Design of an ic-processed polymer nano-liquid chromatography system on-a-chip and method of making it

Abstract

Embodiments in accordance with the present invention relate to packed-column nano-liquid chromatography (nano-LC) systems integrated on-chip, and methods for producing and using same. The microfabricated chip includes a column, frits/filters, an injector, and a detector, fabricated in a process compatible with those conventionally utilized to form integrated circuits. The column can be packed with supports for various different stationary phases to allow performance of different forms of nano-LC, including but not limited to reversed-phase, normal-phase, adsorption, size-exclusion, affinity, and ion chromatography. A cross-channel injector injects a nanolitre/picolitre-volume sample plug at the column inlet. An electrochemical/conductivity sensor integrated at the column outlet measures separation signals. A self-aligned channel-strengthening technique increases pressure rating of the microfluidic system, allowing it to withstand the high pressure normally used in high performance liquid chromatography (HPLC). On-chip sample injection, separation, and detection of mixture of anions in water is successfully demonstrated using ion-exchange nano-LC.

1 . A method of fabricating a nano-liquid chromatography system on-a-chip, the method comprising:
 patterning a sacrificial material on a first side of a substrate to define a column region;   forming an encapsulant over the first side of the substrate and the sacrificial material;   removing the sacrificial material to define a column; and   providing access to an inlet of the column region and an outlet of the column region.   
   
   
       2 . The method of  claim 1  wherein providing access to the column inlet and the column outlet comprises etching through a backside of the substrate to stop on the sacrificial material. 
   
   
       3 . The method of  claim 1  wherein providing access to the column inlet and the column outlet comprises forming a hole through the encapsulant present in a front side of the substrate. 
   
   
       4 . The method of  claim 1  wherein:
 patterning the sacrificial material comprises developing a resist material utilizing lithography; and   removing the sacrificial material comprises stripping the developed resist material.   
   
   
       5 . The method of  claim 4  wherein patterning the sacrificial material further comprises partially developing the resist material to define a constriction at the column outlet. 
   
   
       6 . The method of  claim 4  wherein the constriction comprises an opening narrower than a column packing material. 
   
   
       7 . The method of  claim 4  wherein patterning the sacrificial material further comprises patterning a post to define a constriction at the column outlet. 
   
   
       8 . The method of  claim 4  further comprising reflowing the developed photoresist to form a rounded cross-sectional profile. 
   
   
       9 . The method of  claim 1  wherein forming the encapsulant comprises depositing Parylene. 
   
   
       10 . The method of  claim 9  wherein prior to deposition of the Parylene, a moat is etched into the substrate adjacent to the channel to receive and anchor the deposited Parylene. 
   
   
       11 . The method of  claim 10  wherein the moat etching is self-aligned to the sacrificial material. 
   
   
       12 . The method of  claim 9  wherein prior to deposition of the Parylene, regions adjacent to the channel are roughened by chemical exposure to enhance adhesion with the deposited Parylene. 
   
   
       13 . The method of  claim 12  wherein the roughening is self-aligned to the sacrificial material. 
   
   
       14 . The method of  claim 1  further comprising forming a passivating layer over the encapsulant. 
   
   
       15 . The method of  claim 14  wherein the passivating layer is formed subsequent to removal of the sacrificial material. 
   
   
       16 . The method of  claim 14  wherein the passivating layer is formed prior to removal of the sacrificial material. 
   
   
       17 . The method of  claim 1  further comprising patterning a conducting electrode on the substrate proximate to an expected outlet of the column, prior to patterning the sacrificial material. 
   
   
       18 . The method of  claim 1  wherein the sacrificial material is also patterned to form a sample injector region intersecting the column region, the method further comprising providing access to an inlet of the injector region and to an outlet of the injector region. 
   
   
       19 . The method of  claim 1  wherein a temperature during fabrication does not exceed 200° C. 
   
   
       20 . The method of  claim 1  further comprising introducing a packing material into the column. 
   
   
       21 . A nano-liquid chromatography apparatus on-a-chip comprising:
 a column defined between a substrate and a deposited Parylene layer;   a column inlet in fluid communication with a first end of the column; and   a column outlet in fluid communication with a second end of the column opposite the first end.   
   
   
       22 . The nano-liquid chromatography apparatus of  claim 21  wherein the column is serpentine in shape. 
   
   
       23 . The nano-liquid chromatography apparatus of  claim 21  wherein the deposited Parylene layer remains adhered to the substrate at pressures of 1000 psi or greater within the column. 
   
   
       24 . The nano-liquid chromatography apparatus of  claim 21  wherein the substrate includes a roughened region adjacent to the column and configured to promote adhesion between the deposited Parylene layer and the substrate. 
   
   
       25 . The nano-liquid chromatography apparatus of  claim 24  wherein the roughened region is self-aligned to the column. 
   
   
       26 . The nano-liquid chromatography apparatus of  claim 21  wherein the substrate defines a moat adjacent to the column and configured to receive the deposited Parylene layer and promote adhesion between the deposited Parylene layer and the substrate. 
   
   
       27 . The nano-liquid chromatography apparatus of  claim 21  wherein the moat is self-aligned to the column. 
   
   
       28 . The nano-liquid chromatography apparatus of  claim 21  further comprising a column outlet having a constriction narrower than a column packing material. 
   
   
       29 . The nano-liquid chromatography apparatus of  claim 21  further comprising a column outlet having a constriction configured to cause the outlet to be jammed with packing material during column loading. 
   
   
       30 . The nano-liquid chromatography apparatus of  claim 21  further comprising an injector intersecting the column inlet. 
   
   
       31 . The nano-liquid chromatography apparatus of  claim 21  further comprising a detector positioned downstream the column outlet. 
   
   
       32 . The nano-liquid chromatography apparatus of  claim 31  wherein the detector is positioned immediately adjacent to the column outlet to minimize an intervening dead volume. 
   
   
       33 . The nano-liquid chromatography apparatus of  claim 31  wherein the detector comprises an electrode patterned on the substrate. 
   
   
       34 . The nano-liquid chromatography apparatus of  claim 31  further comprising:
 a second detector positioned upstream of the column inlet; and   a comparator in communication with the detector and the second detector, the comparator configured to output a signal reflecting a difference between the detector and the second detector.   
   
   
       35 . The nano-liquid chromatography apparatus of  claim 21  wherein the column exhibits a rounded cross-sectional profile. 
   
   
       36 . The nano-liquid chromatography apparatus of  claim 21  further comprising a second column defined between the substrate and the deposited Paraylene layer, an inlet of the second column in fluid communication with the first column outlet, the first and second column configured to perform multi-dimensional separation of components of a sample. 
   
   
       37 . The nano-liquid chromatography apparatus of  claim 21  further comprising a second column defined between the substrate and the deposited Paraylene layer, the first column inlet and an inlet of the second column in fluid communication with a common inlet, the first and second column configured to simultaneously perform multiple separation of components of a sample introduced to the common inlet. 
   
   
       38 . The nano-liquid chromatography apparatus of  claim 21  further comprising a packaging jig including:
 a first surface defining an outlet port, the first surface configured to receive the substrate and place the outlet port in fluid communication with the column inlet;   a second surface defining an inlet port configured to receive a liquid from an external source; and   a body including a conduit configured to place the inlet port in fluid communication with the outlet port.   
   
   
       39 . The nano-liquid chromatography apparatus of  claim 38  further comprising a sealing element positioned between the first surface and the substrate. 
   
   
       40 . The nano-liquid chromatography apparatus of  claim 39  wherein the sealing element comprises an o-ring. 
   
   
       41 . The nano-liquid chromatography apparatus of  claim 39  wherein the sealing element comprises a polymer gasket layer. 
   
   
       42 . The nano-liquid chromatography apparatus of  claim 38  wherein positioning the substrate on the first surface at a different orientation relative to the packaging jig places the outlet port in fluid communication with a different chip inlet. 
   
   
       43 . The nano-liquid chromatography apparatus of  claim 38  further comprising a printed circuit board in contact with a side of the substrate opposite the packaging jig, a conducting contact on the printed circuit board in electrical communication with a detector. 
   
   
       44 . The nano-liquid chromatography apparatus of  claim 21  further comprising a column access hole formed through the Parylene on a chip front side and in fluid communication with the column inlet. 
   
   
       45 . The nano-liquid chromatography apparatus of  claim 21  further comprising a column access hole formed through the substrate on a chip back side and in fluid communication with the column inlet. 
   
   
       46 . A method of performing nano-liquid chromatography comprising:
 providing at an inlet of a column defined between a deposited layer adhered to a substrate, a sample including a plurality of components;   flowing a mobile phase down the column to separate the plurality of sample components; and   detecting a changed property at a column outlet to reveal elution of one of the plurality of sample components.   
   
   
       47 . The nano-liquid chromatography method of  claim 46  wherein the sample is provided to a column outlet defined between a deposited Parylene layer adhered to the substrate. 
   
   
       48 . The nano-liquid chromatography method of  claim 46  wherein the sample is provided to the inlet by cross-flow injection. 
   
   
       49 . The nano-liquid chromatography method of  claim 46  wherein the mobile phase is flowed down the column at a pressure of 1000 psi or greater. 
   
   
       50 . The nano-liquid chromatography method of  claim 46  wherein the mobile phase is flowed down the column at a pressure of less than 1000 psi. 
   
   
       51 . The nano-liquid chromatography method of  claim 46  wherein a changed conductance is detected at an electrode present on the substrate at the column outlet. 
   
   
       52 . The nano-liquid chromatography method of  claim 46  further comprising comparing a sensed property of the mobile phase at the column inlet with a sensed property of the component at the column outlet. 
   
   
       53 . The nano-liquid chromatography method of  claim 46  further comprising placing the column inlet in fluid communication with an external source via an inlet port located on a first surface of a packaging jig, the inlet port in fluid communication with the column inlet through an internal jig conduit and an outlet port on a second surface of the packaging jig. 
   
   
       54 . The nano-liquid chromatography method of  claim 53  further comprising sealing the column inlet to the outlet port with an o-ring. 
   
   
       55 . The nano-liquid chromatography method of  claim 53  further comprising sealing the column inlet to the outlet port with a polymer gasket layer. 
   
   
       56 . The nano-liquid chromatography method of  claim 53  further comprising establishing electronic communication with a detector on the substrate through a printed circuit board in contact with a side of the substrate opposite the packaging jig. 
   
   
       57 . The nano-liquid chromatography method of  claim 53  further comprising placing the outlet port into fluid communication with a different chip inlet by positioning the substrate on the second surface at a different orientation relative to the packaging jig. 
   
   
       58 . The nano-liquid chromatography method of  claim 53  wherein the outlet port is placed into fluid communication with the column inlet through an access hole formed through the deposited layer on a chip front side. 
   
   
       59 . The nano-liquid chromatography method of  claim 53  wherein the outlet port is placed into fluid communication with the column inlet through an access hole formed through the substrate on a chip back side.