NEFL and frontotemporal dementia: For this reason, we developed an immunoassay based on the single-molecule array (Simoa) technique15 that allows quantification down to subfemtomolar concentrations (<1 pg/mL) of the analyte and is 25-fold more sensitive than the previous electrochemiluminescence-based method.16 Using this assay, we aimed to investigate serum NfL concentrations in FTD.