Citrate Synthesis of Gold Nanoparticles

The synthesis procedure shown here is from A. D. McFarland, C. L. Haynes, C. A. Mirkin, R. P. Van Duyne and H. A. Godwin, “Color My Nanoworld,” J. Chem. Educ. (2004) 81, 544A. The electrolyte analysis of sports drinks was developed by Andrew Greenburg.

Properties of materials change at the nanoscale. In bulk at the macroscale, the element of gold is gold colored, but at the nanoscale, the element of gold is red to purple in color. The formation of gold nanoparticles can be therefore observed by a change in color since small nanoparticles of gold are red. The layer of absorbed citrate anions on the surface of the nanoparticles keep the nanoparticles separated, and the presence of this colloidal suspension can be detected by the reflection of a laser beam from the particles. Switching to a smaller anion allows the particles to approach more closely and another color change is observed.

Safety:

  • Wear eye protection
  • Chemical Gloves Recommended
  • Never look directly into a laser or shine a laser at another person

Inclusive Teaching Practices:

Inclusive teaching refers to methods that are designed to engage students in learning that is meaningful, relevant, and accessible to all. Equitable learning environments provide supports to address individual student needs and promote learning for all students. Creating an inclusive classroom is a semester long process that should begin before the term with development of your syllabus and lesson plans.

This nanogold particle synthesis lab contains specific inclusive teaching strategies that align with the learning objectives of the experiment. Creating Learning Objectives makes it clear for all students, regardless of their background, what knowledge or skills you expect them to learn by conducting the laboratory/experiment.

Learning Objectives – Students will:
  1. Synthesize gold nanoparticles and observe how the color of nanomaterials can be different than the color of bulk materials.
  2. Explore how changes in reducing agent concentration/strength and mixing speed effect the color of the nanoparticles.
  3. Use various methods to determine whether gold nanoparticles were formed (e.g. diffraction of a laser pointer beam or spectrophotometry).
  4. Measure the effect of the electrolytes in several different solutions on the nanoparticles.
  5. Interpret the collected data to accurately rank materials based upon their impact on the nanoparticles.
  6. Work in groups to practice safe and effective laboratory practices while synthesizing and testing the nanoparticles.

We find that it works best to have students work in groups of 3-4 for this laboratory. Forming functional groups is a challenging process that all instructors face in the classroom.

Some strategies to build functional groups :

  1. Deliberately assign students to small, heterogeneous groups that do not isolate underrepresented students. (e.g., when possible, avoid having one female student in a group with 3 male students.)
  2. Pair students who may be less proficient in English with culturally-sensitive classmates. (Wlodkowski and Ginsberg, 1995)
  3. Balance leadership roles across ethnic and gender groups and monitor the roles in group activities. (Van Note Chism and Pruitt, 1995; McKay, 2001). For example, assign students in each group roles (e.g., recorder, reporter, discussion facilitator). Make sure that students rotate roles regularly.
  4. Help students learn to work in groups by discussing group process issues in class and by addressing issues as they arise. (Saunders and Kardia, 2000) For example, have students explore Constructive and Destructive Group Behaviors to help them understand what positive and negative traits they bring to their group.