**1. Introduction**

Oligonucleotides are polymers of nucleic acids which are building blocks of life. It is one of the key elements of the central dogma of life. Any nucleotide consists of a pentose sugar (ribose in case of RNA and de-oxy ribose for DNA), a phosphate group and any one nitrogenous base (nine-member double ring bases adenine, guanine as purines and six-membered single ring base thymine, uracil and cytosine as pyrimidines). On basis of structure and stability, researchers are working to expand the genetic alphabets [1]. This will extend the diversity of the oligonucleotides and demystification of mystical doctrine like "RNA world hypothesis" [2].
