A simple dry chemistry time-resolved fluorescence immunoassay (TR-FIA) method was developed for the measurement of zeranol in bovine urine samples. The samples were purified by immunoaffinity chromatography and a specificity-enhanced zeranol antibody was employed in the immunoassay. This resulted in a highly selective method, which had only negligible reactivity with Fusarium spp. toxins. The all-in-one-well dry chemistry concept made the assay very simple to use because all the assay-specific reagents were already present in the reaction wells in dry form. Only the addition of diluted sample extract was required to perform the competitive one-step TR-FIA and the results were available in less than 1 h. The analytical limit of detection (mean + 3s) for the immunoassay was 0.16 ng ml(-1) (n = 12) and the functional limit of detection for the whole method, estimated by the analysis of zeranol-free samples, was 1.3 ng ml(-1) (n = 20). The recovery of zeranol at the level of 2 ng ml(-1) was 99% (n = 18) and the within-assay variation ranged between 4.5 and 9.0%.

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We have studied parameters affecting DNA hybridization and lanthanide chelate complementation based signal formation in a separation-free solid-phase assay suitable for spatial multiplexing.

The time-resolved luminescence of lanthanide complexes is a highly sensitive and widely used bioassay technology for clinical diagnostics. With the time-resolved luminescence detection the naturally occurring autofluorescence of biological matrices, solid supports and plastics can be avoided. A major drawback of the current technique is that the luminescent lanthanide labels require ultraviolet (UV) excitation, typically shorter than 360 nm, which is strongly absorbed and can damage living biological systems. The lack of cost-efficient high power solid state excitation light sources for UV excitation further limits the development of low-cost and more compact measurement instruments for time-resolved luminescence and the potential use of lanthanide luminescence in different applications. Switchable lanthanide luminescence is a binary probe technology that inherently enables a high signal modulation in a separation-free detection of targets. The intrinsically luminescent lanthanide chelate is split into two nonluminescent moieties, a lanthanide ion carrier chelate and a light harvesting antenna ligand, each of which can be attached to a separate molecular probe. A luminescent lanthanide complex is formed only when the two probes bind adjacently to the target molecule. Herein we describe a new 365 nm excitable antenna ligand (AL360) for switchable lanthanide luminescence of europium(iii) (Eu) that would enable the use of 365 nm light emitting diodes (LEDs) as an excitation light source for time-resolved fluorescence imaging and detection. With the acquired subpicomolar assay sensitivity it would be applicable for solution or surface arrays and UV LED microscopy.