Mark E. Jones

Interferometric optical fiber microcantilever beam biosensor

With the proliferation of biological weapons, the outbreak of food poisoning occurrences, and the spread of antibiotic resistant strains of pathogenic bacteria, the demand has arisen for portable systems capable of rapid, specific, and quantitative target detection. The ability to detect minute quantities of targets will provide the means to quickly assess a health hazardous situation so that the appropriate response can be orchestrated. Conventional test results generally require hours or even several days to be reported, and there is no change for real-time feedback. An interferometric optical fiber microcantilever beam biosensor has successfully demonstrated real time detection of target molecules. The microcantilever biosensor effectively combines advanced technology from silicon micromachining, optical fiber sensor, and biochemistry to create a novel detection device. This approach utilizes affinity coatings on micromachiend cantilever beams to attract target molecules. The presence of the target molecule causes bending in the cantilever beam, which is monitored using an optical displacement system. Dose-response trials have shown measured responses at nanogram/ml concentrations of target molecules. Sensitivity is expected to extend from the nanogram to the picogram range of total captured mass as the microcantilever sensors are optimized.

Fiber-optic-based biosensors utilizing long period grating (LPG) technology

A biosensor based on long period grating (LPG) technology has been used to demonstrate the detection of large molecules (proteins) and small molecules (pesticides). The LPG sensor is a spectral loss optical fiber based system that provides direct detection of large molecules, by using an antigen or antibody modified hydrogel, without the need for secondary amplification. The binding of the specific target results in a mass increase that produces a localized refractive index change around the LPG region and thus a spectral shift in the observed wavelength loss band. The magnitude of the observed shift can be correlated to target concentration. The HIV protein p24 was directly detected at 1 ng/mL with a specific signal that was 5 - 7 times that of the system noise. A direct and indirect competitive assay was demonstrated with the target atrazine. The sensitivity of the two competitive assay formats was in the range of 10 - 50 ng/mL. In all three-assay examples, the biosensor was regenerated by treatment with 50 mM HCl and reused. The LPG biosensor offers speed (results in less than five minutes), versatility, reuse, specificity and sensitivity.

Long-period gratings as flow sensors for liquid-composite molding

One of the most important issues in liquid composite molding (LCM) is the complete saturation of the preform by the resin to eliminate voids or dry spots in the structure which could later adversely affect the structural integrity of the part. While there have been efforts in developing reliable mold filling simulations for LCM, very few successful flow sensing systems exist for detecting actual resin arrival during mold filling. In this study, the feasibility of using optical fibers with long period gratings (LPG) as sensors for monitoring flow in the LCM process was investigated. An advantage of using LPGs is that they are more robust and less susceptible to background noise than simple bare fibers. Furthermore, the location of resin arrival can be easily identified as the signals from each LPG uniquely correspond to predetermined wavelengths along the source spectrum. The LPGs are sensitive to changes in the refractive index and register a strong signal change when covered with resin. In this study, the LPG sensors were placed in the middle of a preform stack inside a mold and the sensor response after the mold was properly closed, and when the resin covered a particular LPG was monitored. An assortment of preforms, which included random mats and unidirectional fabrics, with a series of fiber volume fractions were used to determine their effects on the sensor response.

Kinetic behavior of polymer-coated long-period-grating fiber-optic sensors.

A new method of analysis employing the time-dependent response of long-period-grating (LPG) fiber-optic sensors is introduced. The current kinetic approach allows analysis of the time-dependent wavelength shift of the sensor, in contrast to previous studies, in which the LPG sensing element has been operated in an equilibrium mode and modeled with Langmuir adsorption behavior. A detailed kinetic model presented is based on diffusion of the analyte through the outer protective membrane coating into the affinity coating, which is bound to the fiber cladding. A simpler phenomenological approach presented is based on measurement of the slope of the time-dependent response of the LPG sensor. We demonstrate the principles of the kinetic methods by employing a commercial Cu+2 sensor with a carboxymethylcellulose sensing element. The detailed mathematical model fits the time-dependent behavior well and provides a means of calibrating the concentration-dependent time response. In the current approach, copper concentrations below parts per 10(6) are reliably analyzed. The kinetic model allows early-time measurement for low concentrations of the analyte, where equilibration times are long. This kinetic model should be generally applicable to other affinity-coated LPG fiber-optic sensors.

Flight Demonstration of Fiber Optic Sensors

Luna Innovations has developed a prototype 8-channel fiber optic sensor system to demonstrate fiber optic sensor operation in flight environments. As an intial flight demonstration, long period grating (LPG) relative humidity sensors along with extrinsic Fabry-Perot interferometric (EFPI) pressure and temperature sensors were installed in an aging Delta 767-300ER jet. The fiber optic signal-conditioning system is a multi-purpose platform that can also be used to operate other types of fiber optic LPG and EFPI sensors, including strain gages, metal-ion corrosion sensors, and fiber Bragg grating (FBG) sensors. The system configuration and operation is described.

Fiber optic affinity ligand sensor for quantification of petroleum and bioremediation

A novel system incorporating optical fiber long-period grating (LPG)-based sensors for rapid detection of biological targets is presented to address the current need for highly responsive, inexpensive, instrumentation for in-situ subsurface bioremediation technologies. With the appropriate configuration, the LPG sensor is able to measure key environmental parameters. The sensor allows for highly sensitive, real-time, refractive index measurements and by applying affinity coatings to the fiber surface, specific binding of molecules can be accomplished using swellable polymers or ligand-based affinity coatings. Advantages of the sensors have are that they are highly responsive, low profile, and can be serially multiplexed within a single-ended probe-like arrangement. This arrangement can be utilized either locally for site characterization or as a distributed sensor to map contaminant levels at multiple depths over a large area. The performance advantages make optical fiber sensors ideal for detection of environmental targets in drinking water, groundwater, soil, and other complex samples. This paper presents recent long-period grating-based sensor results that demonstrate the potential for bioremediation as well as a variety of other chemical and biological sensing applications.