Grantee Research Project Results
Final Report: Aptamer Capture and Optical Interferometric Detection of Cyanobacteria
EPA Grant Number: R833839Title: Aptamer Capture and Optical Interferometric Detection of Cyanobacteria
Investigators: Campbell, Daniel P , Ellington, Andy , Xu, Jie
Institution: Georgia Institute of Technology , The University of Texas at Austin
EPA Project Officer: Aja, Hayley
Project Period: June 1, 2008 through April 30, 2011 (Extended to January 31, 2013)
Project Amount: $600,000
RFA: Development and Evaluation of Innovative Approaches for the Quantitative Assessment of Pathogens and Cyanobacteria and Their Toxins in Drinking Water (2007) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Objective:
The objective of this program is to take the optical interferometric sensor that has been under development at the Georgia Tech Research Institute for the past 2 decades and configured it to detect and monitor a series of cyanobacterial toxins. After initial testing with known antibodies for a series of cyanobacterial toxins, the detection scheme will convert over to aptamers to provide a more rugged, reusable sensor for field deployment.
Cyanobacterial toxins have been recognized as a potential hazard in drinking water throughout the world. These bacteria are ubiquitous, growing wherever the conditions are favorable that includes almost any standing water one can imagine such as a freshwater pond, a swampy area, a dog’s water bowl and even one’s family’s toilet. Cyanobacterial toxins have been categorized into three groups based on their chemical structures. The toxins with highest priority are the neurotoxins anatoxin-a, cylindrospermopsin and most frequently found microcystin-LR. Their chemical structures of the more common toxins are shown in Figure 1.
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Interferometric Sensor</h2>
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Optical biosensors have been the subject of intense interest over the past 2 decades. This is due to the numerous advantages provided by optical methods, such as they can be miniaturized, have multiplexing capabilities, and because optical biosensor technology combines rapid response times with high sensitivity for analyte evaluation. One such emerging technology is the planar waveguide evanescent sensor combined with state-of-the-art surface functionalization chemistries. The waveguide evanescent sensor relies on monitoring the perturbation of the planar waveguide mode effective index resulting from the interaction of the evanescent tail of the mode with a changing ambient medium. For many applications, this medium is a solution containing molecules such as proteins, DNA, RNA, antigens or antibodies, which bind to a layer of receptor molecules immobilized on the waveguide surface. Several transducers have been developed using evanescent field for sensing including interferometer,<a href= "Schneider, 1997 #278")
1 grating coupler2 and SPR.3 The interferometric sensors generally have the highest sensitivity, compared to SPR and grating coupler-based sensors. This is mainly based on possibility of using large interaction length values resulting in enhanced sensitivity. A typical value of 1.5 cm is used for the interferometer, being an order of magnitude larger than the typical values of 1 mm for the grating coupler and 10-100 μm for the SPR sensors. We have developed a planar waveguide interferometric sensor capable of simultaneously detecting a wide array of analytes, including toxins, viruses, spores and whole cell bacteria as well as chemical threats in a fast, direct and sensitive method.1, 4 The waveguide is fabricated with an array of sensing interferometers capable of detecting multiple analytes at once and requiring only a single light source and detector to analyze the multiple sampling channels fabricated onto a single 1.6 x 3.3 cm glass substrate. Sensitivities for this sensor are in the pg/ml, <1000 cfu/ml, <.0005 HA units/ml and/or ppt levels of proteins, spores/cells, viruses and/or chemicals, respectively.
At the heart of the GTRI optical sensor is a planar optical waveguide. Planar waveguides are related to fiber optic waveguides in that a high refractive index material is used to guide the light within its confines through total internal reflection. Whereas a fiber optic’s high refractive index core is surrounded by a lower refractive index cladding, the planar waveguide has the high refractive index waveguiding layer deposited on top of a lower refractive index planar substrate. Planar waveguides have evanescent fields, the tail of the electromagnetic field associated with the propagation of light, sensitive to index of refraction changes in the volume immediately above the waveguide surface. These fields extend up to 500 nanometers (nm) above the surface. Coupling a bioreceptor, such as an antibody, to the waveguide surface provides the basis for a biosensor (Figure 1). Briefly, light from a diode laser is coupled into the planar waveguide with a grating etched in the glass substrate. When a test solution containing the target antigen is introduced to the functionalized waveguide, the antigen binds to the receptor and displaces water near the waveguide surface causing a change in the velocity of the propagating light. To measure this change, an adjacent but unperturbed reference beam is optically combined with the sensing beam (Mach-Zender interferometer), creating an interference pattern of alternating dark and light fringes (Figure 2). When refractive index changes occur in the sensing arm, the interference pattern shifts, producing a resultant change in the relative phase that is measured using a Fourier transform algorithm indicating the presence and concentration of the target antigen. No secondary or reporter antibody is required. With detection sensitivities on the order of 0.01 radians, refractive index changes of less than 10-6 can be measured. This design provides a direct, label-free and reagentless means of detection.
Schneider, B. H.; Edwards, J. G.; Hartman, N. F., Hartman interferometer: versatile integrated optic sensor for label-free, real time quantification of nucleic acids, proteins, and pathogens. Clinical Chemistry 1997, 43 (9), 1757-1763.
Supplemental Keywords:
Interferometric sensor, aptamer, microcystin, waveguide, water, environmental chemistry, health risk assessment, environmental monitoring, drinking water, environmental engineering, microbial contamination, monitoring, real time analysis, microbial risk assessment, gene microarray assay, aquatic organisms, other - risk assessment, early warning, drinking water contaminants, cyanobacteria;, RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Water, Health Risk Assessment, Environmental Chemistry, Drinking Water, Environmental Engineering, Environmental Monitoring, microbial contamination, gene microarray assay, early warning, microbial risk assessment, monitoring, aquatic organisms, drinking water system, drinking water contaminants, other - risk assessment, cyanobacteriaProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.