Colloidal Crystal Engineering with DNA: A Laboratory Experience for Undergraduate Students

Here, we introduce a laboratory experiment for upper-division undergraduate students that provides a hands-on experience geared toward teaching key concepts in nanoscience by taking students through each step of an experiment involving colloidal crystal engineering with DNA. Students synthesize ∼13 nm citrate-capped gold nanoparticles, characterize them using UV-vis spectroscopy, and functionalize them with DNA in the first laboratory period. In the second laboratory period, the nanoparticles are purified via centrifugation and subsequently characterized using UV-vis spectroscopy. Dynamic light scattering and zeta potential measurements are used to compare their size and surface charge before and after DNA modification. DNA linker strands are added to the solutions, which are then slowly cooled to attain the colloidal crystal products. The products are characterized using optical microscopy during the third laboratory meeting. The experiment was implemented at the end of an upper-division laboratory course for chemistry majors and facilitates discussion of the nanoscale size regime, the consequences of miniaturization and relevant techniques that can be used to explore such consequences, and the parallels between colloidal crystals and atomic inorganic crystals. Overall, the experiment teaches students how inorganic particles are synthesized, the crucial role of ligands in stabilizing them, how appropriately designed nanoparticle-DNA conjugates can be viewed as programmable atom equivalents (PAEs), the design rules that govern PAE assembly, and the techniques that can be used to characterize both the individual particles and the crystalline lattices that result from their assembly.