George P. Anderson

Spectral tuning of organic nanocolloids by controlled molecular interactions.

The controlled self-assembly of molecules and interactions between them remain a challenge in creating tunable and functional organic nanostructures. One class of molecular systems that has proven useful for incorporating tunable functionality at different length scales is liquid crystals (LCs) due to its ability to inherently self-organize. Here we present a novel approach to utilize the self-assembly of polymerizable liquid crystals to control the molecular aggregation of stable fluorescent chromophores and create a unique class of organic fluorescent nanocolloids. By adjusting the ratio between the dye and LC molecules inside the nanocolloids, we demonstrate the ability to control the molecular interactions and tune the fluorescent emission spectra of nanocolloid populations under single wavelength excitation. The single absorption spectrum and multiple emission spectra are highly desirable and reminiscent of the spectroscopic signature of quantum dots. These novel fluorescent nanocolloids have broad potential applications in fluorescent imaging and biological labeling.

Fluorescent organic nanoparticles

Fluorescence behavior of nanoparticles of several aromatic compounds was studied. Doped nanoparticles were also studied. Transparent organic nanoparticles dispersed in water were prepared by reprecipitation method. Addition of polyvinyl alcohol in water improved nanoparticle formation significantly. Fluorescence spectra and fluorescence quantum yields were measured by an absolute photoluminescence quantum yield measurement system. Although many organic compounds we studied hardly fluoresced in nanoparticles, fluorescence quantum yields of nanoparticles made of anthracene and its derivatives were relatively high. Doping of anthracene nanoparticles with naphthacene quenched fluorescence of anthracene nanoparticles and strong fluorescence of doped naphthacene was observed. Fluorescence quantum yield of naphthacene doped anthracene nanoparticles was as high as 0.68. Fluorescence lifetimes were also measured. Anthracene nanoparticles had shorter fluorescence lifetimes than anthracene molecules.

Probing kinetic enhancement of β-galactosidase-nanoparticle complexes (Conference Presentation)

Enhancement in enzymatic activity after attachment to nanoparticle surfaces has been observed in numerous enzyme systems, although the underlying mechanism for these enhancements remains largely unknown. This work explores the utility of a model based on a reaction scheme that takes into account some of the many interactions between substrate, product, and nanoparticle that can occur. This model was utilized to make predictions about the type of behavior that should manifest itself with quantum dots peripherally displayed around beta-galactosidase (&beta-gal) and confirmed empirically. &beta-gal is a homotetrameric enzyme which at ~465 kDa is significantly larger than the 4.2 nm diameter green emitting quantum dots utilized to decorate its periphery. Because &beta-gal operates near the diffusion limit, this provides an opportunity to selectively investigate certain aspects of enzyme enhancement when attached to a nanoparticle with minimal perturbation to the native enzyme structure. Enzymatic assays were performed with both free enzyme and quantum dot-decorated enzymes in a side-by-side format where kinetic processes were challenged by increasing viscosity with glycerol and competitive inhibitors such as lactose. The results from this model suggest it is possible to achieve significant enhancements in a diffusion limited enzyme’s catalytic rate ( k cat ) after NP attachment without substantial changes to the enzyme’s structure or function. Because cell free synthetic biology is gaining importance, this approach will yield insights on how enzymes can be utilized ex vivo and how being attached to NP scaffolds yields kinetic enhancement, possibly through enhanced product dissociation.