The present invention provides an immunoconjugate formulation that is substantially free of particles, the immunoconjugate formulation comprising: an immunoconjugate and one or more excipients selected from the group consisting of: sucrose, polysorbate 20, polysorbate 80, cyclodextrin, dextrose, glycerol, polyethylene glycol, mannitol, sodium chloride, and an amino acid, wherein the formulation is a buffered aqueous solution having a pH of 4.5 to 7.6. The present invention also provides an immunoconjugate formulation that is substantially free of aggregates, the immunoconjugate formulation comprising: an immunoconjugate and one or more excipients selected from the group consisting of histidine, sucrose, glycine and sodium chloride, wherein the formulation is a buffered aqueous solution having a pH of 4.5 to 7.6. The present invention further provides an immunoconjugate formulation that is substantially free of both particles and aggregates. A single-use fluorescence-based assay system for determining the presence of at least one analyte in a fluid sample, especially a biological fluid sample, comprises a first reagent comprising fluorescent nanocrystals, and a second reagent comprising a quenching moiety effective under at least a predetermined condition to bind to the first reagent to quench the fluorescence of the nanocrystals. The predetermined condition may be the absence of the analyte in a fluid sample or, in alternative embodiments, the presence of the analyte in the fluid sample. Certain exemplary embodiments comprise a housing and a single-use assay component configured to be received by the housing and operative to receive sample fluid and perform an assay for at least one analyte suspected of being present in the sample fluid. The single-use fluorescence-based assay system optionally further comprises a fluorometer operative to generate excitation illumination at a detection site to cause fluorescence of the nanocrystals in the unquenched condition. In certain embodiments of the single-use fluorescence-based assay system a first reagent comprises fluorescent nanocrystals bearing one or more binding sites for the target analyte and a second reagent comprises the target analyte or an analog of the target analyte conjugated to quenching moieties. The present invention provides an immunoconjugate formulation that is substantially free of particles, the immunoconjugate formulation comprising: an immunoconjugate and one or more excipients selected from the group consisting of: sucrose, polysorbate 20, polysorbate 80, cyclodextrin, dextrose, glycerol, polyethylene glycol, mannitol, sodium chloride, and an amino acid, wherein the formulation is a buffered aqueous solution having a pH of 4.5 to 7.6. The present invention also provides an immunoconjugate formulation that is substantially free of aggregates, the immunoconjugate formulation comprising: an immunoconjugate and one or more excipients selected from the group consisting of histidine, sucrose, glycine and sodium chloride, wherein the formulation is a buffered aqueous solution having a pH of 4.5 to 7.6. The present invention further provides an immunoconjugate formulation that is substantially free of both particles and aggregates.