Autonomous Microfluidic Control by Chemically Actuated Micropumps and Its Application to Chemical Analyses

Open and closed microfluidics for biosensing

Biosensing is vital for many areas like disease diagnosis, infectious disease prevention, and point-of-care monitoring. Microfluidics has been evidenced to be a powerful tool for biosensing via integrating biological detection processes into a palm-size chip. Based on the chip structure, microfluidics has two subdivision types: open microfluidics and closed microfluidics, whose operation methods would be diverse. In this review, we summarize fundamentals, liquid control methods, and applications of open and closed microfluidics separately, point out the bottlenecks, and propose potential directions of microfluidics-based biosensing.

Passive Micropump for Highly Stable, Long-Termed, and Large Volume of Droplet Generation/Transport Inside 3D Microchannels Capable of Surfactant-Free and Droplet-Based Thermocycled Reverse Transcription-Polymerase Chain Reactions Based on a Single Thermostatic Heater

It is still one key challenge for traditional passive micropumps (e.g., surface tension micropump, hydrostatic micropump, enzymatic micropump, degassed-polydimethylsiloxane (PDMS) micropump, etc.) to transport a large volume of two-phased fluid for a long period. Herein we propose a user-friendly and passive approach to realize the microdroplet generation by waiving expensive or complex equipment. The automation principle is systemically studied in this paper. It is affirmed that this micropump can continuously transport over 2000 μL of two-phased aqueous/oil microdroplets over a 4 m long 3D microchannel for 8 h. In addition, variations in flow rate are little within each hour-period, and the evaporation bubbles can be well suppressed under high temperature (95 °C). As a proof of this concept, the novel micropump is applied to droplet-based continuous flow real-time polymerase chain reactions (PCRs), which only require several disposable syringes for oil/aqueous-phase storage, two 34 gauge needles for droplet generation, a Teflon tube for PCR amplification, and a single thermostatic heater for the thermal cycle. The results suggest this droplet generation method is acceptable for a house-made setup of microfluidic PCRs. Besides, the amplification efficiency of the droplet-based microcontinuous flow PCRs here is much higher than the plug-based microcontinuous flow PCRs in our previous work and reaches 91% of the commercial qPCR thermocycler for the target gene of Rubella virus (Rubv). Without expensive microfabrication instruments, this novel method is more accessible to nonprofessionals than previous reports and would extend the droplet-based applications to in-field and real-time analysis.

An autonomous electrochemically-actuated microvalve for controlled transport in stand-alone microfluidic systems

An autonomous stand-alone microfluidic system using an electrochemically-actuated microvalve based on a single bi-metallic Zn/Pt electrode.

Chemistry pumps: a review of chemically powered micropumps

Lab-on-a-chip devices have over recent years attracted a significant amount of attention in both the academic circle and industry, due to their promise in delivering versatile functionalities with high throughput and low sample amount. Typically, mechanical or electrokinetic micropumps are used in the majority of lab-on-a-chip devices that require powered fluid flow, but the technical challenges and the requirement of external power associated with these pumping devices hinder further development and miniaturization of lab-on-a-chip devices. Self-powered micropumps, especially those powered by chemical reactions, have been recently designed and can potentially address some of these issues. In this review article, we provide a detailed introduction to four types of chemically powered micropumps, with particular focus on their respective structures, operating mechanisms and practical usefulness as well as limitations. We then discuss the various functionalities and controllability demonstrated by these micropumps, ending with a brief discussion of how they can be improved in the future. Due to the absence of external power sources, versatile activation methods and sensitivity to environmental cues, chemically powered micropumps could find potential applications in a wide range of lab-on-a-chip devices.

Smartphone-interfaced lab-on-a-chip devices for field-deployable enzyme-linked immunosorbent assay

The emerging technologies on mobile-based diagnosis and bioanalytical detection have enabled powerful laboratory assays such as enzyme-linked immunosorbent assay (ELISA) to be conducted in field-use lab-on-a-chip devices. In this paper, we present a low-cost universal serial bus (USB)-interfaced mobile platform to perform microfluidic ELISA operations in detecting the presence and concentrations of BDE-47 (2,2',4,4'-tetrabromodiphenyl ether), an environmental contaminant found in our food supply with adverse health impact. Our point-of-care diagnostic device utilizes flexible interdigitated carbon black electrodes to convert electric current into a microfluidic pump via gas bubble expansion during electrolytic reaction. The micropump receives power from a mobile phone and transports BDE-47 analytes through the microfluidic device conducting competitive ELISA. Using variable domain of heavy chain antibodies (commonly referred to as single domain antibodies or Nanobodies), the proposed device is sensitive for a BDE-47 concentration range of 10(-3)-10(4 ) μg/l, with a comparable performance to that uses a standard competitive ELISA protocol. It is anticipated that the potential impact in mobile detection of health and environmental contaminants will prove beneficial to our community and low-resource environments.

Lab-in-a-tube: ultracompact components for on-chip capture and detection of individual micro-/nanoorganisms

A review of present and future on-chip rolled-up devices, which can be used to develop lab-in-a-tube total analysis systems, is presented. Lab-in-a-tube is the integration of numerous rolled-up components into a single device constituting a microsystem of hundreds/thousands of independent units on a chip, each individually capable of sorting, detecting and analyzing singular organisms. Such a system allows for a scale-down of biosensing systems, while at the same time increasing the data collection through a large, smart array of individual biosensors. A close look at these ultracompact components which have been developed over the past decade is given. Methods for the capture of biomaterial are laid out and progress of cell culturing in three-dimensional scaffolding is detailed. Rolled-up optical sensors based on photoluminescence, optomechanics, optofluidics and metamaterials are presented. Magnetic sensors are introduced as well as electrical components including heating, energy storage and resistor devices.

Tunable catalytic tubular micro-pumps operating at low concentrations of hydrogen peroxide

Catalytic micropumps consisting of Ti/Cr/Pt microtubes with diameters of 5-10 μm and tunable lengths in the range of 20-1000 μm are reported. Micropumps were fabricated by rolling up metallic nanomembranes into microtubes with an inner platinum layer. When immersed into a solution of hydrogen peroxide, the micropumps are activated by the catalytic decomposition of peroxide into oxygen microbubbles and water. Fluid pumping is demonstrated by the movement of polystyrene particles with a diameter of 1 μm through the catalytic microtubes. Concentrations from 0.009 to 11% H(2)O(2) were employed to study the catalytic generation of microbubbles in micropumps with different lengths. A minimum concentration of 0.06% fuel was determined to be sufficient to actuate the micropumps. Such devices based on rolled-up nanomembranes hold great promise for the integration into Lab-on-a-chip systems for sensing, sorting of particles and drug delivery.