A paper-based fluorescence immunosensor based on internal filter effect using the phosphatase-like activity of Au@CeO2 nanorods for Alzheimer’s disease detection

A simple microfluidic device based on the use of a paper platform modified with AuNPs was developed. The ALP-like CeO 2 nanozyme first converts p-nitrophenyl phosphate ( pNPP ) to PNP . Fluorescence detection of Tau-441 was proposed based on the inner filter effect (IFE) of n-doped graphene quantum dots (NGQDs) and p-nitrophenol (PNP). • A novel device based on the use of a paper platform modified with AuNPs was developed. • Fluorescence detection of Tau protein (Tau-441) was proposed based on the inner filter effect (IFE) of n-doped graphene quantum dots (NGQDs). • The ALP-like CeO 2 nanozyme first converts p-nitrophenyl phosphate ( pNPP ) to p-nitrophenol (PNP) for the rapid analysis of Tau-441 content in human serum samples. The advancement of Alzheimer’s disease (AD) is directly correlated to the phosphorylation damage of Tau protein (Tau-441), which is considered the most reliable indicator for early detection of AD. Nevertheless, the concentration of Tau-441 in human serum remains considerably low. To address this issue, a paper-based fluorescence immunosensor based on internal filter effect (IFE) was developed for the detection Tau-441. The microfluidic paper-based channel was prepared and modified with a gold layer to attach primary antibodies and increase the sensitivity of the sensor. All at once, Au@CeO 2 nanorods was employed as a fluorescence probe to hydrolyze p-nitrophenyl phosphate ( pNPP ), which generates hydrolyzed product p-nitrophenol (PNP) can reduce or quench the fluorescence intensity of N-doped graphene quantum dots (NGQDs). The immunosensor was designed to detect an increase in the amount of Tau-441 collected as the fluorescence intensity of NGQDs decreased. The developed sensor demonstrated satisfactory results in clinical serum samples, offering a promising concept for an immunoassay tagged with nanozymes for early detection of AD. Overall, this microfluidic paper-based fluorescent immunosensor has the potential to improve early diagnosis of AD.