12th December 2019
Continuous improvement in imaging techniques have allowed biologists to explore with accurate methods to label cellular elements as they surpass the limit imposed by the diffraction of light. The resolution is mainly affected by the size of the affinity probes, such as antibodies which are 10-15 nm in size. Moreover, non-specificity, over labeling and mainly stability of antibodies may lead to significant loss of function and reliability in detecting the target of interest. In this regard, fluorescence – tagged aptamers have gained popularity in imaging for detecting cells expressing distinct antigens.
In this view, Gomes de Castro et al., 2017 conducted a comparative study by testing several aptamers and antibodies against various important target membrane receptors such as EGFR, ErbB2 and Epha2. The aptamers were shown to co-localize with endocytic markers such as Dextran (Dex) and Transferrin (Tf) and demonstrated that aptamers can be used to label endosome-like organelles using confocal microscopy (Figure 1).
Figure 1. Subcellular localization of aptamers with classical endocytic markers Dextran (Dex) and Transferrin (Tf) on live HEK293 cells using confocal microscopy.
The higher resolution for epitope labeling, provided by the aptamer, resulted in better structure recognition compared to antibodies (Figure 2).
Figure 2. Direct comparison between aptamer and antibody staining against target EGFR revealing the structures of endosome-like organelles using super resolution microscopy. A. Confocal live scans (A), Pearson’s correlation (B) and quantification of endosome like structures (C) on zoomed organelles showed correlation between transferrin (Tf, green) marker and antibodies (Ab1 and Ab2) was significantly poor as compared to aptamers (Apt) and Tf.
Overall the results suggested that aptamers could reveal more epitopes than most antibodies, thus providing a denser labeling of the stained structures and improving the overall quality of the information extracted from the images. These aptamers being, small probes, are less impaired by steric hindrance, allowing them to penetrate biological samples easily. At Aptamer Group, we offer the advantage of designing aptamers to be optimized for the conditions you want to use them in. This way they are engineered to bind to their target with high specificity and affinity. For example, aptamers can be selected to remain on a cell surface or be internalized which can serve as a targeted drug delivery agent. Moreover, labeling steps (or appropriate functional groups) can be incorporated during synthesis to enable reliable site- specific labeling.
If you would like to know more about aptamers and their applications in microscopy, please contact us using the form below.
Gomes de Castro MA, Höbartner C, Opazo F (2017) Aptamers provide superior stainings of cellular receptors studied under super-resolution microscopy. PLoS ONE 12(2): e0173050. https://doi.org/10.1371/journal.pone.0173050