A cyclo olefin polymer microfluidic chip with integrated gold microelectrodes for aqueous and non-aqueous electrochemistry

Microwave induced thermally assisted solvent-based bonding of biodegradable thermoplastics: an eco-friendly rapid approach for fabrication of microfluidic devices and analyte detection

There is an increasing interest in low-cost, facile and versatile thermoplastic bonding for microfluidic applications that can be easily transitioned from laboratory prototyping to industrial manufacturing. In addition, owing to the surge in the usage of thermoplastic microfluidics and its adverse effect on the environment, it is prudent to source alternative materials that are biodegradable, providing a sustainable, green approach. To address the problems, here we introduce an environment friendly, low-cost and safe welding technology used in the fabrication of microcassettes from biodegradable cellulose acetate (CA) thermoplastics. The thermally assisted solvent based bonding of the thermoplastics was accomplished in a domestic microwave oven with the aid of a polyether ether ketone (PEEK) vise. To characterize the quality of the bonding, our in-house technique was compared with a conventional thermally assisted solvent bonding configuration using a heat press machine and tested under different conditions. Our microwave induced bonding of CA presents three times reduced bonding time with higher bonding strength, good reliability and does not necessitate the use of cumbersome instrumentation. Finally, we demonstrate an electrophoresis application and vitamin C detection accomplished using this biodegradable microcassette presenting comparable results with traditional techniques, illustrating the potential of this fabrication technique in different microfluidic applications.

Electrochemical and Optical Biosensors for the Detection of Campylobacter and Listeria: An Update Look

Foodborne safety has aroused tremendous research interest in recent years because of a global public health problem. The rapid and precise detection of foodborne pathogens can reduce significantly infection diseases and save lives by the early initiation of an effective treatment. This review highlights current advances in the development of biosensors for detection of Campylobacter spp. and Listeria monocytogenes that are the most common causes of zoonosis. The consumption of pathogen contaminated food is responsible for humans hospitalization and death. The attention focused on the recognition elements such as antibodies (Ab), DNA probes and aptamers able to recognize cells, amplicons, and specific genes from different samples like bacteria, food, environment and clinical samples. Moreover, the review focused on two main signal-transducing mechanisms, i.e., electrochemical, measuring an amperometric, potentiometric and impedimetric signal; and optical, measuring a light signal by OLED (Organic Light Emitting Diode), SPR (Surface Plasmon Resonance), and Optical fiber. We expect that high-performance of devices being developed through basic research will find extensive applications in environmental monitoring, biomedical diagnostics, and food safety.

Cost-effective rapid prototyping and assembly of poly(methyl methacrylate) microfluidic devices

The difficulty in translating conventional microfluidics from laboratory prototypes to commercial products has shifted research efforts towards thermoplastic materials for their higher translational potential and amenability to industrial manufacturing. Here, we present an accessible method to fabricate and assemble polymethyl methacrylate (PMMA) microfluidic devices in a "mask-less" and cost-effective manner that can be applied to manufacture a wide range of designs due to its versatility. Laser micromachining offers high flexibility in channel dimensions and morphology by controlling the laser properties, while our two-step surface treatment based on exposure to acetone vapour and low-temperature annealing enables improvement of the surface quality without deformation of the device. Finally, we demonstrate a capillarity-driven adhesive delivery bonding method that can produce an effective seal between PMMA devices and a variety of substrates, including glass, silicon and LiNbO₃. We illustrate the potential of this technique with two microfluidic devices, an H-filter and a droplet generator. The technique proposed here offers a low entry barrier for the rapid prototyping of thermoplastic microfluidics, enabling iterative design for laboratories without access to conventional microfabrication equipment.

Ultrasensitive Single-Molecule Enzyme Detection and Analysis Using a Polymer Microarray

This report describes a novel method for isolating and detecting individual enzyme molecules using polymer arrays of picoliter microwells. A fluidic flow-cell device containing an array of microwells is fabricated in cyclic olefin polymer (COP). The use of COP microwell arrays simplifies experiments by eliminating extensive device preparation and surface functionalization that are common in other microwell array formats. Using a simple and robust loading method to introduce the reaction solution, individual enzyme molecules are trapped in picoliter microwells and subsequently isolated and sealed by fluorinated oil. The sealing is stable for hours in the COP device. The picoliter microwell device can measure enzyme concentrations in the low-femtomolar range by counting the number of active wells using a digital read-out. These picoliter microwell arrays can also easily be regenerated and reused.

3D printed metal molds for hot embossing plastic microfluidic devices

Plastics are one of the most commonly used materials for fabricating microfluidic devices. While various methods exist for fabricating plastic microdevices, hot embossing offers several unique advantages including high throughput, excellent compatibility with most thermoplastics and low start-up costs. However, hot embossing requires metal or silicon molds that are fabricated using CNC milling or microfabrication techniques which are time consuming, expensive and required skilled technicians. Here, we demonstrate for the first time the fabrication of plastic microchannels using 3D printed metal molds. Through optimization of the powder composition and processing parameters, we were able to generate stainless steel molds with superior material properties (density and surface finish) than previously reported 3D printed metal parts. Molds were used to fabricate poly(methyl methacrylate) (PMMA) replicas which exhibited good feature integrity and replication quality. Microchannels fabricated using these replicas exhibited leak-free operation and comparable flow performance as those fabricated from CNC milled molds. The speed and simplicity of this approach can greatly facilitate the development (i.e. prototyping) and manufacture of plastic microfluidic devices for research and commercial applications.

Comparison of Ultrasonic Welding and Thermal Bonding for the Integration of Thin Film Metal Electrodes in Injection Molded Polymeric Lab-on-Chip Systems for Electrochemistry

We compare ultrasonic welding (UW) and thermal bonding (TB) for the integration of embedded thin-film gold electrodes for electrochemical applications in injection molded (IM) microfluidic chips. The UW bonded chips showed a significantly superior electrochemical performance compared to the ones obtained using TB. Parameters such as metal thickness of electrodes, depth of electrode embedding, delivered power, and height of energy directors (for UW), as well as pressure and temperature (for TB), were systematically studied to evaluate the two bonding methods and requirements for optimal electrochemical performance. The presented technology is intended for easy and effective integration of polymeric Lab-on-Chip systems to encourage their use in research, commercialization and education.

Development and calibration of a microfluidic biofilm growth cell with flow-templating and multi-modal characterization

We report the development of a microfluidic flow-templating platform with multi-modal characterization for studies of biofilms and their precursor materials. A key feature is a special three inlet flow-template compartment, which confines and controls the location of biofilm growth against a template wall. Characterization compartments include Raman imaging to study the localization of the nutrient solutions, optical microscopy to quantify biofilm biomass and localization, and cyclic voltammetry for flow velocity measurements. Each compartment is tested and then utilized to make preliminary measurements.

A novel side electrode configuration integrated in fused silica microsystems for synchronous optical and electrical spectroscopy

We present a novel electrode configuration consisting of coplanar side electrode pairs integrated at the half height of the microchannels for the creation of a homogeneous electric field distribution as well as for synchronous optical and electrical measurements. For the integration of such electrodes in fused silica microsystems, a dedicated microfabrication method was utilized, whereby an intermediate bonding layer was applied to lower the temperature for fusion bonding to avoid thereby metal degradation and subsequently to preserve the electrode structures. Finally, we demonstrate the applicability of our devices with integrated electrodes for single cell electrical lysis and simultaneous fluorescence and impedance measurements for both cell counting and characterization.

Nucleic acid and protein extraction from electropermeabilized E. coli cells on a microfluidic chip

Due to the extensive use of nucleic acid and protein analysis of bacterial samples, there is a need for simple and rapid extraction protocols for both plasmid DNA and RNA molecules as well as reporter proteins like the green fluorescent protein (GFP). In this report, an electropermeability technique has been developed which is based on exposing E. coli cells to low voltages to allow extraction of nucleic acids and proteins. The flow-through electropermeability chip used consists of a microfluidic channel with integrated gold electrodes that promote cell envelope channel formation at low applied voltages. This will allow small biomolecules with diameters less than 30 A to rapidly diffuse from the permeabilized cells to the surrounding solution. By controlling the applied voltage, partial and transient to complete cell opening can be obtained. By using DC voltages below 0.5 V, cell lysis can be avoided and the transiently formed pores can be closed again and the cells survive. This method has been used to extract RNA and GFP molecules under conditions of electropermeability. Plasmid DNA could be recovered when the applied voltage was increased to 2 V, thus causing complete cell lysis.

Rapid fabrication of nickel molds for prototyping embossed plastic microfluidic devices

The production of hot embossed plastic microfluidic devices is demonstrated in 1-2 h by exploiting vinyl adhesive stickers as masks for electroplating nickel molds. The sticker masks are cut directly from a CAD design using a cutting plotter and transferred to steel wafers for nickel electroplating. The resulting nickel molds are used to hot emboss a variety of plastic substrates, including cyclo-olefin copolymer and THV fluorinated thermoplastic elastomer. Completed devices are formed by bonding a blank sheet to the embossed layer using a solvent-assisted lamination method. For example, a microfluidic valve array or automaton and a droplet generator were fabricated with less than 100 μm x-y plane feature resolution, to within 9% of the target height, and with 90 ± 11% height uniformity over 5 cm. This approach for mold fabrication, embossing, and bonding reduces fabrication time and cost for research applications by avoiding photoresists, lithography masks, and the cleanroom.

Microfluidic chips with reversed-phase monoliths for solid phase extraction and on-chip labeling

The integration of sample preparation methods into microfluidic devices provides automation necessary for achieving complete micro total analysis systems. We have developed a technique that combines on-chip sample enrichment with fluorescence labeling and purification. Polymer monoliths made from butyl methacrylate were fabricated in cyclic olefin copolymer microdevices and used for solid phase extraction. We studied the retention of fluorophores, amino acids and proteins on these columns. The retained samples were subsequently labeled with both Alexa Fluor 488 and Chromeo P503, and unreacted dye was rinsed off the column before sample elution. Additional purification was obtained from the differential retention of proteins and fluorescent labels. A linear relation between the eluted peak areas and concentrations of on-chip labeled heat shock protein 90 samples demonstrated the utility of this method for on-chip quantitation. Our fast and simple method of simultaneously concentrating and labeling samples on-chip is compatible with miniaturization and desirable for automated analysis.

Fabricating electrodes for amperometric detection in hybrid paper/polymer lab-on-a-chip devices

We present a novel, low-resource fabrication and assembly method for creating disposable amperometric detectors in hybrid paper-polymer devices. Currently, mere paper-based microfluidics is far from being able to achieve the same level of process control and integration as state-of-the-art microfluidic devices made of polymers. To overcome this limitation, in this work both substrate types are synergistically combined through a hybrid, multi-component/multi-material system assembly. Using established inkjet wax printing, we transform the paper into a profoundly hydrophobic substrate in order to create carbon electrodes which are simply patterned from carbon inks via custom made adhesive stencils. By virtue of the compressibility of the paper substrate, the resulting electrode-on-paper hybrids can be directly embedded in conventional, 3D polymeric devices by bonding through an adhesive layer. This manufacturing scheme can be easily recreated with readily available off-the-shelf equipment, and is extremely cost-efficient and rapid with turn-around times of only a few hours.

On-chip electrochemical detection of CdS quantum dots using normal and multiple recycling flow through modes

A flexible hybrid polydimethylsiloxane (PDMS)-polycarbonate (PC) microfluidic chip with integrated screen printed electrodes (SPE) was fabricated and applied for electrochemical quantum dots (QDs) detection. The developed device combines the advantages of flexible microfluidic chips, such as their low cost, the possibility to be disposable and amenable to mass production, with the advantages of electrochemistry for its facility of integration and the possibility to miniaturize the analytical device. Due to the interest in biosensing applications in general and particularly the great demand for labelling alternatives in affinity biosensors, the electrochemistry of cadmium sulfide quantum dots (CdS QDs) is evaluated. Square wave anodic stripping voltammetry (SWASV) is the technique used due to its sensitivity and low detection limits that can be achieved. The electrochemical as well as the microfluidic parameters of the developed system are optimized. The detection of CdS QDs in the range between 50 to 8000 ng mL(-1) with a sensitivity of 0.0009 μA/(ng mL(-1)) has been achieved. In addition to the single in-chip flow through measurements, the design of a recirculation system with the aim of achieving lower detection limits using reduced volumes (25 μL) of sample was proposed as a proof-of-concept.

Microfluidic chips for point-of-care immunodiagnostics

We might be at the turning point where research in microfluidics undertaken in academia and industrial research laboratories, and substantially sponsored by public grants, may provide a range of portable and networked diagnostic devices. In this Progress Report, an overview on microfluidic devices that may become the next generation of point-of-care (POC) diagnostics is provided. First, we describe gaps and opportunities in medical diagnostics and how microfluidics can address these gaps using the example of immunodiagnostics. Next, we conceptualize how different technologies are converging into working microfluidic POC diagnostics devices. Technologies are explained from the perspective of sample interaction with components of a device. Specifically, we detail materials, surface treatment, sample processing, microfluidic elements (such as valves, pumps, and mixers), receptors, and analytes in the light of various biosensing concepts. Finally, we discuss the integration of components into accurate and reliable devices.

A three-layer PMMA electrophoresis microchip with Pt microelectrodes insulated by a thin film for contactless conductivity detection

A three-layer poly (methyl methacrylate) (PMMA) electrophoresis microchip integrated with Pt microelectrodes for contactless conductivity detection is presented. A 50 μm-thick PMMA film is used as the insulating layer and placed between the channel plate (containing the microchannel) and the electrode plate (containing the microelectrode). The three-layer structure facilitates the achievement of a thin insulating layer, obviates the difficulty of integrating microelectrodes on a thin film, and does not compromise the integration of microchips. To overcome the thermal and chemical incompatibilities of polymers and photolithographic techniques, a modified lift-off process was developed to integrate Pt microelectrodes onto the PMMA substrate. A novel two-step bonding method was created to assemble the complete PMMA microchip. A low limit of detection of 1.25 μg ml(-1) for Na(+) and high separation efficiency of 77,000 and 48,000 plates/m for Na(+) and K(+) were obtained when operating the detector at a low excitation frequency of 60 kHz.

Thermoplastic microfluidic devices and their applications in protein and DNA analysis

Microfluidics is a platform technology that has been used for genomics, proteomics, chemical synthesis, environment monitoring, cellular studies, and other applications. The fabrication materials of microfluidic devices have traditionally included silicon and glass, but plastics have gained increasing attention in the past few years. We focus this review on thermoplastic microfluidic devices and their applications in protein and DNA analysis. We outline the device design and fabrication methods, followed by discussion on the strategies of surface treatment. We then concentrate on several significant advancements in applying thermoplastic microfluidic devices to protein separation, immunoassays, and DNA analysis. Comparison among numerous efforts, as well as the discussion on the challenges and innovation associated with detection, is presented.