The oxytocin receptor (OTR) plays a key role in regulating vital physiological functions and is implicated in cancer, pain, and various psychiatric and neurodevelopmental disorders. However, progress in understanding its functional roles in (patho)physiological conditions has been limited by the lack of reliable molecular tools able to accurately and reproducibly detect oxytocin receptor. To address this, we have firstly developed highly potent and selective fluorescent peptide tracers that allow precise localization and functional studies of OTR. Our tracers showed efficient OTR labeling, activation, and internalization in cellular bioassays in both live and fixed overexpression and primary cell systems. Furthermore, the tracers enabled single-molecule tracking of OTR using super-resolution live-cell microscopy and facilitated the isolation of OTR-expressing cells from mixed receptor populations via fluorescence-activated cell sorting (FACS). These capabilities highlight their broad utility for live-cell applications. Secondly, we have produced 13C-labelled oxytocin (OT) via solid-phase peptide synthesis using in house manufactured 13C labelled Fmoc-amino acid building blocks. Both building blocks and 13C-lablled OT showed high isotopic labelling efficiency. 13C-lablled OT was administered intranasal to the Sprague Dawley Rats (10 ug OT will be given to each nostril for a total of 20 ug labeled OT per rat). After 30- and 60-min full brain, truncal blood and cerebrospinal fluid were collected, frozen and stored for processing and quantification via high-resolution LC-MS. Results of this study will provide significant findings on localization of oxytocin receptor via two independent yet complementary approaches and allow quantification of exogenously applied oxytocin levels.