Search

The surface plasmon resonance (SPR) technique has been widely applied to biosensing technologies for the rapid quantification of biomolecules without enzyme and fluorescent labeling. However, the conventional prism-coupling SPR method generally has a detection area of a few mm2, and the large contribution of the background signal forms a barrier to highly sensitive detection. Based on a highly spatially resolved SPR method, the present study constructed a scanning GC-SPR imaging instrument using an objective lens with a high numerical aperture and a plasmonic chip that could be used for grating-coupled SPR. Focusing light on the diffraction limit can suppress background signals and improve detection sensitivity. SPR imaging can also be performed by scanning a focal spot. Using this method, the refractive index of a mixture of water and dimethyl sulfoxide was measured with a detection accuracy of 2.43 × 10−3 RIU. Polydopamine films prepared with a thickness of <5 nm were also measured, and each film thickness was evaluated with high sensitivity from the effective refractive index detected in a small area of <1 µm2. [ABSTRACT FROM AUTHOR]

High-density cultured neuronal networks have been used to evaluate synchronized features of neuronal populations. Voltage-sensitive dye (VSD) imaging of a dissociated cultured neuronal network is a critical method for studying synchronized neuronal activity in single cells. However, the signals of VSD are generally too faint—that is, the signal-to-noise ratio (S/N) is too low—to detect neuronal activity. In our previous research, a silver (Ag) plasmonic chip enhanced the fluorescence intensity of VSD to detect spontaneous neural spikes on VSD imaging. However, no high-density network was cultivated on the Ag plasmonic chip, perhaps because of the chemical instability of the Ag surface. In this study, to overcome the instability of the chip, we used a chemically stable gold (Au) plasmonic dish, which was a plastic dish with a plasmonic chip pasted to the bottom, to observe neuronal activity in a high-density neuronal network. We expected that the S/N in real-time VSD imaging of the Au plasmonic chip would be improved compared to that of a conventional glass-bottomed dish, and we also expected to detect frequent neural spikes. The increase in the number of spikes when inhibitory neurotransmitter receptors were inhibited suggests that the spikes corresponded to neural activity. Therefore, real-time VSD imaging of an Au plasmonic dish was effective for measuring spontaneous network activity in a high-density neuronal network at the spatial resolution of a single cell. [ABSTRACT FROM AUTHOR]

Size effect of metal nanodome arrays on performance characteristics of a plasmonic biosensor is investigated using reflection spectroscopy. Ag and Au nanodome arrays are created by a bottom-up nanofabrication process by which the dome diameter and metal thickness can be controlled. Reflectivity measurements of metal nanodome arrays showed that the wavelengths and width of resonance dip were changed by the dome diameter and metal thickness, respectively. Bulk refractive index (RI) sensing and detection of DNA hybridization were performed to characterize the sensing performance of metal nanodome arrays. Bulk RI sensitivity were significantly improved as the dome diameter enlarged from 100 to 500 nm. In contrast, metal nanodome arrays with smaller diameter exhibited higher sensor signals against the immobilization of DNA modified gold nanoparticles used for signal amplification indicating strong plamonic coupling effects. With respect to the dome diameter, the effect of metal thickness was moderate for the presented sensing scheme. [ABSTRACT FROM AUTHOR]

The fluorescence excited by the enhanced electric field of grating-coupled surface plasmon resonance was detected on biochips. The enhancement of the electric field on a metallic grating surface was calculated using the finite difference time domain method for rectangular, trapezoidal, and sinusoidal models to clarify the grating-surface profile dependence of the enhanced fluorescence. The computational results showed that the enhancement in the trapezoidal model was stronger than that in the other models, and that the groove depth dependence of the enhancement in the trapezoidal model agreed well with the experimental data. The grating surface profile, including the groove depth, was found to be an important parameter of the grating structure for it to couple effectively with light. [ABSTRACT FROM AUTHOR]