Nucleic acid aptamers are short oligonucleotide sequences, and are able to fold into well-defined three dimensional structure via specific conformational changes, and show strongly bind to their targets with high affinity and specificity. The selection of nucleic acid aptamers is performed through an in vitro process (in vitro selection), called SELEX process (systematic evolution of ligands by exponential enrichment).
Nucleic acid aptamers have several advantages with respect to antibodies. Once the aptamers are selected, they can be further synthesized within just a few days in a controlled fashion with high purity and reproducibility. Additionally, aptamers are highly chemically stable over a wide temperature range, retain most of their functionality even after multiple regeneration steps, and can be isolated by in vitro selection without immune response. As oligonucleotides can be easily modified with different reactive chemical groups, their immobilization on surfaces can be easily controlled. Thanks to such flexibility, aptamers are very popular for the design and optimization of novel biosensors.
Aptamers are newly emerged sensing elements that are competitive with or sometimes even better than antibodies due to their various advantages: a compact size, cost effectiveness, chemical stability, in vitro synthesis, easy modification, labeling and so on. Therefore, there have recently been intensive advances in aptamer-based biosensors including electrochemical aptasensors that are more proper to the miniaturization and integration of biosensors for high-throughput analysis and point-of-care (POC).
Oak Bioscience offers four strategies for SELEX:
1) Coated target on microtiter plates
2) Biotinylation target via streptavidin beads
3) Directly conjugated to the beads
4) Using tagged target via affinity column.
The criteria for any of the methods is no change to structure of the target, so the aptamer is specific binding to the target only.