Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state
Reexamination Certificate
1999-09-01
2001-10-02
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
C117S005000, C117S925000, C117S927000
Reexamination Certificate
active
06296700
ABSTRACT:
The present invention relates to a method of producing a structured layer of defined functional molecules on the upper face of a basically substantially flat sheet substrate. For this purpose, the substrate is covered with a monolayer of crystalline cell surface layer (S-layer) containing protein deposited by recrystallisation.
The production of recrystallised S-layers from crystalline cell surface protein layers (bacterial surfaces) on a solid or liquid substrate is known. For example, the fabrication of multilayered S-layers from prokaryotic cells and their application as ultra-filtration membranes has been thoroughly described in EP-B1 154 620. At the present time there are about 400-600 known bacterial species whose cell surface layers have crystalline structures. The lattice contents of these structures are in the range of about 3 to 30 nm. By further developing this type of fabrication method it has been possible to create monolayers of S-layers with a two dimensional crystalline structure on sheet-like surfaces, for example silicon wafer. Experiments of this kind and their results are described in the article entitled, “Monomolecular reassembly of crystalline bacterial cell surface layer (S-layer) on untreated and modified silicon surfaces”, (D). Pum, U. B. Sleytr), published in Supramolecular Science 2 (1995) 193-197. S-layers crested on silicon wafers can be structured by exposure of the layers to radiation through a contact mask, with UV radiation of a predetermined wavelength, for example 193 nm, which results in the S-layer areas of this layer being exposed to UV radiation being ablated, so that the structure of the mask is imaged to the substrate positioned immediately behind it. For use of these structured S-layers on Si-layers in supramolecular engineering, (Supramolecular Engineering), for example for biosensors, functional molecules are deposited or intercalated on the non-ablated regions of the S-layer remaining on the substrate, and immobilised at a defined spacing and regularity became of the lattice structure of the S-layer. Work of this kind has been described, amongst others, in the publication entitled “Crystalline Bacterial Cell Surface Layers (S-Layers): From Cell Structure to Biomimetics”, Prog. Biophys. molec. Biol. Vol. 65, No. 1/2, pp 83-111, 1996.
Experiments of the above kind have similarly been carried out with so-called SAM-layers (
S
elf
A
ssembled
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ono
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ayers). In contrast to S-layers, SAM-layers are formed from elongated lipids, e.g. SH-lipids, which are bound to the surface of a substrate at one end by covalent bonds, and which have a complex function for binding a further SAM-layer or functional molecule at the other, free end. The application of SAM-layers for structured metallisation of a substrate is, for example, described in U.S. Pat. No. 5,079,600 (Schnur et al.). One disadvantage with SAM-layers as opposed to S-layers is, amongst others, that SAM-layers do not have a defined crystalline structure and therefore also no regular base structure for a defined deposition or intercalation of functional molecules, whereas S-layers, due to their strictly ordered lattice structure, facilitate a precisely defined, more or less dense deposition or intercalation of functional molecules. Moreover, with S-layers, access through the pores to the substrate subsequent to coating, for example electrolytic ions, is still possible with S-layers, which is not the case with SAM-layers. An important advantage of S-layers in contrast to SAM-layers is that S-layers can be deposited on a variety of substrates without any problems, e.g. on technologically interesting material types, such as silicon wafers.
The publication “Patterning of Monolayers of Crystalline S-layer Proteins on a Silicon Surface by Deep Ultraviolet Radiation”, Microelectronic Engineering 35 (1997) 297-300, describes a method of fabricating a structured layer in which predefined areas of an S-layer which has been deposited on the surface of the substrate or a previously deposited planarising layer are modified by exposure to short-wave UV radiation, and subsequently the S-layer, and, if appropriate, the planarising layer is removed in the exposed areas. An ArF and KrF excimer laser is used for the exposure, in which the S-layer can be completely removed applying a short exposure to ArF radiation, which is however in comparison only minimally affected by KrF radiation even with lengthier exposure. A resist layer positioned below the S-layer is exposed by KrF radiation and imaged, wherein the S-layer acts as a mask for the resist layer. Furthermore this document discloses the option of selective deposition of a complementary S-layer onto the pre-structured S-layer, as well as the reinforcement of the structured S-layer, in order to make this more resistant than with the plasma etch processes, by coupling additional ligands to the S-layer, through the deposition of heavy metal combinations or through electroless deposition of a metal layer.
What is, however, not indicated in the article in Microelectronic Engineering 35 is whether other structuring options, apart from ablation, exist to allow deposition or intercalation of a substance to just the unexposed areas, for example. Nor is it clear from the article what kind of layer the planarising layer is. The article similarly fails to mention the option for fabricating structures with different surface characteristics and leading from this the deposition of an S-layer only in the areas of the surface with increased hydrophobicity.
The latter option is dealt with in the document published within the priority interval entitled “Deep UV pattering of monolayers of crystalline S-layer protein on silicon surfaces”, Colloids and Surfaces B, Biointerfaces 8 (1997) 157-162. According to this document, deposition of the S-layer occurs only in the hydrophobic areas of a silicon wafer previously generated by creating a silicon oxide layer, the remaining silicon surface however, remains free.
It is, therefore, an object of the present invention to facilitate the comprehensive technological but cost-effective application of S-layers, and if applicable to exploit the available technology in the field of semiconductor processing.
These aims are met by a method of the type mentioned at the beginning, in that the upper face of the substrate being initially structures are fabricated on the upper surface of the substrate with different surface characteristics at least in relation to their hydrophobicity. A monolayer of protein-containing crystalline cell surface layer (S-layer) can be deposited onto this structured surface by recrystallisation, wherein this S-layer is deposited only on the structured areas of the surface displaying increased hydrophobicity, on account of the unusual quality of the S-layers, so that the structured S-layer automatically aligns itself to the defined structures of the substrate. Subsequently, one (single) sort of functional molecule can be immobilised on the S-layer, for example in order to carry out a sensor function. Functional molecules which are suitable are, e.g., enzymes, antibodies, ligands, or metals (metal clusters). Using the method according to the invention, a variety of sensors and their switching logic can be accommodated into a minimal space as required. The invention thus provides a technologically advantageous method, for example for application in sensor technology.
A simple accomplishment of this method, the surface of a substrate is divided into hydrophobic areas on the one hand, and hydrophobic areas on the other, by coating this substrate and structuring this coating by removing the coating in predefined regions, wherein the subsequent deposition of the S-layer by recrystallisation is performed on the hydrophobic areas. As an example, the substrate can be a silicon wafer with a structured oxide layer, in which the silicon surface can be transferred into a hydrophilic state, for example by using the RCA-cleaning method; whereas the regions with the oxide layer remain in an hydrophobic state and provide for t
Loschner Hans
Pum Dietmar
Sleytr Uwe B.
IMS-Ionen Mikrofabrikations Systems GmbH
Kunemund Robert
Vigil Thomas R.
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