In this work, we present core/shell Au@MnO 2 nanoparticles-based visual sensing strategy for mercury ion (Hg 2+ ) detection. The MnO 2 shell of Au@MnO 2 nanoparticles catalyzes the oxidation reaction between tetramethylbenzidine (TMB) and oxygen in the air, generating blue derivative (oxTMB) with an absorption peak at 650 nm. Glutathione (GSH) inhibits the formation of oxTMB, reversing the reaction and turning it back into colorless TMB molecules. While in the existence of Hg 2+ , GSH binds to Hg 2+ due to the strong affinity between the Hg 2+ and the -SH, and in this situation, Au@MnO 2 catalyzes the oxidation of TMB to make the solution become blue. Using the colorimetric sensor, the detection limit of Hg 2+ reached as low as 0.473 nM by UV–vis spectroscopy and 1 nM under the naked eye observation, which is lower than toxicity level of Hg 2+ (10 nM) formulated by the U.S. Environmental Protection Agency.
Exosomes, carrying specific molecular information of their parent cells, have been regarded as a kind of promising noninvasive biomarker for liquid biopsy. Plentiful fluorescence methods have been proposed for exosome assay. However, most of them are dependent on nucleic acid signal amplification strategies, which require complicated sequence design and experimental operation. Herein, a metal-enhanced fluorescence (MEF) biochip based on shell-isolated [email protected] 2 nanoparticle array was designed for simple and sensitive assay of exosomes. The designed method consists of only two parts: signal conversion and MEF amplification. The conversion of exosome signals to DNA signals was realized by means of chain displacement reaction. The subtle conversion effectively averts the effect of steric hindrance on MEF while amplifying the signal easily for the first time. The MEF biochip based on shell-isolated [email protected] 2 nanoparticle array achieves a second signal amplification in a simple way. Profiting from the two signal amplifications, this strategy displays high sensitivity toward exosomes with a detection limit of 4.5 × 10 3 particles μL −1 . Compared with the result without MEF, the sensitivity is enhanced about thirty times. As far as we know, this is the first attempt for exosome assay by using MEF strategy. In addition to the favorable fluorescence enhancement, both shell-isolated [email protected] 2 nanoparticles and [email protected] 2 nanoparticle array show excellent stability in buffer solutions, which is conducive to practical application. Moreover, the proposed method is able to distinguish breast cancer patients from healthy people, showing its potential for exosome-based liquid biopsy.
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