Artificial enzyme mimics based on nanomaterials have attracted sustained attention owing to their multiple advantages compared with natural enzymes. However, there are a few enzyme self-cascade systems for the highly sensitive detection of analytical targets. Herein, we have described a self-cascade catalytic system based on single-component cupric oxide nanoparticles (CuO NPs) for an ultrasensitive fluorescent detection toward glutathione (GSH) and Ag + ions. The limit of detection is lower for nanomolar (nM) and picomolar (pM) levels for GSH and Ag + , respectively. To the best of our knowledge, for the first time, we find that CuO NPs possess the intrinsic GSH-oxidase and peroxidase-like activity as a dual-functional nanozyme, coupling with terephthalic acid (TA) and GSH to construct a self-cascade fluorescent system. The turn-on fluorescence signal of oxidation hydroxyterephthalate (TAOH) is generated in the presence of GSH. Then, the fluorescence of a reaction mixture is quenched after the addition of Ag + ions, operating as a turn-off switch. The turn-on−off switch allows the analysis of GSH and Ag + ions by a change of fluorescence status. The detection limits are 32 nM and 37 pM for GSH and Ag + , respectively. To the best of our knowledge, the approach presented in this work shows the highest sensitivity for Ag + detection among all reported fluorescent/colorimetric methods. Moreover, there is no obvious interference with the addition of other interferences without a masking agent. Our study opens a new avenue for the use of a single nanomaterial as an artificial enzyme self-cascade catalytic system for highly sensitive target analysis in biosensor, diagnosis, and environmental fields.
In this paper, we report a colorimetric sensor for the rapid, selective detection of ascorbic acid (AA) in aqueous solutions. Single-layered MnO nanosheets were established as an artificial oxidase; consequently colorless 3,3´,5,5´-tetramethylbenzidine (TMB) was oxidized to a blue product (oxTMB), with increase in absorbance at 650 nm. The absorbance of the reaction system decreased after introduction AA, which reduced MnO into Mn . Under optimum conditions, a detection limit of 62.81 nM for AA in aqueous solutions could be achieved. The linear response range for AA was 0.25-30 μM with a correlation coefficient of 0.996. Importantly, the MnO nanosheet-TMB chromogenic reaction exhibited great selectivity as there was no interference from other metal ions, amino acids and small biological molecules. The proposed colorimetric sensing of AA could be applied for fruit, juice and pharmaceutical samples. Moreover, the proposed sensor showed satisfying performance, including low cost, easy preparation, rapid detection, and good biocompatibility.
Current ambient ionization sources for mass spectrometry (MS) are typically connected to gas cylinders, high-voltage supply, injection pump, and other accessory equipment, which hinder the popularization of MS in the field of on-site detection. Here, we developed a wireless pocket-size "MasSpec Pointer" (weights 65 g) based on arc discharge powered by a 3.7 V polymer Li battery for ambient ionization MS. A high voltage of 5600 V and 20 kHz was generated from the boost coil to penetrate air and form a plasma. The relative standard deviation (RSD) of the high-voltage pulses is 3.8%, leading to a stable discharge and a good quantification performance. A mini diaphragm pump was used to cool the plasma from ∼600 to ∼40 °C and to blow the plasma into a jet, which facilitates sampling. MasSpec Pointer can work well at both positive-and negative-ion modes without any modification and can quickly test gaseous, liquid, or solid samples. The limit of detection of this device for atrazine (an agrochemical) is lower than 0.1 ng/mL. MasSpec Pointer has shown its ability to pinpoint the double-bond location of fatty acid isomers without derivatization reagents or light illumination. Agrochemicals from the surface of an apple and daily chemicals from the surface of a finger were detected successfully using MasSpec Pointer coupled with a miniature mass spectrometer. We believe the "point-and-shoot" device coupled with mini-MS brings the hope for an age of detecting chemicals on-site by nonprofessionals.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.