pH-Tunable Oxidase-Like Activity of Cerium Oxide Nanoparticles Achieving Sensitive Fluorigenic Detection of Cancer Biomarkers at Neutral pH

摘要

ABSTRACT: The reliable and sensitive detection of cancer-nspecific biomarkers is important for the diagnosis and treatmentnof cancer. Hence, detection of these biomarkers has to benreliably and rapidly performed in diverse settings. A limitationnof the conventional biomarker-screening method of enzyme-nlinked immunosorbent assay (ELISA) is the employment ofnlabile components, such as hydrogen peroxide and horseradishnperoxidase. Previously, we reported that nanoceria is able tonoxidize various colorimertic dyes at acidic pH, such as 3,30n,5,50n-ntetramethylbenzydine (TMB) and 2,2-azinobis-(3-ethylben-nzothizoline-6-sulfonic acid) (AzBTS), and an assay was de-nsigned for screening the folate receptor. Herein, we show thatnthe ability of nanoceria to oxidize a substrate can be tuned bynmodulating the pH. Results showed that nanoceria can oxidizenthe nonfluorescent substrate ampliflu, either to the very stablenfluorescent product resorufin at pH7.0 or to the nonfluorescentnresazurin at pH 4.0. On the basis of these findings, wenconjugated Protein G to immobilize antibodies on the surface of nanoceria, in order to detect the expression of prototypic cancernbiomarkers at pH 7.0, such as the folate receptor and EpCAM.We found that within 3 h, nanoceria identified the expression of thenfolate receptor and EpCAMon lung carcinoma and breast adenocarcinoma cells, respectively. Traditional ELISA had a readout timenof 15 h and a higher detection threshold, while requiring multiple washing steps. Considering these results and nanoceria’s ability tonoxidize ampliflu to its stable fluorescent product at neutral pH, the use of antibody-carrying nanoceria in the lab and point-of-carenmolecular diagnostics is anticipated.