A hybrid paper and microfluidic chip with electrowetting valves and colorimetric detection

Recent innovations in cost-effective polymer and paper hybrid microfluidic devices

Hybrid microfluidic systems that are composed of multiple different types of substrates have been recognized as a versatile and superior platform, which can draw benefits from different substrates while avoiding their limitations. This review article introduces the recent innovations of different types of low-cost hybrid microfluidic devices, particularly focusing on cost-effective polymer- and paper-based hybrid microfluidic devices. In this article, the fabrication of these hybrid microfluidic devices is briefly described and summarized. We then highlight various hybrid microfluidic systems, including polydimethylsiloxane (PDMS)-based, thermoplastic-based, paper/polymer hybrid systems, as well as other emerging hybrid systems (such as thread-based). The special benefits of using these hybrid systems have been summarized accordingly. A broad range of biological and biomedical applications using these hybrid microfluidic devices are discussed in detail, including nucleic acid analysis, protein analysis, cellular analysis, 3D cell culture, organ-on-a-chip, and tissue engineering. The perspective trends of hybrid microfluidic systems involving the improvement of fabrication techniques and broader applications are also discussed at the end of the review.

Phage-based biosensors: in vivo analysis of native T4 phage promoters to enhance reporter enzyme expression

Phage-based biosensors have shown significant promise in meeting the present needs of the food and agricultural industries due to a combination of sufficient portability, speed, ease of use, sensitivity, and low production cost. Although current phage-based methods do not meet the bacteria detection limit imposed by the EPA, FDA, and USDA, a better understanding of phage genetics can significantly increase their sensitivity as biosensors. In the current study, the signal sensitivity of a T4 phage-based detection system was improved via transcriptional upregulation of the reporter enzyme Nanoluc luciferase (Nluc). An efficient platform to evaluate the promoter activity of reporter T4 phages was developed. The ability to upregulate Nluc within T4 phages was evaluated using 15 native T4 promoters. Data indicates a six-fold increase in reporter enzyme signal from integration of the selected promoters. Collectively, this work demonstrates that fine tuning the expression of reporter enzymes such as Nluc through optimization of transcription can significantly reduce the limits of detection.

Advanced Wearable Microfluidic Sensors for Healthcare Monitoring

Wearable flexible sensors based on integrated microfluidic networks with multiplex analysis capability are emerging as a new paradigm to assess human health status and show great potential in application fields such as clinical medicine and athletic monitoring. Well-designed microfluidic sensors can be attached to the skin surface to acquire various pieces of physiological information with high precision, such as sweat loss, information regarding metabolites, and electrolyte balance. Herein, the recent progress of wearable microfluidic sensors for applications in healthcare monitoring is summarized, including analysis principles and microfabrication methods. Finally, the challenges and opportunities for wearable microfluidic sensors in practical applications are discussed.

Active fluidic chip produced using 3D-printing for combinatorial therapeutic screening on liver tumor spheroid

Known for their capabilities in automated fluid manipulation, microfluidic devices integrated with pneumatic valves are broadly used for researches in life science and clinical practice. The application is, however, hindered by the high cost and overly complex fabrication procedure. Here, we present an approach for fabricating molds of active fluidic devices using a benchtop 3D printer and a simple 2-step protocol (i.e. 3D printing and polishing). The entire workflow can be completed within 6 h, costing less than US$ 5 to produce all necessary templates for PDMS replica molding, which have smooth surface and round-shaped pneumatic valve structures. Moreover, 3D printing can create unique bespoke on-off objects of a wide range of dimensions. The millimeter- and centimeter-sized features allow examination of large-scale biological samples. Our results demonstrate that the 3D-printed active fluidic device has valve control capacities on par with those made by photolithography. Controlled nutrients and ligands delivery by on-off active valves allows generation of dynamic signals mimicking the ever-changing environmental stimuli, and combinatorial/sequential drug inputs for therapeutic screening on liver tumor spheroid. We believe that the proposed methodology can pave the way for integration of active fluidic systems in research labs, clinical settings and even household appliances for a broad range of application.

Dynamic control of capillary flow in porous media by electroosmotic pumping

Microfluidic paper-based analytical devices (μPADs) rely on capillary flow to achieve filling, mixing and delivery of liquids. We investigate the use of electroosmotic (EO) pumping as a mechanism for dynamic control of capillary flow in paper-based devices. The applied voltage can accelerate or decelerate the baseline capillary-driven velocity, as well as be used to create a tunable valve that reversibly switches the flow on and off in an electrically controlled manner. The method relies on simple fabrication and allows repeated actuation, providing a high degree of flexibility for automation of liquid delivery. We adapt the Lucas-Washburn model to account for EO pumping and provide an experimentally validated analytical model for the distance penetrated by the liquid as a function of time and the applied voltage. We show that the EO-pump can reduce filling time by 6.5-fold for channels spanning several cm in length, relative to capillary filling alone. We demonstrate the utilization of the EO-pump for a tunable and dynamic flow control that accelerates, decelerates and stops the flow on demand. Finally, we present the use of the EO-pump for fluid flow sequencing on a paper-based device.

Flexible Electronics Based on Micro/Nanostructured Paper

Over the past several years, a new surge of interest in paper electronics has arisen due to the numerous merits of simple micro/nanostructured substrates. Herein, the latest advances and principal issues in the design and fabrication of paper-based flexible electronics are highlighted. Following an introduction of the fascinating properties of paper matrixes, the construction of paper substrates from diverse functional materials for flexible electronics and their underlying principles are described. Then, notable progress related to the development of versatile electronic devices is discussed. Finally, future opportunities and the remaining challenges are examined. It is envisioned that more design concepts, working principles, and advanced papermaking techniques will be developed in the near future for the advanced functionalization of paper, paving the way for the mass production and commercial applications of flexible paper-based electronic devices.

Electrical Textile Valves for Paper Microfluidics

This paper describes electrically-activated fluidic valves that operate based on electrowetting through textiles. The valves are fabricated from electrically conductive, insulated, hydrophobic textiles, but the concept can be extended to other porous materials. When the valve is closed, the liquid cannot pass through the hydrophobic textile. Upon application of a potential (in the range of 100-1000 V) between the textile and the liquid, the valve opens and the liquid penetrates the textile. These valves actuate in less than 1 s, require low energy (≈27 µJ per actuation), and work with a variety of aqueous solutions, including those with low surface tension and those containing bioanalytes. They are bistable in function, and are, in a sense, the electrofluidic analog of thyristors. They can be integrated into paper microfluidic devices to make circuits that are capable of controlling liquid, including autonomous fluidic timers and fluidic logic.

Genetic optimization of a bacteriophage-delivered alkaline phosphatase reporter to detect Escherichia coli

A large fraction of foodborne illnesses are linked to (∼46%) leafy green vegetables contaminated by pathogens harbored in agricultural water. To prevent this, accurate point-of-production detection tools are required to identify and quantify bacterial contaminants in produce before consumers are impacted. In this study, a proof-of-concept model was engineered for a phage-based Escherichia coli detection system. We engineered the coliphage T7 to express alkaline phosphatase (ALP) to serve as the signal for E. coli detection. Wild type phoA (T7ALP) and a dominant-active allele, phoA D153G D330N (T7ALP*) was inserted into the T7 genome, with engineered constructs selected by CRISPR-mediated cleavage of unaltered chromosomes and confirmed by PCR. Engineered phages and E. coli target cells were co-incubated for 16 hours to produce lysates with liberated ALP correlated with input cell concentrations. A colorimetric assay used p-nitrophenyl phosphate (pNPP) to demonstrate significant ALP production by T7ALP and T7ALP* compared to the vector control (T7EV) (p≤ 0.05). Furthermore, T7ALP* produced 2.5-fold more signal than T7ALP (p≤ 0.05) at pH 10. Due to the increase in signal for the modified ALP* allele, we assessed T7ALP* sensitivity in a dose-responsive manner. We observed 3-fold higher signal for target cell populations as low as ∼2 × 10(5) CFU mL(-1) (p≤ 0.05 vs. no-phage control).

Engineering bacteriophage for a pragmatic low-resource setting bacterial diagnostic platform

Bacteriophages represent multifaceted building blocks that can be incorporated as substitutes for, or in unison with other detection methods, to create powerful new diagnostics for the detection of bacteria. The ease of phage manipulation, production, and detection speed clearly highlights that there remains unrealized opportunities to leverage these phage-based components in diagnostics amenable to resource-limited settings. The passage of regulations like the Food Safety Modernization act, and the ever increasing extent of global trade and travel, will create further demand for these types of diagnostics. While phage-based diagnostics have begun to entering the market place, further research is needed to ensure the potential benefits of phage-based technologies for public health are fully realized. We are just beginning to explore the possibilities that phage-based detection can offer us in the future. The combination of engineered phages as well as engineered enzymes could result in ultrasensitive detection systems for low-resource settings. Because the reporter enzyme is synthesized in vivo, we need to consider the options outside of normal enzyme reporters. In this case, common enzyme issues such as purification and long-term stability are less important. Phage-based diagnostics were conceptualized from out-of-the box thinking and the evolution of these systems should be as well.

Bioengineering bacteriophages to enhance the sensitivity of phage amplification-based paper fluidic detection of bacteria

Bacteriophage (phage) amplification is an attractive method for the detection of bacteria due to a narrow phage-host specificity, short amplification times, and the phages' ability to differentiate between viable and non-viable bacterial cells. The next step in phage-based bacteria detection is leveraging bioengineered phages to create low-cost, rapid, and easy-to-use detection platforms such as lateral flow assays. Our work establishes the proof-of-concept for the use of bioengineered T7 phage strains to increase the sensitivity of phage amplification-based lateral flow assays. We have demonstrated a greater than 10-fold increase in sensitivity using a phage-based protein reporter, maltose-binding protein, over the detection of replicated T7 phage viron itself, and a greater then 100-fold increase in sensitivity using a phage-based enzymatic reporter, alkaline phosphatase. This increase in sensitivity enabled us to detect 10(3)CFU/mL of Escherichia coli in broth after 7h, and by adding a filter concentration step, the ability to detect a regulatory relevant E. coli concentration of 100CFU/100mL in inoculated river water after 9h, where the current standard requires days for results. The combination of the paper fluidic format with phage-based detection provides a platform for the development of novel diagnostics that are sensitive, rapid, and easy to use.

UV-nanoimprint lithography as a tool to develop flexible microfluidic devices for electrochemical detection

Research in microfluidic biosensors has led to dramatic improvements in sensitivities. Very few examples of these devices have been commercially successful, keeping this methodology out of the hands of potential users. In this study, we developed a method to fabricate a flexible microfluidic device containing electrowetting valves and electrochemical transduction. The device was designed to be amenable to a roll-to-roll manufacturing system, allowing a low manufacturing cost. Microchannels with high fidelity were structured on a PET film using UV-NanoImprint Lithography (UV-NIL). The electrodes were inkjet-printed and photonically sintered on second flexible PET film. The film containing electrodes was bonded directly to the channel-containing layer to form sealed fluidic device. Actuation of the multivalve system with food dye in PBS buffer was performed to demonstrate automated fluid delivery. The device was then used to detect Salmonella in a liquid sample.

Droplet microfluidics for chip-based diagnostics

Droplet microfluidics (DMF) is a fluidic handling technology that enables precision control over dispensing and subsequent manipulation of droplets in the volume range of microliters to picoliters, on a micro-fabricated device. There are several different droplet actuation methods, all of which can generate external stimuli, to either actively or passively control the shape and positioning of fluidic droplets over patterned substrates. In this review article, we focus on the operation and utility of electro-actuation-based DMF devices, which utilize one or more micro-/nano-patterned substrates to facilitate electric field-based handling of chemical and/or biological samples. The underlying theory of DMF actuations, device fabrication methods and integration of optical and opto-electronic detectors is discussed in this review. Example applications of such electro-actuation-based DMF devices have also been included, illustrating the various actuation methods and their utility in conducting chip-based laboratory and clinical diagnostic assays.