Nanoscale MRI for Selective Labelling and Localised Free Radical Measurements in the Acrosomes of Single Sperm Cells

Free radicals play a major role in sperm development, including maturation and fertilisation, but they are also linked to infertility. Since they are short lived and reactive, they are challenging to detect with state of the art methodologies. Thus, many details surrounding their role remain unknown. One unknown factor is the source of radicals that play a role in the sperm maturation process. Two alternative sources have been postulated: First, the NADPH-oxidase system embedded in the plasma membrane (NOX5) and second, the NADH-dependent oxidoreductase of mitochondria. Due to a lack of localised measurements, the relative contribution of each source for capacitation remains unknown.<br/>To answer this question, we use a new technique called diamond magnetometry which allows nanoscale MRI to perform localised free radical detection. With this new tool, we were able to quantify radical formation in the acrosome of sperm heads. This allowed us to quantify radical formation locally in real time during capacitation. We further investigated how different inhibitors or triggers alter the radical generation. We were able to identify NOX5 as the prominent source of radical generation in capacitation while the NADH-dependent oxidoreductase of mitochondria seems to play a smaller role.