Aptamer-based potentiometric measurements of proteins using ion-selective microelectrodes

We here report or. the first example of an aptamer-based potentiometric sandwich assay of proteins. The measurements are based on CdS quantum dot labels of the secondary aptamer, which were determined with a novel solid-contact Cd2+-selective polymer membrane electrode after dissolution with hydrogen peroxide. The electrode exhibited cadmium ion detection limits of 100 pM in 100 mL samples and of 1 nM in 200 mu L microwells, using a calcium-selective electrode as a pseudoreference electrode. As a prototype example, thrombin was measured in 200 mu L samples with a lower detection limit of 0.14 nM corresponding: to 28 fmol of analyte. The results show great promise foil the potentiometric determination of proteins at very low concentrations in microliter samples.