Wireless swnt sensor integrated with microfluidic system for various liquid sensing applications

Abstract

Sensors based on single-walled carbon nanotubes (SWNT) are integrated into a microfluidic system outfitted with data processing and wireless transmission capability. The sensors combine the sensitivity, specificity, and miniature size of SWNT-based nanosensors with the flexible fluid handling power of microfluidic “lab on a chip” analytical systems. Methods of integrating the SWNT-based sensor into a microfluidic system are compatible with the delicate nature of the SWNT sensor elements. The sensor devices are capable of continuously and autonomously monitoring and analyzing liquid samples in remote locations, and are applicable to real time water quality monitoring and monitoring of fluids in living systems and environments. The sensor devices and fabrication methods of the invention constitute a platform technology, because the devices can be designed to specifically detect a large number of distinct chemical agents based on the functionalization of the SWNT. The sensors can be combined into a multiplex format that detects desired combinations of chemical agents simultaneously.

What is claimed is: 
     
         1 . A sensor device for the detection of a chemical agent in a liquid sample, the device comprising:
 an electrically insulating or semiconducting substrate;   a conductive layer deposited on a surface of the substrate, the conductive layer comprising first and second microelectrodes and having a gap between the first and second microelectrodes;   a microfluidic channel for the passage of said liquid sample, the channel enclosing said gap and fluidically connected on one side of the gap to an inlet port and on another side of the gap to an outlet port;   a nanosensor comprising one or more single-walled carbon nanotubes (SWNT) traversing said gap, one end of the SWNT forming an electrical connection with the first microelectrode and the other end of the SWNT forming an electrical connection with the second microelectrode; and   a detection circuit connected to said first and second microelectrodes and capable of detecting a change in an electrical property of the SWNT;   
       wherein a change in the electrical property of the SWNT during passage of said liquid sample across said gap indicates the presence and/or amount of said chemical agent in said liquid sample. 
     
     
         2 . The sensor device of  claim 1 , wherein the electrical property is resistance or capacitance. 
     
     
         3 . The sensor device of  claim 1 , wherein said SWNT are functionalized such that said electrical property changes specifically in the presence of said chemical agent. 
     
     
         4 . The sensor device of  claim 1 , wherein said SWNT are dielectrophoretically assembled. 
     
     
         5 . The sensor device of  claim 1 , comprising a plurality of first and second microelectrode pairs, each pair having a gap between the microelectrodes of the pair and having a nanosensor comprising one or more SWNT traversing said gap, one end of the SWNT forming an electrical connection with the first microelectrode of the pair and the other end of the SWNT forming an electrical connection with the second microelectrode of the pair, and wherein each gap is enclosed by said microfluidic channel. 
     
     
         6 . The sensor device of  claim 5  that is a multiplex sensor comprising two or more different nanosensors having sensitivity to different chemical agents. 
     
     
         7 . The sensor device of  claim 1 , wherein the chemical agent is selected from the group consisting of H + , metal ions, glucose, bacteria, viruses, and organic compounds. 
     
     
         8 . The sensor device of  claim 1 , further comprising a data processing module capable of processing an output signal from said detection circuit and outputting a signal that provides information on the presence and/or amount of said chemical agent. 
     
     
         9 . The sensor device of  claim 1 , further comprising a wireless transmitter capable of transmitting an output signal from said detection circuit to a remote receiver. 
     
     
         10 . The sensor device of  claim 8 , further comprising a wireless transmitter capable of transmitting an output signal from said data processing module to a remote receiver. 
     
     
         11 . The sensor device of  claim 1 , wherein the substrate comprises silicon, glass, or a polymer. 
     
     
         12 . The sensor device of  claim 1 , wherein the conductive layer comprises a material selected from the group consisting of Au, Ag, Al, Cr, Cu, conductive polymers, metal particle composites, metal-polymer particle composites, nanotubes, and combinations thereof. 
     
     
         13 . The sensor device of  claim 1 , wherein the microfluidic channel is formed from a material selected from the group consisting of polydimethylsiloxane, glass, silicon, polymers, and combinations thereof. 
     
     
         14 . The sensor device of  claim 1 , wherein the SWNT are selected from the group consisting of metallic SWNT, semi-conducting SWNT, insulating SWNT, functionalized SWNT, and mixtures thereof. 
     
     
         15 . The sensor device of  claim 1 , wherein the gap between the first and second microelectrodes is from about 1 μm to about 10 μm in length. 
     
     
         16 . The sensor device of  claim 1 , further comprising one or more microfluidic modules for purifying, processing, or chemically modifying the liquid sample, and the output of said one or more microfluidic modules is connected to said inlet port. 
     
     
         17 . The sensor device of  claim 1 , further comprising a fluid driving mechanism for causing fluid to flow through said microfluidic channel. 
     
     
         18 . The sensor device of  claim 1 , further comprising one or more reservoirs for reagents that are mixed with the liquid sample by one or more microfluidics modules prior to contacting said liquid sample with said nanosensor. 
     
     
         19 . The sensor device of  claim 1 , further comprising a reservoir for fluid waste, wherein said reservoir is fluidically connected with said outlet port. 
     
     
         20 . A method of fabricating a sensor device for the detection of a chemical agent in a liquid sample, the method comprising the steps of:
 (a) depositing a conductive layer onto an insulating or semiconducting substrate, whereby the conductive layer forms a pattern comprising first and second microelectrodes and having a gap between the first and second microelectrodes;   (b) forming a microfluidic channel that covers a portion of the substrate, encloses the gap, and is fluidically connected on one side of the gap to an inlet port and on another side of the gap to an outlet port;   (c) flowing an aqueous suspension of SWNT through said inlet port to fill said enclosed gap with said aqueous suspension;   (d) applying an AC voltage between the first and second microelectrodes, whereby SWNT are dielectrophoretically assembled across the gap and form an electrical connection at one end of the SWNT with the first microelectrode and at another end of the SWNT with the second microelectrode; and   (e) removing said aqueous suspension of SWNT from the microfluidic channel.   
     
     
         21 . The method of  claim 20 , wherein step (b) comprises:
 (b1) forming a microfluidic channel in polydimethylsiloxane (PDMS) using SU-8 replica molding and photolithography;   (b2) exposing the microfluidic channel and the substrate to an oxygen plasma for about 30 seconds;   (b3) bonding the microfluidic channel to the substrate at about 150° C. for about 15 minutes.   
     
     
         22 . The method of  claim 20 , wherein a plurality of first and second microelectrode pairs is formed, each pair having a gap between the microelectrodes of the pair, and the gap is enclosed by the microfluidic channel; and whereby SWNT are dielectrophoretically assembled across each gap and form an electrical connection at one end of the SWNT with the first microelectrode of each pair and at another end of the SWNT with the second microelectrode of each pair. 
     
     
         23 . The method of  claim 22 , wherein steps (c) through (e) are repeated for one or more cycles of SWNT assembly; wherein at each performance of step (d) the voltage is applied between a different pair of microelectrodes; wherein for each performance of steps (c) and (d) the SWNT are differently functionalized, whereby a multiplex sensor is fabricated. 
     
     
         24 . The method of  claim 20 , further comprising:
 (f) attaching to the substrate a detection circuit connected to said first and second microelectrodes and capable of detecting a change in an electrical property of the SWNT.   
     
     
         25 . The method of  claim 24 , further comprising:
 (g) attaching to the substrate a wireless transmitter capable of transmitting an output signal from said detection circuit to a remote receiver.   
     
     
         26 . The method of  claim 24 , further comprising:
 (g) attaching to the substrate a data processing module capable of processing an output signal from said detection circuit and outputting a signal that provides information on the presence and/or amount of said chemical agent.   
     
     
         27 . The method of  claim 26 , further comprising:
 (h) attaching to the substrate a wireless transmitter capable of transmitting an output signal from said data processing module to a remote receiver.   
     
     
         28 . A method of fabricating a sensor device for the detection of a chemical agent in a liquid sample, the method comprising the steps of:
 (a) depositing a conductive layer onto an insulating or semiconducting substrate, whereby the conductive layer forms a pattern comprising first and second microelectrodes and having a gap between the first and second microelectrodes;   (b) depositing an aqueous suspension of SWNT onto the substrate so as to cover the gap between the first and second microelectrodes with the aqueous suspension;   (c) applying an AC voltage between the first and second microelectrodes, whereby SWNT are dielectrophoretically assembled across the gap and form an electrical connection at one end of the SWNT with the first microelectrode and at another end of the SWNT with the second microelectrode;   (d) removing said aqueous suspension of SWNT from the substrate;   (e) forming a parylene shadow mask covering the assembled SWNT;   (f) plasma treating the surface of the substrate having the assembled SWNT;   (g) removing the shadow mask; and   (h) bonding a microfluidic channel to the substrate such that it encloses the gap and the assembled SWNT, and is fluidically connected on one side of the gap to an inlet port and on another side of the gap to an outlet port.   
     
     
         29 . The method of  claim 28 , wherein step (f) comprises forming a microfluidic channel in PDMS using SU-8 replica molding and photolithography and exposing the microfluidic channel and the substrate to an oxygen plasma for about 30 seconds; and wherein step (h) comprises heat bonding the microfluidic channel to the substrate at about 150° C. for about 15 minutes. 
     
     
         30 . The method of  claim 28 , wherein a plurality of first and second microelectrode pairs is formed in step (a), each pair having a gap between the microelectrodes of the pair, and wherein in step (c) SWNT are dielectrophoretically assembled across each gap and form an electrical connection at one end of the SWNT with the first microelectrode of each pair and at another end of the SWNT with the second microelectrode of each pair. 
     
     
         31 . The method of  claim 28 , wherein in step (g) the shadow mask is removed mechanically. 
     
     
         32 . The method of  claim 30 , wherein steps (b) through (d) are repeated for one or more cycles of SWNT assembly; wherein at each performance of step (c) the voltage is applied between a different pair of microelectrodes; wherein for each performance of steps (b) and (c) the SWNT are differently functionalized, whereby a multiplex sensor is fabricated. 
     
     
         33 . The method of  claim 28 , further comprising:
 (i) attaching to the substrate a detection circuit connected to said first and second microelectrodes and capable of detecting a change in an electrical property of the SWNT.   
     
     
         34 . The method of  claim 33 , further comprising:
 (j) attaching to the substrate a wireless transmitter capable of transmitting an output signal from said detection circuit to a remote receiver.   
     
     
         35 . The method of  claim 33 , further comprising:
 (j) attaching to the substrate a data processing module capable of processing an output signal from said detection circuit and outputting a signal that provides information on the presence and/or amount of said chemical agent.   
     
     
         36 . The method of  claim 35 , further comprising:
 (k) attaching to the substrate a wireless transmitter capable of transmitting an output signal from said data processing module to a remote receiver.   
     
     
         37 . A method of detecting or quantifying a chemical agent in a liquid sample, the method comprising the steps of:
 (a) providing a sensor device of  claim 1 ;   (b) flowing the liquid sample into the inlet port of the sensor device so as to fill the enclosed gap; and   (c) observing an output signal from the detection circuit of the sensor device; wherein the observed output signal indicates the presence or absence of, and/or the amount or concentration of, said chemical agent.   
     
     
         38 . The method of  claim 37 , wherein the output signal is monitored over a period of time either continuously or at selected times or time intervals. 
     
     
         39 . The method of  claim 37 , wherein the sensor device comprises a wireless transmitter, and step (c) comprises remotely receiving a signal from the transmitter. 
     
     
         40 . The method of  claim 39 , wherein the sensor device is located at a natural body of water. 
     
     
         41 . The method of  claim 39 , wherein the sensor device is located in a plumbing system or a water purification system. 
     
     
         42 . The method of  claim 39 , wherein the sensor device is implanted in a living organism or in a culture system for a cell, tissue, or organ. 
     
     
         43 . The method of  claim 37 , wherein the chemical agent is selected from the group consisting of H + , metal ions, glucose, bacteria, viruses, and organic compounds. 
     
     
         44 . The method of  claim 39 , wherein the output signal is monitored over a period of time either continuously or at selected times or time intervals. 
     
     
         45 . The method of  claim 37 , further comprising, prior to step (b):
 (a1) processing the liquid sample by filtration, purification, or adding one or more reagents to a liquid sample.   
     
     
         46 . A kit comprising the sensor device of  claim 1 , instructions for use, and optionally one or more reagents used for processing a liquid sample prior to flowing the liquid sample into said inlet port. 
     
     
         47 . A kit comprising the sensor device of  claim 14 c and one or more reagents preloaded into said one or more reservoirs.