In this paper, we review the recent progress in the development of low-cost microfluidic devices based on multifilament threads and textiles for semi-quantitative diagnostic and environmental assays. Hydrophilic multifilament threads are capable of transporting aqueous and non-aqueous fluids via capillary action and possess desirable properties for building fluid transport pathways in microfluidic devices. Thread can be sewn onto various support materials to form fluid transport channels without the need for the patterned hydrophobic barriers essential for paper-based microfluidic devices. Thread can also be used to manufacture fabrics which can be patterned to achieve suitable hydrophilic-hydrophobic contrast, creating hydrophilic channels which allow the control of fluids flow. Furthermore, well established textile patterning methods and combination of hydrophilic and hydrophobic threads can be applied to fabricate low-cost microfluidic devices that meet the low-cost and low-volume requirements. In this paper, we review the current limitations and shortcomings of multifilament thread and textile-based microfluidics, and the research efforts to date on the development of fluid flow control concepts and fabrication methods. We also present a summary of different methods for modelling the fluid capillary flow in microfluidic thread and textile-based systems. Finally, we summarized the published works of thread surface treatment methods and the potential of combining multifilament thread with other materials to construct devices with greater functionality. We believe these will be important research focuses of thread- and textile-based microfluidics in future.

Exploration of microfluidic devices based on multi-filament threads and textiles: A review

Paper-based microfluidic devices have advanced significantly in recent years as they are affordable, automated with capillary action, portable, and biodegradable diagnostic platforms for a variety of health, environmental, and food quality applications. In terms of commercialization, however, paper-based microfluidics still have to overcome significant challenges to become an authentic point-of-care testing format with the advanced capabilities of analyte purification, multiplex analysis, quantification, and detection with high sensitivity and selectivity. Moreover, fluid flow manipulation for multistep integration, which involves valving and flow velocity control, is also a critical parameter to achieve high-performance devices. Considering these limitations, the aim of this review is to (i) comprehensively analyze the fabrication techniques of microfluidic paper-based analytical devices, (ii) provide a theoretical background and various methods for fluid flow manipulation, and (iii) highlight the recent detection techniques developed for various applications, including their advantages and disadvantages.

Fabrication, Flow Control, and Applications of Microfluidic Paper-Based Analytical Devices

Recent advances in thread-based microfluidics for diagnostic applications.

We present an innovative impedance cytometer for the measurement of the cross-sectional position of single particles or cells flowing in a microchannel. As predicted by numerical simulations and experimentally validated, the proposed approach is applicable to particles/cells with either spherical or non-spherical shape. In particular, the optics-free high-throughput position detection of individual flowing red blood cells (RBCs) is demonstrated and applied to monitor RBCs hydrodynamic focusing under different sheath flow conditions. Moreover, the device provides multiparametric information useful for lab-on-a-chip applications, including particle inter-arrival times and velocity profile, as well as RBCs mean corpuscular volume, distribution width and electrical opacity.

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High-throughput electrical position detection of single flowing particles/cells with non-spherical shape

The Discrete-to-Integrated Electronics group (D2In), at the University of Barcelona, in partnership with the Bioelectronics and Nanobioengineering Group (SICBIO), is researching Smart Self-Powered Bio-Electronic Systems. Our interest is focused on the development of custom built electronic solutions for bio-electronics applications, from discrete devices to Application-specific integrated circuit (ASIC) solutions.

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Bioelectronics for Amperometric Biosensors

This paper describes a line-based microfluidic system for rapid and low-cost electrophoresis (CE) separation and electrochemical (EC) detection of ion samples. Instead of using liquid channel for sample separation, thin polyester threads of various diameters are used as the routes for separating the samples with electrophoresis. Hot-pressed PMMA chip with protruding sleeper structures are adopted to set up the polyester threads and for electrochemical detecting the ion samples on the thread. Plasma treatment greatly improves the wetability of thin threads and surface quality of the threads. The measured electrical currents on plasma treated threads are 10 times greater than the threads without treatment. Results indicate that nice redox signals can be obtained by measuring ferric cyanide salt on the polyester thread. The estimated detection limit for EC sensing of potassium ferricyanide (K 3 Fe(CN) 6 ) is around 50 μM. Mixed ion samples of Cl−, Br− and I− are successfully separated and detected using the developed line-based microfluidic device.

Electrophoresis separation and electrochemical detection on a novel line-based microfluidic device

This research reports a novel method for depth position measurement of fast moving objects inside a microfluidic channel based on the chromatic aberration effect. Two band pass filters and two avalanche photodiodes (APD) are used for rapid detecting the scattered light from the passing objected. Chromatic aberration results in the lights of different wavelengths focus at different depth positions in a microchannel. The intensity ratio of two selected bands of 430 nm–470 nm (blue band) and 630 nm–670 nm (red band) scattered from the passing object becomes a significant index for the depth information of the passing object. Results show that microspheres with the size of 20 μm and 2 μm can be resolved while using PMMA (Abbe number, V = 52) and BK7 (V = 64) as the chromatic aberration lens, respectively. The throughput of the developed system is greatly enhanced by the high sensitive APDs as the optical detectors. Human erythrocytes are also successfully detected without fluorescence labeling at a high flow ...

Depth position detection for fast moving objects in sealed microchannel utilizing chromatic aberration.

Detecting the z-position of moving objects in an embedded microchannel is an important but highly challenging problem in the MEMS field. The present study proposes a new depth measurement system based on the chromatic aberration effect under a dark-field illumination scheme. The microchannel is illuminated by dispersed white light and the light scattered from the moving objects is captured by a low numerical aperture (N.A.) objective lens. Due to chromatic aberration effect, sample in various positions will scatter different wavelengths. The depth of each moving object is then determined by inspecting the intensity ratio of the scattered spectral components with wavelengths of 450 nm (blue light) and 670 nm (red light), respectively. Experimental results show that the proposed system enables the object depth to be measured over a range of ±15 μm while using acrylic lens for light aberration. Alternatively, the developed system is capable to discriminate the depth change of 2 μm micro-beads when a higher Abbe number material of BK7 lens is used for light aberration. The depth measurements are obtained without the need for a delicate optical system or scanning process with the developed system. The use of UV-Vis-NIR spectrometer enables this system to analyze the depths of the samples in flow velocity 500 μm/sec. The proposed system provides a straightforward yet highly effective means of determining the depth of moving objects in microfluidic channels in a continuous manner.

Continuous Measurement of Particle Depth in a Microchannel Using Chromatic Aberration

Detecting the z-position of moving particles in an embedded microchannel is important but challenging in MEMS fields, hence this research describes a novel technique for detecting the z-position of moving objects utilizing chromatic aberration. With this simple and novel approach, the depth of moving object can be measured without delicate optical system. Results show that the developed system gives a large detection range of 30 μm with a high linearity. The resolution for this depth detection is estimated to be 0.136 μm. The developed depth detection scheme provides a simple but high performance way to dynamically identify the z-position of micro moving parts in MEMS application.

Shin-Yu Su

Papers

Electrophoresis separation and electrochemical detection on a novel line-based microfluidic device

Depth position detection for fast moving objects in sealed microchannel utilizing chromatic aberration.

Continuous Measurement of Particle Depth in a Microchannel Using Chromatic Aberration

Rapid detecting z-position of moving objects in microchannel utilizing a novel chromatic aberration effect under a dark-field illumination scheme