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.
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.
Surface plasmon resonance (SPR) affinity sensing, the problem of bulk refractive index (RI) interference in SPR sensing, and a sensor developed to overcome this problem are briefly reviewed. The sensor uses a design based on Texas Instruments' Spreeta SPR sensor to simultaneously measure both bulk and surface RI. The bulk RI measurement is then used to compensate the surface measurement and remove the effects of bulk RI interference. To achieve accurate compensation, robust data analysis and calibration techniques are necessary. Simple linear data analysis techniques derived from measurements of the sensor response were found to provide a versatile, low noise method for extracting measurements of bulk and surface refractive index from the raw sensor data. Automatic calibration using RI gradients was used to correct the linear estimates, enabling the sensor to produce accurate data even when the sensor has a complicated nonlinear response which varies with time. The calibration procedure is described, and the factors influencing calibration accuracy are discussed. Data analysis and calibration principles are illustrated with an experiment in which sucrose and detergent solutions are used to produce changes in bulk and surface RI, respectively.
The sensing range of surface plasmon resonance (SPR) refractometry is greater than the thickness of most thin films of interest. Therefore, an SPR sensor will also respond to changes in the refractive index (RI) of the bulk analyte adjacent to the thin film, caused for instance by variations in analyte composition or temperature. These changes in bulk RI degrade the quality of SPR sensing data. One solution to this problem is simultaneously to measure both the SPR response and the bulk RI of the analyte and correct the SPR response for bulk RI variations. We present a simple implementation of this approach which uses critical angle refractometry. Our sensor is based on Texas Instruments' Spreeta<SUP>TM</SUP> SPR sensor. The gold is removed from the portion of the sensor surface which corresponds to angles less than the critical angle. The modified sensor delivers a composite spectrum which may be used for measurements of both the critical angle edge and the SPR dip. Theory of critical angle compensation is presented, and calibration and data analysis issues are outlined. Critical angle compensation for temperature and concentration induced bulk RI changes is demonstrated in detergent adsorption and antibody binding experiments.
The theory and design of a new planar surface plasmon resonance probe are presented. The new sensor is based on a folded light pipe combined with a telecentric lens. The inexpensive sensing elements are constructed from pieces of microscope slide and are easy to manufacture. A prototype probe design capable of measuring 2 samples simultaneously was constructed. This is the first SPR probe capable of multiplexing and first order sensing. Initial experimental refractive index testing for 0% to 41% by weight glucose solutions exhibited a sensitivity of 3 by 10<SUP>-5</SUP> index of refraction units.
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.