For the experiments a four-channel spectroscopic SPR sensor with a temperature controller developed at IPE was used. In general, the SPR assay was based on the attachment of biotinylated DNA probes to the SPR sensor surface via the streptavidin-biotin interaction, with the streptavidin covalently attached to the alkanthiol self-assembled monolayer, subsequent forming of RNA/DNA hybrid duplexes and monitoring of their interaction with RNA-DNA-hybrid antibody.
The respective steps of the assay were as follows:
Streptavidin was covalently attached to the sensor surface via amine coupling according to the previously published protocol (Vaisocherová et al. (2006) Biopolymers 82:394-398).
Biotinylated DNA probes were immobilized in 10mM Tris buffer. The amount of probes was calculated to be of 1012 probes/cm2 and was kept the same across all experiments.
Complementary miRNA strands were bound in 10mM Tris + 15mM MgCl2 to form RNA-DNA hybrid duplexes. The concentration range of miRNA used was 0.1-100nM.
The D5H6 at a concentration of 1µg/ml was used in all experiments.
All the experiments were performed at the temperature of 25°C and the flow rate of 20µl/ml.
The sensor response to the binding of D5H6 antibody obtained for various concentrations of miRNA and corresponding calibration curve are shown at Fig.1. The calibration curve is plotted as a dependence of the sensor response to the binding of D5H6 antibody on the concentration of miRNA and is linear up to the miRNA concentration of 5nM.
As a negative control, the ssDNA (only biotinylated DNA probe) or dsDNA (homo-duplex with DNA analogue of the miRNA) surface was used. In both cases, the nonspecific sensor response to the binding of D5H6 was below 2% which falls into the inter-assay variability range.