The EC response of the sensor has been studied using a portable PalmSens4 potentiostat controlled to a computer equipped with PSTrace 5.6 software. Bare ITO electrode was used as WE, whereas ITO coated with gold served as CE. An external Ag/AgCl electrode was used as a RE. Copper tape was used to provide an electric contact between ITO electrodes and the potentiostat. For experiments we used following solutions: 1 mM 1,1'ferrocenedimethanol (FcDM) in 0.1M KCl, 10 mM K3Fe(CN)6 in 0.1M KCl and 10 mM K4Fe(CN)6 in 0.1M KCl. For the preparation of solutions, we used: KCl powder from POCh (pure p.a.), 98% FcDM from ACROS Organics, K3Fe(CN)6 powder from Sigma-Aldrich, K4Fe(CN)6*3H2O powder from POCh and deionized water from Millipore system. For determining the flow rate, a Harvard Apparatus Syringe infusion pump 11 equipped with silicone tubing (inner diam. 0.8 µm) was used to pump solutions into the microchannel. For the flow injection experiments an injection valve (Cheminert, Vici) with two different of sample loops were used, i.e., 20 cm and 50 cm long. These have an injection volume of 100 µl and 250 µl, respectively. The flow rate was set to 100 µl/min, which is the highest value that ensures that the concentration in the microchannel reaches the same value as in the sample loop (Fig ). For EC measurements the flow rate was 5-10 µl/min. The combined EC-optical setup used for measurements is shown in Fig. .