Timothy M. Chinowsky

Optimal linear data analysis for surface plasmon resonance biosensors

Abstract Surface plasmon resonance biosensors measure the thickness or molecular concentration of a biolayer by analyzing small changes in measured reflection spectra. In this paper, we describe linear spectral analysis techniques designed to produce measurements with the maximum possible signal-to-noise ratio. We show how, under appropriate assumptions, an optimal analysis method may be derived for measuring any system parameter, and how measurements of multiple parameters may be made independent in exchange for an decrease in signal to noise ratio. Compared to two conventional data analysis techniques (quadratic fit and centroid methods) using simulated data, the linear techniques show a 30% increase in signal to noise ratio. In application to actual thiol binding data, the linear method yields a signal to noise ratio 46% greater than that of the centroid method and 65% greater than that of the quadratic fit method. This level of noise reduction was achieved by using the ability of the linear methods to reject noise caused by light source brightness variations.

A portable surface plasmon resonance sensor system for real-time monitoring of small to large analytes

Many environmental applications exist for biosensors capable of providing real-time analyses. One pressing current need is monitoring for agents of chemical- and bio-terrorism. These applications require systems that can rapidly detect small organics including nerve agents, toxic proteins, viruses, spores and whole microbes. A second area of application is monitoring for environmental pollutants. Processing of grab samples through chemical laboratories requires significant time delays in the analyses, preventing the rapid mapping and cleanup of chemical spills. The current state of development of miniaturized, integrated surface plasmon resonance (SPR) sensor elements has allowed for the development of inexpensive, portable biosensor systems capable of the simultaneous analysis of multiple analytes. Most of the detection protocols make use of antibodies immobilized on the sensor surface. The Spreeta 2000 SPR biosensor elements manufactured by Texas Instruments provide three channels for each sensor element in the system. A temperature-controlled two-element system that monitors for six analytes is currently in use, and development of an eight element sensor system capable of monitoring up to 24 different analytes will be completed in the near future. Protein toxins can be directly detected and quantified in the low picomolar range. Elimination of false positives and increased sensitivity is provided by secondary antibodies with specificity for different target epitopes, and by sensor element redundancy. Inclusion of more than a single amplification step can push the sensitivity of toxic protein detection to femtomolar levels. The same types of direct detection and amplification protocols are used to monitor for viruses and whole bacteria or spores. Special protocols are required for the detection of small molecules. Either a competition type assay where the presence of analyte inhibits the binding of antibodies to surface-immobilized analyte, or a displacement assay, where antibodies bound to analyte on the sensor surface are displaced by free analyte, can be used. The small molecule detection assays vary in sensitivity from the low micromolar range to the high picomolar.

Experimental data from a trace metal sensor combining surface plasmon resonance with anodic stripping voltammetry

A technique for sensing metal ions with a combination of surface plasmon resonance and anodic stripping voltammetry is described. Potential enhancements to conventional anodic stripping voltammetry resulting from this technique are discussed. An experimental setup and data showing the simultaneous sensing of 500 nM lead and copper ion are presented and interpreted.

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.

Characterization of a wavelength-tunable surface plasmon resonance microscope

We have built and characterized the operation and performance of a surface plasmon resonance microscope that uses the rotation of an interference filter to vary the imaging wavelength of the system. The operation of the microscope with respect to signal processing, the dynamic range, and the limit of detection of the system, are described.

Quantifying the information content of surface plasmon resonance reflection spectra

Abstract Thin-film sensors based on the principle of surface plasmon resonance (SPR) are often used for real-time refractometry of dielectric and metal thin films. We present mathematical methods based on linear estimation which allow quantitative investigation of the capabilities of the SPR technique relative to an ideal thin-film sensor. These methods use a linear model of the sensor response to determine the best possible uncertainty of film parameters extracted from a given set of measurements. These methods are general in that they may be easily applied to any well-modeled system. We show how these methods may be used to quantify the limitations of the basic SPR technique (in particular, the difficulty of determining the thickness and refractive index of a thin film independently) and also to evaluate the capabilities of more elaborate SPR-based techniques designed to overcome these limitations. As an example, we analyze a two-color SPR technique proposed by Peterlinz and Georgiadis and find that the uncertainty of the thickness and refractive index estimates yielded by this technique have a complex dependence on the dispersion of the thin film and its surrounding solvent.

Optical and electronic design for a high-performance surface plasmon resonance imager

Surface plasmon resonance (SPR) imaging is a versatile technique for detection, quantification, and visualization of bio-molecular binding events which have spatial structure. In this paper, we describe the design principles which we are applying toward construction of a new high-performance SPR imager. We briefly review the basic principles of SPR biosensing and SPR imaging, and discuss the goals for the new design. We focus on two main goals, refractive index (RI) resolution and mechanical simplicity. We address RI resolution as a signal-to-noise issue, using simulations to determine how to maximize the signal (i.e. changes in intensity due to binding events) and minimize the noise. Specific attention is paid to the dominant effects of shot noise. Design concepts for collimating and imaging optics which reduce or eliminate the need for mechanical adjustment are presented. Ray-tracing analysis of the collimating optics is used for detailed analysis of collimator performance.

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.

Airborne surface plasmon resonance biosensing

On March 14, 2003 an experimental aircraft fitted with surface plasmon resonance (SPR) biosensors connected to an air sampling system performed a 90-minute flight over Renton, Washington, demonstrating the first-ever use of SPR sensors for airborne biodetection. In this paper, we describe the instrumentation constructed for this purpose, the experiment conducted, and the results obtained. Instrumentation was based on Texas Instruments’ Spreeta SPR sensors combined with sample collection and fluidic apparatus designed for airborne sensing. Detection targets were two innocuous proteins ovalbumin and horseradish peroxidase. We describe future enhancements necessary to apply this technology on an unmanned airborne vehicle.