Novel paracellular marker based on ᴅ-dipeptide structure for highly sensitive quantification with UPLC-MS/MS for in vitro and in vivo blood-brain barrier permeability analysis. - Bay C; Mühlberg E; Uhl P; Stingl JC; Bajraktari-Sylejmani G; Burhenne J; Weiss J; Sauter M (Fluids and barriers of the CNS, 2026)