A flexible carbon nanotube field-effect transistor-based immunosensor for the selective and sensitive detection of salivary lysozyme: A biomarker of Alzheimer's disease.

In the modern era, Alzheimer's disease (AD) is one of the most common causes of dementia, with its prevalence increasing over time. Collecting brain tissues for research related to neurodegenerative diseases is challenging due to the need for highly trained neurosurgeons to perform surgery and extract brain tissue. Access to human brain tissue is limited, as sampling faces technical, ethical and cost obstacles. Therefore, developing a noninvasive method to detect biomarkers for an accurate diagnosis of AD is crucial. In this study, we selected lysozyme (LYZ) as a model analyte to quantify in saliva because LYZ levels are upregulated in AD patients. Nafion-anchored carbon nanotubes (Nafion/CNTs) nanocomposite was successfully synthesized and deposited on the polyethylene terephthalate (PET) substrate and utilized in the fabrication of FET-based immunosensor, with anti-LYZ covalently immobilized. Under the optimized conditions, the immunosensor displayed a linear correlation in the range of 0.05 to 100 μg/mL with a LOD of 0.05 μg/mL. The immunosensor exhibited high specificity against interfering molecules and was effectively employed in detecting LYZ in human saliva sample, yielding satisfactory recoveries. This noninvasive method for quantifying LYZ as AD biomarker offers a straightforward and sensitive approach to detection, suggesting significant potential applications in clinical diagnostics.