapes. Moreover, the biocompatibility/cell studies are also important before practical use.
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