Method And Apparatus For Controlling Microfluidic Flow

Abstract

An apparatus includes a pump; a gas pressure sensor; a microfluidic chip defining a microfluidic conduit; and a gas conduit providing fluid communication between the pump, the gas sensor and the microfluidic conduit; and a controller coupled to the pump and the gas pressure sensor, whereby the controller controls the pump, thereby controlling the gas pressure at the microfluidic conduit. An apparatus includes a microfluidic chip defining a microfluidic conduit extending from a microfluidic source electrode to a microfluidic ground electrode; a first resistor coupled to the microfluidic source electrode; a first and a second voltage divider, the first divider coupling a first power ground to a side of the first resistor opposite the microfluidic chip, the second divider coupling a second power ground to the lead between the first resistor and the microfluidic source electrode, and a first voltage sensor; and a second voltage sensor. Also included are methods of operating the apparatus.

1 . An apparatus, comprising:
 a) a pump;   b) a gas pressure sensor;   c) a microfluidic chip defining a microfluidic conduit; and   d) a gas conduit providing fluid communication between the pump, the gas sensor and the microfluidic conduit; and   e) a controller coupled to the pump and the gas pressure sensor, whereby the controller controls the pump, thereby controlling the gas pressure at the microfluidic conduit.   
   
   
       2 . The apparatus of  claim 1 , wherein the pump is a peristaltic pump. 
   
   
       3 . The apparatus of  claim 2 , wherein the gas pressure sensor is located off-chip. 
   
   
       4 . The apparatus of  claim 3 , wherein the gas pressure sensor is a macroscopic gas pressure sensor. 
   
   
       5 . The apparatus of  claim 3 , further including a second pump coupled to the controller, a second gas sensor, and a second gas conduit coupled to the second gas sensor, the second pump, and the microfluidic conduit, whereby a gas pressure differential across the microfluidic conduit is determined at the controller. 
   
   
       6 . The apparatus of  claim 3 , wherein the pump, the gas conduit, and the gas sensor define a pressure channel, further including at least one additional pressure channel, wherein each channel is coupled to the controller. 
   
   
       7 . The apparatus of  claim 6 , wherein the controller independently controls the gas pressure at each intersection of the gas conduits and the microfluidic conduits. 
   
   
       8 . The apparatus of  claim 3 , further including a manifold at the gas conduit that directs gas pressure to at least one of at least two microfluidic conduits defined by at least one microfluidic chip. 
   
   
       9 . The apparatus of  claim 8 , wherein the manifold is a switchable manifold, and the controller is coupled to the manifold to switch the pump and the gas pressure sensor between at least two microfluidic conduits. 
   
   
       10 . The apparatus of  claim 9 , wherein the controller independently controls the pressure through the manifold to the microfluidic conduits. 
   
   
       11 . An apparatus, comprising:
 a) a plurality of pressure channels, each pressure channel including
 a pump; 
 a gas pressure sensor; and 
 a gas conduit providing fluid communication between the pump, the gas sensor and a microfluidic conduit defined by a microfluidic chip; and 
   b) a controller coupled to each pump and each sensor, whereby the controller independently controls gas pressure at an intersection of the gas conduit and the microfluidic channel.   
   
   
       12 . The apparatus of  claim 11 , further comprising the microfluidics chip, wherein each gas conduit is coupled to a corresponding microfluidics conduit of the microfluidics chip. 
   
   
       13 . The apparatus of  claim 12 , wherein at least one pump is a peristaltic pump. 
   
   
       14 . The apparatus of  claim 13 , wherein the gas pressure sensor is located off-chip. 
   
   
       15 . The apparatus of  claim 14 , wherein at least one gas pressure sensor is a macroscopic gas pressure sensor. 
   
   
       16 . The apparatus of  claim 15 , further including a junction in the microfluidic chip between at least three said microfluidic conduits, wherein the controller independently controls fluid flow from two of the three conduits to thereby combine fluid from the two microfluidic conduits at a junction with at least one other microfluidic conduit. 
   
   
       17 . The apparatus of  claim 15 , further including a switchable manifold coupling the pump and the gas pressure sensor to at least two said microfluidics conduits defined by at least one microfluidic chip. 
   
   
       18 . A method of controlling microfluidic flow, comprising the steps of:
 a) applying gas pressure to at least one fluid at a microfluidic conduit defined by a microfluidic chip;   b) sensing the gas pressure; and   c) controlling the gas pressure in response to the gas pressure sensed to control microfluidic flow of the fluid in the microfluidic conduit.   
   
   
       19 . The method of  claim 18 , wherein the microfluidics chip includes a plurality of microfluidic conduits, further including independently controlling the microfluidic flow in two or more microfluidic conduits defined by the microfluidic chips. 
   
   
       20 . The method of  claim 19 , wherein at least three microfluidic conduits meet in a junction, further including independently controlling fluid flow from two of the three conduits to thereby combine fluid from the two microfluidic conduits at the junction. 
   
   
       21 . The method of  claim 20 , further including employing a negative feedback loop from an intersection defined by the gas conduit and the microfluidic conduit to the controller to thereby control gas pressure at the intersection. 
   
   
       22 . The method of  claim 18 , wherein the gas pressure is applied with a peristaltic pump. 
   
   
       23 . The method of  claim 18 , wherein the gas pressure is sensed off-chip. 
   
   
       24 . The method of  claim 18 , wherein the gas pressure is sensed with a macroscopic gas sensor. 
   
   
       25 . An apparatus, comprising:
 a microfluidic chip defining a microfluidic conduit extending from a microfluidic source electrode to a microfluidic ground electrode;   a first resistor coupled by an electrical lead to the microfluidic source electrode;   a first and a second voltage divider each including a pair of resistors in series, the first divider coupling a first power ground to a side of the first resistor opposite the microfluidic chip, and the second divider coupling a second power ground to the lead between the first resistor and the microfluidic source electrode, and   a first voltage sensor coupled between the voltage dividers at a point in each voltage divider between the resistors in series; and   a second voltage sensor coupled across at least one said resistor in series in the first voltage divider.   
   
   
       26 . The apparatus of  claim 25 , further including within at least one said voltage divider a variable resistor is coupled to adjust the resistance of that voltage divider to about the resistance of the other voltage divider. 
   
   
       27 . The apparatus of  claim 26 , wherein the variable resistor is adjusted to place the resistance of the voltage dividers within about 0.02% of each other. 
   
   
       28 . The apparatus of  claim 27  further comprising a power supply coupled to the first resistor and the first voltage divider. 
   
   
       29 . The apparatus of  claim 28 , further comprising a controller coupled to the power supply and the voltage sensors, wherein the controller compares the voltages at the voltage sensors to identify a microfluidic current between the microfluidic source electrode and the microfluidic ground electrode, and controls the power supply to control the microfluidic current, thereby controlling microfluidic flow of a fluid in the microfluidic conduit via electromotive force. 
   
   
       30 . The apparatus of  claim 29 , wherein the apparatus is operated in a constant current mode. 
   
   
       31 . The apparatus of  claim 29 , wherein the apparatus is operated in a constant voltage mode. 
   
   
       32 . The apparatus of  claim 25 , wherein the first resistor, the voltage dividers, the voltage sensors, the microfluidic conduit, the microfluidic source electrode, and the microfluidic ground electrode together define an electrical channel, further including at least one additional electrical channel. 
   
   
       33 . The apparatus of  claim 32 , further including a plurality of pressure channels, each pressure channel including:
 a pump;   a gas pressure sensor; and   a gas conduit providing fluid communication between the pump, the gas sensor and the microfluidic conduit.   
   
   
       34 . The apparatus of  claim 33 , wherein for each pressure channel, the controller is coupled to the gas pressure sensor and the pump to thereby sense and control gas pressure in each pressure channel, thereby controlling microfluidic flow via pressure in each microfluidic conduit that is coupled to each said pressure channel. 
   
   
       35 . The apparatus of  claim 33 , wherein at least one microfluidic conduit is coupled to at least one said pressure channel and at least one said electrical channel, whereby the controller independently controls pressure and electrical current to thereby control microfluidic flow in the microfluidic conduit. 
   
   
       36 . A method of determining microfluidic current in a microfluidic chip, comprising the steps of:
 a) applying an electrical current to a fluid in a microfluidic conduit extending from a microfluidic source electrode to a microfluidic ground electrode in a microfluidic chip, thereby causing microfluidic fluid flow,   b) determining a value of the electrical current in the fluid between the electrodes.   
   
   
       37 . The method of  claim 36 , further including controlling the microfluidic fluid flow by controlling the value of the electrical current in the fluid between the electrodes. 
   
   
       38 . The method of  claim 37 , wherein the electrical current is controlled by:
 a) applying the electrical current from a power supply coupled through a first resistor coupled by a lead to the microfluidic source electrode; and   b) determining the value of the electrical current by measuring a first and second voltage corresponding to the value of the electrical current, wherein
 the first voltage is measured at a first voltage sensor coupled between a first and second voltage divider, each divider including a pair of resistors in series and the voltage measured at a point in each voltage divider between the resistors in series, the first divider coupling a side of the first resistor opposite the microfluidic source electrode to a first power ground, and the second divider coupling the lead between the first resistor and the microfluidic source electrode to a second power ground; and 
 the second voltage is measured at a second voltage sensor coupled across at least one said resistor in series in the second voltage divider. 
   
   
   
       39 . The method of  claim 38 , further including within at least one said voltage divider a variable resistor is coupled to adjust the resistance of that voltage divider to about the resistance of the other voltage divider. 
   
   
       40 . The method of  claim 39 , wherein the variable resistor is adjusted to place the resistance of the voltage dividers within about 0.02% of each other. 
   
   
       41 . The method of  claim 40 , wherein the first resistor, the voltage dividers, the voltage sensors, the microfluidic conduit, the microfluidic source electrode, and the microfluidic ground electrode together define an electrical channel, and the further including independently controlling at least two electrical channels. 
   
   
       42 . An apparatus, comprising:
 means to flow fluid in a microfluidic chip; and   means to control fluid flow by an analog signal corresponding to a force that causes fluid flow in the microfluidic chip.