The cause of infertility can be due to a female factor or a male factor. In case of a male factor, it is often due to poor semen quality. However, the cause of poor quality is often unknown. In previous research, infertility problems in men were related to chemical processes in metabolism causing the formation of free radicals. Free radicals are physiological by-products of our body mechanisms. Free radicals are very reactive and can therefore react with a lot of molecules of cells within our body and cause damage. A balance between free radicals, which are also needed for physiological processes in the body, and antioxidants, which defuses the reactive free radicals, is most desirable. However, as stated in literature, there are a lot of factors that can influence extra free radical production, which causes overloading of the system, resulting in damage on cellular level. Free radicals in semen plasma and on the sperm cell could play a role in male infertility. Nonetheless, free radicals are not used as diagnostic markers due to the lack of detection systems, as free radicals are very short-lived. This study aims to introduce a new technique, called diamond magnetometry, to measure free radicals directly on the sperm cell and in serum. Diamond magnetometry involves very small diamond particles as magnetic sensors that engage a reaction with the free radicals on the sperm cell, causing signals that can be measured. To compare local free radical production with systemic free radical production, other diagnostic biomarkers are also measured in serum. It is hypothesized that the composition of seminal microbiome could influence the free radical concentration. Therefore, this study also aims to explore the microbiota composition and see if this has an influence in semen quality and free radical production. At last, this study also want to correlate standard semen parameters (defined by the World Health Organisation), lifestyle factors and food intake, to detect a role for lifestyle in the production of free radicals.