**8. Variants of PCR**

In addition to the above mentioned techniques, numerous other variants of PCR are in use to serve a wide variety of research, diagnostic, and industrial needs, e.g., after exponential PCR, allele specific PCR, asymmetric PCR, arbitrary PCR, core sample PCR, degenerate PCR, dial-out PCR, digital PCR, high-fidelity PCR, hot start PCR, in silico PCR, inter-sequence PCR, ligation-mediated PCR, mini primer PCR, nanoparticle-PCR, overlap-extension PCR, solid-phase PCR, splicing by overlap/overhang extension PCR, suicide PCR, thermal asymmetric interlaced PCR, etc. Some of the important variants of PCR are described below:

## **8.1 Extreme PCR**

In extreme PCR the concentration of primers and polymerase is increased 10–20 times; the amplification rate of instrument reaches about 0.4–2.0 s/. When the primers' concentration is more than 10 mol/L, the polymerase concentration is 1 mol/L, and the extreme PCR is suitable for rapid detection of virulent infectious and bioterrorism pathogens [56].

## **8.2 Photonic PCR**

It is achieved by fast heating and based on energy conversion, thus shortening the PCR time. The specific process is carried out by using electronic resonance light emitting diode. The energy conversion process is more rapid than the conventional cooling process, causing amplification of target DNA within 5 min and thus making the PCR detection more convenient and fast [57, 58].

### **8.3 COLD-PCR**

It is a low denatured temperature-PCR for enriching mutant genes by reducing the reactive temperature of PCR. The basic principle is founded on the base mismatch in any strand of DNA affecting the denaturation temperature. Therefore, the denaturation temperature of the mutant DNA is often lower than that of wild type DNA. The assay is often used for viral gene mutation [59] detection, cancer associated gene mutations (p53) [60, 61], EGFR, KRAS, etc.), beta globulin (HBB) mutations that cause beta thalassemia [62], etc.

#### **8.4 Nanoparticle-PCR**

Gold nanoparticles have superior electrical, optical, thermal, and catalytic activities and have the same properties as single-stranded binding proteins (ssb), which bind to single-stranded DNA and do not interact with double-stranded DNA. Therefore, the

**23**

*Polymerase Chain Reaction*

**8.5 HPE-PCR**

**8.6 LATE-PCR**

**8.7 Digital PCR**

Diagnosis of infections

Diagnosis of genetic defects

Diagnosis and prognosis of cancers

Recombinant DNA technology

**9. Applications of PCR**

*DOI: http://dx.doi.org/10.5772/intechopen.81924*

amplification effect of high GC template can be significantly improved by adding gold nanoparticles as additives to slowdown or touchdown PCR reaction systems [63].

It is an amplification technique for templates with long DNA chains and large numbers of CTG repeats involving the increase in the denaturation temperature of

It generates high concentrations of single-stranded DNA that can be analyzed at the end point using probes which hybridize over a wide temperature range [65].

Digital PCR (dPCR) enables precise and sensitive quantification of nucleic acids in a wide range of applications in both healthcare and environmental analysis. It is based on detection in two discrete optical channels, focused on the quantification of one or two targets within a single reaction [66]. The technique has become a promising quantification strategy that combines absolute quantification with high sensitivity.

The PCR technique and its several advanced variants act as powerful tools with specialized applications which were once impossible by the scientific world [67, 68]. This versatile technique brought enormous benefits and scientific developments such as genome sequencing, gene expressions in recombinant systems, and the study of molecular genetic analysis, including the rapid determination of both paternity and the diagnosis of infectious disease [69, 70]. It enables the in vitro synthesis of nucleic acids through which a DNA segment can be specifically replicated in a semiconservative way. It generally exhibits excellent detection limits [71, 72]. It has significantly transformed

**Application Description Reference**

PCR-based detection systems are used to accurately detect (before disease

degraded and are in low amounts. Such miniscule quantities of aDNA are amplified using PCR techniques to improve their quality and quantity to

PCR techniques are used to generate hybrid DNA with ease and precision. The techniques are also employed to clone DNA in to specific vectors to

[71, 74]

[74–76]

[74, 77]

[78, 79]

[80–82]

[83, 84]

PCR approaches are used to specifically and sensitively diagnose infections (bacterial, viral, protozoan, fungal). They are routinely used in clinical laboratories to confirm and quantify these infectious agents

onset) and confirm (after the onset) many genetic disorders

Phylogenetics Phylogenetic analysis of organisms routinely relies on PCR amplification of phylogenetic markers to identify and classify them

Archeology Ancient DNA (aDNA) recovered from archeological remains are usually

make them analyzable for archeological study

get protein expression

PCR-based approaches can identify cancer genes and analyze their expression to determine genetic predisposition to certain cancers, confirmation of cancer type, their prognosis, and treatment

PCR to solve the problem of high content of DNA (G+C) [64].

amplification effect of high GC template can be significantly improved by adding gold nanoparticles as additives to slowdown or touchdown PCR reaction systems [63].
