Sinclair S. Yee

A fiber-optic chemical sensor based on surface plasmon resonance

Abstract A fiber-optic chemical sensor is presented which utilizes surface plasmon resonance excitation. The sensing element of the fiber has been fabricated by removing a section of the fiber cladding and symmetrically depositing a thin layer of highly reflecting metal onto the fiber core. A white-light source is used to introduce a range of wavelengths into the fiber optic. Changes in the sensed parameters (e.g., bulk refractive index, film thinkness and film refractive index) are determined by measuring the transmitted spectral-intensity distribution. Experimental results of the sensitivity and the dynamic range in the measurement of the refractive indices of aqueous solutions are in agreement with the theoretical model of the sensor.

Surface plasmon resonance sensors based on diffraction gratings and prism couplers: sensitivity comparison

Abstract Theoretical analysis and comparison of the sensitivity of surface plasmon resonance (SPR) sensors using diffraction at gratings and attenuated total reflection (ATR) in prism couplers for two detection methods-resonant angle interrogation and resonant wavelength interrogation is presented. Analytical expressions for sensitivity of these SPR sensors are derived and the influence of the major design parameters of the sensing structures on the sensor sensitivity is discussed. The analysis shows that grating-based SPR sensors using wavelength interrogation are much less sensitive then their prism coupler-based counterparts. In the angular interrogation mode, the sensitivity of SPR sensors using diffraction gratings depends on the diffraction order and does not differ much from that of SPR sensors based on prism couplers.

Spectral surface plasmon resonance biosensor for detection of staphylococcal enterotoxin B in milk

This work evaluates a newly developed wavelength modulation-based SPR biosensor for the detection of staphylococcal enterotoxin B (SEB) in milk. Two modes of operation of the SPR biosensor are described: direct detection of SEB and sandwich assay. In the sandwich assay detection mode, secondary antibodies are bound to the already captured toxin to amplify sensor response. Samples including SEB in buffer and SEB in milk were analyzed in this work. The SPR biosensor has been shown to be capable of directly detecting concentrations of SEB in buffer as low as 5 ng/ml. In sandwich detection mode, the lowest detection limit was determined to be 0.5 ng/ml for both buffer and milk samples. The reported wavelength modulation-based SPR sensor provides a generic platform which can be tailored for detection of various foodborne pathogens and agents for food analysis and testing.

High sensitivity surface plasmon resonace sensor based on phase detection

Abstract A surface plasmon resonance sensing technique based on optical heterodyne phase detection is presented. The theoretical sensitivity of this new method is compared with traditioal surface plasmon resonance technique. The results of phase detection modeling shows a strong dependence on sensor film thickness. With a practical configuration, the resolution of refractive index is predicted to be 5 × 10 −7 refractive index units. An experimental set-up is described and the initial results presented conincide with the theoretical prediction.

Long-range surface plasmons for high-resolution surface plasmon resonance sensors

Abstract We present the application of long-range surface plasmons to a wavelength-modulated surface plasmon resonance sensor. Theoretical design parameters and experimental data are presented for two sensor designs, using either magnesium fluoride or Teflon AF-1600 as a dielectric buffer layer. The demonstrated sensitivity of the long-range surface plasmon resonance sensor in refractometric experiments is up to seven times higher than that of an equivalent conventional surface plasmon resonance (SPR) sensor, while the measured resolution is comparable. According to theoretical design calculations presented, further optimization of materials and layer thickness could reduce the resonance width while achieving even higher sensitivities, thereby creating a sensor with significantly better resolution than conventional SPR sensors.

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.

Free carrier induced changes in the absorption and refractive index for intersubband optical transitions in AlxGa1-xAs/GaAs/AlxGa1-xAs quantum wells

The changes in the real index of refraction and the optical absorption for conduction intersubband transitions in AlxGa1−xAs/GaAs/AlxGa1−xAs quantum wells are examined as a function of the carrier density. Various values for the input optical field and quantum well width are considered in the calculations. The linear contribution due to χ(1) as well as the nonlinear contribution from χ(3) is included. The relationship of the results to device applications such as waveguides and optical modulators is discussed.

A novel multichannel surface plasmon resonance biosensor

Abstract We report a novel multichannel surface plasmon resonance (SPR) sensor based on the combination of parallel sensing channel architecture and the method of spectral discrimination of sensing channels. This sensor configuration provides multichannel performance and, through probing surface processes (e.g. binding of immobilized antibody and antigen in solution) with surface plasmons with different field distributions, it allows distinguishing sensor response to surface and bulk effects, enabling more accurate quantification of biomolecular interaction events. The potential of this mixed-architecture sensor is illustrated in a model biosensing experiment in which the detection of monoclonal anti-dinitrophenyl antibody (a-DNP) is compensated for non-specific adsorption and background refractive index interferences.

Optical lightpipe sensor based on surface plasmon resonance

In this paper, a novel optical sensor using surface plasmon resonance in a symmetrical planar lightpipe is introduced. The new design utilizes a microscope slide with beveled ends as the sensor substrate. Collimated TM polarized white light is used to interrogate the sensing surface at a single angle. Preliminary experimental results for glycerol solutions from 0.6%wt to 16%wt demonstrate a concentration sensitivity of 3.4 multiplied by 10-4 by weight. The corresponding refractive index sensitivity is estimated as 4 by 10-5.

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.