A new minor groove binding asymmetric cyanine reporter dye for real-time PCR

Halogen-containing thiazole orange analogues - new fluorogenic DNA stains

Novel asymmetric monomeric monomethine cyanine dyes 5a–d, which are analogues of the commercial dsDNA fluorescence binder thiazole orange (TO), have been synthesized. The synthesis was achieved by using a simple, efficient and environmetally benign synthetic procedure to obtain these cationic dyes in good to excellent yields. Interactions of the new derivatives of TO with dsDNA have been investigated by absorption and fluorescence spectroscopy. The longest wavelength absorption bands in the UV–vis spectra of the target compounds are in the range of 509–519 nm and these are characterized by high molar absorptivities (63000–91480 L·mol⁻¹·cm⁻¹). All investigated dyes from the series are either not fluorescent or their fluorescence is quite low, but they become strongly fluorescent after binding to dsDNA. The influence of the substituents attached to the chromophores was investigated by combination of spectroscopic (UV–vis and fluorescence spectroscopy) and theoretical (DFT and TDDFT calculations) methods.

A novel label-free fluorescence assay for one-step sensitive detection of Hg2+ in environmental drinking water samples

A novel label-free fluorescence assay for detection of Hg²⁺ was developed based on the Hg²⁺-binding single-stranded DNA (ssDNA) and SYBR Green I (SG I). Differences from other assays, the designed rich-thymine (T) ssDNA probe without fluorescent labelling can be rapidly formed a T-Hg²⁺-T complex and folded into a stable hairpin structure in the presence of Hg²⁺ in environmental drinking water samples by facilitating fluorescence increase through intercalating with SG I in one-step. In the assay, the fluorescence signal can be directly obtained without additional incubation within 1 min. The dynamic quantitative working ranges was 5–1000 nM, the determination coefficients were satisfied by optimization of the reaction conditions. The lowest detection limit of Hg²⁺ was 3 nM which is well below the standard of U.S. Environmental Protection Agency. This method was highly specific for detecting of Hg²⁺ without being affected by other possible interfering ions from different background compositions of water samples. The recoveries of Hg²⁺ spiked in these samples were 95.05–103.51%. The proposed method is more viable, low-costing and simple for operation in field detection than the other methods with great potentials, such as emergency disposal, environmental monitoring, surveillance and supporting of ecological risk assessment and management.

Application of unique sequence index (USI) barcode to gene expression profiling in gastric adenocarcinoma

Accurate expression profiling is imperative for understanding the biological roles of mRNAs. Real-time PCR have been at the forefront of biological innovation in detection and monitoring of gene expression, however, fluorophore-labeled oligonucleotides and double-stranded DNA binding dyes, the two most frequently used dyes in RNA detection, are not very cost effective and have poor specificity, respectively. We have developed a cost effective and specific approach for mRNA expression profiling via added unique sequence index (USI) to cDNAs before amplification. USI is a barcode which enable the detection of each target RNA. Using this method, caudal type homeobox 1 (CDX1) and FAT atypical cadherin 4 (FAT4) expressions were investigated in tumoral and non-tumoral tissues of gastric cancer patients and compared with commercial ABI kit. Both methods indicated that FAT4 and CDX1 expression were significantly reduced in gastric cancer tissues compared with adjacent noncancerous tissues. Moreover, we have shown that this assay is highly sensitive, linear and reproducible. USI barcode not only provides a powerful tool for mRNA detection due to its sensitivity, specificity and cost-effectiveness, but also allows comfortable design for real-time qPCR assays within the least time and empowers the analysis of many transcripts of virtually any organism. Furthermore, USI barcode is highly affordable for large numbers of different samples or small sample sizes without microarray and expensive commercial platforms.

Key Structural Elements of Unsymmetrical Cyanine Dyes for Highly Sensitive Fluorescence Turn-On DNA Probes

Unsymmetrical cyanine dyes, such as thiazole orange, are useful for the detection of nucleic acids with fluorescence because they dramatically enhance the fluorescence upon binding to nucleic acids. Herein, we synthesized a series of unsymmetrical cyanine dyes and evaluated their fluorescence properties. A systematic structure-property relationship study has revealed that the dialkylamino group at the 2-position of quinoline in a series of unsymmetrical cyanine dyes plays a critical role in the fluorescence enhancement. Four newly designed unsymmetrical cyanine dyes showed negligible intrinsic fluorescence in the free state and strong fluorescence upon binding to double-stranded DNA (dsDNA) with a quantum yield of 0.53 to 0.90, which is 2 to 3 times higher than previous unsymmetrical cyanine dyes. A detailed analysis of the fluorescence lifetime revealed that the dialkylamino group at the 2-position of quinoline suppressed nonradiative decay in favor of increased fluorescence quantum yield. Moreover, these newly developed dyes were able to stain the nucleus specifically in fixed HeLa cells examined by using a confocal laser-scanning microscope.

Quantitative Real-Time PCR: Recent Advances

Quantitative real-time polymerase chain reaction is a technique for simultaneous amplification and product quantification of a target DNA as the process takes place in real time in a "closed-tube" system. Although this technique can provide an absolute quantification of the initial template copy number, quantification relative to a control sample or second sequence is typically adequate. The quantification process employs melting curve analysis and/or fluorescent detection systems and can provide amplification and genotyping in a relatively short time. Here we describe the properties and uses of various fluorescent detection systems used for quantification.

Multiplex qPCR for serodetection and serotyping of hepatitis viruses: A brief review

The present review describes the current status of multiplex quantitative real time polymerase chain reaction (qPCR) assays developed and used globally for detection and subtyping of hepatitis viruses in body fluids. Several studies have reported the use of multiplex qPCR for the detection of hepatitis viruses, including hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), hepatitis D virus (HDV), and hepatitis E virus (HEV). In addition, multiplex qPCR has also been developed for genotyping HBV, HCV, and HEV subtypes. Although a single step multiplex qPCR assay for all six hepatitis viruses, i.e., A to G viruses, is not yet reported, it may be available in the near future as the technologies continue to advance. All studies use a conserved region of the viral genome as the basis of amplification and hydrolysis probes as the preferred chemistries for improved detection. Based on a standard plot prepared using varying concentrations of template and the observed threshold cycle value, it is possible to determine the linear dynamic range and to calculate an exact copy number of virus in the specimen. Advantages of multiplex qPCR assay over singleplex or other molecular techniques in samples from patients with co-infection include fast results, low cost, and a single step investigation process.

Real-time PCR detection chemistry

Real-time PCR is the method of choice in many laboratories for diagnostic and food applications. This technology merges the polymerase chain reaction chemistry with the use of fluorescent reporter molecules in order to monitor the production of amplification products during each cycle of the PCR reaction. Thus, the combination of excellent sensitivity and specificity, reproducible data, low contamination risk and reduced hand-on time, which make it a post-PCR analysis unnecessary, has made real-time PCR technology an appealing alternative to conventional PCR. The present paper attempts to provide a rigorous overview of fluorescent-based methods for nucleic acid analysis in real-time PCR described in the literature so far. Herein, different real-time PCR chemistries have been classified into two main groups; the first group comprises double-stranded DNA intercalating molecules, such as SYBR Green I and EvaGreen, whereas the second includes fluorophore-labeled oligonucleotides. The latter, in turn, has been divided into three subgroups according to the type of fluorescent molecules used in the PCR reaction: (i) primer-probes (Scorpions, Amplifluor, LUX, Cyclicons, Angler); (ii) probes; hydrolysis (TaqMan, MGB-TaqMan, Snake assay) and hybridization (Hybprobe or FRET, Molecular Beacons, HyBeacon, MGB-Pleiades, MGB-Eclipse, ResonSense, Yin-Yang or displacing); and (iii) analogues of nucleic acids (PNA, LNA, ZNA, non-natural bases: Plexor primer, Tiny-Molecular Beacon). In addition, structures, mechanisms of action, advantages and applications of such real-time PCR probes and analogues are depicted in this review.

The potential of high resolution melting analysis (hrma) to streamline, facilitate and enrich routine diagnostics in medical microbiology

BACKGROUND

Routine medical microbiology diagnostics relies on conventional cultivation followed by phenotypic techniques for identification of pathogenic bacteria and fungi. This is not only due to tradition and economy but also because it provides pure culture needed for antibiotic susceptibility testing. This review focuses on the potential of High Resolution Melting Analysis (HRMA) of double-stranded DNA for future routine medical microbiology.

METHODS AND RESULTS

Search of MEDLINE database for publications showing the advantages of HRMA in routine medical microbiology for identification, strain typing and further characterization of pathogenic bacteria and fungi in particular. The results show increasing numbers of newly-developed and more tailor-made assays in this field. For microbiologists unfamiliar with technical aspects of HRMA, we also provide insight into the technique from the perspective of microbial characterization.

CONCLUSIONS

We can anticipate that the routine availability of HRMA in medical microbiology laboratories will provide a strong stimulus to this field. This is already envisioned by the growing number of medical microbiology applications published recently. The speed, power, convenience and cost effectiveness of this technology virtually predestine that it will advance genetic characterization of microbes and streamline, facilitate and enrich diagnostics in routine medical microbiology without interfering with the proven advantages of conventional cultivation.

Optimization of potent hepatitis C virus NS3 helicase inhibitors isolated from the yellow dyes thioflavine S and primuline

A screen for hepatitis C virus (HCV) NS3 helicase inhibitors revealed that the commercial dye thioflavine S was the most potent inhibitor of NS3-catalyzed DNA and RNA unwinding in the 827-compound National Cancer Institute Mechanistic Set. Thioflavine S and the related dye primuline were separated here into their pure components, all of which were oligomers of substituted benzothiazoles. The most potent compound (P4), a benzothiazole tetramer, inhibited unwinding >50% at 2 ± 1 μM, inhibited the subgenomic HCV replicon at 10 μM, and was not toxic at 100 μM. Because P4 also interacted with DNA, more specific analogues were synthesized from the abundant dimeric component of primuline. Some of the 32 analogues prepared retained ability to inhibit HCV helicase but did not appear to interact with DNA. The most potent of these specific helicase inhibitors (compound 17) was active against the replicon and inhibited the helicase more than 50% at 2.6 ± 1 μM.

Establishment of real-time quantitative reverse transcription polymerase chain reaction assay for transcriptional analysis of duck enteritis virus UL55 gene

BACKGROUND

Real-time quantitative reverse transcription polymerase chain reaction assay (qRT-PCR) has become the benchmark for detection and quantification of target gene expression level and been utilized increasingly in detection of viral load and therapy monitoring. The dynamic transcription variation of duck enteritis virus UL55 gene during the life cycle of duck enteritis virus in infected cells has not been reported yet.

RESULTS

The newly identified duck enteritis virus UL55 gene was amplified and cloned into pMD18-T vector after digestion to generate a recombinant plasmid pMD18-T/UL55 for the establishment of qRT-PCR as standard DNA. The results of agarose gel electrophoresis and melting curve analysis demonstrated the primers we designed for qRT-PCR were specific and available. We used β-actin as a reference gene for normalization and established two standard curves based on pMD18-T/UL55 and pMD18-T/β-actin successfully. Based on that, the transcriptional analysis of DEV UL55 gene was performed, and the result suggested the expression of UL55 mRNA was at a low level from 0 to 8 h post-infection(p.i.), then accumulated quickly since 12 h p.i. and peaked at 36 h p.i., it can be detected till 60 h p.i.. Nucleic acid inhibition test was carried out for analyzing a temporal regulation condition of DEV UL55 gene, result revealed that it was sensitive to ganciclovir. Synthesis procedures of DEV UL55 gene can be inhibited by ganciclovir.

CONCLUSIONS

The method we established in this paper can provide quantitative values reflecting the amounts of measured mRNA in samples. It's available for detection and quantification, also can be used in DEV diagnosis. The DEV UL55 gene was produced most abundantly during the late phase of replication in DEV-infected cells and the transcription of it depended on the synthesized DNA. DEV UL55 gene is a γ2 gene which occurs last and have a strict requirement for viral DNA synthesis.

1,2-propanediol-trehalose mixture as a potent quantitative real-time PCR enhancer

Background

Quantitative real-time PCR (qPCR) is becoming increasingly important for DNA genotyping and gene expression analysis. For continuous monitoring of the production of PCR amplicons DNA-intercalating dyes are widely used. Recently, we have introduced a new qPCR mix which showed improved amplification of medium-size genomic DNA fragments in the presence of DNA dye SYBR green I (SGI). In this study we tested whether the new PCR mix is also suitable for other DNA dyes used for qPCR and whether it can be applied for amplification of DNA fragments which are difficult to amplify.

Results

We found that several DNA dyes (SGI, SYTO-9, SYTO-13, SYTO-82, EvaGreen, LCGreen or ResoLight) exhibited optimum qPCR performance in buffers of different salt composition. Fidelity assays demonstrated that the observed differences were not caused by changes in Taq DNA polymerase induced mutation frequencies in PCR mixes of different salt composition or containing different DNA dyes. In search for a PCR mix compatible with all the DNA dyes, and suitable for efficient amplification of difficult-to-amplify DNA templates, such as those in whole blood, of medium size and/or GC-rich, we found excellent performance of a PCR mix supplemented with 1 M 1,2-propanediol and 0.2 M trehalose (PT enhancer). These two additives together decreased DNA melting temperature and efficiently neutralized PCR inhibitors present in blood samples. They also made possible more efficient amplification of GC-rich templates than betaine and other previously described additives. Furthermore, amplification in the presence of PT enhancer increased the robustness and performance of routinely used qPCRs with short amplicons.

Conclusions

The combined data indicate that PCR mixes supplemented with PT enhancer are suitable for DNA amplification in the presence of various DNA dyes and for a variety of templates which otherwise can be amplified with difficulty.

1-(5-Carboxy-pent-yl)-2,3,3-trimethyl-3H-indol-1-ium bromide monohydrate

In the title compound, C(17)H(24)NO(2) (+)·Br(-)·H(2)O, the pentyl group chain in the cation extends nearly perpendicular [N-C-C-C = -64.4 (3)°] to the mean plane of the indole ring with the carboxyl end group twisted such that the dihedral angle between the mean planes of the indole and carb-oxy groups measures 43.2 (4)°. Both ions in the salt form inter-molecular hydrogen bonds (O-H⋯Br and O-H⋯O) with the water mol-ecule. As a result of the Br⋯H-O-H⋯Br inter-actions, a zigzag chain is formed in the c-axis direction. The crystal packing is influenced by the collective action of the O-H⋯O and O-H⋯Br inter-molecular inter-actions as well as π-π stacking inter-molecular inter-actions between adjacent benzyl rings of the indole group [centroid-centroid distance = 3.721 (13) Å] and inter-molecular C-H⋯π inter-actions between a methyl hydrogen and the benzyl ring of the indole group. The O-H⋯Br inter-actions form a distorted tetra-hedral array about the central Br atom. A MOPAC AM1 calculation provides support to these observations.

A convenient thiazole orange fluorescence assay for the evaluation of DNA duplex hybridization stability

OBJECTIVE

A simple and rapid method for measuring the hybridization stability of duplexes of DNAs and other oligomers in different environments is described. When added to an oligomer duplex, the thiazole orange (TO) dye intercalates and in this state is fluorescent. Therefore, when duplex dissociation occurs, the release of TO results in a detectable change in fluorescence intensity. This assay was developed primarily to screen antisense oligomer duplexes that are stable in serum and in the cytoplasm but unstable in the presence of their target messenger RNA (mRNA).

METHODS

The two antisense oligomers of this investigation were both 25 mer phosphorothioate (PS) DNAs, one directed against the RIalpha mRNA and the other directed against the mdr1 mRNA. The former duplex was first used in the solution studies, in most cases duplexed with a 16 mer phosphodiester (PO) complementary DNA (i.e., PS-DNA25/PO-cDNA16). Both duplexes were then tested in a series of cell studies using SK-BR-3 (RIalpha+), KB-G2 (mdr1++), and KB-31 (mdr1+/-) cells.

RESULTS

Preliminary measurements in solution showed that maximum fluorescence was achieved when more than ten TO molecules were bound to each duplex. When a 25 mer PO-DNA or PO-RNA with the base sequence of the RIalpha mRNA was added, the dramatic change in fluorescence intensity that followed signified dissociation of the antisense DNA from the study duplex and reassociation with the target DNA. Kinetic measurements showed that this process was completed in about 3 min. Fluorescent measurements of SK-BR-3 (RIalpha+) cells incubated at 37 degrees C with the anti-RIalpha study duplex over time showed a maximum at the point where the loss of fluorescence due to dissociation of the study duplex, probably by an antisense mechanism, began to dominate over the increasing fluorescence due to continuing cellular accumulation. A similar result was observed in the KB-G2 (mdr1+) cells incubated with the anti-mdr1 study duplex.

CONCLUSIONS

When study duplexes shown to be stable in serum were incubated with their target cells, the assay successfully detected evidence of dissociation, most likely by an antisense mechanism. Thus, a TO fluorescence assay has been developed that is capable of detecting the dissociation of DNA duplexes.

BOXTO as a real-time thermal cycling reporter dye

The unsymmetrical cyanine dyes BOXTO (4-[6-(benzoxazole-2-yl-(3-methyl-)-2,3-dihydro-(benzo-1,3-thiazole)-2- methylidene)]-1-methyl-quinolinium chloride)and its positive divalent derivative BOXTO-PRO (4-[(3-methyl-6-(benzoxazole-2-yl)-2,3-dihydro-(benzo-1,3-thiazole)-2-methylidene)]-1-(3-trimethylammonium-propyl)-quinolinium dibromide) were studied as real-time PCR reporting fluorescent dyes and compared to SYBR GREEN I (SG)(2-[N- (3-dimethylaminopropyl)-N-propylamino] -4-[2,3-dihydro-3-methyl-(benzo-1,3-thiazol-2-yl)-methylidene]-1-phenyl- quinolinium).Unmodified BOXTO showed no inhibitory effects on real-time PCR,while BOXTO-PRO showed complete inhibition. Sufficient fluorescent signal was acquired when 0.5-1.0 meu M BOXTO was used with RotorGene and iCycler platforms.Statistical analysis showed that there is no significant difference between the efficiency and dynamic range of BOXTO and SG.BOXTO stock solution (1.5 mM) was stable at -20 degree C for more than one year and 40 meu M BOXTO solution was more stable than 5x SG when both were stored at 4 degree C for 45 days.

A strategy to setup codominant microsatellite analysis for high-resolution-melting-curve-analysis (HRM)

Background

High resolution melting curve analysis (HRM) is a technique that measures exactly the decreasing fluorescence of intercalating dye in the process of dissociation of double stranded DNA. The measurement is immediately following PCR in a one-step, closed-tube method. The shape of the melting curve depends on the GC content, length and sequence of the amplicon. Hence it is a powerful, fast and cheap method to detect Single Nucleotide Polymorphisms (SNPs) and other mutations.

Results

Here we present a strategy to set up microsatellite analysis for HRM including the correct assignment of heterozygous samples by comparative analysis and artificial mixtures of samples. The approach is demonstrated on two Simple Sequence Repeat (SSR) loci of different complexity in the genus Origanum. Following this strategy all alleles of our sample sets could be classified correctly.

Conclusion

HRM can be used in microsatellite analysis and other codominant marker systems implementing a protocol of comparative melting curve assignment with artificial mixtures of samples to overcome difficulties in correctly assigning heterozygous samples. The method is faster, more sensitive and cheaper than standard protocols for microsatellite analysis.

Microwave synthesis of quaternary ammonium salts

The microwave synthesis of several quaternary ammonium salts is described. The synthesis provides comparable or better yields than published methods with reduced reaction times and in the absence of solvent.

Characterization of EvaGreen and the implication of its physicochemical properties for qPCR applications

Background

EvaGreen (EG) is a newly developed DNA-binding dye that has recently been used in quantitative real-time PCR (qPCR), post-PCR DNA melt curve analysis and several other applications. However, very little is known about the physicochemical properties of the dye and their relevance to the applications, particularly to qPCR and post PCR DNA melt curve analysis. In this paper, we characterized EG along with a widely used qPCR dye, SYBR Green I (SG), for their DNA-binding properties and stability, and compared their performance in qPCR under a variety of conditions.

Results

This study systematically compared the DNA binding profiles of the two dyes under different conditions and had these findings: a) EG had a lower binding affinity for both double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA) than SG; b) EG showed no apparent preference for either GC- or AT-rich sequence while SG had a slight preference for AT-rich sequence; c) both dyes showed substantially lower affinity toward ssDNA than toward dsDNA and even lower affinity toward shorter ssDNA fragments except that this trend was more pronounced for EG. Our results also demonstrated that EG was stable both under PCR condition and during routine storage and handling. In the comparative qPCR study, both EG and SG exhibited PCR interference when used at high dye concentration, as evident from delayed Ct and/or nonspecific product formation. The problem worsened when the chain extension time was shortened or when the amplicon size was relatively long (>500 bp). However, qPCR using EG tolerated a significantly higher dye concentration, thus permitting a more robust PCR signal as well as a sharper and stronger DNA melt peak. These differences in qPCR performance between the two dyes are believed to be attributable to their differences in DNA binding profiles.

Conclusion

These findings suggest that an ideal qPCR dye should possess several DNA-binding characteristics, including a "just right" affinity for dsDNA and low or no affinity for ssDNA and short DNA fragments. The favorable DNA-binding profile of EG, coupled with its good stability and instrument-compatibility, should make EG a promising dye for qPCR and related applications.

Comparison of multiple DNA dyes for real-time PCR: effects of dye concentration and sequence composition on DNA amplification and melting temperature

The importance of real-time polymerase chain reaction (PCR) has increased steadily in clinical applications over the last decade. Many applications utilize SYBR Green I dye to follow the accumulation of amplicons in real time. SYBR Green I has, however, a number of limitations that include the inhibition of PCR, preferential binding to GC-rich sequences and effects on melting curve analysis. Although a few alternative dyes without some of these limitations have been recently proposed, no large-scale investigation into the properties of intercalating dyes has been performed. In this study, we investigate 15 different intercalating DNA dyes for their inhibitory effects on PCR, effects on DNA melting temperature and possible preferential binding to GC-rich sequences. Our results demonstrated that in contrast to the results of SYBR Green I, two intercalating dyes SYTO-13 and SYTO-82 do not inhibit PCR, show no preferential binding to GC rich sequences and do not influence melting temperature, T_m, even at high concentrations. In addition, SYTO-82 demonstrated a 50-fold lower detection limit in a dilution series assay. In conclusion, the properties of SYTO-82 and SYTO-13 will simplify the development of multiplex assays and increase the sensitivity of real-time PCR.

Novel, Monomeric Cyanine Dyes as Reporters for DNA Helicase Activity

The dimeric cyanine dyes, YOYO-1 and TOTO-1, are widely used as DNA probes because of their excellent fluorescent properties. They have a higher fluorescence quantum yield than ethidium homodimer, DAPI and Hoechst dyes and bind to double-stranded DNA with high affinity. However, these dyes are limited by heterogeneous staining at high dye loading, photocleavage of DNA under extended illumination, nicking of DNA, and inhibition of the activity of DNA binding enzymes. To overcome these limitations, seven novel cyanine dyes (Cyan-2, DC-21, DM, DM-1, DMB-2OH, SH-0367, SH1015-OH) were synthesized and tested for fluorescence emission, resistance to displacement by Mg(2+), and the ability to function as reporters for DNA unwinding. Results show that Cyan-2, DM-1, SH-0367 and SH1015-OH formed highly fluorescent complexes with dsDNA. Of these, only Cyan-2 and DM-1 exhibited a large fluorescence enhancement in buffers, and were resistant to displacement by Mg(2+). The potential of these two dyes to function as reporter molecules was evaluated using continuous fluorescence, DNA helicase assays. The rate of DNA unwinding was not significantly affected by either of these two dyes. Therefore, Cyan-2 and DM-1 form the basis for the synthesis of novel cyanine dyes with the potential to overcome the limitations of YOYO-1 and TOTO-1.

New amino and acetamido monomethine cyanine dyes for the detection of DNA in agarose gels

Some new monomethine cyanine dyes derived from quinoline and benzothiazole have been prepared and characterized by (1)H and (13)C NMR, FTIR, FABHRMS, and visible spectroscopy. The dyes containing amino and acetamido groups were conveniently synthesized by the condensation of two p-toluenesulfonate heterocyclic quaternary salts and were obtained in the forms of iodide, bromide, and tosylate counteranions. These dyes were compared to ethidium bromide as stains for DNA in electrophoretic gels. The overall results obtained for the sensitivity of these dyes suggest the suitability of acetamido moiety over the amine one and bromide as the counteranion when compared with iodide and tosylate, with a similar capacity of DNA detection in relation to the ethidium bromide stain over the concentration range of 1-3ng.

Postcolumn nucleic acid intercalation for the fluorescent detection of nucleic acids using ion pair reverse phase high-performance liquid chromatography

Here we report a simple and effective procedure enabling the fluorescent detection of nucleic acids following the rapid, high-resolution separation using ion pair reverse phase chromatography. This approach uses postcolumn nucleic acid intercalation of fluorescent dyes with subsequent fluorescent detection, demonstrating more than a 1000-fold increase in sensitivity in the detection of nucleic acids when compared with traditional UV detection. Moreover, a wide range of intercalating dyes can be incorporated, including those known to disrupt the structure of the nucleic acids, thereby enabling the sensitive detection of DNA and RNA with no adverse effect on resolution of the nucleic acids during ion pair reverse phase chromatography. In addition, such approaches allow one to readily distinguish single-stranded DNA from double-stranded DNA following their separation using ion pair reverse phase high-performance liquid chromatography.

6,6'-Disubstituted benzothiazole trimethine cyanines--new fluorescent dyes for DNA detection

The influence of methyl-, 2-hydroxyethyl-, dimethyl-, diethyl- and benzoyl-amino substituents in the 6,6'-positions of benzothiazole heterocycle of trimethine cyanines on their spectral-luminescent properties and behavior in presence of DNA, RNA and BSA was studied. It was shown that incorporation of 6,6'-substituents generally leads to the increase in dyes tendency to aggregation, resulting in the considerable decrease in the emission intensity of the disubstituted dyes as compared to the unsubstituted ones. Emission of the studied 6,6'-disubstited dyes in DNA presence is considerably more intensive than in presence of RNA, that points on the existing of DNA binding preference for the mentioned dyes. Insertion of benzoyl-amino groups into the 6,6'-positions permitted us to design the DNA-sensitive dyes on the basis of symmetric trimethine cyanines with unsubstituted polymethine chain, while typically such dyes slightly respond on the presence of biopolymers. 6,6'-Benzoyl-amino-disubstituted trimethine cyanines are proposed as efficient dyes for DNA detection.

Comparing mono- and divalent DNA groove binding cyanine dyes—Binding geometries, dissociation rates, and fluorescence properties

The unsymmetrical cyanine dyes BOXTO-PRO and BOXTO-MEE were derived from the DNA groove binder BOXTO, by adding a positively charged or a non-ionic hydrophilic tail to BOXTO, respectively. The main objective was to obtain more efficient DNA probes, for instance in electrophoresis and microscopy, by slowing down the dissociation of BOXTO from DNA. The interactions with mixed sequence DNA was studied with fluorescence and absorbance spectroscopy, stopped-flow dissociation and gel electrophoresis. Both the derivatives are groove bound as BOXTO, and have similar fluorescence properties when bound to mixed sequence DNA in free solution. BOXTO-PRO exhibits a slower dissociation than BOXTO from DNA, whereas the dissociation rate for BOXTO-MEE is faster and, unexpectedly independent of the ionic strength. During gel electrophoresis both BOXTO-PRO and BOXTO-MEE exhibit a faster dissociation rate than BOXTO. Still, BOXTO-PRO seems to be a good alternative as DNA probe, especially for applications in free solution where the dissociation is slower than for the corresponding intercalator TOPRO-1.

A kinetic analysis of cyanine selectivity: CCyan2 and Cyan40 intercalation into poly(dA-dT) x poly(dA-dT) and poly(dG-dC) x poly(dG-dC)

A T-jump investigation of the binding of Cyan40 [3-methyl-2-(1,2,6-trimethyl-4(1H)pyridinylidenmethyl)-benzothiazolium ion] and CCyan2 [3-methyl-2-[2-methyl-3-(3-methyl-2(3H)-benzothiazolylidene)-1-propenyl]-benzothiazolium ion] with poly(dA-dT) x poly(dA-dT) and poly(dG-dC) x poly(dG-dC) is performed at I = 0.1M (NaCl), 25 degrees C and pH 7. Two kinetic effects are observed for both systems. The binding process is discussed in terms of the sequence D + P <==> P,D <==> PD(I) <==> PD(II), which leads first to fast formation of a precursor complex P,D and then to a partially intercalated complex PD(I) which converts to the fully intercalate complex PD(II). Concerning CCyan2 the rate parameters depend on the polymer nature and their analysis shows that in the case of poly(dG-dC) x poly(dG-dC) the most stable bound form is the fully intercalated complex PD(II), whereas in the case of poly(dA-dT) x poly(dA-dT) the partially intercalated complex PD(I) is the most stable species. Concerning Cyan40, the rate parameters remain unchanged on going from A-T to G-C indicating that this dye is unselective.

Combining sequence-specific probes and DNA binding dyes in real-time PCR for specific nucleic acid quantification and melting curve analysis

Currently, in real-time PCR, one often has to choose between using a sequence-specific probe and a nonspecific double-stranded DNA (dsDNA) binding dye for the detection of amplified DNA products. The sequence-specific probe has the advantage that it only detects the targeted product, while the nonspecific dye has the advantage that melting curve analysis can be performed after completed amplification, which reveals what kind of products have been formed. Here we present a new strategy based on combining a sequence-specific probe and a nonspecific dye, BOXTO, in the same reaction, to take the advantage of both chemistries. We show that BOXTO can be used together with both TaqMan probes and locked nucleic acid (LNA) probes without interfering with the PCR. The probe signal reflect formation of target product, while melting curve analysis of the BOXTO signal reveals primer-dimer formation and the presence of any other anomalous products.

Detection and monitoring of virus infections by real-time PCR

The employment of polymerase chain reaction (PCR) techniques for virus detection and quantification offers the advantages of high sensitivity and reproducibility, combined with an extremely broad dynamic range. A number of qualitative and quantitative PCR virus assays have been described, but commercial PCR kits are available for quantitative analysis of a limited number of clinically important viruses only. In addition to permitting the assessment of viral load at a given time point, quantitative PCR tests offer the possibility of determining the dynamics of virus proliferation, monitoring of the response to treatment and, in viruses displaying persistence in defined cell types, distinction between latent and active infection. Moreover, from a technical point of view, the employment of sequential quantitative PCR assays in virus monitoring helps identifying false positive results caused by inadvertent contamination of samples with traces of viral nucleic acids or PCR products. In this review, we provide a survey of the current state-of-the-art in the application of the real-time PCR technology to virus analysis. Advantages and limitations of the RQ-PCR methodology, and quality control issues related to standardization and validation of diagnostic assays are discussed.

Applications of real-time polymerase chain reaction for quantification of microorganisms in environmental samples

Due to the advanced development of fluorogenic chemistry, quantitative real-time polymerase chain reaction (qRT-PCR) has become an emerging technique for the detection and quantification of microorganisms in the environment. Compared with the conventional hybridization- and PCR-based techniques, qRT-PCR not only has better sensitivity and reproducibility, but it is also quicker to perform and has a minimum risk of amplicon carryover contamination. This article reviews the principle of this emerging technique, its detection reagents, target DNAs, quantification procedures, and affecting factors. The applications of qRT-PCR for the quantification of microorganisms in the environment are also summarized.

Detection and monitoring of virus infections by real-time PCR

The employment of polymerase chain reaction (PCR) techniques for virus detection and quantification offers the advantages of high sensitivity and reproducibility, combined with an extremely broad dynamic range. A number of qualitative and quantitative PCR virus assays have been described, but commercial PCR kits are available for quantitative analysis of a limited number of clinically important viruses only. In addition to permitting the assessment of viral load at a given time point, quantitative PCR tests offer the possibility of determining the dynamics of virus proliferation, monitoring of the response to treatment and, in viruses displaying persistence in defined cell types, distinction between latent and active infection. Moreover, from a technical point of view, the employment of sequential quantitative PCR assays in virus monitoring helps identifying false positive results caused by inadvertent contamination of samples with traces of viral nucleic acids or PCR products. In this review, we provide a survey of the current state-of-the-art in the application of the real-time PCR technology to virus analysis. Advantages and limitations of the RQ-PCR methodology, and quality control issues related to standardization and validation of diagnostic assays are discussed.

The real-time polymerase chain reaction

The scientific, medical, and diagnostic communities have been presented the most powerful tool for quantitative nucleic acids analysis: real-time PCR [Bustin, S.A., 2004. A-Z of Quantitative PCR. IUL Press, San Diego, CA]. This new technique is a refinement of the original Polymerase Chain Reaction (PCR) developed by Kary Mullis and coworkers in the mid 80:ies [Saiki, R.K., et al., 1985. Enzymatic amplification of beta-globin genomic sequences and restriction site analysis for diagnosis of sickle cell anemia, Science 230, 1350], for which Kary Mullis was awarded the 1993 year's Nobel prize in Chemistry. By PCR essentially any nucleic acid sequence present in a complex sample can be amplified in a cyclic process to generate a large number of identical copies that can readily be analyzed. This made it possible, for example, to manipulate DNA for cloning purposes, genetic engineering, and sequencing. But as an analytical technique the original PCR method had some serious limitations. By first amplifying the DNA sequence and then analyzing the product, quantification was exceedingly difficult since the PCR gave rise to essentially the same amount of product independently of the initial amount of DNA template molecules that were present. This limitation was resolved in 1992 by the development of real-time PCR by Higuchi et al. [Higuchi, R., Dollinger, G., Walsh, P.S., Griffith, R., 1992. Simultaneous amplification and detection of specific DNA-sequences. Bio-Technology 10(4), 413-417]. In real-time PCR the amount of product formed is monitored during the course of the reaction by monitoring the fluorescence of dyes or probes introduced into the reaction that is proportional to the amount of product formed, and the number of amplification cycles required to obtain a particular amount of DNA molecules is registered. Assuming a certain amplification efficiency, which typically is close to a doubling of the number of molecules per amplification cycle, it is possible to calculate the number of DNA molecules of the amplified sequence that were initially present in the sample. With the highly efficient detection chemistries, sensitive instrumentation, and optimized assays that are available today the number of DNA molecules of a particular sequence in a complex sample can be determined with unprecedented accuracy and sensitivity sufficient to detect a single molecule. Typical uses of real-time PCR include pathogen detection, gene expression analysis, single nucleotide polymorphism (SNP) analysis, analysis of chromosome aberrations, and most recently also protein detection by real-time immuno PCR.

Applications of real-time immuno-polymerase chain reaction (rt-IPCR) for the rapid diagnoses of viral antigens and pathologic proteins

One of the major challenges of performing the IPCR has been to establish a robust, sensitive, and specific method which is easily adapted and highly standardized for routine use in a clinical laboratory. Presently, the performance of IPCR typically involves elaborate and multiple, time-consuming steps prone to high variation in reagents and technical application. Further advances in the technology and instrumentation used for the signal detection of IPCR has resulted in the development of real-time IPCR (rt-IPCR). Rt-IPCR is still relatively undeveloped in comparison to the use of both real-time PCR and IPCR as evidenced by the low number (eight citations) of publications in the scientific literature. However, increased use of rt-IPCR has shown that the method displays improved statistical validation of accuracy over IPCR. Inter-assay error is typically 5-10% vs 15-20% for IPCR. The primary advantage of using rt-IPCR in place of IPCR is the immediate interpretation of positive data (quantification of proteins) as the PCR reaction proceeds. This aspect is key to real-time diagnosis and has great importance for specific emergency situations (i.e., biological and environmental contaminations of toxins in biothreat situations), as well as cases where specific tumor/viral antigens and pathologic proteins may be present in body tissues in extremely low concentrations and rapid, early diagnosis is important for immediate palliative treatment. This review summarizes all of the experimental data published to date utilizing the rt-IPCR method for various analytes (vascular endothelial growth factor, mumps Ag, rViscumin, various IgG, gliadin, HIV-1 p24 Ag, Rotavirus VP6, pathologic and recombinant prion, and prostate specific Ag) and describes the molecular scaffold formats, solid formats, instrument detection systems, and probes/primers or fluorescent dyes used in these assays. With further standardization and validation, rt-IPCR has the potential to become the most analytically sensitive method available for the detection of proteins.

Advances in real-time PCR: application to clinical laboratory diagnostics

The polymerase chain reaction (PCR) has become one of the most important tools in molecular diagnostics, providing exquisite sensitivity and specificity for detection of nucleic acid targets. Real-time monitoring of PCR has simplified and accelerated PCR laboratory procedures and has increased information obtained from specimens including routine quantification and differentiation of amplification products. Clinical diagnostic applications and uses of real-time PCR are growing exponentially, real-time PCR is rapidly replacing traditional PCR, and new diagnostic uses likely will emerge. This review analyzes the scope of present and potential future clinical diagnostic applications of this powerful technique. Critical discussions focus on basic concepts, variations, data analysis, instrument platforms, signal detection formats, sample collection, assay design, and execution of real-time PCR.

Real-time reverse transcription PCR (qRT-PCR) and its potential use in clinical diagnosis

qRT-PCR (real-time reverse transcription-PCR) has become the benchmark for the detection and quantification of RNA targets and is being utilized increasingly in novel clinical diagnostic assays. Quantitative results obtained by this technology are not only more informative than qualitative data, but simplify assay standardization and quality management. qRT-PCR assays are most established for the detection of viral load and therapy monitoring, and the development of SARS (severe acute respiratory syndrome)-associated coronavirus qRT-PCR assays provide a textbook example of the value of this technology for clinical diagnostics. The widespread use of qRT-PCR assays for diagnosis and the detection of disease-specific prognostic markers in leukaemia patients provide further examples of their usefulness. Their value for the detection of disease-associated mRNA expressed by circulating tumour cells in patients with solid malignancies is far less apparent, and the clinical significance of results obtained from such tests remains unclear. This is because of conceptual reservations as well as technical limitations that can interfere with the diagnostic specificity of qRT-PCR assays. Therefore, although it is evident that qRT-PCR assay has become a useful and important technology in the clinical diagnostic laboratory, it must be used appropriately and it is essential to be aware of its limitations if it is to fulfil its potential.

Comparison of SYTO9 and SYBR Green I for real-time polymerase chain reaction and investigation of the effect of dye concentration on amplification and DNA melting curve analysis

Following the initial report of the use of SYBR Green I for real-time polymerase chain reaction (PCR) in 1997, little attention has been given to the development of alternative intercalating dyes for this application. This is surprising considering the reported limitations of SYBR Green I, which include limited dye stability, dye-dependent PCR inhibition, and selective detection of amplicons during DNA melting curve analysis of multiplex PCRs. We have tested an alternative to SYBR Green I and report the first detailed evaluation of the intercalating dye SYTO9. Our findings demonstrate that SYTO9 produces highly reproducible DNA melting curves over a broader range of dye concentrations than does SYBR Green I, is far less inhibitory to PCR than SYBR Green I, and does not appear to selectively detect particular amplicons. The low inhibition and high melting curve reproducibility of SYTO9 means that it can be readily incorporated into a conventional PCR at a broad range of concentrations, allowing closed tube analysis by DNA melting curve analysis. These features simplify the use of intercalating dyes in real-time PCR and the improved reproducibility of DNA melting curve analysis will make SYTO9 useful in a diagnostic context.

The use of real-time PCR methods in DNA sequence variation analysis

BACKGROUND

Real-time (RT) PCR methods for discovering and genotyping single nucleotide polymorphisms (SNPs) are becoming increasingly important in various fields of biological sciences. SNP genotyping is widely used to perform genetic association studies aimed at characterising the genetic factors underlying inherited traits. The detection and quantification of somatic mutations is an important tool for investigating the genetic causes of tumorigenesis. In infectious disease diagnostics there is an increasing emphasis placed on genotyping variation within the genomes of pathogenic organisms in order to distinguish between strains.

METHODS

There are several platforms and methods available to the researcher wishing to undertake SNP analysis using real-time PCR methods. These use fluorescent technologies for discriminating between the alternate alleles of a polymorphism. There are several real-time PCR platforms currently on the market. Two of the key technical challenges are allele discrimination and allele quantification.

CONCLUSIONS

Applications of this technology include SNP genotyping, the sensitive detection of somatic mutations and infectious disease subtyping.

Nucleic acid amplification-based techniques for pathogen detection and identification

Nucleic acid amplification techniques have revolutionised diagnostic and research industries. Current technologies that allow the detection of amplification in real-time are fast becoming industry standards, particularly in a diagnostic context. In this review, we describe and explore the application of numerous real-time detection chemistries and amplification techniques for pathogen detection and identification, including the polymerase chain reaction, nucleic acid sequence-based amplification, strand displacement amplification and the ligase chain reaction. The emergence of newer technologies, such as lab-on-a-chip devices and photo-cleavable linkers, is also discussed.

Quantitative real-time PCR for cancer detection: the lymphoma case

Advances in the biologic sciences and technology are providing molecular targets for diagnosis and treatment of cancer. Lymphoma is a group of cancers with diverse clinical courses. Gene profiling opens new possibilities to classify the disease into subtypes and guide a differentiated treatment. Real-time PCR is characterized by high sensitivity, excellent precision and large dynamic range, and has become the method of choice for quantitative gene expression measurements. For accurate gene expression profiling by real-time PCR, several parameters must be considered and carefully validated. These include the use of reference genes and compensation for PCR inhibition in data normalization. Quantification by real-time PCR may be performed as either absolute measurements using an external standard, or as relative measurements, comparing the expression of a reporter gene with that of a presumed constantly expressed reference gene. Sometimes it is possible to compare expression of reporter genes only, which improves the accuracy of prediction. The amount of biologic material required for real-time PCR analysis is much lower than that required for analysis by traditional methods due to the very high sensitivity of PCR. Fine-needle aspirates and even single cells contain enough material for accurate real-time PCR analysis.

Cyanine dyes as intercalating agents: kinetic and thermodynamic studies on the DNA/Cyan40 and DNA/CCyan2 systems

The interaction of cyanines with nucleic acids is accompanied by intense changes of their optical properties. Consequently these molecules find numerous applications in biology and medicine. Since no detailed information on the binding mechanism of DNA/cyanine systems is available, a T-jump investigation of the kinetics and equilibria of binding of the cyanines Cyan40 [3-methyl-2-(1,2,6-trimethyl-4(1H)pyridinylidenmethyl)-benzothiazolium ion] and CCyan2 [3-methyl-2-[2-methyl-3-(3-methyl-2(3H)-benzothiazolylidene)-1-propenyl]-benzothiazolium ion] with CT-DNA is performed at 25 degrees C, pH 7 and various ionic strengths. Bathochromic shifts of the dye absorption band upon DNA addition, polymer melting point displacement (DeltaT = 8-10 degrees C), site size determination (n = 2), and stepwise kinetics concur in suggesting that the investigated cyanines bind to CT-DNA primary by intercalation. Measurements with poly(dA-dT).poly(dA-dT) and poly(dG-dC).poly(dG-dC) reveal fair selectivity of CCyan2 toward G-C basepairs. T-jump experiments show two kinetic effects for both systems. The binding process is discussed in terms of the sequence D + S left arrow over right arrow D,S left arrow over right arrow DS(I) left arrow over right arrow DS(II), which leads first to fast formation of an external complex D,S and then to a partially intercalated complex DS(I) which, in turn, converts to DS(II), a more stable intercalate. Absorption spectra reveal that both dyes tend to self-aggregate; the kinetics of CCyan2 self-aggregation is studied by T-jump relaxation and the results are interpreted in terms of dimer formation.

Emerging technologies for the detection and genetic characterization of protozoan parasites

The development and adaptation of new technologies for the genetic characterization and identification of parasites continue to accelerate, providing an increasing number of research and analytical tools. We review emerging technologies that have applications in this area, including real-time PCR and microarrays, and discuss the fundamental principles of some of these technologies and how they are applied to characterize parasites. We give special consideration to the application of genetic data to biological questions, where selection of the most appropriate technique depends on the biological question posed by the investigator.

Advances in real-time PCR: application to clinical laboratory diagnostics

The polymerase chain reaction (PCR) has become one of the most important tools in molecular diagnostics, providing exquisite sensitivity and specificity for detection of nucleic acid targets. Real-time monitoring of PCR has simplified and accelerated PCR laboratory procedures and has increased information obtained from specimens including routine quantification and differentiation of amplification products. Clinical diagnostic applications and uses of real-time PCR are growing exponentially, real-time PCR is rapidly replacing traditional PCR, and new diagnostic uses likely will emerge. This review analyzes the scope of present and potential future clinical diagnostic applications of this powerful technique. Critical discussions focus on basic concepts, variations, data analysis, instrument platforms, signal detection formats, sample collection, assay design, and execution of real-time PCR.

Real-time Fluorescent PCR Techniques to Study Microbial-Host Interactions

This chapter describes how real-time polymerase chain reaction (PCR) performs and how it may be used to detect microbial pathogens and the relationship they form with their host. Research and diagnostic microbiology laboratories contain a mix of traditional and leading-edge, in-house and commercial assays for the detection of microbes and the effects they impart upon target tissues, organs, and systems. The PCR has undergone significant change over the last decade, to the extent that only a small proportion of scientists have been able or willing to keep abreast of the latest offerings. The chapter reviews these changes. It discusses the second-generation of PCR technology-kinetic or real-time PCR, a tool gaining widespread acceptance in many scientific disciplines but especially in the microbiology laboratory.