A microfluidic device comprises: a sensor provided in a sensing chamber; a liquid inlet and liquid outlet connecting to the sensor chamber for respectively passing liquid into and out of the sensing chamber and; a sample input port in fluid communication with the liquid inlet; a liquid collection channel downstream of the sensing chamber outlet; a flow path interruption between the liquid outlet and the liquid collection channel, preventing liquid from flowing into the liquid collection channel from upstream; a buffer liquid filling from the sample input port to the sensing chamber, and filling the sensing chamber and filing from the liquid outlet to the flow path interruption; an activation system operable to complete the flow path between the liquid outlet and the liquid collection channel such that the sensor remains unexposed to gas or a gas/liquid interface.