Fluorescent optrode for proteins based on a diketopyrrolopyrrole derivative: Practical application to total protein determination in urine

•Methodology for protein quantification using a new optical sensor.•Application to determine total proteins in urine.•Diketopyrrolopyrrole (DPP) luminescent optical fibre sensor.•DPP derivative emits visible light as a solid.•Proteins in urine not statistically different with optrode and conventional method.