Surface plasmon resonance (SPR) is a quantum electromagnetic phenomenon that occurs when p-polarized light, under conditions of total internal reflection (TIR), strikes an electrically conducting metal layer at the interface between two media with different refractive indices. The SPR technique is considered one of the most important analytical tools for biomolecular interactions, due to its remarkable characteristics such as no requirement of labeling, real-time detection capability, cost- effectiveness, and high specificity and sensitivity.
Gold is usually chosen as the metal film for SPR. The gold surface could be modified with a self-assembling layer of long-chain thiols, to which a hydrogel could be further attached, providing an efficient substrate for covalent immobilization of biomolecules and a proper environment for biomolecular interactions. With the development of nanotechnology, nanomaterials have been increasingly used in SPR biosensors. One of nanomaterials’ common properties is their high specific surface area, which enables the immobilization of an enhanced amount of bioreceptor units. The use of functional nanomaterials significantly improves the sensor performance and increases the sensitivity and selectivity of the sensing platform.
The unique FOPPR™ technology is a proprietary technology that combines optical waveguides with noble metal nanoparticles for sensitive and reliable molecular detection. In FOPPR™, gold nanoparticles (AuNPs) are coated onto an unclad optical fiber. Total internal reflection occurs as light propagates along the fiber and results in an evanescent field that causes the AuNPs to undergo particle plasmon resonance (PPR). Particle plasmons are charge density collective oscillation confined to metallic nanoparticles. PPR band (also known as localized surface plasmon resonance (LSPR) band) is a strong extinction band exhibited characteristically by metallic nanoparticles. The extinction cross-section and peak wavelength of the PPR band are highly dependent on the local refractive index of the nanoparticle’s surrounding medium, and thus, the binding events to those functionalized nanoparticles. The extreme sensitivity of this optical property to changes in the surrounding environment makes FOPPR™ an ideal technology for monitoring real-time interactions between a variety of molecular species, including but not limited to organic drugs, oligonucleotides, proteins, and viruses.
Schematic diagram of FOPPR™ technology
Molecular detection is achieved through the capture of free-flowing analytes by bioreceptors chemically bound to the FOPPR™ sensing surface. When the target analyte is introduced to the sensing surface by the sample fluid, the binding interaction between the analytes and the bioreceptors results in a change in refractive index near the sensing surface. The refractive index change on the sensing surface causes an immediate change in the optical response proportional to the mass concentration of the bound analyte.
The label-free detection of biomolecular interactions based on FOPPR™ technology has a wide range of applications in biochemical research, drug discovery and diagnostic development. Amerigo Scientific offers FOPPR™-based services for biomarkers screening and analysis.