▎ 摘　　要

NOVELTY - Method (M1) for producing nanoparticle involves (a) producing fluorescent quantum dot, and (b) forming a hollow shell portion made of a magnetic material surrounding the core portion made of the quantum dots. The nanoparticle comprises a core portion made of fluorescent quantum dot, and a hollow shell portion made of a magnetic material surrounding the core portion. The nanoparticle for detecting or quantifying a target substance whose minimum inner diameter of the shell portion is larger than the maximum outer diameter of the core portion. USE - The method (M1) is useful for producing nanoparticle. The nanoparticle is useful in kit for detecting or quantifying target substance. The target substance is a virus, protein, peptide, DNA, or RNA (all claimed). ADVANTAGE - The method (M1) produces nanoparticle which detects target substance with high sensitivity in a rapid and simple manner. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following: (1) a method (M2) for detecting or quantifying a target substance involves using the nanoparticles produced by the above-mentioned production method (M1); and (2) a kit comprising the nanoparticles, and an electrochemical measurement electrode to which a probe specific to the target substance is bound.