Apparatus and methods for sensing fluid levels

Abstract

Devices and methods are disclosed for sensing the level of a fluid in a reservoir. The device comprises a generator for generating symmetrical pulses of electric potential, a ground generator in communication with the above generator, means for sensing resistance, and a latch circuit in communication with the above means for sensing resistance. In a method of the invention, a first electric potential is applied to an electrode within the reservoir. The first electric potential has a predetermined value and duration. The resistance of fluid within the reservoir is measured during application of the first electric potential. A second electric potential is applied to the electrode after the measurement for a period of time substantially equivalent to the duration of the first electric potential and of a value substantially equivalent to and opposite to the predetermined value of the first electric potential.

1 - 11 . (canceled)  
   
   
       12 . A method for synthesizing an array of biopolymers on a surface of a substrate, said method comprising, in multiple rounds of subunit additions, adding one or more polymer subunits at each of multiple feature locations on said surface to form one or more arrays on said surface, each round of subunit additions comprising: 
 (a) bringing said substrate and a dispensing system for dispensing said polymer subunits for the synthesis of said biopolymers into a dispensing position relative to said feature locations on said surface, said dispensing system comprising a plurality of reservoirs and a droplet dispensing device comprising a plurality of droplet dispensers, each of said dispensers in fluid communication with a respective reservoir,    (b) dispensing said polymer subunits to said feature locations,    (c) repeating steps (a)-(b).    wherein the level of liquid reagent in each of said reservoirs is sensed at predetermined intervals by a method comprising: 
 (i) applying a first electric potential to an electrode within said reservoir, said first electric potential having a predetermined value and duration,  
 (ii) measuring resistance of said liquid reagent within said reservoir during application of said first electric potential, and  
 (iii) applying a second electric potential to said electrode after said measurement for a period of time substantially equivalent to the duration of said first electric potential and of a value substantially equivalent to and opposite to the predetermined value of said first electric potential.  
   
   
   
       13 . A method according to  claim 12  wherein said biopolymers are polynucleotides or polypeptides.  
   
   
       14 . A method according to  claim 13  further comprising exposing the array to a sample and reading the array.  
   
   
       15 . A method comprising forwarding data representing a result obtained from a reading of an array exposed according to the method of  claim 14 .  
   
   
       16 . A method comprising transmitting to a remote location data representing a result of an interrogation obtained by reading of an array exposed according to the method of  claim 14 .  
   
   
       17 . A method comprising receiving data representing a result of an interrogation obtained by reading of an array exposed according to the method of  claim 14 .  
   
   
       18 . A method according to  claim 13  wherein multiple arrays are synthesized on the surface of said substrate and said substrate is diced into individual sections comprising one or more arrays.  
   
   
       19 . A method according to  claim 12  further comprising after step (b) removing said substrate and/or said dispensing system from said relative dispensing position.  
   
   
       20 . A method for synthesizing an array of biopolymers on a surface of a substrate, said method comprising, in multiple rounds of subunit additions, adding one or more polymer subunits at each of multiple feature locations on said surface to form one or more arrays on said surface, each round of subunit additions comprising: 
 (a) bringing said substrate and a dispensing system for dispensing said polymer subunits for the synthesis of said biopolymers into a dispensing position relative to said activated discrete sites on said surface, said dispensing system comprising a plurality of reservoirs and a droplet dispensing device comprising a plurality of droplet dispensers, each of said dispensers in fluid communication with a respective reservoir,    (b) dispensing said polymer subunits to said discrete sites,    (c) removing said substrate and/or said dispensing system from said relative dispensing position, and    (d) repeating steps (a)-(c).    wherein the level of liquid reagent in each of said reservoirs is sensed at predetermined intervals by a method comprising applying a symmetrical pulse of electric potential to an electrode within said reservoir, said symmetrical pulse comprising first and second electric potentials of substantially equal intensity and duration but opposite value, wherein resistance of said liquid reagent within said reservoir is measured only during application of said first electric potential.    
   
   
       21 . A device for sensing the level of a fluid in a reservoir, said device comprising in communication: 
 (a) a generator for generating symmetrical pulses of electric potential,    (b) a ground generator,    (c) means for sensing resistance, and    (d) a latch circuit.    
   
   
       22 . A device according to  claim 21  wherein said means for sensing resistance comprises a probe for placing in said reservoir.  
   
   
       23 . A device according to  claim 21  wherein said means for sensing resistance comprises a resistance amplifier.  
   
   
       24 . A device according to  claim 21  wherein said generator for generating a symmetrical pulse of electric potential is a switching circuit.  
   
   
       25 . A method for sensing the level of a fluid in a reservoir, said method employing the device of  claim 21  and comprising: 
 (a) applying a first electric potential to an electrode within said reservoir, said first electric potential having a predetermined value and duration,    (b) measuring resistance of said fluid within said reservoir during application of said first electric potential, and    (c) applying a second electric potential to said electrode after said measurement for a period of time substantially equivalent to the duration of said first electric potential and of a value substantially equivalent to and opposite to the predetermined value of said first electric potential.    
   
   
       26 . An apparatus for synthesizing an array of biopolymers on the surface of a support, said apparatus comprising: 
 (a) a plurality of reservoirs for containing reagents for synthesizing said biopolymers,    (b) a droplet dispensing device comprising a plurality of droplet dispensers, each in fluid communication with a respective reservoir,    (c) a plurality of fluid level sensors, one for each of said reservoirs, wherein each of said fluid level sensors is a device according to  claim 21 , and    (d) a mechanism for moving a substrate with respect to said droplet dispensing device.    
   
   
       27 . A fluid dispensing apparatus comprising: 
 (a) a plurality of reservoirs,    (b) a droplet dispensing device comprising a plurality of droplet dispensers, each in fluid communication with a respective reservoir,    (c) a plurality of fluid level sensors, one for each of said reservoirs, wherein each of said fluid level sensors is a device according to  claim 21 .    
   
   
       28 . A fluid dispensing apparatus comprising: 
 (a) a plurality of reservoirs,    (b) a droplet dispensing device comprising a plurality of droplet dispensers, each in fluid communication with a respective reservoir,    (c) a plurality of fluid level sensors, one for each of said reservoirs, wherein each of said fluid level sensors is a device according to  claim 24 .    
   
   
       29 . A device for sensing the level of a fluid in a reservoir, said device comprising: 
 (a) a switching circuit,    (b) a ground generator in communication with said switching circuit,    (c) a resistance amplifier in communication with said switching circuit,    (d) latch circuit in communication with said resistance amplifier and    (e) a probe in communication with said resistance amplifier.    
   
   
       30 . A device according to  claim 29  wherein the probe is an electrode.  
   
   
       31 . A fluid dispensing apparatus comprising: 
 (a) a plurality of reservoirs,    (b) a droplet dispensing device comprising a plurality of droplet dispensers, each in fluid communication with a respective reservoir,    (c) a plurality of fluid level sensors, one for each of said reservoirs, wherein each of said fluid level sensors is a device according to  claim 29.