Kyu Young Han’s group at the College of Optics and Photonics (CREOL) and Yoon-Seong Kim’s lab at Burnett School of Biomedical Sciences at the University of Central Florida are using single-molecule pull-down (SiMPull) assays to understand and diagnose Parkinson’s disease. The researchers used single-molecule total internal reflection fluorescence (TIRF) microscopy to visualize single proteins captured by fluorescently labeled antibody and in vivo crosslinker to preserve native states of biological samples, including cultured cells and postmortem brain tissues. They demonstrated that SiMPull assay is highly specific and ultrasensitive for detecting a minute amount of alpha-synuclein (a-SYN). In addition, the tissue lysates from the substantia nigra of human Parkinson’s disease (PD) brain showed a 3.3-fold higher number of a-SYN molecules and a 2.4-fold higher oligomeric population compared to control brain. Intriguingly, using recombinant a-SYN protein under oligomer-induced condition, they were able to observe many fibrillar a-SYNs with various sizes and shapes that were not observed in the PD brain. Measuring low concentration of proteins in biospecimens is important in clinics that use protein biomarkers for diagnosis of diseases. However, in many cases, the concentration information does not tell everything because proteins are complexed with other biomolecules or they could be oligomerized by themselves. Particularly, oligomeric proteins have been a hallmark of many neurodegenerative diseases and got a lot of attention. For example, in PD, the second most common neurodegenerative disease, oligomers and aggregates of a-SYN protein have been implicated as key players in pathogenesis. Thus, the determination of a-SYN expression levels and its oligomerization states is crucial. The SiMPull technique was originally invented by Dr. Taekjip Ha at Johns Hopkins University School of Medicine and his graduate student Ankur Jain; however, it has been used mostly for revealing molecular mechanisms of biomolecular complexes. This powerful single-molecule assay can be highly useful in diagnostic applications using various specimens, including cerebrospinal fluids, for many neurodegenerative diseases. High-throughput platform and multicolor imaging will allow the dynamic range of the detection to increase and the study of other molecules in complex with oligomeric proteins.