Towards an electrowetting-based digital microfluidic platform for magnetic immunoassays

Abstract

We demonstrate ElectroWetting-On-Dielectric (EWOD) transport and SQUID gradiometer detection of magnetic nanoparticles (MNPs) suspended in a 2 microl de-ionized water droplet. This proof-of-concept methodology constitutes the first development step towards a highly sensitive magnetic immunoassay platform with SQUID readout and droplet-based sample handling. Magnetic AC-susceptibility measurements were performed on MNPs with a hydrodynamic diameter of 100 nm using a high-Tc dc Superconducting Quantum Interference Device (SQUID) gradiometer as detector. We observed that the signal amplitude per unit volume is 2.5 times higher for a 2 microl sample droplet compared to a 30 microl sample volume.

Position and feedback for digital microfluidic system based on light intensity information

“…One of the important investigations using capacitive detection of droplets in EWOD devices was which proved that capacitance measurements could detect droplets. 12,13 Multiple droplets can be successfully located, and droplets of uniform size are generated by using this method. 14,15 The main problem with this method is that it takes a lot of time to collect the capacitance values of all electrodes and analyze them, especially in complex EWOD devices.…”

Magnetic Nanoparticles and microNMR for Diagnostic Applications

“…To detect biomarkers using MNPs, various detection technologies have been developed 12. These include techniques that use magnetometers, such as superconducting quantum interference device (SQUID) 13-15, magnetoresistive sensors 16-19, and Hall sensors 20, which directly measure the magnetic fields from magnetically-labeled biological targets.…”

Low-voltage electrowetting on a lipid bilayer formed on hafnium oxide

“…Electrowetting, or the electrical manipulation of liquid contact angles on solid surfaces, finds use in a variety of microfluidic applications, including liquid displays ll-3], liquid lenses [4][5][6], and miniaturized bioassays [7][8]. The development of reliable, low-voltage electrowetting systems is essential for realizing portable electrowetting devices.…”

“…Applied voltage in the form of an AC sine wave from V to-Vat 300Hz was incremented from 0 V to a maximum voltage (forward sweep), resulting in wetting, and then decremented back to 0 V (reverse sweep), resulting in dewetting. The water drop contact angle(8), the capacitance between the grounded substrate and the water drop (C), and the diameter of the contact area between the water drop and the hafnium oxide were recorded for each applied voltage. The system was allowed approximately Go-90 seconds to equilibrate at each applied voltage before measurements were recorded.…”