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Emergent Materials

, Volume 2, Issue 1, pp 113–122 | Cite as

Investigation of the herbal synthesis of silver nanoparticles using Cinnamon zeylanicum extract

  • Sadiya Anjum
  • Gideon Jacob
  • Bhuvanesh GuptaEmail author
Original Article

Abstract

In the present investigation, biosynthesis of silver nanoparticles (AgNPs) using Cinnamon zeylanicum bark extract was described. The extraction of Cinnamon zeylanicum bark was carried out in various solvents such as aqueous, ethanol, and dimethyl sulfoxide (DMSO) with different polarity. The aldehyde content and antioxidant activity of each extract were estimated. Subsequently, these extracts were used for the synthesis of AgNPs and the growth of nanoparticles was periodically monitored by UV–visible spectroscopy and observed the drastic change in the appearance of the colloidal solutions. The correlation between total aldehyde content, antioxidant activity, and the size of the nanoparticles was investigated. Different shapes and sizes of the nanoparticles in ethanol (spherical), aqueous (polygonal), and DMSO (spherical) were observed by high-resolution transmission electron microscope (HRTEM). The antimicrobial activity of the nanoparticles was investigated against both gram-positive Staphylococcus aureus and gram-negative Escherichia coli bacteria. These results suggest that aqueous extract is appropriate for the synthesis of nanoparticles and optimized for further investigations for the development of infection-resistant materials.

Keywords

Silver nanoparticles Antimicrobial activity Cinnamon zeylanicum Aldehyde content Antioxidant activity 

1 Introduction

In the past few decades, increasing bacterial resistance towards conventional antibiotic drugs is posing a paramount risk to the healthcare sector. There is enormous interest in the development of safe and effective antimicrobial agents which are capable of killing a wide spectrum of microbes with improved activity compared to conventional drugs [1]. In view of the fact, silver (Ag) is a safe inorganic antibacterial agent with broad-spectrum activity and it minimizes the chances of resistance by bacteria since it targets multiple components in bacterial cells. Among different salts of Ag, silver nanoparticles (AgNPs) have been recognized as the most suitable candidate for defeating pathogens. There are various reports available on the excellent antimicrobial activities of AgNPs [2, 3]. Therefore, AgNPs are used in several biomedical applications as additives and as coating materials for the development of infection-resistant surfaces or materials [4, 5, 6, 7]. As we know that a wide variety of AgNP-based product gains enormous attention but the toxicological and environmental issues should be the point of concern. In a previous report, the antibacterial effect of picosecond laser-generated AgNPs and their toxicity to human cells were investigated. The study concluded that the nanoparticles had broad antibacterial efficiency against microbes but with minimal human cell toxicity [8].

The conventional method of nanoparticle synthesis involves the use of various chemicals (such as hydrazine, sodium borohydride, aldehydes, and citrates), radiation sources, functional polymers, and many more as a reducing agent which not only cause environmental concerns but also involve high-cost and excessive use of energy and resources [9, 10, 11, 12]. Considering all these factors, the research in the last decade has shifted their focus towards exploring various plant extracts as a potential alternative for the synthesis of metal nanoparticles due to its less toxic nature which makes them safer to human [13, 14, 15]. Plant extracts comprise various biochemicals such as terpenoids, alkaloids, phenolics, aldehydes, proteins, and amino acids, which reduce metal ions to nanoparticles and stabilize them. Plant extracts are easily available and can be easily scaled up for industrial synthesis with less contamination. There have been several reports for the growth of metal nanoparticles by biosynthesis using different plant extracts [16, 17, 18, 19, 20, 21, 22, 23, 24]. The major challenge in design biosynthesis of the nanoparticle is to have proper control over size and morphology of the nanoparticles by controlling the reaction conditions.

Therefore, we used Cinnamon zeylanicum bark for the biosynthesis of AgNPs. The bark is widely used as a spice in cooking and also as medicinal used to treat diarrhea and other problems of the digestive system. The bark extracts contain a high concentration of cinnamaldehyde, eugenol, and linalool with high-antioxidant activity [25]. The aim of this present investigation is to explore the responsible factor in Cinnamon zeylanicum bark extract for morphological control of AgNPs and to investigate the various chemicals involved in the bioreduction [26, 27]. Cinnamon zeylanicum barks were extracted in different solvents having different polarities, i.e., aqueous, ethanol, and DMSO, and then the reduction of silver ions was estimated. Recently, influence of different solvents over the synthesis of cinnamon nanoparticles was investigated and observed that the variation of solvent medium altered the morphology of the nanoparticles [28]. The relationship among antioxidant activity, total phenolic content, and aldehyde content for each solvent extract were investigated. The synthesized AgNPs were characterized by using spectral analysis like UV–vis spectroscopy, HRTEM, and energy-dispersive X-ray analysis (EDX). Furthermore, the biosynthesized AgNPs were tested for their antibacterial activity against E. coli and S. aureus strains. The major finding of this work is related to the identification of specific biochemicals present in the extracts involved in the reduction and stabilization of AgNPs and their antimicrobial activity.

2 Experimental

2.1 Materials

Silver nitrate (AgNO3), sodium phosphate, ammonium molybdate, Folin and Ciocalteu’s Phenol (FCP) reagent, ethanol, sodium carbonate (Na2CO3), and sulfuric acid (H2SO4) were purchased from Merck. DMSO was purchased from Qualigens chemicals. Tannic acid and 2,4-dinitrophenylhydrazine (DNPH) were purchased from Central Drug House (CDH) laboratory chemicals, India. Methanol was purchased from Fischer scientific chemicals. Commercially available Cinnamon zeylanicum bark was purchased from local market. Luria broth and agar-agar were obtained from Hi Media Laboratories, India. Bacterial strains of E. coli (ATCC 35218) and S. aureus (ATCC 25923) were provided by AIIMS, India. All chemicals were of analytical grade and were used without any further purification.

2.2 Extraction of Cinnamon Zeylanicum bark

Cinnamon zeylanicum bark was washed with water and acetone to remove impurities and was dried before using for further experiments. Different solvents, ethanol, water, and DMSO were subjected to the extraction process. Cinnamon zeylanicum bark pieces (1 g) were dipped into each solvent (50 mL) for 6 h under stirring. Different composition of bark and solvents were investigated. The extraction in aqueous medium was carried out at 80 °C, while extraction in ethanol and DMSO were carried out at ambient temperature and were filtered and stored under refrigeration. Subsequently, Cinnamon zeylanicum bark extracts were used for the synthesis of AgNPs.

2.3 Estimation of total polyphenol content

The total polyphenolic content of Cinnamon zeylanicum bark extract was estimated using standard Folin-Ciocalteu’s colorimetric method [29]. Tannic acid was used as a reference reagent for the estimation of total phenol content in different extracts. One milliliter of Cinnamon zeylanicum bark extract in different solvent was mixed with 0.5 mL of Folin-Ciocalteu’s reagent and diluted with 5 mL of water. After 5 min of mixing, 1.5 mL of 20% Na2CO3 was added for neutralization and the volume was made up to 10 mL with water. This solution was incubated for 120 min at ambient temperature after which an intense blue color was observed. The data is expressed in milligrams of tannic acid equivalence (TAE). All the experiments were performed in triplicate measurements and values were presented with standard deviation.

2.4 Estimation of total aldehyde content

The total aldehyde content was estimated using DNPH as earlier reported method [30]. A total of 100 μL of each solvent extract was added to 10 mL of freshly prepared DNPH solution. The solutions were allowed to stand for 60 min at ambient temperature and after which were centrifuged at 700 rpm for 10 min. Absorbance of the unreacted DNPH in the supernatant liquid was measured at wavelength, λmax. = 326 nm. The total aldehyde content was calculated according to Eq. 1:
$$ \mathrm{Total}\ \mathrm{aldehyde}\ \mathrm{content}\ \left(\mathrm{mmol}\right)/\mathrm{g}=\left(\frac{\mathrm{Reacted}\ \mathrm{DNPH}\ \left(\mathrm{mmol}/\mathrm{g}\right)}{198.14\times 0.0001}\right) $$
(1)

2.5 Total antioxidant activity

The total antioxidant activity of the Cinnamon zeylanicum bark extracts in different solvents was estimated by phosphomolybdenum assay [31]. The antioxidant activity was estimated by the reduction of phosphomolybdic acid to a green-colored complex of phosphomolybdenum. The molybdate reagent solution was prepared by adding 1 mL of 0.6 M sulfuric acid, 9 mg of ammonium molybdate, 8 mg of sodium phosphate into 20 mL of distilled water, and the volume were made up to 50 mL in distilled water. A 0.5 mL of Cinnamon zeylanicum bark extracts was added to 3 mL of distilled water and 1 mL molybdate solution. The solution was incubated at 95 °C for 90 min and then was normalized at ambient temperature for 30 min. The absorbance was monitored at 695 nm. Ascorbic acid was taken as reference and all the samples were performed in triplicates. The total antioxidant activity was expressed in phosphomolybdenum reduction potential using Eq. 2:
$$ \mathrm{Antioxidant}\ \mathrm{Activity}\ \left(\%\right)=\left(\frac{A_c-{A}_s}{A_c}\right)\times 100 $$
(2)

Where Ac is the absorbance of the control and As is the absorbance of the Cinnamon zeylanicum bark extract sample.

2.6 Synthesis of silver nanoparticles

A 25 mL (50% v/v) of each extract solution was used for the reduction process and was added to 25 mL of aqueous AgNO3 solution of 100 mg/L concentration. The solutions were kept at 60 °C during the reduction process and similar conditions were maintained for each extract. The color change of the colloidal solution was monitored by visual inspection. Digital images of the samples were also captured with a digital still camera (Cannon 550D) at an optical zoom of × 4.

2.7 Characterizations of AgNPs

The nanoparticle formation was monitored periodically using a UV–vis spectrophotometer (Shimadzu 4520) at a wavelength in between 300 to 600 nm. The characteristic plasmon resonance peak of monodispersed AgNPs appeared around ~ 420 nm. The morphology and size of the AgNPs were observed under a JEOL JEM-1400. High-resolution transmission electron microscopy (HRTEM) operated at 200 KV equipped with Olympus Soft Imaging Solutions GmbH (software: iTEM; TEM Camera: Morada 4008 × 2672-pixel max) recording system. For HRTEM analysis, the samples were prepared by placing one drop of the colloidal solution on a carbon-coated grid and dried at ambient temperature. Energy-dispersive X-ray spectroscopy (EDAX) studies were also carried out in parallel to find evidence for the presence of Ag in nanoparticles. The structural morphology of the bacteria was studied using STEREOSCAN 360 (Cambridge scientific industries) scanning electron microscope (SEM), with gold coating.

2.8 Antimicrobial studies

Antimicrobial studies of biosynthesized AgNPs in different extracts were carried out by the zone of inhibition method, according to test method AATCC 100–1998 [4, 5, 6, 7, 12]. The antibacterial efficiency of the AgNPs was monitored against gram-positive bacteria S. aureus and gram-negative bacteria E. coli. Freshly obtained colonies of S. aureus and E. coli were suspended in Luria Broth and the turbidity was adjusted to 0.5 McFarland standards. Two hundred microliters of this suspension was spread on Luria-Agar plates to obtain a semi-confluent growth. AgNPs-impregnated disks (0.9 mm diameter) and negative control disks were placed on the inoculated plates. The plates were kept for incubation for 24 h at 37 °C and the inhibition zones were measured using photographic images of the agar plates.

The interaction of the AgNPs with bacterial colonies and their mechanism of action against both E. coli and S. aureus were observed by HRTEM. The bacterial cells were treated with colloidal solution of AgNPs for different time durations. The samples were prepared by adding one drop of the sample onto a carbon-coated copper grid and then were dried at 40 °C. The presence of Ag inside the cell and interaction at the cell membrane was confirmed using EDAX.

3 Results and discussion

The present investigation is aimed at developing an eco-friendly and cost-effective route for the synthesis of AgNPs using Cinnamon zeylanicum bark extract. Cinnamon zeylanicum bark extracts were achieved by solvent extraction process in solvents having different polarities—aqueous, ethanol, and DMSO. The major component of the extract is cinnamaldehyde (~ 75%) which plays a vital role in the Ag reduction process (Fig. 1). Subsequently, extracts in different solvents were used for the growth of AgNPs by the reduction of silver ions and also tuned the morphology and size of the nanoparticles. The influence of total polyphenol content, antioxidant activity, and total aldehyde content in extracts was investigated and discussed in the later sections.
Fig. 1

Extraction of Cinnamon zeylanicum extract in different polarity of solvents

3.1 Total polyphenol content, total aldehyde content, and antioxidant activity

The bioreduction of metal ions is mainly dependent on the presence of biomolecules in the extracts and it is necessary to investigate the correlation between antioxidant activity and other biomolecules present in the extracts. It has been reported that the antioxidant property of the extracts is directly proportional to the phenolic components, which is synthesized by secondary plant metabolites involving both biotic and abiotic stresses [24, 32]. The total phenolic content of Cinnamon zeylanicum bark extract for different solvents was estimated using standard Folin-Ciocalteu’s colorimetric method and the values are expressed in milligrams per milliliter of TAE. The results showed a significant variation of TAE values (Fig. 2a) and follow the trend ethanol < aqueous < DMSO extracts.
Fig. 2

Total polyphenol content, aldehyde content, and antioxidant activity of different solvent extracts. Values are presented as mean ± SE (n = 3). The total aldehyde content and total antioxidant activity of Cinnamon zeylanicum bark extract followed the trend DMSO extract < aqueous extract < ethanol extract

The high concentration of cinnamaldehyde in the Cinnamon zeylanicum bark extract may be responsible for the high-antioxidant activity in the extracts. The total aldehyde content followed the trend as similar to the antioxidant activity ethanol > aqueous > DMSO (Fig. 2b). The correlation coefficient between antioxidant activity and aldehyde content was high at R2 = 0.9926 (Fig. 3b). According to previous reports, the antioxidant activity and reducing power of the Cinnamon zeylanicum bark extracts are highly correlated with each other [26, 33]. Therefore, the total aldehyde content is responsible for the reducing potential of the extract to achieve AgNPs. The growth of the nanoparticles in different solvent extracts was observed in further experiments by monitoring the shape, size, and morphology of the nanoparticles. The antioxidant activity of the extracts in different solvents was determined using phosphomolybdenum reduction assay and results were calculated in percentage (Fig. 2c). The relationship between the total polyphenol content and antioxidant activity in different solvent extracts was investigated and shown in Fig. 3a. There was no strong correlation observed in between total phenolic content and antioxidant activity of the extracts which contradicts the previous reports based on other plant extracts [24, 32]. A plausible reason could be due to the presence of other biomolecules in the Cinnamon zeylanicum bark extract, which may have increased the antioxidant activity as compared to the polyphenol content.
Fig. 3

Relationship of a total phenolic content and antioxidant activity and b Total aldehyde content and total antioxidant activity. Correlation coefficients between total phenolic content and antioxidant activity was low (R2 = − 0.9115). Correlation coefficients between total phenolic content and total aldehyde content were high (R2 = 0.9926)

3.2 AgNPs characterization

The biosynthesis of AgNPs using Cinnamon zeylanicum bark extracts in different solvents was visually observed by the change in color of the colloidal solutions against reduction time. Each solvent showed different bioreduction behaviors with respect to the reduction time. In aqueous extract, the color changed from yellow to dark brown within 15 min of reduction time indicating the immediate formation of AgNPs. Whereas in ethanol extract, the reduction process was relatively slow, the hazy color colloidal solution changed to pale yellow after 1 h of reduction time (Fig. 4a, b). The pale-yellow color may indicate the formation of a smaller size of nanoparticles in the size range of 2–10 nm. In DMSO extract, the color change to light yellow and then to intense orange after 3 h of reduction time (Fig. 4c) The visual inspection of bioreduction of silver ions is very similar to previous reports related to the biosynthesis using plant extracts [34, 35]. The color variation of the colloidal solution may indicate the growth of different morphologies of the nanoparticles in different solvent medium. The variation in the reduction time for the growth of nanoparticles in different solvents is directly related to the presence of biomolecules in each extract. As seen in Fig. 4, the reduction was faster in aqueous extract in comparison to other solvent extracts. The reduction process may be affected by the polarity of the solvents, therefore, the reaction was relatively slow in less polar solvents, such as ethanol and DMSO.
Fig. 4

Visual appearance of colloidal solution of silver nanoparticles with varying reduction time. a Ethanol extract, b aqueous extract, c DMSO extract; reaction temperature 60 °C

The results in Fig. 5 show UV–visible spectra of nanoparticles in different extracts with respect to reduction time. The growth of nanoparticle was monitored at different time intervals from 5 min to 6 h with characteristic plasmon band in a range of 410–450 nm. The spectrum displayed a peak around 421, 426, and 435 nm for ethanol, aqueous, and DMSO extracts, respectively. The plasmon peak for DMSO appears only after 3 h of reduction time which clearly indicates a slow reaction rate. The rate of reaction was the slowest in DMSO extract due to the low aldehyde content value and thus, a slow reduction process was observed which leads to the growth of more agglomerated nanoparticles. Also, the shifting in position of peak with respect to reduction time clearly indicates the change in size and shape of the nanoparticles as the peak shifted towards higher wavelength. The intensity of the peak increased continuously with increasing time where the sharp variation in the absorption maxima indicated the variation in the particle size distribution.
Fig. 5

UV−vis absorbance spectrum of synthesized AgNPs in different solvents. a Ethanol, b aqueous, c DMSO from 375 to 600 nm is shown, with the absorbance maximum occurring at λmax = 421.5 nm (ethanol), λmax = 426 nm (aqueous), and λmax = 436 nm (DMSO)

HRTEM analysis was further carried out to monitor the morphologies in terms of shape and size of the nanoparticles in different solvent extracts (Fig. 6). The TEM images show noticeable difference in the appearance of nanoparticles in different solvents. It seems that during nanoparticle growth, the biomolecules present in the extract not only act as a reducing agent but also stabilize the growth of nanoparticles which help in the balancing of electrostatic force during the formation of nanoparticles. The nanoparticles in ethanol extract were spherical in shape with a size in the range of 2–10 nm with narrow distribution of particles. In a recent study, the solvent influence over the nanoparticle synthesis was investigated in which solvents control the morphology of the nanoparticles [36]. In aqueous extract, the nanoparticles were observed in the size range of 5–25 nm with polygonal and elongated shaped particles. Whereas in DMSO extract, the particles were spherical in shape in the size range of 10–50 nm. Moreover, the particles in ethanol and DMSO extracts were more uniformly distributed as compared to the aqueous extract. The presence of the high concentration of reducing agents in ethanol extract observed rapid bioreduction and thus, restricting the crystal growth. This is due to the presence of a high concentration of aldehyde content in extract which is responsible for the fast bioreduction. Similar results were observed by Kumar et al, where the particle shapes were spherical and elliptical [27]. It can be concluded that the polarity of the solvent affects the growth of nanoparticles with simultaneous stabilization of the electrostatic forces which does allow the ions to adsorb on the growing nuclei. Aqueous extract exhibits high polarity which induces hydrolytic reactions and supports the growth of polygonal and elliptical nanoparticles [24].
Fig. 6

HRTEM images of silver nanoparticles synthesized in a ethanol, b aqueous, and c DMSO extracts of Cinnamon zeylanicum at different reaction times

HRTEM coupled with EDX analysis was carried out to confirm the presence of pure silver without any other metals. The EDX spectrum shows the distinctive energy peak at ~ 0.2 keV, which is the characteristic peak of carbon and oxygen. Along with characteristic peak, a new sharp peak appeared at 3 keV which corresponds to the presence of silver in the sample. (Figure attached as supplementary information S1).

3.3 Correlation of aldehyde content with metal reduction and particle size

The relationship between the total aldehyde content and the morphology and the size of AgNPs were visualized in different solvents (ethanol, aqueous, and DMSO). As mentioned above, the antioxidant activity of the plant extract is mainly responsible for the bioreduction process. Good correlation was observed between the total aldehyde content and antioxidant activity shown in the previous section. Trend was observed as ethanol > aqueous > DMSO. Identical trend was observed in the case of the size of nanoparticles growing in ethanol extract having the smaller size and narrow distribution, whereas the nanoparticles growing in DMSO extract have larger sizes. Thus, the extract having high concentration of reducing biomolecules tuned the fast reduction of metal ions and also control the growth of nanoparticles. In case of DMSO extract, the reduction rate was slow due to low reducing potential and this extended time provides a suitable time for ionic interaction which leads to the larger size of the nanoparticles. These nanoparticles can then be further studied for enhanced antibacterial properties owing to their respective sizes.

4 Antimicrobial studies

4.1 Zone of inhibition

The antibacterial activity of the AgNPs was evaluated and is shown in Fig. 7. The extracts in different solvents did not show any inherent antimicrobial property. They only participate in the reduction process and stabilize the growth of AgNPs which is confirmed by zone of inhibition results. It can be seen that nanoparticles show high antimicrobial activity in E. coli as compared to S. aureus. The zone of inhibition measured in E. coli was 4.23 ± 0.5mm, 4.18 ± 0.09 mm, and 2.81 ± 0.3 mm for ethanolic, aqueous, and DMSO extracts, respectively. In S. aureus, the zone of inhibition was observed to be 3.21 ± 0.09 mm, 2.95 ± 0.1 mm, and 1.73 ± 0.3 mm for ethanolic, aqueous, and DMSO extracts, respectively. The high antimicrobial activity of AgNPs is mainly influenced by the size of the particles. The small size of the nanoparticles demonstrated relatively high antimicrobial activity in comparison to large particles. Therefore, particles growing in ethanolic extracts were smaller in size and possess high antimicrobial activity whereas particles growing in DMSO shows less activity.
Fig. 7

Zone of inhibition for silver nanoparticles in different solvent extracts against aE. coli and bS. aureus strains. The zone of inhibition is highlighted with a dashed circle indicating antibacterial effect

4.2 Mechanism of bactericidal action

The bactericidal action of nanoparticles with E. coli and S. aureus cells were analyzed by HRTEM analysis and the results are displayed in Fig. 8. The morphology of the bacterial cells before and after the treatment with AgNPs was monitored under HRTEM where we can see the interaction of the bacterial cell with nanoparticles. Sharp difference was observed in the characteristic morphology of the bacterial cells after interaction with AgNPs. Untreated bacterial cell of E. coli and S. aureus appeared normal with their characteristic shapes. In Fig. 8b after 10 min of treatment, the nanoparticles were dispersed inside the bacterial cell and led the release of cytoplasm due to the rupture of the plasma membrane of bacteria. After internalization of the nanoparticle, the cytoplasmic fluid can be seen to accumulate at one corner of the cell. The rupture of plasma membrane can be inferred from the structural deformation of the characteristic shape of the E. coli cells after the treatment with AgNPs. A significant number of Ag nanoparticles were found inside the bacterial cell and also attached to the membrane surface which may release Ag+ ions and may disturb the osmoregulation and permeability of the cell [37, 38]. In Fig. 8c, the bacterial cell shape was completely distorted and leakage of the cytoplasmic contents is seen which may be due to the fragmentation of the cell wall. In Fig. 8e similar observation of structural deformation of E. coli was observed by SEM analysis. Arrows indicate the presence of AgNPs inside the E. coli cells which is confirmed by EDAX analysis which shows the significant peak of Ag at 3.0 keV (Fig. 8f).
Fig. 8

a HRTEM images of E. coli cells untreated and after treatment with silver nanoparticles for b 30 min, c 60 min, and d 90 min. e SEM image of bacterial cell after treatment, and f EDX analysis of the bacteria shows the presence of silver

Several factors are involved in the bactericidal and bacteriostatic mechanism of AgNPs. This can be an alteration in the structure of the plasma membrane, and affecting the osmoregulation of the cell or the nanoparticles may penetrate into the cell and cause leakage of the cytoplasmic contents and after internalization, they can affect the replication of DNA, generate ROS, and can affect respiration of the bacterial cell. In case of the gram-negative E. coli cells, a high percentage of the AgNPs were found inside the bacterial cell, as also reported by previous reports [39]. The AgNPs may also cause inhibition of respiratory enzymes and cause ATP and ROS production. Ag nanoparticles can also release Ag+ ions which interact with the thiol groups present in the enzymes necessary for respiration and cause cell death [40]. These mechanisms may occur simultaneous resulting in a quick antibacterial action on the cell.

In case of gram-positive S. aureus cells, a large number of nanoparticles were found on the surface of the cells rather than inside them as in E. coli. This may be due to the difference in the composition of the cell wall. The cell wall of gram-positive bacteria has a thick peptidoglycan layer and is more difficult to penetrate inside the cells due to its rigid structure as compared to the gram-negative bacteria which possess a thinner peptidoglycan layer [41]. A significant shrinkage and deformation in shape were observed after 10 min of treatment which may affect the permeability and electron transport of the cell. In Fig. 9c, the AgNPs were penetrated inside the cell membrane and the clustering of nanoparticles was observed. The exact mechanism is not clear but the nanoparticles could have released Ag+ ions which might have disturbed the permeability of the cell [37]. This is supported by the attachment of the nanoparticles at the surface of the cell and also the clustering of nanoparticles. In Fig. 9d and e, the particles have completely entered the cell forming even bigger cluster of particles. And complete destruction of the bacterial cell is seen which may be due to the many pathways as described above.
Fig. 9

a HRTEM images of S. aureus cells untreated and after treatment with silver nanoparticles for b 30 min, c 60 min, and d 90 min. e SEM image of bacterial cell after treatment and f EDX analysis of the bacteria shows the presence of silver

5 Conclusion

AgNPs have been synthesized using Cinnamon zeylanicum bark extracts in different polar solvents. The results of this study show a very strong correlation between the aldehyde content, antioxidant activity, and growth of the nanoparticles. It was noticed that different solvent extracts have significant impact on the antioxidant activity and lead to the formation of nanoparticles with different shapes and sizes. The particles grow in different extracts showing size variations from 2 to 50 nm. AgNPs demonstrated both bacteriostatic and bactericidal activity with respect to their size and shape. Microscopic analysis of E. coli and S. aureus cells treated with the AgNPs illustrated their interaction with the cell wall, which facilitated their subsequent entry inside the cells. In conclusion, these nanoparticles could be effectively used for the development of infection-resistant material such as a nano-coating or impregnation for surgical devices, instruments, and wound healing bandages. The subsequent work related to the impregnation of these AgNPs in polymer matrix and their application will be communicated soon.

Notes

Acknowledgements

The authors duly acknowledge the facilities provided by Central Research Facility (CRF) at IIT Delhi. Authors are also thankful to Prof. Arti Kapil, Department of Microbiology, AIIMS, New Delhi for providing bacterial strains.

Supplementary material

42247_2019_23_MOESM1_ESM.docx (126 kb)
ESM 1 (DOCX 126 kb)

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© Qatar University and Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Bioengineering Laboratory, Department of Textile TechnologyIndian Institute of TechnologyNew DelhiIndia

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