A method for directly detecting the presence of a test substance in a test fluid, comprising:
- providing a first fluid, the test fluid, in which a test substance particle is present in a first case and the test substance particle is not present in a second case,
- wherein the test substance particle has binding sites of a first type,
- providing
- a first nanobead fluid containing a first magnetic nanobead with a complementary binding site of a first type,
- a second nanobead fluid containing a second magnetic nanobead with a binding site of a second type,
- a third nanobead fluid containing a non-magnetic nanobead with a complementary binding site of a first type, a complementary binding site of a second type, and a complementary binding site of a third type,
- a marker fluid containing a marker particle with a binding site of a third type,
- wherein, in the presence of corresponding binding partners in the same fluid,
- a binding site of a first type of a test substance particle forms a binding of a first type with a complementary binding site of a first type of a magnetic nanobead of a first type and/or of a non-magnetic nanobead,
- a binding site of a second type of a magnetic nanobead of a second type forms a binding of a second type with a complementary binding site of a second type of a non-magnetic nanobead,
- a binding site of a third type of a marker particle forms a binding of a third type with a complementary binding site of a third type of a non-magnetic nanobead,
- creating a second fluid
- by mixing the test fluid with the first nanobead fluid and mixing at least the first magnetic nanobead of the resulting fluid with the third nanobead fluid, whereupon the resulting fluid is referred to as the second fluid,
- removing the first magnetic nanobead from the second fluid by means of a first magnetic force,
- wherein, in the first case, the test substance particle bound to the first magnetic nanobead and the non-magnetic nanobead bound to the test substance particle are also removed from the second fluid
- or, in the second case, the non-magnetic nanobead remains in the second fluid,
- creating a third fluid
- by mixing the second nanobead fluid and the marker fluid into the second fluid, whereupon the mixture is referred to as the third fluid,
- removing the second magnetic nanobead from the third fluid by means of a second magnetic force,
- wherein, in the first case, due to the absence of the non-magnetic nanobead in the third fluid, the marker particle is not indirectly bound to the second magnetic nanobead, and therefore it remains in the third fluid after the second magnetic nanobead is removed, or
- wherein, in the second case, the non-magnetic nanobead is bound to the second magnetic nanobead and the marker particle is bound to the non-magnetic nanobead, and therefore the marker particle is removed from the third fluid together with the second magnetic nanobead and the non-magnetic marker particle.