Method of releasing one or more droplets of a first fluid with one or more droplets of a second fluid within a microfluidic apparatus wherein the method comprises - providing a main channel carrying one or more droplets of the second fluid immersed in a carrier fluid, - providing an auxiliary channel, formed as a reservoir having a predefined closed volume and comprising the first fluid, fluidly coupled to the main channel at two intersections (T1, T2), with a first intersection via a first orifice configured to create a first fluid interface between the carrier fluid and the first fluid in the auxiliary channel, and with a second intersection downstream to the first intersection via a second orifice configured to create a second fluid interface between the carrier fluid and the first fluid, - imparting a flow of the carrier fluid into the main channel, inducing therefrom a difference of pressure between the first and second orifice generating a balance condition such that a meniscus of the second fluid interface is maintained in the auxiliary channel, at the vicinity of the second orifice, - creating a balance deviation, with regard to the balance condition, greater than a predefined threshold, thereby triggering a release of a volume of the first fluid from the second fluid interface into the main channel, wherein the balance deviation with regard the balance condition at the second fluid interface is generated by: - at least one droplet of the second fluid passing in the main channel between the first intersection and the second intersection, thereby increasing the pressure drop and triggering a release of a volume of the first fluid from the second fluid interface, and/or - an actuator allowing a release of a volume of the first fluid from the second fluid interface. - providing a main channel carrying one or more droplets of the second fluid immersed in a carrier fluid, - providing an auxiliary channel, formed as a reservoir having a predefined closed volume and comprising the first fluid, fluidly coupled to the main channel at two intersections (T1, T2), with a first intersection via a first orifice configured to create a first fluid interface between the carrier fluid and the first fluid in the auxiliary channel, and with a second intersection downstream to the first intersection via a second orifice configured to create a second fluid interface between the carrier fluid and the first fluid, - imparting a flow of the carrier fluid into the main channel, inducing therefrom a difference of pressure between the first and second orifice generating a balance condition such that a meniscus of the second fluid interface is maintained in the auxiliary channel, at the vicinity of the second orifice, - creating a balance deviation, with regard to the balance condition, greater than a predefined threshold, thereby triggering a release of a volume of the first fluid from the second fluid interface into the main channel, - at least one droplet of the second fluid passing in the main channel between the first intersection and the second intersection, thereby increasing the pressure drop and triggering a release of a volume of the first fluid from the second fluid interface, and/or - an actuator allowing a release of a volume of the first fluid from the second fluid interface.