Abstract text

A new detection method, for detecting a target substance using formation of an aggregate due to binding of a target substance and a binding substance that binds thereto, that is excellent in detection accuracy, and sensitivity, and a new detection reagent used for the same are provided. Modifying substances having a maximum diameter of about 50 nm or less bind to a binding substance that binds to a target substance, and a modified binding substance is prepared as a binding reagent. A target substance in a sample is detected by bringing this modified binding reagent into contact with the sample, and optically detecting an aggregate that is formed by binding of the modified binding substance and the target substance in the sample. Preferably, the modifying substance includes biotin or a biotin derivative and further includes avidin or an avidin derivative, and the avidin or the avidin derivative binds to the biotin or the biotin derivative. Further, preferably, the biotin or the biotin derivative binds to the binding substance via a spacer.