(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
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`(19) World Intellectual Property Organization
`International Bureau
`
`
`
`(43) International Publication Date
`29 May 2008 (29.05.2008)
`
`International Patent Classification:
`
`G03F 7/30 (2006.01)
`G03F 7/00 (2006.01)
`
`G03F 7/09 (2006.01)
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`International Application Number:
`PCT/SG2006/000362
`
`International Filing Date:
`24 November 2006 (24.11.2006)
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`(74)
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`(81)
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`(51)
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`(21)
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`(22)
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`(25)
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`(26)
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`(71)
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`(72)
`(75)
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`(10) International Publication Number
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`WO 2008/063134 A1
`
`LEE, Yong Yeow [SG/SG]; Block 113 Bedok Reservoir
`Road, #047242, Singapore 470113 (SG). LECK, Kwong
`J00 [SG/SG]; 5A Bartley Road, Singapore 539760 (SG).
`
`Agent: SCHIWECK, Wolfram; Viering, Jentschura &
`Partner, P.O. Box 1088, Rochor Post Office, Rochor Road,
`Singapore 911833 (SG).
`
`Designated States (unless otherwise indicated, for every
`kind of national protection available): AE, AG, AL, AM,
`AT, AU, AZ, BA, BB, BG, BR, BW, BY, BZ, CA, CH, CN,
`CO, CR, CU, CZ, DE, DK, DM, DZ, EC, EE, EG, ES, FI,
`GB, GD, GE, GH, GM, GT, HN, HR, HU, ID, IL, IN, IS,
`JP, KE, KG, KM, KN, KP, KR, KZ, LA, LC, LK, LR, LS,
`LT, LU, LV, LY, MA, MD, MG, MK, MN, MW, MX, MY,
`MZ, NA, NG, N1, NO, NZ, OM, PG, PH, PL, PT, RO, RS,
`RU, SC, SD, SE, SG, SK, SL, SM, SV, SY, TJ, TM, TN,
`TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW.
`
`Filing Language:
`
`Publication Language:
`
`English
`
`English
`
`except US):
`(for all designated States
`Applicant
`AGENCY FOR SCIENCE, TECHNOLOGY AND
`RESEARCH [SG/SG]; 20 Biopolis Way, #07—01 Centros,
`Singapore 138668 (SG).
`Inventors; and
`Inventors/Applicants (for US only): KIM, Nam Yong
`[KR/SG]; 56 Duchess Avenue, #04—05, Singapore 269199
`(SG). YING, Y. Jackie [US/SG]; 31 Toh Avenue, Sin—
`gapore 508056 (SG). ZHANG, Hua [CN/SG]; 10 Dover
`Rise, #12—10 Heritage View, Singapore 138680 (SG).
`
`(84)
`
`Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM,
`ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM),
`
`[Continued on next page]
`
`(54) Title: METHOD OF PRODUCING A PATTERN OF DISCRIMINATIVE WETTABILITY
`
`(57) Abstract: The present invention relates to a method of
`producing a pattern of discriminative wettability on the surface
`of a substrate (2). The method includes patterning the surface
`of the substrate such that a plurality of accessible surface ar
`eas is defined. The method also includes depositing only on
`the plurality of accessible surface areas photocatalytic matter
`(4), and depositing on the entire surface oxidisable matter (5).
`The oxidisable matter (5) is of a wettability that differs from
`the wettability of the photocatalytic matter (4), and at least es—
`sentially inert to an exposure of electromagnetic radiation that
`is sufficient to cause the photocatalytic matter (4) to catalyse
`the oxidation of the oxidisable matter (5). The method fur—
`ther includes exposing the entire surface to electromagnetic
`radiation, such that the photocatalytic matter (4) catalyses the
`oxidation of such oxidisable matter (5) that is in contact there—
`with. Thereby the oxidisable matter (5) is removed from the
`plurality of surface areas and the photocatalytic matter (4) on
`these surface areas exposed, While the oxidisable matter (5) is
`at least essentially preserved on the remaining surface of the
`substrate.
`
`
`
`
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`Published:
`European (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI,
`FR, GB, GR, HU, IE, IS, IT, LT, LU, LV, MC, NL, PL, PT, i with international search report
`RO, SE, SI, SK, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA,
`GN, GQ, GW, ML, MR, NE, SN, TD, TG).
`
`

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`WO 2008/063134
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`PCT/SG2006/000362
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`METHOD OF PRODUCING A PATTERN OF DISCRIMINATIVE WETTABILITY
`
`1
`
`FIELD OF THE INVENTION
`
`[001] The present invention relates to a method of producing a pattern of discriminative
`
`wettability on the surface of a substrate.
`
`BACKGROUND OF THE INVENTION
`
`[002] Microarrays of biomaterials, consisting of either DNA, proteins or cells, have
`
`found widespread applications in disease diagnosis, pathogen detection, biomarker discovery
`
`and analysis of biomarker interaction. Often the scope and performance of bio—microarrays
`
`are determined by the quality of coatings employed for surface patterning. Patterned surfaces
`
`have been fabricated by many methods including micro-contact printing micro-fluidic
`
`lithography and conventional photolithography.
`
`[003] Using such methods, hydrophilic-hydrophobic micropatterns have also been
`
`obtained. Kanta et al. (Langmuir [2005] 21, 5790-5794) obtained a silica pattern on a titania
`
`surface by photolithography using a photoresist on the titania surface, fOIIOWed by silica
`
`coating and subsequent heat exposure. However, the accurate removal of photoresist both by
`
`means of a photomask and a final thermal lift—off pose practical challenges Japanese patent
`
`application 2005-003803 discloses a method of manufacturing hydrophobicity difference
`
`patterns by irradiating fluoroalkylsilane coated glass in the presence of an additional titanium
`
`oxide coated glass plate. In the method of this publication, the two surfaces are separated by
`
`a distance of less than 200 um. A different approach of obtaining a micropattern generates a
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`surface with silicon—hydrogen bonds (English abstract of international patent application WO
`
`2006/046699). In some areas the silicon—hydrogen surface is then reacted with a water-
`
`repellent compound in a hydrosilylation reaction, While in other areas it is reacted to a
`
`hydrophilic area.
`
`[004] Methods such as micro—contact printing and micro-fluidic lithography have
`
`limited practical applications due to several disadvantages. They lack for example reliability
`
`and consistency, particularly in industrial scale—up. Furthermore, the methods of micro—
`
`contact printing and micro-fluidic lithography are often incompatible with popular coating
`
`conditions, such as long exposure to organic solvents or high—temperature vapour-phase
`
`deposition. Similarly, conventional photolithographic methods for surface patterning limit
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`5
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`10
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`15
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`20
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`WO 2008/063134
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`2
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`the range of coating reagents and methods available due to the presence of photoresist films.
`
`In addition, the photoresist films could leave residual materials on the surface, which could
`
`interfere with subsequent surface coating. Most important of all, these patterned surfaces can
`
`be used only once in spite of the significant fabrication cost and time involved.
`
`[005] These methods are generally also cost intensive, so that it would be desirable to
`
`provide a micropattern, at least parts of which can be reused without the requirement to
`
`produce a new substrate with an entire new pattern.
`
`[006] Furthermore the wettability properties of titanium oxide change upon storage, in
`
`particular after an exposure to irradiation such as UV light or storage under room light. In an
`
`10
`
`approach to avoid this disadvantage, Gu et al. (Angew. Chem. Int. Ed (2002) 41, 12, 2068-
`
`2070) suggested the fabrication of a fluoroalkylsilane film on a titanium oxide surface
`
`followed by two repeated steps of replacing the fluoroalkylsilane film in selected areas by
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`(1) polystyrene or silica spheres that are subsequently fluoridated, and (2) silica spheres.
`
`[007] Accordingly, it is an obj ect of the present invention to provide a method of pattern
`
`15
`
`of discriminative wettability on a surface that avoids these disadvantages and that can be
`
`reused without the requirement of fabricating an entire new substrate.
`
`SUMMARY OF THE INVENTION
`
`[008]
`
`In one aspect the present invention provides a method of producing a pattern of
`
`20
`
`discriminative wettability on the surface of a substrate. The method includes providing a
`
`substrate. The method further includes patterning the surface of the substrate. By a
`
`respective patterning a plurality of accessible surface areas is defined. The method also
`
`includes depositing only on said plurality of accessible surface areas photocatalytic matter.
`
`The method further includes depositing on the entire surface, including the plurality of
`
`25
`
`accessible surface areas, oxidisable matter. The oxidisable matter is of a wettability that
`
`differs from the wettability of the photocatalytic matter. The oxidisable matter is furthermore
`
`at least essentially inert to an exposure of electromagnetic radiation that is sufficient to cause
`
`the photocatalytic matter to catalyse the oxidation of the oxidisable matter. The method also
`includes exposing the entire surface to electromagnetic radiation. As a result
`the
`
`30
`
`photocatalytic matter catalyses the oxididation of such oxidisable matter that is in contact
`therewith. Thereby the oxidisable matter is removed from the plurality of surface areas. The
`
`photocatalytic matter on these surface areas is thereby exposed. Furthermore the oxidisable
`matter on the remaining surface of the substrate is at least essentially preserved. As a result a
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`WO 2008/063134
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`PCT/SG2006/000362
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`pattern of discriminative wettability is formed.
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`3
`
`[009] By this method of the invention the remaining area of the surface is thus covered
`
`with oxidisable matter. The plurality of surface areas is covered with photocatalytic matter.
`
`According to some embodiments of the method of the invention the photocatalytic matter is
`
`removed by etching, thereby uncovering the plurality of surface areas and exposing the
`
`substrate surface in the respective surface areas. The surface can then be reused for e.g.
`depositing photocatalytic matter thereon.
`
`[010] According to a particular embodiment, the method includes depositing on the
`
`entire surface, including the plurality of accessible surface areas, oxidisable matter that is
`
`hydrophobic. The hydrophobic oxidisable matter is of a lower wettability for water when
`
`compared to the photocatalytic matter. As indicated above,
`
`the hydrophobic oxidisable
`
`matter is at
`
`least essentially inert to an exposure of electromagnetic radiation that
`
`is
`
`sufficient to cause the photocatalytic matter to catalyse the oxidation of the hydrophobic
`
`oxidisable matter. As a result of exposing the entire surface to electromagnetic radiation the
`
`photocatalytic matter catalyses the oxididation of such hydrophobic oxidisable matter that is
`
`in contact
`
`therewith. Thereby the hydrophobic oxidisable matter is removed from the
`
`plurality of surface areas. The 'photocatalytic matter on these surface areas is thereby
`
`exposed. Furthermore the hydrophobic oxidisable matter on the remaining surface of the
`
`substrate is at
`
`least essentially preserved. As a result a pattern of discriminative
`
`hydrophobicity, and thereby of discriminative wettability, is formed.
`
`10
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`15
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`20
`
`[011] According to some embodiments, this method of the invention further includes
`
`depositing a substance, which may include a molecule with a linking moiety, on the
`
`photocatalytic matter that covers the plurality of surface areas. Depositing such matter may
`
`be used for immobilising a molecule on the plurality of surface areas, for example Via a
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`25
`
`respective linking moiety.
`
`[012]
`
`In another aspect the present invention provides a further method of producing a
`
`pattern of discriminative wettability on the surface of a substrate. This method also includes
`
`providing a substrate. The method further includes depositing on the entire surface of the
`
`substrate photocatalytic matter. Further, the method includes vapour coating the entire
`
`30
`
`surface with oxidisable matter. The oxidisable matter is of a wettability that differs from the
`
`wettability of the photocatalytic matter. The oxidisable matter is fiirthermore at
`
`least
`
`essentially inert to an exposure of electromagnetic radiation that is sufficient to cause the
`
`photocatalytic matter to catalyse the oxidation of the oxidisable matter. The method further
`
`

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`WO 2008/063134
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`.
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`PCT/SG2006/000362
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`4
`
`includes patterning the surface of the substrate. By a respective patterning a plurality of
`
`accessible surface areas is defined. The method also includes exposing only said plurality of
`
`accessible surface areas to electromagnetic radiation. As a result the photocatalytic matter
`
`catalyses the oxidation of such oxidisable matter that is in contact therewith. Thereby the
`
`oxidisable matter is removed from the plurality of surface areas. The photocatalytic matter
`
`on these surface areas is' thereby exposed. Furthermore the oxidisable matter on the
`
`remaining surface of the substrate is at least essentially preserved. As a result a pattern of
`
`discriminative wettability is formed.
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`10
`
`[013]
`In further aspect the present invention provides a further method of producing a
`pattern of discriminative wettability on the surface of a substrate. The method includes
`providing a substrate. The method further includes depositing on the entire surface of the
`substrate photocatalytic matter. Further, the method includes depositing on the entire surface
`
`oxidisable matter. The oxidisable matter is of a wettability that differs from the wettability of
`
`the photocatalytic matter. The oxidisable’matter is furthermore at least essentially inert to an
`
`15
`
`exposure of electromagnetic radiation that is sufficient to cause the photocatalytic matter to
`catalyse the oxidation of the oxidisable matter. The method further includes patterning the
`
`surface of the substrate. By a respective patterning a plurality of accessible surface areas is
`
`defined. The method also includes exposing only said plurality of accessible surface areas to
`
`electromagnetic radiation. As a result the photocatalytic matter catalyses the oxididation of
`
`20
`
`such oxidisable matter that is in contact therewith. Thereby the oxidisable matter is removed
`
`from the plurality of surface areas. The photocatalytic matter on these surface areas is
`
`thereby exposed. Furthermore the oxidisable matter on the remaining surface of the substrate
`
`is at least essentially preserved. The method further includes at least essentially removing the
`
`photocatalytic matter by means of etching. Thereby the method includes at least essentially
`uncovering the plurality of surface areas of the substrate. Thereby the method also includes
`
`25
`
`at least essentially preserving the oxidisable matter on the remaining surface of the substrate.
`
`As a result a pattern of discriminative wettability is formed.
`
`[014]
`
`In yet a further aspect
`
`the invention relates to a pattern of discriminative
`
`wettability on the surface of a substrate, obtained by a method of the present invention.
`
`30
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[015] The invention will be better understood with reference to the detailed description
`
`when considered in conjunction with the non-limiting examples and the accompanying
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`WO 2008/063134
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`PCT/SG2006/000362
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`drawings, in which:
`
`[016] Figure 1 depicts a surface of a substrate (2) with a pattern of discriminative
`
`wettability, as well as schematic indications referring to methods of producing a respective
`
`invention. The pattern includes
`pattern according to the present
`photocatalytic matter (4) and oxidisable matter (5).
`
`surface areas of
`'
`
`[017] Figure 2A depicts a schematic representation of a method according to the
`
`present invention. The box depicts the basic steps of the method. I: On a surface (1) of a
`
`substrate (2) a plurality of accessible surface areas (3) is patterned, on which photocatalytic
`
`matter is to be deposited. II: Photocatalytic matter (4) is deposited on the respective surface
`
`10
`
`areas. III: Since the photocatalytic matter (4) only covers the plurality of accessible surface
`
`areas,
`
`the remaining surface area of the substrate remains unaltered. IV: Hydrophobic
`
`oxidisable matter (5) is deposited on the surface (1). V: Both the previously unaltered
`
`surface of the substrate (2) and the photocatalytic matter (4) are covered with the
`
`hydrophobic oxidisable matter (5), which therefore covers the entire surface (1). VI: The
`
`15
`
`entire surface covered with the hydrophobic oxidisable matter
`
`(5)
`
`is exposed to
`
`electromagnetic radiation. VII: As a result
`
`the photocatalytic matter (4) oxidises the
`
`hydrophobic oxidisable matter (5) that is in contact therewith, causing the removal of such
`
`hydrophobic oxidisable matter that covers the photocatalytic matter (4). VIII: Optionally the
`
`uncovered titanium oxide may be removed by etching. IX: Thereby the substrate surface (1)
`
`20
`
`is uncovered in the plurality of surface areas and only the remaining surface area of the
`substrate remains covered by the hydrophobic oxidisable matter (5). X: As a further option, a
`
`substance that includes a molecule with a linking moiety (6) can be deposited on the
`
`plurality of surface areas. XI: Thereby the photocatalytic matter (4) is covered with such
`
`substance (6). XII: A target molecule (7) with an affinity for the linking moiety (6) can be
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`25
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`deposited on the plurality of surface areas. XIII: As a result, the target molecule (7) is
`
`immobilised via the molecule with a linking moiety (6). The substance including a molecule
`
`with a linking moiety (6), as well as any target molecule (7) immobilised thereon, may be
`
`removed together with the titanium oxide by etching (VIII). Alternatively, the substance
`
`including a molecule with a linking moiety (6),
`
`including any target molecule (7)
`
`30
`
`immobilised thereon, may be removed by exposing the entire surfaced to electromagnetic
`
`radiation (XIV). The uncovered titanium oxide may then be removed by etching (VIII). The
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`hydrophobic oxidisable matter may also be removed, for example by means of an oxygen
`
`plasma (XV).
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`WO 2008/063134
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`PCT/SG2006/000362
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`6
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`[018] Fig. 2B depicts a schematic representation of exemplary methods of depositing
`
`photocatalytic matter (4) on the plurality of surface areas (cf. Fig. 2A). According to one
`
`method, there is placed a photomask (4) above the surface (1) of a substrate (2), to cover the
`
`remaining surface (I) of the substrate.
`
`II: Using a sputter photocatalytic matter (4)
`
`is
`
`deposited on the surface. III: Due to the use of the photomask the photocatalytic matter (4)
`
`only covers the plurality of surface areas (of. Fig. 2A).
`
`[019] Fig. 2C depicts a schematic representation of a further method according to the
`
`present invention. On a surface (1) there is deposited photocatalytic matter (2) using a
`
`sputter (I). Hydrophobic oxidisable matter (5) is deposited on the substrate (1) (II). A
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`10
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`photomask (7)
`
`is placed above the hydrophobic surface (III), which is exposed to
`
`electromagnetic radiation (IV) via the photomask, causing the photocatalytic matter to
`
`catalyse the removal of hydrophobic oxidisable matter that covers the photocatalytic matter.
`
`Optionally the uncovered photocatalytic matter may be removed by etching (V), thereby
`
`exposing the substrate surface.
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`15
`
`[020] Figure 3 depicts examples of haloalkylsilanes that may be used as hydrophobic
`
`oxidisable matter in a method according to the invention.
`
`[021] Figure 4 depicts advancing or receding contact angles of water on mixed anatase-
`
`amorphous titanium oxide surfaces subjected to different periods of UV irradiation. The
`
`uncertainty in contact angle measurement was 3: 2°.
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`20
`
`[022] Figure 5A depicts a photograph of a glass chip with a surface that comprises a
`
`pattern of discriminative hydrophobicity. Stained aqueous solution (dark) is adsorbed only
`on the hydrophilic areas of the surface. Figure 5B shows a typical fluorescence image of a
`
`respectively patterned glass chip, where the wash solution (0.05 % Tween 20 in 50 mM Tris
`
`buffer containing 10 uM Fluorescein) is adsorbed only onto the hydrophilic glass areas.
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`25
`
`[023] Figure 6 depicts the adsorption and growth of HepG2 cells on hydrophilic areas
`
`of a surface produced according to a method of the invention, comprising pattern of
`
`discriminative hydrophobicity. Photos were taken on (A, D) day l, (B, E) day 6, and (C, F)
`
`day 8, after the chip was seeded with 0.8 pl of HepG2 cells (20 cells/pl).
`
`DETAILED DESCRIPTION OF THE INVENTION
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`30
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`[024] The present invention provides a method of producing a pattern of discriminative
`
`wettability on the surface of a substrate. Any surface may be used for the method of the
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`7
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`invention, on which a selected photocatalytic matter and selected oxidisable matter can be
`
`deposited (see below). The surface may for instance be of any shape and material, as long as
`
`it is capable of accommodating a photocatalytic matter and oxidisable matter, and as long as
`
`it is compatible with the selected conditions for depositing and irradiating. Any desired
`
`substrate may be used. Generally, the substrate may for example be made of or comprise any
`
`material, as long as its surface is suitable for the method of the invention (see above).
`
`Typically the substrate is of a solid material. As an example, a suitable surface, including a
`
`surface of such a substrate, may comprise a metal, a metalloid, ceramics, a metal oxide, a
`
`metalloid oxide or oxide ceramics. Examples of suitable metalloids include, but are not
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`10
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`limited to silicon, boron, germanium, antimony and composites thereof. Examples of
`
`suitable metals include, but are not limited to iron (e.g. steel), aluminium, gold, silver,
`
`chromium, tin, copper, titanium, zinc, aluminium, lead and composites thereof. A respective
`
`oxide of any of these metalloids and metals may be used as a metalloid oxide or metal oxide
`
`respectively. As an illustrative example, the surface may be of quartz or glass. As a finther
`
`15
`
`illustrative example, a silicon oxide or germanium oxide surface may be obtained by etching
`
`a silicon substrate or germanium substrate, respectively, with piranha solution, i.e. a mixture
`
`of sulphuric acid and hydrogen peroxide solution at a molar ratio of 7:3. Examples of
`
`ceramics include, but are not limited to, silicate ceramics, oxide ceramics, carbide ceramics
`
`or nitride ceramics.
`
`20
`
`[025] As indicated above,
`
`the surface of the substrate may be of any geometric
`
`properties. The surface may for example be at least essentially smooth. The surface may also
`
`be rough to any degree as long as it allows for the deposition of a selected photocatalytic
`
`matter and selected oxidisable matter. Where desired, the roughness of the surface may be
`
`altered. As an illustrative example, a metal oxide or metalloid oxide surface, e.g. a silicon
`
`25
`
`oxide surface, may be ground by means of sand paper (Ferrari, M., et a1. Applied Physics
`
`Letters (2006) 88, 203125-1—203125—3). As a further illustrative example, the surface may be
`
`etched (cf. 6. g. Cao, M. et al., J. Phys. Chem. B (2006) 110, 26, 13072-13075), for example
`using NaOH, KOI-I, a mixture of HF, HN03 and ethanol, a “buffered” HF solution
`
`containing NI-I4F, or by ion bombardment using reactive ion etching. In typical embodiments
`
`30
`
`the surface is at
`
`least essentially homogenous.
`
`In some embodiments the surface is
`
`furthermore at least essentially flat. The surface may be polar or apolar, e. g. hydrophilic or
`
`hydrophobic. It may for instance be of different, similar or of the same hydrophobic
`
`properties when compared to the properties of the hydrophobic oxidisable matter used in the
`
`method of the present invention.
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`PCT/SG2006/000362
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`8
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`[026] The method of the invention includes providing a substrate with a surface as
`
`described above and patterning the surface of the substrate such that a plurality of accessible
`
`surface areas is defined. Patterning the surface of the substrate usually includes selecting
`
`thereon a plurality of areas. On the plurality of surface areas photocatalytic matter is to be
`
`deposited as described below. The selected plurality of areas may include areas of any
`
`dimension and size. Some or all of the respective areas may be identical, similar or different
`
`in size and shape. In some embodiments all areas of the plurality of surface areas are
`
`identical. In some embodiments each area of the plurality of surface areas is of a maximal
`
`width in the plane of the surface that is that is below about 2 cm. As an example, the
`
`10
`
`maximal Width in the plane of the surface may be selected in the range of about 0.1 um to
`
`about 5 cm, such as the range of about 1 um to about 1 cm or the range of 10 um to about to
`
`about 10 mm, for instance the range of about 100 um to about 2000 um. As an illustrative
`
`example, the maximal width in the plane of the surface may be about 10 um to about 500
`
`mm. In some embodiments some or all areas of the plurality of surface areas may be of a
`
`15
`
`uniform width in the plane of the surface. An area of the plurality of surface areas may for
`
`instance be of the shape of a circle when viewed from above the respective surface. In other
`
`embodiments a respective area may include any number of widths in the plane of the surface.
`
`An area of the plurality of surface areas may for instance be of the shape of an egg, letters V,
`
`U, X or H, a triangle, a rectangle, a square, or any oligoedron. In some embodiments the
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`areas of the plurality of surface areas define a micro pattern. In some embodiments any
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`number of these areas, including all areas of the plurality of surface areas, is connected to
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`form a continuous pattern. In other embodiments any number of separate areas is arranged in
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`such a way that as a whole they appear as a pattern.
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`[027] Patterning the surface of the substrate may furthermore include the use of
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`additional matter in order to distinguish the selected plurality of areas from the remaining
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`area of the surface. As an example, the remaining surface of the substrate may be covered
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`with a mask, such as a photomask. It may in some embodiments be desired to select a
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`photomask with an elastomeric film/coating of a selected thickness. Such a selection may for
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`example be desired in order to improve the resolution of depositing photocatalytic matter on
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`the surface of the substrate. An elastomeric film is likely to improve the contact between the
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`mask and substrate and to minimize the diffusion of photocatalytic material between mask
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`and substrate. It may furthermore be desired to apply additional pressure to further improve
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`the contact. As another example, a photoresist may be deposited on the remaining surface of
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`the substrate (cf. Fig. 2B for a graphic illustration). As yet a further example a plurality of
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`stamps may be positioned above the plurality of accessible surface areas.
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`[028] The method of the invention further includes depositing only on the plurality of
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`accessible surface areas photocatalytic matter. The term "photocatalytic matter" as used
`herein refers to any matter that fulfils the following two conditions. Firstly, photocatalytic
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`matter is capable of catalysing a chemical reaction, such as an oxidation. Secondly, this
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`capability is altered when exposed to electromagnetic radiation such as light. Photocatalytic
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`matter may for instance be inactive when not exposed to electromagnetic radiation, but its
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`capability of catalysing a chemical reaction is accelerated or induced upon being exposed to
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`electromagnetic radiation. Photocatalytic matter may also be capable of catalysing a
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`chemical reaction when not exposed to electromagnetic radiation, but
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`the respective
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`capability is partially or completely lost upon exposure to electromagnetic radiation. In
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`typical embodiments, the photocatalytic matter becomes capable of catalysing a chemical
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`reaction once exposed to electromagnetic radiation.
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`[029] A respective chemical reaction typically results in degrading chemical compounds
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`and/or biological material. For the purpose of the method of the present invention the
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`photocatalytic matter should at least be capable of assisting or starting a chemical reaction
`that can be exploited to degrade a desired hydrophilic compound (see below). For this
`purpose there is in some embodiments no additional reagent required,
`in particular in
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`embodiments where the photocatalytic matter catalyses a degradation reaction itself (see the
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`2O
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`Examples below for an illustration). As an illustrative example, where titanium dioxide is
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`used as the photocatalytic matter, an exposure to light, in particular UV light, causes the
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`generation of active oxygen as a result of a photo redox reaction. The active oxygen is
`capable of oxidising matter in contact with or Vicinity to the titanium dioxide. A standard
`method used in the art to assess the photocatalytic activity of matter of interest includes
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`bringing 4-mtrophenol or rhodamine in vicinity or contact
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`to the matter of interest,
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`irradiating with e.g. UV light, and monitoring or determining the degradation of 4-
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`nitrophenol or respectively rhodamine. Another standard method includes contacting water
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`with the photocatalytic matter
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`[030] Any photocatalytic matter may be used in the method of the present invention that
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`is capable of causing selected oxidisable matter to be at least essentially degraded (see
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`below). The photocatalytic matter may for instance comprise a single photocatalytic
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`compound, a mixture of photocatalytic compounds or a composite material of compounds
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`that possesses photocatalytic activity. Two illustrative examples of a photocatalytic
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`compound are a metal oxide and a metal sulphide. Examples of a metal oxide include, but
`are not limited to, a titanium oxide, a tin oxide, a lanthanum oxide, a tantalum oxide, a
`gadolinium oxide, a tungsten oxide, a nickel oxide, a copper oxide, a niobium oxide, a
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`ruthenium oxide, a cerium oxide and any combination thereof. As three illustrative
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`examples, a titanium oxide, in the following also abbreviated as' TiOx (in which x is typically
`1 or 2), may be titanium dioxide, TiOz (in e.g. anatase or rutile forms), a niobium oxide may
`be Nb205, and a tantalum oxide may be Ta205. Three illustrative examples of a metal
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`sulphide are zinc sulphide, ZnS, molybdenum sulphide, M082, and cadmium sulphide, CdS.
`An illustrative example of a composite material of compounds that possesses photocatalytic
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`activity is a mixed oxide of at least two metals. Examples of a mixed oxide of at least two
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`metals include, but are not limited to, a zirconium/titanium oxide, a tantalum/titanium oxide,
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`a silver/chromium oxide, a silver/molybdenum oxide,
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`a silver/manganese oxide,
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`a
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`silver/tungsten oxide, a potassium/ cerium/tantalum oxide, a potassium/cerium/niobium
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`oxide.
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`[031] The photo catalytic matter may be of any wettability. It may for example be of the
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`same or a different wettability when compared to the surface of the substrate as provided in
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`the method of the invention. In some embodiments the photocatalytic matter is hydrophilic.
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`[032] Where desired, the photocatalytic matter may also include a cocatalyst molecule
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`such as platinum, palladium, ruthenium a ruthenium oxide, an iridium oxide or a nickel
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`oxide. Likewise, a dopant such as iron, palladium or a platinum complex may be used where
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`desired. Those skilled in the art will be aware of the fact that the photocatalytic activity of
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`respective matter, e.g. a metal oxide, may to any degree depend on the state and form of the
`matter used, including the presence of surface defects. Gong et al. (Nature Materials (2006)
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`5, 665-670) have for instance characterised the atomic steps on the surface of anatase TiOz,
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`which may be used as the photocatalytic matter in a method of the present invention, and
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`determined the stabilities of the respective oxide steps.
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`[033] The photocatalytic matter may be deposited by any means. In embodiments where
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`the photocatalytic matter is a metal oxide or a mixture of metal oxides, it may for example be
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`deposited by flame hydrolysis deposition (Fl-ID), plasma enhanced chemical vapour
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`deposition (PECVD), inductive coupled plasma enhanced chemical vapour deposition (ICP-
`CVD) or the sol-gel method. In some embodiments the photocatalytic matter is for example
`deposited by means of sputtering.
`In some embodiments the photocatalytic matter is
`deposited by means of the sol-gel process. As an illustrative example, a titanate sol may be
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`generated by hydrolysis of tetrabutyl-titanate or tetrapropyl-titanate. Any suitable protocol,
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`such as sol-gel protocols using acid-catalysed, base-catalysed and two-step acid—base
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`catalysed procedures may be followed. In some embodime