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Bionanocomposite of Au decorated MnO2 via in situ green synthesis route and antimicrobial activity evaluation
⁎Corresponding authors. yaminsynergic@gmail.com (M. Yameen), bosalvee@yahoo.com (M. Iqbal), shalmejale@pnu.edu.sa (S.H. Al-Mijalli), m.aziz@qu.edu.sa (M. Fatima)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Green synthesis gaining a significant importance for the preparation of nanoparticles (NPs) and NPs-based biocomposites gained much attention in biological applications. In the current study, gold (Au) nanoparticles were prepared via green approach using cinnamon extract. The Au nanocomposite (NC) was prepared with MnO2 nanofiber mesh structure. The NC was characterized by XRD, SEM, FT-IR, EDX, UV–visible and DLS techniques. The MnO2 nanofibers diameter was in 10–25 nm range, which was arranged in a mesh form and Au NPs was combined with nanofibers randomly. The MnO2-Au NC antimicrobial activity was measured against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus strains. The antimicrobial activity of MnO2-Au NC was highly promising against tested microorganisms in comparison to control (ciprofloxacin, a standard drug). The antimicrobial activity of MnO2-Au NC was found in following order; > S. aureus > E. coli > P. aeruginosa with the zones inhibition of 22, 18 and 15 (mn), respectively. The MIC (minimum inhibitory concentration) values were 316, 342 and 231 (µg/mL) for E. coli, P. aeruginosa and S. aureus, respectively. In view of promising antimicrobial activity, the MnO2-Au NC prepared via green approach could have potential applications in medical field and future study can be engrossed on the biocompatibility evaluation of MnO2-Au NC using bioassays.
Keywords
Bionanocomposites
Cinnamon extract
Manganese oxide nanofibers
Gold nanoparticles
Green approach
Antimicrobial activity
1 Introduction
The resistance of microbes against antibiotics is one of main factors for the inefficacy of antibiotics against infectious microorganisms, which drawn a significant consideration of researchers to develop new antimicrobial agents. In this regard, the nanotechnology meets this challenge and furnished NPs having typical properties and diverse applications in every life sphere. The noble metals-based NPs gained much attention especially for biological applications due to their ideal theragnostic aptitudes (Nazir et al., 2021; Safardoust-Hojaghan et al., 2021; Ghanbari and Salavati-Niasari, 2021) and Au NPs are ideal for biomedical applications. At current, biocomposites are gaining importance in view of their promising properties versus NPs prepared via chemical synthesis. The biocomposites have been employed successfully in the biomedical field. The Au NPs have been fabricated by employing different techniques, i.e., chemical, physical and biological routes (Karami et al., 2021; Mortazavi-Derazkola et al., 2017; Salavati-Niasari et al., 2009). Among synthesis approaches, the green route is an eco-benign and sustainable approach being used for the designing of nanomaterials since no hazardous chemical is involved during green processing versus chemically routes (Masjedi-Arani and Salavati-Niasari, 2017; Beshkar et al., 2017; Zinatloo-Ajabshir et al., 2016; Yapaoz and Attar, 2019). Different bioresources have been used to fabricate the nanomaterial, which furnished the NPs of different sizes and morphologies (Tavakoli et al., 2015; Ansari et al., 2018; Bulut Kocabas et al., 2020). Plants are the rich source of bioactive compounds like, sugars, vitamins and polyphenolics that can severe as an agent for the reduction of ions to atom and bioactive in the extract also facilitates the capping and stabilization of NPs and green route is virtuous substitute of chemical synthesis approach where templates and solvents are used (Amer and Awwad, 2021; Awwad et al., 2020; Awwad et al., 2020).
Transition metals, i.e., Ni, V, W, Mn and their oxide are widely used for synthesis of composite materials due to their physical and electrochemical properties. Among Transition metals, the MnO2 is one of the attractive and promising material for electrochemical, magnetic and catalytic application due to its natural abundant in earth, low cost, wide potential range, nontoxic and environmentally nature. MnO2 is also considered as promising oxidants and act as antibacterial agent, used in sensing, photocatalysis and in pharmaceuticals applications (Rahmat et al., 2019; Sanda et al., 2021; Awwad et al., 2020). The composite/doped materials facilitate the charge transmission from metals to the electronegative metal, resulting the formation of more stabilized oxidation state, which have been used for different applications, i.e., Seitz el al. (Seitz et al., 2015) prepared doped MnOx for photocatalysis. Also, Au NPs decorated with metal showed higher catalytic activity for alcohol oxidation (Alhumaimess et al., 2014). The Au NPs deposition of metal oxide have been demonstrated to promote the oxygen evolution in a reaction . Recently, Sun et al also prepared MnO2 composites with good catalytic activity (Sun et al., 2017) and Gorlin et al reported the deposition of Au NPs on MnOx by sputtering, which showed higher activity versus MnOx (Gorlin et al., 2014). As mention in Table 1, a lot of studies have been performed for Au NPs preparation by green for different applications. However, Cinnamon extract has not been utilized to fabricate the Au NPs. Hence, the present study was designed to prepare the Au NPs using Cinnamon extract and its composite with MnO2 was also prepared. The as-synthesized material was studied by XRD, SEM, EDX, FTIR, UV–visible and DLS approaches. The MnO2-Au NC antimicrobial efficacy was studied against panel of strains by disc diffusion method along with MIC.
S. No
NPs and NCs
Tested strains
ZOI (mm)
References
1
MnO2 and Ag NPs
E. coli, E. faecalis
5–16
(Mahlangeni et al., 2020)
2
MnO2 nanocolloids
P. aeruginosa, E. coli, S. typhi
32–35
(Rahmat et al., 2019)
3
Mn NPs
S. aureus, E. coli
16–24.5
(Kamran et al., 2019)
4
Zeolite\ZnO-CuO
NCsB. subtilis
18.9
(Alswat et al., 2017)
5
TiO2/ZnO NCs
S. aureus
E. coli
19.5
23(Suo et al., 2019)
6
Ag NPs
P. aeruginosa
10
(Ajaypraveenkumar et al., 2015)
7
MnO2-Au NC
E. coli
S. aureus
P. aeruginosa.24
30
14Present work
2 Material and methods
2.1 Chemicals and reagents
2.1.1 Extract preparation
The chemical and reagents were acquired form Sigma-Aldrich. The Cinnamon extract was prepared and used for the fabrication of Au NPs. Briefly, 0.4 g of dried Cinnamon powder was dispersed in 100 mL of deionized water and heating was performed at 100 °C for 2 h. Then, the contents are filtered and resultant extract was kept at 4 °C for further use.
2.2 MnO2-Au NC preparation
Manganese oxide nanofibrous mesh was fabricated following previously reported protocol (Tehseen et al., 2018). In a typical synthesis scheme, MnO2 was dispersed in 100 mL deionized water and incubated at 80 °C with stirring at 600 rpm. Then during stirring, 5 mL of HAuCl4 (1 M) was added and incubated for 30 min. Now, 5 mL of Cinnamon extract was supplemented and the content was incubated at 80 °C with stirring at 600 rpm. The mixture was stirred for 12000 rpm for 10 min for the separation of particle, which was washed thoroughly with deionized water several time. Finally, the sample was dried at 60 °C for 12 h and placed in a desiccator at room temperature till further analysis. The scheme for the synthesis of MnO2-Au NC is portrayed in Fig. 1.
Scheme adopted for the synthesis of MnO2-Au NC.
2.3 Characterization
The XRD spectra was recorded using X’pert Pro PAN analytical (Germany) diffractometer using CuKa radiation (λ = 1.5406A), operated at 40 kV and 30 mA in 10-80° degree range. The morphology was studied by SEM (FESEM-JSM-7500F-JEOL, Japan). Sample was prepared by dispersing powder in water (1 mg/mL) and subjected to analysis. DLS experiment was performed for determination of particle size as well as surface charge of the prepared martial (Nano-ZS; Malvern Instruments). FT-IR was used to determine the functional groups using Perkin Elmer System 2000 FT-IR spectrometer. UV–visible was performed in 200–700 nm domain (CECIL (Aquarius) 7000 series). For EDX analysis Hitachi S-4800 Japan was used.
2.4 Antimicrobial activity
The antimicrobial activity was evaluated as reported elsewhere (Rahmat et al., 2019). Antimicrobial activity was examined for S. aureus; P. aeruginosa and E. coli strains. The media (Nutrient agar, a growth media for bacteria) was autoclaved at 121 °C for the period of 15 min. The wicks paper discs (9 mm) were sterilized. A 20 mL media (Nutrient agar) was added in Patri plates along with 20 μL of fresh bacterial culture. The Patri plates were kept at room temperature till the media was solidified. With the help of forcep, disc containing 500 μL MnO2-Au NC (50 mg/mL) were placed flat on the medium (growth media) and Petri plates were incubated at 37 °C for 24 h. The NC inhibited the bacterial growth, which was recorded with zone reader in mm. All the run was performed in triplicate and data obtained was averaged. For the measurement of MIC, the method reported elsewhere was followed (Sarker et al., 2007).
3 Results and discussion
3.1 XRD analysis
The structural analysis was performed by XRD study and response thus obtained is shown in Fig. 2. The peaks recorded were of 220, 300, 211, 420, 521, 202 and 312 indices and matched precisely with JCPDS card no. 44-0141. No extra peaks were observed, which indicate the purity of prepared material. The composite showed a peak of Au in addition to the MnO2, which is an indication of MnO2 composite formation with Au. Also, these findings are in line with reported studies, i.e., a hydrothermal treatment was adopted for the fabrication of MnO2 by (Hlaing and Win, 2012) and a very uniform MnO2 nanorods with diameters of 30–50 nm were obtained under control of conditions (temperature and reaction time). Also, PLAL has been used for the fabrication of MnO2 NCs. The PLAL furnished high crystalline MnO2 NCs with crystallite size of 52 nm (Rahmat et al., 2019).
XRD pattern of MnO2-Au NC.
3.2 UV–Vis analysis
The MnO2-Au NC UV–Vis was performed in 200 to 800 nm range and response this observed is presented in Fig. 3. In UV–Vis absorption spectrum, two characteristic peaks were observed at 245 nm and 490 nm, which are corelated with MnO2 and Au, respectively. The visual appearance of ruby red color also reveals the formation of Au nanoparticles. The absorption bands in 197–270 nm and 450–785 nm range were recorded in case of MnO2, while in case of MnO2-Au NC, the intensity of the absorption peak in 450–785 nm range reduced significantly, which is indication of interaction Au with MnO2 in NC formation.
UV–VIS spectrum of MnO2-Au NC.
3.3 DLS analysis
The dynamic light scattering (DLS) is an analytical tool used to measure the hydrodynamic diameter of NPs in liquid medium. It also provides information about the surface charge of the fabricated materials. The zeta potential of the MnO2 nanofibers mesh was −26.3 mV (Fig. 4a). The negative values revealed the higher stability of the NC (Liu et al., 2014). Moreover, a reduction in value of zeta potential was observed in MnO2-Au, i.e., −12.2 mV (Fig. 4b), which is also an indication of NC formation of MnO2 and Au NPs.
(a) Zeta potential of MnO2 and (b) MnO2-Au NC.
3.4 FT-IR analysis
FT-IR spectra of MnO2 nanofiber mesh and MnO2-Au NPs NC are shown in Fig. 5. In the spectra, a characteristic peak of MnO is observe at 570 and 690 (cm−1). In case of MnO2-Au NPs NC, a band at 3321 cm−1 was observed due to OH stretching vibration. The band observed at 1053 cm−1 was assigned to the —CO— stretching. A band at 1634 cm−1 is due to —C⚌C— stretching and bending at 2127 cm−1 is due to C—H functional group. The analysis revealed that Cinnamon extract comprises a variety of phytochemicals, which are responsible for the reduction, stabilizing of Au atom (Fig. 6). Moreover, in comparison to the MnO2 nanofiber, a band at 570 and 690 (cm−1) are due to Mn-O bending vibration. While for MnO2-Au NPs NC, the absorption bands are shifted slightly (blue shift) to 668 and 707 (cm−1), respectively, which is due to interaction between Au NPs and MnO2 nanofibers. These results are also in line with reported studies, where the interaction of the hydroxyl group (O—H) with Mn atoms is documented. The peaks appeared at 665, 641, and 611 (cm−1) were corelated with Mn—O bonding. With the growth of Au NPs on the surface of Mn—O, the absorption bands shifted to 1682, 670, 645 (cm−1) revealed the successfully incorporation of Au atoms on the surface of MnO2 nanofibers.
FT-IR spectra of MnO2 NFs mesh and MnO2-Au NC.
FT-IR spectra of extract used for the preparation of Au NPs.
3.5 Surface morphology
The properties of the NPs depend on the morphology and size of the particles. Hence, the morphology was studied by FE-SEM and outcome is portrayed in Fig. 7a. The MnO2 formed a nanofiber structure and the fibers diameter was in 10–25 nm range and length was several microns. The length to diameter ratio was found to be enough high, which reveals the fibrous morphology. Moreover, the MnO2 forms a mesh like structure and the pores of the meshes were in 10–500 nm range. The fibers are highly flexible due to their extra-long length, which makes the loops and curves in the fibers. The mesh structure has various advantages like it has high surface area, mesh precludes the fibers from aggregation, which resultantly may offer high activity during catalytic and photocatalytic activity. The average diameter of Au NPs was estimated to be 14 nm (Fig. 7a-d), which are randomly distributed over the surface of the MnO2 nanofibers. Au NPs with high electronegativity can affect the physicochemical attributes of MnO2 nanofibers due to ideal surface-to-volume ratio (Liu et al., 2014).
FE-SEM analysis, (a) MnO2 nanofibers and (b-d) MnO2-Au NC.
3.6 Elemental analysis
The elemental composition of the MnO2-Au NC was studied by EDX analysis and response this obtained is depicted in Fig. 8. The EDX analysis furnished data, which contains peaks corresponding to the elemental composition of the sample being analyzed. EDX spectrum of MnO2-Au NC depicts the presence of C, O, Mn and Au elements. No peak for impurity was observed ensuring purity of the prepared composite material. It can be concluded that a successful decoration of Au NPs was achieved on MnO2 nanofiber mesh structure. The Mn and Au proportion in the NC was 10.14 and 1.94 (%), respectively. The findings revealed that the MnO2-Au NC fabricated are in highly pure form since no additional peaks are detected in the EDX spectrum.
(a) EDX analysis of MnO2 nanofibers and (b) MnO2-Au NC.
3.7 Antimicrobial activity
The MnO2-Au NC antimicrobial activity was assessed against three microbial strains, which was compared with standard antibiotic ciprofloxacin. The antimicrobial activity of MnO2-Au NPs NC was perfumed versus S. aureus, P. aeruginosa and E. coli strains and responses are presented Fig. 9. The ciprofloxacin was used as a standard to compare the antimicrobial activity of MnO2-Au NPs. The MnO2-Au NPs showed excellent antimicrobial activity against selected microbes and the zones of inhibition were in following order; S. aureus > E. coli > P. aeruginosa. The zones of inhibition in case of S. aureus, E. coli and P. aeruginosa were recorded to be 22, 18 and 15 (mm), respectively, whereas this value was 32–36 mm in case of ciprofloxacin in case of S. aureus, E. coli and P. aeruginosa. Previous studies also supports the findings of present investigation that composite based are good antimicrobial agents, i.e., E. coli growth was significantly inhibited by the Ag/MnO2 NCs (Rahmat et al., 2019). Also, Ag doped MnO2 showed promising activity against S. aureus, S. epidermis, B. subtilis, E. coli, S. abony and K. pneumonia strains (Kunkalekar et al., 2014). Similarly, CS-MnO2 also furnished auspicious antimicrobial activity against panel of microbial strain (Anwar, 2018) and ternary nanocomposite of MnO2 also showed auspicious activity against E. coli and S. aureus strains (Venkatesh et al., 2017). Also, present investigation revealed that the MnO2-Au NC is highly active antimicrobial agent, which could have potential biological application as an antimicrobial agent (Table 1). Previous studies showed that TiO2/ZnO NCs and ZnO NPs, the MnO2-Au NC showed higher antimicrobial activity. In comparison to Ag NPs along, the MnO2-Au NC also showed higher efficiency.
Antimicrobial activity (zone of inhibition) of MnO2-Au NC.
The MIC was also studied of MnO2-Au NC against S. aureus, P. aeruginosa and E. coli and results are portrayed in Fig. 10. The MIC value is the considered the lowest concentration of the tested compound, which inhibited the microbial growth (no growth observed at MIC value). The MIC values were found to be in line with the antibacterial activity. The MIC value was 231 µg/mL (lowest) in case of S. aureus, whereas this value was 316 µg/mL for E. coli and 342 µg/mL in case of P. aeruginosa. The standard antibiotic (ciprofloxacin) showed the MIC values 105, 126 and 61 (µg/mL) against E. coli, P. aeruginosa and S. aureus, respectively. The higher antibacterial activity is due to the different interactive effect of MnO2-Au NC with microbial cell due to ions formation and reactive oxygen species (ROS) generation, which collectively leads to cell to death (Fig. 11). The antibacterial activity of the NPs depends upon various factors, i.e., absorption rate, release of metabolites, metabolic functions and distribution in the cell. The NPs binds with the cell of microorganism, attached with the surface through active moieties and then, diffused inside the cell and interactive with the cell different components. For example, if the NPs binds/interact with proteins, which is an important biomolecule in cell to perform different functions, i.e., it takes part in the formation of cell wall, ribosomes, cell membrane and nucleic acids and if protein synthesis is inhibited inside the cell and them, all activities related to protein are stopped and resultantly, cell death occur. The overall proposed antimicrobial mechanism is explained in Fig. 10. The binds with cell wall of microbe, penetrates into cell membrane and cause membrane destruction and disrupt (proteins, enzymes, and DNA). The NPs produce ROS inside the cell and these ROS induce oxidative stress and resultantly, metabolic pathways are disturbed and cell occurred.
Minimum inhibitory concentration (MIC, µg/mL) MnO2-Au NC.
Antimicrobial activity mechanism of MnO2-Au NC.
The antibacterial activity of the NPs depends upon various factors, i.e., absorption rate, release of metabolites, metabolic functions and distribution in the cell. The NPs binds with the cell of microorganism, attached with the surface through active moieties and then, diffused inside the cell and interactive with the cell different components. For example, if the NPs binds/interact with proteins, which is an important biomolecule in cell to perform different functions, i.e., it takes part in the formation of cell components (wall, membrane, ribosome and nucleic acids) and if protein synthesis is inhibited inside the cell and them, all activities related to protein are stopped and resultantly, cell death occur. The overall proposed antimicrobial mechanism is explained in Fig. 10. The binds with cell wall of microbe, penetrates into cell membrane and cause membrane destruction and disrupt (proteins, enzymes, and DNA). The NPs produce ROS inside the cell and these ROS induce oxidative stress and resultantly, metabolic pathways are disturbed and cell occurred. These ROS include hydroxyl radicals (OH•), and superoxide ions O2−• These free radicals interact with biomolecules, which disintegrate the plasma membrane and cause lipid oxidation. The hydrogen peroxide produced cause toxicity to the cell and ultimately, leads to the cell death (Sharma et al., 2021). The NPs and NC prepared promising antibacterial activity versus related nanomaterials prepared chemical methods. Hence, the adoption of green route is more feasible to prepare the NPs (Awwad et al., 2020; Awwad et al., 2020; Awwad and Amer, 2020; Al Banna et al., 2020; Igwe and Nwamezie, 2018; Remya et al., 2017) and their composites for biomedical applications.
4 Conclusions
The Au NPs was prepared by green route using cinnamon extract and nanocomposite of Au was prepared with MnO2 nanofibrous mesh. The characteristics of MnO2-Au NC was studied by SEM, XRD, FT-IR, EDX, UV–visible and DLS techniques. The MnO2 nanofibers diameter was in 10–25 mm range. The length to diameter ratio was found to be enough high, which reveals the fibrous morphology. The MnO2 forms a mesh like structure and the pores of the meshes were in 10–500 nm range and Au atom was distributed randomly on the surface of nanofibers. The MnO2-Au NC showed promising antimicrobial activity against S. aureus, E. coli and P. aeruginosa. The MIC values were 231–342 µg/mL range for E. coli, P. aeruginosa and S. aureus, respectively. The MnO2-Au NC furnished auspicious. In view of promising antimicrobial activity and could have potential applications in medical field, which need further studied for the evaluation of biocompatibility of MnO2-Au NC.
Acknowledgement
This research was funded by the Deanship of Scientific Research at Princess Nourah bint Abdulrahman University through the Fast-track Research Funding Program.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
