Real-time detection of the chemokine CXCL12 in urine samples by surface plasmon resonance

► We developed an effective SPR method to detect functional analytes in urine. ► The technique uses virions bearing a GPCR in the context of the cell membrane. ► We tested for CXCL12 in urine from rheumatoid arthritis patients. ► The use of virions is robust, simple and reproducible. ► The assay detects ligand binding in an environment that mimics in vivo conditions.