Handheld microcantilever-based sensor for detecting tobacco-specific nitrosamines

Abstract

A method and system for detecting tobacco-specific nitrosamines. The method includes exposing at least one microcantilever beam to a medium, which may contain tobacco-specific nitrosamines, and measuring a deflection of the microcantilever beam, wherein the deflection indicates a presence of tobacco-specific nitrosamines in the medium. The at least one microcantilever beam can include a silicon base layer and a gold-coated receptor layer with a plurality of thiol molecules having a sulfur head and carboxyl-terminated group. The at least one microcantilever beam can include a silicon base layer and a metal or metal oxide coated receptor layer. Alternatively, the microcantilever beam can be formed by co-absorbing tobacco-specific nitrosamines and silane molecules on a silicon microcantilever surface, wherein the template molecules of tobacco-specific nitrosamines physically co-adsorb between the silane molecules. The template molecules of tobacco-specific nitrosamines are then washed away with a solvent to form a silane monolayer having tobacco-specific nitrosamine cavities.

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         10 . A handheld microcantilever-based sensor system useful for identifying tobacco-specific nitrosamines comprising:
 at least one microcantilever beam having a receptor layer and a piezo-resistor, wherein exposure of the receptor layer to a medium causes a deflection of the microcantilever beam and the piezo-resistor converts the deflection into an electrical signal; and   a detection system, which reads the electrical signal.   
     
     
         11 . The system of  claim 10 , wherein:
 (a) the microcantilever beam comprises a silicon base layer and the receptor layer comprising a metal or a metal oxide coating;   (b) the receptor layer is formed by co-absorbing tobacco-specific nitrosamines and silane molecules on a surface of the microcantilever beam wherein template molecules of tobacco-specific nitrosamines physically co-adsorb between the silane molecules, and washing away the template molecules of tobacco-specific nitrosamines with a solvent to form a silane monolayer having tobacco-specific nitrosamine cavities;   (c) the system does not comprise a laser, or a photosensitive detector;   (d) the medium is in either a liquid or a gas phase;   (e) the piezo-resistor comprises a highly doped silicon layer of the microcantilever beam;   (f) the deflection changes electrical resistivity of the piezo-resistor;   (g) the deflection is caused by a physical or chemical reaction of the receptor layer and one or more molecules in the medium, and/or a volume change of the receptor layer;   (h) the at least one microcantilever beam has an overall length of 100 to 400 micrometers, a width of 20 to 70 micrometers, a thickness of 0.5 to 1.5 micrometers, and a spring constant of about 0.4 to 0.8 N/m; and/or   (i) the electrical signal indicates the presence of tobacco-specific nitrosamines in the medium and a detection range for tobacco-specific nitrosamines is from 400 to 50000 ppb in the medium.   The system of  claim 11 , wherein the metal or metal oxide coating is comprised of aluminum (Al), platinum (Pt), or palladium (Pd) and wherein the at least one microcantilever undergoes deflection due to an interaction between the metal or metal oxide coating and the medium.   
     
     
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         13 . The system of  claim 10 , further comprising:
 an array of microcantilever beams, and wherein the array of microcantilevers comprises at least one microcantilever beam having a receptor layer has a combination of a silicon base layer and a receptor layer comprising a gold coating with a plurality of thiol molecules having a sulfur head and a carboxyl-terminated group on the gold coating: and at least one microcantilever beam having a silicon base layer and a receptor layer comprising a metal or metal oxide coating;   (b) a test chamber having an inlet and an outlet to circulate the medium, at least one channel adapted to contain a test sample and a cleaning agent, a syringe pump, at least one medium source and optionally a switch attached to the inlet and adapted to direct the test sample or the cleaning agent to the test chamber; and/or   (c) a computing apparatus adapted to receive information from the detection system, store data and display data.   
     
     
         14 . A method of functionalizing a microcantilever beam having a piezo-resistor, comprising:
 coating a microcantilever beam with a receptor layer, wherein exposure of the receptor layer to a medium causes a deflection of the microcantilever beam;   wherein the piezo-resistor converts the deflection into an electrical signal.   
     
     
         15 . The method of  claim 15 , wherein:
 (a) the microcantilever beam comprises a silicon base layer and the receptor layer having a gold coating;   (b) the receptor layer is formed by depositing a plurality of thiol molecules having a sulfur head and a carboxyl-terminated group onto the gold-coated receptor layer, and forming a monolayer of thiol molecules with the carboxyl-terminated group on the gold-coated receptor layer of the microcantilever beam, wherein the microcantilever beam undergoes a chemical reaction when exposed the medium;   (c) the microcantilever beam has a silicon base layer, the receptor layer has a metal or metal oxide coating, the receptor layer comprises aluminum (Al), platinum (Pt), or palladium (Pd), and the at least one microcantilever undergoes deflection due to an interaction between the metal or metal oxide coating and the medium;   (d) the receptor layer is formed by co-absorbing tobacco-specific nitrosamines and silane molecules on a surface of the microcantilever beam wherein template molecules of tobacco-specific nitrosamines physically co-adsorb between the silane molecules, and washing away the template molecules of tobacco-specific nitrosamines with a solvent to form a silane monolayer having tobacco-specific nitrosamine cavities;   (e) one side of the microcantilever beam includes silane molecules and the other side includes a gold coating having a plurality of thiol molecules having a sulfur head group and a methyl-terminated group, which blocks absorption of the silane molecules;   (f) the medium is in either a liquid or a gas phase;   (g) the piezo-resistor comprises a highly doped silicon layer of the microcantilever beam;   (h) the deflection changes electrical resistivity of the piezo-resistor; and/or   (i) the deflection is caused by a physical or chemical reaction of the receptor layer and tobacco-specific nitrosamines in the medium, and/or a volume change of the receptor layer.   
     
     
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         17 . The method of  claim 16 , wherein the terminal group in the thiol molecule comprises —OH., —NH 2  or —COOH moieties. 
     
     
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         21 . The method of  claim 16 , wherein the thiol molecules are comprised of a hydrocarbon chain of  6  to  18  carbon atoms. 
     
     
         22 . The system of  claim 11 , wherein the metal or metal oxide coating comprises a gold coating with a plurality of thiol molecules having a sulfur head and a carboxyl-terminated group. 
     
     
         23 . The system of  claim 14 , wherein the system includes the array of microcantilever beams and:
 (a) each microcantilever beam in the array is independently addressable;   (b) each microcantilever beam in the array has a receptor layer and a piezo-resistor;   (c) the array is a one-dimensional or two-dimensional array;   (d) the array has four to sixteen microcantilever beams;   (e) the microcantilever beams in the array are separated by a space between 50 to 500 micrometers wide;   (f) the microcantilever beams in the array are on a single chip;   (g) the computing apparatus is adapted to positively identify the presence of or confirm the absence of trace amounts of tobacco-specific nitrosamines in the medium;   and/or   (h) the thiol molecules are comprised of a hydrocarbon chain of 6 to 18 carbon atoms.   
     
     
         24 . The system of  claim 14 , further comprising electronic components or devices to suppress background noise and to monitor and evaluate electronic output from each microcantilever beam in the array.