Electrochemical detection has a great potential in microfluidic systems due to its easy miniaturization without losing analytical performance. In addition, the use of nanomaterials in electroanalysis improves sensitivity, selectivity, and reproducibility. The topic of this review is the use of nanomaterials (nanoparticles, nanotubes, graphene) in electrochemical detection for capillary electrophoresis and microfluidic systems (microchips and paper based analytical devices). This review covers from 2015 up to now and it is a continuation of our previous review, also published in Electrophoresis journal. The following aspects of the surveyed articles are mainly addressed: type of nanomaterial, protocol of working electrode preparation (composite, drop casting and others), advantages of nanomaterial employment and application field (clinical, food, environmental and home security). The use of nanomaterials is still an interesting approach to improve the analytical performance of electrochemical detection based on microfluidic devices. Along the review, readers will find new protocols for working electrode modification, new carbon nanomaterials and promising applications in the aforementioned fields.

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In proteomics and clinical analysis, LIF and MS are the most used detectors coupled to separation techniques. MS offers good sensitivity and analyte identification ability but, as counterbalance, it is expensive and it needed background electrolytes compatible with mass spectrometers. LIF detection offers the highest sensitivity but, in general, proteins, peptides and amino acids are not fluorescents so it is necessary the use of fluorescence tags. This fact hindered the potential sensitivity of LIF detection due to the difficulty of labeling analytes at extremely low concentrations. In the context of micro- and nanofluidics, electrochemical detection (ED) is an excellent alternative to LIF and MS because it offers several advantages such as easy miniaturization, simpler methods, lower cost and high sensitivity in spite of decreasing the electrode size and sample volume. Among ED techniques, amperometric detection (AD and PAD) are the most used. The problem is that the sensitivity is not enough for the majority of proteomics and clinical applications. To overcome this handicap, electrochemical derivatization reagents have been employed with excellent results allowing limits of detection in nanomolar range. This review surveys all papers related to electrochemical derivatization reagents employed for amino acids, peptides and proteins in separation techniques. Additionally, we highlight the possibilities of this electrochemical tags in the context of micro- and nano- separation techniques and showed potential electrochemical tags which could be employed in the near future for proteomics applications.

Carbon and metallic-based nanostructures have been progressively implemented as innovative electrochemical detectors in CE and microchip electrophoresis (ME). For both type of nanomaterials and toward selected examples, this review details the impact of these nanomaterials for enhanced detection performance in CE, ME, and paper-based microfluidic devices. The analytical performance and the analytical potential in real world applications is also presented and discussed.

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