A biosensor system comprising: a capsule comprising: a housing configured for ingesting in a mammal GI tract and having a longitudinal axis, at least some portions of the housing (5, 6, 7) being transparent to radiation of a sensing wavelength, and wherein the housing comprises a base wall facing in a direction having a primarily radial component, and first and second walls (6, 7) substantially facing each other in the longitudinal direction, said walls forming an external space which is open to access by fluids, a radiation emitter and a radiation detector arranged to emit radiation into said external space and to detect radiation from said external space, through said transparent portions of the housing, a drive circuit for the radiation emitter and a signal processing circuit linked to the detector, a wireless interface (50, 61, 60) with an antenna for wireless transmission of data to an external device and/or a processor for locally processing and storing detection data, characterized in that: the base wall is transparent for detection of fluorescence light emitted in the radial direction within the external space, and the housing comprises a fluorescence detector arranged to detect fluorescence through the transparent base wall, and said detection may be simultaneously with absorption detection or separately from absorption detection. a capsule comprising: a housing configured for ingesting in a mammal GI tract and having a longitudinal axis, at least some portions of the housing (5, 6, 7) being transparent to radiation of a sensing wavelength, and wherein the housing comprises a base wall facing in a direction having a primarily radial component, and first and second walls (6, 7) substantially facing each other in the longitudinal direction, said walls forming an external space which is open to access by fluids, a radiation emitter and a radiation detector arranged to emit radiation into said external space and to detect radiation from said external space, through said transparent portions of the housing, a drive circuit for the radiation emitter and a signal processing circuit linked to the detector, a wireless interface (50, 61, 60) with an antenna for wireless transmission of data to an external device and/or a processor for locally processing and storing detection data, characterized in that: the base wall is transparent a housing configured for ingesting in a mammal GI tract and having a longitudinal axis, at least some portions of the housing (5, 6, 7) being transparent to radiation of a sensing wavelength, and wherein the housing comprises a base wall facing in a direction having a primarily radial component, and first and second walls (6, 7) substantially facing each other in the longitudinal direction, said walls forming an external space which is open to access by fluids, a radiation emitter and a radiation detector arranged to emit radiation into said external space and to detect radiation from said external space, through said transparent portions of the housing, a drive circuit for the radiation emitter and a signal processing circuit linked to the detector, a wireless interface (50, 61, 60) with an antenna for wireless transmission of data to an external device and/or a processor for locally processing and storing detection data, characterized in that: the base wall is transparent for detection of fluorescence light emitted in the radial direction within the external space, and the housing comprises a fluorescence detector arranged to detect fluorescence through the transparent base wall, and said detection may be simultaneously with absorption detection or separately from absorption detection. within the external space, and the housing comprises a fluorescence detector arranged to detect fluorescence through the transparent base wall, and said detection may be simultaneously with absorption detection or separately from absorption detection.