An immunosorbent assay system was integrated into a glass microchip. Polystyrene beads were introduced into a microchannel, and then human secretory immunoglobulin A (s-IgA) adsorbed on the bead surface was reacted with colloidal gold conjugated anti-s-IgA antibody and detected by a thermal lens microscope. The scale merits of liquid microspace on the molecular behavior remarkably contributed to reduced assay time. The integration cut the time necessary for the antigen-antibody reaction by 1/90, thus shortening the overall analysis time from 24 h to less than 1 h. Moreover, troublesome operations required for conventional immunosorbent assays could be replaced by simple operations.

A new design and construction methodology for integration of complicated chemical processing on a microchip was proposed. This methodology, continuous-flow chemical processing (CFCP), is based on a combination of microunit operations (MUOs) and a multiphase flow network. Chemical operations in microchannels, such as mixing, reaction, and extraction, were classified into several MUOs. The complete procedure for Co(II) wet analysis, including a chelating reaction, solvent extraction, and purification was decomposed into MUOs and reconstructed as CFCP on a microchip. Chemical reaction and molecular transport were realized in and between continuous liquid flows in a multiphase flow network, such as aqueous/aqueous, aqueous/organic, and aqueous/organic/aqueous flows. When the determination of Co(II) in an admixture of Cu(II) was carried out using this methodology, the determination limit (2sigma) was obtained as 18 nM, and the absolute amount of Co chelates detected was 0.13 zmol, that is, 78 chelates. The sample analysis time was faster than that of a conventional processing system. Moreover, troublesome operations such as phase separation and acid and alkali washing, all necessary for the conventional system, were simplified. The CFCP methodology proposed here can be applied to various on-chip applications.

A bead-bed immunoassay system was structured on a microchip and applied to determine carcinoembryonic antigen (CEA), which is a commonly used marker of colon cancer. Polystyrene beads precoated with anti-CEA antibody were introduced into a microchannel, and then a serum sample containing CEA, the first antibody, and the second antibody conjugated with colloidal gold were reacted successively. The resulting antigen-antibodies complex, fixed on the bead surface, was detected using a thermal lens microscope (TLM). A highly selective and sensitive determination of an ultratrace amount of CEA in human sera was made possible by a sandwich immunoassay system that needs three antibodies for an assay. A detection limit dozens of times lower than the conventional ELISA was achieved. Moreover, when serum samples for 13 patients were assayed with this system, there was a high correlation (r = 0.917) with the conventional ELISA. The integration reduced the time necessary for the antigen-antibody reaction to approximately 1%, thus shortening the overall analysis time from 45 h to 35 min. Moreover, troublesome operations required for conventional heterogeneous immunoassays could be much simplified. This microchip-based diagnosis system is the first microchip-based system that is practically useful for clinical diagnoses with short analysis time, high sensitivity, and easy procedures.

We have fabricated nanometer-sized channels, demonstrated a technique for the introduction of liquid into the channels, and carried out time-resolved fluorescence measurements of aqueous solutions. In this study, 330-nm- and 850-nm-sized channels were fabricated on fused-silica substrates by fast atom beam etching and hydrofluoric acid bonding methods. A liquid introduction method utilizing capillary action was demonstrated. The liquid introduction was observed under an optical microscope, and the liquid velocity during the introduction was analyzed by surface energy and macroscale hydrodynamics. The liquid velocity due to capillary action in the nanometer-sized channel seemed more than four times slower than the estimation. Then, aqueous solutions of rhodamine 6G (R6G), sulforhodamine 101 (SR101), and rhodamine B (RB) in the channels were measured by time-resolved fluorescence spectroscopy; spectra of the same solution in a 250-microm-sized channel were also measured as a reference for the macrospace. Although the fluorescence spectra in the 330-nm-, 850-nm- and 250-microm-sized channels agreed with one another, the fluorescent decays in the nanometer-sized channels were faster for R6G and SR101 and slower for RB than the respective decays in the 250-microm-sized channels. The results suggested the solutions had lower dielectric constants and higher viscosities in the nanometer-sized channels.

An ion-pair solvent extraction was performed in a microchannel fabricated in a quartz glass chip. the aqueous solution of Fe-bathophenanthrolinedisulfonic acid complex and the chloroform solution of tri-n-octylmethylammonium chloride were introduced into the microchannel, and a parallel two-phase laminar flow was formed. The ion-pair product extracted in chloroform was monitored by the thermal lens microscope. The ion-pair product was gradually extracted from aqueous solution into chloroform when the flow was very slow or stopped, while nothing was extracted into chloroform when the flow was fast. The time for extraction in the present 250 microns microchannel, 45 s, roughly coincided with the molecular diffusion time, and the extraction time was at least 1 order shorter compared with the ordinary extraction time using a separatory funnel and mechanical shaking. The microspace in the microchannel was characterized by the large specific interface area and short diffusion distance, and these characteristics may contribute to highly efficient extraction without mechanical shaking. The success of this molecular transport may lead to the integration of more complicated separation and chemical operations on a microchip and more applications.

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The photothermal effect of an ultratrace amount of nonfluorescent molecules in liquid was determined by optimizing the optical arrangement for a thermal lens microscope. The optimized experimental setup could be determined from the evaluation of probing volume and the concentration of the sample solutions even when the expectation of the molecule number in the probing region was less than a single molecule. The minimum expectation, which is explained as being the time average, was 0.4 molecule of Pb(II) octaethylporphyrin (OEP) in benzene. The concentrations in the 9.7 x 10(-11)-7.8 x 10(-10) M region used in this work corresponded to the expected number of 0.4-3.4 molecules, and the calibration curve in this region showed good linearity. Taking into account the enhancement factor of solvent, the molar absorption coefficient of solute, and the optimization of the optical arrangement, the present result, which was the determination limit of 0.34, was consistent with that previously reported. The relation between molecular behavior in the probing volume and the signal was discussed. The average temperature rise in the probing volume by the photothermal effect for the single OEP molecule was estimated as 3.1 muK, and this value was detectable, based on conventional thermal lens measurements for bulk scale sample.

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