A facile preparation of FePt-loaded few-layer MoS2 nanosheets nanocomposites (F-MoS2-FePt NCs) and their application for colorimetric detection of H2O2 in living cells
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Rapid and sensitive detection of H2O2 especially endogenous H2O2 is of great importance for series of industries including disease diagnosis and therapy. In this work, uniform FePt nanoparticles are successfully anchored onto Few-layer molybdenum disulfide nanosheets (F-MoS2 NSs). The powder X-ray diffraction, transmission electron microscopy, UV–Vis spectra and atomic force microscopy were employed to confirm the structure of the obtained nanocomposites (F-MoS2-FePt NCs). The prepared nanocomposites show efficient peroxidase-like catalytic activities verified by catalyzing the peroxidation substrate 4,4′-diamino-3,3′,5,5′-tetramethylbiphenyl (TMB) with the existence of H2O2.
The optimal conditions of the constructed colorimetric sensing platform is proved as 35 °C and pH 4.2. Under optimal catalytic conditions, the detection limit for H2O2 detection reaches 2.24 μM and the linear ranger is 8 μM to 300 μM. Furthermore, the proposed colorimetric sensing platform was successfully utilized to detect the intracellular H2O2 of cancer cells (MCF-7).
These findings indicated that the F-MoS2-FePt-TMB-H2O2 system provides a potential sensing platform for hydrogen peroxide monitoring in living cells.
KeywordsFew-layer MoS2 nanosheets FePt Colorimetric H2O2 Intracellular H2O2
Hydrogen peroxide (H2O2) takes an essential position in many biochemical reactions, such as metabolism of proteins and carbohydrates. Furthermore, it can be used as a significant indicator of the occurrence of many serious disease especially cancer [1, 2]. Consequently, a sensitive, cost-effective, rapid and easy operation method for H2O2 determination would be demanded for bioassays and environmental applications . Up to now, several techniques for H2O2 determination, such as chromatography , chemiluminescence, electrochemistry [5, 6] and colorimetric method , have been reported. Among these techniques, colorimetric route has several outstanding advantages, including visibility, low cost, easy automation, portability and operation convenience . Although enormous progresses have been made, sensitive and rapid detection of H2O2 still remains highly need. Recently, due to its high selectivity, many nanometerials were employed to construct colorimetric sensors to detect H2O2.
Conventional enzymes are especially effective when catalyze series of reactions under mild conditions. However, conventional enzymes have rigorous limitations in practical use because they usually show insufficient stability in cruel conditions, additionally, they are hard to purify and preserve . Therefore, over the past few decades, an explosion of interests have been drawn to study enzyme-mimic materials aiming to get high efficiency without the mentioned shortcomings. To date, versatile nanomaterials, such as CoS NPs , Fe3O4 NPs [11, 12], Copper nanoclusters , metal–organic framework , WS2 nanosheets , graphene oxide [15, 16], and kinds of metals [5, 17, 18] are used to fabricate nano-enzymes and exhibit effective catalytic activities suggesting prospective potentials in numerous bio-field, accompanied by series of advantages, including cost-effective, simple process, readily available raw materials, easy purification of products, low cost and long guarantee period [19, 20].
Molybdenum disulfide (MoS2), with a graphene-like lamellar structure, is composed of S–Mo–S sandwich structure and held by weak van der Waals forces. The few-layer MoS2 nanosheets (F-MoS2 NSs) with excellent 2D structure possess a direct bandgap of 1.8 eV, which is much higher than the indirect bandgap in bulk MoS2 NSs (1.2 eV) . Hence, great efforts have been devoted to prepare few-layer MoS2 NSs and they are applied in sensing, catalysis, supercapacitors and so on [22, 23, 24, 25, 26, 27]. Furthermore, based on its super-large specific surface areas and abundant active edges, MoS2 NSs have been utilized as base material to integrate with series of nanomaterials to further improve their catalytic performance . A variety of monometallic nanoparticles (MNPs), such as Ag [29, 30], Pd , Pt , Au [32, 33] and Co NPs  have been successfully decorated on 2D MoS2 NSs. The obtained MoS2-MNPs can enhance their intrinsic properties. However, it is extremely difficult to further enhance the catalytic efficiency. Therefore, bimetallic nanoparticles (BNPs) were developed to improve the catalytic abilities [35, 36, 37, 38, 39, 40, 41].
Results and discussion
Characterization of FePt nanoparticles, F-MoS2 NSs and F-MoS2-FePt NCs
The way to prepare F-MoS2-FePt NCs is depicted in Scheme 1, while the experiments details are described in the experimental section. In this work, few-layer MoS2 NSs (F-MoS2) are obtained by exfoliating bulk MoS2 via lithium intercalation–exfoliation. To investigate the thickness of the as-prepared MoS2 NSs, atomic force microscopy (AFM) is utilized to measure as-prepared MoS2 NSs. As shown in Additional file 1: Figure S1, the altitude of as-prepared MoS2 NSs is around 2 nm, implying as-prepared MoS2 NSs have 2–3 layers [25, 42].
Peroxidase-like activity of the obtained FePt, F-MoS2 NSs and F-MoS2-FePt NCs
UV spectrum is utilized to estimate the catalytic activities of F-MoS2-FePt NCs, bulk MoS2 NSs, F-MoS2 NSs and FePt NPs. As illustrated in Fig. 3C, the absorbance of F-MoS2-FePt NCs reaches the highest value among all the materials. Moreover, the absorbance of F-MoS2 NSs is much higher than bulk MoS2 NSs, which is attributed to the higher specific surface area and more exposed active sites. Furthermore, the time-dependent mode of the UV–Vis spectra at 652 nm for these materials is also investigated. As depicted in Fig. 3D, the UV spectra of F-MoS2-FePt NCs at 652 nm reach the balance within 100 s and the highest value is obtained, which indicates the strong synergistic effect between F-MoS2 NSs and FePt NPs .
Kinetic investigation of F-MoS2-FePt NCs as peroxidase mimics
Detection of H2O2 and sensing of the intracellular H2O2
In this work, a sensitive and rapid colorimetric sensing platform for H2O2 detection utilizing F-MoS2-FePt NCs as artificial enzyme is constructed. The uniformly prepared FePt NPs are anchored on the surface of exfoliated few-layer MoS2 NSs by a facile operation. Series of experiments are carried out to verify the peroxidase-like catalytic activity of the obtained NCs. Under optimal conditions, the linear range of H2O2 detection is between 8 and 300 μM and the detection limit is 2.24 μM. Compared with other reported methods, F-MoS2-FePt NCs-based colorimetric sensing platform for H2O2 detection is a sensitive, simple and cost-effective method. To improve the stability and transmembrane performance of F-MoS2-FePt NCs, the surface of the prepared NCs is modified by SH-PEG-FA for intracellular H2O2 detection, which indicates that the sensor could be applied in living cells testing and has potential in disease diagnosis and therapy.
ZH performed experiments; ZD, XH, BY and QL drew the TOC, scheme and figures, YY wrote the paper with support from XZ. All authors contributed to the general discussion. All authors read and approved the final manuscript.
Financial support from the National Natural Science Foundation of China (Grant Nos.: 21675073, 51872150), Primary Research and Development Plan of Shandong Province (2017GGX20115) and Shandong Province Natural Science Foundation (Nos.: ZR2017BB070, ZR2018MB034) are gratefully acknowledged.
The authors declare that they have no competing interests.
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