Apparatus and methods for performing electrochemical reactions

A method of monitoring a reaction product in a reaction vessel, the method comprising:

• flowing a first reagent within an apparatus, the apparatus comprising:
• a reaction vessel coupled to an electronic sensor for monitoring a reaction product in the reaction vessel, wherein the reaction vessel includes a microwell array integrated with a sensor array;
• a fluidics system for sequentially delivering a plurality of reagents to the reaction vessel, the fluidics system including a plurality of reagent reservoirs in fluidic communication via a plurality of flow paths with a fluidics circuit and to a common passage in fluidic communication between the fluidics circuit and the reaction vessel, a solution reservoir containing a solution in fluidic communication with the common passage via a branch passage connected with the common passage at a junction between the fluidics circuit and the reaction vessel, and a valve disposed between the solution reservoir and the junction;
• and
• an electrode in contact with the solution within the branch passage, the electrode being disposed between the valve and the junction, the electrode being in electrical communication with the reaction vessel through fluid extending from the branch passage and through the common passage, wherein the electrode avoids direct contact with the plurality of reagents and uses the conductive solution for electrical contact, the electronic sensor generating an output signal depending on a voltage of the electrode;
• flowing the solution through the branch channel and the common passage;
• and
• flowing a second reagent within the apparatus.