The invention relates to a device (1) for detecting the emission of a target particle (6) at an emission wavelength, said device comprising: a photo-detector (2, 2A, 2B) comprising a sensitive detection surface having a high optical index; wherein said target particle (6) can be positioned in the vicinity of said sensitive surface in an analysis medium (13) having a low optical index; said device being characterized in that it further comprises: a mask (3) covering said sensitive surface, said mask including at least one area (4) opaque at said emission wavelength and at least one hole (5), said hole being capable of receiving the target particle; and in that the mask includes at least one interface; 7 said device further comprising at least one groove (10, 10A, 10B) provided at said interface, each of said at least one groove surrounding each of said at least one hole.