Programmable large area digital microfluidic array with integrated droplet sensing for bioassays

Abstract

We describe a new device concept for digital microfluidics, based on an active matrix electrowetting on dielectric (AM-EWOD) device. A conventional EWOD device is limited by the number of electrical connections that can be made practically, which restricts the number and type of droplet operations. In an AM-EWOD, the patterned electrodes of a conventional EWOD device are replaced by a thin film transistor (TFT) array, as found in a liquid crystal display (LCD), facilitating independent control of each electrode. The arrays can have many thousand individually addressable electrodes, are fully reconfigurable and can be programmed to support multiple simultaneous operations. Each element is 210 μm × 210 μm in size and contains a circuit that measures the electrical impedance of the liquid above it. This is used to determine the presence and size of a droplet, a method that can improve assay reliability and accuracy. This sensor provides feedback, error detection and closed loop control of an assay sequence. We describe the design, fabrication and testing of a 64 × 64 format AM-EWOD device with impedance sensor functionality. A colorimetric assay is implemented on the device and used to measure glucose in human blood serum. Results are compared with the same assay performed on a microtitre plate.

Interpreting Assays with Control Flow on Digital Microfluidic Biochips

“…In particular, DMFBs are often I/O limited, especially for portable point-of-care devices. Our approach is compatible with direct addressing (which uses one control pin per electrode), cross referencing [Fan et al 2003], and active matrix addressing [Noh et al 2011;Hadwen et al 2012] DMFBs; the latter two devices use M + N control pins to control M×N electrodes. Our approach, however, is not compatible with pin-constrained DMFBs, which are designed to be assay-specific and allow one control pin to control multiple electrodes .…”

“…For example, we ran the largest assay, the protein assay, on a 30 × 20 DMFB that could fit six mixers and reran the interpreter; list-scheduler produced a schedule of 111s, only 2 seconds longer than the compiler's schedule length. With new, highly-scalable DMFBs being developed [Noh et al 2011;Hadwen et al 2012], increasing the array size does not increase the complexity and cost of a DMFB as it did in the past; trading DMFB size for algorithmic simplicity is becoming an easy trade-off to make.…”

Droplet Manipulations in Two Phase Flow Microfluidics

“…In addition, real-time detection of the droplet position by measuring the capacitance of a set of electrodes [52], or electronic paper displays [53] illustrate this point. Thin film transistor arrays used in liquid crystal displays have also been used for EWOD, giving control to over 4000 electrodes with impedance spectroscopy for droplet position detection [54].…”

A Novel Technique for Multiple Faults and Their Locations Detection and Start Electrode Selection in Microfluidic Digital Biochip

“…Capacitive sensing is a technique by which we can identify the presence of a droplet at a test electrode. 23,24 A droplet is dispensed from source reservoir and placed on the test electrode. Then the neighboring edges are checked by traversing the droplet to the next electrode and backtrack it as shown in Fig.…”