What type of microscopy is used to observe live cells?

Phase-contrast microscopy is specifically designed to enhance the contrast of live cells and other transparent specimens that are otherwise difficult to visualize under standard light microscopy. This technique utilizes differences in the phase of light waves that pass through objects with different refractive indices—like cells in a culture medium. By converting these phase differences into variations in brightness, phase-contrast microscopy allows for the observation of living cells without the need for staining or fixing, which could kill the cells or alter their natural state.

This method is extremely valuable in biological research and clinical diagnostics, as it enables scientists and technicians to study dynamic processes within live cells, such as cell division, movement, and interactions, while preserving their viability. This makes phase-contrast microscopy an essential tool in cell biology and medical laboratories.

Other microscopy techniques listed, such as transmission and scanning electron microscopy, require samples to be prepared in ways that typically involve fixation or dehydration, rendering them unsuitable for observing live cells. Fluorescence microscopy can also be used on live cells, but its effectiveness often relies on the use of fluorescent labels, which may affect cell viability and behavior. Hence, phase-contrast microscopy stands out as the most appropriate choice for observing live cells.