Microfluidic device using a gold pillar array and integrated electrodes for on-chip endothelial cell immobilization, direct RBC contact, and amperometric detection of nitric oxide

Recombinant-Chemosynthetic Biosensors for Probing Cell Surface Signaling of Red Blood Cells and Other Cells

The complex signaling mechanisms in red blood cells (RBCs) enable them to adapt to physiological stresses such as exposure to low O2 levels, metabolic demands, oxidative stress, and shear stress. Since Ca2+ is a crucial determinant of RBC fate, various ion channels, pumps, and exchangers regulate the delicate balance of Ca2+ influx and efflux in RBCs. Elevated intracellular Ca2+ can activate processes such as membrane phospholipid scrambling and alter RBC deformability, which is essential for effective capillary transit. However, the dynamic information about Ca2+ regulation in RBCs is limited. Although static mapping and bioanalytical methods have been utilized, the absence of a nucleus and the presence of hemoglobin create challenges for real-time probing of RBC signaling, necessitating innovative approaches. This work introduces a synthetic chemistry-recombinant protein-based strategy to assemble sensors at genetically intact healthy human RBC surfaces for measuring dynamic signaling. Using this approach, we measured autocrine regulation of RBC Ca2+ influx in response to low O2 tension-induced ATP release. The study also explores the utilization of synthetic glycosylphosphatidylinositol (GPI) anchor mimics and sortagging for targeting sensors to the surfaces of primary as well as immortalized cells. This demonstrated the wide applicability of this approach to probe dynamic signaling in intact cells.

3D-Printed Microfluidic-Based Cell Culture System With Analysis to Investigate Macrophage Activation

In this paper, we describe the development of 3D-printed microfluidic cell culture devices that can be coupled with a circulation system to study the dynamics of both intracellular and extracellular (release) processes. Key to this approach is the ability to quantitate key analytes on a minutes timescale with either on-line (in this study, quantitating nitric oxide production using an amperometric flow cell) or off-line (in this work, quantitating intracellular itaconate production with LC/MS) analytical measurements. To demonstrate the usefulness of this approach, we chose to study macrophage polarization as a function of the extracellular matrix (silk) fiber size, a major area of research in tissue engineering. It was found that the use of larger fibers (1280 nm vs. smaller 512 nm fibers) led to increases in the production of both nitric oxide and itaconate. These findings set the foundation for future research for the creation of finely tuned microfluidic 3D cell culture approaches in areas where flow and the extracellular matrix play a significant role in barrier transport and where integrated analysis of key markers is needed.

Ultrahigh-sensitivity multi-parameter tacrolimus solution detection based on an anchor planar millifluidic microwave biosensor

To detect drug concentration in tacrolimus solution, an anchor planar millifluidic microwave (APMM) biosensor is proposed. The millifluidic system integrated with the sensor enables accurate and efficient detection while eliminating interference caused by the fluidity of the tacrolimus sample. Different concentrations (10-500 ng mL^-1) of the tacrolimus analyte were introduced into the millifluidic channel, where it completely interacts with the radio frequency patch electromagnetic field, thereby effectively and sensitively modifying the resonant frequency and amplitude of the transmission coefficient. Experimental results indicate that the sensor has an extremely low limit of detection (LoD) of 0.12 pg mL^-1 and a frequency detection resolution (FDR) of 1.59 (MHz (ng mL^-1)). The greater the FDR and the lower the LoD, the more the feasibility of a label-free biosensing method. Regression analysis revealed a strong linear correlation (R² = 0.992) between the concentration of tacrolimus and the frequency difference of the two resonant peaks of APMM. In addition, the difference in the reflection coefficient between the two formants was measured and calculated, and a strong linear correlation (R² = 0.998) was found between the difference and tacrolimus concentration. Five measurements were performed on each individual sample of tacrolimus to validate the biosensor's high repeatability. Consequently, the proposed biosensor is a potential candidate for the early detection of tacrolimus drug concentration levels in organ transplant recipients. This study presents a simple method for constructing microwave biosensors with high sensitivity and rapid response.

Red blood cells in type 1 diabetes and multiple sclerosis and technologies to measure their emerging roles

Autoimmune diseases affect over 40 million people in the United States. The cause of most autoimmune diseases is unknown; therefore, most therapies focus on treating the symptoms. This review will focus on the autoimmune diseases type 1 diabetes (T1D) and multiple sclerosis (MS) and the emerging roles of red blood cells (RBCs) in the mechanisms and treatment of T1D and MS. An understanding of the role of the RBC in human health is increasing, especially with respect to its role in the regulation of vascular caliber and vessel dilation. The RBC is known to participate in the regulation of blood flow through the release of key signaling molecules, such as adenosine triphosphate (ATP) and the potent vasodilator nitric oxide (NO). However, while these RBC-derived molecules are known to be determinants of blood flow in vivo, disruptions in their concentrations in the circulation are often measured in common autoimmune diseases. Chemical and physical properties of the RBC may play a role in autoimmune disease onset, especially T1D and MS, and complications associated with downstream extracellular levels of ATP and NO. Finally, both ATP and NO are highly reactive molecules in the circulation. Coupled with the challenging matrix posed by the bloodstream, the measurement of these two species is difficult, thus prompting an appraisal of recent and novel methods to quantitatively determining these potential early indicators of immune response.

Fully 3D printed fluidic devices with integrated valves and pumps for flow injection analysis

The use of a PolyJet 3D printer to create a microfluidic device that has integrated valves and pumps is described. The process uses liquid support and stacked printing to result in fully printed devices that are ready to use within minutes of fabrication after minimal post-processing. A unique feature of PolyJet printing is the ability to incorporate several different materials of varying properties into one print. In this work, two commercially available materials were used: a rigid-transparent plastic material (VeroClear) was used to define the channel regions and the bulk of the device, while the pumps/valves were printed in a flexible, rubber-like material (Agilus30). The entire process, from initial design to testing takes less than 4 hours to complete. The performance of the valves and pumps were characterized by fluorescence microscopy. A flow injection analysis device that enabled the discrete injections of analyte plugs was created, with on-chip pumps being used to move the fluid streams. The injection process was found to be reproducible and linearly correlated with changes in analyte concentration. The utility was demonstrated with the injection and rapid lysis of fluorescently-labeled endothelial cells. The ability to produce a device with integrated pumps/valves in one process significantly adds to the applicability of 3D printing to create microfluidic devices for analytical measurements.

3D-Printed Microfluidic Device with In-line Amperometric Detection that Also Enables Multi-Modal Detection

Microfluidic amperometric detectors often include a reservoir to house auxiliary and reference electrodes, making subsequent detection downstream challenging. Here, we present an in-line microfluidic device with amperometric detection that incorporates a three-electrode set-up, made possible by threading electrodes into a 3D-printed flow cell. The electrodes consist of a commercially available threaded reference electrode and electrodes fabricated in commercially available fittings. This approach centers the working electrode in the fluidic channel enabling the use of a pillar working electrode that is shown to increase sensitivity, as compared to a traditional thin-layer electrode. In addition, the working and auxiliary electrodes can be directly opposed, with this configuration leading to a more uniform potential being applied to the working electrode as well as fewer issues with any iR drop. To demonstrate the ability to incorporate a separate mode of detection downstream from the electrochemical flow cell, the device is modified to include a mixing T for introduction of reagents for chemiluminescent detection of ATP (via the luciferin-luciferase reaction), leading to a single 3D-printed device that can be used to detect norepinephrine and ATP, nearly simultaneously, by amperometry and chemiluminescence, respectively. This approach opens numerous possibilities, where microfluidics with in-line amperometry can be used in continuous circulation studies or in conjunction with other downstream detection events to study complex systems.