In the last years, the development of biosensing devices is constantly increasing. Specifically and among all types of biosensors, protein-only biosensors, as one part of those sensing devices, stand out due to their ease production and use. Taking advantage of the properties of some proteins and insertional fusion technologies, useful and cheap enzymatic biosensors can be generated. In this dissertation, the characterization of an HIV-1 protein-only biosensor, called NF795gpC, was described. Insertion of small peptides in permissive solvent exposed sites of the enzyme beta-galactosidase, as it was described previously by other authors, allowed the synthesis of proteins responding to specific antibodies. The interaction between protein and antibody can produce slight modifications in the sensor modulating its activity. The characterization of that interaction and the modification of other parameters, improved the knowledge of these specific biosensors, and may be the basis for the future development of other proteins able to detect other infectious diseases. The development of a sensing assay based on enzymes could represent big advances in public health.