Lateral Transport of Solutes in Microfluidic Channels Using Electrochemically Generated Gradients in Redox-Active Surfactants

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

Transient concentration gradients generated and detected electrochemically in continuous flow microchannels were investigated by numerical simulations and amperometric measurements. Operating conditions including device geometry and hydrodynamic regime were theoretically delineated for producing gradients of various profiles with tunable characteristics. Experiments were carried out with microfluidic devices incorporating a dual-channel-electrode configuration. Under these conditions, high electrochemical performance was achieved both to generate concentration gradients and to monitor their dynamics along linear microchannels. Good agreement was observed between simulated and experimental data validating predictions between gradient properties and generation conditions. These results demonstrated the capability of electrochemical microdevices to produce in situ tunable concentration gradients with real-time monitoring. This approach is versatile for the active control in microfluidics of microenvironments or chemical gradients with high spatiotemporal resolution.

Influence of the Phase State of Self-Assembling Redox Mediators on their Electrochemical Activity

Self-assembling redox mediators have the potential to be broadly useful in a range of interfacial electrochemical contexts because the oxidation state and state of assembly of the mediator are closely coupled. In this paper, we report an investigation of the self-assembly of single- and double-tailed ferrocenyl amphiphiles (FTMA and BFDMA, respectively) at the surfaces of Pt electrodes and the impact of the dynamic assembled state of the amphiphiles on their rate of oxidation. We conclude that frozen aggregates of BFDMA adsorb to the surfaces of the Pt electrodes, and that slow dynamics of reorganization BFDMA within these aggregates limits the rate of electrooxidation of BFDMA. In contrast, FTMA, while forming assemblies on the surfaces of Pt electrodes, is characterized by fast reorganization dynamics and a corresponding rate of oxidation that is an order of magnitude greater than BFDMA.

Redox-responsive delivery systems

Stimuli-responsive systems for the transport and delivery of materials to a given location at a specific time are highly valuable in numerous applications. The characteristics of the delivery system are dictated by the requirements of a particular application, which include the nature of the stimulus for actuation of the delivery process. Electron transfer has moved to the forefront as a stimulus for responsive delivery systems, particularly for those used in drug and reagent delivery, and for analyte transport/separation avenues. Interest in redox-activated delivery of materials arises from the abundance of redox-active stimuli that can be used to make delivery occur, the often simple chemical nature of the activation process, and the ease of constructing delivery vehicles with an integrated redox-responsive trigger group. This review is focused on vesicle- and micelle-based vehicles whose contents can be delivered by a redox stimulus due to their potential to meet the needs of key applications.