Fabrication of pH-Adjusted Boronic Acid–Aptamer Conjugate for Electrochemical Analysis of Conjugated N-Glycolylneuraminic Acid

In this work, the boronic acid–aptamer conjugate (BAAC) is elaborately designed and explored as a recognition unit. The admirable properties of the pH-dependent boronic acid ester are integrated with the specific capturing capability of the modified aptamer; thus, BAAC can efficiently and selectively bind with the target by adjusting the pH values. An electrochemical biosensor based on pH-adjusted BAAC has been further developed for the analysis of CNeu5Gc, an important biomarker of different kinds of cancer. The boronic acid moiety in BAAC can react with CNeu5Gc to form a BAAC–CNeu5Gc complex under acidic conditions, followed by the release of CNeu5Gc from the complex and subsequent capture by the aptamer moiety with the adjustment of the pH value to alkalinity. With simplicity, high specificity, and efficiency, the biosensor exhibits a wide linear range from 2.816 to 3603.960 ng/mL with a low detection limit of 1.224 ng/mL and can be applied to analyze CNeu5Gc in animal food samples. Besides, this work can also provide a kind of modified aptamer, i.e., the chemical capturing group-modified aptamer, to give a new viewpoint for the exploration of other functionalized aptamers.