Measuring system for non-invasive in vivo measurement of blood analytes by Raman spectroscopy, the measuring system comprising a measuring probe with a housing having a skin engaging surface for engaging a subject's skin, the housing comprising - a first optical system (1,3,4) arranged for providing source light to the skin engaging surface wherein the source light is configured as a collimated beam to illuminate a surface of the skin by said collimated beam for penetrating the skin by said source light for interacting with the blood analytes, wherein angles between rays of light in the collimated beam are within a threshold value of 10 degrees; and - a second optical system (5,6,2) with an entrance configured to collect light from the illuminated part of the surface of the skin for capturing scattered Raman light from the blood analytes emanating from the illuminated surface of the skin for measurement of the blood analytes; wherein the first optical system (1,3,4) is arranged to provide the collimated beam at an oblique incidence angle (θi) with respect to a normal of the skin engaging surface; and wherein the entrance of the second optical system (5,6,2) is arranged at a distance (d) from the skin engaging surface outside a path of a specular reflection of the collimated beam off the illuminated part of the surface of the skin when the skin engaging surface engages the skin for spatially separating the scattered Raman light from the specular reflection; the system further comprising - a light source arranged for providing the source light to the measuring probe; - a spectrometer arranged for receiving the Raman light from the measuring probe and projecting a Raman spectrum of the Raman light; - a photodetector arranged for measuring the projected Raman spectrum; and - a processor arranged for reading out measurement data from the sensor and calculating a presence and/or concentration of the blood analytes based on the Raman spectrum; characterized in that the entrance of the second optical system (5,6,2) is configured to face towards the illuminated surface of the skin such that a majority of the scattered Raman light is collected from an illuminated region of the skin, wherein said illuminated region of the skin has an area of more than 5 mm 2. - a first optical system (1,3,4) arranged for providing source light to the skin engaging surface wherein the source light is configured as a collimated beam to illuminate a surface of the skin by said collimated beam for penetrating the skin by said source light for interacting with the blood analytes, wherein angles between rays of light in the collimated beam are within a threshold value of 10 degrees; and - a second optical system (5,6,2) with an entrance configured to collect light from the illuminated part of the surface of the skin for capturing scattered Raman light from the blood analytes emanating from the illuminated surface of the skin for measurement of the blood analytes; - a light source arranged for providing the source light to the measuring probe; - a spectrometer arranged for receiving the Raman light from the measuring probe and projecting a Raman spectrum of the Raman light; - a photodetector arranged for measuring the projected Raman spectrum; and - a processor arranged for reading out measurement data from the sensor and calculating a presence and/or concentration of the blood analytes based on the Raman spectrum;