Functionalized silicon dioxide self-referenced plasmonic chip as point-of-care biosensor for stroke biomarkers NT-proBNP and S100ß.

Surface plasmon resonance (SPR) biosensors are often used in the detection of solid, liquid or gaseous samples in diagnostics, pharmaceutics and military defense. Plasmon waveguide resonance (PWR) mode is obtained when a dielectric waveguide layer is added to the metal film. In this study, a self-referenced PWR (SRPWR) silicon dioxide (SiO2) chip was examined. The self-referenced measurement is important to compensate for temperature fluctuations, other instabilities and allows RI signal measurement without an additional reference sample, thus minimising the sample volume needed. The chip was fabricated with a multi-layer of metals and dielectrics, consisting of a 420 nm SiO2 layer, a 40 nm Ag layer and another 480 nm SiO2 layer. This chip was shown to give one internal plasmon excited on the bottom interface SiO2/Ag, which is used as self-reference in the detection. The top layer acts as a waveguide layer and can be designed to give modes with ultrahigh penetration depth. A direct assay was developed, where the recognition molecule (specific antibody) was immobilized onto the SiO2 plasmonic chip surface, via a covalent coupling protocol based on 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde. The SRPWR biosensor was developed for the sensing of two chosen stroke biomarkers: NT-proBNP and S100ß, which are sensitive and specific for stroke diagnostics. For both biomarkers, a linear decreasing pattern in the RI signal was recognized with the increasing biomarkers concentrations. Biomarkers detection was conducted in deionized water and validation was done in spiked porcine plasma. The SiO2 based plasmonic chip demonstrates a limit-of-detection of less than 1 ng/mL that is clinically relevant for both stroke biomarkers.

Point-of-Care Surface Plasmon Resonance Biosensor for Stroke Biomarkers NT-proBNP and S100ß Using a Functionalized Gold Chip with Specific Antibody.

Surface-plasmon-resonance (SPR) is a quantum-electromagnetic phenomenon arising from the interaction of light with free electrons at a metal-dielectric interface. At a specific angle/wavelength of light, the photon's energy is transferred to excite the oscillation of the free electrons on the surface. A change in the refractive-index (RI) may occur, which is influenced by the analyte concentration in the medium in close contact with the metal surface. SPR has been widely used for the detection of gaseous, liquid, or solid samples. In this study, a functionalized specific SPR chip was designed and used in a novel point-of-care SPR module (PhotonicSys SPR H5) for the detection of the stroke biomarkers NT-proBNP and S100ß. These biomarkers have proven to be good for stroke diagnosis, with sensitivity and specificity of >85%. Specific detection was done by binding a biomolecular-recognizing antibody onto the Au SPR-chip. Detection was tested in water and plasma samples. NT-proBNP and S100ß were detected in a range of concentrations for stroke, from 0.1 ng/mL to 10 ng/mL. The RI of the blank plasma samples was 1.362412, and the lowest concentration tested for both biomarkers showed a prominent shift in the RI signal (0.25 ng/mL NT-proBNP (1.364215) and S100ß (1.364024)). The sensor demonstrated a clinically relevant limit-of-detection of less than ng/mL.