This review highlights the role of electrochemical approaches in the sensing of antioxidants and their antioxidant capacity with especial attention to the analytical possibilities of electrochemistry in the direct evaluation of antioxidant capacity exhibited by food and biological samples due to the termed dietary, natural or biological antioxidants (mainly polyphenols, and vitamins C and E). The analytical potency of the electrochemistry is comprehensively stated and the selected results found in the literature are summarized and discussed critically. The main electrochemical approaches used have been cyclic voltammetry (CV) and flow injection analysis with amperometric detection (FIA-ED). In addition, miniaturization is going to break new frontiers in the evaluation of antioxidant activity.

Microfluidic devices using carbon nanotube (CNT) materials (single-walled and two multiwalled (MWCNT)) for the analysis of selected analyte groups of significance in foods such as dietary antioxidants, water-soluble vitamins, vanilla flavors, and isoflavones involved in representative food samples have been explored for the first time. Ultrafast separations resulted in well-defined and resolved peaks with enhanced voltammetric current in comparison with those obtained from unmodified screen-printed electrodes, turning MWCNT into an ideal material for electrochemical sensing in food analysis. Resolution was improved by a factor of 2, and sensitivity was dramatically enhanced with amplification factors toward calibration slopes from 4- to 16-fold. In both qualitative and quantitative domains, this impressive performance of CNTs integrated on microfluidics allowed solving specific challenges in food environments such as the direct detection of analytes in complex natural samples and unambiguous analytes in the control of fraud, which was not possible on nonmodified surfaces, avoiding the integration of complex preconcentration steps on these microdevices. The use of these unique materials in microfluidics for food analysis has opened new expectations in "lab-on-a-chip" domains.

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"Lab-on-a-chip" approaches based on the novel marriage between an electrokinetic microfluidic platform and nanotechnology is proposed for analytical domains. Conceptually, the analytical challenges are linked with the analytical promises offered from the integration of lab-on-a-chip and nanotechnologies. The analytical suitability of the electrokinetic microfluidic platform with multi-walled carbon nanotubes as detectors is proposed based on its dual format/use as a flow and separation system, independently. Two relevant applications of high significance, determination of total isoflavones and fast detection of antioxidant profiles were chosen to demonstrate their analytical potential. For both analytical uses, the target challenges, the strategy proposed, the expected role of microfluidics and carbon nanotubes and future prospects are discussed and demonstrated. A good analytical performance of the proposed microfluidic platform in terms of reliability, versatility and fast analytical solutions is demonstrated.

CE microchips are the first generation of micrototal analysis systems (-TAS) emerging in the miniaturization scene of food analysis. CE microchips for food analysis are fabricated in both glass and polymer materials, such as PDMS and poly(methyl methacrylate) (PMMA), and use simple layouts of simple and double T crosses. Nowadays, the detection route preferred is electrochemical in both, amperometry and conductivity modes, using end-channel and contactless configurations, respectively. Food applications using CE microchips are now emerging since food samples present complex matrices, the selectivity being a very important challenge because the total integration of analytical steps into microchip format is very difficult. As a consequence, the first contributions that have recently appeared in the relevant literature are based primarily on fast separations of analytes of high food significance. These protocols are combined with different strategies to achieve selectivity using a suitable nonextensive sample preparation and/or strategically choosing detection routes. Polyphenolic compounds, amino acids, preservatives, and organic and inorganic ions have been studied using CE microchips. Thus, new and exciting future expectations arise in the domain of food analysis. However, several drawbacks could easily be found and assumed within the miniaturization map.