The present and future of minimally invasive methods for Alzheimer's disease diagnosis

Objective and methods: Invasive and noninvasive methods for diagnosing Alzheimer's disease (AD) are discussed and efforts to test less invasively are presented. The literature for this review was searched using Google Scholar (http://scholar.google.com), PubMed (http://www.ncbi.nlm.nih.gov/pubmed) and Scopus (www.scopus.com) database. According to the method of acquiring samples required for AD diagnosis, they were divided into invasive and noninvasive methods. Sample acquisition sites and biomarkers recently proposed for diagnosis in a less invasive way are presented and the potential of using aptamers to replace conventional antibody-based AD diagnostic methods is briefly introduced. Results and conclusion: Neuropsychological screening test is performed first to diagnose AD and to screen out patients with suspected dementia. On the other hand, brain imaging is one of the last test methods used to confirm AD. Immunoassays and mass spectrometry are invasive methods that require specific samples from a patient for analysis. Both methods are performed as a final step to confirm the diagnosis of AD. There are several studies on noninvasive diagnosis of AD with faster and more convenient tests. Existing AD biomarkers Aβ and tau and several biomarkers have been found in tear, saliva, and urine samples. If the usefulness of other biomarkers is evaluated through additional studies, samples can be obtained in a noninvasive manner and used in the diagnosis of AD. In addition, there are attempts to combine biosensors and nanomaterials to overcome limitations of existing diagnostic methods. A biosensor combining an aptamer and a nanomaterial has been reported. It appears to effectively detect AD-associated biomarkers. Identification of new biomarkers related to AD and research on the development of aptamer-based biosensors can serve as a stepping stone for minimally invasive diagnosis of AD.