Alzheimer's disease is a severe neurodegenerative disorder of the brain that is characterized by progressive loss of memory and cognitive decline. With the ageing population, AD is a major public health problem affecting nearly 35 million people worldwide with numbers projected to rise to 115.4 million by 2050. AD is the only cause of death among the top ten causes that has no prevention or cure . It is believed that novel treatment of AD needs to start early or even at the prodromal stage in order to be effective. Therefore, there is an urgent need to find accurate methods of early detection before patients with AD develop clinical dementia. This study aims to identify biomarkers for AD in local Chinese population. this study hypothesizes blood-based proteomics, retinal imaging, ASL-MRP and tau PET can improve the accuracy and staging of AD.