These biosensors have been developed to detect key biomarkers, such as brain-derived neurotrophic factor (BDNF) and neurofilament light chain (NfL), which play important roles in the development and progression of many neurological diseases, including multiple sclerosis, Alzheimer’s disease, and Parkinson’s disease [121]. Here, BDNF is linked to early-onset autosomal dominant Alzheimer disease.