A disposable bio-nano-chip using agarose beads for high performance immunoassays

Grasping and Releasing Agarose micro Beads in Water Drops

The micromanipulation of micro objects is nowadays the focus of several investigations, specially in biomedical applications. Therefore, some manipulation tasks are required to be in aqueous environment and become more challenging because they depend upon observation and actuation methods that are compatible with MEMS Technology based micromanipulators. This paper describes how three grasping-releasing based tasks have been successfully applied to agarose micro beads whose average size is about 60 μm: (i) the extraction of a single micro bead from a water drop; (ii) the insertion of a single micro bead into the drop; (iii) the grasping of a single micro bead inside the drop. The success of the performed tasks rely on the use of a microgripper previously designed, fabricated, and tested.

Low cost 3D microfluidic chips for multiplex protein detection based on photonic crystal beads

Point-of-care testing (POCT) devices used in multiplex bioassays are in great demand for clinical, environmental and biomedical applications. Photonic crystal beads (PCBs), as structural color self-coding carriers, can be integrated with microfluidic chips to realize convenient and highly sensitive biomarker detection. Here we developed a three dimensional (3D) microfluidic chip based on PCBs, which is low cost and easy to manufacture for mass production and application. The chip was fabricated with polyethylene terephthalate, polymethyl methacrylate sheets, a Ni square mesh grid and transparent double-sided tape. In practice, the target molecules could be captured by PCBs immobilized with probes in a flow-through manner. It was found that the as-proposed chip needed less washing and its background was effectively reduced in comparison with a flow-over chip. Besides, the limit of detection (LOD) of anti-human alpha fetoprotein (AFP) was calculated to be 18.92 ng mL^-1, which could meet the need of clinical detection of AFP. Furthermore, the chip demonstrated the feasibility of simultaneous detection of human immunoglobulin G, carcinoembryonic antigen and AFP, which suggests that it has a broad application prospect in multiplex bioassays.

Transport of biomolecules to binding partners displayed on the surface of microbeads arrayed in traps in a microfluidic cell

Arrays of probe molecules integrated into a microfluidic cell are utilized as analytical tools to screen the binding interactions of the displayed probes against a target molecule. These assay platforms are useful in enzyme or antibody discovery, clinical diagnostics, and biosensing, as their ultraminiaturized design allows for high sensitivity and reduced consumption of reagents and target. We study here a platform in which the probes are first grafted to microbeads which are then arrayed in the microfluidic cell by capture in a trapping course. We examine a course which consists of V-shaped, half-open enclosures, and study theoretically and experimentally target mass transfer to the surface probes. Target binding is a two step process of diffusion across streamlines which convect the target over the microbead surface, and kinetic conjugation to the surface probes. Finite element simulations are obtained to calculate the target surface concentration as a function of time. For slow convection, large diffusive gradients build around the microbead and the trap, decreasing the overall binding rate. For rapid convection, thin diffusion boundary layers develop along the microbead surface and within the trap, increasing the binding rate to the idealized limit of untrapped microbeads in a channel. Experiments are undertaken using the binding of a target, fluorescently labeled NeutrAvidin, to its binding partner biotin, on the microbead surface. With the simulations as a guide, we identify convective flow rates which minimize diffusion barriers so that the transport rate is only kinetically determined and measure the rate constant.

Polysiloxane layers created by sol-gel and photochemistry: ideal surfaces for rapid, low-cost and high-strength bonding of epoxy components to polydimethylsiloxane

In this article we introduce and compare three techniques for low-cost and rapid bonding of stereolithographically structured epoxy components to polydimethylsiloxane (PDMS). In short, we first create a polysiloxane layer on the epoxy surface via silane surface coupling and polymerization. Afterwards, the modified epoxy surface can be bonded to a PDMS component at room temperature using a handheld corona discharger, which is a commonly used low-cost technique for bonding two PDMS components. Using these methods bonds of desirable strength can be generated within half an hour. Depending on the epoxy resin, we found it necessary to modify the silanization procedure. Therefore, we provide a total of three different silanization techniques that allow bonding of a wide variety of stereolithographically structurable epoxy resins. The first technique is a UV-light induced silanization process which couples a silane that contains an epoxy-ring ((3-glycidoxypropyl)trimethoxysilane (GPTMS)). For surfaces that cannot be modified with this silane we use dimethoxydimethylsilane (DMDMS). This silane can either be coupled to the surface by a sol-gel process or UV-light induced polymerisation. The sol-gel process which is a heat induced surface modification technique results in high bond strengths. Because of the heat which triggers the sol-gel process, this technique is limited to epoxy polymers with high glass transition temperatures. For the majority of stereolithographically structured epoxy resins which typically have glass transition temperatures of around 60 °C the light-induced bonding technique is preferable. For all three techniques we performed DIN EN-conform tensile testing demonstrating maximum bond strengths of up to 350 kPa which is comparable with bond strengths reported for PDMS-to-PDMS bonds. For all bond methods, long-term stability as well as hydrolytic stability was assessed.

On the Slow Diffusion of Point-of-Care Systems in Therapeutic Drug Monitoring

Recent advancements in point-of-care (PoC) technologies show great transformative promises for personalized preventative and predictive medicine. However, fields like therapeutic drug monitoring (TDM), that first allowed for personalized treatment of patients' disease, still lag behind in the widespread application of PoC devices for monitoring of patients. Surprisingly, very few applications in commonly monitored drugs, such as anti-epileptics, are paving the way for a PoC approach to patient therapy monitoring compared to other fields like intensive care cardiac markers monitoring, glycemic controls in diabetes, or bench-top hematological parameters analysis at the local drug store. Such delay in the development of portable fast clinically effective drug monitoring devices is in our opinion due more to an inertial drag on the pervasiveness of these new devices into the clinical field than a lack of technical capability. At the same time, some very promising technologies failed in the clinical practice for inadequate understanding of the outcome parameters necessary for a relevant technological breakthrough that has superior clinical performance. We hope, by over-viewing both TDM practice and its yet unmet needs and latest advancement in micro- and nanotechnology applications to PoC clinical devices, to help bridging the two communities, the one exploiting analytical technologies and the one mastering the most advanced techniques, into translating existing and forthcoming technologies in effective devices.

Mass transfer in the biomolecular binding of a target against probe molecules on the surface of microbeads sequestered in wells in a microfluidic cell

Diagnostic tools which screen the binding interactions of a protein target against a display of biomolecular probes to identify molecules which bind the target are central to cell proteomic studies, and to diagnostic assays. Here, we study a microfluidic design for screening interactions in which the probe molecules are hosted on microbeads sequestered in wells arranged at the bottom of a microfluidic flow channel. Assays are undertaken by streaming an analyte solution with a fluorescently labelled target through the cell, and identifying the fluorescing beads. Numerical simulations are first constructed for the analyte flow over the microbeads in the well array, and the increase in the target concentration on the microbead surface. The binding profile is expressed as a function of the ratio of the convective to the diffusive transport rates (Peclet number or Pe), and the ratio of the kinetic to the diffusive rates (Damkohler number, Da). For any Pe, as Da becomes small enough, the transport is determined by the intrinsic kinetic binding rate. As Pe increases, a thin concentration boundary layer develops over the top surface of the microbead because of the convective flow, and target binds more rapidly. However, the relatively stagnant layers of liquid in the well provide a diffusion barrier which slows the target transport, and for any Da and Pe the transport is slower than equivalent patches of probes arranged on the channel wall. Experiments are also undertaken at high Pe, using the binding of fluorescently labelled NeutrAvidin as a target to probes of its binding partner, biotin, on the microbead surface. The binding profile is compared to the simulations to measure the kinetic rate constant, and this comparison shows that the transport in the cell is not kinetically limited because of the diffusion barriers created by the stagnant liquid layer in the well. Simulations and experiments on microbeads which are only partially recessed in the well demonstrate an increase in the mass transfer rate as more of the microbead surface intersects the flow and the diffusion limitation due to the stagnant layer of liquid surrounding the bottom part of the microbead is minimized.

Reagents in microfluidics: an 'in' and 'out' challenge

Microfluidic devices are excellent at downscaling chemical and biochemical reactions and thereby can make reactions faster, better and more efficient. It is therefore understandable that we are seeing these devices being developed and used for many applications and research areas. However, microfluidic devices are more complex than test tubes or microtitre plates and the integration of reagents into them is a real challenge. This review looks at state-of-the-art methods and strategies for integrating various classes of reagents inside microfluidics and similarly surveys how reagents can be released inside microfluidics. The number of methods used for integrating and releasing reagents is surprisingly large and involves reagents in dry and liquid forms, directly-integrated reagents or reagents linked to carriers, as well as active, passive and hybrid release methods. We also made a brief excursion into the field of drug release and delivery. With this review, we hope to provide a large number of examples of integrating and releasing reagents that can be used by developers and users of microfluidics for their specific needs.

A lipobead microarray assembled by particle entrapment in a microfluidic obstacle course and used for the display of cell membrane receptors

Platforms which can display cell membrane ligands and receptors as a microarray library of probes for screening against a target are essential tools in drug discovery, biomarker identification, and pathogen detection. Membrane receptors and ligands require their native bilayer environment to retain their selectivity and binding affinity, and this complicates displaying them in a microarray platform. In this study, a design is developed in which the probes are first incorporated in supported lipid bilayers formed around micron-sized particles (lipobeads), and the microbeads themselves are then arrayed on a surface by hydrodynamic capture in a microfluidic obstacle course of traps. The traps are "V" shaped open enclosures, which are arranged in a wide channel of a microfluidic device, and capture the lipobeads (slightly smaller than the channel height) as they are streamed through the course. Screening assays are undertaken directly in the device after assembly, by streaming a fluorescently labeled target through the device and detecting the bead fluorescence. Conditions are first established for which the supported bilayers on the bead surface remain intact during the capture and assay steps, using fluorescent tags in the bilayer to infer bilayer integrity. Numerical calculations of the hydrodynamic drag coefficient on the entrapped beads are presented in conjunction with the stability experiments to develop criteria for the bilayer stability as a function of the screening assay perfusion rate. Simulations of the flow streamlines are also presented to quantify the trapping efficiency of the obstacle course. Screening assays are illustrated, assaying fluorescently labeled NeutrAvidin with biotin, and labeled cholera toxin with its ganglioside binding ligand, GM1. Sequential capturing of sets of lipobeads (one at a time, and with each set bearing a different probe), followed by indexing the bead positions after each set is entrapped, allows for the construction of an indexed array of multiple probes without the need for particle encoding and is illustrated using the NeutrAvidin-biotin pair. Finally, the lipobead platform is used for quantitatively measuring the kinetic rate constants for the binding of a probe (biotin) to a target (NeutrAvidin).

A microfluidic chip for direct and rapid trapping of white blood cells from whole blood

Blood analysis plays a major role in medical and science applications and white blood cells (WBCs) are an important target of analysis. We proposed an integrated microfluidic chip for direct and rapid trapping WBCs from whole blood. The microfluidic chip consists of two basic functional units: a winding channel to mix and arrays of two-layer trapping structures to trap WBCs. Red blood cells (RBCs) were eliminated through moving the winding channel and then WBCs were trapped by the arrays of trapping structures. We fabricated the PDMS (polydimethylsiloxane) chip using soft lithography and determined the critical flow velocities of tartrazine and brilliant blue water mixing and whole blood and red blood cell lysis buffer mixing in the winding channel. They are 0.25 μl/min and 0.05 μl/min, respectively. The critical flow velocity of the whole blood and red blood cell lysis buffer is lower due to larger volume of the RBCs and higher kinematic viscosity of the whole blood. The time taken for complete lysis of whole blood was about 85 s under the flow velocity 0.05 μl/min. The RBCs were lysed completely by mixing and the WBCs were trapped by the trapping structures. The chip trapped about 2.0 × 10(3) from 3.3 × 10(3) WBCs.

A glass fiber sheet-based electroosmotic lateral flow immunoassay for point-of-care testing

We have developed a quantitative immunoassay chip targeting point-of-care testing. To implement a lateral flow immunoassay, a glass fiber sheet was chosen as the material for the microfluidic channel in which the negative charge on the fiber surfaces efficiently generates the electroosmotic flow (EOF). The EOF, in turn, allows controllable bound/free separation of antigen/antibody interactions on the chip and enables precise determination of the antigen concentration. In addition, the defined size of the porous matrix was suitable for the filtration of undesired large particles. We confirmed the linear relationship between the concentration of analyte and the resulting fluorescence intensity from the immunoassay of two model analytes, C-reactive protein (CRP) and insulin, demonstrating that analyte concentration was quantitatively determined within the developed chip in 20 min. The limits of detection were 8.5 ng mL(-1) and 17 ng mL(-1) for CRP and insulin, respectively.

Multifunctional protein particles with dual analytical channels for colorimetric enzymatic bioassays and fluorescent immunoassays

Advanced multifunctional protein particles encapsulated enzymes and antibodies were developed for enzymatic bioassays and immunoassays with colorimetric and fluorescent channels. A colorimetric channel based on color-substrate precipitation was assigned for enzymatic bioassays for the measurement of hydrogen peroxide with the lowest detectable concentration of 10 μM. A fluorescent channel based on fluorescent labeled antibodies was assigned for immunoassays for the measurement of mouse immunoglobulin G (M IgG) with the lowest detectable concentration of 1.25 μgL(-1). The protein microparticles were fabricated with a template-assisted self-assembly technique termed "Protein Activation Spontaneous Self-assemble" (PASS). The multifunctional protein particles prepared with the PASS method have the advantages of high loading of analytical biomolecules, integrated biological functions, porous structure, and more importantly, they are optically transparent and fluorescence inactive. These unique features make our protein particles a new generation of bead-based platforms to perform enzyme bioassays and immunoassays.