Abstract: The invention provides a biosensor for at least partial insertion in a fetal scalp, for monitoring an analyte in the body of the fetus, wherein the biosensor comprises a needle and a microdialysis element for sampling the analyte. The invention also provides a sensing system comprising the biosensor, configured to flow a liquid through the microdialysis element. The invention can be used for e.g. lactate sensing as well as releasing a pharmaceutical. Hence, the biosensor and/or sensing system may also be used for delivery of a pharmaceutical or nutrient to a fetus.

Abstract: The invention provides a method for labeling an analyte comprising a primary amino group, the method comprising: a. a labeling process comprising reacting the analyte with a dialdehyde in the presence of a label, wherein the label bears a charge, and b. an analysis process comprising subjecting the labeled analyte to MS, preferably LC-MS-MS. Herein, preferably, the labeling process comprises reacting an analyte with a dialdehyde, wherein the dialdehyde carries a label bearing a charge, to provide a labeled analyte carrying the charge. The present invention also provides a labeling method to provide a labeled analyte carrying a charge, wherein the labeling method comprises a labeling process comprising reacting an analyte with a dialdehyde, wherein the analyte comprises a primary amino group and wherein the dialdehyde carries a label bearing the charge. The dialdehyde is preferably an aromatic dialdehyde, most preferably an aromatic 1,2- or 1,3-dicarboxaldehyde.