Surface Plasmon Resonance is an advanced and highly sensitive optical technology that can measure refractive index changes on a sensor chip’s gold surface due to a change in mass that occurs during a binding event.  This change can be used to monitor biological interactions such as the concentration of target molecules, kinetic rates and affinity constants.  BiOptix has developed a novel ultra-sensitive detection platform known as Enhanced Surface Plasmon Resonance (E-SPR).  E-SPR or phase-based SPR differs from standard surface plasmon resonance detection methods in that it combines the high sensitivity of SPR with the high stability and lower noise of common path interferometry.


The following demonstrations outline the process of Enhanced Surface Plasmon Resonance (E-SPR) and the phase-based technology of the BiOptix 404pi.  Click on an image to launch the video.

Meet the 404pi

Overview of the 404pi system and its features and technology.

BiOptix Software for the 404pi

See the capabilities and get a feel for the latest software for the 404pi.

SPR: Measurement Principle

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.

SPR: Optics

The 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.

SPR:  Phase Changes

These phase changes are induced by mass increase at the surface that results from the specific interaction of an analyte with the ligand attached to the chip 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.

SPR:  Detection of Minute Phase Changes

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.

For additional information or to request a product demonstration, please contact a BiOptix product specialist at: 303-545-5550 or

BiOptix:  Kinetics with Confidence.