Abstract
The characteristics of a waveguide-coupled bimetallic (WcBiM) chip in a miniaturized surface plasmon resonance (SPR) sensor and its detection capability for a low molecular weight biomolecule were investigated. The configuration of the WcBiM chip was gold (Au)/waveguide (ZnS-SiO2)/silver (Ag). In the intensity measurement mode, the sensitivity could be improved by reducing the full width at half maximum (FWHM) of the reflectance curve. The FWHM of the WcBiM chip is narrower than that of the Au chip, which suggests that the slope of the reflectance curve for the WcBiM chip is steeper. In order to generate enhanced resolution, the reflectance should be monitored at the specific angle where the slope is the steepest in the reflectance curve. For the detection of biotin that is a low molecular weight biomolecule, streptavidin was formed on the SPR sensor chip surface. The response of the SPR to biotin at various concentrations was then acquired. The sensitivities of the WcBiM chip and the Au chip were 0.0052%/(ng/ml) and 0.0021%/(ng/ml), respectively. The limit of detection of the biotin concentration for both the WcBiM and Au chips was calculated. The values were 2.87 ng/ml for the WcBiM chip and 16.63 ng/ml for the Au chip. Enhancement of the sensitivity in the intensity detection mode was achieved using the WcBiM chip compared with the Au chip. Therefore, sufficient sensitivity for the detection of a disease-related biomarker is attainable with the WcBiM chip in the intensity measurement mode using a miniaturized SPR sensor.
Highlights
With continuous research and advancement over the last several decades, a surface plasmon resonance (SPR) sensor has been developed as a promising technology for biomolecular interaction analysis due to its merits of real-time monitoring and higher sensitivity compared with any other sensor system [1,2,3]
We experimentally investigated the characteristics of a waveguide-coupled bimetallic (WcBiM) chip in the intensity measurement mode using the miniaturized SPR sensor system, and extended the study to the system sensitivity for the detection of biotin with very low molecular weight (MW 341.38) at a low concentration level
The reflectance curves for the designated incident angle were obtained by successive numerical fitting of the intensity profiles from 2D-CMOS for both WcBiM and Au chips
Summary
With continuous research and advancement over the last several decades, a surface plasmon resonance (SPR) sensor has been developed as a promising technology for biomolecular interaction analysis (e.g., antigenantibody reaction, DNA) due to its merits of real-time monitoring and higher sensitivity compared with any other sensor system [1,2,3]. The SPR-based sensor relies on the extraordinary optical properties of noble metals such as gold (Au), silver (Ag), aluminum (Al), and copper (Cu) [8]. Among these metals, Au has been commonly used as an SPR sensor chip since it has merits of great stability, durability, and outstanding biocompatibility [8,9,10]. A single Au layer leads to stable performance, the commercialized Au-based sensor chip has a sensitivity limitation when it comes to the detection of biomolecules with very low molecular weight or trace level concentration [11]. As materials for the waveguide layer, Si3N4 [18], SiO2 [19], and ZnO [20] have been extensively studied
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