Nanotechnology 101
Due: Thursday, October 20th
Lab: Bottom-Up Nanotechnology
There are two general approaches for the production of nanostructures: top-down and
bottom-up. This lab will focus on a synthesis of gold nanostructures created using a
bottom-up, “bench-top” synthesis approach.
One of the most captivating aspects of studying structures on the nanoscale is that they
exhibit fascinating size-dependent properties. When nanostructures are very similar in
size to the wavelength of visible light (350-700 nm), the nanostructures and light interact
in interesting ways. The optical properties (and thus color) of certain nanostructures
depend strongly on the nanostructures’ sizes and shapes. The size-dependent optical
properties of gold nanostructures can be exploited for a variety of applications,
including as sensors.
Purpose:

To use a bottom-up approach for the synthesis of gold nanoparticles.

To observe the effect of size on optical properties of gold nanoparticles.

To create and test a gold nanoparticle-based “salt sensor.”

To use the sensor to detect the presence of salt in a series of unknowns.
Materials:

Hydrogen tetrachloroaurate (III) hydrate (HAuCl4 x H2O), 1 mM solution

Sodium citrate tribasic dihydrate (Na3C6H5O7 x 2H2O), 38.8 mM solution

Sodium chloride (NaCl)

Sugar (sucrose)

Beaker (50 ml)

Graduated cylinder

Spatula

Test tubes

Test tube rack

Stir/hot plate, stir bar

Pipettes

Cuvettes

SpectroVis (one instrument per class)
Waste disposal: All solutions should be collected in the waste beaker in the front of the
classroom.
Procedure (work in pairs or groups of three):
Part 1. Synthesis of Gold Nanoparticles
1. Measure out 30 ml hydrogen tetrachloroaurate (III) hydrate solution into a 50
or 100 ml graduated cylinder.
2. Pour the measured hydrogen tetrachloroaurate (III) hydrate solution into a 50
ml beaker.
3. Add a magnetic stir bar and heat the solution to boiling on a stir/hot plate
while stirring.
4. After the solution begins to boil, add 3 ml of the sodium citrate tribasic
dehydrate solution
5. Continue to boil and stir the solution until it is deep red in color (about 10
min). As the solution boils, add distilled water to keep the total solution
volume near 33 ml.
6. When the solution is a deep red color, turn off the hot plate and stirrer and let
the solution cool to room temperature.
7. Prepare (and label!) two “standard” solutions in test tubes or small beakers:
a. ~2 M salt standard: dissolve 0.5 g NaCl in 5 ml distilled water.
b. ~2 M sugar standard: dissolve 2 g sugar in 5 ml distilled water.
Save these solutions for step 9.
8. Prepare five test tubes by adding 3 mL of the gold nanoparticle solution and
3 mL of distilled water to each test tube. Label the test tubes.
9. With a dropper, add 5-10 drops of solution into vials as described:
Test Tube 1
Test Tube 2
Test Tube 3
Test Tube 4
Test Tube 5
Sugar
solution
Salt solution
Unknown A
Unknown B
Unknown C
10. Record your observations on the table in the data section.
Part 2. Analysis of Colloidal Gold
1. Obtain five cuvettes.
2. Fill one cuvette about ¾ full with one of your solutions. Repeat so that you
have one cuvette for each solution.
3. Find the cuvette with distilled water (near or in the SpectroVis) and place it
in the sample chamber of the SpectroVis.
4. Follow the instructions in the dialog box to complete the calibration, and then
click OK.
5. Place one of your cuvette samples in the sample chamber of the SpectroVis.
6. Click
.
7. Click
to end data collection.
8. Record the wavelength of maximum absorbance for each solution in the data
table.
9. Repeat analysis for each solution.
Post-Lab:
At the beginning of class on Thursday, October 20th, please turn in your data table and
(on a separate sheet of paper) your short answers to the conclusion questions. Please
type your answers or write them very clearly.
Data:
Vial Number
1
2
3
4
5
Testing
Solution
Sugar
Salt
Unknown A
Unknown B
Unknown C
Observations
(Color)
λ of maximum
absorbance
(
)
Conclusion Questions:
1. Based on the fact that the citrate anions cover the surface of each nanoparticle,
explain what keeps the nanoparticles from sticking together (aggregating) in the
original solution.
2. Why does adding the salt solution produce a different result from adding the
sugar solution?
3. Identify each of the unknowns and explain your reasoning. (Hint: can you
determine if one of the unknowns contains salt and sugar?)
4. How could the optical property dependence of gold nanostructures be used to
detect the binding of biomolecules, such as DNA or antibodies, which stick to
one another or to other molecules?
5. What does the absorbance tell us about the color?
(Hint: the complementary color of the solution is the wavelength most absorbed.)