On-demand in situ generation of oxygen in a nanofluidic embedded planar microband electrochemical reactor

Abstract

In situ generation of reagents and their subsequent use downstream presents new opportunities to amplify the utility of nanofluidic devices by exploiting the confined geometry to address mass transport limitations on reaction kinetics and efficiency. Oxygen, an inherently valuable reactant, can be produced from electrolysis of water, a process that can be conveniently integrated within a nanofluidic system. Here, we construct and characterize a nanofluidic device consisting of a planar microband electrode embedded within a nanochannel for in situ electrochemical generation and optical monitoring of O2. Fluorescein, a dye with a pH-sensitive emission intensity, was used to monitor the spatiotemporal characteristics of the oxidation of H2O, using the co-produced H+. Application of anodic potentials at the nanochannel-embedded electrode results in a decrease in fluorescence intensity, which reflects the decreasing solution pH. A combination of fluorescence intensity and chronoamperometric response was used to quantitatively determine proton generation, and the H+/O2 stoichiometry was then used to determine the concentration of the O2 in the channel. Comparison of the experimental results to finite element simulations validates the use of fluorescein emission intensity to spectroscopically determine the local oxygen concentration in the nanochannel. By varying the applied potential, spatially averaged O2 concentrations ranging from 0.13 to 0.41 mM were generated. The results demonstrate a convenient route to in situ modulation of the dissolved O2 level in a nanofluidic device and the use of an optical probe to monitor its spatial and temporal distribution under flow conditions.

Electrochemical Performance of Micropillar Array Electrodes in Microflows

“…This work provides an applicable guideline for parameters design and structure optimization of the μEDS. In addition, nanochip-based electrochemical detection system (nEDS) with nanoelectrode in nanoflows is one of main research directions recently [ 45 , 46 ], which has the characteristic [ 47 , 48 , 49 , 50 ] of lower reagent consumption, faster analysis time and larger surface-to-volume ratio comparted with μEDS. The presented method in the study can be applied to analyze and optimize the electrochemical performance of nEDS.…”

Nanofluidics: A New Arena for Materials Science

“…Despite the difficulty, some impressive works through bypassing the hurdles have been reported. Most of these works focused on the integration of electrical components (for example, electrodes) to enable electrical measurements (impedance and resistance), electrochemical reaction and detection, or external physical operation for nanofluidic devices.…”

“…By using this smart strategy, Lemay and co‐workers developed nanofluidic electrochemical systems for integrated detection of electrochemical processes and enzymatic reactions in sample volumes of few femtoliters (Figure h,i) . A third strategy is to fabricate nanochannels with embedded transverse electrodes, as presented by Ziaie and co‐workers, Yamamoto and co‐workers, and Bohn and co‐workers . Because nanoscale accuracy alignment is not necessary for this case, conventional photolithography can easily meet the requirement of fabrication.…”

“…l,m) Fluorescence images showing fluorescence intensity change due to electrochemical generation of H + during electrochemical oxidation of water before (l) and after (m) application of a working potential pulse. j–m) Reproduced with permission . Copyright 2015, Springer.…”

Electrochemical Generation and Detection of Transient Concentration Gradients in Microfluidic Channels. Theoretical and Experimental Investigations

“…Few studies have focused on the generation of controllable concentration gradients combined with concentration monitoring. In this context, electrochemical reactions in microfluidic systems hold considerable promise both for generation (Mitrovski and Nuzzo, 2005; Klauke et al, 2006; Liu and Abbott, 2011; Contento and Bohn, 2014; Xu et al, 2015) and detection (Contento and Bohn, 2014) of concentration gradients. Indeed, electrochemical techniques are suitable for miniaturization and they are easy to implement in microfluidic devices.…”