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Abstract: A method for the accurate determination of the melting temperature (T m) of surface-immobilized DNA duplexes that exploits the fluorescence-quenching properties of gold is reported. A thiolated single-stranded DNA probe is chemisorbed onto a gold surface and then hybridized to a fluorophore-labeled complementary sequence. On formation of the duplex, the fluorescence of the label is effectively quenched by the gold surface. As the temperature is increased and the duplex denatures, the fluorophore label moves away from the gold surface and the fluorescence signal is again observed. The increase in fluorescence is measured as the temperature is ramped, and using first-derivative plots, the T m is determined. To demonstrate the approach, the T m of the cystic fibrosis DF508 mutation was determined in three different phases: in solution, in suspension immobilized on gold nanoparticles, and immobilized on gold film-coated substrate. The technique was further applied to optimize conditions for differentiation between a surface-immobilized DF508 mutant probe and a mutant/wild-type target exploiting increasing stringency in varying salt and formamide concentrations. The approach has application in optimization of assay conditions for biosensors that use gold substrates as well as in melting curve analysis. [ABSTRACT FROM AUTHOR]

Abstract: We describe a new DNA sequencing method called sequencing by denaturation (SBD). A Sanger dideoxy sequencing reaction is performed on the templates on a solid surface to generate a ladder of DNA fragments randomly terminated by fluorescently labeled dideoxyribonucleotides. The labeled DNA fragments are sequentially denatured from the templates and the process is monitored by measuring the change in fluorescence intensities from the surface. By analyzing the denaturation profiles, the base sequence of the template can be determined. Using thermodynamic principles, we simulated the denaturation profiles of a series of oligonucleotides ranging from 12 to 32 bases and developed a base-calling algorithm to decode the sequences. These simulations demonstrate that DNA molecules up to 20 bases can be sequenced by SBD. Experimental measurements of the melting profiles of DNA fragments in solution confirm that DNA sequences can be determined by SBD. The potential limitations and advantages of SBD are discussed. With SBD, millions of sequencing reactions can be performed on a small area on a surface in parallel with a very small amount of sequencing reagents. Therefore, DNA sequencing by SBD could potentially result in a significant increase in speed and reduction in cost in large-scale genome resequencing. [Copyright &y& Elsevier]

Abstract: We investigated three probe design strategies used in quantitative polymerase chain reaction (PCR) for sensitivity in detection of the PCR amplicon. A plasmid with a 120-bp insert served as the DNA template. The probes were TaqMan, conventional molecular beacon (MB), and shared-stem molecular beacon (ATssMB and GCssMB). A shared-stem beacon probe combines the properties of a TaqMan probe and a conventional molecular beacon. It was found that the overall sensitivities for the four PCR probes are in the order of MB>ATssMB>GCssMB>TaqMan. The fluorescence quantum yield measurements indicate that incomplete or partial enzymatic cleavage catalyzed by Taq polymerase is the likely cause of the low sensitivities of two shared-stem beacons when compared with the conventional beacon probe. A high-fluorescence background associated with the current TaqMan probe sequence contributes to the relatively low detection sensitivity and signal-to-background ratio. The study points out that the nucleotide environment surrounding the reporting fluorophore can strongly affect the probe performance in real-time PCR. [Copyright &y& Elsevier]

Commercialization of several genetically modified crops has been approved worldwide to date. Uniplex polymerase chain reaction (PCR)-based methods to identify these different insertion events have been developed, but their use in the analysis of all commercially available genetically modified organisms (GMOs) is becoming progressively insufficient. These methods require a large number of assays to detect all possible GMOs present in the sample and thereby the development of multiplex PCR systems using combined probes and primers targeted to sequences specific to various GMOs is needed for detection of this increasing number of GMOs. Here we report on the development of a multiplex real-time PCR suitable for multiple GMO identification, based on the intercalating dye SYBR Green I and the analysis of the melting curves of the amplified products. Using this method, different amplification products specific for Maximizer 176, Bt11, MON810, and GA21 maize and for GTS 40-3-2 soybean were obtained and identified by their specific Tm. We have combined amplification of these products in a number of multiplex reactions and show the suitability of the methods for identification of GMOs with a sensitivity of 0.1% in duplex reactions. The described methods offer an economic and simple alternative to real-time PCR systems based on sequence-specific probes (i.e., TaqMan chemistry). These methods can be used as selection tests and further optimized for uniplex GMO quantification. [Copyright &y& Elsevier]

Obtaining full-length cDNA is important for many molecular biology methods like cDNA library construction or RACE-PCR (rapid amplification of cDNA ends). We have found that the inclusion of betaine alone and in combination with trehalose in reverse transcription results in longer cDNA synthesis products. As shown on the 14-kb long clathhrin mRNA with real-time PCR, a combination of 2 M betaine and 0.6 M trehalose leads to almost 9 times more cDNA with a length of 12.5 kb. This is due to the ability of betaine to resolve secondary structures of the RNA, thereby decreasing its melting temperature. The application of betaine in combination with trehalose should prove useful in all laboratory methods relying on full-length cDNA. [Copyright &y& Elsevier]

Locked nucleic acid (LNA) is a modified RNA nucleotide that can be incorporated at specific positions to generate probes with the desired length, melting temperature ( T M ), and specificity. Here, we describe a method of multiplex genotyping based on dramatic shifts in the T M of a single dual-labeled LNA probe. Using this method, two varieties of the hairtail fish Trichiurus lepturus can be distinguished from each other, as well as from Trichiurus japonicus , based on a 1- to 2-bp difference in a fragment of mitochondrial cytochrome oxidase subunit 1. The shift in T M was 15 °C for a 1-bp mismatch and 27 °C for a 2-bp mismatch, indicating remarkable specificity. We anticipate that the method will be widely useful in applications such as species identification that require accurate, multiplex, and efficient detection of DNA polymorphisms. [ABSTRACT FROM AUTHOR]

Denaturation bubble-mediated strand exchange amplification (SEA) is a novel, rapid isothermal nucleic acid amplification has been applied for point-of-care molecular diagnostic in food safety, meat adulteration, forest disease and animal disease. Nevertheless, the absence of specialized strategy for SEA primers design led to long-time of primer screening progress before SEA reaction execution, which would largely increase the time consuming when SEA is utilized for detecting other new targets. In this present work, we investigated the impact of the following primers' attributes on SEA efficiency, including Tm value, 3′ end G/C content, self-complementary and 3′ complementary, according to which we demonstrated that optimal Tm value and reaction temperature were all 61 °C, while 3′-terminal nucleotide should be G/C, as the SEA reaction induced by the primers possessing these attributes exhibited significantly lower threshold time (Tt) value. Moreover, self-complementary and 3′ complementary of primers should be avoided. Besides, we also discussed the consideration priority order of these factors, which was self-complementary and 3′ complementary, Tm value and 3′ end G/C content in turn. Because the SEA primer design strategy is first presented, our work will greatly promote the application of SEA in point-of-care test. Image 1 • SEA-specific primer design strategy was firstly presented. • Primers designed based on this strategy possessed higher detection efficiency. • This strategy is suitable for multiple species-specific primer design. • This strategy contributes to the popularization of SEA in POCT field. [ABSTRACT FROM AUTHOR]