METHOD FOR IDENTIFYING HIGH-AFFINITY COMPLEXES MADE OF TWO LIGANDS AND ONE RECEPTOR, DEVICE FOR IMPLEMENTING THE METHOD AND SELF-ASSEMBLING CHEMICAL LIBRARY FOR USE IN THE METHOD

Abstract

The present invention relates to a method for the sensitive identification of high-affinity complexes made of two ligands (2, 3, 4, 5, 6, 7) and one receptor (1). A large number of different ligands (2, 3, 4, 5, 6, 7) of a chemical library are hereby contacted with at least one receptor (1) in a solution. The ligands of the library have a single-strand DNA (8, 9) or RNA with a base length of 2 to 10 bases or alternatively more than 10 bases. In addition, the solution is incubated for a specific period of time and complexes made of two ligands (2, 3, 4, 5, 6, 7) and one receptor (1) are identified.

Claims

1-29. (canceled)

30. A method for sensitive identification of high-affinity complexes made of two ligands and one receptor, comprising the steps of: i) interaction of a large number of different complexes made of ligands of a chemical library with at least one receptor in a solution, the ligands of the library having a single-strand DNA or RNA with a base length of more than 2 bases, which is bonded chemically covalently to the ligands, and only 2 to 10 bases of the single-strand DNA or RNA of a first part of the ligands being complementary to bases of the single-strand DNA or RNA of a second part of the ligands, and the ligands being complexed to form ligand complexes via hybridisation of the DNA or RNA; ii) incubation of the solution for a specific period of time, complexes made of ligand complexes and the receptor being produced; iii) identification of the resulting complexes made of ligand complexes and the receptor, wherein the solution is incubated at a temperature at which, between the first part of the ligands and the second part of the ligands, an equilibrium of hybridisation to form ligand complexes and dissociation to form free ligands arises.

31. The method according to claim 30, wherein only 3 to 9 bases of the single-strand DNA or RNA of a first part of the ligands are complementary to the single-strand DNA or RNA of a second part of the ligands.

32. The method according to claim 30, wherein the length of the DNA or RNA of the first part of the ligands and/or the length of the DNA or RNA of the second part of the ligands is at least 20 bases.

33. The method according to claim 30, wherein the first part of the ligands has L different ligands and the second part of the ligands has M different ligands so that L M difference ligand complexes are formed.

34. The method according to claim 30, wherein the solution is incubated in step ii) at a temperature of 1° C. to 50° C.

35. The method according to claim 30, wherein the solution is incubated in step ii) for a period of time of 0.1 to 48 hours.

36. The method according to claim 30, wherein the receptor is immobilized on a substrate selected from the group consisting of glass, ceramic, biopolymer, sepharaose, synthetic polymer and hydrogel.

37. The method according to claim 30, wherein the receptor comprises or consists of a protein, a DNA, a RNA, a cell and/or an organic molecule with a molecular mass ≤200 kDa.

38. The method according to claim 30, wherein the ligand comprise or consist of a molecule selected from the group consisting of protein, peptide, lipid, carbohydrate, dsDNA, ssDNA, dsRNA and ssRNA, aptamer, organic molecule with a molecular mass ≤200 kDa.

39. The method according to claim 30, wherein the complexes made of ligand complexes and the receptor are identified via an analytical method selected from the group consisting of mass spectrometry, HPLC, gas chromatography, IR spectroscopy and DNA sequencing of a DNA or RNA barcode.

40. The method according to claim 30, wherein the single-strand DNA or RNA in the first part of the ligands and/or the single strand DNA or RNA in the second part of the ligands comprises a base sequence which codes for the chemically covalently-bonded ligands.

41. The method according to claim 30, wherein the single-strand DNA or RNA of the ligands of the library is hybridized in regions to form a complementary base sequence of a further single-stranded DNA or RNA, 2 to bases on the further single-strand DNA or RNA of a first part of the ligands being complementary to bases of the single-strand DNA or RNA of a second part of the ligands and binding to the complementary bases, during the method, a Y-form being configured, and a ligase being added during the method, which ligates chemically covalently the further single-strand DNA or RNA of the first part of the ligands to the further single-strand DNA or RNA of the second part of the ligands.

42. The method according to claim 41, wherein, in the case of a single-strand DNA or RNA of a first part of the ligands, i) which has the ligand at the 5′ end thereof, has the bases which are complementary to the bases of the single-strand DNA or RNA of a second part of the ligands, at the 5′ end thereof, and the 2 to 10 bases of the further single-strand DNA or RNA, which are complementary to bases of the single-stranded DNA or RNA of a second part of the ligands, are disposed at the 3′ end of the further single-strand DNA or RNA; or ii) which has the ligand at the 3′ end thereof, has the bases, which are complementary to the bases of the single-strand DNA or RNA of a second part of the ligands, at the 3′ end thereof, and the 2 to 10 bases of the further single-strand DNA or RNA, which are complementary to bases of the single-strand DNA or RNA of a second part of the ligands, are disposed at the 5′ end of the further single-strand DNA or RNA.

43. A chemical library, comprising ligands which have bonded chemically covalently a single-strand DNA or RNA with a base length of more than 2 bases, wherein only 2 to 10 bases of the single-strand DNA or RNA of a first part of the ligands are complementary to bases of the single-strand DNA or RNA of a second part of the ligands.

44. The library according to claim 43, wherein only 3 to 9 bases of the single-stranded DNA or RNA of a first part of the ligands are complementary to the single-strand DNA or RNA of a second part of the ligands.

45. The library according to claim 43, wherein the length of the DNA or RNA of the first part of the ligands and/or the length of the DNA or RNA of the second part of the ligands is at least 20 bases.

46. The library according to claim 43, wherein the first part of the ligands has L different ligands and the second part of the ligands has M different ligands so that the library has LM different ligand complexes.

47. The library according to claim 43, wherein the ligands comprise or consist of a molecule selected from the group consisting of protein, peptide, lipid, carbohydrate, dsDNA, ssDNA, dsRNA and ssRNA, aptamer, organic molecule with a molecular mass ≤200 kDa.

48. The library according to claim 43, wherein the single-strand DNA or RNA of the ligands of the library is hybridised respectively in regions to form a complementary base sequence of a further single-strand DNA or RNA, 2 to 10 bases of a first further single-strand DNA or RNA of a first part of the ligands being complementary to bases of the second single-strand DNA or RNA of a second part of the ligands.

49. The library according to claim 48, wherein the single-strand DNA or RNA of a first part of the ligands, i) which has the ligand at the 5′ end thereof, has the bases, which are complementary to the bases of the single-strand DNA or RNA of a second part of the ligands, at the 5′ end thereof, and the 2 to 10 bases of the further single-strand DNA or RNA, which are complementary to bases of the second single-strand DNA or RNA of a second part of the ligands, are disposed at the 3′ end of the further single-strand DNA or RNA; or ii) which has the ligand at the 3′ end thereof, has the bases, which are complementary to the bases of the single-strand DNA or RNA of a second part of the ligands, at the 3′ end thereof, and the 2 to 10 bases of the further single-strand DNA or RNA, which are complementary to bases of the single-strand DNA or RNA of a second part of the ligands, are disposed at the 5′ end of the further single-strand DNA or RNA.

50. A method in which the library according to claim 43 is used for selective and sensitive identification of high-affinity ternary ligand-receptor complexes.

Description

[0072] The subject according to the invention is intended to be explained in more detail with reference to the subsequent Figures without wishing to restrict said subject to the specific embodiments illustrated here.

[0073] FIG. 1 shows a large number of different ligands 2, 3, 4, 5, 6, 7 of a chemical library and at least one receptor 1. The ligands 2, 3, 4, 5, 6, 7 are bonded respectively chemically covalently to a single-strand DNA 8, 9, the single-strand DNA 8, 9 having a base length of more than 10 bases. The single-strand DNA 8, 9 codes respectively for the respective ligand, to which it is bonded, via the base sequence thereof. In this embodiment, 18 bases of the single-strand DNA 8 of a first part of the ligands 2, 6, 7 are complementary to bases of the single-strand DNA 9 of a second part of the ligands 3, 4, 5 (see broken line between the single-strand DNAs 8, 9). Here only a specific ligand pair (formed by the ligands of the reference numbers 2 and 3) binds with high affinity to the receptor 1. Other ligand pairs (formed by the ligands of the reference numbers 4, 5, 6, 7) bind weakly as far as not at all to the receptor 1. As a result of the high number of complementary bases between the single-strand DNAs 8, 9 of two ligands 2, 3, 4, 5, 6, 7, the ligand complexes are stabilised, which causes high sensitivity during use thereof in a detection method. In order to achieve a dynamic of the hybridisation and dissociation, permanent heating (dissociation) and cooling (re-association or hybridisation), i.e. an energy supply, is necessary.

[0074] FIG. 2 shows an illustration corresponding to FIG. 1, with the difference that, in this embodiment, only 6 bases of the single-strand DNA of a first part of the ligands are complementary to bases of the single-strand DNA or RNA of a second part of the ligands (otherwise the molecules and references are identical to FIG. 1). As a result of the lower number of complementary bases, the advantage arises that the association (hybridisation) of two ligands is highly dynamic already at room temperature (15° C. to 30° C.), i.e. permanent hybridisation and dissociation takes place. The high-affinity binding to receptor, present in the case of specific ligand pairs, restricts the dissociation of these ligand pairs, as a result of which complexes made of receptor and high-affinity ligand pairs are populated for longer, “accumulate” in the course of time and finally are populated more highly in the equilibrium. It is advantageous in this embodiment that the dynamic of the association and hybridisation takes place at room temperature, i.e. in contrast to the embodiment of FIG. 1, no thermal energy need be supplied. The disadvantage of this embodiment is lower sensitivity than in the embodiment in FIG. 1 since the lower number of base pairs (6 instead of 18) makes the ligand complex and hence the complex of ligands with the receptor more unstable, as a result of which the latter is populated less highly in the equilibrium than in the embodiment in FIG. 1.

[0075] FIG. 3 clarifies, via a reaction equation, how the high-affinity ligand pairs “accumulate” as complex with the receptor in the course of time (see first arrow above). In addition to the molecules mentioned already from FIG. 1 and FIG. 2, the ligand pairs also have a single-strand DNA 10, 11 which is complementary respectively also to the single-strand DNA bonded covalently to the ligand (otherwise the molecules and references are identical to FIG. 1). This additional single-strand DNA 10, 11 can be generated for example via suitable primers and a PCR reaction. The lower arrow 12 symbolises a ligation reaction (e.g. by the addition of a ligase enzyme which leads to the two additional single-strand DNAs 10, 11 being ligated to each other chemically covalently. The advantage hereby is that the ligated DNA fragment is coded respectively for a specific ligand pair via the base sequence thereof, which pair can be hence identified easily via DNA sequencing.

[0076] FIG. 4 describes a microfluidic device according to the invention. Immobilised receptor, which was filled into the container via the opening 15 with valve is situated in a container 14. The container 14 is connected on the one side and on the other side to a pipe, through which a liquid can be guided. The pipe is in a zone which can be heated. Heating can be effected via an IR radiator as heating source 13. Furthermore the device has a cooling zone 17. Optionally, this zone comprises a cooling device. In addition, the pipe, here in the cooling region 17, has an outlet 16 with a valve out of which liquid with (free) ligands can be removed and can be supplied for analysis. In addition, after a specific incubation time, immobilised receptor charged with high-affinity ligands can be removed via the opening 15.

[0077] FIG. 5 shows the result of an experiment which verifies the effectiveness of the method according to the invention. Iminobiotin was used as ligand which has been bonded chemically covalently respectively to ssDNA (=im-ssDNA). The im-ssDNA was divided, in equal parts, into a first part of im-ssDNA1 and a second part of im-ssDNA2, im-ssDNA1 and im-ssDNA 2 having a different number of bases which are complementary to each other according to the experiment (e.g. 6 complementary bases in the case of “6-mer”). Im-ssDNA1 was coupled chemically covalently to the fluorescent dye Cy5 in order to enable, on the one hand, detection and quantification of free im-ssDNA1 or the free binary complex made of im-ssDNA1 and im-ssDNA2 without receptor and, on the other hand, detection of the ternary im-ssDNA1⋅im-ssDNA2⋅receptor complex. As receptor, immobilised streptavidin was used and, as solution, an aqueous buffer with pH 9.2 was used. The Figure shows the ratio of the quantity of ligand-receptor complex to ligands not bonded to the receptor (“bonded/unbonded” on the y-axis) under competitive conditions, i.e. in the presence of iminobiotin-free ssDNA (ssDNA) as example of a non-affine ligand (see “one-arm”, “6-mer”, “8-mer” and “21-mer” on the x-axis) or non-competitive conditions, i.e. without the presence of competitive ssDNA (“21-mer, no comp.” on the x-axis).

[0078] Apart from in the non-competitive experiment (“21-mer, no comp.” on the x-axis), the iminobiotin-free ssDNA was present in the solution in 300 times excess. In the experiment with the title “one-arm” (also a 6-mer), only im-ssDNA1 was present, i.e. no im-ssDNA2, so that no binary ligand complexes were able to be formed. The “one-arm” experiment hence shows the binding ratio for a monomeric iminobiotin to streptavidin. In direct comparison to the “6-mer” experiment, it becomes clear that, under the tested competitive conditions with dimeric iminobiotin (=binary ligand complex), the binding equilibrium is displaced clearly in the direction of ligand-receptor complex. This effect is more clearly pronounced by the higher stabilisation due to hybridisation of 8 base pairs in the “8-mer” experiment. If the number of complementary bases rises further however (e.g. here 21 complementary bases in the “21-mer” experiment), then the quantity of obtained ligand-receptor complex falls to a value which corresponds approximately to the value of the “one-arm” experiment.

[0079] This observation can be explained by the fact that the Cy5-labelled iminobiotin-bonded ssDNA (im-ssDNA1) is “trapped” in low-affinity binary complexes with iminobiotin-free ssDNA (ssDNA) and therefore can no longer bind to complementary Cy5-free, but iminobiotin-containing, ssDNA (im-ssDNA2). This effect is observed therefore only in the “21-mer” experiment since here a formed im-ssDNA1⋅ssDNA complex is so stable that, at room temperature (without further energy supply), dissociation of this complex in practice no longer takes place. In the case of a number of complementary bases of 6 and 8 bases (“6-mer” or “8-mer”), this effect does not however occur since here the formation of the im-ssDNA1⋅ssDNA complex is not static, but is dynamic and hence, in the case of this lower number of complementary bases, an iminobiotin-bonded ssDNA (im-ssDNA1) which is “blocked” by ssDNA becomes free again and can react with a further iminobiotin-bonded ssDNA (im-ssDNA2) to form a high-affinity binary complex. Consequently, in the case of a number of base pairs of 6 and 8, an “accumulation” of complexes made of receptor (here streptavidin) and high-affinity ligand pairs (here a pair of two iminobiotin-molecules) is achieved at room temperature, as a result of which this method is superior, with respect to sensitivity, to a static method. The sensitivity can be increased by a number of 21 base pairs being used and being alternately heated (dissociation) and cooled (hybridisation), i.e. energy is supplied.

[0080] FIG. 6 shows a Y-form which the total complex adopts in a preferred embodiment of the invention. The first ligand 2 which is bonded chemically covalently to the first single-strand DNA 8 has a portion 18 which codes for the first ligand 2. The second ligand 3 which is bonded chemically covalently to the second single-strand DNA 9 has a portion 19 which codes for the second ligand 3. Here, six bases of the first single-strand DNA 8 are complementary to six bases of the second single-strand DNA 9 and, during the method, can form base pairs 20 (see the lines between the single-strand DNAs 8, 9). Furthermore, the first single-strand DNA 8, in this embodiment, is hybridised in regions (here: at the 3′ end) with a first additional single-strand DNA 10. The first additional single-strand DNA 10 is characterised in that it comprises an “overhang” of two to twelve bases (here: five bases, located at the 3′ end thereof) which are complementary to two to twelve bases of the second single-strand DNA 9 (here: five bases) and which, with the complementary bases, can form base pairs 20 during the method (see the lines between the additional first single-strand DNA 10 and the second single-strand DNA 9).

[0081] If the second ligand 3 is hybridised via the second single-strand DNA 9 in regions with a suitable second additional DNA 11, then formation of the total complex is effected (here: in Y-form) such that the first additional DNA 10 is brought together with the second additional DNA 11 such that they can be ligated chemically covalently via addition of a ligase enzyme. If a ligase enzyme is added in the method, then it is achieved that ligation products of both single-strand additional DNAs 10, 11 which code for high-affinity ligand complexes accumulate in the course of the method. As a result, the sensitivity of detection thereof rises. Since the accumulation product concerns DNA, this can be amplified even further (e.g. by PCR), as a result of which the sensitivity of the method is increased again. In addition, sequencing of the ligated DNA allows a rapid conclusion to be made with respect to the two ligands 2, 3 since the ligated DNA has the portions 18, 19 which codes for both ligands 2, 3.

[0082] The invention can be characterized by the following aspects: [0083] 1. Method for sensitive identification of high-affinity complexes made of two ligands (2, 3, 4, 5, 6, 7) and one receptor (1), comprising the steps [0084] a) interaction of a large number of different complexes made of ligands (2, 3, 4, 5, 6, 7) of a chemical library with at least one receptor (1) in a solution, the ligands (2, 3, 4, 5, 6, 7) of the library having a single-strand DNA (8, 9) or RNA with a base length of more than 10 bases, which is bonded chemically covalently to the ligands (2, 3, 4, 5, 6, 7), and more than 10 bases of the single-strand DNA (8) or RNA of a first part of the ligands (2, 6, 7) being complementary to bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), and the ligands being complexed to form ligand complexes via hybridisation of the DNA (8, 9) or RNA; [0085] b) incubation of the solution for a specific period of time, complexes made of ligand complexes and the receptor (1) being produced; [0086] c) dissociation of the ligand complexes to form free ligands; [0087] d) re-hybridisation of the free ligands to form further ligand complexes; [0088] e) incubation of the solution for a specific period of time, further complexes made of the further ligand complexes and the receptor (1) being produced; [0089] f) identification of the resulting complexes made of ligand complexes and the receptor (1), [0090] characterised in that incubation takes place at a temperature at which the first part of the ligands (2, 6, 7) and the second part of the ligands (3, 4, 5) are hybridised in the solution to form ligand complexes, [0091] or comprising the steps [0092] i) interaction of a large number of different complexes made of ligands (2, 3, 4, 5, 6, 7) of a chemical library with at least one receptor (1) in a solution, the ligands (2, 3, 4, 5, 6, 7) of the library having a single-strand DNA (8, 9) or RNA with a base length of more than 2 bases, which is bonded chemically covalently to the ligands (2, 3, 4, 5, 6, 7), and only 2 to 10 bases of the single-strand DNA (8) or RNA of a first part of the ligands (2, 6, 7) being complementary to bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), and the ligands being complexed to form ligand complexes via hybridisation of the DNA (8, 9) or RNA; [0093] ii) incubation of the solution for a specific period of time, complexes made of ligand complexes and the receptor (1) being produced; [0094] iii) identification of the resulting complexes made of ligand complexes and the receptor (1), [0095] characterised in that the solution is incubated at a temperature at which, between the first part of the ligands (2, 6, 7) and the second part of the ligands (3, 4, 5), an equilibrium of hybridisation to form ligand complexes and dissociation to form free ligands (2, 3, 4, 5, 6, 7) arises. [0096] 2. Method according to aspect 1, characterised in that, if more than 10 bases of the single-strand DNA (8) or RNA of a first part of the ligands (2, 6, 7) are complementary to bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), the ligand complexes are dissociated by increasing the temperature of the solution, in particular to a temperature of 35° C. to 95° C., preferably 50° C. to 95° C., particularly preferably 70° C. to 95° C., in particular 80° C. to 95° C. [0097] 3. Method according to one of the preceding aspects, characterised in that, if more than 10 bases of the single-strand DNA (8) or RNA of a first part of the ligands (2, 6, 7) are complementary to bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), the dissociation of the ligand complexes is implemented in a part of the solution which is spatially at a spacing from the receptor, preferably such that the receptor is not functionally impaired by the conditions which lead to the dissociation. [0098] 4. Method according to one of the preceding aspects, characterised in that, if more than 10 bases of the single-strand DNA (8) or RNA of a first part of the ligands (2, 6, 7) are complementary to bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), the free ligands are re-hybridised by lowering the temperature of the solution, in particular to a temperature of 1° C. to 30° C., preferably 5° C. to 28° C., particularly preferably 10° C. to 25° C., in particular 15° C. to 20° C. [0099] 5. Method according to one of the preceding aspects, characterised in that, if more than 10 bases of the single-strand DNA (8) or RNA of a first part of the ligands (2, 6, 7) are complementary to bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), steps c) to e) are repeated at least once or twice, preferably at least 3 or 4 times, particularly preferably at least 5 or 6 times, in particular at least 7 or 8 times. [0100] 6. Method according to one of the preceding aspects, characterised in that, if more than 10 bases of the single-strand DNA (8) or RNA of a first part of the ligands (2, 6, 7) are complementary to bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), at least 20 bases, preferably at least 40 bases, particularly preferably at least 100 bases, in particular at least 200 bases, of the single-strand DNA (8) or RNA of a first part of the ligands (2, 6, 7) are complementary to the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5). [0101] 7. Method according to one of the preceding aspects, characterised in that, if only 2 to 10 bases of the single-strand DNA (8) or RNA of a first part of the ligands (2, 6, 7) are complementary to bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), only 3 to 9 bases, preferably only 5 to 9 bases, particularly preferably only 6 to 8 bases, of the single-strand DNA (8) or RNA of a first part of the ligands (2, 6, 7) are complementary to the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5). [0102] 8. Method according to one of the preceding aspects, characterised in that the length of the DNA (8) or RNA of the first part of the ligands (2, 6, 7) and/or the length of the DNA (9) or RNA of the second part of the ligands (3, 4, 5), is at least 20 bases, preferably at least 40 bases, particularly preferably at least 100 bases, in particular at least 200 bases. [0103] 9. Method according to one of the preceding aspects, characterised in that the first part of the ligands (2, 6, 7) has L different ligands (2, 6, 7) and the second part of the ligands (3, 4, 5) has M different ligands (3, 4, 5) so that LM different ligand complexes are formed. [0104] 10. Method according to one of the preceding aspects, characterised in that the solution is incubated in at least one of steps b), e) and ii) at a temperature of 1° C. to 50° C., preferably 5° C. to 37° C., particularly preferably 10° C. to 25° C., in particular 15° C. to 20° C. [0105] 11. Method according to one of the preceding aspects, characterised in that the solution is incubated in at least one of steps b), e) and ii) for a period of time of 0.1 to 48 hours, preferably 0.2 to 24 hours, particularly preferably 0.5 to 12 hours, in particular 1 to 6 hours. [0106] 12. Method according to one of the preceding aspects, characterised in that the receptor (1) is immobilised, preferably on a substrate selected from the group consisting of glass, ceramic, biopolymer, sepharose, synthetic polymer and hydrogel. [0107] 13. Method according to one of the preceding aspects, characterised in that the receptor (1) comprises a protein, a DNA, an RNA, a cell and/or an organic molecule with a molecular mass 200 kDa, preferably 100 kDa, particularly preferably 10 kDa, in particular 3 kDa, or consists thereof. [0108] 14. Method according to one of the preceding aspects, characterised in that the ligands (2, 3, 4, 5, 6, 7) comprise a molecule selected from the group consisting of protein, peptide, lipid, carbohydrate, dsDNA, ssDNA, dsRNA and ssRNA, aptamer, organic molecule with a molecular mass 200 kDa, preferably 100 kDa, particularly preferably 10 kDa, in particular 3 kDa, or consist thereof. [0109] 15. Method according to one of the preceding aspects, characterised in that the complexes made of ligand complexes and the receptor (1) are identified via an analytical method, preferably selected from the group consisting of mass spectrometry, HPLC, gas chromatography, IR spectroscopy and DNA sequencing, in particular via DNA sequencing of a DNA- or RNA barcode. [0110] 16. Method according to one of the preceding aspects, characterised in that the single-strand DNA (8) or RNA in the first part of the ligands (2, 6, 7) and/or the single-strand DNA (9) or RNA in the second part of the ligands (3, 4, 5) comprises a base sequence which codes for the chemically covalently-bonded ligands, this base sequence being hybridised preferably at least in regions to form a complementary base sequence of a further single-strand DNA or RNA. [0111] 17. Method according to one of the preceding aspects, characterised in that the single-strand DNA (8, 9) or RNA of the ligands (2, 3, 4, 5, 6, 7) of the library is hybridised in regions to form a complementary base sequence of a further single-strand DNA or RNA, 2 to 10 bases of the further single-strand DNA or RNA of a first part of the ligands (2, 6, 7) being complementary to bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5) and binding to the complementary bases, during the method, preferably a Y-form being configured, and a ligase being added during the method, which ligates chemically covalently the further single-strand DNA or RNA of the first part of the ligands (2, 6, 7) to the further single-strand DNA or RNA of the second part of the ligands (3, 4, 5). [0112] 18. Method according to aspect 17, characterised in that, in the case of a single-strand DNA (8) or RNA of a first part of the ligands (2, 6, 7), [0113] i) which has the ligand (2, 6, 7) at the 5′ end thereof, has the bases which are complementary to the bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), at the 5′ end thereof, and the 2 to 10 bases of the further single-strand DNA (10) or RNA, which are complementary to bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), are disposed at the 3′ end of the further single-strand DNA (10) or RNA; or [0114] ii) which has the ligand (2, 6, 7) at the 3′ end thereof, has the bases, which are complementary to the bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), at the 3′ end thereof, and the 2 to 10 bases of the further single-strand DNA (10) or RNA, which are complementary to bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), are disposed at the 5′ end of the further single-strand DNA (10) or RNA. [0115] 19. Microfluidic device for implementing the method according to one of the aspects 1 to 18, characterised in that the device comprises: [0116] a) a container (14) for receiving immobilised receptor (1), the container (14) having an access (15) with valve which serves for injection of ligands (2, 3, 4, 5, 6, 7) of a library and for isolation of ligand-receptor complexes and the container (14) having an inlet and an outlet for a fluid pipe; [0117] b) a fluid pipe which is connected to an inlet and an outlet of the container (14) and which has an outlet (16) with valve at one place; [0118] c) a heating device (13) which is disposed in a first region of the fluid pipe; and [0119] d) a cooling region (17) which is situated in a second region of the fluid pipe, different from the first. [0120] 20. Microfluidic device according to aspect 19, characterised in that the cooling region (17) has a cooling device and/or the cooling region (17) is disposed in the region of the outlet (16) with valve. [0121] 21. Microfluidic device according to one of the aspects 19 or 19, characterised in that the device has a pump which is disposed such that it can pump a liquid through the fluid pipe and/or the container (14) of the device has filters which prevent passage of immobilised receptor into the fluid pipe. [0122] 22. Chemical library, comprising ligands (2, 3, 4, 5, 6, 7) which have bonded chemically covalently a single-strand DNA (8, 9) or RNA with a base length of more than 2 bases, characterised in that only 2 to 10 bases of the single-strand DNA (8) or RNA of a first part of the ligands (2, 6, 7) are complementary to bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5). [0123] 23. Library according to aspect 22, characterised in that only 3 to 9 bases, preferably only 5 to 9 bases, particularly preferably only 6 to 8 bases, of the single-strand DNA (8) or RNA of a first part of the ligands (2, 6, 7) are complementary to the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5). [0124] 24. Library according to one of the aspects 22 or 23, characterised in that the length of the DNA (8) or RNA of the first part of the ligands (2, 6, 7) and/or the length of the DNA (8) or RNA of the second part of the ligands (3, 4, 5) is at least 20 bases, preferably at least 40 bases, particularly preferably at least 100 bases, in particular at least 200 bases. [0125] 25. Library according to one of the aspects 22 to 24, characterised in that the first part of the ligands (2, 6, 7) has L different ligands (2, 6, 7) and the second part of the ligands (3, 4, 5) has M different ligands (3, 4, 5) so that the library has LM different ligand complexes. [0126] 26. Library according to one of the aspects 22 to 25, characterised in that the ligands (2, 3, 4, 5, 6, 7) comprise a molecule selected from the group consisting of protein, peptide, lipid, carbohydrate, dsDNA, ssDNA, dsRNA and ssRNA, aptamer, organic molecule with a molecular mass 200 kDa, preferably 100 kDA, particularly preferably 10 kDa, in particular 3 kDa, or consist thereof. [0127] 27. Library according to one of the aspects 22 to 26, characterised in that the single-strand DNA (8, 9) or RNA of the ligands of the library is hybridised respectively in regions to form a complementary base sequence of a further single-strand DNA (10, 11) or RNA, 2 to 10 bases of a first further single-strand DNA (10) or RNA of a first part of the ligands (2, 6, 7) being complementary to bases of the second single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5). [0128] 28. Library according to aspect 27, characterised in that the single-strand DNA (8) or RNA of a first part of the ligands (2, 6, 7), [0129] i) which has the ligand (2, 6, 7) at the 5′ end thereof, has the bases, which are complementary to the bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), at the 5′ end thereof, and the 2 to 10 bases of the further single-strand DNA (10) or RNA, which are complementary to bases of the second single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), are disposed at the 3′ end of the further single-strand DNA (10) or RNA; or [0130] ii) which has the ligand (2, 6, 7) at the 3′ end thereof, has the bases, which are complementary to the bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), at the 3′ end thereof, and the 2 to 10 bases of the further single-strand DNA (10) or RNA, which are complementary to bases of the single-strand DNA (9) or RNA of a second part of the ligands (3, 4, 5), are disposed at the 5′ end of the further single-strand DNA (10) or RNA. [0131] 29. Use of the library according to one of the aspects 22 to 28 for selective and sensitive identification of high-affinity ternary ligand-receptor complexes.