Antimicrobial Effects of Silver Nanoparticles Student Lab Activity

Home , Petri dish, Test tube, Test tube rack

Purpose: This lab was developed to test claims that colloidal silver has anti-microbial effects. Many products are on the market that have nanoparticles of silver in them. These include socks, clothing and food containers. One of their advertising claims is that the silver nanoparticles inhibit the growth of bacteria and hence reduce odors and/or spoilage.

Materials:  1 mM silver nitrate  Scissors  38.8 mM (1%) sodium citrate  Tweezers  Hot plate  E. coli bacteria culture  Small test tubes  Filter paper  250 mL beaker  Q-tip swabs  Disposable transfer pipets  Incubator  Agar plates  Small plastic petri dishes

Procedure:

1. Make colloidal silver using the following method: a. Add 2 mL of silver nitrate to a small test tube. b. Place this test tube in a 250 mL beaker of hot water. c. Leave in the beaker of hot water for about 10 minutes. d. Add 7 drops of sodium citrate to the test tube containing hot silver nitrate. e. Continue to heat until the silver nitrate solution turns color (yellowish). f. Remove test tubes and set in a test tube rack to cool. 2. Cut filter paper into small squares. 3. Place filter paper squares in a small petri dish and pour the test tube of colloidal silver over the squares. 4. Let the filter paper squares soak for about 10 minutes (can be even longer). 5. While waiting for the filter paper to soak, mark the bottom of a petri plate with initials, divide the bottom into sections and label each of the sections. Remember to set up control for comparison. 6. Use a 1 mL disposable transfer pipet and spread 1 drop of the bacteria culture on the agar plate using a Q-tip swab. 7. After 10 minutes of soaking, place filter paper squares in the designated areas. 8. Incubate the petri plates overnight at 37 degrees Celsius. 9. On the second day of this activity, the petri plates should be removed from the incubator and examined.

Analyze Data:

1. Draw your petri plate; be sure to include your labels.

2. Describe the bacterial growth in each labeled section.

3. How do you explain any differences that you observe?

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Questions:

1. Are products containing silver nanoparticles justified in claiming that these products have antimicrobial effects?

2. What conclusions can you draw about the effect of silver nanoparticles to bacterial cell growth based on these images?

SEM images of Healthy E. coli (left) and E. coli cultured in the presence of silver nanoparticles (right)

University of Illinois • Caltech • Stanford University • North Carolina A&T