Kyung-Mi Song

Aptamers and Their Biological Applications

Recently, aptamers have attracted the attention of many scientists, because they not only have all of the advantages of antibodies, but also have unique merits, such as thermal stability, low cost, and unlimited applications. In this review, we present the reasons why aptamers are known as alternatives to antibodies. Furthermore, several types of in vitro selection processes, including nitrocellulose membrane filtration, affinity chromatography, magnetic bead, and capillary electrophoresis-based selection methods, are explained in detail. We also introduce various applications of aptamers for the diagnosis of diseases and detection of small molecules. Numerous analytical techniques, such as electrochemical, colorimetric, optical, and mass-sensitive methods, can be utilized to detect targets, due to convenient modifications and the stability of aptamers. Finally, several medical and analytical applications of aptamers are presented. In summary, aptamers are promising materials for diverse areas, not just as alternatives to antibodies, but as the core components of medical and analytical equipment.

Label-free detection of kanamycin based on the aptamer-functionalized conducting polymer/gold nanocomposite.

Highly sensitive label-free detection of kanamycin is achieved with an aptamer sensor based on a conducting polymer/gold self-assembled nanocomposite. The sensor probe is fabricated by covalently immobilizing an in vitro selected DNA aptamer for kanamycin onto gold nanoparticle (AuNP)-comprised conducting polymer, poly-[2, 5-di-(2-thienyl)-1H-pyrrole-1-(p-benzoic acid)] (poly-DPB). The self-assembling of DPB on AuNP is investigated by TEM and UV-vis spectroscopy and the modification of the aptamer sensor is characterized using XPS and electrochemical impedance spectroscopy. The probe is applied to detect kanamycin by using voltammetric techniques. The sensor shows a pair of redox peaks around 0.26/ 0.08 V (vs. Ag/AgCl) for kanamycin captured by the aptamer-immobilized probe. The parameters that can affect the response, such as aptamer concentration, incubation time, temperature, and pH are optimized. The calibration plot shows a linear range from 0.05 μM to 9.0 μM kanamycin with a detection limit of 9.4±0.4 nM. The proposed aptamer sensor is examined with a real sample.

Dual-aptamer-based delivery vehicle of doxorubicin to both PSMA (+) and PSMA (-) prostate cancers.

We have designed a dual-aptamer complex specific to both prostate-specific membrane antigens (PSMA) (+) and (-) prostate cancer cells. In the complex, an A10 RNA aptamer targeting PSMA (+) cells and a DUP-1 peptide aptamer specific to PSMA (-) cells were conjugated through streptavidin. Doxorubicin-loaded onto the stem region of the A10 aptamer was delivered not only to PSMA (+) cells but to PSMA (-) cells, and eventually induced apoptosis in both types of prostate cancer cells. Cell death was monitored by measuring guanine concentration in cells using differential pulse voltammetry (DPV), a simple and rapid electrochemical method, and was further confirmed by directly observing cell morphologies cultured on the transparent indium tin oxide (ITO) glass electrode and checking their viabilities using a trypan blue assay. To investigate the in vivo application of the dual-aptamer system, both A10 and DUP-1 aptamers were immobilized on the surface of thermally cross-linked superparamagnetic iron oxide nanoparticles (TCL-SPION). Selective cell uptakes and effective drug delivery action of these probes were verified by Prussian blue staining and trypan blue staining, respectively.

A highly sensitive aptasensor towards Plasmodium lactate dehydrogenase for the diagnosis of malaria

Finding a highly sensitive diagnostic technique for malaria has challenged scientists for the last century. In the present study, we identified versatile single-strand DNA aptamers for Plasmodium lactate dehydrogenase (pLDH), a biomarker for malaria, via the Systematic Evolution of Ligands by EXponential enrichment (SELEX). The pLDH aptamers selectively bound to the target proteins with high sensitivity (K(d)=16.8-49.6 nM). The selected aptamers were characterized using an electrophoretic mobility shift assay, a quartz crystal microbalance, a fluorescence assay, and circular dichroism spectroscopy. We also designed a simple aptasensor using electrochemical impedance spectroscopy; both Plasmodium vivax LDH and Plasmodium falciparum LDH were selectively detected with a detection limit of 1 pM. Furthermore, the pLDH aptasensor clearly distinguished between malaria-positive blood samples of two major species (P. vivax and P. falciparum) and a negative control, indicating that it may be a useful tool for the diagnosis, monitoring, and surveillance of malaria.

Simultaneous electrochemical detection of both PSMA (+) and PSMA (-) prostate cancer cells using an RNA/peptide dual-aptamer probe

Using an RNA/peptide dual-aptamer probe, both PSMA (+) and PSMA (-) prostate cancer cells were simultaneously detected by electrochemical impedance spectroscopy. This approach can be applied as a general tool for early diagnosis of prostate cancer.