Critical to our ability to respond effectively to a biothreat attack is the development of sensitive and specific sensor systems that can easily be used for rapid screening of potential victims for infection due to biothreat agents and detection of pathogens in the environment. To help address these needs, we have developed a Reagentless Optical Biosensor (ROB) based on protein specific assays and waveguide-based evanescent fluorescence excitation. Modeled on host pathogen interactions, the sensor's membrane based assay provides rapid, sensitive detection without the addition of reagents. We report here the development of two waveguide based detection systems: a laboratory sensor test-bed system and a handheld, battery operated, prototype. Evanescent fluorescence excitation using planar optical waveguides provides spatial filtering of background auto-fluorescence found in many natural samples, thereby permitting direct analysis of complex environmental and medical samples. The waveguide based assay is fully self-contained in a small, exchangeable cartridge that is optically coupled to the sensor detection system making ROB simple to use and offering the possibility of inexpensive, disposable sensor elements. Using assays for cholera toxin we compare results using flourimetry of vesicle solutions against results for our waveguide based test-bed and prototype sensor systems.
We have developed a method for simple and highly sensitive detection of multivalent proteins using an optical waveguide sensor. The optical biosensor is based on optically tagged glycolipid receptors imbedded within a fluid phospholipid bilayer membrane formed on the surface of a planar optical waveguide. The binding of multivalent toxin initiates a fluorescence resonance energy transfer resulting in a distinctive spectral signature that is monitored by measuring emitted luminescence above the waveguide surface. The sensor methodology is highly sensitive and specific, and requires no additional reagents or washing steps. Demonstration of the utility of protein-receptor recognition using planar optical waveguides is shown here by the detection of cholera toxin.
Pekka Ayras, David Geraghty, Seppo Honkanen, Karen Grace, Basil Swanson, Karl Shrouf, Xiaoguang Yang, Pekka Katila, Matti Leppihalme, Ari Tervonen, Nasser Peyghambarian
A chemical sensor scheme, based on selective sensing surfaces and highly sensitive integrated optical transduction is presented. Self-assembly techniques are used to covalently attach species selective films onto the surface of silicon nitride waveguides. Exposure to targeted analytes results in selective absorption of these molecules onto the waveguide surface, causing a change in the effective refractive index of the guided modes. These relative changes in effective refractive indices of TM and TE modes are measured using Zeeman interferometry. The measurements demonstrate reversible, real time sensing of volatile organic compounds at ppm level. Improvements in the waveguide design are proposed to further increase the sensor performance.
Karen Grace, Karl Shrouf, Seppo Honkanen, Pekka Ayras, Pekka Katila, Matti Leppihalme, Roger Johnston, Xiaoguang Yang, Basil Swanson, Nasser Peyghambarian
We present a chemical sensor scheme based on selective sensing surfaces and highly sensitive integrated optical transduction methods. Using self-assembly techniques, species selective thin-films are covalently attached to the surface of Si3N4 channel waveguides to produce robust sensor elements. Exposure to targeted analytes results in the selective absorption of these molecules onto the waveguide surface causing a change in the effective refractive index of the guided modes. These relative changes in effective refractive index between TE and TM modes are precisely measured using Zeeman interferometry. Our measurements demonstrate reversible, real time sensing of volatile organic compounds at ppm levels.
A novel scheme of a laser-based chemical sensor has been examined. The scheme is based on the lasing frequency shift of a DBR laser as a result of refractive index change of the sensitive coating in the presence of chemicals in question. The applicability and advantages of different schemes are discussed. The results of preliminary experiments related to the construction and stability of an external cavity DBR laser and interferometric measurements of refractive index change are presented.
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