Detection of Aβ protofibrils using SP-PLA. (A) Assays were performed in buffer (blue diamonds), in 10% CSF (red squares), and in 50% CSF (green triangles). (B) Comparison of SP-PLA (red squares) versus ELISA (blue diamonds) for detection of Aβ protofibrils in 10% CSF. The X-axes show concentrations of Aβ protofibrils in pg/ml and the Y-axes show cycle threshold values for real-time PCR. In B the right Y-axis indicates the OD A450nm for ELISA. The vertical red and blue lines indicate the limit of detection for SP-PLA and ELISA, respectively, calculated as 2-fold standard deviations above the background signals. Error bars indicate standard deviations from the mean for triplicates for each reaction.