Cytokine detection is an essential topic for biomedical research. Herein we demonstrated an ex-vivo device based on a silica optical fibre for monitoring of locally variable cytokine IL-6 concentrations using a sandwich immunoassay scheme. The fibre was designed to be introduced into the perforated catheter with micrometre size holes drilled along its length to enable fluid exchange between the outside and inside of the catheter. An exposed optical fibre (diameter 125 μm) modified with a layer of gold nanoparticles was functionalized with the IL-6 capture antibody to form the sensing interface. The IL-6 detection antibody which was loaded on the fluorescently labelled magnetic nanoparticles, was used for reporting the analyte signal. This device was successfully applied to detect cytokine IL-6 with the detection limit of 1 pg mL-1 in the sample volume of 1 μL. It has the linear detection range of 1-400 pg mL-1 and is capable of detecting localised IL-6 secreted by BV2 cells following their liposaccharide stimulation. This universal biological detection system is suitable as a platform for the in-vivo devices able to monitor multiple health conditions.