How Surface Plasmon Resonance Works & How We Save You Time & Money

The basic instrumentation of SPRI includes an optical measurement system, a fluid handling system, and a sensor chip. Combining these three components is critical and provides the high sensitivity, accuracy, and precision that all scientists require in an assay.

Optical Measurement System

This system comprises a light source and a detector. However, its configuration depends on the design of the instrument itself. Regardless, the light source is used to illuminate the sensor chip, while the detector measures the unique spectrum created by SPR.

Most instruments today rely on a laser to shine laser light through a prism beneath the sensor chip that generates a type of condition that results in a plasmonic wave traveling across the surface of the gold film (part of the sensor chip). The electrical field of this wave extends into the space above the sensor’s surface, where its intensity is measured using the detector.

Fluid Handling System

This fluidics system provides a constant stream of buffer for the coupling process. This stream passes through the flow cell and across the sensor chip, providing a stable flow and environment for the analyte being analyzed. The analyte is inserted into the flowing buffer so that it may interact with the sensor surface. This system is also used for ligand immobilization and analyte regeneration, as well as cleaning.

Sensor Chip

This component is a gold film coated on a glass substrate that has been chemically modified to make it easier to immobilize one of the binding partners onto the biosensor’s surface.

The immobilized molecule is known as the ligand, and the molecule in the solution is known as the analyte. The sensor chip in the device interacts with the fluidic system by using a small flow cell, which allows the analyte to be injected at different concentrations in a very repeatable manner.

This method uses an electrically insulated or dielectric prism, which is why it is considered a prism-based SPR system. A thin, metallic film and the analyte to be observed are put onto the prism. Surface plasmon electromagnetic waves occur when the polarized light is shown through the prism at a specific angle, called the resonant angle.

These waves are also called surface plasmon polariton. Because the metallic layer is placed directly on the prism, this technique allows for more efficient plasmon wave generation.

The Otto configuration consists of a dielectric prism, metallic film, and an analyte, similar to the Kretschmann-Raether configuration. However, the difference is that the analyte and the metallic film are not attached to the prism. Instead, there is a thin gap of air or another low index spacer between the prism and the conductive layers.

The light in the prism is internally reflected, and an evanescent wave is created within the air gap. This wave excites the surface plasmon and creates surface plasmon polaritons. This technique is often used to look at SPR in solid-phase mediums.

First introduced in 1983, grating couplers use the physical phenomenon of diffraction grating rather than a prism. Diffraction grating is an optical technique that can disperse light of many different wavelengths, such as white light, and diffracts each wavelength at a different angle. This diffraction is accomplished by having the light strike a grating plate with grooves at specific depths and intervals.

In SPR, this grating plate is covered with a conductive metal, like gold or silver. The angle of the light is dependent on the biomolecules on the outside of the grating. By varying the angle of the incident light and capturing the resulting reflected light, a binding curve can be formed and information about the molecules can be determined.

By combining electrochemistry with a powerful optical method like SPR, researchers can monitor and understand biochemical processes much more effectively, simultaneously observing optical and electrochemical properties.

The surface effects that can be studied using ESPR include thin film formation, adsorption/desorption, redox-initiated conformation changes, and polymer formation. And because SPR is sensitive to both the adsorbed layer on the gold electrode and dielectric properties, electrochemically modulated diffusion layers can be detected.

Early detection of any severe disease is an essential first step in a patient’s treatment. The earlier the diagnosis, the quicker you can begin to receive treatment. In January of 2019, Monash University announced that they had developed a new method for the early detection of cancer. Associate Professor Qiaoliang Bao and other researchers found a new material that has improved sensitivity in spotting cancerous molecules in DNA and MicroRNA.

Their team used antimonene materials to develop a surface plasmon resonance sensor that identified biomarkers MicroRNA-21 and MicroRNA-155. This relatively low-cost and non-destructive testing could alert people whether or not they have cancer, making proactive treatment feasible.