The voltage-operating window for many electrokinetic microdevices is limited by electrolysis gas bubbles that destabilize microfluidic system causing noise and irreproducible responses above ∼3 V DC and less than ∼1 kHz AC at 3 Vpp. Surfactant additives, SDS and Triton X-100, and an integrated semipermeable SnakeSkin® membrane were employed to control and assess electrolysis bubbles from platinum electrodes in a 180 by 70 μm, 10 mm long microchannel. Stabilized current responses at 100 V DC were observed with surfactant additives or SnakeSkin® barriers. Electrolysis bubble behaviors, visualized via video microscopy at the electrode surface and in the microchannels, were found to be influenced by surfactant function and SnakeSkin® barriers. Both SDS and Triton X-100 surfactants promoted smaller bubble diameters and faster bubble detachment from electrode surfaces via increasing gas solubility. In contrast, SnakeSkin® membranes enhanced natural convection and blocked bubbles from entering the microchannels and thus reduced current disturbances in the electric field. This data illustrated that electrode surface behaviors had substantially greater impacts on current stability than microbubbles within microchannels. Thus, physically blocking bubbles from microchannels is less effective than electrode functionalization approaches to stabilize electrokinetic microfluidic systems.

Hematocrit (HCT) tests are widely performed to screen blood donors and to diagnose medical conditions. Current HCT test methods include conventional microhematocrit, Coulter counter, CuSO4 specific gravity, and conductivity-based point-of-care (POC) HCT devices, which can be either expensive, environmentally inadvisable, or complicated. In the present work, we introduce a new and simple microfluidic system for a POC HCT determination. HCT was determined by measuring current responses of blood under 100 V DC for 1 min in a microfluidic device containing a single microchannel with dimensions of 180 μm by 70 μm and 10 mm long. Current responses of red blood cell (RBC) suspensions in PBS or separately plasma at HCT concentrations of 10, 20, 25, 30, 35, 40, 45, 50, 55, 60, and 70 vol% were measured to show feasibility of the microfluidic system for HCT determination. Key parameters affecting current responses included electrolysis bubbles and irreversible RBC adsorption; parameters were optimized via addition of nonionic surfactant Triton X-100 into sample solution and carbonizing electrode surfaces. The linear trend line of current responses over a range of RBC concentrations were obtained in both PBS and plasma. This work suggested that a simple microfluidic device could be a promising platform for a new POC HCT device.

Cell dielectrophoretic responses have been extensively studied for biomarker expression, blood typing, sepsis, circulating tumor cell separations, and others. Surfactants are often added to the analytical buffer in electrokinetic cellular microfluidic systems to lower surface/interfacial tensions. In nonelectrokinetic systems, surfactants influence cell size, shape, and agglomeration; this has not been systematically documented in electrokinetic systems. In the present work, the impacts of the Triton X-100 surfactant on human red blood cells (RBCs) were explored via ultraviolet-visible spectroscopy (UV-Vis) and dielectrophoresis (DEP) to compare nonelectrokinetic and electrokinetic responses, respectively. The UV-Vis spectra of Triton X-100 treated RBCs were dramatically different from that of native RBCs. DEP responses of RBCs were compared to RBCs treated with low concentrations of Triton X-100 (0.07–0.17 mM) to ascertain surfactant effects on dielectric properties. A star-shaped electrode design was used to quantify RBC dielectric properties by fitting a single-shell oblate cell model to experimentally-derived DEP spectra. The presence of 0.07 and 0.11 mM of Triton X-100 shifted the RBC’s DEP spectra yielding lower crossover frequencies (fCO). The single-shell oblate model revealed that cell radius and membrane permittivity are the dominant influencers of DEP spectral shifts. The trends observed were similar for 0.11 mM and 0.07 mM Triton X-100 treated cells. However, a further increase of Triton X-100 to 0.17 mM caused cells to only exhibit negative DEP. The magnitude of the DEP force increased with Triton X-100 concentration. This work indicates that dynamic surfactant interactions with cell membranes alter cell dielectric responses and properties.

The ability to strategically induce or suppress cell lysis is critical for many cellular‐level diagnostic and therapeutic applications conducted within electrokinetic microfluidic platforms. The chemical and structural integrity of sub‐cellular components is important when inducing cell lysis. However, metal electrodes and electrolytes participate in undesirable electrochemical reactions that alter solution composition and potentially damage protein, RNA, and DNA integrity within device microenvironments. For many biomedical applications, cell viability must be maintained even when device‐imposed cell‐stressing stimuli (e.g., electrochemical reaction byproducts) are present. In this work, we explored a novel and tunable method to accurately induce or suppress device‐imposed artifacts on human red blood cell (RBC) lysis in non‐uniform AC electric fields. For precise tunability, a dielectric hafnium oxide (HfO2) layer was used to prevent electron transfer between the electrodes and the electric double layer and thus reduce harmful electrochemical reactions. Additionally, a low concentration of Triton X‐100 surfactant was explored as a tool to stabilize cell membrane integrity. The extent of hemolysis was studied as a function of time, electrode configuration (T‐shaped and star‐shaped), cell position, applied non‐uniform AC electric field, with uncoated and HfO2 coated electrodes (50 nm), and absence and presence of Triton X‐100 (70 µM). Tangible outcomes include a parametric analysis relying upon literature and this work to design, tune, and operate electrokinetic microdevices to intentionally induce or suppress cellular lysis without altering intracellular components. Implications are that devices can be engineered to leverage or minimize device‐imposed biological artefacts extending the versatility and utility of electrokinetic diagnostics.

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