A diagnostic device includes a photodiode formed by a body of semiconductor material having a first surface, an integrated optical structure on the first surface and having a second surface, and at least one detection region on the second surface. The at least one detection region includes at least one receptor that binds to a corresponding target molecule that can be mated with a corresponding marker, which, when excited by radiation having a first wavelength, emits radiation having a second wavelength that can be detected by the photodiode. The integrated optical structure includes at least a first layer of a first material having a first refractive index. The first layer has a thickness substantially equal to an integer and odd multiple of one fourth of the first wavelength divided by the first refractive index.