Microfluidic device, system and method

Abstract

A combination of capillary forces and gas pressure is used to control the movement of liquid samples within a microfluidic device. A liquid sample introduced to a proximal portion of a capillary channel of a microfluidic device moves by capillary action partway along the capillary channel. As the liquid sample moves, a pressure of a gas acting upon a distal gas-liquid interface of the liquid sample increases by an amount sufficient to stop further movement of the liquid sample. To initiate further movement of the liquid sample, a pump connected to a distal portion of the capillary channel decreases the pressure of the gas acting upon the distal gas-liquid interface of the liquid sample by an amount sufficient to permit the liquid sample to move by capillary action further along the capillary channel of the microfluidic device.

It is claimed: 
     
         1 . A micro fluidic system, comprising:
 (a) a capillary flow channel comprising a proximal opening and a distal opening;   (b) a dry reagent and a detection zone disposed within the capillary flow channel, the detection zone being disposed distal to the dry reagent;   (c) a pump in fluidic communication with the distal opening of the capillary flow channel;   (d) a liquid sample disposed within a proximal portion of the capillary flow channel, the liquid sample comprising a gas-liquid interface disposed within the capillary flow channel proximal to the reagent; and   (e) a gas disposed within the capillary flow channel distal to the gas-liquid interface of the liquid sample, the gas exerting a pressure on the gas-liquid interface of the liquid sample, the pressure being sufficient to prevent the liquid sample from advancing along the capillary flow channel toward the reagent.   
     
     
         2 . The micro fluidic system of  claim 1  further comprising a controller configured to operate the pump to decrease the gas pressure in the capillary flow channel by an amount sufficient to cause the liquid sample to advance along the capillary flow channel until at least the gas-liquid interface of the liquid sample contacts the reagent. 
     
     
         3 . The microfluidic system of  claim 2  wherein the controller is configured to operate the pump to decrease the gas pressure in the capillary flow channel by an amount sufficient to cause the liquid sample to advance along the capillary flow channel until all of the reagent has been contacted by at least some of the liquid sample. 
     
     
         4 . A method for determining the presence of a target in a liquid sample, the method comprising:
 (a) receiving a sample of blood obtained from a patient;   (b) introducing the at least a portion of the blood sample to a filter of a microfluidic device, a distal portion of the filter being in fluidic contact with a proximal portion of a capillary flow channel disposed within the microfluidic device, the filter configured to separate red blood cells from a liquid portion of the blood sample;   (c) allowing at least a portion of the liquid portion of the blood sample to advance toward a distal portion of the capillary flow channel until a gas pressure acting upon a distal gas-liquid interface of the liquid portion of sample stops the liquid portion from advancing further;   (d) subsequently, decreasing the gas pressure acting upon the distal gas-liquid interface to permit the liquid portion of sample to advance a further distance along the capillary flow channel; and   (e) subsequently, determining the presence of the target in the liquid portion of sample within the capillary flow channel.   
     
     
         5 . A method for determining the presence of a target in a liquid sample, the method comprising:
 (a) positioning a microfluidic device in an operable relation with a reader for the microfluidic device, the microfluidic device comprising a capillary flow channel comprising a proximal opening and a distal opening;   (b) positioning a pump in fluidic relation to the distal portion of the capillary flow channel;   (c) introducing a liquid sample to the proximal portion of the capillary flow channel, the liquid sample advancing by capillary flow along only a portion of the capillary flow channel until a gas pressure acting upon a distal gas-liquid interface of the liquid sample prevents the liquid sample from advancing further along the capillary flow channel;   (d) actuating a pump to decrease the pressure of gas acting upon the distal gas-liquid interface of the liquid sample so that the liquid sample advances a further distance along the capillary flow channel; and   (e) determining the presence of the target in the liquid sample within the capillary flow channel   
     
     
         6 . The method of  claim 5 , further comprising disconnecting the pump from fluidic relation to the distal portion of the capillary flow channel prior to determining the presence of the target in the liquid sample. 
     
     
         7 . The method of  claim 5  wherein the step of actuating the pump comprises first actuating the pump a first rate to cause the liquid sample to advance at a first rate along the capillary flow channel and then actuating the pump at a second higher rate to cause the liquid sample to advance at a second higher rate along the capillary flow channel. 
     
     
         8 . A microfluidic device, comprising:
 (a) a filter, the filter having an upper surface, a lower surface and a perimeter;   (b) a substrate having a surface, the lower surface of the filter and the surface of the substrate defining a spatially-dependent capillarity therebetween, the capillarity decreasing from a central portion of the lower surface of the filter toward the perimeter along at least two opposed directions.   
     
     
         9 . The microfluidic device of  claim 8 , wherein the surface of the substrate is convex. 
     
     
         10 . The microfluidic device of  claim 8  wherein a gap between the lower surface of the filter and the surface of the substrate increases from a central portion of the lower surface of the filter toward the perimeter along at least two opposed directions. 
     
     
         11 . A microfluidic device, comprising:
 (a) a first substrate having a first surface defining:
 (i) a recess having a first depth; 
 (ii) a groove, a proximal portion of the groove disposed adjacent to the recess, the proximal portion of the groove having a second depth less than the first depth; and 
 (iii) a filter contact surface having a third depth less than the first depth. 
   (b) a second substrate having a second surface opposed to the first surface of the first substrate;   (c) a capillary channel defined by the groove and the second surface of the second substrate, the capillary channel having a proximal opening at the proximal portion of the groove; and   (d) a filter disposed between the first surface of the first substrate and the second surface of the second substrate, wherein the filter has a first surface and a first portion of the first surface of the filter contacts the filter contact surface and a second portion of the first surface of the filter and a portion of the recess define a cavity therebetween, the cavity being in fluidic communication with the proximal opening of the capillary channel.   
     
     
         12 . The microfluidic device of  claim 11 , wherein the filter contact surface comprises a ridge extending proximally from the proximal portion of the groove. 
     
     
         13 . The microfluidic device of  claim 11 , wherein the ridge extends substantially parallel to a major axis of a proximal portion of the capillary channel. 
     
     
         14 . The microfluidic device of  claim 11 , wherein the cavity comprises a first portion offset from a first side of the ridge and a second portion offset from a second, opposite side of the ridge. 
     
     
         15 . The microfluidic device of  claim 11 , wherein a proximal edge of the filter and the proximal portion of the capillary channel define a gap therebetween.