Kyle S. Johnston

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.

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.

New analytical technique for characterization of thin films using surface plasmon resonance

Abstract A theoretical technique is presented for simultaneously determining the thickness and dispersive refractive index of a homogeneous thin film applied to a surface plasmon resonance sensor. The technique has the potential for real-time characterization of film parameters while immersed in air, vacuum or liquid media. Experimental realization requires a calibrated wavelength-modulated surface plasmon resonance sensor that is measured at several angles of illumination. A fine-tuned numerical model is used to generate general solutions that describe the sensor response for each angle of illumination. A differential technique and an assumption of a linear dispersion are used to produce a unique solution for the thickness and dispersive refractive index of the film. For a simulated 183 nm thick glass film, results shows 1% thickness prediction error and refractive index prediction error on the order of 3 × 10−3.

A surface plasmon resonance sensor probe based on retro-reflection

Abstract A new surface plasmon resonance (SPR) sensing probe is presented. The probe is based on retro-reflection, consisting of a stable, one-piece substrate that is simple to construct. The orientation of the sensing surface requires a minimal sample volume, and the device is easily optimized for maximum sensitivity in different applications. The sensor presented here exhibited a sensitivity of 3.36×10 −5 refractive index units. The versatility and simplicity of this new sensor configuration provide the potential to introduce SPR sensing techniques to industrial applications.

PERFORMANCE COMPARISON BETWEEN HIGH AND LOW RESOLUTION SPECTROPHOTOMETERS USED IN A WHITE LIGHT SURFACE PLASMON RESONANCE SENSOR

Abstract To verify the conclusions of earlier research, the response of a planar substrate white light surface plasmon resonance sensor was simultaneously measured with high resolution (1024 channel) and low resolution (16 channel) spectrophotometers. The sensor’s response to a series of sucrose solutions was calibrated using data from both systems. Multivariate analyses based on principle component regression and locally weighted parametric regression were performed on both high and low resolution data; the calibration errors from the low-resolution system were smaller than those from the best calibration that could be obtained from the high-resolution system. Other analysis techniques (a center of mass analysis and a linear technique based on the derivative of the baseline spectrum) allowed the 16 channel system to perform high resolution monitoring of small signal offset from a baseline; both techniques allowed resolution of shifts in the resonance location as small as 0.02 nm.

SPR imaging-based salivary diagnostics system for the detection of small molecule analytes

Abstract:  Saliva is an underused fluid with considerable promise for biomedical testing. Its potential is particularly great for monitoring small‐molecule analytes since these are often present in saliva at concentrations that correlate well with their free levels in blood. We describe the development of a prototype diagnostic device for the rapid detection of the antiepileptic drug (AED) phenytoin in saliva. The multicomponent system includes a hand‐portable surface plasmon resonance (SPR) imaging instrument and a disposable microfluidic assay card.

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.

First-order surface plasmon resonance sensor system based on a planar light pipe

A novel first-order optical sensor using surface plasmon resonance in a planar light pipe is introduced. The phenomenon of discrete angular bands of light in high-numerical-aperture light pipes is discussed, and the operating theory of the sensor is explained. The fabrication of two different prototype sensor configurations is presented. The operating theory of the sensors is verified by comparing experimental results with theoretical predictions of sensor performance.

Prototype of a multi-channel planar substrate SPR probe

Abstract The implementation and testing are presented for a prototype configuration of a surface plasmon resonance (SPR) probe with a planar substrate. The design and theory have been previously reported and are given in summary. This is the first SPR based probe design capable of multiplexing and first order sensing. The sensor is based on a folded light pipe combined with a telecentric lens. The inexpensive and easy to manufacture sensing substrates can be constructed from pieces of microscope slide. Experimental testing of glucose solutions indicates a resolution of better than 3×10 −5 index of refraction unit can be obtained. Results of testing the probe in a series of applications including orange juice reconstitution motor oil mixing and heparin biosensing are also presented.

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.