Lactate plays a key role in exercise physiology and metabolic studies as it is produced by the body as part of normal metabolic processes and has recently gained importance in relation to human sweat. Previous research has focused on blood lactate as an indicator of exercise intensity, but recent studies are moving towards the analysis of sweat lactate, providing a broader understanding of lactate dynamics. The aim of this thesis is to investigate the development and performance evaluation of a sweat lactate biosensor. Sweat lactate concentrations is investigated through a series of experiments and analyses under different conditions: time, temperature, contamination, nanoparticle involvement.