Particles having a magnetic core and outer glass layer for separating biological material

Magnetic glass particles are prepared containing a magnetic core coated with a glass layer having a substantially pore-free glass surface. The particles are used for separating biological material such as nucleic acids. A preferred process of preparing the particles is by forming a mixture of magnetic cores with a sol formed from an alcohol and a metal alkoxide, spray-drying the mixture to coat the cores with a layer of gelled sol, and heating the coated cores to obtain the magnetic glass particles. Preferably, the particles have an average particle size of less than 100 .mu.m and any pores of the glass surface have a diameter of less than 10 nm. The magnetic core may be a composite material containing a mica core and magnetite particles immobilized on the mica core, and the glass layer may contain boron oxide. Magnetic core materials include magnetite (Fe.sub.3 O.sub.4) and Fe.sub.2 O.sub.3. In using the magnetic glass particles to separate a biological material, the particles are contacted with a fluid containing the biological material such that the biological material binds to the glass surface, and the bound biological material is separated from the fluid such as by using a magnetic field. Before applying a magnetic field, the magnetic particles may sediment when contacted with the biological material.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 Subject matter of the invention are magnetic particles having a glass
 surface, and a procedure for purifying a biological material, especially
 nucleic acids, using glass particles in the presence of chaotropic salts.
 Yet another subject matter of the invention is a procedure for isolating
 these biological materials and a procedure for concentrating biological
 materials and transferring them from solutions having a high concentration
 of salts to solutions having a low concentration of salts.
 2. Description of the Related Art
 Many biological materials, especially nucleic acids, present special
 challenges in terms of isolating them from their natural environment. On
 the one hand they are often present in very small concentrations and, on
 the other, they are often found in the presence of many other solid and
 dissolved substances that make them difficult to isolate or measure.
 For this reason, many procedures and materials for isolating nucleic acids
 from their natural environment have been proposed in recent years. In
 Proc. Natl. Acad. USA 76, 615-691 (1979), for instance, a procedure for
 binding nucleic acids in agarose gels in the presence of sodium iodide in
 ground flint glass is proposed.
 The purification of plasmid DNA from bacteria on glass dust in the presence
 of sodium perchlorate is described in Anal. Biochem. 121, 382-387 (1982).
 In DE-A 37 34 442, the isolation of single-stranded M13 phage DNA on glass
 fiber filters by precipitating phage particles using acetic acid and lysis
 of the phage particles with perchlorate is described. The nucleic acids
 bound to the glass fiber filters are washed and then eluted with a
 menthol-containing buffer in Tris/EDTA buffer.
 A similar procedure for purifying DNA from lambda phages is described in
 Anal. Biochem. 175, 196-201 (1988).
 The procedure known from the prior art entails the selective binding of
 nucleic acids to glass surfaces in chaotropic salt solutions and
 separating the nucleic acids from contaminants such as agarose, proteins
 or cell residue. To separate the glass particles from the contaminants
 according to the prior art, the particles are either centrifuged or fluids
 are drawn through glass fiber filters. This is a limiting step, however,
 that prevents the procedure from being used to process large quantities of
 samples.
 The use of magnetic particles to immobilize nucleic acids after
 precipitation by adding salt and ethanol is described in Anal. Biochem.
 201, 166-169 (1992) and PCT GB 91/00212. In this procedure, the nucleic
 acids are agglutinated along with the magnetic particles. The agglutinate
 is separated from the original solvent by applying a magnetic field and
 performing a wash step. After one wash step, the nucleic acids are
 dissolved in a Tris buffer. This procedure has a disadvantage, however, in
 that the precipitation is not selective for nucleic acids. Rather, a
 variety of solid and dissolved substances are agglutinated as well. As a
 result, this procedure can not be used to remove significant quantities of
 any inhibitors of specific enzymatic reactions that may be present.
 A porous glass in which magnetic particles are embedded is described in
 U.S. Pat. No. 4,233,169.
 Magnetic, porous glass is also available on the market that contains
 magnetic particles in a porous, particular glass matrix and is covered
 with a layer containing streptavidin. This product can be used to isolate
 biological materials, e.g., proteins or nucleic acids, if they are
 modified in a complex preparation step so that they bind covalently to
 biotin.
 SUMMARY OF THE INVENTION
 The task of the invention was to provide better materials for immobilizing
 biological materials and a simple procedure for isolating biological
 materials, especially nucleic acids, that is also suitable for use in
 routine diagnostic procedures.
 Subject matter of the invention are magnetic particles with an outer glass
 surface that is substantially pore-free, or that has pores with less than
 10 nm diameter. Yet another subject matter of the invention are
 ferromagnetic particles having a glass surface, a procedure for isolating
 biological materials, especially nucleic acids, and a procedure for the
 manufacture of magnetic glass particles.

DETAILED DESCRIPTION OF THE INVENTION
 Particles, according to the expert, are solid materials having a small
 diameter. Particles like these are often also referred to as pigments.
 According of the present invention, those particles are especially suited
 that have an average particle size of less than 100 .mu.m. More preferably
 they have an average particle size of between 10 and 60 .mu.m. The
 distribution of particle size is preferably relatively homogeneous. In
 particular, there are almost no particles &lt;10 .mu.m or &gt;60 .mu.m in size.
 Those materials are referred to as magnetic that are drawn to a magnet,
 i.e., ferromagnetic or superparamagnetic materials, for instance. In
 addition, those materials that are called softly magnetic are also
 understood to be magnetic, e.g., ferrites. Especially preferred according
 to the present invention are ferromagnetic materials, especially if they
 have not yet been premagnetized. Premagnetization in this context is
 understood to mean bringing in contact with a magnet, which increases the
 remanence. Especially preferred are ferromagnetic materials, such as
 magnetite (Fe.sub.3 O.sub.4) or Fe.sub.2 O.sub.3.
 An outer surface of a particle is understood to mean the contiguous surface
 from which perpendicular lines can be drawn outwards towards the
 particle's environment that do not cut through the particle itself.
 A pore is understood to be a recess in the outer surface of the particle.
 The surface reaches so far into the particle that a perpendicular line
 drawn in the recess on the surface cuts the particle at least once in the
 direction of the adjacent environment of the particle. In addition, pores
 reach into the particle to a depth that is greater than one radius of the
 pore.
 A glass according to the present invention is understood to be an amorphous
 material that contains silicium. Glass can contain other materials such as

B.sub.2 O.sub.3 (0-30%)
 Al.sub.2 O.sub.3 (0-20%)
 CaO (0-20%)
 BaO (0-10%)
 K.sub.2 O (0-20%)
 Na.sub.2 O (0-20%)
 MgO (0-18%)
 Pb.sub.2 O.sub.3 (0-15%)
 Glass can also contain a smaller percentage (0-5%) of a number of other
 oxides such as Mn.sub.2 O.sub.3, TiO.sub.2, As.sub.2 O.sub.3, Fe.sub.2
 O.sub.3, CuO, CoO, etc. Surfaces made of a composition of borosilicate
 glass, flint glass or silica have proven to be especially effective.
 Borosilicate glasses, which are especially preferred in terms of nucleic
 acid yield, have a boroxide content of more than 25%. A glass having a
 70/30 composition of SiO.sub.2 /B.sub.2 O.sub.3 is especially preferred.
 Especially preferred according to the present invention are glasses that
 are formed using the gel sol process and then dried and compressed. The
 basic principles of this process are known and were described, for
 instance, in C. J. Brinker, G. W. Scherer "Sol Gel Science--The Physics
 and Chemistry of Sol Gel Processing", Academic Press Inc. 1990, Sol-Gel
 Optics, Processing and Applications, Lisa C. Klein, Ed., Kluwer Academic
 Publishers 1994, p. 450 ff., and in DE-A-1941191, DE-A-3719339,
 DE-A4117041 and DE-A4217432. The principle has not been described for
 magnetic particles to date, however. The fact that the process could be
 used to create magnetic particles that have very surprising
 characteristics when used to isolate biological materials, especially
 nucleic acids, was not expected. In the gel-sol process, alkoxides of
 network-forming components, e.g., SiO.sub.2, B.sub.2 O.sub.3, Al.sub.2
 O.sub.3, TiO.sub.2, ZrO.sub.2, GeO.sub.2, combined with oxides and salts
 of other components, e.g., in an alcohol solution, and then hydrolized.
 The equation below describes the procedure for making sodium boroaluminium
 silicate glass:
 ##STR1##
 Water is added to begin the hydrolysis process of the starting components.
 The reaction proceeds relatively quickly because the alkali ions have a
 catalytic effect on the speed of hydrolysis of the silicic acid ester.
 Once the gel is formed it can be dried and densified by means of a thermal
 process to form glass.
 The sol:pigment ratio has a considerable effect on the yield of magnetic
 pigments provided by this invention. The ratio is limited by the fact that
 the portion of pigment must be so small that the mass created can still be
 pumped or sprayed. If the portion of the pigment is too small, the fine
 portion, e.g., of non-magnetic material, becomes too great and causes
 interference. Ratios of 10 to 25 g pigment: 100 ml sol were found to be
 useful in terms of pigment yield.
 To create a powder, the slurry is preferably sprayed through a nozzle and
 the aerosol is dried as it falls. The nozzle is preferably heated to speed
 up the drying of the slurry. Depending on the nozzle geometry, the nozzle
 temperature is preferably from 120 to 200.degree. C. A compromise is found
 by utilizing a sufficient evaporation speed but avoiding overheating.
 To optimize the yield, the densification temperature should be as high as
 possible. If it is too high, however, the particles will stick together
 and form agglomerates that must be sieved out. Additional treatment of the
 particles in at too high temperature will result in a loss of magnetic
 properties. Too high temperatures should therefore be omitted.
 A substantially pore-free surface is understood to mean a surface with
 pores (as described above) covering less than 5%, but preferably less than
 2%, and especially preferred, less than 0.1% of its area. If pores are
 present, they preferably have a diameter of less than 10 nm and,
 especially preferred, 1 nm.
 Especially preferred according to the present invention are particles that
 contain a mica core coated with TiO.sub.2 and magnetite particles
 immobilized on it. In this design, the composite material formed is
 surrounded by the glass layer. Both the core and the magnetite particles
 are crystalline and non-porous. The spaces on the surface of the mica that
 are not occupied by the magnetite particles are covered by a glass layer
 that is thicker than at the tips of the magnetite particles, basically
 resulting in a non-porous glass surface.
 The non-porosity of the magnetic particles is based only on the outer
 surface and not on the inside of the particle. The particle can therefore
 be porous on the inside only if the surface is enclosed by a substantially
 pore-free glass or a glass surface having pores with a diameter of less
 than 10 nm.
 Surprisingly, the magnetic particles provided by the invention are
 especially suited for isolating biological materials from samples. Long
 nucleic acids in particular are not destroyed--or only minimally--when
 they are immobilized on them. In addition, the core material is a natural
 resource and therefore causes little ecological concern. Moreover, the
 particles according to the invention are inexpensive and easy to
 manufacture.
 Yet another object of the invention are ferromagnetic particles having a
 glass surface. Superparamagnetic particles are described in the prior art.
 It has been demonstrated that ferromagnetic particles covered with a glass
 surface offer considerable advantages for isolating biological materials.
 If the ferromagnetic particles have not been brought in contact with a
 magnetic field, gravity is the only force that can cause them to sediment
 out. They can be resuspended easily and quickly by shaking the solution.
 The sedimentation procedure that does not utilize a magnetic field
 preferably proceeds more slowly than the immobilization of biological
 materials on the surface of the particles. This is especially true for
 nucleic acids. The ferromagnetic particles can be easily collected at a
 specific location in the sample fluid by means of a magnet. The fluid is
 then separated from the particles and, therefore, from the immobilized
 biological materials.
 The glass surface of the ferromagnetic particles provided by the invention
 can be pore-free or contain pores. For the reasons given above for the
 magnetic particles provided by the invention, it is preferable for the
 outer surface of the ferromagnetic particles to also be substantially
 pore-free or to have pores with a diameter of less than 10 nm. The
 ferromagnetic particles provided by the invention also preferably have a
 particle size of between 10 and 60 .mu.m, and especially preferred, of
 between 20 and 50 .mu.m. Especially preferred are particles with surface
 pores (if present) having a diameter of less than 10 nm and, especially
 preferred, 1 nm. An example of a ferromagnetic particle according to the
 invention is the composite material described-above which is made of mica
 and magnetite particles surrounded by a glass layer.
 Yet another object of the invention is a procedure for isolating a
 biological material by
 bringing a sample containing the biological material in a fluid in contact
 with the magnetic particles according to the invention or the
 ferromagnetic particles according to the invention under conditions in
 which the biological material binds to the particle surface, and
 separating the biological material from the fluid.
 Biological materials are understood to mean materials with a particular or
 molecular basis. They include, in particular, cells such as viruses or
 bacteria, as well as isolated human and animal cells such as leucocytes,
 and immunologically active low and high molecular chemical compounds such
 as haptens, antigens, antibodies and nucleic acids. Nucleic acids such as
 DNA or RNA are especially preferred.
 Samples according to the invention include clinical samples such as blood,
 serum, oral rinses, urine, cerebral fluid, sputum, stool, biopsy specimens
 and bone marrow samples. The sample can also be of a type used for
 environmental analysis, food analysis or molecular biology research, e.g.,
 from bacterial cultures, phage lysates and products of amplification
 procedures such as the PCR.
 The particles according to the invention have an inner core to which the
 outer glass surface is applied. The core can be a composite material, or
 it can be a simple iron core. The core can also consist of a crystalline,
 ceramic or glass-like structure in which iron oxide is embedded.
 The procedure described can be used to isolate native or modified
 biological material. Native biological material is understood to be
 material, the structure of which was not irreversibly changed compared
 with the naturally-occurring biological materials. This does not mean that
 other components of the sample can not be modified, however. If cells are
 isolated, for example, the medium surrounding the cells can be modified,
 but not the cells themselves. If nucleic acids are isolated, they should
 be cut or modified in their native form, i.e., non-denatured, not cut or
 not modified by coupling them with reactive groups. The concept of native
 biological material therefore does not encompass biotinylated nucleic
 acids in particular. Examples of native biological materials are phage DNA
 or cellular nucleic acids from blood.
 Modified biological materials include materials that do not occur in
 nature, e.g., nucleic acids that are modified by attaching to them groups
 that are reactive, detectable or capable of immobilization. An example of
 this are biotinylated nucleic acids.
 In certain cases the sample can be used without pretreatment in the
 isolation procedure according to the invention. In many cases, however,
 the sample should be lysed using an appropriate method, releasing the
 biological material contained in the sample. Procedures for lysing samples
 are known by the expert and can be chemical, enzymatic or physical in
 nature. A combination of these procedures is applicable as well. For
 instance, lysis can be performed using ultrasound, high pressure, by shear
 forces, using alkali, detergents or chaotropic saline solutions, or by
 means of proteinases or lipases.
 With regard for the lysis procedure to obtain nucleic acids, special
 reference is made to Sambrook et al.: Molecular Cloning, A Laboratory
 Manual, 2nd Addition, Cold Spring Harbour Laboratory Press, Cold Spring
 Harbour, N.Y. and Ausubel et al.: Current Protocols in Molecular Biology
 1987, J. Viley and Sons, N.Y.
 In addition to the biological material to be isolated, the sample can also
 contain other components in a fluid such as cell residue, proteins, salts
 and other substances that are not to be isolated. This sample, which
 preferably contains the biological material in native form, is brought in
 contact with the particles under conditions in which the target biological
 material binds to the particle surface. The conditions for this depend on
 the type of biological material involved, but are basically known. They
 also depend on the method by which the biological material is bound to the
 surface. If immunological interactions are utilized for the binding, for
 instance, conditions must be selected that are suitable for the formation
 of immunocomplexes. If modified nucleic acids are used, the binding can
 take place via the groups of nucleic acids that represent the
 modification, e.g., biotin via binding with streptavidin-coated surfaces.
 With nucleic acids in particular, however, a direct binding of nucleic
 acids to glass is preferred because among other reasons the nucleic acids
 do not have to be modified and even native nucleic acids can be bound. The
 procedure for binding native nucleic acids to glass particles can be
 analogous to the procedure described in the prior art. It is preferably
 performed in the presence of chaotropic salts with a concentration of
 between 2 and 8 mol/l, and preferably between 4 and 6 mol/l. Chaotropic
 salts can be sodium iodite, sodium perchlorate, guanidinium thiocyanate,
 guanidinium isothiocyanate or guanidinium hydrochlorite. Other compounds
 are also possible.
 To bring the sample in contact with the particles, the sample is mixed with
 the particles and incubated for a period of time sufficient for the
 binding to occur. Experts are usually familiar with the duration of the
 incubation step from procedures for performing treatment with non-magnetic
 particles. This step can be optimized by determining the quantity of
 immobilized biological material on the surface at different points in
 time. Incubation times of between 10 seconds and 30 minutes can be
 appropriate for nucleic acids.
 Depending on the size and type of magnetic particles, the particles either
 separate out of the fluid during the incubation period itself or the
 suspension remains intact for a longer period of time. If the particles
 are very small and superparamagnetic, the suspension remains intact for a
 longer period of time. If the particles are of larger size, the particles
 slowly separate out of the fluid during the incubation period. Aggregates
 of this nature form in particular when ferromagnetic particles are
 involved. When the ferromagnetic particles are not premagnetized, as is
 preferred, a very gentle separation is guaranteed.
 Immobilization is preferably not performed via precipitation by lowering
 the solubility of the materials to be immobilized. Rather, immobilization
 is based on biospecific interactions (capture molecules) or adsorption.
 This largely prevents contaminants from being non-specifically included.
 After incubation, the biological material is separated from the fluid. This
 is achieved in general by separating the material bound to the magnetic
 particles using a magnetic field. For instance, the magnetic particles can
 be pulled to the wall of the vessel in which incubation was performed. The
 fluid containing the sample contents that were not bound to the magnetic
 particles can then be removed. The removal procedure used depends on the
 type of vessel in which incubation was performed. Suitable steps include
 removing the fluid via pipetting or aspiration.
 The magnetic particles can then be purified one or more times using a wash
 solution, if desired. A wash solution is used that does not cause the
 biological material to be deliberated from the particle surface but that
 washes away the undesired contaminants as thoroughly as possible. This
 wash step preferably takes place by incubating the wash solution with the
 particles. The particles are preferable resuspended during this step,
 e.g., by means of shaking or applying a magnetic field that is not
 identical to the first magnetic field. The contaminated wash solution is
 preferably separated just like the sample in the step described above for
 binding the biological material.
 After the last wash step, the magnetic particles can be dried briefly in a
 vacuum, or the fluid can be allowed to evaporate. A pretreatment step
 using acetone may also be performed.
 If desired, the biological material purified in this manner can be
 separated from the magnetic particles. This step also depends on the
 manner in which the biological material was bound to the magnetic
 particles. If the biological material is native nucleic acids and the
 magnetic particles are glass-coated particles, the nucleic acids can be
 removed from the particles according to the invention using an elution
 buffer having a low salt content. Buffers of this nature are known from DE
 3724442 and Analytical Biochemistry 175, 196-201 (1988). The elution
 buffers with a low salt content are in particular buffers with a content
 of less than 0.2 mol/l. In an especially preferred embodiment, the elution
 buffer contains Tris. In another special embodiment, the elution buffer is
 demineralized water.
 In yet another embodiment, the purification and isolation procedure
 described is performed after the cells (e.g., viral particles or
 prokaryotic or eukaryotic cells) are separated immunomagnetically from a
 bodily fluid or tissue. In this step, the sample is incubated, e.g., while
 shaking, with magnetic particles to which an antibody against an antigen
 on the cell is immobilized. These particles can be particles according to
 the invention or commercially available particles (e.g., MACS Microbreads
 from Miltenyi Biotec GmbH, Bergisch Gladbach, Germany). After a magnetic
 field is applied, one or more wash steps are performed using a saline
 solution. Particles are obtained to which the desired cells are bound. The
 bound cells are then resuspended in a saline buffer. In a preferred
 embodiment, this saline buffer is a chaotropic saline solution so that the
 nucleic acids contained in the cell are released from the cells.
 An especially advantageous procedure for isolating nucleic acids from
 samples containing cells is achieved by combining the isolation of cells
 described above with the isolation of nucleic acids--preferable in their
 native form--also described above, on the magnetic particles according to
 the invention. The advantage of this embodiment is its potential
 simplicity (single-tube method), high sensitivity (especially important in
 medical microbiology and oncology), and the ease with which it can be
 automated.
 The biological materials isolated using the procedure according to the
 invention can now be used further as necessary. For instance, they can be
 used as a substrate for various enzymatic reactions. When nucleic acids
 are involved, they can be used for sequencing, radioactive or
 non-radioactive labelling, amplification of one or more of the sequences
 they contain, transcription, hybridization with labelled probe nucleic
 acids, translation or ligation. An advantage of the procedure according to
 the invention is that it is very easy to separate the biological material
 from the fluid. In the prior art, a centrifugation step was used to
 separate the glass particles from contaminants, or, when the biological
 material is bound to glass fiber filters the fluid is drawn through the
 filters. This is a limiting step that makes it difficult to process large
 quantities of sample.
 The biological materials can be separated from contaminants more
 effectively using the particles according to the invention. In particular,
 inhibitors for certain enzymatic reactions can be removed to a large
 extent according to the invention. The yield of biological material is
 relatively high. Fractionation of long nucleic acids was not observed. The
 particles according to the invention can preferably be magnetized more
 quickly.
 FIG. 1 illustrates the isolation of nucleic acids from a sample containing
 cells. The sample (specimen) that contains cells is pretreated in a
 sample-specific fashion so that the cells in which the nucleic acids are
 to be detected are present in the proper form.
 When samples are used from which bodily fluids were removed, for instance,
 this entails adding reagents, e.g., to liquify viscous samples such as
 saliva. An antibody bound to a solid phase, preferably a bead, that can
 detect and bind the cell is added to a vessel containing the sample
 treated in this fashion. Antigens on the cell surface have proven to be
 suitable partners for the antibody, for instance. The specificity of the
 antibody can depend on the specificity of the analysis to be performed. If
 the solid phase is the wall of the vessel, the cells are bound directly to
 the wall. If the solid phase is comprised of beads, they are separated
 from the fluid using suitable separation methods. This can be performed by
 means of filtration, for instance. If magnetic beads are used, they can be
 separated out by applying a magnetic field to the outside wall of the
 vessel. The separated cells are washed with a fluid to remove contaminants
 (that would interfere with the detection) along with the medium
 surrounding the cells. The conditions are preferably such that the cells
 are neither separated from the solid phase nor destroyed. The cells are
 then destroyed, i.e., lysed. This can be performed, for instance, by
 treating the cells with chaotropic salts. Other possibilities include the
 application of proteinases and detergents.
 In the preferred embodiment, the particles according to the invention are
 added to the lysis mixture. After a suitable period of time for the lysis
 to take place--which can be optimized by loading the surface with nucleic
 acids--the particles are separated from the surrounding fluid that
 contains additional cell components that are not to be detected. This is
 performed preferably by applying a magnetic field by placing a magnet
 against the vessel wall.
 To remove any contaminants that may still be present, a wash step is
 preferably performed with a fluid that does not cause the nucleic acids to
 be determined to be separated from the glass surface. An elution buffer
 having reagent conditions under which the nucleic acids separate from the
 glass surface is added to remove the nucleic acids from the glass surface.
 These conditions are low salt conditions in particular. Depending on the
 intended further use of the nucleic acids, the fluid can now be separated
 from the particles and processed further. This separation step is
 preferably performed via application of a magnetic field so that the
 particles are separated from each other.
 The following examples explain the invention in greater detail.
 EXAMPLE 1
 Manufacture of the Magnetic Particles According to the Invention
 Six different sols were used. The sols were manufactured as follows:
 Sol 1 (SiO.sub.2 :B.sub.2 O.sub.3 =7:3):
 Synthesis was performed in a 250 ml round flask while stirring constantly.
 86.6 ml tetraethyl orthosilicate
 +7 ml anhydrous, non-denatured ethanol
 +14.1 ml 0.15 M HCl
 A biphasal mixture is produced. Stir it at room temperature until it
 becomes a single phase. Add dropwise
 +37.8 ml trimethylborate
 then keep the sol at 50.degree. C. for 2 hours. Add
 +14.1 ml 0.15 M HCl
 Sol 2 (SiO.sub.2 :B.sub.2 O.sub.3 =4:1):
 Synthesis was performed in a 250 ml round flask while stirring constantly.
 100.5 ml tetraethyl orthosilicate
 +7 ml anhydrous, non-denatured ethanol
 +16.3 ml 0.15 M HCl
 A biphasal mixture is produced. Stir it at room temperature until it
 becomes a single phase. Add dropwise
 +25.6 ml trimethylborate
 then keep the sol at 50.degree. C. for 2 hours. Add
 +16.3 ml 0.15 M HCl
 Sol 3 (SiO.sub.2 :B.sub.2 O.sub.3 =85:15):
 Synthesis was performed in a 250 ml round flask while stirring constantly.
 107.8 ml tetraethyl orthosilicate
 +7 ml anhydrous, non-denatured ethanol
 +17.5 ml 0.15 M HCl
 A biphasal mixture is produced. Stir it at room temperature until it
 becomes a single phase. Add dropwise
 +19.4 ml trimethylborate
 then keep the sol at 50.degree. C. for 2 hours. Add
 +17.5 ml 0.15 M HCl
 Sol 4 (SiO.sub.2 :B.sub.2 O.sub.3 =4:1; 2 Mol % P.sub.2 O.sub.5):
 Synthesis was performed in a 250 ml round flask while stirring constantly.
 100.5 ml tetraethyl orthosilicate
 +7 ml anhydrous, non-denatured ethanol
 +16.3 ml 0.15 M HCl
 A biphasal mixture is produced. Stir it at room temperature until it
 becomes a single phase. Add dropwise
 +25.6 ml trimethylborate
 then keep the sol at 50.degree. C. for 2 hours. Add
 +16.3 ml 0.15 M HCl
 +1.63 g P.sub.2 O.sub.5
 Sol 5 (SiO.sub.2 :B.sub.2 O.sub.3 =4:1 Mol % Al.sub.2 O.sub.3):
 Synthesis was performed in a 250 ml round flask while stirring constantly.
 100.5 ml tetraethyl orthosilicate
 +7 ml anhydrous, non-denatured ethanol
 +16.3 ml 0.15 M HCl
 A biphasal mixture is produced. Stir it at room temperature until it
 becomes a single phase. Add dropwise
 +25.6 ml trimethylborate
 then keep the sol at 50.degree. C. for 2 hours. Add
 +16.3 ml 0.15 M HCl
 +3.06 9 AlCl.sub.3
 Sol 6 (SiO.sub.2 :B.sub.2 O.sub.3 =4:1 Mol % ZrO.sub.2):
 Synthesis was performed in a 250 ml round flask while stirring constantly.
 100.5 ml tetraethyl orthosilicate
 +7 ml anhydrous, non-denatured ethanol
 +16.3 ml 0.15 M HCl
 A biphasal mixture is produced. Stir it at room temperature until it
 becomes a single phase. Add dropwise
 +25.6 ml trimethylborate
 +5.15 ml zircon(IV)-proylate, 70% solution by weight in 1-propanol
 then keep the sol at 50.degree. C. for 2 hours. Add
 +16.3 ml 0.15 M HCl
 After another 2 hours at 50.degree. C., 22.5 g Iriodin 600 (black mica) was
 added for each 150 ml sol and stirred. It was then coated with a spray
 dryer (Buchi 190, Mini Spray Dryer). The temperature of the spray dryer
 nozzle was 134.degree. C.
 The powder obtained in the spray drying process was then subjected to a
 temperature treatment step in a nitrogen atmosphere (90 l/h). The
 temperature was increased at a rate of 1 k/min and the powder was
 maintained at a densification temperature for 2 hours. For coating with
 sol 1, this temperature was 750.degree. C., and 860.degree. C. for coating
 with sol 2. The temperature was 800.degree. C. for all other coating
 processes. After the temperature treatment process the oven was turned off
 and the powder was brought to room temperature. Agglomerates were sifted
 out using a 50 .mu.m sieve.
 EXAMPLE 2
 Manufacture of GMP1, GMP2, GMP3 and GMP4
 GMP1, GMP2, GMP3 and GMP4 are pigments from different production lots that
 were obtained from sol 1 (example 1) in a process described in example 1,
 under the following conditions:

Parameter GMP1 GMP2 GMP3 GMP4
 Aging of the sol (h) 36 36 36 36
 (30.degree. C.)
 Percentage of pigment in 5 15 8 20
 sol (g/100 ml)
 Nozzle air flow (%) 100 100 100 100
 Air pressure (bar) 6 6 6 3
 Nozzle temperature 135 120 130 143
 (.degree. C.)
 Densification tempera- 534 534 534 615
 ture (.degree. C.)
 subsequent O.sub.2 - (300.degree. C.) (300.degree. C.) (300.degree. C.)
 (400.degree. C.)
 treatment (1 hour)
 Pigment yield low high medium high
 DNA yield low high high high
 EXAMPLE 3
 PCR Sample Pretreatment from Human Whole Blood Using Magnetic Glass
 Particles
 Nucleic Acid Isolation
 10 mg each from 3 lots of glass magnetic particles (GMP 2-4) were placed in
 Eppendorf test tubes. The exact sample weights are indicated in Table 1.
 Three-fold determinations were performed.
 40 .mu.l proteinase K (20 mg/ml, made from lyophilisate) were added via
 pipetting to each 200 .mu.l of thawed whole blood and mixed immediately.
 In the next step, 200 .mu.l binding buffer (6 M guanidine-HCl, 10 mM
 Tris-HCl, 10 mM urea, 30% Triton X-100, pH 4.4) were added, mixed, and
 then incubated for 10 minutes at 70.degree. C. 200 .mu.l i-propanol were
 added, and the preparation was then mixed on the vortex mixer for 10
 seconds. The sample was left at room temperature for 20 minutes, then
 mixed once more for 10 seconds. The magnetic separation step was performed
 for at least 30 seconds in a magnetic particle separator from Boehringer
 Mannheim (ID# 1 641 794). The supernatant was removed and analyzed as
 described below.
 The magnetic particles were washed with 500 .mu.l wash buffer (20 mM NaCl,
 10 mM Tris-HCl, pH 7.5 (25.degree. C.), 80% ethanol) by mixing for 10
 seconds, leaving them at room temperature for 1 minute, then mixing for 10
 seconds. They were then pulled to the vessel wall using the magnetic
 particle separator. The supernatant was removed and discarded. The wash
 procedure was repeated until the wash fluid was colorless (4 times in
 all). The nucleic acids were then eluted 3.times. with 200 .mu.l each time
 of elution buffer prewarmed to 70.degree. C. (10 mM Tris-HCl, pH 8.5),
 then mixed for 10 seconds, left at room temperature for 10 minutes, and
 mixed for 10 minutes.
 Preparing the Supernatant
 The supernatant obtained after the first binding to the magnetic glass
 particles was investigated as follows for its nucleic acid content: the
 supernatant was placed in a filter tube (Boehringer Mannheim ID# 1744003,
 as provided in the High Pure PCR Product Purification Kit, for instance)
 and centrifuged for 1 hour at 8000 rpm in an Eppendorf tabletop
 centrifuge. The flow-through material was discarded and the filter tube
 was washed 2.times. with 500 .mu.l wash buffer (centrifugation as
 described above). The filter tube was centrifuged briefly to dryness, and
 then eluted with 2.times.200 .mu.l 1.times. elution buffer prewarmed to
 70.degree. C. by centrifuging once more.
 Analyzing the Eluate and Sample Supernatant
 10 .mu.l of sample buffer were added to 50 .mu.l of the eluate and the
 supernatant prepared using the filter tube, respectively. 45 .mu.l of this
 preparation were separated in an 0.8% agarose gel using electrophoresis at
 120 V for 90 minutes.
 Various dilutions of the eluate and the prepared supernatants were measured
 using spectroscopy at 260 and 280 nm in a Uvikon 710 (Kontron).
 Two 5 .mu.l aliquots of eluate were investigated in duplicate
 determinations using Expand.TM. Long Template PCR (Boehringer Mannheim ID#
 1681834) with specific primers for the human tPA gene (expected length of
 product: 15 kb).