from Martin A. Lee, David J. Squirrell, Dario L. Leslie and Tom Brown writing in Real-Time PCR: Advanced Technologies and Applications:

The development of fluorescent methods for the closed tube polymerase chain reaction has greatly simplified the process of quantification. Current approaches use fluorescent probes that interact with the amplification products during the PCR to allow kinetic measurements of product accumulation. These probe methods include generic approaches to DNA quantification such as fluorescent DNA binding dyes. There are also a number of strand-specific probes that use the phenomenon of Fluorescent Energy Transfer. In this chapter we describe these methods in detail, outline the principles of each process, and describe published examples. This text has been written to provide an impartial overview of the utility of different assays and to show how they may be used on various commercially available thermal cyclers.

Further reading: Real-Time PCR: Advanced Technologies and Applications

from Martin A. Lee, David J. Squirrell and Dario L. Leslie writing in Real-Time PCR: Advanced Technologies and Applications:

A range of factors can cause false negative results in real-time PCR through effects on one or more of the reaction components. Consequently applications requiring a high level of confidence need to be designed to control for the occurrence of false negatives. Whilst an external, or batch, control is often used, the ideal control is an internal one included in the reaction cocktail in a multiplex assay. Here we discuss the application and development of molecular mimics as controls in real-time PCR and explain concepts and experimental considerations to aid in the optimisation of controlled multiplexed assays.

Further reading: Real-Time PCR: Advanced Technologies and Applications

from Jacob Moran-Gilad and Nick Saunders writing in Real-Time PCR: Advanced Technologies and Applications:

There are significant risks associated with the introduction of new diagnostic assays based on real-time PCR. A consistent approach to the management of the development, validation, verification and implementation of such assays is essential to meet good practice. Adoption of a strategic framework which is followed rigorously by the team is important to ensure that the project is successful. The project core team must have clearly defined roles and produce adequate documentation that can be assessed by a separate review team. Project planning should include aspects such as setting clear objectives, identification of materials and the resources required to complete the project. Of particular importance for real-time PCR diagnostics is the inclusion of adequate positive controls. Tools for the selection of appropriate positive controls are presented and discussed here as a key aspect of diagnostic PCR project management. Following the introduction of assays to practice it is vital to maintain the standard operating procedure to ensure that it is followed consistently and so that any necessary changes are documented and adequately validated. The users of diagnostic assays must be aware of the contents of the project dossiers or have other means to verify their provenance and performance. Project documentation should be maintained to ensure that the quality of the validation data is strengthened over time.

Further reading: Real-Time PCR: Advanced Technologies and Applications

from Jim Huggett, Tania Nolan and Stephen A. Bustin writing in Real-Time PCR: Advanced Technologies and Applications:

The capacity to amplify and detect trace amounts of nucleic acids has made the polymerase chain reaction (PCR) the most formidable molecular technology in use today. Its versatility and scope was further broadened first with the development of reverse transcription (RT)-PCR, which opened up the entire RNA field to thorough exploration and then, most conspicuously, with its evolution into real-time quantitative PCR (qPCR). Speed, simplicity, specificity, wide linear dynamic range, multiplexing and high throughput potential, reduced contamination risk, simplified detection and data analysis procedures as well as availability of increasingly affordable instrumentation and reduced reagent cost have made qPCR the molecular method of choice when quantifying nucleic acids. Detection of pathogens, SNP analyses and quantification of RNA, even real-time analysis of gene expression in vivo have become routine applications and constant enhancements of chemistries, enzymes, mastermixes and instruments continue to extend the scope of qPCR technology by promising added benefits such as extremely short assay times measured in minutes, low reagent usage and exceptionally rapid heating/cooling rates. The whole process is driven by the insatiable demand for ever-more specific, sensitive, convenient and cost-effective protocols. However, it has also become clear that variable pre-assay conditions, poor assay design and incorrect data analysis have resulted in the regular publication of data that are often inconsistent, inaccurate and often simply wrong. The problem is exacerbated by a lack of transparency of reporting, with the details of technical information wholly inadequate for the purpose of assessing the validity of reported qPCR data. This has serious consequences for basic research, reducing the potential for translating findings into valuable applications and potentially devastating implications for clinical practice. In response, guidelines proposing a minimum standard for the provision of information for qPCR experiments ("MIQE") have been launched. These aim to establish a standard for accurate and reliable qPCR experimental design as well as recommendations to ensure comprehensive reporting of technical detail, indispensable conditions for the maturing of qPCR into a robust, accurate and reliable nucleic acid quantification technology.

Further reading: Real-Time PCR: Advanced Technologies and Applications

from Scott D. Rose, Richard Owczarzy, Joseph R. Dobosy and Mark A. Behlke writing in Real-Time PCR: Advanced Technologies and Applications:

Although the vast majority of primers and probes employed in qPCR applications today are synthesized using unmodified DNA bases, selective use of chemically-modified bases and non-base modifying groups can prevent primer-dimer artifacts, improve specificity, and allow for selective amplification of sequences that differ by as little as a single base. A wide variety of chemical modifications have been characterized for use in qPCR. As a general class, the modifications that are in greatest use today increase the binding affinity of the oligonucleotides (i.e., increase the melting temperature, Tm). Tm-enhancing modifications allows both primers and probes to be shorter, improving the differential Tm (DTm=Tm match-Tm mismatch) between perfect match and mismatch hybridization. These modifications have widespread application in allele-specific PCR and in the detection of single nucleotide polymorphisms (SNPs). Conversely, a second class of base modifications are in common use that decrease specificity and improve duplex formation in the presence of base mismatches. Although these modifications lower Tm, they have less of an impact on primer stability than do actual mismatched bases. Universal bases permit use of primers and probes in polymorphic loci when it is desirable to detect all sequence variants and minimize mismatch discrimination.

Further reading: Real-Time PCR: Advanced Technologies and Applications

from Nick A. Saunders writing in Real-Time PCR: Advanced Technologies and Applications:

Real-time PCR arrays are tools that allow convenient testing of samples in many assays concurrently, parallel testing of many samples or testing of multiple samples and targets simultaneously. It is desirable to standardise and automate primer and probe selection due to the large number of assays that must be designed. Furthermore, it is useful to use probe selection techniques that increase the robustness of the individual assays since this will increase the level of compatibility between the assays and decrease the complexity of interpretation of the outputs. A simple approach to creating real-time PCR arrays is to use microtitre plates which currently have capacities of 96, 384 or 1536 features. Such arrays can be populated with user designed assays or with tests selected form a menu of over one million that are commercially available. A primary application of such arrays has been to verify gene expression data obtained using hybridisation. Cramming additional features into a device of manageable scale has led to the introduction of nanolitre volume arrays that diverge from the microtitre plate pattern. Several thousand different reactions can now be included in a single real-time PCR array. The reduction in scale also has advantages in terms of the volumes of materials required. As real-time arrays are miniaturised the number of pipetting steps required increases and it is often necessary to pre-configure them commercially leading to relative inflexibility. This limitation has prompted the development of arrays that include microfluidic channels and valves. These 'chips' can be loaded via relatively few liquid handling steps to create custom applications.

Further reading: Real-Time PCR: Advanced Technologies and Applications

from Chaminda Salgado and Waqar Hussain writing in Real-Time PCR: Advanced Technologies and Applications:

Myriad methods for the extraction and purification of nucleic acids prior to PCR are currently used throughout the community. While these methods have many unique and bespoke aspects, they broadly follow a sequence of lysis, isolation, washing and elution to get from a complex biological sample to purified nucleic acid that can be used in a PCR reaction. Various common methods available for each stage are described and potential sequences for particular sample types can be discerned. The potential for these methods to be automated are discussed and the process options summarized with respect to the speed of the methods, technical skill required and the resultant purity and yield that can be expected.

Further reading: Real-Time PCR: Advanced Technologies and Applications

from Melvyn Smith writing in Real-Time PCR: Advanced Technologies and Applications:

The real-time polymerase chain reaction is now established as one of the core technologies for diagnosing infectious diseases. The early stages of the technique's development were followed by a dramatic increase in the number of diagnostic assays being published, together with the introduction of commercially produced tests. Each of the numerous publications showed a number of differences in the approach to validating the newly-produced assays and in the quality and quantity of the data supporting their validation. As a result, many workers have, at times, found it difficult to reproduce the published results from other laboratories. These difficulties can arise from e.g. a lack of information in the publication, differences in equipment between laboratories, the use of different extraction methods and sequence variations in the pathogen being detected. Over the years a number of authors have voiced their concerns over the subject of what constitutes a properly validated assay, highlighting the issues of basic scientific good practice and the responsibilities of journals in publishing full validation data. This chapter summarises the recent work covering validation and verification methodology in order to provide a practical guide to help inform and standardise the process.

Further reading: Real-Time PCR: Advanced Technologies and Applications

from Alan McNally writing in Real-Time PCR: Advanced Technologies and Applications:

The detection and diagnosis of veterinary infectious diseases is an area in which the potential of Real-time PCR has been best demonstrated. In particular Real-time PCR has been successfully applied as a front line tool in the diagnostic algorithm for notifiable veterinary viral pathogens such as Avian Influenza, foot-and-mouth disease, bluetongue virus, as well as rabies and Newcastle disease virus. The rapidly transmissible nature of these agents necessitates near real-time detection and diagnosis in suspected infected animals to allow implementation of control procedures. This chapter will highlight the importance of Real-time PCR in facilitating this rapid diagnosis, and the effect such rapid detection has had on containing and controlling veterinary infectious disease outbreaks.

Further reading: Real-Time PCR: Advanced Technologies and Applications