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Surface Plasmon Resonance & SPR Instruments

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Surface plasmon resonance imaging

Observing how a chemical substance or biological ligand interacts with a transducer can be referred to as biosensing.

Biotech diagram

Surface plasmon resonance imaging (SPRI) is a high throughput optical biosensing technique used to study small molecules and provide data on the affinity, specificity, and kinetics of biomolecular interactions.

It is also referred to as surface plasmon resonance microscopy (SPRM) and provides its data by measuring the target molecules’ real-time binding association rates and dissociation rates. It is considered a fundamental principle behind many biosensor applications, diatom photosynthesis, and various lab-on-a-chip sensors.

Surface Plasmon Resonance (SPR) technology is combined with imaging devices to form SPRI and can be used in several different ways.

It is most commonly used to analyze molecular interactions because, unlike many other immunoassays, such as ELISA, SPR assays allow for real-time, label-free detection of biomolecular interactions and provide higher-throughput analysis than many traditional methods.

Surface plasmon resonance is also used for measuring the adsorption onto the surface of metal nanoparticles or onto a planar metal surface (such as gold or silver), as it is the basis behind many other tools that material adsorption onto planar metal. This includes using SPR as a characterization tool for lipid nanoparticles (LNPs) used in drug discovery.

Other SPR applications include observing protein-to-protein, protein-to-antibody, DNA-to-protein, and many other molecular exchanges. Unlike similar analytical techniques, SPR can be used to look at both binding kinetics and binding affinity.

A plasmon refers to the minimum amount, or quantum, of rapid oscillations of electron densities in conducting medium or plasma densities. Surface plasmon relates to this oscillation as it occurs on the surface of a conducting medium such as a metallic surface.

When polarized light hits an electrically conducting surface, such as a metal, some light is absorbed by the object’s surface electrons and resonates with the electrons along the material’s surface. Specifically, it occurs at the interface of the media with different refractive indices. These resonated electrons are the surface plasmons.

Surface plasmon resonance excites electrons on the surface of a conductive layer and detects the resulting oscillations of free electrons. This means that the excited electrons absorb some of the incident light, and the resulting reflected light will now contain an absorption line. This absorption line can then be used to determine various qualities of the material.

SPR Instrumentation, Techniques, & Methods

An open hand with a DNA strand coming out of the palm

Though the critical components of SPR instrumentation are similar across all types, the modes of excitation vary. Three of the most commonly used methods include the Kretschmann-Raether configuration, Otto configuration, and grating coupled.  

In addition to these methods, another important method has been developed as a hybrid method in which electrochemistry and SPR is combined to create a novel SPR technique. It is referred to as electrochemical SPR (ESPR).

Instrumentation

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.

Kretschmann-Raether Configuration

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.

Otto Configuration

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.

Grating Couplers

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.

Electrochemical

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.

Possible Early Detection of Cancer

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.

Surface Plasmon Resonance Instrument Leases to Fit Every Need

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Founder-Friendly Leases

Our lease agreements are founder-friendly and flexible, helping you preserve working capital, strengthen the cash flow of your business, and keep business credit lines open for expansions, staffing, and other crucial operational expenses and business development opportunities.

2-5 Year Lease Lengths

Leases range from 2 to 5 years. Length will depend on several factors, including how long you want to use the equipment, equipment type, and your company’s financial position. These are standard factors leasing companies consider and help us tailor a lease agreement to fit your needs.

Your Choice of Manufacturer

We don’t carry an inventory. This means you’re not limited to a specific set of manufacturers. Instead, you can pick the equipment that aligns with your business goals and preferences. We’ll work with the manufacturer of your choice to get the equipment in your facility as quickly as possible.

Maintenance & Repair Coverage

Bundle preventive maintenance and repair coverage with your lease agreement. You can spread those payments over time. Easily maintain your equipment, minimize the chances something will break down, repair instrumentation quickly, and simplify your payment processes.

End-of-Lease Options

At the end of your lease, you have multiple options. You can either renew the lease at a significantly lower price, purchase the machine outright based on the fair market value of the original pricing, or call it a day and we’ll come the pick up the equipment for you free of charge.

No Loan-Like Terms

Our leases do not include loan-like terms, which can be restrictive or harmful in certain situations. We do not require debt covenants, IP pledges, collateral,  or equity participation. Our goal is to maximize your flexibility. When you lease with us, you’re collaborating with a true business partner.

In-House Underwriting Process

Our underwriting is done in-house. You can expect quicker turnaround, allowing you respond to your equipment needs as they arise. We require less documentation than traditional lenders and financiers and can get the equipment you need in operation more quickly.

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