Functionalization of stable fluorescent nanodiamonds towards reliable detection of biomarkers for Alzheimer's disease

Background: Stable and non-toxic fluorescent markers are gaining attention in molecular diagnostics as powerful tools for enabling long and reliable biological studies. Such markers should not only have a long half-life under several assay conditions showing no photo bleaching or blinking but also, they must allow for their conjugation or functionalization as a crucial step for numerous applications such as cellular tracking, biomarker detection and drug delivery. Results: We report the functionalization of stable fluorescent markers based on nanodiamonds (NDs) with a bifunctional peptide. This peptide is made of a cell penetrating peptide and a six amino acids long beta-sheet breaker peptide that is able to recognize amyloid beta (A beta) aggregates, a biomarker for the Alzheimer disease. Our results indicate that functionalized NDs (fNDs) are not cytotoxic and can be internalized by the cells. The fNDs allow ultrasensitive detection (at picomolar concentrations of NDs) of in vitro amyloid fibrils and amyloid aggregates in AD mice brains. Conclusions: The fluorescence of functionalized NDs is more stable than that of fluorescent markers commonly used tostain A beta aggregates such as Thioflavin T. These results pave the way for performing ultrasensitive and reliable detection of A beta aggregates involved in the pathogenesis of the Alzheimer disease.