Technology

Surface Plasmon Resonance-enhanced Common Path Interferometry (SPR-CPI) is a novel detection technology that combines SPR and interferometry in a robust, cost effective platform to provide extremely sensitive label-free biomolecule interaction analysis in a microarray format.

Illustration of the biodetector operations Click on the image to see a Flash demo.

BiOptix's original molecular detector was based on a technology called holographic interferometry. After significant R&D effort on the prototype instrument, design specifications were met, but this approach proved to be too costly and impractical to manufacture. When this became obvious, the common path interferometric detection principle was conceived by BiOptix Chief Scientific Adviser, Dr. John Hall (2005 Physics Nobel Laureate). This principle became the foundation for our current technology.

The principle is based on measuring index of refraction changes at an affinity layer during exposure to an analyte. This is accomplished by measuring relative phase changes of two components of polarized light within a single beam.

Optical system transforms laser-diode emitted light into s- and p- polarized components within the same beam. Amplitude and phase of each component are tuned for maximum sensitivity. Click on the image to see a Flash demo.

These phase changes are induced by mass increase at the surface that results from the specific interaction of a ligand with a capture agent under Total Internal Reflection (TIR) conditions. Any change in the effective index of refraction of the affinity layer, such as through the addition/binding of chemical or biological molecules, generates an optical phase shift, and alters the laser beam's polarization state. Comparison of the beam's two polarization states (s and p) enables detection of minute phase changes, which characterize the rate and extent of the surface interaction to thereby yield information for accurate bio-molecule identification and quantification.

A combination of features and innovative solutions positions the BiOptix SPR-CPI technology as the leader in terms of performance and versatility for commercial label free biomolecule interaction analysis. The addition of surface plasmon resonance increases both dynamic range and sensitivity compared to a pure CPI or TIR-based technology. CPI's single beam path provides higher stability and lower noise than competing biosensors based on conventional dual beam interferometry.

Biodetector measures phase change of the p-polarized light reflected from the biochip surface. The phase change depends on the amount of captured biological or chemical material. Click on the image to see a Flash demo.

It also yields a simplified overall opto-mechanical scheme, which eases integration of SPR-CPI into a variety of instrument configurations and can be deployed as a subsystem in larger biomolecule analysis systems. The "direct" measurement of the phase shift during an assay provides additional sensitivity enhancement over other common SPR techniques that measure intensity or angle shift, which are the common physical properties used to generate signal in most commercial label-free technologies.

Multiplex array analysis with the SPR-CPI system is enabled because it collects relative phase state information within the beam reflected from the sample cell and projects this information as a two dimensional image within the beam's cross section.

This allows discrete areas of the sample cell array to be interrogated simultaneously by use of photo-diode arrays aligned to the reflected beam from the sample cell. It is this unique integration of capture agent microarray, SPR-CPI and photodiode detection that promote simultaneous screening and multiplexed readout.

Simultaneous detection of multiple molecules is possible by attaching different antibodies to different array cells. Empty cells are used for calibration and temperature drift compensation. Click on the image to see a Flash demo.

In summary, the combination of SPR signal enhancement with common path interferometry for biological molecular interaction analysis is an innovation that significantly advances the field and scope of label free detection technologies.

BiOptix technology has significant advantages: