Dimensions of a 500 µm and 5 µm oxygen microsensor tip. The inner dimensions of the two sensors are similar. However, with the thicker glass walls of the 500 µm sensor, you get a more robust sensor.
pH microelectrode tip
The pH sensor tip consists of two pieces of glass glued together. The sensing part of the sensor is made of exposed, proton sensitive pH glass. Even though the tip is only a few µm, the pH measurement will be an integration of the microenvironment from the total pH sensing glass.
The microsensor tip is inserted into a steel needle giving the sensor maximal strength on the longitudinal axis. However, because of the joint construction between glass and steel, lateral movements of the needle may cause the glass sensor to break inside the needle. So they look sturdier, but for some applications they are in fact more fragile than a normal sensor.