Simultaneous quantification of two plant viruses by double-label time-resolved immunofluorometric assay

Development of a dual-label time-resolved fluorometric immunoassay for the simultaneous detection of two recombinant proteins in potato

Immunological methods such as ELISA have been traditionally employed to quantify protein levels in plants improved through modern biotechnology. Combined trait products (i.e., plants producing multiple recombinant proteins) created by introducing multiple genetic traits by transformation or traditional breeding methods have prompted the need for the development of analytical assay technologies capable of detecting and quantifying multiple proteins in a single assay. The development of a two-site, sandwich, dual-label, time-resolved fluorometry-based immunoassay (TRFIA) capable of simultaneously quantitating two recombinant proteins (CP4 EPSPS and Cry3A) in plant sample extracts of genetically improved potato cultivars is reported here. The performance characteristics of TRFIA were similar to or exceeded those of current ELISA methods used to detect and quantitate these proteins. TRFIA is a practical and reliable assay for the quantitation of proteins in genetically improved potato plants and offers an alternative approach to conventional ELISA methods with the added benefit of multiple analyte detection.

Time-resolved fluorometry in end-point and real-time PCR quantification of nucleic acids

Two time-resolved fluorescence-based methods for nucleic acid quantification are described and their results are compared. Both methods use an exogenous internal standard to eliminate errors arising from different steps of the assay. The first method is a competitive end-point assay, where the standard competes for the same primers with the actual target sequence, prostate-specific antigen (PSA) cDNA. The standard and target are quantified in a dual-label plate hybridization with lanthanide-labelled probes after a fixed number of PCR cycles. The second method is based on real-time monitoring of PCR and on the use of a novel homogeneous signal generation principle that relies on the use of a 5'-->3' exonucleolytic DNA polymerase and a probe labelled with an environment sensitive, stable and fluorescent lanthanide chelate. In this assay, a non-competitive, exogenous internal standard is used. Both assays have a wide linear range (50-5 x 10(6) and 10-5 x 10(7) input PSA cDNA molecules for the end-point and real-time assays, respectively) and there is a strong correlation between the results obtained with the two assays (r = 1.0). Being somewhat faster to perform, the real-time format is better suited for assays that require high throughput.

Feasibility studies of simultaneous multianalyte amperometric immunoassay based on spatial resolution

A multianalyte immunoassay concept based on the geometric separation of different analyte-specific antibodies has been demonstrated. The assay and amperometric detection are done in a cell with two working electrodes controlled at the same potential, and the amperometric signal at each electrode is monitored. The distance between any two adjacent electrodes in this prototype is 2.5 mm, and during the course of amperometric measurement, the product formed at one electrode does not reach the other working electrode within 20 min after the addition of enzyme substrate. Thus, the method relies on the spatial resolution between the different antibodies being such that measurements are taken before cross-interference due to diffusion can occur. Identical enzyme labels (alkaline phosphatase, ALP) and substrates (p-aminophenyl phosphate, PAPP) are used for all analytes. Alkaline phosphatase-conjugated rat anti-mouse IgG was immobilized by passive adsorption. Our studies showed that this concept is feasible and can be applied to the simultaneous measurement of multiple analytes.

Ultrasensitive bioanalytical assays using time-resolved fluorescence detection

This article reviews the use of time-resolved fluorimetric detection of lanthanide chelate luminescence as a detection method for ultrasensitive bioanalytical assays. Assay formats and detection methods, and the principle of time-resolved fluorimetric detection, are described. Detection systems, assay formats, reagents, and instrumentation for time-resolved fluorimetric detection are outlined. A review of published and commercially available immunoassays and DNA hybridization assays using time-resolved fluorimetric detection of lanthanide chelate luminescence is given.

Time-resolved detection of lanthanide luminescence for ultrasensitive bioanalytical assays

The principles and practice of the application of time-resolved lanthanide chelate luminescence (or fluorescence) as a detection method for ultrasensitive bioanalytical assays such as immunoassays and nucleic acid hybridization assays are reviewed. The various lanthanide chelate-based detection systems which have been developed for use in heterogeneous and homogeneous assay formats are described, including reagents, assay methods, and instrumentation, along with recent improvements in these methods. Detection systems described include those based on dissociative enhancement of lanthanide ions, direct labeling with luminescent chelates, enzyme-amplified lanthanide luminescence, lanthanide luminescence quenching, and energy transfer.

Di- and tetracarboxylate derivatives of pyridines, bipyridines and terpyridines as luminogenic reagents for time-resolved fluorometric determination of terbium and dysprosium

A group of compounds composed of pyridine, 2,2'-bipyridine and 2,2':6',2''-terpyridine as the energy absorbing, triplet sensitizing moieties and two or four carboxylic acids as the chelating groups were synthesized and their ability to enhance terbium ion luminescence was elucidated. The dicarboxylic acid derivatives form highly luminescent Tb3+ chelates with luminescence quantum yields approaching 50%. Additional groups, such as methoxy groups or additional pyridine rings in the aromatic structure can be utilized to shift the excitation maxima towards longer wavelengths in order to produce more practicable excitation for practical use. The ligands giving the highest Tb3+ emissions were further evaluated in a two-step fluorescence enhancement system constructed for specific binding assays based on the simultaneous use of three or four ions as the labels (Eu3+, Tb3+, Sm3+ and Dy3+). In the two-step procedure, the first step comprises dissociative fluorescence enhancement based on an acidic solution of an aromatic beta-diketone used as the luminogenic ligand, whereafter Eu3+ and Sm3+ are quantitated. In the second step, the lanthanide ions form new chelates with the added ligands. These ligands are able to transfer the excitation energy they have absorbed with high efficiency to the chelated ions and produce high ion luminescence for Tb3+ and Dy3+.

Simultaneous detection of two cystic fibrosis alleles using dual-label time-resolved fluorometry

A simple dual-label hybridization test for normal and mutant cystic fibrosis (CF) alleles is described. The assay is based on time-resolved fluorometry (TRF), which allows the simultaneous detection of DNA probes labelled with different lanthanides from one hybridization reaction. DNA was liberated from dried blood disks, normally used in neonatal screening programmes, by boiling in alkaline solution. A 138 bp region including the site of deletion, delta F-508, which is present on about 70% of cystic fibrosis chromosomes, was amplified using the polymerase chain reaction (PCR). The presence or absence of normal and mutant alleles was then determined in a solution hybridization using allele specific oligonucleotide probes labelled either with europium (Eu) or with samarium (Sm) chelates. A common biotinylated probe was used for binding the hybrids onto microtitration wells coated with streptavidin. Some 5 x 10(7) molecules of the normal allele (Eu) and 5 x 10(8) molecules of the mutant allele (Sm) could be detected simultaneously in a single hybridization reaction. The assay was simple to perform and made it possible to reduce the number of hybridizations needed to interpret the sample as being normal, carrier or mutant with regard to the mutation, delta F-508.