Microcantilever (MC) sensors can provide ultrasensitive bio-chemical detection. Monitoring the bending response of large arrays of MC sensors coated with a library of receptors will produce a characteristic 'breath-print' corresponding to the breath composition; this promises to be suitable for non-invasive medical diagnostics. While MC arrays with hundreds of individual sensors can be produced readily, conventional MC readout methods are not suitable for the parallel readout of tens or hundreds of individual sensors. We have developed a MC sensor-array readout method based on phase-shifting interferometric microscopy (PSIM) which allows for the simultaneous monitoring of the response of all MCs within the field of view of the readout microscope optics. Based on this sensor technology, we have built an exhaled breath-analysis research instrument for the Point of Care Diagnostics Development Unit at the University of Leicester, UK. In this paper, we describe the PSIM readout system and the breath-analysis instrument that will be used to test sensor surface coatings and develop sensor sets with response patterns suitable for clear correlation to patients' health condition.