The Antibacterial Effects Of Silver Nanoparticles Biology

Essay add: 12-10-2017, 19:38   /   Views: 15

As bacteria mutate and become resistant to different antibiotics, we must discover and develop new ways to fight these bacteria. For many years silver has been known to have antibacterial properties. This has been shown by the Ancient Greeks who used silver utensils to cook and this was seen to be more sanitary [] . Silver has also been used in the modern world in many different areas in the form of silver nanoparticles for example in toys, baby pacifiers, clothing and in laundry detergents. [] The nanoparticles have a coating around them which reduces the quantity of the elementary form of silver, and therefore are not harmful to humans as the amount of silver ions released is very low. [] However these low amounts are enough to kill microorganisms therefore silver nanoparticles are every beneficial to humans. They are quite effective as an antibacterial because the bacteria have a low chance of developing a resistance to it. [] Furthermore it is used in medicine in dressing and bandages. I thought that there was a need to investigate the antibacterial effects of silver nanoparticles and see how effective they are. As the nanoparticles are tremendously small, they have a very large surface area to volume ratio. This increases the ability to collide with other particles and therefore the antibacterial effectiveness is increased [] . The evidence present above shows why the study of this topic is significant to us and why new methods must be developed to combat diseases.

Research Question

To What Extent Do Silver Nanoparticles in a Right Guard Antiperspirant

Affect the Growth of E. Coli and S. Albus Bacteria?

Preliminary Knowledge

Human flora

There are two types of glands in the body that cause humans to sweat, the eccrine and apocrine sweat glands. [] The eccrine glands are found all over the body and they have no odour because they are mainly composed of vitamin c, water, salt and uric acid. [] The apocrine glands are located in the groin region and arm pits, although the sweat produced by these glands is odourless, they produce a distinct smell. It is in fact the bacteria that rapidly multiply in the presence of sweat, as they feed of the sweat and reproduce. [] 

Every person has different types of bacteria growing on their skin and there be about one hundred and eighty different types of bacteria growing on the skin at one time. [] Not all these bacteria are pathogenic, most of them are friendly bacteria that cause no harm to the human. The body surface of humans first gets colonized by bacteria when the mother's water breaks and birth takes place. These bacteria on our skin have many functions but in my opinion the most beneficial function is that fact that they compete with pathogens for essential nutrients and attachment sites. The most frequent bacteria occurring on the skin is s.albus, which was one of the types of bacteria I used in my investigation.

Properties and uses of silver Nanoparticles

A nanoparticle is any minute particle that is in the range of 100 to 5 nanometers in diameter and is commonly found in the form of a sphere. [] Silver is a transitional metal which has the atomic number 47 and atomic mass of 107.87. Silver has antibacterial effects because it is used in hospitals and hotels to control infectious agents and it used in space station to sterilise recycled water. In the late 1970s, it was discovered by Robert O. Becker that silver ions promote bone growth and kill surrounding bacteria [] . It is believed that silver has the ability to kill around 650 different disease causing organisms. Currently topical dressings with silver as the main constituent have been widely used as a treatment for infections in burns, open wounds and chronic ulcers. The Silver nanoparticles can be advantageous in healing diabetic wounds that are affected by many secondary infections. The fact that they cause minimal scars is one of its advantages. Some other properties of nanoparticles are microbe detection, fluotescent labelling [] destroying of tumours, and acting as multifunctional therapeutic agents. [] 

Production of silver nanoparticles

Preparing silver nanoparticles that are stable enough to considerably inhibit bacteria growth is a very hard procedure. There are several methods in which by nanoparticles are created.

One of them is to produce them by using sources that create nanoparticles in supersaturated vapours [] and is then transported through apparatus to form beams of particles in a vacuum. Most of nanoparticles produced are very reactive therefore a very clean environment is required. They can also be formed by the use of thermal plasma or by inert gas condensation. [] 

How and Why silver nanoparticles affect bacteria

Micro organisms such as bacteria contain many enzymes. Enzymes are biological catalysts that initiate or speed up reactions; these enzymes carry out precise functions for example transport. Their activities and functions can be inhibited when the silver ions break through into the micro organism cell and come into contact with the enzyme. Silver ions not only affect the functions of the enzymes but they also affect the stability of their structure. By altering the structure the enzymes do not work as effectively and therefore this could lead to some reactions not taking place. [] Essential cell components of the bacteria are removed in the process when the structural changes take place. The bacteria fight back by forming a layer around the cell membrane; however the nanoparticles are able to penetrate through this layer of resistance as well. This means that cell division of the bacteria also comes to a halt as complexes are formed between the silver ions and the DNA/RNA. [] 

Silver nanoparticles are very effective because they have large surface area to volume ratio which means that the nanoparticles have a substantial amount of direct contact with its surroundings. In addition, their relative minute size allows them to pass through the outer membranes of cells and enter the inner mechanisms of them. [] 

Differences between gram-positive and gram-negative bacteria (s. albus and E. coli)

Bacteria are either classed as gram negative or positive depending on their membrane structures. The position of the peptidoglycan [] , determines the structural difference. For example gram positive bacteria have peptidoglycan layer of about thirty nanometres thick but do not consist of a outer membrane. On the other hand, gram negative bacteria have a thin layer of peptidoglycan of about two to three nanometres between the outer and cytoplasmic membrane. [] 


To find out how and to what extent silver nanoparticles affect different bacterium and the reasons for this.

Hypothesis and Prediction

I believe that the use of silver nanoparticles will dramatically decrease the amount of bacteria compared to the antiperspirant that does not have silver nanoparticles. This is because for all bacteria to metabolise oxygen they need to use enzymes and the silver ions denature these enzymes. By doing this, the bacteria will lack oxygen and therefore they will die. Furthermore the silver nanoparticles damage the cell membranes and therefore the DNA of the bacteria cannot make any copies. In my opinion, I believe that silver nanoparticles in will have more effect on the E. Coli as it is a gram negative bacteria [] and less of an effect on S. Albus as it is a gram positive pathogen. [] This is because according to the digest journal volume 3, nanoparticles have a significant more effect on gram negative organisms than gram positive strains regardless of the resistance the strain puts up. [] 



My independent variable is the ability to alter the antiperspirant, one with silver nanoparticles and one without. I will also have a control where I will not use an antiperspirant.


My dependent variable will be the amount of bacteria that has been killed.


To ensure that my experiment is fair, I must make sure that there are no other factors affecting the results of the experiment. There are many things that could alter my results and affect the bacteria. To reduce any possible errors and anomalies I have created the following table which states what was controlled, why it needed to be controlled and how it was controlled.

Table 1: A Table to show what was controlled, why it needed to be controlled and how it was controlled.Control VariableWhy it needed to be controlledHow it was controlledType of bacteria

If the type of bacteria is varied, then I might not get an accurate account of the results as different bacteria act in different ways and the antiperspirant may affect some types of bacteria more than others.

I controlled this by using two types of bacteria, one of which was gram positive and the other gram negative. I will test out the antiperspirant on both of these bacteria and then compare these.


The antiperspirant could affect the bacteria in different ways if the temperature is changed as the bacteria could die if the temperatures are too high or too low. This would result in an unfair test as I wouldn't know what factors caused the bacteria to die.

I controlled this by carrying out all my experiments in the same room and made sure that the room stayed roughly the same temperature by making sure windows were closed and radiators were turned off. I also made sure that I did my experiment on the same day so the temperature was approximately the same.


If the time I spray the bacteria changes then the test would be unfair as the longer I spray the bacteria, the longer the bacteria is exposed to the spray and therefore more bacteria will die. This means that my test will not be accurate.

I controlled this by spraying the bacteria for five seconds, then leaving it to rest for a while then spraying each one for 5 seconds again.

Type of anti-perspirant

Different antiperspirants have different ingredients and work in different ways. This could mean that they would react with the bacteria in various ways making it an unfair test. If I changed the type of antiperspirant I would not be able to say for definite what killed the bacteria.

I controlled this by using the same brand of antiperspirant which was Right Guard. I also chose to use the same scent of antiperspirant which was Energy Burst. This would make sure that my test remains fair.

Distance of spray from agar plate

By changing the distance of the spray from agar plate would mean that the bacteria will be exposed to different quantities of the spray. This would make it an unfair test as some bacteria will be effected more than others.

I controlled this by using a tube which I covered the petri with and I placed the spray just above this each time. This ensured that the distance stayed constant.

Amount of bacteria

If I didn't know how much bacteria I had before I sprayed the antiperspirant then I wouldn't know if or how much the antiperspirant affected it. If I had different amounts of bacteria then it wouldn't be a fair test as different amounts of bacteria will die.

I controlled this by counting the bacteria using a haemocytometer set. I then carefully diluted the bacteria and used an auto pipette to place bacteria into the petri dish.


Prepared petri dishes containing agar medium and nutrients x 24

Bacteria from the technicians-

Marker pens for labeling dishes

Masking tape.

Inoculating loop


Glass Rod

Right Guard deodorants with and without silver nanoparticles

Distilled water.

200, 50, 20 m auto pipette

Plastic tubes

Plastic pipe



Firstly the petri dishes need to be prepared with the agar medium and nutrients

Place the cover glass onto the haemocytometer slide ensuring that it is secure

Using a pipette place the E. Coli under the cover glass into one of the counting chambers

Then carefully place the haemocytometer slide under a microscope

Focus the microscope so that you can only see a 16 square grid

Count all the bacteria within these squares

Multiply this by 25 as there are 25 of these grids

Record this number

Repeat the above steps for S. Albus using the other counting chamber

Dilute the both types of bacteria with distilled water correctly so that roughly 500 cells are plated

Using an auto pipette gather 1ml of the first type of bacteria and place onto the agar dish

Use a inoculating tube to spread the bacteria evenly across the agar dish

Place the inoculating tube into some ethanol and heat this using a Bunsen burner

Repeat the previous three steps for all the dishes and bacteria

Put plastic piping on top of agar dish

Hold spray directly above the tube

Spray for 5 seconds

Wait for 30seconds then replace the lid onto the agar

Repeat the previous four steps for other spray and carry out all other repeats

Leave for a day in an incubator.

Count the amount of bacteria that has been killed


Table 1 A table to show the amount of bacteria killed using anti-perspirants with and without silver nanoparticles

With silver nanoparticles

Without silver nanoparticles








Repeat 1

Repeat 2

Repeat 3


Repeat 1

Repeat 2

Repeat 3

Graphs and Charts

……… Chart

Chart 1,

………. Graph

Chart 2,


analysis of data

From my results I can verify my prediction to be true as i said that the use of silver nanoparticles will dramatically decrease the amount of bacteria compared to the antiperspirant that does not have silver nanoparticles. However from my results we can see that the antiperspirant without silver nanoparticles has killed some bacteria.

(I will add to this section after I get the results)

Explanation of Data CollectedReasoned Relation to the Research Question

To What Extent Do Silver Nanoparticles in a Right Guard Antiperspirant Affect the Growth of E. Coli and S. Albus Bacteria?

After collecting, analysing and interpreting my data I must decide whether the antiperspirant does what the manufacture says and kills bacteria. We can see that the antiperspirant with silver nanoparticles kills more bacteria than the antiperspirant without it. However the there isn't that much of a significant difference between the two sprays which could mean that the claims could be false. The manufacture could make the spray more expensive so that they could get more money as the consumer would buy it thinking that it would dramatically kill more bacteria. Furthermore they would think that the product is more effective in its job.


Every scientific experiment contains errors due to external factors, this experiment is no different. As my experiment has never been carried out before, there is no literature value to compare my results with. Nevertheless I can still discuss the problems that occurred with my experiment and the efficiency of it.

Inaccuracies could have occurred in some stages of my experiment. Firstly it was difficult to count the bacteria using the haemocytometer set and the microscope. It was hard to count the bacteria in each square as it was hard to distinguish which square the bacteria was in, this meant that some bacteria could have been counted more than once.

Another factor that could have caused anomalies or inaccuracies would be the fact that I did not know how many nanoparticles were in each can of Right Guard Energy Burst Antiperspirant. This meant that I didn't know how many silver nanoparticles were sprayed on each agar dish. Some may have had more than others with means that I do not know exactly to what extent the silver nanoparticles affect the bacteria.

One factor that could altered my results could have been when disinfecting the inoculating tube. To make sure that the bacteria didn't mix and spread from each agar dish to the next, I placed the inoculating loop in some ethanol and heated it with a Bunsen burner. However if the inoculating tube was too hot when spreading the bacteria then some bacteria may have died and therefore this could have caused my results to have changed. To overcome this I could use a different inoculating tube for each type of bacteria and wait a couple of minutes for the tube to cool down before using it the next time.

I believe that my experiment was a success as I was able to draw conclusions from my data. However I believe that my study can be developed to draw other conclusions. This will be mentioned in the Unanswered Questions Chapter.

Unanswered Questions

To investigate further, I want to find out how much nanoparticles are needed exactly to kill a specific amount of bacteria. Investigating this could help manufactures, use the correct amount of nanoparticles necessary to kill bacteria in their products and save themselves money. In my experiment I didn't know how much nanoparticles were sprayed onto each agar dish.

Furthermore I could find out more about which types of bacteria is found on the human skin and test them as well. By doing this I would be able to find what bacteria is the most vulnerable also I would be able to test if the antiperspirant does what that manufactures claims and kills these bacteria.

After doing these further investigations and research I believe that I would come to a more detailed conclusion as the data would be more significant.

Article name: The Antibacterial Effects Of Silver Nanoparticles Biology essay, research paper, dissertation