Tailoring Molecular Permeability of Nanochannel-Micelle Membranes for Electrochemical Analysis of Antioxidants in Fruit Juices without Sample Treatment.

Antioxidants are widely found or used in food, pharmaceutical, and cosmetics industries; thus, rapid and sensitive detection of antioxidants is of great interest. The present work reports a simple and fast electrochemical method for direct analysis of antioxidants in fruit juices by modulating the permeability of mesochannels on the electrode surface. This goal was achieved by growing vertical silica mesochannel array (SMA) with a channel diameter of 2-3 nm on the indium tin oxide (ITO) electrode surface using the cylindrical micelles (CMs) as the template. As-prepared electrodes, designed as CM@SMA/ITO, are only permeable to lipophilic antioxidants, e.g., retinol, with the hydrophobic hydrocarbon cores of CMs. After excluding CMs from silica mesochannels, the ITO electrode modified with bare SMA, namely SMA/ITO, possesses a high density of silanol groups on the channel wall and thus is only permeable to hydrophilic antioxidants, such as ascorbic acid (AA). Two types of sensors allowed the selective analyses of retinol and AA in buffer solutions and demonstrated a wide linear range for retinol (1-60 μM) and AA (10-2000 μM), respectively, and a low detection limit (0.65 μM for retinol and 0.52 μM for AA). Moreover, the SMA/ITO electrode can selectively determine the concentration of AA in orange juice. The CM@SMA/ITO electrode can measure the sum activity of lipophilic antioxidants, such as retinol, α-tocopherol, and others possibly coexisting, in carrot juice. In addition, the ultrasmall mesochannels and CMs could effectively exclude the access of large substances, rendering an excellent antifouling and anti-interference ability for direct analysis of antioxidants in fruit juices without sample pretreatment.