Ralph C. Jorgenson

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.

Simultaneous determination of refractive index and absorbance spectra of chemical samples using surface plasmon resonance

Abstract A technique for using surface plasmon resonance to characterize dispersive refractive-index and absorption profiles is reported. This is accomplished by simultaneously exciting surface plasmon resonance at multiple angles and multiple wavelengths and then analyzing the resulting resonance profiles. By calibrating with liquids of known refractive index profiles, the refractive index spectrium of solid or liquid samples can be measured. Preliminary experimental results demonstrate a refractive index sensitivity of 6 × 10 −4 between 580 and 700 nm for refractive indices from 1.3 to 1.5.

Novel surface-plasmon-resonance-based fiber optic sensor applied to biochemical sensing

A fiber optic chemical sensor is presented which utilizes surface plasmon resonance excitation. The sensor is advantageous since it eliminates the traditional bulk optic prism in favor of a relatively simple and inexpensive design. This configuration allows for remote sensing and multiplexing. The sensing element of the multi-mode fiber optic has been fabricated by removing a section of the fiber cladding and symmetrically depositing a thin layer of highly reflecting metal directly onto the fiber core. A white light source is used to introduce a range of optical wavelengths into the optical fiber. A fiber optic spectrograph is used at the output of the fiber optic sensor to measure the transmitted spectral intensity distribution (light intensity versus wavelength). There are two sensor configurations presented. The system should find general utility as a dip-probe for quantification of proteins in solution.

Improving surface-enhanced Raman spectroscopy (SERS) for better sensors

Surface-enhanced Raman spectroscopy (SERS) results in million-fold enhancements of the Raman signal. SERS has recently been recognized as a promising platform for reversible, rapidly responding sensors. Techniques for monitoring ions, aromatics, and chlorinated ethylenes in aqueous solutions have been demonstrated. High specificity is achieved because of the distinct Raman signal of each analyte. A major obstacle to implementing this technology is the lack of appropriate SERS substrates compatible with optical-fiber excitation and collection. Typically, SERS spectra are collected from a monolayer of analyte over an area the size of a laser spot or slit image. The minuscule quantity of analyte results in SERS spectra with modest signal-to-noise ratios. We report a new technique for fabricating island-film SERS surfaces over larger areas. This technique is intrinsically compatible with optical fibers. The SERS signal will increase in direction proportion to the area or volume of analyte observed.

Characterization of porous Sol-Gel films on fiber optic surface plasmon resonance sensors

Fiber optic surface plasmon resonance sensors are used to characterize thin porous sol-gel films applied to the sensor surfaces. Techniques for coating the sensors and curing the films are discussed. Experimental and analytical methods are presented for using analysis of wavelength modulated surface plasmon resonance spectra to determine pore volume and refractive index of the films.

In-situ Characterization Of Adsorbed Protein Films Using Surface Plasmon Resonance

The adsorption kinetics of the protein fibrinogen onto gold at concentrations of .03, .30,3.00 and 30.00 mgml were studied using surface plasmon resonance, SPR. Traditionally, SPR studies have been limited to determining only two of the three unknown parameters of a thin dielectric film (i.e. protein film), thickness, real and imaginary refractive index. By modulating the bulk index of refraction, we show that all three parameters of the protein film can be determined.