Electrochemiluminescent detection of epilepsy biomarker miR-134 using a metal complex light switch

The detection of a key biomarker in epilepsy, miR-134, using an environmentally sensitive electrochemiluminescent luminophore, [Ru(DPPZ)2 PIC]2+, is reported, DPPZ is dipyrido[3,2-a:2′,3′-c]phenazine) and PIC is (2,2′-bipyridyl)-2(4-carboxy phenyl) imidazo [4,5][1,10] phenanthroline. A thiolated capture strand is first labelled with [Ru(DPPZ)2 PIC]2+ and then adsorbed onto a gold electrode. No significant electrochemiluminescence, ECL, is observed for immobilised Ru-labelled capture strands which is consistent with the light-switch dye being exposed to the aqueous solution. In sharp contrast, binding of the target turns on ECL. The ECL intensity, IECL, depends on the number of adenine “spacer” bases between the end of the capture sequence and the dye. The ECL intensity for the optimised system increases linearly with increasing miR-134 concentration from 100 nM to approximately 20 μM. Single and double base mismatches produce IECL that are only approximately 30% and 8% respectively of that observed for the fully complementary target reflecting differences in their association constants. Significantly, the presence of BSA protein causes IECL to increase by less 5% in either the single or duplex circumstances. Finally, the ability of the sensor to quantify miR-134 in unprocessed plasma samples from healthy volunteers and people with epilepsy is reported.