Nanosensors for Detection of Aquatic ToxinsEPA Grant Number: R829599
Title: Nanosensors for Detection of Aquatic Toxins
Investigators: Gawley, Robert E.
Institution: University of Miami
EPA Project Officer: Lasat, Mitch
Project Period: March 1, 2002 through February 28, 2005
Project Amount: $350,000
RFA: Exploratory Research: Nanotechnology (2001) RFA Text | Recipients Lists
Research Category: Nanotechnology , Water Quality , Safer Chemicals
Description:Design and prepare nanoscale sensors for the detection of marine toxins domoic acid, brevetoxin, ciguatoxin, cylindrospermopsin, and tetrodotoxin.
Approach:Most of these marine toxins bind specifically to protein receptor sites with a high affinity (Kd typically in the nM range). The protein receptor sites for several of these toxins have been characterized, and include two characteristic features. One is an array of amino acid side chains that complement structural features of the toxin, which facilitates and strengthens binding of the toxin into the receptor site. A second feature is a solvent-excluded pocket in which the amino acid side chains are arrayed. This preorganized feature of toxin receptor sites will be mimicked by design of synthetic receptors at the nanoscale (nanosensors). To optimize the sensitivity and the selectivity of the nanosensor, we will employ combinatorial synthesis techniques to optimize binding in libraries of peptidic host molecules immobilized on solid support (polystyrene beads). Unlike side chain arrays in the native (protein) receptors, we will not limit ourselves to L-amino acids, or even to natural amino acids. In this way, we will be able to produce short peptide sequences that wrap around toxins and bind them by providing an array of side chains similar to the native receptor. To mimic the solvent-excluded pocket of protein receptor sites, we will incorporate the combinatorially-designed peptide at the core of a dendritic polymer, still on a solid support.
The marriage of combinatorial design and dendrimer synthesis on solid support will provide large libraries (up to 100,000 members) of polypeptide hosts inside dendritic polymers, with each individual host molecule attached uniquely to a polystyrene bead. This is a novel approach in nanosensor design. To our knowledge, this is the first time combinatorially designed peptidic hosts have been incorporated into a dendrimer. Qualitative evaluation of toxin binding can be done simply with a fluorescence microscope! Quantitative analysis will be done with a specific host after it has been synthesized in bulk.
Expected Results:At present, environmental monitoring for aquatic toxins is most commonly done by mouse bioassay. Alternative methods, such as liquid chromatography coupled with mass spectroscopy (LC-MS), are extraordinarily expensive and not suitable for high-throughput analysis. In order to move away from mouse bioassay, an inexpensive, fast method is needed. We anticipate that this project will identify nanoscale sensors attached to polystyrene beads that can detect toxins using only a hand-held UV lamp and a magnifying glass.
The science behind the design of toxin sensors will lead to further developments as well. These synthetic receptors could also be used to immobilize the toxins. Although beyond the scope of the present work, the same design features we will use for mimicking toxin receptor sites can also be used to mimic enzyme receptor sites. Thus, by using models of enzyme active sites, we anticipate being able to use this methodology to mimic enzyme reactions to produce solid phase catalysts.