(12) United States Patent 

Johnson et ai. 

(54) 	 SURFACE CHARGE MODIFICATION 

WITHIN PREFORMED POLYMER 

MICROCHANNELS WITH MULTIPLE 

APPLICATIONS INCLUDING MODULATING 

ELECTROOSMOTIC FLOW AND CREATING 

MICROARRAYS 

(75) 	 Inventors: Timothy J. Johnson, Gaithersburg, MD 

(US); Emanuel A. Waddell, Jr., 

Gaithersburg, MD (US); David J. Ross, 

Gaithersburg, MD (US); Laurie E. 

Locascio, North Potomac, MD (US) 

(73) 	 Assignee: The United States of America as 

represented by the Secretary of 

Commerce, Washington, DC (US) 

( *) Notice: 	 Subject to any disclaimer, the term of this 

patent is extended or adjusted under 35 

U.S.c. 154(b) by 504 days. 

(21) 	 Appi. No.: 09/905,566 

(22) 	 Filed: Jul. 13,2001 

(65) 	 Prior Publication Data 

US 2002/0023840 Al Feb. 28, 2002 

Related U.S. Application Data 

(60) 	 Provisional application No. 60/260,577, filed on Jan. 9, 

200l. 

(51) 	 Int. CI. 

BOlD 61/42 (2006.01) 

C02F 1/469 (2006.01) 

111111 1111111111111111111111111111111111111111111111111111111111111 


US006982028B2 

(10) Patent No.: US 6,982,028 B2 

(45) Date of Patent: Jan. 3, 2006 

(52) 	 U.S. CI. ....................... 204/454; 204/600; 204/601; 

204/602; 204/450; 204/451 

(58) 	 Field of Classification Search ................. 204/454, 


204/451,450,600,601,602 

See application file for complete search history. 

(56) References Cited 

PUBLICATIONS 

Locascio et aI., "Measurement of electroosmotic flow in 

plastic imprinted microfluid devices and the effect of protein 

adsorption on flow rate", Journal of Chromatography A, 

857,275-284(1999).* 

* cited by examiner 

Primary Examiner-Ling-Sui Choi 

(74) Attorney, Agent, or Firm-Butzel Long 

(57) ABSTRACT 

A method is described for modifying performed channels 

fabricated in a variety of substrate materials including 

PMMA. The method involves exposing a portion of a fluid 

flow channel to light at a fluence and wavelength which 

modifies the surface charge of the substrate at the exposure 

site. The method can be used to modulate electro osmotic 

flow in channels or to immobilize chemical compounds or 

biological species in the fluid flow channels at the modified 

surfaces. The method can be used to fabricate or modify 

microfluidic systems 

25 Claims, 9 Drawing Sheets 
u.s. Patent Jan. 3, 2006 Sheet 1 of 9 US 6,982,028 B2 

CHANNEL 

SIDE VIEW 

NON-MODIFIED 

~ 

CHANNEL 

FLUID -VELOCllY

-


CHANNEL 

TOP VIEW 

FIG.1 a FIG.1 b 


CHANNEL 

SIDE VIEW 

LI
 t 

LASER-MODIFIED REGION 

-


CHANNEL 


TOP VIEW 


FIG.1 c FIG.1 d 
u.s. Patent Jan. 3, 2006 Sheet 2 of 9 US 6,982,028 B2 

FIG.2a FIG.2b 

FIG.3a FIG.3b 
u.s. Patent Jan. 3, 2006 Sheet 3 of 9 US 6,982,028 B2 

FIG.4a FIG.4b 

u.s. Patent Jan. 3, 2006 Sheet 4 of 9 US 6,982,028 B2 

I 

CONTROLLABLE VACCUM

CHUCK X-Y STAGE 8 

FIG.5 
u.s. Patent Jan. 3, 2006 Sheet 5 of 9 US 6,982,028 B2 

1lII11II11II1I11II11I1III ~ FIG.6a 

FIG.6b 

FIG.6c 

u.s. Patent Jan. 3, 2006 Sheet 6 of 9 US 6,982,028 B2 

FIG.6d 


FIG.6e 

u.s. Patent Jan. 3, 2006 Sheet 7 of 9 US 6,982,028 B2 

FIG.7a 


FIG.7b 


FIG.7c 

u.s. Patent Jan. 3, 2006 Sheet 8 of 9 US 6,982,028 B2 

FIG.7d 


FIG.7e 

u.s. Patent Jan. 3, 2006 Sheet 9 of 9 US 6,982,028 B2 

UV Modified Region 

FIG.8a 

FIG.8b 

FIG.8e 

LIGHT EXPOSURE 

tttt tttt 

HYDROPHOBIC 

PATCH 

1 

HYDROPHOBIC 

MICROCHANNEL 

FIG.9a FIG.9b 

" / HYDROPHILIC 

REGIONS 

FIG.9c 
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US 6,982,028 B2 


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SURFACE CHARGE MODIFICATION 


WITHIN PREFORMED POLYMER 


MICROCHANNELS WITH MULTIPLE 


APPLICATIONS INCLUDING MODULATING 


ELECTROOSMOTIC FLOW AND CREATING 


MICROARRAYS 


RELATED APPLICATION 


This application is based on United States Provisional 

Patent Application Ser. No. 60/260,577 filed Jan. 9, 2001, 

the complete disclosure of which is expressly incorporated 

herein by reference. 

TECHNI CAL FIELD 

The present invention relates to micro-total-analytical 

systems having fluid flow channels. More particularly, the 

present invention is directed to methods to modify and 

control fluid flow in micro-total-analytical systems and to 

immobilize chemical components and species thereon, and 

to micro-total-analytical systems which have been treated 

according to the techniques of the present invention. 

BACKGROUND ART 

Over the past decade there has been a significant focus of 

research on the development of micro-total-analytical systems which are referred to as ,u-TAS or lab-on-a-chip 

devices. This technology is based on the use of a series of 

microfluidic channels or microchannels for the movement, 

separation, reaction, and/or detection of various chemicals 

(e.g. proteins, DNA, chemical compounds, etc.). Movement 

of the fluids within the microchannels can be effected by 

means of applied pressure gradients or electric fields applied 

along the length of the channel. In the latter phenomenon, 

known as electroosmosis, the larger the magnitude of the 

applied electric field or the greater the surface charge, the 

greater the induced fluid velocity. 

The development of lab-on-a-chip devices has progressed 

rapidly, however there are still several issues that must be 

resolved. Most of these issues stem from the need to control 

flow and/or immobilize reagents within the fluid flow channels. Such control or immobilization can be achieved 

through the modification of the surface charges. Since 

electroosmotic flow is a result of surface charge, the ability 

to change the charge is critical to the optimization of 

lab-on-a-chip devices. One method for controlling and 

changing the surface charge is through the use of wall 

coatings, which has been shown to increase, decrease, or 

even reverse the electro osmotic flow in specific regions of 

the channels. Unfortunately, the use of wall coatings complicates and increases the costs of the fabrication process. 

Moreover, such coatings may become unstable over time. 

Surface charge modification of the microchannels is also 

used to selectively bind molecules such as DNA, proteins, 

molecules, etc. therein. Such bound molecules can then be 

used in devices that function as chemical sensors, DNA or 

protein microarrays, etc. Current reported methods for binding proteins require a rather complex soft lithography technique. Another process uses a two-step lamination technique 

or a two-step bovine serum albumin (BSA) blocking technique to pattern proteins. These procedures tend to complicate the fabrication process. 

DISCLOSURE OF THE INVENTION 

According to various features, characteristics and 

embodiments of the present invention which will become 

apparent as the description thereof proceeds, the present 

invention provides a method of modifying fluid flow in a 

channel formed in a polymeric substrate which involves: 

exposing a portion of the channel to laser light at a fluence 

and wavelength(s) which are sufficient to change a surface 

charge at the exposed portion of the channel. 

The present invention also provides a method of immobilizing a chemical species in a channel formed in a polymeric substrate which involves: 

exposing a portion of the channel to laser light at a fluence 

and wavelength(s) which are sufficient to ablate and/or 

change a surface charge at the exposed portion of the 

channel. 

The present invention further provides a micro-totalanalytical system having a polymeric substrate with a fluid 

flow channel, wherein a portion of the fluid flow channel 

which has been surface-charged modified by exposure to 

laser light. 

BRIEF DESCRIPTION OF DRAWINGS 

The present invention will be described with reference to 

the attached drawings which are given as non-limiting 

examples only, in which: 

FIG. 1a is a schematic of a non-modified imprinted 

channel with a depiction of the electroosmotic flow profile. 

FIG. 1b is a top view of a time series of images of 

electroosmotic flow profiles within a non-modified 

imprinted channel. FIG. 1e is a schematic of a UV-modified 

imprinted channel with a depiction of the electro osmotic 

flow profile. FIG. 1d is a top view of a time series of images 

of electro osmotic flow profiles within a UV-modified 

imprinted channel. 

FIGS. 2a and 2b are top views of electroosmotic flow 

profiles for a UV-Iaser-modified surface within an imprinted 

channel at an applied electric field of 488 V/cm (FIG. 2a), 

and of 732 V/cm (FIG. 2b). 

FIGS. 3a and 3b are top views of a trapezoidally-shaped, 

imprinted microchannel with a linear array of ablated spots 

for the binding of fluorescein-labeled BSA imaged using 

white light microscopy (FIG. 3a), and fluorescence microscopy (FIG. 3b). 

FIGS. 4a and 4b are top views of a trapezoidally-shaped 

microchannel with a 2D array of ablated spots for the 

binding of fluorescein-labeled BSA imaged using white light 

microscopy (FIG. 4a), and fluorescence microscopy (FIG. 

4b). 

FIG. 5 is a schematic diagram of a UV-Iaser system used 

to modify polymer micro channels according to one embodiment of the present invention. 

FIGS. 6a-6e are progressive views of electroosmotic flow 

of a sample plug through a typical non-modified S-shaped 

microchannel. 

FIGS. 7a-7e are progressive views which illustrate electroosmotic flow of a sample plug in an S-shaped micro channel in which the outer wall of each non-linear region has 

been surface charge modified according to the present invention. 

FIG. 8a is a top-view image of a trapezoidal-shaped, 

imprinted channel with a 90 degree turn. FIGS. 8b and 8e are 

a time series of images of a fluorescein plug of fluid 

undergoing electroosmotic flow in a non-modified, 

imprinted channel with a 90 degree turn and a UV-modified, 

imprinted channel with a 90 degree turn, respectively. The 

outer wall of the imprinted channel in FIG. 8e has been 

surface charge modified according to the present invention. 
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FIGS. 9a-ge depict how laser modification can create 

hydrophiliclhydrophobic regions within a preferred hydrophobic microchannel. 

BEST MODE FOR CARRYING OUT THE 


INVENTION 


The present invention is directed to a simple fabrication 

method to modulate the surface charge of a solid substrate. 

The present invention is based upon the discovery that the 

surface charge of a polymeric substrate, such as a poly 

(methyl methacrylate) (PMMA) substrate, a polycarbonate 

substrate, a poly( ethylene terephthalate glycol) substrate, 

etc., can be modified by exposing the surface to a light 

source that will chemically modify and/or ablate the surface. 

Moreover, the amount of surface charge created depends on 

a number of factors including, the substrate material, the 

wavelength of the light source, the fluence (defined as the 

light power divided by the exposure area), the exposure 

time, the number of times that the same surface is exposed 

to the light source, and the local process environment. 

During the course of the present invention, a laser was 

used to chemically modify a surface of a pre-formed channel 

in a polymeric substrate. Such chemical modification of the 

surface was found to effect fluid flow control and/or immobilization of various chemicals and chemical species due to 

modification of the surface charges. Effective fluid flow 

control has been verified from electrokinetic flow profile 

studies comparing flow in modified and non-modified, preformed microchannels. 

The principles of the present invention have been applied 

to simple, one-step processes with ultraviolet (UV) laser 

pulses for patterning proteins (or other charged entities) in a 

linear or two-dimensional micro array pattern within preformed microfluidic channels. For the flow modification 

studies, the fluence level of the UV laser was adjusted so that 

there was no physical or structural changes to the channel, 

but so that there was a change in the surface charge on the 

UV-exposed surface as evidenced by the increase in fluid 

velocity over that surface. 

FIGS. la and Ib are schematic drawings and captured 

top-view images of electroosmotic flow profiles within a 

non-modified, imprinted channel as observed by fluorescence microscopy, respectively. The electric field strength 

used in FIG. Ib was 266 V/cm and the time step between 

images was 67 ms. FIGS. Ie and Id are schematic drawings 

and captured top-view images of electro osmotic flow profiles within a UV-modified, imprinted channel as observed 

by fluorescence microscopy, respectively. The electric field 

strength used in FIG. Id was 244 V/cm and the time step 

between images was 67 ms. It can be seen in FIG. 1 d that 

the fluid at the top of the channel is moving faster than the 

fluid at the bottom due to the increase in charge on the 

UV-modified surface. 

The lack of ablation upon exposure to the UV light is 

referred to as subablation. The effect of the laser-modified 

surface on the electroosmotic flow profile is evidenced more 

clearly at higher electric field strengths, as shown in FIGS. 

2a and 2b. FIGS. 2a and 2b are top views of electroosmotic 

flow profiles as observed by fluorescence microscopy for a 

UV-Iaser-modified surface within the pre-formed, imprinted 

channel, and an applied electric field of 488 V/cm (FIG. 2a), 

and 732 V/cm (FIG. 2b). The time step between images was 

50 ms. 

The surface-charge modification of pre-formed microchannels can also be used to selectively bind biological 

species or other chemical compounds. 

FIGS. 3a and 3b are top views of a trapezoidally-shaped 

microchannels with a linear array of ablated spots for the 

binding of fluorescein isothiocyanate (FITC) labeled BSA 

imaged using white light microscopy (FIG. 3a), and fluorescence microscopy (FIG. 3b). The fluorescence in FIG. 3b 

shows selective binding of BSA to the ablated spots compared to the surrounding, non-irradiated surface. 

FIGS. 4a and 4b are top views of a trapezoidally-shaped 

microchannel with a two-dimensional array of ablated spots 

for the binding of FITC-Iabeled BSA imaged using white 

light microscopy (FIG. 4a), and fluorescence microscopy 

(FIG.4b) 

The higher fluences were used to ablate material to create 

an increase in surface charge and surface area for the 

selective binding of proteins without the use of laminate or 

other blocking techniques. 

The technique of using a laser to create an increase in the 

surface charge of a solid substrate is not limited to ablation 

level fluences for micoarrays or subablation level fluences 

for electroosmotic flow modifications. Ablation level fluences create a higher surface charge than sub ablated surfaces. Also, ablated surface can have a higher surface area 

compared to native or sub ablated surfaces. Therefore, it is to 

be understood that application of the techniques of the 

present invention provide benefits from ablation level fluences for some purpose and sub ablation level fluences for 

other purposes. 

Furthermore, it is to be understood that the application of 

this technique is not limited to the use of a laser but to any 

light source of sufficient energy to induce a chemical modification of the surface. 

In the following illustrative examples, experiments were 

conducted to demonstrate the ability to modify the surface 

charge on a polymeric substrate. For illustrative purposes a 

poly(methyl methacrylate) (PMMA) substrate was used in 

the following examples. Inasmuch as the examples are 

merely illustrative, it is to be understood that the techniques 

of the present invention are not limited to the specific 

polymeric substrates or wavelengths of lights of light used 

in the examples. 

In the following examples a poly(methyl methacrylate) 

(PMMA) substrate was provide with channels formed by an 

imprinting method. Prior to imprinting, the PMMAsubstrate 

was cleaned with compressed air. Channels were imprinted 

in the substrate material using a silicon stamp with a 

trapezoidal-shaped raised channel. It is to be understood that 

a polymeric substrate having channels made utilizing techniques other than imprinting, including for example injection molding, embossing, lithography, machining, etc. could 

also be used according to the present invention. 

FIG. 5 is a schematic diagram of a UV-Iaser system used 

to modify polymer microchannels according to one 

embodiment/of the present invention. The excimer laser 

system (LMT-4000, Potomac Photonics, Inc., Lanham, Md.) 

of FIG. 5 was used to surface-modify PMMA substrates at 

fluences below, the ablation threshold so that, although no 

change in the physical dimensions of the substrate occurred, 

a change in the surface charge of the exposed surface did 

occur. If ablation of the substrate surface is not a concern, 

the surface can be modified at higher fluences, with an even 

greater effect on surface charge, but a change in physical 

dimensions and characteristics of the channel will occur. The 

system depicted in FIG. 5 contains a laser light source 1, an 

aperture 2 for delimiting the size and shape of the beam 3, 

a focusing lens 4, a visible light source 5, a CCD camera 6 

to image the ablation process, and a controllable X-Y stage 
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US 6,982,028 B2 


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7 with a vacuum chuck 8 to hold the substrate 9 in place. 

Also, a nozzle 10 is present to sweep gas over the substrate 

9 during processing, and a vacuum 11 is located on the 

opposite side to remove debris. 

EXAMPLE 1 

In this example the UV-Iaser system depicted in FIG. 5 

was used to modify the surfaces of imprinted channels in a 

PMMA substrate (discussed above) for electro osmotic flow 

modification. First, the PMMA substrate with the preformed imprinted channels was placed on the vacuum chuck 

8 and a vacuum was applied to keep the PMMA substrate 

stationary. A beam-defining aperture 2 was chosen so that 

the light, after being focused, exposed a square area of 

1.70xlO-5 cm2 on the surface of the PMMAsubstrate. Other 

exposure areas can be used depending on what is desired. 

The power level per pulse was set to an average of 6.4 f1l, 

and the frequency of pulses was set to 200 Hz (pulse 

duration of 7 ns). Nitrogen was used as the sweep gas, and 

the laser was exposed to a single surface of the micro channel 

as the stage moved at a rate of 1 mm/sec in one direction. 

Other operating parameters can be used depending on what 

is desired. 

EXAMPLE 2 

In this example, the UV-Iaser system depicted in FIG. 5 

was used to create ablated spots on the bottom of an 

imprinted channel. First, the PMMA with the preformed 

imprinted channel (discussed above) was placed on the 

vacuum chuck 8 and a vacuum was applied to keep the 

PMMA substrate stationary. A beam-defining aperture 2 was 

chosen such that the light, after being focused, exposed a 

circular area of 2.2x10-7 cm2 for a linear array or 9.1x10-8 

cm2 for two-dimensional micro arrays on the surface of the 

PMMA substrate. The power level per pulse was set to an 

average of 1.48 f1l for the linear arrays and 0.182 f1l for the 

two-dimensional microarrays. The frequency of pulses was 

set to 200 Hz with an average pulse duration of 7 ns. 

Nitrogen was swept over the surface during UV-light exposure. After ablating the spots, the PMMA substrate was 

sonicated for 10 minutes in a water solution to remove any 

weakly bounded particulates that were generated during the 

ablation process. Other light exposure areas and other operating parameters can be used depending on what is desired. 

EXAMPLE 3 

In this example, the imprinted and laser modified microchannel in the PMMA substrate from Examples 1 was 

covered and sealed with an additional sheet of PMMAwhich 

is referred to herein as the "lid." Circular holes having a 

diameter of 3 mm were formed in the lid to provide access 

to the underlying channel(s). The holes also served as fluid 

reservoirs. In order to seal the micro channel, the lid was 

placed on top of the channel and the two pieces were 

clamped together between glass slides and bonded by placing them in a circulating air oven at 103° C. for 12 minutes. 

The channels were 2-5 cm in length and 30,um deep. The 

channels had a trapezoidal cross section defined by the 

silicon template with a 25 ,urn width at the bottom and a 70 

,urn width at the top. 

EXAMPLE 4 

In this example, fluorescein isothiocyanate labeled 

Bovine Serum Albumin (FITC-BSA) was immobilized at 

the ablated spots on the bottom of an imprinted channel from 

Example 2. The FITC-BSA was obtained from SigmaAldrich (St. Louis, Mo.) and was concentrated to 1 mg/ml in 

a phosphate buffered saline (PBS) solution. The channel was 

submerged in the FTIC-BSA solution for varying times 

ranging from 30 mins to 17 h. Afterwards, the substrate was 

rinsed three times under agitation with PBS. A drop of the 

PBS was then placed over the channel and then covered with 

a coverslip for observation by microscopy. 

As noted above, FIGS. 1-3 illustrate how the techniques 

presented in the Examples control fluid flow and immobilization of chemical species. 

The present invention has many practical applications. 

For example, the principles of the present invention can be 

used to modify electroosmotic flow and eliminate band 

broadening due to micro channel turns. 

As micro fluidic devices increase in complexity due to the 

integration of various physical manipulations and chemical 

reactions, a corresponding increase in the number, and 

complexity, of micro channels on a single microchip will 

take place. This increase in complexity will often lead to the 

incorporation of various turns in the micro channel design. 

This is especially true for microchannels that are responsible 

for the separation of chemical species because these channels often require the greatest channel length. Unfortunately, 

the introduction of turns leads to analyte dispersion due to 

the difference in length scales between the inside and the 

outside of the turn. This is known as the racetrack effect 

because the fluid on the inside of the turn will complete the 

turn sooner than the fluid on the outside due to the shorter 

distance. Furthermore, for electrokinetic flow, the strength 

of the applied electric field is greater on the inside of the turn 

than on the outside of the turn. Therefore the fluid on the 

inside of the turn will travel faster than fluid on the outside 

of the turn. 

FIGS. 6a-6e are progressive views which depict electroosmotic flow of a sample plug in a non-modified, 

S-shaped microchannel. The analyte dispersion or racetrack 

effect depicted in FIGS. 6a-6e is due to the nonuniform 

electric field in the curved microchannel as well as the 

differences in length scales between the inside and outside of 

the turn. These factors lead to analyte dispersion as shown 

in FIGS. 6a-6e. Thus, when turns are introduced into a 

separation channel (or any other channel), analyte dispersion 

will occur. This effect leads to a reduction in the separation 

efficiency of the channel and inhibits the reduction of the 

overalllab-on-a-chip size. 

The present invention will help (1) reduce or eliminate 

analyte dispersion for electrokinetic flow through curved or 

non-linear microchannels, (2) maintain a geometrically 

simple microchannel curve, and (3) reduce the expense and 

the complexity of microchannel fabrication. For example, 

the entire curved microchannel can be formed using any 

suitable technique such as an imprint technique, an injection 

molding technique, etc., and then the outside of the already 

formed curve can be exposed to light according to the 

present invention to increase the surface charge on the 

outside surface. Thus, the outside of the analyte plug will 

increase in speed to keep up with the fluid on the inside of 

the curve, thereby reducing plug dispersion. 

FIGS. 7a-7e are progressive views which illustrate electroosmotic flow of a sample plug in an S-shaped micro channel which has been surface-charge modified according to the 

present invention. The plug remains uniform due to surfacecharge modification of the outside of each turn of the 

channel. 

FIGS. 8a is a top-view image of a trapezoidal-shaped, 

imprinted channel with a 90 degree turn as viewed by 
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white-light microscopy. FIGS. Sb and Se are a time series of 

images of a fluorescein plug of fluid undergoing electro osmotic flow as viewed by fluorescence microscopy. FIG. Sb 

is flow in a non-modified, imprinted channel with a 90 

degree turn, at an applied electric field of 454 V/cm, and 

imaged at time points of 0,83, and 417 ms. FIG. Se is flow 

in a UV-modified, imprinted channel with a 90 degree turn, 

at an electric field 476 V/cm, and imaged at time points of 

0, 67, and 333 ms. The outer wall of the imprinted channel 

in FIG. Se has been surface charge modified over a length of 

500 ,um (as shown in FIG. Sa) according to the present 

invention, which results in a final plug that is more compact 

(FIG. Se) compared to the extent of plug-broadening in the 

non-modified channel (FIG. Sb). 

The principles of the present invention can also be used to 

provide a simple, one-step technique for selectively binding 

various chemicals and chemical species in predefined patterns. For example, biological species such as DNA, 

proteins, and/or other chemical compounds or species can be 

bound or immobilized within a pre-formed microchannel. 

Such binding or immobilization can be achieved by producing highly charged spots using the laser techniques 

described above, and then selectively immobilizing (either 

covalently or non-covalently) one or more types of chemicals or biological species. Such microchannel arrays can be 

used for the purpose of drug discovery, chemical sensing and 

similar or related applications. 

The principles of the present invention can be used in 

conjunction with chemical means for modifying the surface 

charge of a substrate. For example, modulation of the 

surface charge of a substrate by chemical derivatization (e.g. 

wall coatings; etc.) can be conducted after the surface is 

modified by laser treatment according to the present invention. In such instances, an increase in the surface charge of 

laser-modified regions leads to an increase in surface reactivity for further chemical derivatization. 

It has also been found that the laser treatment used to 

modify the surface change according to the present invention can also be used to modulate mechanical or electrokinetic fluid flow by altering the wetting properties, i.e. 

hydrophobicity/hydrophilicity, of a surface. For example, 

hydrophobic patches produced in a hydrophilic microchannel utilizing the laser surface-charge modification techniques of the present invention can hinder or stop flow 

thereby acting as a passive valve for microsystems. 

FIGS. 9a-ge show how laser modifications create 

hydrophilic/hydrophobic regions within a pre-formed 

hydrophobic microchannel. FIG. 9a illustrates a hydrophobic microchannel. FIG. 9b depicts how laser light is selectively directed onto portions of the hydrophobic micro channel. FIG. ge depicts how the laser-exposed areas become 

hydrophilic while the unexposed areas remain hydrophobic. 

Although the present invention has been described with 

reference to particular means, materials and embodiments, 

from the foregoing description, one skilled in the art can 

easily ascertain the essential characteristics of the present 

invention and various changes and modifications can be 

made to adapt the various uses and characteristics without 

departing from the spirit and scope of the present invention 

as described in the attached claims. 

What is claimed is: 

1. A method of modifying fluid flow in a channel formed 

in a substrate which comprises: exposing only one or more 

discrete, isolated portions of the channel to light at a fluence 

which is sufficient to change a surface charge at the one or 

more discrete, isolated exposed portions of the channel. 

2. A method of modifying fluid flow in a channel formed 

in a substrate according to claim 1, wherein the one or more 

discrete, isolated portions of the channel is exposed to light 

at a fluence and wavelength(s) which are sufficient to alter 

the surface charge at the exposed portion of the channel, and 

wherein the substrate is not ablated by the light. 

3. A method of modifying fluid flow in a channel formed 

in a substrate according to claim 1, wherein the fluence 

causes ablation of the substrate. 

4. A method of modifying fluid flow in a channel formed 

in a substrate according to claim 3, wherein the one or more 

discrete, isolated portions of the channel which is exposed to 

light comprises at least one of a wall of the channel, a bottom 

of the channel, and one or more portions thereof. 

5. A method of modifying fluid flow in a channel formed 

in a substrate according to claim 3, wherein the channel is 

linear. 

6. A method of modifying fluid flow in a channel formed 

in a substrate according to claim 3, wherein the channel is 

non-linear. 

7. A method of modifying fluid flow in a channel formed 

in a substrate according to claim 3, wherein the one or more 

discrete, isolated portions of the channel is exposed to at 

least one of a linear and non-linear pattern of light. 

S. A method of modifying fluid flow in a channel formed 

in a substrate according to claim 3, wherein the substrate is 

a member selected from the group consisting of polymeric, 

glass, silica, ceramic, and composites thereof. 

9. A method modifying fluid flow in a channel formed in 

a polymeric substrate according to claim 3, wherein the 

substrate is selected from the group consisting of a poly 

(methyl methacrylate) substrate, a polycarbonate substrate, a 

poly( ethylene terephthalate glycol) substrate, a polystyrene 

substrate, and a poly(vinyl chloride) substrate. 

10. A method of modifying fluid flow in a channel formed 

in a substrate according to claim 3, wherein the substrate 

comprises a microfluidic system. 

11. A method of modifying fluid flow in a channel formed 

in a substrate according to claim 2, wherein the one or more 

discrete, isolated portions of the channel which is exposed to 

light comprises at least one of a wall of the channel, a top 

of the channel, a bottom of the channel, and portions thereof. 

12. A method of modifying fluid flow in a channel formed 

in a substrate according to claim 3, wherein the channel is 

linear. 

13. A method of modifying fluid flow in a channel formed 

in a substrate according to claim 3, wherein the channel is 

non-linear. 

14. A method of modifying fluid flow in a channel formed 

in a substrate according to claim 3, wherein the portion of 

the channel is exposed to at least one of a linear and 

non-linear pattern of light. 

15. A method of modifying fluid flow in a channel formed 

in a substrate according to claim 3, wherein the substrate is 

a member selected from the group consisting of polymeric, 

glass, silica, ceramic, or composites thereof. 

16. A method of modifying fluid flow in a channel formed 

in a polymeric substrate according to claim 3, wherein the 

substrate is selected from the group consisting of a poly 

(methyl methacrylate) substrate, a polycarbonate substrate, a 

poly( ethylene terephthalate glycol) substrate, a polystyrene 

substrate, and a poly(vinyl chloride) substrate. 

17. A method of modifying fluid flow in a channel formed 

in a substrate according to claim 3, wherein the substrate 

comprises a microfluidic system. 

IS. A method of immobilizing a chemical species in a 

channel formed in a substrate which comprises: exposing the 
US 6,982,028 B2 


9 10 
 one or more discrete, isolated portions of the channel to light 

at a fiuence which is sufficient to change a surface charge at 

the exposed portion of the channel; and applying a chemical 

species to the exposed portion of the channel. 

19. A method of immobilizing a chemical species in a 5 

channel formed in a substrate according to claim 18, wherein 

the chemical species comprises a chemical compound. 

20. A method of immobilizing a chemical species in a 

channel formed in a substrate according to claim 18, wherein 

the chemical species comprises a biological species. 10 

21. A method of immobilizing a chemical species in a 

channel formed in a substrate according to claim 18, wherein 

the one or more discrete, isolated portions of the channel that 

is exposed to the light comprises at least one of a wall of the 

channel, a bottom of the channel, and portions thereof. 15 

22. A method of immobilizing a chemical species in a 

channel formed in a substrate according to claim 18, wherein 

the substrate is a member selected from the group consisting 

of polymeric, glass, silica, ceramic, or composites thereof. 

23. A method of immobilizing a chemical species in a 

channel formed in a polymeric substrate according to claim 

22, wherein the substrate is selected from the group consisting of a poly(methyl methacrylate) substrate, a polycarbonate substrate, a poly( ethylene terephthalate glycol) 

substrate, a polystyrene substrate, and a poly(vinyl chloride) 

substrate. 

24. A method of immobilizing a chemical species in a 

channel formed in a substrate according to claim 18, wherein 

the substrate comprises a microfiuidic system. 

25. A method for immobilizing a chemical species in a 

channel formed in a substrate according to claim 24, wherein 

a microarray is formed in the microfiuidic system. 

* * * * *