Research Experience for Undergraduates

Silica nanospheres, developed in the laboratory of Professor Randy Duran and shown in the TEM image above, serve as a novel means for the enclosure of an organic solvent within a porous shell. Technologies based on the nanospheres would use them as containers for collection (our focus) or release of small lipophilic molecules; two possibilities for practical application of this technology are the detoxification of blood as well as environmental cleanup . Important in any attempt to develop nanosphere technologies would be an understanding of the movement of molecules into and out of the nanospheres.

Our work employs electrochemistry and fluorescence spectrometry in an attempt to determine the relative concentrations of molecules in solution and in the nanospheres, to model the diffusion of small molecules into and out of the nanospheres, and to locate the introduced molecules within the nanospheres. Specifically, because the peak cyclic voltammetry current in our system is proportional to small molecule concentration , electrochemistry allows us to quickly and accurately measure changes in the concentration of small molecules in solution. This would ideally enable us to find the speed and extent to which the nanospheres remove a drug-like molecule from into solution. Thus far, nanospheres have been quite effective in removing the small molecules tested from the biologically relevant medium of water. In the case of thicker-shelled nanosphere specimens, electrochemistry has also given us data on the kinetics of small molecule diffusion, and this data is in agreement with the complicated time-dependency expected for diffusion across a spherical boundary.

In addition to giving concentration data through fluorescence intensity, the small molecule we have chosen for fluorescence spectrometry is solvatochromic (the wavelengths of absorption and emission depend on the medium of solvation). Thus, fluorescence can also tell us about the positioning of the small molecule within the nanospheres. Careful study of a variety of small molecules in conjuction with nanospheres of varying shell thickness should allow us to gain useful insight regarding diffusion into and out of silicon nanospheres. Beyond practical applications, the nanosphere diffusion system is unique in its combination of inhomogenous layers and spherical symmetry. Experimental systems involving truly spherical diffusion are somewhat uncommon, especially on a nanometer scale; analysis with Einstein's diffusion equation may prove an interesting theoretical challenge.