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The treatment of Alzheimer's disease (AD) has been hampered by a lack of sensitive and specific non-invasive diagnostic methods. Quantum dots (QD) are nano-crystals with unique photo-physical properties that bypass some of the limitations of conventional dyes and imaging tools. This study is aimed to evaluate the fluorescence properties of a QD probe conjugated with an anti-Aβ antibody (QD-Aβ-Ab). Healthy mice and mice bearing mutated human APP695swe and APP717 V- F transgenes received intracerebroventricular injection of the probe for subsequent imaging. Immunohistochemistry revealed that Aβ was distributed in the hippocampus CA1 area in the APP transgenic mice. Fluorescence microscopy demonstrated that fluorescence was mainly observed in the hippocampus area, the cerebral cortex, sagittal septum and striatum of APP transgenic mice. In vivo imaging of mice receiving the QD-Aβ-Ab probe showed that healthy mice exhibited a narrow range of fluorescence and lower fluorescence intensity compared with APP transgenic mice. The mean fluorescence intensity of brain tissues of healthy C57BL mice was 12.3784 ± 3.9826, which was significantly lower than that of 10- and 16-month-old APP transgenic mice (45.03 ± 2.66 and 46.69 ± 3.22, respectively; P < 0.05). In this study we present the first direct evidence that QD-Aβ-Ab conjugate probes can track in vivo state of Aβ accumulation in mice and the findings suggest that such probes may be of potential use for early molecular diagnostic imaging of AD. [ABSTRACT FROM AUTHOR]