Microanalysis system with automatic valve operation, pH regulation, and detection functions

A microanalysis system with functions including automatic valve operation for mixing solutions, pH regulation, and detection based on electrochemiluminescence (ECL) was fabricated. Automatic valve operation was achieved by means of direct electrowetting using one of two solutions as a part of an electronic circuit. A valve formed with a gold electrode was opened when the second solution was filled in a compartment, causing the mixing of the two solutions. The pH regulation was achieved by using a nonstandard three-electrode system. The pH of the solution could be changed as desired by changing the working electrode potential, and the negative feedback function maintained the pH at a constant level. The ECL was generated on a platinum working electrode. Amino acids were detected as model analytes. A reagent solution containing tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+) and a sample solution containing an amino acid were mixed, and the pH was adjusted using the pH regulator. When +1.1 V (vs. Ag/AgCl) was applied to the electrode, red luminescence was observed. An increase in the ECL intensity was observed with an increase in the concentration. Amino acids of concentrations ranging from sub nM to 1 mM could be determined on the integrated device.