Europium cryptate-tethered ribonucleotide for the labeling of RNA and its detection by time-resolved amplification of cryptate emission

Review: immunoassays in DNA damage and instability detection

The review includes information on the current state of knowledge of immunometric methods with emphasis on the possibility of deoxyribonucleic acid (DNA) damage detection. Beginning with basic immunoassay enzyme-linked immunosorbent assay (ELISA), this review describes methods such as tyramide signal amplification (TSA), enhanced polymer one-step staining (EPOS), and time resolved amplified cryptate emission (TRACE) as improvements of ELISA's developed over time to obtain more accurate results. In the second part of the review, surface plasmon resonance (SPR) and quantum dots (QDs) are presented as the newest outlooks in the context of immunoanalysis of biological material and molecular studies. The aim of this review is to briefly present immunoassays with emphasis on DNA damage detection; therefore, the types of methods are listed and described, types of signal indicators, basic definitions such as antigen and antibody are given. Every method is considered with an exemplary application focusing on DNA studies, DNA damage and instability detection.

Luminescent lanthanide cryptates: from the bench to the bedside

The design and application of luminescent lanthanide cryptates for sensing biological interactions is highlighted through the review of the work performed in our laboratory and with academic collaborations. The path from the initial applications probing biochemical interaction in vitro to "state-of-the-art" cellular assays toward clinical applications using homogeneous time-resolved fluorescence technology is described. An overview of the luminescent lanthanide macrocyclic compounds developed at Cisbio in the recent past is given with an emphasis on specific constraints required by specific applications. Recent assays for drug-discovery and diagnostic purposes using both antibody-based and suicide-enzyme-based technology are illustrated. New perspectives in the field of molecular medicine and time-resolved microscopy are discussed.

Site-specific fluorescent labeling of RNA molecules by specific transcription using unnatural base pairs

Site-specific fluorescent labeling of RNA molecules was achieved by specific transcription using an unnatural base pair system. The unnatural base pairs between 2-amino-6-(2-thienyl)purine (s) and 2-oxo(1H)pyridine (y), and 2-amino-6-(2-thiazolyl)purine (v) and y function in transcription, and the substrates of y and 5-modified y bases can be site-specifically incorporated into RNA, opposite s or v in DNA templates, by T7 RNA polymerase. Ribonucleoside 5'-triphosphates of 5-fluorophore-linked y bases were chemically synthesized from the nucleoside of y. These fluorescent substrates were site-specifically incorporated into RNA by transcription mediated by the s-y and v-y pairs. By using this fluorescent labeling method, specific positions of Raf-binding and theophylline-binding RNA aptamers were fluorescently labeled, and the specific binding to their target molecules was detected by their fluorescent intensities. This site-specific labeling method using an unnatural base pair system will be useful for analyzing conformational changes of RNA molecules and for detecting interactions between RNA and its binding species.

Immunoassay of total prostate-specific antigen using europium(III) nanoparticle labels and streptavidin-biotin technology

Nanoparticle labels conjugated with biomolecules are used in a variety of different assay applications. We investigated the possibility of using europium(III)-labeled 68-nm nanoparticles coated with monoclonal antibodies or streptavidin (SA) to detect prostate-specific antigen (PSA) in serum. The selection of a suitable antibody pair and interference caused by the combination of nanoparticle label and structurally complex analyte were of special interest. A set of antibodies recognizing different epitope areas of PSA was mapped to find the optimal antibody pair for the immunometric nanoparticle-based assay. Different assay configurations were tested to obtain a good correlation with a conventional method based on biotinylated detection antibodies and europium(III) chelate-labeled streptavidin. Monoclonal capture antibody 5E4 was covalently coated on a microtitration well surface; biotinylated 5H6 monoclonal antibody (Mab) was used for detection, and europium(III)-labeled streptavidin-coated nanoparticles were utilized for signal generation. Total PSA concentrations were determined from a panel of male serum samples to test the developed assay. The correlation of the nanoparticle-based and reference assays was good; y=0.9844x-0.1252, R2=0.98, n=27; and the lowest limit of detection of the assay (LLD=0.83 ng/l) was 35-fold lower than for the reference method. The assay application presented here, where a structurally complex analyte is detected, combines the exceptionally high affinity of streptavidin-biotin technology and the high specific activity of long lifetime fluorescence nanoparticle labels. The general characteristics of this combination should permit the development of various immunoassay applications featuring high sensitivity, rapidity, and low consumption of reagents.

A separation-free assay for the detection of mutations: Combination of homogeneous time-resolved fluorescence and minisequencing

Single nucleotide primer extension reaction has been widely used in DNA testing, and several detection methods based on this core allelic discrimination have been developed. Most of the reported formats are based on a two step protocol involving first, a liquid phase extension reaction, then a physical separation process (chromatography, electrophoresis, capture on solid support, mass spectrometry). Here we describe a new strategy based on homogeneous time-resolved fluorescence (HTRF), which does not involve any separation process and which allows a simple "mix and measure" protocol. In this approach, a 5'-(europium) cryptate-labeled primer is elongated by a biotinylated dideoxynucleoside-triphosphate, followed by the addition of a streptavidin-acceptor conjugate, which gives rise to a long-life fluorescence resonance energy transfer (FRET) signal between the cryptate donor and the acceptor. We present the development of HTRF technology as applied to the diagnosis of tumor suppressor gene p53 (TP53) mutations, and its application to the analysis of genomic DNA from human tumoral samples. The sensitivity of the reported method is compared to the corresponding fluorescent polarization assay.

Time resolved amplification of cryptate emission: a versatile technology to trace biomolecular interactions

Fluorescence resonance energy transfer (FRET) in association with a time-resolved fluorescence mode of detection was used to design a new homogeneous technology suitable to monitor biomolecular interactions. A lanthanide cryptate characterised by a long lived fluorescence emission was used as donor and a cross-linked allophycocyanine was used as acceptor. This new donor/acceptor pair displayed an exceptionally large Forster radius of 9 nm. This allowed to build up a set of labelling strategies to probe the interactions between biomolecules with an emphasis on fully indirect cassette formats particularly suitable for high throughput screening applications. Herein we describe the basics of the technology, review the latest applications to the study of molecular interactions involved in cells and new oligonucleotides based assays.

Homogeneous time resolved fluorescence resonance energy transfer using rare earth cryptates as a tool for probing molecular interactions in biology

A homogeneous assay technology using time resolved fluorescence and fluorescence resonance energy transfer is described. A new class of fluorescent complexes, the cryptates, have been used as fluorescent donor with cross-linked allophycocyanin as acceptor. This new donor/acceptor shows an exceptionally high Förster distance R0 of 9 nm. This allows to build up a set of strategies to probe the interactions of biomolecules in biology, particularly for high throughput screening applications. In this article, we describe the basics of the technology and review applications developed for studying different key molecular interactions involved in cellular processes.

A homogeneous europium cryptate-based assay for the diagnosis of mutations by time-resolved fluorescence resonance energy transfer

Oligonucleotide ligation assay (OLA) is considered to be a very useful methodology for the detection and characterization of mutations, particularly for clinical purposes. The fluorescence resonance energy transfer between a fluorescent donor and a suitable fluorophore as acceptor has been applied in the past to several scientific fields. This technique is well adapted to nucleic acid analysis such as DNA sequencing, DNA hybridization and polymerase chain reaction. We describe here a homogeneous format based on the use of a rare earth cryptate label as donor: tris-bipyridine-Eu(3+). The long-lived fluorescence of this label makes it possible to reach a high sensitivity by using a time-resolved detection mode. A non-radiative energy transfer technology, known as time-resolved amplification of cryptate emission (TRACE((R))) characterized by a temporal and spectral selectivity has been developed. The TRACE((R)) detection of characterized single nucleotide polymorphism using the OLA for allelic discrimination is proposed. We demonstrate the potentialities of this OLA-TRACE((R)) methodology through the analysis of K-ras oncogene point mutations.