A method for monitoring formation of latex particle pairs by chemilumnescence is described. Molecular oxygen is excited by a photosensitizer and an antenna dye that are dissolved in one ofthe particles. 1A02dlffse to the second particle and initiates a hi quantum yield chemilu ent reaction of an olefin that is dissolved in it. An alternative homogeneous method utilizes immunochemical aggregation of ligand-or receptor-labeled particles (latex agglutination) (3). Detection of agglutination by conventional light scattering requires formation of large aggregates and has limited sensitivity. Low-angle light scattering measurements provide higher sensitivity but require rigorously exclusion of adventitious particles (4,5).In the present study, nonenzymatic channeling of 1.02 is used to provide exquisitely sensitive real-time monitoring of particle-particle interactions. The prepared by adding concentrated ammonia to 500-kDadextran (Pharmacia) that had been activated by reaction with epichlorohydrin and Zn(BF4)2. The product was purified by precipitation with methanol. Fluorescein-biotin (Fl-biotin) was prepared by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDAC) coupling of Fl-5'-COOH to 1,12-diamino-4,9-dioxadodecane followed by reaction with biotinyl-6-aminohexanoic acid N-hydroxysuccinimide ester (biotin-LC-NHS, Pierce). Bis-(6-hydroxyhexyl) disulfide and 6-amino-

Luminescent oxygen channeling assay (LOCI) is a homogeneous immunoassay method capable of rapid, quantitative determination of a wide range of analytes--including high and very low concentrations of large and small molecules, free (unbound) drugs, DNA, and specific IgM. Assays have been carried out in serum and in lysed blood. Reliable detection of 1.25 microU/L thyrotropin (TSH) and 5 ng/L hepatitis B surface antigen (HBsAg) corresponds to detection limits approximately 3- and approximately 20-fold lower, respectively, than those of the best commercially available assays. An assay of chorionic gonadotropin is capable of quantification over a 10(6)-fold range of concentrations without a biphasic response. Latex particle pairs are formed in the assay through specific binding interactions by sequentially combining the sample and two reagents. One particle contains a photosensitizer, the other a chemiluminescer. Irradiation causes photosensitized formation of singlet oxygen, which migrates to a bound particle and activates the chemiluminescer, thereby initiating a delayed luminescence emission. Assay times range from 1 to 25 min.

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An automated enzymatic method was developed for the measurement of D-arabinitol in human serum. The assay is based on a novel, highly specific D-arabinitol dehydrogenase from Candida tropicalis. This enzyme catalyzes the oxidation of D-arabinitol to D-ribulose and the concomitant reduction of NAD+ to NADH. The NADH produced is used in a second reaction to reduce p-iodonitrotetrazolium violet (INT) to INT-formazan, which is measured spectrophotometrically. The entire reaction sequence can be performed automatically on a COBAS MIRA-S clinical chemistry analyzer (Roche Diagnostic Systems, Inc., Montclair, N.J.). Replicate analyses of human sera supplemented with D-arabinitol over a concentration range of 0 to 40 microM demonstrated that the pentitol could be measured with an accuracy of +/- 7% and a precision (standard deviation) of +/- 0.4 microM. Serum D-arabinitol measurements correlated with those determined by gas chromatography (r = 0.94). The enzymatic method is unaffected by L-arabinitol, D-mannitol, or other polyols commonly found in human serum. Any of 17 therapeutic drugs potentially present in serum did not significantly influence assay performance. Data illustrating the application of the assay in patients for possible diagnosis of invasive candidiasis and the monitoring of therapeutic intervention are presented. The automated assay described here was developed to facilitate the investigation of D-arabinitol as a serum marker for invasive Candida infections.