Determination of Glycoproteins by Microchip Electrophoresis Using Os(VI)-Based Selective Electrochemical Tag.

Glycoproteins are excellent biomarkers for diagnosis and prognosis of several illnesses. α-1-Acid glycoprotein (AGP) and transferrin (Tf) are the main glycoproteins present in the serum, whose levels are increased during disease or injury. In this work, a selective detection of these glycoproteins using a microchip electrophoresis-electrochemical detection (ME-ED) platform is proposed for the first time. Because of the reduced sensitivity of glycoproteins, they were labeled with an electrochemical tag (osmium(VI) complex), which binds only to glycans, increasing the amperometric signal. Interestingly, oxidation potential of glycoprotein-Os(VI) adducts started at +0.50 V (vs Ag/AgCl) while nontagged glycoproteins started at +0.60 V. So, when the detection potential is set at +0.50 V, only glycoproteins tagged with Os(VI) complex are detected, avoiding the interference of the rest of the proteins. Determination of AGP and Tf was successfully demonstrated in the analysis of a certified human serum reference material yielding excellent accuracy (Er ≤ 4%) in just 400 s. This work offers new possibilities for ED for glycoprotein analysis in microfluidic systems, which has been dominated by fluorescence and MS detection until now. It is worth mentioning that ED has two interesting advantages with respect to others in the point-of-care testing field: easy miniaturization (bedside devices) and low cost.