A new optical chemical sensor was developed for chemical sensing based on light-excited surface plasmon measurement. Concentration of the chemical species is found in liquid or gas without the help of a reagent but by measuring the resonance condition of the surface plasmon on the sensing metal surface. The resonance condition is given by the dielectric constant of the sample faced on the metal. The developed sensor can be compact and simple, because of the absence of mechanical moving parts, by using multichannel angular light intensity detection with a photodiode array and a Fourier transform optical setup. Experimental results are shown for measurement of ethanol concentration in water. The detection limit for ethanol in water was 10(-4) wt./wt. by the experiments with the developed system.
A simple fluorescence lifetime imaging system using a gated micro-channel plate (MCP) image intensifier coupled to a CCD camera has been developed. Nanosecond-level time-resolved fluorescence images of a sample under a pulsed light excitation can be detected directly. With a rapid lifetime determination method for multigate detection, fluorescence lifetime imaging can be promptly performed. In the present system, laser excitation of sample and shutter action of an image intensifier are fully synchronized by means of an optical fiber delay line. In order to compensate for fluctuations in the excitation source, a simple intensity monitor circuit was developed. Details of the instrumental system and verification measurements on two component samples are presented.
A multilayer surface plasmon resonance system was designed for high-precision chemical sensor applications. In this sensor, the angular distribution of reflectance from a thin metal film-which is in contact with a sample-is measured. An absorption peak is observed whose angular distribution of reflectance, owing to the excitation of surface plasmon resonance, is measured. The refractive index of the sample is determined from this peak angle. The resolution limit for refractive-index measurements is determined by the absorption peak width. We describe a multilayer system in which an additional layer is added to the conventional Kretschmann geometry; as a result, peak widths are significantly reduced. The angular distribution of reflectance is calculated using Fresnel's formulas and multiple-reflectance theory in order to understand the effect of thickness and refractive index of the additional layer. By optimizing the thickness of the layer, peak widths are reduced to approximately one third of that obtained using the Kretschmann geometry. Experimental results demonstrate the feasibility of this approach.
A method is described for estimating the spectra of pure components from the spectra of unknown mixtures with various relative concentrations. This method is based on principal component analysis and a constrained nonlinear optimization technique and is applicable to qualitative analysis of mixtures of more than three components. The method gives two curves as the estimate of a component spectrum: one consists of the set of the maxima and the other consists of the set of the minima for all sampling points subject to a priori information. Experimental results of the estimation of the infrared absorption spectra of xylene-isomer mixtures are shown; the noise problem with this method is also discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.