Kevin C. Langry

Force spectroscopy of the double-tethered concanavalin-A mannose bond.

We present the measurement of the force required to rupture a single protein-sugar bond using a methodology that provides selective discrimination between specific and nonspecific binding events and helps verify the presence of a single functional molecule on the atomic force microscopy tip. In particular, the interaction force between a polymer-tethered concanavalin-A protein (ConA) and a similarly tethered mannose carbohydrate was measured as 47 +/- 9 pN at a bond loading rate of approximately 10 nN/s. Computer simulations of the polymer molecular configurations were used to determine the angles that the polymers could sweep out during binding and, in conjunction with mass spectrometry, used to separate the angular effects from the effects due to a distribution of tether lengths. We find that when using commercially available polymer tethers that vary in length from 19 to 29 nm, the angular effects are relatively small and the rupture distributions are dominated by the 10-nm width of the tether length distribution. In all, we show that tethering both a protein and its ligand allows for the determination of the single-molecule bond rupture force with high sensitivity and includes some validation for the presence of a single-tethered functional molecule on the atomic force microscopy tip.

A fiber-optic sensor system for monitoring chlorinated hydrocarbon pollutants

We have developed and field-tested a fiber-optic chemical sensor system for use in environmental monitoring and remediation. The system detects chlorinated hydrocarbon pollutants with colorimetry, and is based on an irreversible chemical reaction between the target compound and a specific reagent. The reaction products are detected by their absorption at 560 nm and can be monitored remotely with optical fibers. Continuous measurements are made possible by renewing the reagent from a reservoir with a miniature pumping system. The sensor has been evaluated against gas chromatography standards and has demonstrated accuracy and sensitivity (5 ppbw) sufficient for the environmental monitoring of trichloroethylene and chloroform. Successful preliminary field tests have been conducted in a variety of contamination monitoring scenarios.

Intraoral fiber-optic-based diagnostic for periodontal disease

The purpose of this initial study was to begin development of a new, objective diagnostic instrument that will allow simultaneous quantitation of multiple proteases within a single periodontal pocket using a chemical fiber optic senor. This approach could potentially be adapted to use specific antibodies and chemiluminescence to detect and quantitate virtually any compound and compare concentrations of different compounds within the same periodontal pocket. The device could also be used to assay secretions in salivary ducts or from a variety of wounds. The applicability is, therefore, not solely limited to dentistry and the device would be important both for clinical diagnostics and as a research too.

Role of Grain Boundaries in Exceptionally H 2 Sensitive Highly Oriented Laser Ablated Thin Films of SnO2

A comparative study on growth, electrical conductivity, and sensor characteristics of highly oriented (transparent) and randomly oriented thin films of SnO 2 grown by pulsed laser (KrF: λ =248 nm) ablation technique have been carried out. Sensors made of randomly oriented polycrystalline films (deposited at 725°C on alumina) exhibited a sensitivity of about 90% for 50 ppm of H 2 at sensor operating temperatures above 240°C with a good response (∼30 s) and retracing times (180 s). Sensors made of a axis orientated films [deposited on LaAlO 3 (100) at 525°C] exhibited an exceptionally high sensitivity of 30 to 40°C even for I ppm of H 2 at 310°C with a shorter response time of about 15 s. However, the retrace time was very long (about 20 min). Sensors made of predominantly (101) orientated films [grown at 525C on sapphire (1102)] exhibited an exceptional sensitivity of 90% even for 5 ppm H 2 at 300°C also had remarkably short response times of a axis oriented films as well as the quick retracing times of polycrystalline films. Thin films, which exhibited exceptionally high sensitivity showed large changes in electrical conductivity and activation energy as function of oxygen partial pressure. Atomic force microscopy investigation reveals that the films are highly granular with average size of about 150-200 nm which is ten times larger than the critical size of 8 nm (2 x L D, as L D being 8 nm for SnO 2 ). Analysis of results based on the model for carrier transport across the grain boundaries in polycrystalline semiconductors reveals that the surface harrier height of the grain boundaries is responsible for the large variation in activation energy and sensitivity.

Ionic optodes: role in fiber optic chemical sensor technology

Fiber optic chemical sensors and solid state devices are two versatile sensing technologies for detecting analytes in a host of media. Obvious differences distinguish these technologies: however, they share significant features and issues related to analyte identification and selectivity. This report reviews transduction schemes used in fiber optic sensors for monitoring aqueous ionic species and examines some critical concerns that may hinder commercial acceptance. © 1999 Society of Chemical Industry

Fiber optic sensor for continuous monitoring of chlorinated solvents in the vadose zone and in groundwater: field test results

A fiber optic chemical sensor has been designed for groundwater and vadose zone monitoring of volatile halogenated hydrocarbons. The principle of detection is a quantitative, irreversible chemical reaction that forms visible light absorbing products. This absorption is measured remotely using fiber optics. Modifications of our previous sensor design have resulted in lower detection limits and increased durability. In this paper we describe the measurement system and present the new sensor design along with calibration data and preliminary field test results.

Simple-reversible fiber-optic chemical sensors using solvatochromic dyes

There are many environmental and process-control sensor applications where speed and reversibility are more important than selectivity. These might include monitoring the fate and transport of contaminants in laboratory columns and microcosms, measuring hydrocarbons in waste treatment streams, mapping the extent of a plume of a known contaminant, or monitoring solvent concentrations (e.g., acetone, dichloromethane, etc.) in a manufacturing process stream. In each case, there is prior knowledge of the type of contaminant and interferences, and in many cases the target molecule is at a relatively high concentration. For such applications, the sensor should be fast and reversible to allow real-time tracking of rapidly changing concentrations; however, it does not need to be very selective and might even respond to a wide variety of compounds. We are exploring new types of sensors for these applications. The sensors are based on reversible color changes that occur when solvatochromic (SV) dyes experience polarity changes. The optical sensors are made by immobilizing the SV dye in a polymer film that is coated on the end of a clad optical fiber or on the sides (i.e., evanescent region) of an unclad optical fiber. For the sensors described here interaction of a fluorescent SV dye with analyte vapors changes the amount of light absorbed by the dye and thus the fluorescence intensity that is measured with the optical fiber. Initial experiments have focused on fuel-related contaminants (e.g., xylene, benzene), and commercial solvents (e.g., acetone, dichloromethane--DCM). This paper will focus on the xylene and DCM results.

Preliminary field demonstration of a fiber optic trichloroethylene sensor

We have developed a differential-absorption fiber-optic sensor for use in groundwater and vadose zone monitoring of certain volatile organochiorides. The principle of detection is a quantitative irreversible chemical reaction that forms visible light-absorbing products. The sensor has been evaluated against gas chromatographic (GC) standard measurements and has demonstrated accuracy and sensitivity sufficient for the environmental monitoring of trace levels of trichioroethylene (TCE) and chloroform. This sensor is currently under evaluation in monitoring well and vadose zone applications. In this paper we describe the principles of the existing single measurement sensor technology and show preliminary field test results.

MiDAS (Micro-dot Array Sensor): toward a rapid, in-vivo, reproducible, multianalyte biosensor using inkjet printing technology

The Microdot Array Sensor (MiDAS) platform for making optical fiber-based sensors using inkjet printing technology is a paradigm shifting technology for delivering low cost, rapid, in-vivo, reproducible, multianalyte biosensors. A fast-response, reproducible, pH sensor is demonstrated. The MiDAS platform is very adaptable to new and existing indicator chemistries and can be used for detecting blood/gas and enzyme biomarkers.

Thermoelectric cooled, purge-and-trap device for enhancing the utility of fiber optic VOC sensors

A thermoelectric cooled, purge-and-trap device (TEC) has been developed to enhance the utility of fiber optic VOC sensors. This simple device consists of a thin copper radiator sandwiched between two thermoelectric coolers. Two water-cooled, copper heat sinks are used to maintain the hot side surfaces of the thermoelectric coolers at 5 degrees C, allowing internal surface temperatures of the radiator to be controlled between 5 degrees C to -43 degrees C. This paper describes the use of the TEC with a reversible, fiber optic, carbon tetrachloride sensor. The sensor by itself has a detection limit of around 1,000 ppmv carbon tetrachloride in nitrogen. When the sensor is used with the TEC, vapor phase concentrations down to 100 ppmv can be measured.