miRNA are known as short RNA molecules that usually consist of 18 – 25 nucleotides and are considered as posttranscriptional regulators of gene expression occurring in plants and animals [1]. Over 60% of all genes which encode proteins are controlled by miRNA [2]. miRNA is engaged in various processes including differentiation, proliferation and apoptosis as well as inflammation. Hence, they might be considered as potential biomarkers of diseases such as cancer, neurodegenerative and cardiovascular [3]. A huge challenge is the actual detection of miRNA because of their short length, low concentration and matrix interferences. The miRNA analysis can be performed with the following techniques such as real-time PCR, northern blotting and microarray [4-6]. However, the above mentioned techniques are rather sophisticated and are costly. An alternative could be the application of electrochemical techniques which are characterized with low detection limits, possibility of miniaturization and high sensitivity. In such a case miRNA could be detected using biosensors containing receptor layers formed of single-stranded DNA or PNA.

Herein, we present the studies on the development of ssDNA/PNA – based receptor layers for the electrochemical analysis of miRNA 141, which is a biomarker of pancreatic cancer. Various receptor layers were tested including unlabelled ssDNA, methylene blue-labelled DNA as well as PNA-based. The formation of ssDNA/PNA receptor layer along with its binding to miRNA was confirmed using QCM and SPR techniques. The electrochemical studies revealed that it was not possible to obtain low detection limits for miRNA when MB-labelled ssDNA or PNA molecules were applied. On the contrary, detection limit of 10^-4 nM was reached with the application of unlabelled ssDNA molecules. The further analysis showed the possibility of detection of point mutation in ssDNA or miRNA sequence as well as miRNA detection in spiked serum sample.

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