Electrochemical aptasensor for human osteopontin detection using a DNA aptamer selected by SELEX

- A DNA aptamer against OPN, a tumor biomarker, selected by SELEX iterative in vitro process is reported for the first time.
- An electrochemical (square wave voltammetry) signal-off DNA aptasensor was designed exhibiting affinity towards OPN.
- The DNA aptasensor had satisfactory sensitivity and selectivity towards OPN, with low signal interferences from other proteins.
- The DNA aptasensor had a LOD of 1.3 ± 0.1 nM (synthetic human plasma) within OPN levels found breast cancer patients.
- Preliminary results showed that DNA aptasensor can detect OPN in real human plasma, similarly to the standard ELISA method.

A DNA aptamer with affinity and specificity for human osteopontin (OPN), a potential breast cancer biomarker, was selected using the SELEX process, considering its homology rate and the stability of its secondary structures. This aptamer exhibited a satisfactory affinity towards OPN, showing dissociation constants lower than 2.5 nM. It was further used to develop a simple, label-free electrochemical aptasensor against OPN. The aptasensor showed good sensitivity towards OPN in standard solutions, being the square wave voltammetry (SWV), compared to the cyclic voltammetry, the most sensitive technique with detection and quantification limits of 1.4 ± 0.4 nM and 4.2 ± 1.1 nM, respectively. It showed good reproducibility and acceptable selectivity, exhibiting low signal interferences from other proteins, as thrombin, with 2.6-10 times lower current signals-off than for OPN. The aptasensor also successfully detected OPN in spiked synthetic human plasma. Using SWV, detection and quantification limits (1.3 ± 0.1 and 3.9 ± 0.4 nM) within the OPN plasma levels reported for patients with breast cancer (0.4-4.5 nM) or with metastatic or recurrent breast cancer (0.9-8.4 nM) were found. Moreover, preliminary assays, using a sample of human plasma, showed that the aptasensor and the standard ELISA method quantified similar OPN levels (2.2 ± 0.7 and 1.7 ± 0.1 nM, respectively). Thus, our aptasensor coupled with SWV represents a promising alternative for the detection of relevant breast cancer biomarkers.

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