Designing stimuli-responsive upconversion nanoparticles based on an inner filter effect mimetic immunoassay for phenylketonuria accuracy diagnosis

Abstract

Phenylketonuria (PKU) is the most common inborn error of amino acid metabolism caused by an inherited deficiency in L-phenylalanine-4-hydroxylase (PAH) activity. It is usually controlled by diet and monitored regularly with markers, as PKU is not curable. However, conventional methods for target biomarker analysis are invasive and labor intensive. Here, we report a rapid and sensitive, mimetic immunoassay for detecting phenylpyruvate (PhPY) based on stimuli-responsive upconversion nanoparticles with an inner filter effect (IFE). The strong and specific binding of PhPY and Fe3+ forms a complex with maximum absorption at approximately 640 nm. Upon the addition of LiYF4:Er,Ho@LiYF4 UCNPs (maximum emission at 699 nm), the inner filter effect is triggered along with a concurrent decrease in fluorescence. The proposed method demonstrates ultra sensitivity with a detection limit of 79.63 μg L-1, which is superior to most reported methods, thereby enabling phenylpyruvate assays on human urine.