Towards early diagnosis and screening of Alzheimer's disease using frequency locked whispering gallery mode microtoroids.

Alzheimer's disease (AD) is a form of dementia marked by amyloid plaques and neurofibrillary tangles in the brain. Amyloid beta (Aβ) is an AD biomarker which is linked to these plaques and tangles. Measuring Aβ levels can help with early AD diagnosis and aid in drug studies and delaying dementia. This is challenging, however, due to low AD biomarker levels in biofluids. Here we use FLOWER (frequency-locked optical whispering evanescent resonator) to quantify levels of post-mortem cerebrospinal fluid (CSF) Aβ42 in control, mild cognitive impairment (MCI), and AD participants. FLOWER measures the resonant wavelength shift of a microtoroid due to changes in the refractive index within its evanescent field. FLOWER can measure CSF Aβ42 (area under curve, AUC = 0.92) with higher performance than ELISA (AUC = 0.82) and can distinguish between control and MCI samples. This demonstrates FLOWER's ability to screen CSF samples for diagnosis of AD.