A photonic sensor chip (100, 200, 1000) comprising - a semiconductor substrate (112, 212, 1012) having a front side (114, 214, 1014) and a back side (116, 216, 1016); - at least one cavity (118, 218, 1018) extending from the back side (116, 216, 1016) through an entire depth of the semiconductor substrate (112, 212, 1012); - a front-end-of-line fabricated, hereinafter FEOL, photonic plane (124, 1024) located on the front side (114, 214, 1014) of the semiconductor substrate (112, 212, 1012) and comprising a FEOL waveguide made of crystalline silicon; - a back-end-of-line fabricated, hereinafter BEOL, electrical interconnect stack on top of the FEOL photonic plane; - comprised by the FEOL photonic plane, at least one photonic particle sensor element (120, 1020) with an active-surface element (122, 222, 1022) having an exposed active surface facing towards the back side (116, 216, 1016) of the semiconductor substrate (112, 212, 1012) and configured for capturing selected particles from at least one fluid or gas to which the active surface is exposable, wherein the least one cavity (118, 218, 1018) provides access to the active surface from the back side (116, 216, 1016) of the semiconductor substrate (112, 212, 1012); wherein - the photonic particle sensor element (120, 1020) is configured to receive an optical input wave via the photonic plane (124, 1024), to expose particles captured by the active-surface element (122, 222, 1022) to interact with the optical input wave and to provide a resulting optical output wave having a spectral component indicative of the interaction between the optical input wave and the captured particles; and wherein - the FEOL waveguide is arranged in the FEOL photonic plane and, in sections outside the cavity, embedded between the semiconductor substrate (112, 212, 1012) and the BEOL electrical interconnect stack, and extending from the sections outside the cavity into the cavity, to and from the active-surface element, for guiding the optical input wave to the active-surface element and for guiding the resulting optical output wave from the active-surface element to a light detector of the photonic particle sensor element, which is configured to generate an output signal in response to receiving the optical output wave; the photonic sensor chip further comprising - an electrically drivable phase shifter element, which is configured to set and maintain a predetermined phase shift to be effected by the active-surface element alone, that is, without influence by particles to be detected. - a semiconductor substrate (112, 212, 1012) having a front side (114, 214, 1014) and a back side (116, 216, 1016); - at least one cavity (118, 218, 1018) extending from the back side (116, 216, 1016) through an entire depth of the semiconductor substrate (112, 212, 1012); - a front-end-of-line fabricated, hereinafter FEOL, photonic plane (124, 1024) located on the front side (114, 214, 1014) of the semiconductor substrate (112, 212, 1012) and comprising a FEOL waveguide made of crystalline silicon; - a back-end-of-line fabricated, hereinafter BEOL, electrical interconnect stack on top of the FEOL photonic plane; - comprised by the FEOL photonic plane, at least one photonic particle sensor element (120, 1020) with an active-surface element (122, 222, 1022) having an exposed active surface facing towards the back side (116, 216, 1016) of the semiconductor substrate (112, 212, 1012) and configured for capturing selected particles from at least one fluid or gas to which the active surface is exposable, wherein the least one cavity (118, 218, 1018) provides access to the active surface from the back side (116, 216, 1016) of the semiconductor substrate (112, 212, 1012); wherein - the photonic particle sensor element (120, 1020) is configured to receive an optical input wave via the photonic plane (124, 1024), to expose particles captured by the active-surface element (122, 222, 1022) to interact with the optical input wave and to provide a resulting optical output wave having a spectral component indicative of the interaction between the optical input wave and the captured particles; and wherein - the photonic particle sensor element (120, 1020) is configured to receive an optical input wave via the photonic plane (124, 1024), to expose particles captured by the active-surface element (122, 222, 1022) to interact with the optical input wave and to provide a resulting optical output wave having a spectral component indicative of the interaction between the optical input wave and the captured particles; and wherein - the FEOL waveguide is arranged in the FEOL photonic plane and, in sections outside the cavity, embedded between the semiconductor substrate (112, 212, 1012) and the BEOL electrical interconnect stack, and extending from the sections outside the cavity into the cavity, to and from the active-surface element, for guiding the optical input wave to the active-surface element and for guiding the resulting optical output wave from the active-surface element to a light detector of the photonic particle sensor element, which is configured to generate an output signal in response to receiving the optical output wave; the photonic sensor chip further comprising - an electrically drivable phase shifter element, which is configured to set and maintain a predetermined phase shift to be effected by the active-surface element alone, that is, without influence by particles to be detected.