A biomarker is a feature that may be measured and assessed objectively as a sign of normal biological or pathological processes, or pharmacological responses to a treatment intervention. A perfect biomarker is one that is repeatable, stable over time, widely available, and directly represents the disease process in question. Alzheimer's disease (AD) is one of the most common dementias among the elderly around the world. A combination of clinical criteria, including a neurological examination, mental status tests, and brain imaging, is used to make a preliminary diagnosis of Alzheimer's disease. However, the diagnosis of AD becomes challenging based on the foregoing clinical tests, especially in individuals with mild or early stages of AD. As a result, biomarkers that exhibit strong symptoms of Alzheimer's disease and also give conclusive diagnosis of early-onset AD become necessary.