Gold thiolate and photochemically functionalized microcantilevers using molecular recognition agents

Abstract

Highly sensitive sensor platforms for the detection of specific reagents, such as chromate, gasoline and biological species, using microcantilevers and other microelectromechanical systems (MEMS) whose surfaces have been modified with photochemically attached organic monolayers, such as self-assembled monolayers (SAM), or gold-thiol surface linkage are taught. The microcantilever sensors use photochemical hydrosilylation to modify silicon surfaces and gold-thiol chemistry to modify metallic surfaces thereby enabling individual microcantilevers in multicantilever array chips to be modified separately. Terminal vinyl substituted hydrocarbons with a variety of molecular recognition sites can be attached to the surface of silicon via the photochemical hydrosilylation process. By focusing the activating UV light sequentially on selected silicon or silicon nitride hydrogen terminated surfaces and soaking or spotting selected metallic surfaces with organic thiols, sulfides, or disulfides, the microcantilevers are functionalized. The device and photochemical method are intended to be integrated into systems for detecting specific agents including chromate groundwater contamination, gasoline, and biological species.

1 . Functionalized cantilevers comprising: 
 at least one cantilever mounted on a base, said at least one cantilever having a top surface and a bottom surface;    a coating disposed on said at least one cantilever, said coating exhibiting a binding interaction with one or more agents, said coating having been disposed by a method selected from the group consisting of gold-thiol and photochemical hydrosilylation; and    a means for detecting said binding interaction.    
     
     
         2 . Functionalized cantilevers according to  claim 1  wherein said binding interaction causes a change in surface stress in the cantilever.  
     
     
         3 . Functionalized cantilevers according to  claim 1  wherein said binding interaction is reversible using electrocycling.  
     
     
         4 . Functionalized cantilevers according to  claim 1  further comprising at least one metallic coating on said top surface selected from the group consisting of Au, Pt, Cu, Pd, Al, and Ti.  
     
     
         5 . Functionalized cantilevers according to  claim 1  wherein said coating further comprises an organic monolayer.  
     
     
         6 . Functionalized cantilevers according to  claim 5  wherein said organic monolayer is at least one monolayer selected from the group consisting of 4-mercaptopyridine, 12-mercaptododecyltriethylammonium bromide, 11-undecenyltriethylammonium bromide, thiol-based pyridines and quaternary ammonias.  
     
     
         7 . Functionalized cantilevers according to  claim 1  wherein said means for detecting further comprises at least one method selected from the group consisting of optical, piezoresistive, piezoelectric, and capacitive.  
     
     
         8 . Functionalized cantilevers according to  claim 7  wherein said means for detecting further comprises a detection threshold of approximately of 4×10 −9  M of chromate.  
     
     
         9 . Functionalized cantilevers according to  claim 1  wherein said agent is directly detected in at least one mixture selected from the group consisting of liquid, neutral aqueous solutions, acidified aqueous solutions, vapor, and gas.  
     
     
         10 . Functionalized cantilevers according to  claim 1  wherein said cantilevers are disposed in an array.  
     
     
         11 . Functionalized cantilevers according to  claim 10  wherein said coating is at least one coating selected from the group consisting of agent selective, partially agent selective, and agent non-selective.  
     
     
         12 . Functionalized cantilevers according to  claim 11  wherein said array further comprises at least one reference microcantilever.  
     
     
         13 . A method for modifying the gold surface of at least one gold-coated microcantilever comprising the steps of: 
 a. cleaning said microcantilever in a cleaning mixture,    b. immersing said microcantilever in a coating mixture thereby forming a self assembled monolayer on the gold surface,    c. rinsing said microcantilever with a rinsing mixture.    
     
     
         14 . The method of  claim 13  wherein said cleaning step further comprises the sequential steps of: 
 a. rinsing in acetone,    b. rinsing in absolute ethanol,    c. rinsing in deionized water,    d. rinsing in piranha solution,    e. rinsing in ultrapure deionized water, and    f. rinsing and soaking in absolute ethanol.    
     
     
         15 . The method of  claim 14  wherein said piranha solution further comprises a mixture of approximately 7 parts H 2 SO 4  (98%) and approximately 3 parts H 2 O 2  (31%).  
     
     
         16 . The method of  claim 13  wherein said coating mixture further comprises at least one agent selected from the group consisting of alkylthiol, arylthiol, and dialkanesulfides.  
     
     
         17 . The method of  claim 16  wherein said agent further comprises at least one agent selected from the group consisting of quaternary ammonias, crown ethers, azacrown compounds, borate esters, ureas, antibody-antigens, organic acids, organic esters, organic amides, organic amines, organic aldehydes, phosphonic acids, phosphonic esters, buckyballs, and hydroxyls.  
     
     
         18 . The method of  claim 13  wherein said coating mixture further comprises an aqueous solution of approximately 5×10 −3  M of 4-MPy (95%) in approximately 0.1 N H 2 SO 4 .  
     
     
         19 . The method of  claim 13  wherein said coating mixture further comprises an aqueous solution of approximately 5×10 −3  M of 4-MPy (95%) in absolute ethanol.  
     
     
         20 . A method for modifying the silicon surface of at least one microcantilever comprising the steps of: 
 a. cleaning said at least one microcantilever silicon surface,    b. hydrogen terminating said at least one microcantilever silicon surface,    c. carbon linking a molecular recognition agent to a selected hydrogen terminated silicon surface using photochemical hydrosilylation, and    d. repeating steps a. thru c. for selected molecular recognition agents.    
     
     
         21 . The method of  claim 20  wherein said cleaning step further comprises the sequential steps of: 
 a. rinsing in acetone,    b. rinsing in absolute ethanol,    c. rinsing in deionized water,    d. rinsing in piranha solution,    e. rinsing in ultrapure deionized water, and    f. rinsing in absolute ethanol.    
     
     
         22 . The method of  claim 20  wherein said hydrogen terminating step further comprises: 
 a. immersing said silicon surface in approximately 40% NH 4 F argon-purged solution, and    b. drying said silicon surface in argon.    
     
     
         23 . The method of  claim 20  wherein said carbon linking step further comprises: 
 a. disposing said hydrogen termination silicon surface in a molecular recognition agent solution,    b. irradiating at least one microcantilever with ultraviolet light, and    c. rinsing said surface.    
     
     
         24 . The method of  claim 23  wherein said molecular recognition agent further comprises at least one agent selected from the group consisting of alkylthiol, arylthiol, and dialkanesulfides.  
     
     
         25 . The method of  claim 24  wherein said molecular recognition agent further comprises at least one agent selected from the group consisting of quaternary ammonias, crown ethers, azacrown compounds, borate esters, ureas, biomolecule-selective antibody-antigens, DNA, proteins, organic acids, organic esters, organic amides, organic amines, organic aldehydes, phosphonic acids, phosphonic esters, buckyballs, and hydroxyls.  
     
     
         26 . The method of  claim 25  wherein said quaternary ammonias further comprise 11-undecenyltriethylammonium bromide.  
     
     
         27 . The method of  claim 23  wherein said ultraviolet light is emitted from a mercury lamp.  
     
     
         28 . Functionalized MEMS comprising: 
 at least one MEM having a top surface and a bottom surface;    a coating disposed on said at least one MEM, said coating exhibiting a binding interaction with one or more agents, said coating having been disposed by a method selected from the group consisting of gold-thiol and photochemical hydrosilylation; and    a means for detecting said binding interaction.    
     
     
         29 . Functionalized MEMS according to  claim 28  wherein said binding interaction causes a change in surface stress in the MEM.  
     
     
         30 . Functionalized MEMS according to  claim 28  wherein said binding interaction is reversible using electrocycling.  
     
     
         31 . Functionalized MEMS according to  claim 28  further comprising at least one metallic coating on said top surface selected from the group consisting of Au, Pt, Cu, Pd, Al and Ti.  
     
     
         32 . Functionalized MEMS according to  claim 28  wherein said coating further comprises an organic monolayer.  
     
     
         33 . Functionalized MEMS according to  claim 32  wherein said organic monolayer is at least one monolayer selected from the group consisting of 4-mercaptopyridine, 12-mercaptododecyltriethylammonium bromide, 11-undecenyltriethylammonium bromide, thiol-based pyridines and quaternary ammonias.  
     
     
         34 . Functionalized MEMS according to  claim 28  wherein said means for detecting further comprises at least one method selected from the group consisting of optical, piezoresistive, piezoelectric, and capacitive.  
     
     
         35 . Functionalized MEMS according to  claim 34  wherein said means for detecting further comprises a detection threshold of approximately of 4×10 −9  M of chromate.  
     
     
         36 . Functionalized MEMS according to  claim 28  wherein said agent is directly detected in at least one mixture selected from the group consisting of liquid, neutral aqueous solutions, acidified aqueous solutions, vapor, and gas.  
     
     
         37 . Functionalized MEMS according to  claim 28  wherein said MEMS are disposed in an array.  
     
     
         38 . Functionalized MEMS according to  claim 37  wherein said coating is at least one coating selected from the group consisting of agent selective, partially agent selective, and agent non-selective.  
     
     
         39 . Functionalized MEMS according to  claim 38  wherein said array further comprises at least one reference MEM.