Control of electrolyte solution in nanofluidic channels

Abstract

Various embodiments provide an exemplary lab-on-a-chip (LOC) system that serves as an analytical tool and/or as a separation medium for an electrolyte solution including various charged molecular species. The LOC system can include an integrated nanofluidic FET device in combination with suitable analysis systems. By applying and controlling a longitudinal electric field and a transverse electric potential, the flow and the pH of the electrolyte solution in the nanofluidic channels can be controlled.

1 . A system for controlling an electrolyte solution, comprising:
 a nanofluidic channel array disposed in a substrate, wherein the nanofluidic channel array comprises a plurality of nanofluidic channels and an electrically insulating surface layer for insulating an electrolyte solution within each nanofluidic channel from the substrate;   a power supply sufficient to apply an electric potential along a length of each nanofluidic channel such that the electric potential forms a longitudinal electric field along each nanofluidic channel;   a multi-gate nanofluidic field-effect-transistor (FET) comprising a plurality of FET gates within the substrate, wherein the plurality of FET gates are spaced along a length direction of the plurality of nanofluidic channels and the multi-gate FET; and   a leakage current path between the plurality of FET gates and an exposed surface of the insulating surface layer, such that a leakage current generated by the multi-gate FET is sufficient to change at least one of a direction of an electroosmotic (EO) flow, a speed of an EO flow, and a pH value of an electrolyte solution within the nanofluidic channel array.   
     
     
         2 . The system of  claim 1 , wherein the electrically insulating surface layer comprises SiO 2  and a density of a leakage current generated by the multi-gate FET is larger in magnitude with a negative gate electric potential V G  than with a positive gate electric potential V G . 
     
     
         3 . The system of  claim 1 , wherein the multi-gate FET is sized to generate a gate potential sufficient to electrolyze water near each FET gate. 
     
     
         4 . The system of  claim 1 , further comprising an IR spectroscopy system aligned with the substrate such that the nanofluidic channel array is disposed along a direction of IR propagation from an IR source of the IR spectroscopy system. 
     
     
         5 . The system of  claim 4 , wherein the wherein IR spectroscopy system comprises multiple internal reflection Fourier transform infrared spectroscopy (MIR-FTIRS). 
     
     
         6 . The system of  claim 1 , wherein the substrate is a double-side-polished Si(100) substrate comprising an edge and the IR spectroscopy system is positioned such that an IR beam output by the IR spectroscopy system is directed onto the edge. 
     
     
         7 . The system of  claim 1 , wherein the nanofluidic channel is insulated from the substrate by an SiO 2  electrically insulating surface layer having a thickness ranging from about 50 nm to about 500 nm. 
     
     
         8 . The system of  claim 1 , wherein each FET gate comprises a doped layer having a thickness ranging from about 0.5 μm to about 5 μm. 
     
     
         9 . The system of  claim 1 , further comprising an optically transparent cover attached to a surface of the substrate which seals the nanochannel array. 
     
     
         10 . The system of  claim 9 , further comprising:
 at least one end well in fluidic communication with the nanofluidic channel array; and   at least one hole through the optically transparent cover, wherein the hole through the optically transparent cover exposes the end well.   
     
     
         11 . The system of  claim 1 , wherein the nanofluidic array comprises between about 2 and about 10 8  nanofluidic channels. 
     
     
         12 . The system of  claim 1 , wherein each nanofluidic channel has a length of between about 100 micrometers and about 10 centimeters and a width of less than about 1000 nm. 
     
     
         13 . The system of  claim 1 , wherein the plurality of FET gates are a doped layer within the substrate and at least a portion of each FET gate underlies each nanofluidic channel of the nanofluidic channel array. 
     
     
         14 . The system of  claim 1 , wherein each FET gate surrounds each nanofluidic channel. 
     
     
         15 . The system of  claim 1 , further comprising:
 at least one substrate beveled edge; and   a spectroscopy system aligned with the substrate such that a beam output by the spectroscopy system is directed onto the substrate beveled edge.   
     
     
         16 . The system of  claim 1 , further comprising:
 the leakage current generated by the multi-gate FET is sufficient to induce a first change of a pH value of an electrolyte solution within the nanofluidic channel array upon application of a gate electric potential V G ; and   the leakage current generated by the multi-gate FET is sufficient to induce a second change of a pH value of the electrolyte solution within the nanofluidic channel array upon prolonged application of the gate electric potential V G  due to water electrolysis caused by the leakage current.   
     
     
         17 . The system of  claim 1 , wherein a length direction of the plurality of FETs is generally perpendicular to the length direction of the plurality of nanofluidic channels. 
     
     
         18 . The system of  claim 1 , wherein the system is a lab-on-a-chip (LOC) system. 
     
     
         19 . A lab-on-a-chip system, comprising:
 a substrate comprising at least one beveled edge;   a nanofluidic channel array disposed in the substrate, wherein the nanofluidic channel array comprises a plurality of nanofluidic channels and each nanofluidic channel comprises an electrically insulating surface layer for electrically insulating an electrolyte solution within each nanofluidic channel from the substrate;   a power supply sufficient to apply an electric potential to a length of each nanofluidic channel such that the electric potential forms a longitudinal electric field along each nanofluidic channel;   a multi-gate nanofluidic field-effect-transistor (FET) comprising a plurality of FET gates within the substrate, wherein:
 a length direction of the plurality of FET gates is generally perpendicular to a length direction of the plurality of nanofluidic channels; 
 a leakage current path between the plurality of FET gates and an exposed surface of the insulating surface layer, such that a leakage current generated by the multi-gate FET is sufficient to flow through the leakage path to an electrolyte solution within the nanofluidic channel array; and 
   an IR spectroscopy system aligned with the substrate such that the nanofluidic channel array is disposed along a direction of IR propagation from an IR source of the IR spectroscopy system, and further aligned such that an IR beam output by the IR spectroscopy system is directed onto the beveled edge of the substrate.   
     
     
         20 . The lab-on-a-chip system of  claim 19 , wherein the multi-gate FET is sized to generate a leakage current which is sufficient to change at least one of a direction of an electroosmotic (EO) flow and a speed of an EO flow of an electrolyte solution within the nanofluidic channel array.