Detection of Amyloid-beta 42 Using a Waveguide-Coupled Bimetallic Surface Plasmon Resonance Sensor Chip in the Intensity Measurement Mode

Abstract

The waveguide-coupled bimetallic (WcBiM) surface plasmon resonance (SPR) chip had been utilized in the intensity interrogation detection mode to detect amyloid-beta 42 (A beta 42), a biomarker of the Alzheimer disease. The SPR reflectance curve of the WcBiM chip has the narrower full-width-at-half-maximum (FWHM) compared with the SPR reflectance curve of the conventional gold (Au) chip, resulting in the steeper gradient. For the enhancement of resolution, the light source was fixed at an angle where the slope of the reflectance curve is the steepest, and the change in the reflectance was monitored. For the detection of A beta 42, the antibody of A beta 42 (anti-A beta 42) was immobilized on the WcBiM SPR chip using the self-assembled monolayer. The SPR responses, the average changes in the reflectance to the A beta 42 at the concentrations of 100 pg/ml, 250 pg/ml, 500 pg/ml, 750 pg/ml, 1,000 pg/ml, and 2,000 pg/ml were 0.0111%, 0.0305%, 0.0867%, 0.1712%, 0.3021%, and 0.5577%, respectively, for the three replicates. From linear regression analysis, the calibration curve indicated that the SPR response had a linear relation with A beta 42 with the concentration in the range of 100 pg/ml to 2,000 pg/ml. A control experiment showed the anti-A beta 42-modified surface of the WcBiM chip had a high specificity to A beta 42. Thus, the enhanced resolution by utilizing the WcBiM SPR chip in the intensity interrogation detection mode aids the diagnosis of the Alzheimer disease by detecting the A beta 42 around the criteria concentration (500 pg/ml) without any labeling.