Method for the Sequential Online Analysis of Enzyme Reactions Based on Capillary Electrophoresis

Drop-by-drop chemical reaction and sample introduction for capillary electrophoresis

In this paper, we report a novel sample introduction and chemical reaction strategy by drop-by-drop inkjet injection for an electrophoretically mediated microanalysis (EMMA). This method makes it possible to achieve an on-line introduction of reactant solutions by alternately ejecting small plugs, with an overlapping region of the plugs for mixing the reactants by electrophoresis, supporting chemical reactions, followed by electrophoretic separation of the final compounds. As a proof-of-concept of the method, the EMMA of an inkjetted mixture of 4-fluoro-7-nitrobenzofurazan (NBD-F) and amino acids was carried out as a model chemical reaction. The product NBD-amino acids were quantified by detection with laser induced fluorescence. The optimal conditions for the procedure were: inkjet driving voltage: +40-44 V; pulse width: 20-24 μs; drop-by-drop injection of reactant solutions: alternately 2 drops × 25 times for the amino acid solution and the NBD-F solution; zone overlapping voltage and time: 3 kV and 2 s; incubation time after overlapping: 5 min; separation voltage: 18 kV. Under the optimized conditions, a significant enhancement in sensitivity and a sensitive quantitative analysis were realized. The results obtained were comparable with those using the off-line labeling method. This method is rapid, cost-effective, and readily automated for EMMA.

Recent advances in CE-mediated microanalysis for enzyme study

This review gives an overview of the recent developments and applications in the use of CE-mediated microanalysis for enzyme studies. The period covers mid-2011 until mid-2013. Both off-line and in-line enzyme assays with their applications using CE are described in this article. For the in-capillary enzyme reaction, the techniques using electrophoretically mediated microanalysis (EMMA) as well as immobilized enzyme reactor (IMER) are discussed. The applications include the evaluation of enzyme activity, enzyme kinetics, enzyme inhibition, screening of enzyme inhibitors, and the study of enzyme-mediated drug metabolism.

Online enzyme discrimination and determination of substrate enantiomers based on electrophoretically mediated microanalysis

We proposed the first application of an electrophoretically mediated microanalysis (EMMA) method for fast online discrimination and determination of substrate enantiomers, which was achieved by just one EMMA assay. Lactate dehydrogenase (LDH)-catalyzed reaction was studied to evaluate the feasibility and performance of the presented method. The L- and D-LDH chiral enzymatic reactions, which are highly stereoselective to the lactate enantiomers, were initiated successively in one capillary, and the corresponding products, nicotinamide adenine dinucleotide (NADH), were online discriminated and detected by UV absorption. Excellent linear dependence of the two NADH peak intensities on the concentration of the corresponding lactate enantiomers was obtained within a wide range of 0.1-10 mM. The limit of detection was 26 μM for D-lactate and 49 μM for L-lactate (S/N = 3). Good repeatability of online chiral discrimination was demonstrated with relative standard deviation (RSD) < 6.3% for NADH peak height and RSD < 1.5% for migration time (n = 5). K(m) values for L- and D-lactate were measured and were consistent with those of the off-line enzyme assays. The presented method was successfully applied to determine the L-/D-lactate in several yogurt and wine samples. Our study shows a new application of the EMMA method utilizing high stereoselectivity of enzymes for fast online chiral analysis.