Takeyuki Kawaguchi

Merocyanine J aggregates: Formation and structural change on chemical and thermal treatments

Abstract The effect of counterions of a merocyanine dye, 3-carboxymethyl-5[2-(3-octadecyl-2(3H)-benzoselenazolinylidene)ethylidene]-2-thioxo-4- thiazolidinone, on the formation of J aggregates was investigated with the monomolecular films on water and the Lamgmuir-Blodgett films. As the counterions, ammonia and various amines as well as some metal ions were employed. The dye formed J aggregates with λmax at 620–630 nm on the subphase containing Co2+, ammonia and primary amines of small size such as methylamine, ethylamine and ethylenediamine. On the subphase containing Ba2+ and Ca2+, on the contrary, the dye formed J aggregates with λmax at 600 nm. A chelate structure in the rhodanine ring was assumed to play an important role in J aggregation. The J aggregates in the film transferred onto a solid substrate were destroyed thermally and restored on subsequent treatment with water vapour as well as with ammonia vapour. In-plane anisotropy of the dye orientation did not change on treatment with aqueous HCl vapour, while the anisotropy disappeared on thermal treatment. The thermal and chemical destruction of the J aggregates was found to be based on different mechanisms.

Langmuir-Blodgett films of merocyanine J aggregates: Preparation and structural change on irradiation by laser light

Abstract J aggregate formation of a merocyanine dye, 3-carboxymethyl-5-[2- (3-octadecyl-2(3H)-benzoselenazolinylidene)ethylidene]-2-thioxo-4-thiazolidinone, and the structural change on irradiation by laser light were investigated. The dye formed two types of J aggregates as well as monomer on the subphase depending on the species of metal ions. On the aqueous solution containing Ca2+, Ba2+ and Cd2+ ions J aggregates with γmax = 600–610 nm formed while on the aqueous solution containing other metal ions such as Na+, K+, Co2+, Ni2+, Zn2+, Er3+ and Lu3+ J aggregates with γmax = 620–630 nm formed. Monolayer aggregates containing Ba2+ (former type) and Co2+ (latter type) were transferred onto substrates as X-type Langmuir-Blodgett films (LB1 and LB2 respectively). On irradiation by laser light with γ = 600±20 nm and a power density of 700 μW cm−2, the absorption spectra of both films changed dramatically owing to the dissociation of J aggregates. The dissociation was proved to proceed thermally. The rate constants for LB1 and LB2, assuming first-order reaction, were estimated to be 4.6 × 10-3 s−1 and 1.4 × 10−3 s−1 respectively. The apparent activation energy for B1 was estimated to be 7.5 kcal mol-1.

A device for visual detection of antigens and antibodies by means of light interference

Abstract A device for visual detection of antigens and antibodies was investigated. The device is composed of a light-reflecting substrate, a light-interfering layer and an immobilized antibody (antigen) layer. The detection is based on the colour change due to light interference before and after reaction of the immobilized antibody (antigen) with antigen (antibody) in an aqueous specimen. Theoretical analysis of the light interference suggested that the application of a light-reflecting layer on the surface of the device after an antigen-antibody reaction is effective for both glancing angle and clarity. Colloidal gold was found to be a good candidate for the layer. With a device of Ferrotype TM /SiO 2 (1000 A)/(mixed monomolecular film of anti-human IgG and methyl arachidate), 1 × 10 −7 g ml −1 of human IgG could be visually detected from the normal direction of the device.

Counter-ion effect of merocyanine J aggregates: formation and structural change upon chemical and thermal treatments

Abstract The counter-ion effect of the J aggregate of a merocyanine dye having a long alkyl chain was investigated with monomolecular films on water and with Langmuir-Blodgett films. As the counter-ions, various amines as well as Ba 2+ , Ca 2+ and Co 2+ were employed. The destruction and restoration of the J aggregate were also discussed in relation to the structure.

A highly sensitive device for visual detection of antigens and antibodies by means of light interference

Abstract A highly sensitive device for the visual detection of antigens and antibodies by means of light interference has been investigated. The detection is based on the change in the light interference colour after the antigen-antibody reaction of an immobilized antibody (antigen) with an antigen (antibody) in a specimen. We investigate selective staining of the antibody part by colloidal gold treatment at an optimized pH value (colloidal gold method). We have also investigated selective staining of the antigen part on the immobilized antibody by treatment with a secondary antibody bearing colloidal gold (sandwich method). Both methods are found to enhance the sensitivity. According to the colloidal gold method, less than 1 ng/ml of anti-hCG can be visually detected by using a device with immobilized hCG. With the sandwich method, 1 ng/ml of human IgG can be visually detected by using a device with immobilized anti-human IgG.

LB film immobilized immunosensor with a charge detection type amplifier

Abstract In order to fabricate a miniturized solid-state sensor, a novel potentiometric immunosensor was designed by incorporating a new amplification system of charge detection type and an electrode covered with immunogloblin-G (IgG, antigen) immobilized in a Langmuir-Blodgett (LB) film. A surface potential change of 1 μV generated by the immuno-reaction between IgG and anti-IgG (antibody) could be measured with the amplification system, which made it possible to detect the anti-IgG with concentrations less than 5 x 10-8M. The intensity of surface potential change observed in the reaction was successfully correlated with the activity of the immobilized IgG by using luminescent enzyme immunoassay.

A novel method of visual detection of antigens and antibodies by means of light interference

A novel method for detection of antigens and antibodies is proposed. The detection is based on the color change due to the light interference upon the antigen-antibody reaction with an antibody (or antigen) immobilized on a substrate with a light interference layer. By theoretical analysis, the application of a light-reflecting layer (colloidal gold) to the device after the reaction was found to be effective to visualization and contrast. With immobilized anti-human IgG, 1·10−7 g/ml of human IgG was sucessfully detected.