Aptamer is short sequence of synthetic oligonucleotides which bind to their cognate target specifically while maintaining similar or higher sensitivity as antibody. Small size, chemical synthesis, low batch variation, cost effectiveness, long shelf life and above all low immunogenicity provide advantages over antibody. The in-vitro selection of aptamer applying a conjoining approach of chemistry and molecular biology is referred as Systematic Evolution of Ligands by Exponential enrichment (SELEX). These initial products of SELEX are considered as first generation aptamers, further modified chemically in an attempt to make it stable in biofluid avoiding nuclease digestion and renal clearance. These types of aptamers are called second generation aptamers. While modification is incorporated, enough care should be taken to maintain its sensitivity and specificity. These modifications and several improvisations have widened the window frame of aptamer application that is currently not only restricted to in-vitro system, but have been used in molecular imaging for disease pathology and treatment. In food industry it is used as sensor for detection of different diseases or fungal infections. In this review we have discussed a brief history of its journey, process of synthesis, different types of modifications to improve its characters. We have also focused on its applications and highlighted its role as therapeutic plus diagnostic; theranostic tools. Finally, the review is concluded with a brief discussion on future prospective in immunotherapy, as well as in identification of novel biomarkers in stem cell, and also in single cell proteomics (scProteomics) to study intra or intertumor heterogeneity at protein level.