This sensor is the miniaturized fiber optic chemical sensor designed for all research applications were a small tip size of ca 140 µm are necessary. Needle type pH micro sensors are ideal for pH profiling in sediments/biofilms or invasive work with a high spatial resolution and measurement in very small volumes. The pH sensitive tip of an optical fiber is protected inside a stainless steel needle. Such a design is the best for an easy penetration through skin, a rubber septum or any other harsh material as well as secure for transportation. For measurement purposes the sensor must be pushed out from the needle.