Derivatization agents for electrochemical detection in amino acid, peptide and protein separations: The hidden electrochemistry?

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.