Electrochemiluminescent monolayers on metal oxide electrodes: Detection of amino acids

The electrochemical and photochemical properties of [Ru(bpy)2dcb]Cl2 monolayers and their subsequent use for the detection of amino acids, e.g., proline, is reported; dcb is 4,4′-dicarboxy-2,2′-bipyridine and bpy is 2,2′-bipyridine. The ability of such a complex to form stable monolayers enables its utilization for the detection of oxalate and several amino acids, producing significant ECL. The electrochemical response of the Ru2+/3+ couple is electrochemically reversible and the monolayers show excellent stability with the response decreasing by less than 8% after continuous scanning over 4 h. The ECL and current responses increase linearly with increasing analyte concentration 0.2 ⩽ [Proline] ⩽ 1 nM while for hydroxy-proline the dynamic range is from 1 to 10 nM. The ECL signal was monitored at ∼644 nm, representing the λmax for the [Ru(bpy)2dcb]Cl2 monolayers. This wavelength is shifted by approximately 28 nm compared to the photoexcited λmax for the same system. This technique is simple, rapid, selective and sensitive, and shows potential for the high-throughput quantitation of amino acids if adapted with other techniques such as FIA or LC systems.