In one example, testing cells extend along a length of a slot. Each testing cell includes a microfluidic channel extending from the slot, a pump to move fluid from the slot into the channel, a discharge nozzle through which fluid exits the channel, a fluid discharger to discharge fluid from the channel through the nozzle and a photosensor. A light guide is provided to receive light from an external light source and is to serially transmit the light to the microfluidic channel of each of the plurality of testing cells.在一範例中，多個測試胞元沿一槽之一長度延伸。每個測試胞元包括從該槽延伸之一微流溝道、用以從該槽移動流體至該溝道之一泵、流體透過它離開該溝道之一排放噴嘴、用以從該溝道通過該噴嘴排放流體之一流體排放器及一光感測器。一光導被提供用以從一外部光源接收光線及用以連續地傳送該光線至該等多個測試胞元之每一者之該微流溝道。
