This research project aims to identify and synthesize silver nanoparticles in the best green method by using different natural flower tea extracts, and to investigate the effectiveness of its antibacterial activity. It hopes to use and apply these silver nanoparticles in water purification and treatment.
In this investigation, we have successfully carried out a plant-based green biosynthesis of silver nanoparticles. It has been significantly achieved using different natural flower tea extracts as the synthesized silver nanoparticles were confirmed and characterized by spectroscopy. Our experimental results significantly show that microwave assisted green synthesized silver nanoparticles using Rose flower extract (0.2g/mL) has the highest quantity of silver nanoparticles. Besides, these silver nanoparticles have the highest antibacterial (E.coli) activity, comparable to commonly used antibacterial agent, Ampicillin. To avoid the chemical toxicity, microwave accelerated green synthesis of silver nanoparticles using Rose flower extract is proposed as a simple, cost-effective and environmental friendly approach, and more effective in a variety of applications.
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Ch.1 Introduction
1.1 Problem
Silver nanoparticles with wide applications have an eye catching role owing to their distinctive physical and chemical properties such as catalytic, optical, magnetic and electrical properties (Figure 1.1.1). The interest in synthesizing silver nanoparticles using green methods has been increasing in recent years. Physical and Chemical methods (such as chemical reduction, gamma-ray irradiation, micro-emulsion, laser ablation, electrochemical reduction) are both conventionally used for synthesis of silver nanoparticles, however due to many limitations and disadvantages like high operation cost, energy inefficiency of these methods, the focus of research has been recently shifted towards the development of clean, simple, low-cost and eco-friendly synthesis protocols. However, limited studies have been performed on improving the synthesized silver nanoparticles’ stability and antibacterial properties [1,2].
Figure 1.1.1 Various applications of silver nanoparticles (AgNPs).
Antibacterial activity of green synthesized AgNPs using flower tea extract
1.2 Possible answers to the problem
There is a growing need to develop an environmentally friendly process for the synthesis of nanoparticles that does not employ toxic chemicals. Biosynthesis of nanoparticles is an approach where the main reaction occurring is reduction/oxidation.
With the antioxidant or reducing properties of plant extracts, they are usually responsible for the reduction of metal compounds into their respective nanoparticles.
Nowadays, green chemistry procedures using various biological systems such as yeast, fungi, bacteria and plant extract for the synthesis of nanoparticles are commonly used [3]. Among them, plant extract based biosynthesis of metal nanoparticles especially silver and gold is found to be more advantageous because it does not require elaborate processes such as intracellular synthesis and multiple purification steps [4]. In this research project, in search for green synthesis of sliver nanoparticles from natural plant or flower source, in the present study dried flower tea extracts have been evaluated for their ability to synthesize sliver nanoparticles and its antibacterial activity have been compared with commonly used antibiotic, ampicillin as a positive control. To the best of our knowledge, this is the first report regarding synthesis of silver nanoparticles using flower tea extract and showing its antibacterial activity.
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1.3 Objectives
1. To compare and evaluate the effectiveness of the green synthesis of silver nanoparticles using eight different flower teas extracts, and identify the best one.
2. To investigate and compare the effectiveness of four different methods used in the green synthesis of silver nanoparticles.
3. To investigate and compare the efficiency of the green synthesized silver nanoparticles using different flower tea extracts in antibacterial activity against
Escherichia coli.
1.4 Hypothesis
This research hypothesis that there are natural, renewable and low-cost bio-reducing and capping agents from the flower tea extracts which can use to synthesis silver nanoparticles. And these green synthesized sliver nanoparticles are effective in antibacterial activity.
Antibacterial activity of green synthesized AgNPs using flower tea extract
Ch.2 Experimental methods
2.1 Preparation of flower tea extracts for the synthesis of silver nanoparticles
In our experiment, in order to screen different natural flower tea with high production capability of silver nanoparticles, we compared eight flower tea extracts for their synthesis of silver nanoparticles.
These eight types of flower teas include (Table 2.1.1 & Figure 2.1.1):
Table 2.1.1
1. Rose (Rosa)(玫瑰花茶)
2. Butterfly pea (Clitoria ternatea)(蝶豆花茶) 3. Roselle (Hibiscus sabdariffa)(洛神花茶) 4. Chrysanthemum (Chrysanthemum)(菊花茶) 5. Jiaogulan (Gynostemma pentaphyllum)(絞股蘭茶) 6. Calendula (Calendula)(金盞花茶)
7. Osmanthus fragrans (Osmanthus fragrans) (桂花茶) 8. Jasmine (Jasminum)(茉莉花茶)
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Figure 2.1.1 Different natural flower teas. (a) Rose; (b) Roselle; (c)
Chrysanthemum; (d) Butterfly pea; (e) Jiaogulan; (f) Osmanthus fragrans; (g) Jasmine; (h) Calendula.The varieties of natural flower teas were purchased from local supermarkets and pharmacies. 2 grams of different flowers teas were cut into small pieces (Figure 2.1.2);
(a) (b)
(c) (d)
(e) (f)
(g) (h)
Antibacterial activity of green synthesized AgNPs using flower tea extract
15 ml of distilled deionized water was added. The mixture was then filtered through a strainer, poured into test tubes in order to obtain an aqueous flower tea extracts. (Figure 2.1.3)
Figure 2.1.2 Various types of natural flower teas samples
Figure 2.1.3 Photo of the aqueous extracts from eight types of flower teas.
Tube1: Rose extract, Tube2: Butterfly pea extract, Tube3: Roselle extract, Tube4:
Chrysanthemum extract, Tube5: Jiaogulan extract, Tube6: Calendula extract. Tube7:
Osmanthus fragrans extract, Tube8: Jasmine extract, Tube9: Control.
2.2 Synthesis of silver nanoparticles
Silver nanoparticles were synthesized by adding the corresponding flower tea
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volume ratio at room temperature, pH 7 for 24 hours. Recent studies showed that optimization experiments indicating the application of 1:1 green extract/AgNO3 ratio is required to achieve particles with spherical morphology [3].
The solutions mixtures were incubated for silver nanoparticle synthesis in the four different methods as below Table 2.2.1. After some period of incubation, the colour of the mixture solution changed from yellow colour to dark brown colour. This colour change indicates the formation of silver nanoparticles.
Table 2.2.1
(a) Exposed to light for 24 hours with table lamp (light-induced) (b) Left in dark for 24 hours
(c) Left in normal light and dark room conditions for 24 hours ((10 hours with light and 14 hours at night, and room temperature) (d) Assisted with microwave treatment (Power of 800W [High-Mid/
Mid-Low power], a short pulse of 30 sec to 1 min)
After incubation, each solution mixture was transferred to eppendrof microtubes.
The solution mixtures were centrifuged at 13,000 rpm for 4 minutes. The supernatant was discarded and the pellet was washed with deionized water to remove any impurities.
Antibacterial activity of green synthesized AgNPs using flower tea extract
suggesting the successful synthesis of silver nanoparticles. (Figure 2.2.1) The synthesized silver nanoparticles pellet was purified and suspended in distilled deionized water.
Figure 2.2.1 Dark brown pellets sediment during centrifugation showing the
synthesis of silver nanoparticles.2.3 Characterization of synthesized silver nanoparticles
Adsorption spectra of synthesized silver nanoparticles were measured by UV-visible spectrophotometer. UV-Visible spectroscopy was operated in the wavelength range from 300 nm to 800 nm at a resolution of 10nm. The reaction mixture has an absorption maximum of 430 nm suggesting the formation of silver nanoparticles.
2.4 Investigate the efficiency of synthesized silver nanoparticles in antibacterial activity
In this experiment, the efficiency of silver nanoparticles in antibacterial activity was assayed by standard disk diffusion method against Escherichia coli. If the synthesized silver nanoparticles in our samples were efficient in killing bacteria, a clear
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in antibacterial activity was determined by measuring the diameters of the zone of inhibition. The larger the zone of inhibition, the more efficient of synthesized silver nanoparticles in antibacterial activity against E. coli.
Ch.3 Results
3.1 The effectiveness of different methods used in the synthesis of silver nanoparticles
For the synthesis of silver nanoparticles using different flower tea extract, after 24 hours of incubation at room temperature or assisted microwave treatment (four different methods), a drastic change in color from pale yellow to dark brown was observed. The color of the reaction mixture intensified to brown indicating the formation of silver nanoparticles as shown in Figure 3.1.1. This is the first kind of report on biosynthesis of silver nanoparticles using natural flower tea extract. The characteristic color change obtained may perhaps be due to reduction of AgNO3 [3,4]. The control AgNO3 solution remained as such without any change in color (Figure 3.1.1).
Antibacterial activity of green synthesized AgNPs using flower tea extract
Figure 3.1.1 Photo of the reaction mixture of synthesized silver nanoparticles from
eight types of flower teas with assisted microwave treatment.Tube1: Rose extract, Tube2: Butterfly pea extract, Tube3: Roselle extract, Tube4:
Chrysanthemum extract, Tube5: Jiaogulan extract, Tube6: Calendula extract. Tube7:
Osmanthus fragrans extract, Tube8: Jasmine extract, Tube9: Control.
After centrifugations and purification on the eight types of synthesized silver nanoparticles, UV-vis spectroscopy was performed in order to compare and analyze the concentration of synthesized silver nanoparticles in the samples. The reaction mixture has an absorption maximum of 430 nm suggesting the formation of silver nanoparticles as shown in Fig. 3.1.2 (a-d). Similar phenomenon was also reported by Srikar,et al.
[2].
The results from four different green syntheses were compared using UV-vis spectroscopy. The peak that appeared indicated the amount of silver nanoparticles in the sample. The more intense the absorbance peak is; the more synthesized silver nanoparticles were produced. It can be observed that a stronger and stronger absorbance
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with assisted microwave treatment method [Figure 3.1.2. (d)]. The peak was quite distinct and there was no obvious absorption in the range of 450–800 nm, which indicated that negligible aggregation occurs in this reactive system and the nanoparticles were well dispersed.
Here are the results from each of the four green synthesis methods: