Droplet microfluidic device and methods of sensing the results of an assay therein
A method of determining the result of an assay in a microfluidic device includes the steps of: dispensing a sample droplet onto a first portion of an electrode array of the microfluidic device; dispensing a reagent droplet onto a second portion of the electrode array of the microfluidic device; controlling actuation voltages applied to the electrode array to mix the sample droplet and the reagent droplet into a product droplet; sensing a dynamic property of the product droplet; and determining an assay of the sample droplet based on the sensed dynamic property. The dynamic property is a physical property of the product droplet that influences a transport property of the product droplet on the electrode array. Example dynamic properties of the product droplet include the moveable state, split-able state, and viscosity based on droplet properties. The method may be used to perform an amoebocyte lysate (LAL) assay.
1. A method of determining a result of an assay in an active matrix electrowetting on dielectric (AM-EWOD) microfluidic device comprising the steps of:
dispensing a sample droplet from a sample reservoir onto a first portion of an electrode array of the microfluidic device;
dispensing a reagent droplet from a reagent reservoir onto a second portion of the electrode array of the microfluidic device;
controlling actuation voltages applied to the electrode array of the microfluidic device to mix the sample droplet and the reagent droplet into a product droplet;
sensing a dynamic property of the product droplet, wherein a dynamic property is a physical property of the product droplet that influences droplet transport on the microfluidic device, and the dynamic property depends on the result of the assay being performed;
wherein sensing the dynamic property includes the steps of:
controlling actuation voltages applied to the product droplet to affect a droplet transport operation at a first position on the electrode array on the microfluidic device, and sensing the product droplet with a first sensor at the first position;
sensing the product droplet with a second sensor at a second position on the electrode array on the microfluidic device different from the first position; and
executing application software with control electronics to automatically determine the sensed dynamic property based on a result of the droplet transport operation using transport measurements sensed by the first and second sensors; and
executing application software with the control electronics to automatically determine the result of the assay of the sample droplet directly from the sensed dynamic property by equating either a positive or negative result for a target species in the sample droplet to the result of the transport operation;
wherein the transport property of the product droplet is a maximum average speed of movement of the product droplet across the electrode array portion by actuation of the electrode array portion, the actuation voltages applied to the product droplet are controlled to move the product droplet as the transport operation, and the positive or negative result of the assay is determined based upon the maximum average speed of movement of the product droplet in response to the actuation voltages.
2. The method of determining a result of an assay of claim 1 , further comprising the steps of:
dispensing a first reagent droplet on the second portion of the electrode array of the microfluidic device;
controlling actuation voltages applied to the electrode array of the microfluidic device to mix the sample droplet and the first reagent droplet into an intermediate product droplet;
dispensing a second reagent droplet onto a third portion of the electrode array of the microfluidic device; and
controlling actuation voltages applied to the electrode array of the microfluidic device to mix the intermediate product droplet and the second reagent droplet into the product droplet.
3. The method of determining a result of an assay of claim 1 , wherein determining the result of the assay of the sample droplet comprises determining whether a chemical species is present in the sample droplet.
4. The method of determining a result of an assay of claim 1 , wherein the assay comprises a nucleic acid amplification assay, and determining the result of the assay of the sample droplet comprises determining whether a target quantity of nucleic acid is present in the assay.
5. The method of determining a result of an assay of claim 1 , wherein the assay comprises a blood coagulation assay, and determining the result of the assay of the sample droplet comprises determining whether a clot has formed based on the sensed dynamic property.