Jose L. Melendez

A commercial solution for surface plasmon sensing

A novel, fully integrated surface plasmon resonance (SPR) transducer is described which is based on the encapsulation of the required electro-optical components within the optical material, through a molding process. Prototype sensors based on this approach have been successfully fabricated and tested. Results are shown for sensing of refractive index variations in alcohol solutions. Additionally, the SPR transducer is shown to function as a biological sensor.

Detection of Staphylococcus aureus enterotoxin B at femtomolar levels with a miniature integrated two-channel surface plasmon resonance (SPR) sensor

Surface plasmon resonance (SPR) biosensors offer the capability for continuous real-time monitoring. The commercial instruments available have been large in size, expensive, and not amenable to field applications. We report here an SPR sensor system based on a prototype two-channel system similar to the single channel Spreeta devices. This system is an ideal candidate for field use. The two-channel design provides a reference channel to compensate for bulk refractive index (RI), non-specific binding and temperature variations. The SPR software includes a calibration function that normalizes the response from both channels, thus enabling accurate referencing. In addition, a temperature-controlled enclosure utilizing a thermo-electric module based on the Peltier effect provides the temperature stability necessary for accurate measurements of RI. The complete SPR sensor system can be powered by a 12V battery. Pre-functionalized, disposable, gold-coated thin glass slides provide easily renewable sensor elements for the system. Staphylococcus aureus enterotoxin B (SEB), a small protein toxin was directly detectable at sub-nanomolar levels and with amplification at femtomolar levels. A regeneration procedure for the sensor surface allowed for over 60 direct detection cycles in a 1-month period.

Development of a surface plasmon resonance sensor for commercial applications

Abstract An optical tabletop system based on surface plasmon resonance (SPR) for refractive-index determination has been developed to demonstrate the feasibility of a miniaturized and integrated concept which is also described. The tabletop system is constructed from the ‘miniaturizable’ components required to realize a manufacturable, integrated minisensor utilizing the SPR phenomenon for transduction. The tabletop system exhibits adequate sensitivity, stability, and reproducibility while maintaining overall system simplicity. The sensor system is excited by a near-infrared light-emitting diode (LED) available in die form, since a laser source is impractical for the miniaturized sensor. The light is optically coupled into a plastic prism because the minisensor optics are readily molded using plastics or epoxy, rather than glass. The angular composition of the diverging reflected radiation is then separated and quantified by a photodiode array (also available in die form) consisting of pixels on a 63 μm pitch. A sputtered gold film is used as the SPR excitation layer. The sensor system performance is qualified using aqueous solutions containing ethylene glycol. The response to changes in concentration of the ethylene glycol is found to be on the order of one part in 10 4 . This translates to a refractive-index change of approximately 10 −5 . The stability of the system response has been investigated by quantifying the response change in water over a two-day period. The stability is excellent when temperature compensation is implemented. The components utilized in the tabletop system are consistent with the development of a low-cost miniature integrated surface plasmon sensor. Such a device has been constructed. A sketch of a minisensor is shown, along with preliminary response data.

Construction of biosensors using a gold-binding polypeptide and a miniature integrated surface plasmon resonance sensor

Surface plasmon resonance (SPR) biosensors were constructed on miniature integrated sensors. Recognition elements were attached to the sensor surface using a gold-binding repeating polypeptide. Biosensors with fluorescyl groups attached to their surfaces were functional for at least 1 month of daily use with little decrease in response to the binding of an anti-fluorescyl monoclonal antibody. The coupling of protein A to the gold-binding polypeptide on the sensor surface enabled the biosensor to detect the binding of antibodies to the protein A and provided a sensor with convertible specificity. The system described herein provides a simple and rapid approach for the fabrication of highly specific, durable, portable and low cost SPR-based biosensors.

Integrated analytical sensors: the use of the TISPR-1 as a biosensor

Abstract The TISPR-1 integrated surface plasmon resonance (SPR) sensor has features that make it ideal for use in a distributed sensor environment. This sensor, combined with simple bio-films, is shown to be capable of a wide variety of bio-assays. Data for a direct-binding assay for creatine kinase MB (CK-MB), for a displacement assay for dinitrophenol-glycine (DNP-GLY) and a competition assay for trinitrotoluene (TNT) are presented. Also, current and projected TISPR-1 sensor system limits of detection are discussed.

Fundamental system for biosensor characterization: application to surface plasmon resonance (SPR)

The aim of the described research is to develop a general system for characterizing and developing signal transduction systems for microbiosensors. The approach that we are using is applicable to signal transduction systems based on surface plasmon resonance, chemiluminescence, fluorescence, mass as well as other phenomena. The specific goal of our approach is to develop a general system that will allow for the systematic characterization of the effects of the affinity of the sensor specificity element for the target analyte, the effect of analyte mass on signal size and the general performance of the sensor system with respect to sensitivity and selectivity. At the same, time this system should allow for the characterization of the distribution of biospecificity elements on the sensor surface. We chose the anti-fluorescein monoclonal antibody approach for this development system, since the antigen fluorescein can be attached to many different molecules and organisms through free amine groups via reaction with fluorescein isothiocyanate. Also, well characterized monoclonal antibodies with a broad range of Kd values are available. We also describe rapid procedures for generating proteins for use in biosensor applications.

The role of the insulator in determining 1/f noise in Hg 1− x Cd x Te integrating MIS devices

The low frequency 1/f noise charge found in Hg1-xCdxTe integrating metal-insulator-semiconductor (MIS) devices operating at 40K and low bias above threshold is found to be independent of integration time. The signal theory of random processes is utilized to demonstrate that 1/f noise charge resulting from carrier number fluctuations due to insulator traps should not depend on integration time, while 1/f noise charge resulting from 1/f noise in any current filling the MIS well should be proportional to integration time. This distinction allows for the determination of effective insulator trap densities from low temperature 1/f noise data on simple MIS structures. The technique is applied to a number of n-channel and p-channel devices and the effective trap densities in ZnS are determined.

Detection of a polynitroaromatic compound using a novel polymer-based multiplate sensor

A novel sensor concept for detection of polynitroaromatic compounds has been developed in a partnership between Texas Instruments and the University of New Hampshire. The objective for this sensor is to demonstrate an explosive detection system designed specifically for field use. Our approach incorporates manufacturability and low cost while emphasizing field compatibility, usability, hand-held portability, selectivity, and sensitivity. The new device incorporates a novel multi-plate configuration and is based on colorimetric changes that occur when polynitroaromatic compounds react with polyvinylchloride polymer films containing Jeffamine T-403. Response time and characteristic absorbance for the films will be presented along with a description of the device. The results represent a first step toward a potential solution for detection of vapors utilizing chemically sensitive optical polymers.

Compositional dependence of cation impurity gettering in Hg 1-x Cd x Te

Cation impurity gettering in Hg1−xCdxTe is described in the context of process models which include the interactions of the impurities and the dominant native point defects. Experimental results are presented using secondary ion mass spectroscopy (SIMS) profiles of Au redistribution in Hg1−xCdxTe (x = 0.2,0.3,0.4) following Hg anneals and ion mills, which are processes known to inject excess Hg interstitials. In either process, the IB impurity distributes preferentially to high vacancy regions. The junction depth of the low to high impurity transition is determined by SIMS. For Hg-rich anneals of Au-doped high vacancy concentration material, the impurity junction behavior with respect to anneal time and temperature is compared to that expected for type converted electrical junctions in vacancy-only material. For milled Au-doped Hg0.7Cd0.3Te with a high vacancy concentration, the impurity junction depths are approximately proportional to the amount of material removed, as was the case with x = 0.2 material. Hg anneal type-conversion rates are found to have a strong compositional dependence which compares favorably with the strong self-diffusion coefficient dependence on x-value. In contrast, the mill conversion rate has a weak x-value dependence. Effects of trace vs dominant Au levels compared to the background vacancy concentration are quantified. True decoration of intrinsic defect processes requires Au <<[Cation Vacancies].

Integrated fault detection capability for Spreeta biosensors

This paper presents integrated fault detection capability of the Spreeta biosensor technology. A specific feature is discussed based on multi-point image characterization. Multi-point image characterization provides a means to monitor biosensor surface damage, as well as sample anomalies such as macroparticulates are bubbles.