Internally calibrated quantification of VEGF in human plasma by fluorescence immunoassays in disposable elastomeric microfluidic devices

A Solution to the Clearance Problem of Sacrificial Material in 3D Printing of Microfluidic Devices

3D-printing is poised to enable remarkable advances in a variety of fields, such as artificial muscles, prosthetics, biomedical diagnostics, biofuel cells, flexible electronics, and military logistics. The advantages of automated monolithic fabrication are particularly attractive for complex embedded microfluidics in a wide range of applications. However, before this promise can be fulfilled, the basic problem of removal of sacrificial material from embedded microchannels must be solved. The presented work is an experimental proof of principle of a novel technique for clearance of sacrificial material from embedded microchannels in 3D-printed microfluidics. The technique demonstrates consistent performance (~40-75% clearance) in microchannels with printed width of ~200 µm and above. The presented technique is thus an important enabling tool in achieving the promise of 3D printing in microfluidics and its wide range of applications.

Applications of microfluidics for molecular diagnostics

Diagnostic assays implemented in microfluidic devices have developed rapidly over the past decade and are expected to become commonplace in the next few years. Hundreds of microfluidics-based approaches towards clinical diagnostics and pathogen detection have been reported with a general theme of rapid and customizable assays that are potentially cost-effective. This chapter reviews microfluidics in molecular diagnostics based on application areas with a concise review of microfluidics in general. Basic principles of microfabrication are briefly reviewed and the transition to polymer fabricated devices is discussed. Most current microfluidic diagnostic devices are designed to target a single disease, such as a given cancer or a variety of pathogens, and there will likely be a large market for these focused devices; however, the future of molecular diagnostics lies in highly multiplexed microfluidic devices that can screen for potentially hundreds of diseases simultaneously.

Miniaturized technology for protein and nucleic acid point-of-care testing

The field of point-of-care (POC) testing technology is developing quickly and producing instruments that are increasingly reliable, while their size is being gradually reduced. Proteins are a common target for POC analyses and the detection of protein markers typically involves immunoassays aimed at detecting different groups of proteins such as tumor markers, inflammation proteins, and cardiac markers; but other techniques can also be used to analyze plasma proteins. In the case of nucleic acids, hybridization and amplification strategies can be used to record electromagnetic or electric signals. These techniques allow for the identification of specific viral or bacterial infections as well as specific cancers. In this review, we consider some of the latest advances in the analysis of specific nucleic acid and protein biomarkers, taking into account their trend toward miniaturization and paying special attention to the technology that can be implemented in future applications, such as lab-on-a-chip instruments.

Microfluidic blood filtration device

Rapid decentralized biomedical diagnostics have become increasingly necessary in a medical environment of growing costs and mounting demands on healthcare personnel and infrastructure. Such diagnostics require low-cost novel devices that can operate at bedside or in doctor offices using small amounts of sample that can be extracted and processed on the spot. Thus, point-of-care sample preparation is an important component of the necessary diagnostic paradigm shift. We therefore introduce a microfluidic device which produces plasma from whole blood. The device is inexpensive, reliable, easy to fabricate, and requires only 3.5 kPa pressure to operate. The device is fully compatible with microfluidic diagnostic chips. The output 23-gauge microtube of the former can be directly plugged into the input ports of the latter allowing immediate applicability in practice as a sample-prep pre-stage to a variety of emergent microfluidic diagnostic devices. In addition, the shown approach of filter encapsulation in elastomer has principle importance as it is compatible with and applicable to microfluidic sample-prep integration with analytical stages within the same elastomeric chip. This can eventually lead to finger-prick blood tests in point-of-care settings.

Integrated electrokinetic magnetic bead-based electrochemical immunoassay on microfluidic chips for reliable control of permitted levels of zearalenone in infant foods

Microfluidic technology has now become a novel sensing platform where different analytical steps, biological recognition materials and suitable transducers can be cleverly integrated yielding a new sensor generation. A novel "lab-on-a-chip" strategy integrating an electrokinetic magnetic bead-based electrochemical immunoassay on a microfluidic chip for reliable control of permitted levels of zearalenone in infant foods is proposed. The strategy implies the creative use of the simple channel layout of the double-T microchip to perform sequentially the immunointeraction and enzymatic reaction by applying a program of electric fields suitably connected to the reservoirs for driving the fluidics at different chambers in order to perform the different reactions. Both zones are used with the aid of a magnetic field to avoid in a very simple and elegant way the non-specific adsorption. Immunological reaction is performed under a competitive enzyme-linked immunosorbent assay (ELISA) where the mycotoxin ZEA and an enzyme-labelled derivative compete for the binding sites of the specific monoclonal antibody immobilised onto protein G modified magnetic beads. Horseradish peroxidase (HRP), in the presence of hydrogen peroxide, catalyses the oxidation of hydroquinone (HQ) to benzoquinone (BQN), whose back electrochemical reduction was detected at +0.1 V. Controlled-electrokinetic fluidic handling optimized conditions are addressed for all analytical steps cited above, and allows performing the complete immunoassay for the target ZEA analyte in less than 15 minutes with unique analytical merits: competitive immunoassay currents showed a very well-defined concentration dependence with a good precision as well as a suitable limit of detection of 0.4 µg L(-1), well below the legislative requirements, and an extremely low systematic error of 2% from the analysis of a maize certified reference material revealing additionally an excellent accuracy. Also, the reliability of the approach is demonstrated by the analysis of selected infant foods yielding the strictest ZEA permitted levels and excellent recoveries of 103 and 101% for solid and liquid samples, respectively.

Heterogeneous immunoassays in microfluidic format using fluorescence detection with integrated amorphous silicon photodiodes

Miniaturization of immunoassays through microfluidic technology has the potential to decrease the time and the quantity of reactants required for analysis, together with the potential of achieving multiplexing and portability. A lab-on-chip system incorporating a thin-film amorphous silicon (a-Si:H) photodiode microfabricated on a glass substrate with a thin-film amorphous silicon-carbon alloy directly deposited above the photodiode and acting as a fluorescence filter is integrated with a polydimethylsiloxane-based microfluidic network for the direct detection of antibody-antigen molecular recognition reactions using fluorescence. The model immunoassay used consists of primary antibody adsorption to the microchannel walls followed by its recognition by a secondary antibody labeled with a fluorescent quantum-dot tag. The conditions for the flow-through analysis in the microfluidic format were defined and the total assay time was 30 min. Specific molecular recognition was quantitatively detected. The measurements made with the a-Si:H photodiode are consistent with that obtained with a fluorescence microscope and both show a linear dependence on the antibody concentration in the nanomolar-micromolar range.