Abstract: Device for applying a measured quantity of water-soluble or water-dispersible reagent to a water-containing solid medium for use in molecular diffusion or affinity separation procedures is provided in the form of a film consisting essentially of a film-forming solid organic polymeric binder which is soluble in water to the extent of at least 1% by weight at 20.degree.C. and dispersed in said binder a measured quantity of said reagent, said film being of a size and shape adapted to be placed in contact with said medium to permit said reagent and binder to diffuse completely into said medium. The device is used by placing it in face-to-face contact with a water-containing solid medium.

Abstract: A hydratable or hydrated gel medium for use in bioassay of a test substance contains fixed in a localized zone a reagent for the test substance. Assays are conducted rapidly by diffusing the test substance followed by an indicator substance also reactive with the reagent into the zone and measuring a change in characteristics within the zone caused by the reaction of the indicator substance.

Abstract: A modified agarose or agar containing alkylated, alkenylated, acylated or hydroxyalkylated agarose in which the alkyl, alkenyl, and acyl groups contain from 1 to 3 carbon atoms and the hydroxyalkyl groups contain from 1 to 4 carbon atoms, which modified product has a gelling temperature at least 1.degree.C. lower than the gelling temperature of the corresponding unmodified agarose or agar. The modified material also has a lowered melting point and a higher clarity than the unmodified. The product is made by alkylation, etc. either in a non-aqueous solvent or in an aqueous alkaline solvent; in the latter case the aldehyde end group of the unmodified material may be first blocked by reduction to the hydroxyl group. The compounds are useful as thickeners, for electrophoresis and for diffusive Interactions.