Abstract
Straight long-range surface plasmon-polariton (LRSPP) waveguides as biosensors for label-free detection are discussed. The sensors consist of 5-μm-wide 35-nm-thick gold stripes embedded in a low-index optical-grade fluoropolymer (CYTOPTM) with fluidic channels etched to the Au surface of the stripes. This work demonstrates the application of the LRSPP biosensors for the detection of human cardiac troponin I (cTnI) protein. cTnI is a biological marker for acute myocardial infarction (AMI), often referred to as a heart attack, which can be diagnosed by elevated levels of cTnI in patient blood. Direct and sandwich assays were developed and demonstrated over the concentration range from 1 to 1000 ng/mL, yielding detection limits of 430 pg/mL for the direct assay and 28 pg/mL for the sandwich assay (1 standard deviation), the latter being physiologically relevant to the early detection or onset of AMI. In addition, a novel approach for data analysis is proposed, where the analyte response is normalized to the response of the antibody layer.
Highlights
Biodetection using evanescent optical waveguide biosensors does not require molecular labeling because the inherent principle of detection is based on sensing changes in refractive index at the sensor surface as biomolecules bind thereon
long-range surface plasmon-polariton (LRSPP) waveguide biosensors are fabricated using common semiconductor lithographic techniques at a wafer scale, so the overall cost of this novel plasmonic platform can be significantly reduced compared to conventional surface plasmon resonance (SPR) technology
This sensor can be modified with properchemistry for a broad scope of detection problems which are based on affinity binding
Summary
Biodetection using evanescent optical waveguide biosensors does not require molecular labeling (e.g., fluorescent or enzymatic tags) because the inherent principle of detection is based on sensing changes in refractive index at the sensor surface as biomolecules (mass) bind thereon. This allows for direct real-time detection, which in addition, yields kinetic parameters for the bio-interaction [1]. Compared to modified SPR prism-based sensors, LRSPP waveguides have an additional advantage: due to wave confinement in the plane transverse to the direction of propagation, various integrated waveguide configurations such as Y-junctions, S-bends, and phase-sensitive Mach-Zehnder Interferometers (MZIs) can be constructed [11,12]. Present results on the detection of human cardiac troponin I
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