What's important in selection of a suitable microscope objective?

An inverted microscope is recommended for observing flow in microfluidic chips, as most observation surfaces are located on the bottom (non-inlet) side. A key parameter in selecting a suitable objective is the working distance.

For thin-bottom chips, the working distance is less critical, as the distance to the channel is typically below 175 µm. However, it is still recommended to minimize the size of the objective itself where possible, to allow more space for movement within the holder.

For chips with regular (thicker) bottoms, the working distance becomes a critical factor. Most standard objectives are designed for use with a #1.5 cover slip, which has a thickness of only 170 µm. However, the bottom thickness of typical microfluidic chips is usually in the range of 400–900 µm. Therefore, long working distance objectives—often referred to as non-cover glass objectives—are more suitable.

Whenever possible, we recommend using dry objectives, as they simplify the setup and eliminate the need for immersion media. In many cases, it is feasible to use the edge of the channel or another well-defined feature as a reference point for manual size correction. This approach can reduce the need for optical corrections provided by the objective itself.