A cartridge for apparatus for analysing a sample comprising a fluid as a flow cell for receiving the sample. The cell is formed from a substantially rigid support surface (102), a sensor comprising an electrical mechanical transducer (92), for example a wafer of quartz crystal and adhesive means, such as double sided adhesive tape (100) attaching the sensor to the support surface. The support surface and sensor are spaced from each other by a membrane, which may form part of the double sides adhesive tape so as to define the flow cell between the support surface and the sensor. The flow cell also has an opening (for example, 111) through which, in use, the sample passes. The sensor, forming part of the flow cell, comes into contact with the sample to enable the sample to be analysed.