The performance of these biosensors was tested for their ability to detect Alzheimer's disease serum biomarkers in both 1× PBS and undiluted human serum. The results showed that the aptamer-functionalized CNT FETs had an expansive analytical range with ultralow LODs of 45 aM and 55 aM, for Aβ40 and Aβ42, respectively. They used multiple blocking steps on the sensor and were able to decrease nonspecific adsorption from the biological matrix, leading to an improvement in selectivity ratio by up to 800%, even when samples containing similar proteins.