Catalysis and Nanomaterials Laboratory

12. J. A. Kloepfer, R. E. Mielke, M. S. Wong, K. H. Nealson, G. Stucky and J. L. Nadeau, "Quantum Dots as Strain- and Metabolism-Specific Microbiological Labels" Appl. Environ. Microbiol. 69, 4205-4213 (2003). DOI:10.1128/AEM.69.7.4205-4213.2003

Biologically conjugated quantum dots (QDs) have shown great promise as multiwavelength fluorescent labels for on-chip bioassays and eukaryotic cells. However, use of these photoluminescent nanocrystals in bacteria has not previously been reported, and their large size (3 to 10 nm) makes it unclear whether they inhibit bacterial recognition of attached molecules and whether they are able to pass through bacterial cell walls. Here we describe the use of conjugated CdSe QDs for strain- and metabolism-specific microbial labeling in a wide variety of bacteria and fungi, and our analysis was geared toward using receptors for a conjugated biomolecule that are present and active on the organism’s surface. While cell surface molecules, such as glycoproteins, make excellent targets for conjugated QDs, internal labeling is inconsistent and leads to large spectral shifts compared with the original fluorescence, suggesting that there is breakup or dissolution of the QDs. Transmission electron microscopy of whole mounts and thin sections confirmed that bacteria are able to extract Cd and Se from QDs in a fashion dependent upon the QD surface conjugate.

11. J. N. Cha, M. H. Bartl, M. S. Wong, A. Popitsch, T. J. Deming and G. D. Stucky, "Microcavity Mode Lasing from Block Peptide Hierarchically Assembled Quantum Dot Spherical Resonators" Nano Lett. 3, 907-911 (2003). DOI:10.1021/nl034206k

Quantum dot (QD) resonators for microcavity lasing applications were successfully synthesized by a single system diblock copolypeptide mediated process. Using specifically tailored block peptides and nanoparticles, we present here the cooperative assembly of cadmium selenide (CdSe) QDs and silica nanoparticles into 3-dimensional microcavities with a high QD volume fraction. These hollow QD microspheres are a perfect combination of both quantum and optical confinement, in which the electronic states of the 3-dimensional confined semiconductor nanocrystals are coupled to the photonic states of the spherical microcavity. We show that the specific interaction between the mode properties of the cavity with the emission of its QD building blocks leads to room-temperature microcavity lasing without the use of additional mirrors, substrate spheres, or gratings.

10. J. N. Cha, H. Birkedal, M. H. Bartl, M. S. Wong and G. D. Stucky, "Spontaneous Formation of Nanoparticle Vesicles from Homopolymer Polyelectrolytes" J. Am. Chem. Soc. 125, 8285-8289 (2003). DOI:10.1021/ja0279601

Nanoparticle vesicles were spontaneously assembled from homopolymer polyamine polyelectrolytes and water-soluble, citrate-stabilized quantum dots. The further addition of silica nanoparticles to a solution of quantum dot vesicles generated stable micrometer-sized hollow spheres whose walls were formed of a thick, inner layer of close-packed quantum dots followed by an outer layer of silica. The method employed here to assemble both the nanoparticle vesicles and the hollow spheres is in direct contrast to previous syntheses that use either tailored block copolymers or oil-in-water emulsion templating. We propose that the formation of charge-stabilized hydrogen bonds between the positively charged amines of the homopolymer polyelectrolytes and the negatively charged citrate molecules stabilizing the quantum dots is responsible for the macroscopic phase separation in this completely aqueous system. The ease and processibility of the present approach gives promise for the production of a diverse array of materials ranging in applications from drug delivery to catalysis to micrometer-scale optical devices.