Micro-sized porous nontoxic etched silver cluster, a process for the preparation thereof and the use thereof as an anti-microbial agent

Abstract

The present invention relates to a method for synthesizing micro-sized porous nontoxic silver clusters with enhanced antimicrobial properties. The method involves the mixing of a silver salt, glucose, and a metal carbonate in a polar solvent, followed by a hydrothermal reaction and subsequent washing and drying steps. Plasma or acid Etching further refines the porous structure. The resulting clusters exhibit significant porosity, large surface area, and superior antibacterial activity, outperforming conventional silver nanoparticles. This innovation holds potential applications in diverse fields requiring efficient antimicrobial agents.

Description

Technical fieldMicro-sized porous nontoxic etched silver cluster (MSPNESC) and its preparation as an antimicrobial agent. This field involves the synthesis and characterization of silver clusters with enhanced physico-chemical properties, particularly their antimicrobial activity. The invention explores a process that includes mixing silver salt, glucose, and metal carbonate in a polar solvent, subjecting the mixture to a hydrothermal reaction, and subsequently washing, drying, calcining, and etching to produce the desired porous micro-sized silver clusters.The invention's technical field also encompasses testing and evaluating the properties of these porous silver clusters, primarily their efficacy as antibacterial agents, both when used alone and in combination with standard antibiotics or gels. Additionally, the size of the silver clusters is highlighted as a notable attribute, as they are designed to have a micro-sized dimension, preventing them from penetrating the skin while still maintaining long-lasting antibacterial effects even after washing.Background of the inventionSilver nanoparticles have garnered significant attention in scientific research due to their unique physical and biological properties, making them highly promising in various fields, including biology, medicine, and electronics. Their small size and high surface area-to-volume ratio provide them with distinctive characteristics that differ from bulk silver.The use of abundant and common materials for silver nanoparticle synthesis presents several advantages, such as cost-effectiveness and compatibility with pharmaceutical applications. Silver's exceptional electrical conductivity has led to its extensive use as a conductor in circuits and semiconductor materials, along with its application in various industries and health sectors, including healthcare products, paints, consumer goods, medical devices, cosmetics, and pharmaceuticals.The antimicrobial properties of silver and its ion derivatives have been a subject of intense investigation. They demonstrate a broad spectrum of antimicrobial activity by irreversibly binding to nucleophilic groups present in microorganisms like bacteria, viruses, yeast, fungi, and protozoa. This binding to cellular components disrupts the normal growth and reproduction cycle of these pathogens, ultimately leading to their death.The invention revolves around addressing the need for an innovative antimicrobial agent with enhanced properties, while overcoming potential drawbacks associated with conventional silver nanoparticles. The invention focuses on "micro-sized porous nontoxic etched silver clusters" as the solution. These porous clusters are intended to have excellent antibacterial activity while being non-toxic and safe to use.Description of the inventionProblem to be solvedIn recent years, the focus of scientific research has shifted towards providing silver nanoparticles. This shift is primarily motivated by cost considerations and the need for improved relative activity in various healthcare applications. By creating micro-sized porous nontoxic etched silver clusters, as described in the invention, it is possible to enhance the antimicrobial properties of silver while maintaining its safety and reducing costs.In healthcare, these micro-sized porous silver clusters hold promise as a medicine and as an antimicrobial agent for wound care products such as bandages, stitchers, hydrogels, creams, lotions, catheters, and dressings. The porous structure of the silver clusters likely facilitates better interaction with pathogens and improved delivery of antimicrobial effects, making them ideal candidates for innovative medical applications.Means to solve the problemThe invention aims to propose "micro-sized porous nontoxic etched silver clusters" as an innovative approach to enhance the antimicrobial properties of silver. These clusters are intended to be safe and non-toxic while exhibiting potent antibacterial activity. The invention builds upon the idea of utilizing silver for its antimicrobial effects but seeks to overcome potential skin penetration issues associated with nano-sized particles. The background sets the stage for the invention's objectives, emphasizing the cost-effective and straightforward process of preparing these porous clusters and their potential to complement standard antibiotics and gels.Effects of the InventionThe key advantage of these micro-sized clusters lies in their ability to exert an antibacterial effect for an extended period without penetrating the skin. This addresses concerns related to the use of nano-sized particles, making the proposed micro-sized clusters more practical and safer for long-term antimicrobial applications.The background also emphasizes the simplicity and cost-effectiveness of the process for preparing these micro-sized porous silver clusters. By mixing silver salt, glucose, and metal carbonate in a polar solvent and subsequently subjecting the mixture to a series of controlled reactions, the invention aims to achieve a product with enhanced physico-chemical and functional properties, primarily antimicrobial activities.Brief Description of the Accompanying DrawingsFIG 1 is a FESEM images of micro-sized porous nontoxic silver cluster produced according to the method A). Before calcination, (B-D) after calcination under different scale.FIG 2 is a FESEM images of micro-sized porous nontoxic etched silver cluster after calcination under different scale (A-B) produced according to the method.FIG 3 is a FESEM elemental mapping images of micro-sized porous nontoxic etched silver cluster. The Scanning area of SEM image and their corresponding mapping elements images.FIG. 4 is a XRD spectrum of the micro-sized porous nontoxic etched silver cluster after calcination produced according to the method.FIG 5 is a nitrogen adsorption / desorption isotherms of micro-sized porous nontoxic etched silver cluster prepared according to the method which indicate the mesoporous characters of the cluster. BET Surface Area: 0.216 m2 / g. Average Pore Size is 29 ÅFIG. 6 is a series of photographs showing inhibition zones of various bacteria due to antibacterial activity of of micro-sized porous nontoxic etched silver cluster prepared according to the method compared with commercial Ag nanoparticles.Detailed Description of the inventionIn the current disclosure, the term "comprising" when applied to a component signifies the possibility of additional components being encompassed, unless explicitly specified otherwise.Within the entirety of this disclosure, the expression "parts by weight" denotes a weight proportion of each constituent.In the context of this specification, the phrase "A and / or B" signifies the inclusivity of "A and B," or alternatively, "A or B."Subsequently, a more detailed exposition of the present invention shall ensue.In an embodiment of the present invention, the disclosed method involves a sequential series of steps to generate micro-sized porous silver clusters. These steps encompass the mixing of a silver salt, glucose, and a metal carbonate within a polar solvent, followed by subjecting the mixture to a hydrothermal reaction under elevated temperature conditions. The resultant reaction yields micro-sized clusters of silver particles, which are subsequently subjected to a series of solution-based washes and subsequent drying procedures. The dried products then undergo a calcination process involving heating. This calcinated product is subsequently subjected to an etching process, resulting in the creation of porous micro-sized silver clusters. Notably, these clusters exhibit antibacterial activity, both in isolation and when utilized in conjunction with conventional antibiotics, gels, and similar agents.In an embodiment of the present invention, a method for fabricating porous micro-sized silver clusters featuring a hollow porous structure is disclosed. This method is capable of yielding porous micro-sized silver clusters with a substantially expanded outer surface area, accompanied by remarkable antibacterial and adsorption properties.Hereinafter, a comprehensive elucidation of each procedural facet encompassed by the method in accordance with an embodiment of the present invention shall be proffered.According to a specific embodiment of the present invention, the initial step involves the admixture of a silver salt, glucose, and a metal carbonate within a polar solvent. Subsequently, the resulting amalgamation is introduced into a hydrothermal reactor, where it is subjected to elevated temperature conditions for a defined duration. Notably, the incorporation of glucose, an organic substance encompassing carbon and hydrogen elements, serves a multifaceted purpose. Firstly, it acts as a teratogenic agent, facilitating the generation of silver nanoparticles and the concomitant clustering thereof. Additionally, the presence of metal carbonate serves the pivotal role of fostering the creation of a porous structure, primarily achieved through the evolution of carbon dioxide during the reaction process. Crucially, the silver salt, serving as a precursor, functions as the elemental source of silver content within the process.The micro-sized clusters contained silver particles, washing the products with a series of the solution, and drying products. The dried products were calcinated with heating. The calcinated product etching and produced porous micro-sized silver clusterIn accordance with an embodiment of the present invention, the polar solvent employed in the process encompasses potential constituents such as, but not restricted to, water, ethanol, methanol, tetrahydrofuran, diethyl ether, acetone, dimethyl sulfoxide, and dimethylformamide. It is important to note that the mentioned solvents are not exhaustive and are provided for illustrative purposes.Similarly, with regard to the glucose component, an embodiment of the present invention encompasses its L-form (left-handed form), D-form (right-handed form), or other osaccharides forms, and is not limited solely to the examples listed. To elaborate, examples of monosaccharides encompass fructose and galactose; disaccharides include sucrose, lactose, and maltose; while polysaccharides comprise starch and glycogen.Furthermore, within the context of the present invention, the silver precursor is inclusive of materials such as silver nitrate, silver halide salt, silver acetate, and silver carbonate, among others, and is not confined solely to the enumerated options.The ensuing micro-sized porous silver clusters, distinguished by their etched porous structure, are meticulously prepared through the subsequent method. Embodiments of the present invention encompass a pivotal step involving the preparation of these clusters. This is achieved through the sequential process of mixing silver salt, glucose, and metal carbonate within a polar solvent, which is subsequently subjected to a hydrothermal reaction facilitated by heating. The resultant outcome includes micro-sized clusters containing silver particles. These clusters undergo a thorough series of solution-based washes, succeeded by a drying phase. Subsequently, the dried products are subjected to a calcination process involving heating. This calcinated product undergoes etching, leading to the creation of porous micro-sized silver clusters. Importantly, these clusters exhibit noteworthy antibacterial activity, whether employed independently or in conjunction with established antibiotics, gels, or similar agents.In accordance with an embodiment of the present invention, the saccharide compound is combined in a ratio of 300 to 1000 parts by weight, 500 to 1000 parts by weight, 400 to 900 parts by weight, 500 to 900 parts by weight, relative to 100 parts by weight of the silver salt. It is further combined in proportions of 500 parts by weight to 800 parts by weight, 400 parts by weight to 800 parts by weight, 500 parts by weight to 700 parts by weight, or 600 parts by weight to 700 parts by weight. The metal carbonate is introduced in quantities ranging from 1 to 5 parts by weight, 1 to 4 parts by weight, 1 to 3 parts by weight, 2 to 4 parts by weight, or 2 to 3 parts by weight, relative to 100 parts by weight of the silver salt. When utilizing glucose and metal carbonate within the specified ranges, the resultant outcome typically entails the formation of a well-defined porous cluster structure, leading to a notably superior yield of the resultant prepared porous micro-sized silver clusters.In accordance with another embodiment of the present invention, the polar solvent is employed in volumes ranging from 1 ml to 10 ml, 1 ml to 8 ml, 1 ml to 6 ml, 1 ml to 4 ml, 1 ml to 3 ml, or 2 ml based on 1 g of glucose. It can alternatively be used in amounts ranging from 2 ml to 3 ml, or 2.3 ml to 2.6 ml.In accordance with yet another embodiment of the present invention, when combining glucose, metal carbonate, silver salt, and the polar solvent, an exemplary procedure entails the initial mixing of the glucose compound with a polar solvent, followed by the addition and subsequent mixing of the carbonate compound. Subsequently, the silver salt can be introduced and mixed, although the sequence of addition for each component may be subject to variation.According to an embodiment of the present invention, the mixing procedure may be conducted through agitation at rotational speeds ranging from 300 revolutions per minute (rpm) to 1000 rpm, and the stirring process can extend for a duration of 10 minutes or more. The duration of stirring is not constrained and should suffice to ensure complete dissolution of the glucose, metal carbonate, and silver salt within the polar solvent.Subsequent to the completion of the mixing phase, the resultant mixture can be introduced into a hydrothermal reactor to initiate the ensuing reaction. During this reaction, the glucose compound, acting as a teratogenic agent, contributes to the generation of silver clusters from the silver salts and metal carbonate present within the reactor. Notably, thermal reaction engenders the release of carbon dioxide bubbles, which in turn contributes to the formation of a porous structure within the clusters.According to another embodiment of the present invention, the reactive phase is conducted within temperature ranges spanning from 150°C to 250°C, 170°C to 250°C, 150°C to 230°C, 170°C to 230°C, 190°C to 230°C, or 170°C to 210°C, over time intervals of 100 minutes to 200 minutes, 100 minutes to 170 minutes, 110 minutes to 170 minutes, 100 minutes to 150 minutes, 110 minutes to 150 minutes, 120 minutes to 150 minutes, or 120 minutes to 140 minutes. Specifically, temperatures within the range of 190°C to 210°C are viable. Conducting the reaction within the aforementioned temperature and time parameters fosters the effective formation of a porous cluster structure, thereby leading to a highly favorable yield of the resulting micro-sized porous silver clusters.Upon completion of the reaction, the resulting composition is subjected to one or more washing cycles utilizing deionized water and / or ethanol, thus effectively eliminating residual unreacted components and by-products, as outlined above.Following the washing phase, the resultant product is subjected to drying at temperatures spanning from 60°C to 80°C for a duration of 10 to 18 hours, yielding micro-sized porous silver clusters.Subsequent to the acquisition of the micro-sized porous silver clusters as described above, a calcination process is employed to further refine the material and engender the formation of micro-sized porous silver clusters characterized by a porous structure. The calcination step serves to eliminate unreacted glucose and reduce the carbon content within the porous silver clusters, thereby enhancing the porosity of the resultant structure.According to another embodiment of the present invention, the calcination is conducted within temperature ranges of 400°C to 600°C, 400°C to 570°C, 430°C to 600°C, 400°C to 540°C, 430°C to 570°C, 460°C to 600°C, 400°C to 510°C, 430°C to 540°C, 460°C to 570°C, 490°C to 600°C, 430°C to 510°C, 460°C to 540°C, 490°C to 570°C, 460°C to 510°C, 490°C to 540°C, or at a temperature of 490°C to 510°C, for a duration of 2 hours to 4 hours, 2 hours to 3.5 hours, 2.5 hours to 4 hours, 2 hours to 3 hours, 2.5 hours to 3.5 hours, or 3 hours to 4 hours. Conducting the calcination within the prescribed temperature and time parameters ensures a superior yield of micro-sized porous silver clusters exhibiting the intended structure.In alignment with an additional embodiment of the present invention, the micro-sized porous silver clusters are prepared utilizing the aforementioned method and exhibit an average cluster diameter ranging from 300 nm to 3 μm. These silver clusters manifest a porous hollow structure housing silver particles of dimensions 30 nm to 50 nm. Notably, the attainment of an average particle diameter within the specified range corresponds to exceptional antimicrobial properties exhibited by the resulting micro-sized porous silver clusters characterized by the intended structure.The micro-sized porous silver clusters, as outlined in an embodiment of the present invention, exhibit exceptional porosity, resulting in a substantial external surface area. This distinctive structural attribute contributes to their superior adsorption capacity and noteworthy antibacterial efficacy.The etching process applied to the micro-sized porous silver clusters leads to an augmentation in their antimicrobial activity by generating a larger surface area.The micro-sized porous silver clusters, characterized by their porous configuration in accordance with an embodiment of the present invention, display an average pore size ranging from 0.1 Å to 70 Å. When the pore size falls within the specified range, the subsequent plasma and acid etching processes serve to further amplify the surface area, consequently enhancing their activity and affording an exceptional antibacterial effect.Moreover, the micro-sized porous silver clusters, also characterized by their porous structure according to an embodiment of the present invention, exhibit a BET surface area spanning from 0.25 m2 / g to 700 m2 / g. When the BET surface area aligns within the aforementioned range, the heightened porosity and substantial external surface area synergistically contribute to their exceptional antibacterial properties.The examination of the prepared micro-sized porous etched silver clusters is conducted through the utilization of field emission scanning electron microscopy (FESEM). This analysis is performed using a Hitachi S-4800 instrument, with the samples being subject to a preliminary treatment involving 5nm Pt sputtering prior to the observation process.FIGURE 1 depicts FESEM images illustrating the micro-sized porous nontoxic silver clusters produced in accordance with Method A. Panels (B-D) capture the post-calcination states under varying scales.FIGURE 2 presents FESEM images revealing the micro-sized porous nontoxic silver clusters subsequent to etching, also generated in accordance with the aforementioned method. The images are presented under distinct scales (A-B).FIGURE 3 showcases FESEM elemental mapping images portraying the micro-sized porous nontoxic etched silver clusters. The scanning area within the SEM image corresponds to the elemental mapping elements' images, confirming the presence of Silver elements alongside Si (Silicon) attributed to the glass substrate.FIGURE 4 illustrates the XRD pattern derived from X-ray diffraction analysis conducted using an X-ray diffractometer. The analysis encompasses the micro-sized porous nontoxic etched silver clusters prepared through the method. The XRD pattern extends across the range of 10 to 80°. Within this spectrum, discernible peaks corresponding to the (111), (200), (220), and (311) orientations of silver crystals are evident. This attests to the absence of components featuring alternative crystal structures within the micro-sized porous nontoxic etched silver clusters produced through this method.The pore size of the micro-sized porous nontoxic etched silver clusters produced through this method underwent quantification. Specifically, pore size distribution data was acquired utilizing the Micro meristics ASAP2020 software package. The calculation of the pore size was based on NLDFT (non-local density functional theory). Similarly, the BET surface area of the micro-sized porous nontoxic etched silver clusters prepared through this method was ascertained via adsorption and desorption analysis. The outcome of these analyses indicates a notably elevated BET surface area, measuring approximately 0.216 m2 / g.Experimental Example 6: Evaluation of antibacterial activityThe assessment of antimicrobial properties was conducted under the following specified conditions. Bacterial strains, namely Bacteria 1 (S. aureus 6538) and Bacteria 2 (E. coli 25113), were individually cultivated over a duration of 24 hours. Subsequently, both bacterial strains were re-inoculated into 1 part by weight of each 100 parts by weight of LB liquid medium and allowed to culture for a subsequent 4-hour period. A volume of 100 μl of the resultant culture solution was evenly spread onto a culture plate. In addition, sterile disks were impregnated with 100 μg / ml concentrations of a gentamicin solution, a commercial dispersion containing Nano-sized silver powder (100 μg / ml), and a dispersion of micro-sized porous nontoxic etched silver clusters prepared utilizing the present method (100 μg / ml).Each antimicrobial-laden disk was positioned onto the culture plate with the aid of tweezers. The resultant configuration facilitated the measurement of the diameter of the transparent inhibition zone encompassing the antimicrobial disk, signifying the area where bacterial growth was impeded due to antimicrobial activity. The measured values are tabulated and presented in Table 1 for reference.TableFIGURE 6 illustrates a comparative assessment of the antimicrobial efficacy of the micro-sized porous nontoxic etched silver clusters, prepared utilizing the outlined methodology, juxtaposed against conventional silver nanoparticles. The results of the antimicrobial evaluation concerning Bacteria 1 are portrayed in Panel A of FIGURE 6, while the antibacterial assessment outcomes for Bacteria 2 are presented in Panel B of FIGURE 6.Upon reference to FIGURE 6 in conjunction with the data presented in Table 1, it becomes evident that the micro-sized porous nontoxic etched silver clusters, produced as per the aforementioned method, exhibit an inhibition zone of broader extent compared to that observed for gentamicin, a commercially accessible antimicrobial agent. Notably, even in comparison to traditional silver nano-powder, it is ascertainable that the antimicrobial attributes of the micro-sized porous nontoxic etched silver clusters are either comparable or exhibit a superior level of expression. Particularly noteworthy is the exceptional antimicrobial efficacy displayed towards Bacteria 2.

Claims

1. A micro-sized porous nontoxic etched silver cluster, comprising silver particles with enhanced physico-chemical and functional properties, exhibiting antimicrobial activity. The micro-sized porous nontoxic etched silver cluster of claim 1, wherein the cluster can be prepared by a process comprising mixing silver salt, glucose, and metal carbonate in a polar solvent, and subjecting the mixture to a hydrothermal reaction with heating for a predetermined period.

2. The micro-sized porous nontoxic etched silver cluster of claim 2, wherein the silver particles contained in the cluster are of micro-sized dimensions.

3. The micro-sized porous nontoxic etched silver cluster of claim 2, wherein the hydrothermal reaction facilitates the formation of the micro-sized porous silver clusters.

4. The micro-sized porous nontoxic etched silver cluster of claim 2, wherein the product obtained from the hydrothermal reaction is subjected to a series of washes and drying before being calcined with heating.

5. The micro-sized porous nontoxic etched silver cluster of claim 5, wherein the calcined product undergoes an etching process to further enhance the antimicrobial activity of the silver cluster.

6. The micro-sized porous nontoxic etched silver cluster of claim 1, wherein the cluster demonstrates excellent antibacterial activity both independently and when used in combination with standard antibiotics or gels.

7. A process for the preparation of a micro-sized porous nontoxic etched silver cluster, comprising the steps of: a) Mixing silver salt, glucose, and metal carbonate in a polar solvent to form a mixture. b) Subjecting the mixture to a hydrothermal reaction in a hydrothermal reactor with heating for a predetermined period. c) Washing and drying the product obtained from the hydrothermal reaction. d) Calcining the dried product with heating. e) Etching the calcined product to produce a porous micro-sized silver cluster with enhanced antimicrobial activity.

8. The process of claim 8, wherein the hydrothermal reaction promotes the formation of micro-sized silver clusters within the porous structure.

9. The process of claim 8, wherein the etching process further enhances the antibacterial properties of the micro-sized porous nontoxic etched silver cluster.

10. The method according to claim 9, wherein the etching process for producing the micro-sized porous nontoxic etched silver cluster is executed utilizing acids or plasma etching techniques.