In this work, we integrate µIMZI sensor as an element of a microfluidic system. In contrast to the work of Li et al. in , where the microfluidic channel was laser micromachined together with the microcavity inside an optical fiber, we have implemented an external microfluidic system capable to accommodate also additional elements of the microsystem, such as electrodes. Since the size of the sensing area is a way smaller than for other investigated up to date and integrated with microfluidics optical fiber sensors, the liquid exchange in the cavity has been discussed theoretically and experimentally. Moreover, to show possibility of combining other elements in such an approach, a multi-domain i.e., optical, and electrochemical (EC), µIMZI-based microfluidic system has been developed and analysed. In contrast to the sensing concept reported in , where EC reactions where initiated directly in the cavity, we investigated the capability of the system for optical measurements of EC reactions taking place outside the cavity. This solution is universal and allows for combining other devices with the system.