Method of detecting target substance and target-substance detection kit

A detection method of detecting presence or absence of, or a concentration of a target substance in a sample solution through detection of presence or absence of, or a number of magnetic markers, comprising the steps of:

• (1) reacting the target substance in the sample solution with a first target substance trapping member immobilized on a sensing element and with a second target substance trapping member immobilized on a gel particle, and forming a composite material by bonding the first target substance trapping member and the second target substance trapping member through intermediation of the target substance, thereby holding the gel particle on the sensing element;
• (2) adjusting a magnetic marker precursor comprising the gel particle and a magnetic material precursor existing in the gel particle by bringing the magnetic material precursor into contact with the gel particle which is held on the sensing element through formation of the composite material;
• (3) synthesizing a magnetic material from the magnetic material precursor held on the gel particle, thereby adjusting the magnetic markers comprising the gel particle and the magnetic material existing in the gel particle;
• and
• (4) detecting the presence or absence of, or the number of the magnetic markers with the sensing element.