Wicking microfluidic approach to separate blood plasma from whole blood to facilitate downstream assays.

Separation of blood plasma or serum from blood is essential for accurate analysis. Conventional blood separation requires instrumentation, reagents, and large sample volumes, limiting this process to laboratory environments with trained personnel. Full implementation of effective blood separation and analysis on microliter sample volumes for point of care (POC) diagnostics has proven extremely challenging resulting in a growing market demand, with common challenges such as expensive device fabrication processes or devices being comprised of materials which are not easily disposable. We developed a membrane-based wicking microfluidic device which is made using a simple fabrication process. This device uses a unique 3D flow channel geometry, fabricated in a polycaprolactone-filled glass microfiber membrane, to efficiently separate microliter sample volumes of blood. Colorimetric assay chemistries were integrated to demonstrate utility of these devices in POC diagnostics. The devices are capable of separating both fresh and anticoagulant-treated blood at microscale sample volumes (<15.0 µL). Modifications to the base device are also reported herein which increased sample volume capacity and separation efficiency. Integrated colorimetric assay enabled semi-quantitative detection of conjugated bilirubin in real blood samples (1.0-1.5 mg/dL). These blood separation devices, fabricated on polycaprolactone-filled glass microfiber, enabled effective blood plasma (anticoagulant-treated blood) and serum (fresh blood) separation with microscale sample volumes. Sample volume capacity and separation efficiency are customizable for specific applications and devices can be integrated with downstream assay chemistries to develop complete POC devices that offer blood separation and diagnostics at the same time on a single membrane.

Chromatographic Separation and Visual Detection on Wicking Microfluidic Devices: Quantitation of Cu2+ in Surface, Ground, and Drinking Water.

Copper is widely applied in industrial and technological applications and is an essential micronutrient for humans and animals. However, exposure to high environmental levels of copper, especially through drinking water, can lead to copper toxicity, resulting in severe acute and chronic health effects. Therefore, regular monitoring of aqueous copper ions has become necessary as recent anthropogenic activities have led to elevated environmental concentrations of copper. On-site monitoring processes require an inexpensive, simple, and portable analytical approach capable of generating reliable qualitative and quantitative data efficiently. Membrane-based lateral flow microfluidic devices are ideal candidates as they facilitate rapid, inexpensive, and portable measurements. Here we present a simple, chromatographic separation approach in combination with a visual detection method for Cu2+ quantitation, performed in a lateral flow microfluidic channel. This method appreciably minimizes interferences by incorporating a nonspecific polymer inclusion membrane (PIM) based assay with a "dot-counting" approach to quantification. In this study, hydrophobic polycaprolactone (PCL)-filled glass microfiber (GMF) membranes were used as the base substrate onto which the PIM was evenly dispensed as an array of dots. The devices thus prepared were then selectively exposed to oxygen radicals through a mask to generate a hydrophilic surface path along which the sample was wicked. Using this approach, copper concentrations from 1 to 20 ppm were quantified from 5 µL samples using only visual observation of the assay device.

Patterned polycaprolactone-filled glass microfiber microfluidic devices for total protein content analysis.

Membrane based microfluidic devices have gained much popularity in recent years, as they make possible rapid, inexpensive analytical techniques that can be applied to a wide variety of areas. The ability to modify device hydrophilicity and hydrophobicity is critically important in fabricating membrane based microfluidic devices. Polar hydrophilic membranes, such as glass microfiber (GMF) membranes, hold great potential as they are inexpensive, chemically inert, and stable. Filling of these membranes with non-polar polymers such as polycaprolactone (PCL) converts the hydrophilic GMF into a hydrophobic medium. Controlled alteration of the surface chemistry of PCL/GMF substrates allows for the fabrication of microfluidic patterns on the surface. Using this approach, we have developed a simple and rapid technique for fabrication of highly adaptable complex multidimensional (2D and 3D) microfluidic pathways on a single membrane. PCL-filled GMF media were masked and selectively exposed to oxygen radicals so that the exposed surface became permanently superhydrophilic in its behavior. The desired microfluidic pattern was cut into the mask prior to assembly and exposure, and the mask was removed after exposure to reveal the ready-to-use microfluidic device. To verify and demonstrate the performance of this novel fabrication method, a colorimetric total protein assay was applied to the determination of protein concentrations in real samples.

Detection of water contamination from hydraulic fracturing wastewater: a µPAD for bromide analysis in natural waters.

Due to the rapid expansion in hydraulic fracturing (fracking), there is a need for robust, portable and specific water analysis techniques. Early detection of contamination is crucial for the prevention of lasting environmental damage. Bromide can potentially function as an early indicator of water contamination by fracking waste, because there is a high concentration of bromide ions in fracking wastewaters. To facilitate this, a microfluidic paper-based analytical device (µPAD) has been developed and optimized for the quantitative colorimetric detection of bromide in water using a smartphone. A paper microfluidic platform offers the advantages of inexpensive fabrication, elimination of unstable wet reagents, portability and high adaptability for widespread distribution. These features make this assay an attractive option for a new field test for on-site determination of bromide.