Gold nanoparticle–enzyme conjugates based FRET for highly sensitive determination of hydrogen peroxide, glucose and uric acid using tyramide reaction
In this paper, we report a new strategy for highly sensitive determination of hydrogen peroxide, glucose and uric acid based on fluorescence resonance energy transfer (FRET) using gold nanoparticles (AuNPs) as energy acceptors. The principle is based on highly sensitive reaction of tetramethyl rhodamine (TMR) labeled tyramide and hydrogen peroxide catalysed by horseradish peroxidase (HRP), and the fluorescence spectrum of TMR (EXmax 575 nm) partially overlaps with the visible absorption bands of AuNPs. We demonstrated an efficient FRET between tyramide labeled TMR (as energy donors) and HRP (BSA) conjugated AuNPs (as energy acceptors) due to the formation of TMR-labeled HRP–AuNPs or TMR-labeled BSA–AuNPs in the presence of H2O2. We observed that the quenching of the fluorescence signal depended linearly on the H2O2 concentration within a range of concentrations from 25 to 400 nM and the detection limit of this assay was 10 nM. Based on the principle for determination of H2O2, we developed a new strategy for assay of glucose and uric acid by coupling with glucose oxidase (GOx)-mediated and uricase-mediated reaction. The established methods were successfully used for determination of glucose and uric acid levels in human sera, and the results obtained are in good agreement with commercially available methods. Our methods are at least 1 order of magnitude more sensitive than the commercially available methods. More importantly, our method described here can be extended to other assay designs using different oxidase enzymes, energy donors and energy acceptors, such as fluorescent quantum dots, near-infrared (NIR)-to-visible upconversion nanoparticles and even other metallic nanoparticles.