A palm-sized differential surface plasmon resonance (SPR) meter, which consisted of a single light source, a prism, a divided mirror, and a single linear CCD element, was developed aiming at the miniaturization of an SPR instrument for use in field analysis of endocrine disrupting chemicals. The size and weight of the meter were 160 cm (W) × 10 cm (H) × 6 cm (D) and 770 g, respectively. The SPR meter composed of an Sprode with the sample and reference sensor-cells was found to be very effective for compensating drift and fluctuation of sensor signals as well as temperature variation at the same time without time lag. The effectiveness was due to a subtraction function of reference signal from the sample signal. The basic performance of the meter was a drift of within 0.001° in SPR measurement over 4300 s and a angle stability of within 0.0004° at a 10° incident LED light beam. Also, the SPR meter was applied to the immunoassay of 2,4-dichlorophenol (2,4-DCP) using a solid extraction technique. A good linear relationship between the concentration of 2,4-DCP and the SPR signal was obtained with the present meter. It was possible to determine 10 ppb of 2,4-DCP with the developed meter. A new concept of a divided mirror and the Sprode was thought to be useful for miniaturization of the SPR instrument aimed at on-site analysis.
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