Optical sensors, especially fiber optic sensors, make a universal platform for the implementation of biological research. They allow for, e.g., a Label-free and selective detection of a wide range of biological materials in solutions, including DNA, proteins, viruses and bacteria, all done quickly and with high measurement reliability. Directly after fabrication, the optical fiber structures can measure temperature, stress and refractive index. In order to achieve selectivity for a specific biological analyte, biofunctionalization is necessary, during which the sensor surface is subjected to a series of processes of binding and activating chemical and biological layers. The biofunctionalisation processes we use have been developed and improved during almost 10 years of cooperation with the team of the Institute of Physical Chemistry PAN in Warsaw, Institute of Immunology and Experimental Therapy PAN in Wrocław and other scientific and business partners. Our work resulted in the attachment of toxins, proteins, DNA, viruses and living cells, including bacterial ones, onto the sensors surfaces.