A detection device detects an analyte that may be contained in a specimen. The detection device includes a plurality of gold nanoparticles, an optical trapping light source, an illumination light source, an objective lens, an image pick-up device, and a computation unit. The plurality of gold nanoparticles are each modified with a probe DNA allowing the analyte to specifically adhere thereto. The optical trapping light source emits polarized light for assembling the plurality of gold nanoparticles together. The objective lens focuses and introduces the polarized light into a liquid containing a specimen and the plurality of gold nanoparticles. The image pick-up device receives light from the liquid. The computation unit detects an analyte based on a signal received from the image pick-up device.