Plasmonic Technology: Novel Approach to Ultrasensitive Immunoassays

Abstract

, we have taken advantage of the favorable properties of surface plasmon-coupled emission (SPCE) to improve fluorescence-based immunoassays. SPCE occurs when excited fluorophores near conducting metallic structures efficiently couple to surface plasmons. These surface plasmons, appearing as free electron oscillations in the metallic layer, produce electromagnetic radiation that preserves the spectral properties of fluorophores but is highly polarized and directional. SPCE immunoassays provide several advantages over other fluorescencebased methods. This review explains new approaches to fluorescence immunoassays, including our own use of SPCE for simultaneous detection of more than one fluorescent marker and performance of immunoassays in the presence of an optically dense medium, such as whole blood. © 2005 American Association for Clinical ChemistryBiological markers in physiologic fluids are very useful tools in clinical diagnostics. Sensitive and reliable detection of specific biomarkers is crucial in disease identification, therapy, and patient screening. Reliable and quick detection of low concentrations of markers is particularly important in a disease such as acute myocardial infarction (AMI).1 Myoglobin (Myo), although not completely cardiac specific, is one of the earliest markers to increase after AMI (1-6 ) and has been recommended for use in combination with other markers, such as creatine kinase-MB, troponin I, and troponin T, as an early diagnostic indicator for AMI (1,(7)(8)(9)(10). The immunoassay technique is widely used in this procedure (11 ).Immunoassay based on fluorescence detection is one approach to high-sensitivity detection of biomarkers (12)(13)(14)(15)(16) . Different fluorescence detection approaches include polarization (17-21 ), resonance energy transfer (22-24 ), and time-resolved gated assays based on long-lived lanthanide emission (25-28 ). New approaches to fluorescence immunoassays are being developed, including multiphoton excitation (29 -31 ), with the emphasis on highthroughput immunoassays (32-35 ).The sensitivity of fluoroimmunoassays is typically limited by background fluorescence, which is present in most biological samples and in the optical elements of the instrumentation. In this report, we describe a new immunoassay format that provides increased sensitivity and background rejection by efficient light collection of emissions occurring near the bioaffinity surface. In this approach, a fluorescently labeled reporting molecule (antibody) is bound near a metallic surface, and the binding produces a highly directional and polarized emission. This effect is based on the resonant coupling of excited fluorophores with collective electron motions/oscillations at the interface between a thin metal film (typically silver or gold) and a dielectric bulk material. The so-called surface plasmons comprise an electromagnetic wave confined to the interface between the metal film and the transparent medium, and the electromagnetic wave of the surface plasmons is coupled to oscillatio...

Modal Analysis of Surface Plasmon Resonance Sensor Coupled to Periodic Array of Core-Shell Metallic Nanoparticles

“…Here, the sensor is analyzed with only immobilized CSNps and the result is a radiating TM field in a specific angle of coupling in the prism that corresponds to this nanoparticle. However, when using different ligand substances, for multichannel evaluation, different coupling angles would be detected, each angle related to a different particle of interest [30].…”

Rapid saliva processing techniques for near real‐time analysis of salivary steroids and protein

“…SPR is a biosensor transduction technology that measures very small changes in the refractive index of a noble metal surface, usually gold, upon binding of mass to that surface. It is used extensively in monitoring biomolecular binding interactions and in biosensor immunoassays (40). Briefly, the SPR biosensor system was composed of a six-port twoway HPLC grade injection valve (Rheodyne, Rohnert Park, CA), an M6 pump (VICI Valco Instruments, Houston, TX), and a fluidics interface to the Spreeta chip, all enclosed in a temperature-controlled box and maintained at 251C.…”

Nanophotonics for Molecular Diagnostics and Therapy Applications

“…Several studies report on the modulation of fluorophores at the vicinity of nanoparticles (e.g., gold, silver, and quantum dots) [70,71], an interaction that has found application in a variety of systems to detect biologically relevant targets with particular focus upon AuNPs due to their ease in functionalization with biomolecules [72][73][74][75]. Several methods based on the quenching of fluorescence have been proposed for DNA detection consisting of fluorophore-labeled ssDNA electrostatically adsorbed onto gold nanoparticles [76], carbon nanotubes [77], and carbon nanoclots [78], where the presence of a complementary target triggers desadsorption of the newly formed dsDNA from the nanostructures due to the electrostatic variation between ssDNA and dsDNA, and fluorescence emission is restored.…”