Back-Scattering Interferometry (BSI) Technology
Back-Scatter Interferometry is an advanced, optical technique allowing for highly sensitive qualitative and quantitative, label-free detection of molecular interactions in free-solution or on-surface supports.
The on-line addition of Science Magazine recently reported that BSI technology enables free-solution, label-free, molecular interaction kinetic and end-point assays at zeptomole levels of sensitivity, using a biosensor with a simple optical train comprised of a He-Ne laser, a microfluidic channel, and a position sensor.
Benefits of Back-Scatter Interferometry
BSI has significant advantages over ELISA as well as label-free, molecular interaction biosensor approaches such as microcalorimetry, surface plasmon resonance, and other wave-guide technologies. Demonstrating zeptomole sensitivity, using very small sample volumes (< 2 microliters), and requiring little apriori knowledge of the molecular interactors, BSI technology significantly accelerates assay development. BSI can measure over six logs of equilibrium dissociation constant range, and operates in both free-solution and surface-bound modes. Compared to all other biosensor technologies, BSI substantially accelerates discovery and assay development for life science and medical research.
An easy-to-use, ultra-sensitive, and low-cost platform, BSI measures molecular interaction kinetics and performs quantitative, end-point assays. BSI technology can be used to discover new biomarkers, rapidly develop assays, and run routine, quantitative molecular interaction-based assays in seconds at picomolar concentrations in either free-solution or surface-bound, label-free modes.
Components of the technology
The Back-Scattering Interferometer employs a simple optical train comprised of a coherent light source (commonly a low-power He-Ne or red diode laser), a microfluidic channel (formed in glass, fused silica, or plastic), and a phototransducer (Figure 1).
The interaction of the laser beam with the fluid-filled channel results in a high-contrast interference pattern (Figure 1). The profile of this fringe pattern changes in a predictable manner with molecular binding events within the optical channel. Analysis of fringe positional changes, performed by a phototransducer located in the direct backscatter direction, has facilitated the measurement of RI changes with resolution on the order of 10-6 within a 188 pL volume.
Figure 1: Experimental setup for BSI. Samples to be tested for molecular interaction are introduced and mixed within a temperature controlled microfluidic chip. Alternatively samples are premixed prior to introduction. Coherent light from a HeNe laser is directed towards the microchip fluidic channel, which functions to create the fringe pattern characteristic of BSI. The BSI fringe pattern is directed to a CCD array. An image is extracted and the positional shift of these fringes is monitored to provide binding signal.
Figure 2 illustrates graphically the transformation of phase shift images captured by the CCD camera to sinusoidal waves which shift slightly with changes in RI. The computer converts these to time-dependent response curves.
Figure 2: BSI signal processing. Interference fringes are imaged by the CCD camera. Custom software extracts a sinusoidal wave from the fringe images. A proprietary algorithm is then applied to determine positional shifts of these fringes to a resolution of 50 nanometers. Change in fringe position as a function of time is plotted as the response curve for the binding event. Molecular binding is depicted as an increase in the binding curve's intensity.
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