Biomolecular synthesis of quantum dot composites

Nanometer size or so-called Quantum-dot size particle composites can exhibit large optical nonlinearities which make them of interest for many applications such as optically addressed switching and thresholding. They are also inexpensive and could support array addressing. An important advantage of these kinds of nonlinear media is that they can be produced in bulk and one has control over the particle type, size, shape and concentration. One can also select the host medium in which the particles are placed. Further, depending on the particular physical mechanism exploited for the bulk material's nonlinear properties, one has a choice of response times from picoseconds to seconds. Indeed, by engineering a material to have nonlinear properties arising from two different physical mechanisms, bistable behavior is expected. These many degrees of freedom permit the fine tuning of the optical nonlinearity in order to tailor it for specific applications. This produces a degree of flexibility not offered by alternative nonlinear media. A biomimetic approach utilizing biomolecular self-assembly is described to form nanometer particle size composites for uses, such as, nonlinear optical media. Yeast tRNA was utilized as an ion-exchange/nucleation site within a polymeric matrix (polyacrylamide). Cadmium ion-exchange and subsequent sulfide precipitation resulted in formation of nanometer particle size composites. Illumination of samples with an Argon laster (514 nm) utilizing the Z-scan measurement method resulted in third order nonlinearity values of +2.7×10esu.