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 Ru^2+/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 λ_max for the [Ru(bpy)₂dcb]Cl₂ monolayers. This wavelength is shifted by approximately 28 nm compared to the photoexcited λ_max 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.