No abstract

SELEX (systematic evolution of ligands by exponential enrichment) is a process that involves the progressive purification from a combinatorial library of nucleic acid ligands with a high affinity for a particular target by repeated rounds of partitioning and amplification. With the development of aptamer technology over the last decade, various modified SELEX processes have arisen that allow various aptamers to be developed against a wide variety of molecules, irrespective of the target size. In the present review, the separation methods used in such SELEX processes are reviewed.

Aptamers selected against various kinds of targets have shown remarkable specificity and affinity, similar to those displayed by antibodies to their antigens. To employ aptamers as genotyping reagents for the identification of pathogens and their strains, in vitro selections were carried out to find aptamers that specifically bind and distinguish the closely related human influenza A virus subtype H3N2. The selected aptamer, P30-10-16, binds specifically to the haemagglutinin (HA) region of the target strain A/Panama/2007/1999(H3N2) and failed to recognize other human influenza viruses, including another strain with the same subtype, H3N2. The aptamer displayed over 15-fold-higher affinity to the HA compared with the monoclonal antibody, and efficiently inhibited HA-mediated membrane fusion. These studies delineate the application of aptamers in the genotyping of viruses.

Aptamers are nucleic acid ligands that are generated artificially by in vitro selection and behave similar to antibodies. The development of aptamer-based sensing systems or strategies has been in vogue for the past few decades, because aptamers are smaller in size, stable, cheaper and undergo easier modifications. Owing to these advantages, several facile aptamer-based colorimetric strategies have been created by controlling the assembly and disassembly of aptamers on unmodified gold nanoparticle probes. As these kinds of assay systems are rapid and can be visualized unaided by instruments, they have recently become an attractive method of choice. The formation of purple-colored aggregates (attraction) from the red dispersed (repulsion) state of GNPs in the presence of mono- or divalent ions is the key principle behind this assay. Due to its simplicity and versatility, this assay can be an alternative to existing diagnostic assays. Here, we have investigated the critical elements involved in colorimetric assays, and have screened different proteins and small ligands to evaluate biofouling on GNPs.