Magnetic beads retention device for sandwich immunoassay: comparison of off-chip and on-chip antibody incubation

We use magnetic microbeads, which are magnetically self-assembled in chains in a microfluidic chip, as reaction substrates to implement two different sandwich immunoassay protocols for the detection of mouse monoclonal target antibodies. The magnetic chains form when the chip is placed in a magnetic field, and are geometrically trapped and accurately positioned in a microchannel with periodically enlarged cross-sections. In the first immunoassay protocol, capture and target antibodies are incubated off-chip, while exposure to the detection antibody is performed on-chip. In the second protocol, the complete immunoassay is fully executed on-chip. In the ‘off-chip incubation-on-chip detection' protocol, antibodies can be detected down to a concentration of 50ng/mL in a total assay time of 120min, while consuming 1.5mL of target antibody solution. Using the full on-chip protocol, our system is able to detect target antibodies in the range of a few ng/mL in 30min, using only a few tens of nanoliters of target antibody solution and reagents. The ‘off-chip incubation-on-chip detection' protocol is also applied for dosing antibodies obtained from the supernatant of a cell culture mediu

Magnetic beads retention device for sandwich immunoassay: comparison of off-chip and on-chip antibody incubation

We use magnetic microbeads, which are magnetically self-assembled in chains in a microfluidic chip, as reaction substrates to implement two different sandwich immunoassay protocols for the detection of mouse monoclonal target antibodies. The magnetic chains form when the chip is placed in a magnetic field, and are geometrically trapped and accurately positioned in a microchannel with periodically enlarged cross-sections. In the first immunoassay protocol, capture and target antibodies are incubated off-chip, while exposure to the detection antibody is performed on-chip. In the second protocol, the complete immunoassay is fully executed on-chip. In the ‘off-chip incubation–on-chip detection’ protocol, antibodies can be detected down to a concentration of 50 ng/mL in a total assay time of 120 min, while consuming 1.5 mL of target antibody solution. Using the full on-chip protocol, our system is able to detect target antibodies in the range of a few ng/mL in 30 min, using only a few tens of nanoliters of target antibody solution and reagents. The ‘off-chip incubation–on-chip detection’ protocol is also applied for dosing antibodies obtained from the supernatant of a cell culture medium

Electromagnetically Actuated Ball Valve Micropumps

We present two types of oscillating diaphragm micropumps configured with passive ball valves and using electromagnetic actuation. One type is made out of poly(methyl methacrylate) (PMMA), while the other one is made out of borosilicate glass. Both were produced using the powder blasting microfabrication method. The pumping resonant frequency was measured to be within the range of 20 – 30 Hz for both prototypes. At the resonance, a maximum back-pressure of 280 mbar and a maximum water flow rate of about 5 mL/min were obtained. The experimental results can be well described by a simple hydrodynamic model of the system

Pumping of mammalian cells with a nozzle-diffuser micropump

We discuss the successful transport of jurkat cells and 5D10 hybridoma cells using a reciprocating micropump with nozzle-diffuser elements. The effect of the pumping action on cell viability and proliferation, as well as on the damaging of cellular membranes is quantified using four types of well-established biological tests: a trypan blue solution, the tetrazolium salt WST-1 reagent, the LDH cytotoxicity assay and the calcium imaging ATP test. The high viability levels obtained after pumping, even for the most sensitive cells (5D10), indicate that a micropump with nozzle-diffuser elements can be very appropriate for handling living cells in cell-on-a-chip applications

Magnetic Particle-Scanning for Ultrasensitive Immunodetection On-Chip

We describe the concept of magnetic particle-scanning for on-chip detection of biomolecules: a magnetic particle, carrying a low number of antigens (Ag's) (down to a single molecule), is transported by hydrodynamic forces and is subjected to successive stochastic reorientations in an engineered magnetic energy landscape. The latter consists of a pattern of substrate-bound small magnetic particles that are functionalized with antibodies (Ab's). Subsequationuent counting of the captured Ag-carrying particles provides the detection signal. The magnetic particle-scanning principle is investigated in a custom-built magneto-microfluidic chip and theoretically described by a random walk-based model, in which the trajectory of the contact point between an Ag-carrying particle and the small magnetic particle pattern is described by stochastic moves over the surface of the mobile particle, until this point coincides with the position of an Ag, resulting in the binding of the particle. This model explains the particular behavior of previously reported experimental dose-response curves obtained for two different ligand-receptor systems (biotin/streptavidin and TNF-alpha) over a wide range of concentrations. Our model shows that magnetic particle-scanning results in a very high probability of irrununocomplex formation for very low Ag concentrations, leading to an extremely low limit of detection, down to the single molecule-per-particle level. When compared to other types of magnetic particle-based surface coverage assays, our strategy was found to offer a wider dynamic range (>8 orders of magnitude), as the system does not saturate for concentrations as high as 10(11) Ag molecules in a 5 mu L drop. Furthermore, by emphasizing the importance of maximizing the encounter probability between the Ag and the Ab to improve sensitivity, our model also contributes to explaining the behavior of other particle-based heterogeneous immunoassays

Single potential electrophoresis on-chip using Pressure Pulse Injection

We propose two new injection techniques for use in electrophoresis microchips, which we call 舖Front Gate Pressure Injection舗 and 舖Back Gate Pressure Injection舗. Both techniques enable a controlled and variable size sample introduction with reduced bias compared to electrokinetic gated injection. A continuous flow of sample and buffer solution is electrokinetically driven near to the entrance of the separation channel, using a single voltage that is constant in time. A short sample plug is then injected in the separation channel by a 0.1 sec pressure pulse. The latter is generated using the mechanical deflection of a poly(dimethylsiloxane) membrane that is loosely placed on a dedicated chip reservoir. Back Gate Pressure Injection was found to significantly decrease the injection bias compared to a classical gate flow injection while keeping the separation efficiency for fluorescein / rhodamine B solutions