WO2007127722A2

WO2007127722A2 - Surface-modified substrate and method of its preparation

Info

Publication number: WO2007127722A2
Application number: PCT/US2007/067284
Authority: WO
Inventors: Georges Belfort; Arpan Nayak; Hongwei Liu; Amit Kumar Dutta
Original assignee: Rensselaer Polytechnic Institute
Priority date: 2006-04-24
Filing date: 2007-04-24
Publication date: 2007-11-08
Also published as: WO2007127722A3

Abstract

A surfaced-modified substrate having at least a first operating state and a second operating state, which comprises a switchable compound having at least one measurable, selectively configurable property responsive to a change in at least one preselected condition, and a selected substrate having a substrate surface adapted to have said switchable compound deposited on at least a portion of said substrate surface to form said surface-modified substrate and to enable said surface-modified substrate to selectively switch between said at least first and second operating states in response to the change in said preselected condition. The switchable compound selected should substantially retain its measurable configurable property after being deposited or grafted onto the substrate surface. A method of synthesizing the surface-modified substrate is also provided.

Description

SURFACE-MODIFED SUBSTRATE AND METHOD OF ITS PREPARATION

STATEMENT OF GOVERNMENT INTEREST

The U.S. government has certain rights in this invention.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This application claims benefit of U.S. provisional application serial number 60/745,512, filed April 24, 2006, which is incorporated herein by reference.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates in general to a substrate having a surface modified with a switchable material to enable the modified substrate to selectively assume a first operating state or a second operating state in response to a change in the modified substrate's operating condition, and a method of making the modified substrate.

The surface chemistry of synthetic membranes is of great interest to the bioprocessing of protein-containing solutions, to the filtration of medically relevant solutions, and to the performance of membrane-based sensors. For biosensors, controlling the polarity of the membrane and reducing nonspecific protein adsorption would significantly improve signal to noise ratios. This may also be useful as a switch to control diffusive transport to biosensor elements (enzymes, chemoreceptors, etc.) by changing the polarity of the protective membrane when desired. For bioprocessing, it has direct bearing on the efficacy of producing and delivering desirable proteins and other biologically derived molecules at high yield and purity. The performance of synthetic polymer membranes when filtering bioprocessing and biomedical fluids is severely limited by the interaction of proteins with membrane surfaces. Currently, expensive and labor-intensive methods such as controlling the pH and ionic strength of the feed solution, periodic cleaning, and back flushing are used to deal with the loss of filtration performance resulting from protein adhesion. It would therefore be extremely attractive to have an in situ cleaning procedure in which filtration performance could be re-established with minimum need for expensive cleaning chemicals and down time owing to back flushing. Synthesizing membranes with polymers that reduce such interactions has resulted in improved filtration performance.

Consequently, there remains a need for a simple and inexpensive approach or alternative to membranes synthesized from traditional protein-adhesion-resistant monomers such as polyethylene glycol and other hydrophilic monomers. There is also a need for a substrate having a surface selectively switchable between at least two operational states, which suitable for the type of application that the substrate will be used perform.

All references cited herein are incorporated by reference in their entireties.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a surfaced-modified substrate having at least a first operating state and a second operating state, which comprises of a switchable compound having at least one measurable configurable property responsive to a change in at least one preselected condition, and a selected substrate having a substrate surface adapted to have the switchable compound deposited on at least a portion of the substrate surface to form the surface-modified substrate and to enable the surface-modified substrate to selectively switch between the at least first and second operating states in response to the change in the preselected condition. The switchable compound selected should preferably substantially retain its measurable configurable property after being deposited on the substrate surface. The switchable compound may be permanently bonded or affixed to or selectively removable from the substrate surface.

Another object is to provide a method of synthesizing a surfaced-modified substrate of the present invention. The method preferably comprises providing a switchable compound having at least one measurable configurable property responsive to a change in at least one preselected condition, providing a selected substrate having a substrate surface adapted to have the switchable compound deposited on at least a portion of the substrate surface to form the surface-modified substrate and to enable the surface-modified substrate to selectively switch between the at least first and second operating states in response to the change in the preselected condition, contacting the switchable compound with the portion of the substrate surface having the switchable compound deposited thereon, and depositing the switchable compound on the substrate surface.

The present inventors have also developed an improved filtration membrane product by grafting environmentally responsive polymers onto synthetic membranes using simple inexpensive methods such as photograft-induced polymerization, which can be easily incorporated into the membrane synthesis process, as an alternative method to the approaches that use traditional protein-adhesion-resistant monomers such as polyethylene glycol and other hydrophilic monomers. The inventors further combined a UV-grafting process, such as the process described in U.S. Patent 6,852,769, issued to Belfort, et al., with photoresponsive spiropyran molecules to produce an optically reversible switching membrane surface. Further, the present inventors have demonstrated that the concepts and principles of this invention can be applied to functionalize other types of surfaces, such as a metal-containing surface. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

Fig. 1 A is a schematic representation of graft polymerization of spiropyran vinyl monomer on a PES membrane; Fig. 1 B is a schematic representation of a grafted PES membrane with the grafted spiropyran in a closed, apolar state after exposure to visible light for 1 hour; Fig. 1 C is a schematic representation of a grafted PES membrane with the grafted spiropyran in an open, polar state after UV irradiation at 254 nm for 1 hour;

Fig. 2 shows the chemical structure of the vinyl spiropyran monomers in two configurations - open and closed - as a function of UV and visible (Vis) irradiation; Fig. 3 is a schematic representation of the chemical structure of vinyl spiropyran monomer in two configurations - open and closed - as a function of UV and Vis irradiation;

Fig. 4 shows a color change of spiropyran-grafted PES membrane after exposure to UV irradiation at 254 nm for 1 hour and visible light for 5 min. in air; Fig. 5 shows five ATR/FTIR spectra of the unmodified PES ultrafiltration membrane and the spiropyran-grafted PES membrane after two cycles of exposure to UV irradiation at 254 nm for 1 hour and visible light for 5 min (note: the peak at « 1663 cm^"1 decreases whereas the peak at ~ 1720-1725 cm^"1 increases in intensity during exposure to UV at 254 nm); Fig. 6A shows the ratio of peak heights, R = {h₁₇₂o/h₁₄87)l{hi663/hi487), from

ATR/FTIR spectra from Fig. 5 as a function of alternating exposure to 254-nm UV light (1 hour) and visible light (5 min) or cycle number;

Fig. 6B shows the surface wettability changes as measured by the sessile contact angle of the grafted PES membrane with a water droplet after alternating exposure to 254-nm UV light (1 hour) and visible light (5 min) or cycle number;

Fig. 6C shows adsorption of BSA in PBS (1 OmM; pH 7.4) at 22 ± 1 °C for 1 hour on the as-received PES membrane and on modified PES membranes with grafted vinyl spiropyran in the closed (visible light) and open (254-nm UV light) configuration;

Fig. 6D shows mass flux of PBS at pH 7.4 and 22 ± 1 °C permeating through modified PES membranes with grafted vinyl spiropyran in the closed (visible light) and open (254-nm UV light) configuration after exposure to BSA adsorption;

Fig. 7 is a schematic diagram showing synthesis of a spiropyran monomer of the present invention;

Fig. 8 is a schematic diagram showing synthesis of a disulfide spiropyran of the present invention; and Fig. 9 shows light regulated release of RNase-A from spiropyran functionalized gold surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Disclosed herein is a surfaced-modified substrate having at least a first operating state and a second operating state, which comprises a switchable compound (or material) having at least one measurable, selectively configurable property, and a suitable substrate having a substrate surface adapted to have the switchable compound deposited on at least a portion of the substrate surface. The switchable compounds employed in the present invention are condition responsive materials, which, for example, change their structural configuration in response to a change in or exposure to a certain pH, radiation, ionic strength, electrical charge or a combination of two or more of these conditions. A switchable compound that is responsive to a change in more than one operating condition may also be employed. Examples of suitable switchable compounds include but is not limited to vinyl monomer (such as a spiropyran), vinyl azobenzene (cis to trans), azobenzene derivatives, N-isopropyl acrylamide (NIPAM), 2- (dimethylamine)ethylmethacrylate, methacrylic acid, acrylic acid, anionic extracellular polysaccharide, N-methacryloyl-L-Lysine and O-methacryloyl-L-serine.

In particular, spiropyran, vinyl azobenzene and azobenzene derivatives are responsive visible and/or UV light, N-isopropyl acrylamide is responsive to temperature, methacrylic acid, 2-(dimethylamine)ethylmethacrylate, N-methacryloyl-L-Lysine and O- methacryloyl-L-serine are responsive to pH. Examples of ionic strength responsive compounds include acrylic acid and anionic extracellular polysaccharide.

It is understood that the examples listed above are merely illustrative and that other suitable condition responsive materials could be utilized in lieu thereof.

Deposition of the switchable compound on the substrate enables the modified substrate to selectively switch between the first and second operating states in response to a selected change in the modified substrate's operating condition. Switchable compound preferably retains its measurable configurable property (or properties) after deposition of the switchable compound on the substrate surface. In an embodiment, the switchable compound enables the surface-modified substrate to assume the first operating state when exposed to visible light and the second operating state when exposed to UV light. Preferably, in the first operating state, the switchable compound deposited on the substrate has a closed, non-polar form, and, in the second operating state, the switchable compound deposited on the selected substrate has an open, polar form. In another embodiment, the first operating state is achieved by exposure of the modified substrate to visible light for about 1 hour, and the second operating state is achieved by exposure of the surface-modified substrate to UV light for about 1 hour at 254 nm. Although not restricted thereto, the substrate may be a ceramic material, a silica material, a glass material, a carbon-based material, a metallic or metal-containing material (e.g., gold), a metal-organic material, fabric material, synthetic resin material, a polymeric material (e.g., film or membrane), an organic polymeric material, a polymeric material having radical generation sites, a polyethersulfone (PES) polymer membrane, a homogeneous blend of polyethersulfone polymer and phonoxy resin polymer, ultrafiltration membrane, a microporous membrane, UV-sensitive polymer, or a polymer sensitized with a sensitizing agent (e.g., benzophenone or AIBN) to undergo graft polymerization. The metallic or metal-containing material can be gold, platinum, palladium, silver, rhodium, titanium oxide, lead oxide, tin oxide or magnesium oxide. Deposition of the switchable compound on the substrate may be achieved, for example, through graft polymerization, such as the UV-grafting process described in U.S. Patent 6,852,769. When a vinyl monomer and a UV-sensitive polymer (e.g., PES) are used, for example, exposure of the polymer to UV radiation preferably produces radical sites onto which vinyl monomers can graft and polymerize. Certain polymers substrates may require a suitable sensitizing agent (e.g., benzophenone) to extract the photons and form radicals so that the vinyl groups can react and attach covalently.

Examples of suitable methods for depositing switchable compounds onto membranes include UV-induced photo-polymerization, chemical modification by coating or at membrane casting stage, and low- and room-temperature plasma. Depending on the type of substrate used, suitable functionalization chemistry or linker chemistry may be employed to achieve the desired deposition of the switchable compound. The switchable compound may be uniformly, non-uniformly or randomly deposited on the selected substrate. Further, the switchable compound may be deposited over the entire, or a part, of the surface of the substrate in a predetermined or random pattern. It is further contemplated that two or more switchable compounds, each responsive to a different operating condition or different ranges of a selected operating condition, may be employed in the modified substrate of the present invention. It will be understood and appreciated that the manner of depositing the switchable compound will depend on the type of substrate employed. For example, if a metallic or metal-containing substrate is used, the switchable compound can be covalently or otherwise fixedly bonded to the substrate.

In an embodiment, a functional (or pendent) group is added to the switchable compound to enable the compound to be deposited (e.g., attached, bonded, grafted, etc.) onto the target substrate surface. For example, an optically active spiropyran, or a disulfide spiropyran, can be modified or provided with a suitable functional group to enable the compound to bond with the surface of the substrate. To bond with a polymer membrane surface, the spiropyran compound can be provided with a vinyl functional group, to bond with a gold surface, the spiropyran compound can be provided with a thiol group, and to bond with a surface containing -OH group, the spiropyran compound can be provided with a -COOH group. It will be appreciated that numerous other suitable functional group(s) can be employed, depending on the switchable compound, the type of substrate surface, the type of bond between the switchable compound and the substrate surface and/or the type of bonding technique used.

Also disclosed is a method of preparing the surface-modified substrate of the present invention. The method preferably comprises providing a switchable compound having at least one measurable configurable property responsive to a change in at least one preselected condition, providing a suitable substrate having a substrate surface adapted to have the switchable compound deposited on at least a portion of the substrate surface to form the surface-modified substrate and to enable the surface- modified substrate to selectively switch between the at least first and second operating states in response to the change in the preselected condition, and contacting and depositing the switchable compound on a desired portion of the substrate surface. In an embodiment, the contacting step comprises immersing the substrate in a solution containing the switchable compound, and the substrate is removed from the switchable compound containing solution prior to the grafting and/or polymerizing the switchable compound onto the substrate surface. While the invention has many applications, which include but are not limited to employing the surface-modified substrate as a valve of a microfluidic chamber or channel, a vehicular window, a textile material, a glass surface, surface of chromatographic beads, a sensor surface, an electroconductive material in an electrode or DNA chip, optical fiber, thermositer or piezo electrical element, the features and advantages of the present invention will be understood from the following examples with reference to the accompanying drawings. These examples are provided for purposes of illustration, but are not intended to limit the invention by any means or in any manner.

EXAMPLE 1 : Optically Reversible Switching Membrane Surface Vinyl monomers with desirable functionality are easily grafted and polymerized onto UV-sensitive polymers such as poly(ether sulfone)(PES) membranes by using a UV-induced graft polymerization method. A schematic representation of graft polymerization of vinyl monomer on a PES membrane is shown in Fig. 1 A. Exposure of a PES synthetic membrane to 300-nm UV radiation produces radical sites onto which vinyl monomers such as vinyl spiropyran can graft and polymerize. The spiropyrans are comprised of a group of light-switchable photochromic organic molecules that are colorless, nonpolar, and in a "closed" form in the visible light. When exposed to UV and visible light, spiropyrans isomerize and produce a colored polar "open" merocyanine form and a white nonpolar "closed" form, respectively. See Fig. 1 B-C and Figs. 2-4. Light-switching of monolayers of azobenzene and spiropyran has been studied on solid substrates. Previously, binding of photochromic moieties to solid substrates required complicated and multi-step procedures, whereas the inventors have developed a relatively simple two-step dip and UV-irradiation process that could be easily incorporated into a commercial manufacturing process. One of the challenges was to synthesize an optically active vinyl spiropyran, e.g., 1 '-(2- propylcarbamylmethacrylamide)ethyl)-3',3'-dimethyl-6-nitrospiro[2H-1 ]benzo-pyran-2,2'- indoline, and determine whether the photografting process that uses UV light at 300 nm would allow the vinyl spiropyran molecules to graft and retain their switchable properties. A commercial PES 30-kDa synthetic membrane filter was chosen as a model membrane surface because of its high sensitivity to 300-nm UV radiation and because it is one of the most widely used polymeric materials that is used to produce commercial ultrafiltration membranes and support layers for reverse osmosis and nanofiltration membranes.

The synthesized vinyl spiropyran was photografted onto the 30-kDa PES ultrafiltration membranes by graft polymerization. Attenuated total reflection Fourier transform infrared spectroscopy (ATR/FTIR) was used to demonstrate that the vinyl monomers were grafted onto the PES membranes. In Fig. 5, ATR/FTIR spectra are compared for the unmodified PES membrane with those of the grafted-spiropyran- modified PES membranes. The peaks at 1410, 1487, 1579, and 1663 cm^"1 are owing to the -SO₂ group, the aromatic-ring stretch of C=C, the aromatic C — H stretch, and the aromatic C=O stretch, respectively. The last peak may shift depending on the chemical and charge environment. Under exposed visible light for 5 min and on a dry membrane, the peak at « 1663 cm^"1 is maximized whereas the peak at « 1720-5 cm^"1 is reduced. Similarly, under 254-nm UV radiation for 1 h on a dry membrane, the peak at « 1663 cm^"1 is reduced whereas that at « 1720-5 cm^"1 is increased. If the ratio of peak heights, R=(Z? 172o/hi 487)1 '{h₁₆63/h U87), is defined as a measure of the ratio of the relative chemical surface condition under ultraviolet radiation versus that under visible-light exposure, we can follow this ratio with changing irradiation exposure in Fig. 6A. The reference peak at 1487 cm^"1 is a measure of the carbon — carbon aromatic-ring stretch and is used as an internal standard as it is independent of the grafting process. Similarly, measuring the sessile contact angle of the grafted dry PES membrane with a water droplet after alternating exposure to 254-nm UV (1 h) and visible light (5 min) demonstrates changes in surface wettability. See Fig. 6B. About a 16° drop in contact angle was obtained through this process. This is similar in magnitude to that reported by Lahann and co-workers who used electrical potential to induce a polarity change in a self-assembled polar molecule on a gold surface. See, e.g., Lahann, et al., Science 2003, 299, 371-374. As protein-membrane interactions can determine success or failure for many processes including those mentioned above, we demonstrate, through two related experiments, that the switchable hydrophilic (on exposure to 254-nm UV light) and hydrophobic (with visible light) surfaces (1 ) exhibit low and high protein adsorbabilities, respectively, and (2) display high and low buffer- permeations rates after protein adsorption, respectively. Results for these two experiments are shown in Figs. 6C and 6D. Bovine serum albumin (BSA; 67 kDa, pi 4.7) was used as a model protein for the adsorption experiments. From the data shown in Fig. 6C, the as-received PES membrane exhibited the highest adsorbed amount of BSA in 10 mm phosphate buffered saline (PBS) buffer solution at pH 7.4 and 22 ± 1 °C followed by the grafted vinyl spiropyran in the "closed" (visible light) and "open" (254-nm UV light) configuration. The "closed" configuration of the vinyl spiropyran surface adsorbed about 26% more protein than the "open" configuration of the surface. These surfaces, with adsorbed protein on them, were then tested to see if this difference in protein adsorption translated into higher permeation flux. The modified membranes were then placed into a filtration test cell and the permeation rate of freshly prepared PBS at pH 7.4 and 22 ± 1 °C measured. See Fig. 6D. As expected, the "closed" configuration of the vinyl spiropyran gave about a 17% lower permeation flux as compared with the "open" configuration of the vinyl spiropyran surface. The contact angle measurements of the base PES membrane, of the base PES membrane after washing with ethyl acetate solvent, and of the base PES membrane irradiated with 254- nm UV light for 1 h were also obtained. No noticeable change in contact angle was observed in this control experiment. However, irradiation with UV light under wet rather than dry conditions reduces the switching time from "closed" to "open" conformation by about one third. The results presented herein demonstrate the reversible conversion of a photografted, photoresponsive, polymeric synthetic membrane surface from polar to nonpolar character. It has been shown that a UV/Vis-switchable moiety such as spiropyran can be grafted onto a commercial photoactive polymer such as PES by using a very simple photograft polymerization method. Both molecular (ATR/FTIR) and classical (color, contact angle, protein adsorption, and subsequent buffer ultrafiltration) measurements were used to confirm the reversible polar-apolar reaction of grafted spiropyran owing to exposure of UV/Vis radiation. Rather than inducing a physical movement (conformational change) of long-chain SAMs (self-assembled monomers) toward an electrode by changing the surface potential of a gold substrate, a photoresponsive molecule (e.g., vinyl spiropyran) was synthesized and grafted onto, for example, a PES membrane. This was accomplished by combining a UV grafting process with the photoresponsive properties of spiropyran molecules, to produce an optically reversible switching membrane surface. The relative ease of this grafting and switching process should suggest many industrial opportunities including those dependent on surface wettability and molecular adhesion. While the UV/Vis radiation has been described as a preferred trigger, it will be appreciated that triggers, such as temperature, pH, and ionic strength, can be utilized with vinyl functional groups and photosensitive (or non-photosensitive) PES materials. Besides membrane filtration and sensors, there is a need to consider surface properties of materials for catheters, surgical instruments, and pulmonary breathing tubes that are exposed to body fluids, and for spot detection for genomic analysis and nanoprocessing in micro-fluidic devices.

EXAMPLE 2: Synthesis of Vinyl Spiropyran

3-aminopropyl methacrylamide hydrochloride was obtained from Polysciences Inc. All other chemicals were purchased from Aldrich Chemical Co. and used without further purification. 1 -(2-carboxyethyl)-2,3,3-trimethylindolenine iodide (1), 1 '-(2- carboxyethyl) -3',3'-dimethyl -6- nitro spiro-[2H-1 ]benzopyran-2,2'-indoline (2), and 1 '- (2-(carbosuccinimidyloxy)ethyl)-3',3'-dimethyl-6-nitrospiro[2H-1 ]benzopyran-2,2'- indoline (3) were synthesized according to literature methods. See, e.g., Fissi, et al., Macromolecules 1995, 28, 302-309. Fig. 7 shows a scheme for the synthesis of vinyl spiropyran, 1 '-(2-(propylcarbamylmethacrylamide)ethyl)-3',3'-dimethyl-6-nitrospiro[2H- 1 ]benzo- pyran-2,2'-indoline, represented by structure (I). NMR spectra were measured on a Varian spectrometer by using tetramethylsilane (TMS) as the internal standard. Mass spectra were recorded by using electrospray ionization. 1 '-(2-(Propylcarbamylmethacrylamide)ethyl)-3',3'-dimethyl-6-nitrospiro[2H-

1 ]benzo- pyran-2,2'-indoline (I) synthesis: The mixture of 3 (3.26 g, 6.83 mmol), 3- aminopropyl methacrylamide hydrochloride (1.34 g, 7.50 mmol), and triethyl amine (1 ml_, 7.19 mmol) was stirred in N,N-dimethylformamide (DMF; 50 ml_) at room temperature for 20 h. After the evaporation of DMF, the residue was dissolved in chloroform, washed with water and then purified by silica-gel column chromatography (eluent, ethyl acetate/hexane; 1 :1 v/v) to give a vinyl spiropyran of structure (I) as a yellow solid (2.6 g, 76%). ¹H NMR (500 MHz, CDCI₃): δ=7.99 (m, 2H; 5-H and 7-H), 7.18 (t, 1 H; 6'-H), 7.08 (d, 1 H; 4'-H), 6.89 (m, 2H; 4-H and 5'-H), 6.75 (d, 1 H; 8-H), 6.67 (d, 1 H; 7'-H), 6.51 (m, 1 H; NH), 6.39 (m, 1 H; NH), 5.87 (d, 1 H; 3-H), 5.74 (s, 1 H; CH₂), 5.35 (s, 1 H; CH₂), 3.68 (m, 1 H; CH₂N), 3.51 (m, 1 H; CH₂N), 3.20 (m, 4H; CH₂), 2.56 (m, 1 H; CH₂CO), 2.44 (m, 1 H; CH₂CO), 1 .93 (s, 3H; CH₃), 1 .58 (m, 2H; CH₂), 1 .27 (s, 3H; CH₃), 1 .17 ppm (s, 3H; CH₃); 13C NMR (300 MHz, CDCI₃): d=18.9, 20.1 , 26.0, 29.8, 35.9, 36.3, 40.2, 53.1 , 107.0, 1 15.7, 1 18.9, 120.0, 120.2, 122.0, 122.2, 123.0, 126.1 , 128.0, 128.5, 136.1 , 139.9, 141 .2, 146.7, 159.7, 169.2, 171 .9 ppm.

MS calcd C₂₈H₃₂N₄O₅: 504.24. Found [M₊H]⁺: 505.2, [M₊Na]⁺: 527.1.

EXAMPLE 3: Preparation of Modified PES Membrane

30-kDa PES membranes were modified by using a UV-induced graft polymerization method, such as the method described in Taniguchi, et al., J. Membr. Sci. 2004, 231 , 147-157, U.S. Patent 6,852,769, issued to Belfort, et al., Pieracci, et al., Chem. Mater. 2000, 12, 2123-2133, and Kaeslev, et al., Membr. Sci. 2001 , 194, 245- 261. Rayonet photochemical chamber reactor system (Model RPR-100, Southern New England, Ultraviolet Co., Branford, CT) containing 300-nm UV lamps (« 15% of the energy was at <280 nm) was used. The membranes were dipped in spiropyran monomer solution (1 % w/v in ethyl acetate) for 1 h with stirring at 22 ± 1 °C, removed from the monomer solution, purged with N₂ for 10 min, and irradiated with 300-nm UV light in water-saturated N₂ for 4 min. After photografting, the membranes were again cleaned with ethyl acetate by shaking overnight to remove homopolymer and unreacted monomer from the membrane. Then, the modified membranes were vacuum dried for use. EXAMPLE 4: Attenuated Total Reflectance Fourier Transform Infra-Red (ATR-FTIR)

Spectroscopy

ATR/IR (Magna-IR 550 Series II, Thermo Nicolet Instruments Corp., Madison, Wl) was used to obtain a measure of the degree of grafting. By using an incident angle of 45°, the penetration or sampling depth was approximately 0.1-1.0 mm. Spectra were collected at a gain of 8 and resolution of 2 cm^"1 with 512 scans for each sample.

EXAMPLE 5: Unmodified PES Membrane

The PES membrane with a 30-kDa molecular-weight cut off from lot 9140E was obtained from Pall Corp. (East Hills, NY). These Omega series have been slightly hydrophilized by the manufacturer by an undisclosed process as evidenced by the small carbonyl peak at ~ 1663 cm^"1.

EXAMPLE 6: Contact Angle The sessile contact angle of water in air on the membrane substrates was measured by using an optical system (SIT camera, SIT66, Dage-MTI, Michigan, IN) converted to a video display. Water droplets of 2.5 ml_ were placed on the membrane substrates at different positions and the contact angles were measured. At least five measurements were made and the average reported.

EXAMPLE 7: BSA Adsorption

BSA (bovine serum albumin) was dissolved in PBS buffer solution (10 mm; pH 7.4) to prepare a 1 mg ml_^"1 protein solution. Membrane swatches (3 cm²) were immersed in the BSA solution for 2 h 22 ± 1 °C. The amount of adsorbed protein was determined by staining with Ponceau S solution (Ponceau S (2%), trichloroacetic acid (30%), and sulfosalicylic acid (30%)). Membranes with adsorbed protein were immersed for 1 h into a solution of Ponceau S, washed thoroughly with deionized water, immersed for 1 h in acetic acid (5% v/v), and again washed with deionized water. Then the protein-dye complex was quantitatively eluted with NaOH solution (3 ml_, 100 mm) for 1 h. Next, the membranes were removed, the solutions neutralized with HCI (50 ml_, 6m), and the absorbance of the red colored solutions was measured at 515 nm. Protein amounts were calculated based on a calibration which was performed with known BSA amounts (m_BsA = 0.001-1 mg) onto clean unmodified PES membranes (A₅₁₅ _nm=0.6799m_Bs_A+0.0754; R²=0.9944).

EXAMPLE 8: PBS Filtration PBS buffer solution (10 mm; pH 7.4) was used as the feed. The PBS buffer solution was composed of NaCI (137 mm) and KCI (2.7 mm) in deionized water. Membranes were immersed in the BSA solution (1 mg ml_^"1 in PBS buffer) for 5 min to induce protein adsorption. Then, PBS permeation flux through the membranes with adsorbed BSA was measured. A dead-end stirred cell (Model 8010, Millipore Corp., Bedford, MA) filtration system was used for PBS flux measurements through the membranes. The active membrane area was 3.8 cm². All filtration experiments were conducted at a constant transmembrane pressure of 69 kPa, a stirring rate of 500 rpm, and a system temperature of 22 ± 1 °C.

EXAMPLE 9: Synthesis of Disulfide Spiropyran

All the chemicals were purchased from Aldrich Chemical Co. and used without further purification. (1 1 -Mercaptoundecyl) ammonium Chloride (1) and 1 '-(2- carboxyethyl) -3',3'-dimethyl -6- nitro spiro[2H-1 ]benzopyran-2,2' -indoline (3) were synthesized according to literature methods. See, e.g., Tien, et al., Microfabrication through Electrostatic Self- Assembly, Langmuir 1997, 13, 5349-5355. Fig. 8 shows a scheme for the synthesis of a disulfide spiropyran, represented by structure (II). Mass spectra were recorded by using electrospray ionization.

0.5 M iodine methanol solution was added to (1 1 -Mercaptoundecyl) ammonium Chloride (1) (2.39 g, 10 mmol) in methanol (30 ml_) until the solution turned yellow. The reaction was quenched with sodium bisulfide. The mixture was made basic with NaOH and extracted with ether. The ether layer was dried with anhydrous MgSO4, and the volume was reduced in half. Dry HCI gas was bubbled through the ether solution, and a white precipitate separated, which was collected and washed with ether to give (2), Di(1 1 -aminoundecyl) Disulfide Dihydrochloride, (1.1 g, 46 %). MS calculated C₂₂H₄₈N₂S₂: 404.3, Found [MH]⁺: 405.3 Synthesis of disulfide spiropyran (II): To a stirred solution of 1 -(2-carboxyethyl) -

3 ,3 -dimethyl -6- nitro spiro[2H-1 ]benzopyran-2,2 -indoline (3) (874 mg, 2.3 mmol) in

DMF (20 ml) was added 1 -hydroxybenzotriazole (0.388g, 2.87mmol), compound (2)

(478 mg, 1 mmol), and triethyl amine (0.3 ml, 2.2 mmol). After addition of 1 -(3-N,N- dimethyl- amiopropyl)-3-ethylcarbodiimide chlorohydrate (0.55g, 2.87mmol), the reaction mixture was stirred overnight at room temperature. After the evaporation of

DMF, the residue was dissolved in chloroform, washed with water, dried, concentrated, and then purified by silica-gel column chromatography (eluent, ethyl acetate/hexane;

1 :1 v/v) to give a disulfide spiropyran of structure (II) as a yellow solid (0.6 g, 46 %). MS calculated C₆₄H₈₄N₆O₈S₂: 1 128.6., Found [M]⁺: 1 128.6

EXAMPLE 10: Functionalized Gold Surface

The gold coated quartz crystal was incubated with 2 mM ethanolic disulfide spiropyran solution for 24 hours to prepare a self assembled monolayer of covalently attached spiropyran onto gold surface. The adsorption-desorption experiment was done using a quartz crystal microbalance with dissipation monitoring (QCM-D). The black line indicates the change in dissipation whereas the grey line indicates the change in dissipation for the 7th overtone (Fig. 9). The primary frequency of the quartz crystal used for this experiment was 5 MHz. The change in frequency is related to the mass adsorbed by Sauebrey equation (Saurbrey, Z. Z. Physica 1959, 155, 206-222):

Mass adsorbed (m) = 17.7 x (F7/7)

Where m is the mass adsorbed in ng/cm2

F7/7 is the normalized frequency (Hz) for the 7th overtone.

The RNase-A (2 μM) was adsorbed onto the spiropyran functionalized gold surface at a flow rate of 100 μl/min for -60 min followed by washing with the phosphate buffered saline (PBS) buffer. The change in dissipation after buffer was 15.5 Hz.

Irradiation of UV light (254 nm, 0.2 W/cm², -30 min) resulted in increase in frequency to 8 Hz due to desorption of protein and thermal stress of the crystal. Removal of the UV light released the thermal stress of the crystal and the final frequency was 1 1.5 Hz. The UV irradiation resulted in ~ 26 % release of the adsorbed protein from the spiropyran coated gold surface.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

Claims

WHAT IS CLAIMED IS:

1. A surfaced-modified substrate having at least a first operating state and a second operating state, comprising: a switchable compound having at least one measurable configurable property responsive to a change in at least one preselected condition; and a selected substrate having a substrate surface adapted to have said switchable compound deposited on at least a portion of said substrate surface to form said surface- modified substrate and to enable said surface-modified substrate to selectively switch between said at least first and second operating states in response to the change in said preselected condition; wherein said switchable compound retains the at least one measurable configurable property after deposition of said switchable compound on said substrate surface.

2. The surfaced-modified substrate of claim 1 , wherein the selected substrate is a polymeric material, an organic polymeric material or a polymeric material having radical generation sites, wherein the preselected condition is pH, radiation, ionic strength, electrical charge or a combination of two or more conditions thereof, and wherein the switchable compound is a vinyl monomer.

3. The surface-modified substrate of claim 1 , wherein the selected substrate is a polyethersulfone (PES) polymer membrane, a homogeneous blend of polyethersulfone polymer and phonoxy resin polymer, ultrafiltration membrane, a microporous membrane, UV-sensitive polymer, or a polymer sensitized with a sensitizing agent to undergo graft polymerization.

4. The surface-modified substrate of claim 1 , wherein the switchable compound is responsive to visible and UV light.

5. The surface-modified substrate of claim 1 , wherein the switchable compound enables the surface-modified substrate to assume the first operating state when exposed to visible light and the second operating state when exposed to UV light.

6. The surface-modified substrate of claim 5, wherein in the first operating state, the switchable compound deposited on the selected substrate has a closed, non-polar form, and wherein in the second operating state, the switchable compound deposited on the selected substrate has an open, polar form.

7. The surface-modified substrate of claim 5, wherein the first operating state is achieved by exposure of the surface-modified substrate to visible light for about 1 hour, and wherein the second operating state is achieved by exposure of the surface-modified substrate to UV light for about 1 hour at 254 nm.

8. The surface-modified substrate of claim 1 , wherein the switchable compound is a spiropyran compound, a spiropyran of structure (I), a disulfide spiropyran of structure (II), vinyl azobenzene (cis to trans), N-isopropylacrylamide, 2- (dimethylamine)ethylmethacrylate, N-methacryloyl-L-Lysine or O-methacryloyl-L-serine.

9. The surface-modified substrate of claim 1 , wherein the switchable compound is terminated by a vinyl group activatable by exposure to UV radiation, and is deposited on the selected substrate by UV-induced graft polymerization.

10. The surface-modified substrate of claim 3, wherein the sensitizing agent is benzophenone or AIBN.

1 1. The surface-modified substrate of claim 1 , wherein the substrate surface is on a valve of a microfluidic chamber or channel, a window of a car, a textile material, a glass surface or a sensor surface, and wherein switchable compound is uniformly, non- uniformly or randomly deposited on the selected substrate.

12. The surface-modified substrate of claim 7, wherein the selected substrate is a polyethersulfone (PES) polymer membrane, wherein the switchable compound is a vinyl spiropyran monomer responsive to light and UV light, and wherein the switchable compound is deposited on the selected substrate by exposure to 300-nm UV irradiation to induce grafting and polymerization.

13. The surface-modified substrate of claim 1 , wherein the substrate is a metallic substrate.

14. The surface-modified substrate of claim 13, wherein the substrate is a gold or gold-plated surface, and the switchable compound is deposited by covalent bonding.

15. A method of preparing the surface-modified substrate, comprising the steps of: providing a switchable compound having at least one measurable configurable property responsive to a change in at least one preselected condition; providing a selected substrate having a substrate surface adapted to have the switchable compound deposited on at least a portion of the substrate surface to form said surface-modified substrate and to enable the surface-modified substrate to selectively switch between the at least first and second operating states in response to the change in the preselected condition; contacting the switchable compound with the portion of the substrate surface having the switchable compound deposited thereon; and depositing the switchable compound on the substrate surface, wherein the switchable compound retains the at least one measurable configurable property after deposition of the switchable compound on the substrate surface.

16. The method of claim 15, wherein the substrate surface is on a valve of a microfluidic chamber or channel, a window of a car, a textile material, a glass surface or a sensor surface, and wherein the switchable compound is uniformly, non-uniformly or randomly deposited on the selected substrate.

17. The method of claim 15, wherein the selected substrate is a polyethersulfone (PES) polymer membrane, wherein the switchable compound is a spiropyran monomer responsive to light and UV light, wherein the contacting step comprises immersing the polyethersulfone (PES) polymer membrane in a solution containing spiropyran monomer, wherein the polyethersulfone (PES) polymer membrane is removed from the solution before the grafting step, wherein the depositing step comprises irradiating the polyethersulfone (PES) polymer membrane with 300-nm UV light to graft and polymerize spiropyran monomer onto the substrate surface.

18. The method of claim 15, wherein the selected substrate is a polymeric material, an organic polymeric material or a polymeric material having radical generation sites, wherein the preselected condition is pH, radiation, ionic strength, electrical charge or a combination of two or more conditions thereof, and wherein the switchable compound is a vinyl monomer.

19. The method of claim 15, wherein the selected substrate is a polyethersulfone (PES) polymer membrane, a homogeneous blend of polyethersulfone polymer and phonoxy resin polymer, ultrafiltration membrane, a microporous membrane, UV- sensitive polymer, or a polymer sensitized with a sensitizing agent to undergo graft polymerization.

20. The method of claim 15, wherein the switchable compound enables the surface-modified substrate to assume the first operating state when exposed to visible light, and to assume the second operating state when exposed to UV light, wherein in the first operating state, the switchable compound deposited on the selected substrate has a closed, non-polar form, and wherein in the second operating state, the switchable compound deposited on the selected substrate has an open, polar form.

21. The method of claim 20, wherein the first operating state is achieved by exposure of the surface-modified substrate to visible light for about 1 hour, and wherein the second operating state is achieved by exposure of the surface-modified substrate to UV light for about 1 hour at 254 nm.

22. The method of claim 15, wherein the switchable compound is a spiropyran compound, a spiropyran of structure (I), a disulfide spiropyran of structure (II), vinyl azobenzene (cis to trans), N-isopropylacrylamide, 2-(dimethylamine)ethylmethacrylate, N-methacryloyl-L-Lysine or O-methacryloyl-L-serine.

23. The method of claim 15, wherein the switchable compound is terminated by a vinyl group activatable by exposure to UV radiation, and is deposited on the selected substrate by UV-induced graft polymerization.

24. The method of claim 19, wherein the sensitizing agent is benzophenone or

AIBN.