Active chemically-sensitive sensors with reset switch

Abstract

Methods and apparatus relating to FET arrays for monitoring chemical and/or biological reactions such as nucleic acid sequencing-by-synthesis reactions. Some methods provided herein relate to improving signal (and also signal to noise ratio) from released hydrogen ions during nucleic acid sequencing reactions.

What is claimed is: 
     
         1 . A chemical sensor, comprising:
 a chemically-sensitive field effect transistor including a floating gate conductor having an upper surface;   a material defining an opening extending to the upper surface of the floating gate conductor, the opening adapted for containing an analyte fluid having an operating pH; and   a conductive element within the opening and contacting the upper surface of the floating gate conductor, the conductive element adapted for exposure to the analyte fluid, wherein the conductive element has a point of zero charge that approximates the operating pH of the analyte fluid.   
     
     
         2 . The chemical sensor of  claim 1 , further comprising:
 a reference electrode to determine the operating pH of the analyte fluid.   
     
     
         3 . The chemical sensor of  claim 1 , wherein the operating pH of the analyte fluid is 7.6 pH units. 
     
     
         4 . The chemical sensor of  claim 1 , wherein the operating pH range of the analyte fluid is between 6 and 9.5 pH units. 
     
     
         5 . The chemical sensor of  claim 1 , wherein the conductive element includes silicon nitride, silicon oxynitride, aluminum, aluminum oxide, tantalum, tantalum oxide, tantalum pentoxide, tin or stannic, tin oxide or stannic oxide, and silicon dioxide, Zirconium, Molybdenum, Hafnium, Tungsten, or combinations and/or mixtures thereof. 
     
     
         6 . The chemical sensor of  claim 1 , wherein the conductive element comprises a layer of a mixture of at least two metals. 
     
     
         7 . The chemical sensor of  claim 1 , wherein the conductive element comprises a stacked monolayer of at least two metals. 
     
     
         8 . The chemical sensor of  claim 7 , wherein the stacked monolayer comprises a first single layer of a first metal disposed on a substrate and a second single layer of a second metal disposed on the first single later of the first metal. 
     
     
         9 . The chemical sensor of  claim 1 , wherein the conductive element comprises a combination of a layer of a mixture of at least two metals and a stacked layer of at least two metals. 
     
     
         10 . The chemical sensor of  claim 1 , wherein the conductive element comprises a mixture of electrically conductive materials. 
     
     
         11 . The chemical sensor of  claim 10 , wherein the mixture of electrically conductive materials provides a predetermined buffer capacity of the conductive element. 
     
     
         12 . The chemical sensor of  claim 11 , wherein the electrically conductive materials include silicon nitride, silicon oxynitride, aluminum, aluminum oxide, tantalum, tantalum oxide, tantalum pentoxide, tin or stannic, tin oxide or stannic oxide, and silicon dioxide, Zirconium, Molybdenum, Hafnium, Tungsten, or combinations and/or mixtures thereof. 
     
     
         13 . The chemical sensor of  claim 10 , wherein the mixture of electrically conductive materials is selected to minimize an interaction of byproducts of a chemical reaction occurring in the analyte fluid with the conductive element. 
     
     
         14 . The chemical sensor of  claim 10 , wherein the mixture of electrically conductive materials is selected based on a pH sensitivity of the conductive element and an intrinsic buffering capacity of the conductive element. 
     
     
         15 . The chemical sensor of  claim 14 , wherein a native oxide is formed on at least one of the electrically conductive materials. 
     
     
         16 . The chemical sensor of  claim 7 , wherein the at least two metals are co-sputtered. 
     
     
         17 . The chemical sensor of  claim 7 , wherein deposition of the stacked monolayer is performed by alternating the at least two metals comprising the stacked monolayer. 
     
     
         18 . The chemical sensor of  claim 7 , wherein the stacked monolayer is deposited using diffusion/doping techniques. 
     
     
         19 . The chemical sensor of  claim 9 , wherein the mixture of electrically conductive materials is based on a number of available buffering sites of the conductive element. 
     
     
         20 . The chemical sensor of  claim 1 , wherein a reaction region proximate to an interface between an upper surface of the conductive element and the analyte fluid.