The characteristics of a waveguide-coupled bimetallic surface plasmon resonance (WcBiM SPR) sensor using (3-dimethylaminopropyl)-3-ethylcarbodiimide(EDC)-N-hydroxysuccinimide(NHS)-activated protein A was investigated, and the detection of IgG using the EDC-NHS-activated protein A was studied in comparison with protein A and a self-assembled monolayer (SAM). The WcBiM sensor, which has a narrower full width at half maximum (FWHM) and a steeper slope, was selected since it leads to a larger change in the reflectance in the intensity detection mode. A preparation of the EDC-NHS-activated protein A for site-directed immobilization of antibodies was relative easily compared to the engineered protein G and A. In antigen–antibody interactions, the response to IgG at the concentrations of 50, 100, and 150 ng/ml was investigated. The results showed that the sensitivity of the WcBiM sensor using the EDC-NHS-activated protein A, protein A, and SAM was 0.0185 [%/(ng/ml) ], 0.0065 [%/(ng/ml) ], and 0.0101 [%/(ng/ml) ], respectively. The lowest detectable concentrations of IgG with the EDC-NHS-activated protein A, protein A, and SAM were 4.27, 12.83, and 8.24 ng/ml , respectively. Therefore, the increased sensitivity and lower detection capability of the WcBiM SPR chip with the EDC-NHS-activated protein A suggests that it could be used in early diagnosis where the trace level concentrations of biomolecules should be detected.
Protein is a widely used sensing substrate in the biosensing technology. In the study conducted here, we used odorant
binding protein, LUSH from <i>Drosophila</i> as a biosensing substrate in a miniaturized surface plasmon resonance (SPR)
sensor. LUSH contains the specific alcohols binding sites, which mediates the detection of alcohols and pheromone. We
first modified the surface of the gold sensor chip using the self assembled monolayer in the chloroform solution. The
saturated concentration was determined prior to the detection of alcohols and pheromone at various concentrations. The
results showed that the LUSH was saturated at 1000 μg/ml on the gold sensor chip. The detection response of LUSH was
significant at higher concentration of alcohols. LUSH detected ethanol at concentration ≥50%; propanol was detected at
≥25% whereas pheromone was detected at ≥1.25 μg/μl. The results provide some fundamental information on the
potential use of LUSH-based SPR as a simple and easy protein-based sensor in the near future.
The EDC-activated protein A has been utilized to directionally immobilize anti-IgG in a miniaturized SPR sensor to
enhance IgG detection capability. The SPR sensor chips modified by a self-assembled monolayer (SAM), protein A and
the EDC-activated protein A as the linkage layer were compared by the SPR sensor. The SAM was formed on the Au
(gold) surface sensor chip by immersing it in the SAM solution. The protein A was formed by injecting their solution to
the Au chip. Thirdly, for the EDC-activated protein A, chemical procedure was carried out for the reactable surface of
the Au chip. Anti-IgG, bovine serum albumin (BSA) and IgG (50 ng/ml, 100 ng/ml, 150 ng/ml) had been sequently
injected into the SPR sensor. In results, the signal of the anti-IgG immobilized by the SAM was the largest increment
among three linkage layers. However, the SPR sensor chip modified by EDC-activated protein A showed the highest
sensitivity to IgG. From these results, we concluded that the SPR sensor using the EDC-activated protein A can be used
to detect biomolecules with trace level concentration for early diagnosis of disease.
In this study, a performance of a waveguide coupled bimetallic (WCBiM) chip in a miniaturized surface plasmon
resonance (SPR) sensor in a reflectance detection mode was investigated by comparison with a conventional gold (Au)
chip. The WCBiM chip makes sharper slope in the SPR curve than conventional Au chip. The detection abilities of both
sensor chips were tested by monitoring an interaction between streptavidin and biotin (very low molecular weight).
Firstly, an incident light was fixed at an angle which was steepest slope in the scanned the SPR curve; then, the output
signal was measured at fixed angle. The streptavidin diluted to 50 μg/ml in the phosphate buffered saline (PBS) was
injected into a fluidic module of the SPR sensor. Next, the biotin diluted to 50 ng/ml, 100 ng/ml, 150 ng/ml and 200
ng/ml in the PBS were injected into the sensor. In results, the reflectance increments of the lowest concentration of the
biotin (50 ng/ml) using the WCBiM chip and Au chip were 0.11 % and 0.04 %, respectively. Experimental results
showed that detection ability of the WCBiM chip was about three times larger than that of conventional Au chip. In
conclusion, the miniaturized SPR sensor in the reflectance detection mode using the WCBiM chip was expected to detect
the biomolecules at trace level concentration or low molecular weight with high resolution.