Upconversion nanoparticles grafted molybdenum disulfide nanosheets platform for microcystin-LR sensing
Introduction
Molybdenum disulfide (MoS2), a well-known transition metal dichalcogenide (TMDC), is composed of S-M-S triple layer through weak van der Waals interactions (Ha et al., 2014, Raja et al., 2016, Zhang et al., 2016). As a novel 2D layer structure analogous to graphene, MoS2 is becoming more and more popular attributed to its outstanding properties such as mechanical properties (Wang et al., 2015b), superior electrical performance (Prasai et al., 2015), unusual optical properties (Tan et al., 2014, Yin et al., 2012) and photothermal properties (Chou et al., 2013), and shows high fluorescence quenching ability and specific affinity toward ssDNA (Zhu et al., 2013). In the past few years, MoS2 nanosheets were reported to have great promise in nanoelectronics, optoelectronics, photovoltaics and energy harvesting (Li et al., 2012; Radisavljevic et al., 2011; Zhou et al., 2013). However, we believe this is not the limit, it still has enormous developing space in biosensor.
Lanthanide ions doped upconversion nanoparticles (UCNPs) can convert near-IR light to UV and visible light via a process known as photon upconversion (Chan et al., 2015, Zhou et al., 2015). The phenomenon has aroused a great deal of attention in recent years because of many conceivable advantages, such as weak autofluorescence background, enhanced signal-to-noise ratio, resistance to photobleaching, easy tunability of emission wavelength, high sensitivity for detection and so on (Park et al., 2015). These unique properties render UCNPs useful in photodynamic therapy (Idris et al., 2012), photocatalysis (Chen et al., 2013), biological imaging (Liu et al., 2014a, Maji et al., 2014), biosensing (He et al., 2016, Tsang et al., 2016), etc. It has been reported that hexagonal-phase NaYF4 crystals are the most efficient host materials for upconverting lanthanide ions owing to the low phonon energy of the crystal lattice (Haase and Schafer, 2011). However, UCNPs are still in its infancy of fluorescence quenching by surface defects and surface associated ligands. Fortunately, the emerging of nanoparticles with core-shell structure grants the upconversion nanoparticles more intense fluorescence by repairing the defects on the surface of crystals (Sun et al., 2013, Wang et al., 2014, Wang et al., 2011). Moreover, significant efforts have been devoted to demonstrate that the active core/active shell (Yb3+-doped shell) structure is superior to the inactive shell structure (Vetrone et al., 2009).
Aptamers are ssDNA or RNA molecules that bind specific targets with high affinity, specificity and selectivity, and can be selected to bind to specific target molecules (Rotem et al., 2012, Sun and Zu, 2015). They exhibit many unparalleled merits compared with antibodies or other biomimetic receptors: aptamers can be selected to bind essentially any molecule of choice, have easy and cost-effective synthesis with high reproducibility, purity comparable or even better target affinity, and straightforward chemical modification (Hu et al., 2016, Zhao et al., 2015).
Microcystin-LR (MC-LR), the first chemically identified and widely studied microcystin among more than 80 microcystin congeners, poses a growing and serious threat in water supplies throughout the world (Eissa et al., 2014). Acute poisoning by MC-LR can cause skin irritation, diarrhea and damage to the liver (Xiang et al., 2014). Therefore, the exploration of new methods for MC-LR detection at low concentration has become an increasingly prominent issue. Several analytical techniques have been developed for MC-LR determination, such as immunoassays (Gan et al., 2016, Ruiyi et al., 2013, Xiang et al., 2014, Zhu et al., 2011), high-performance liquid chromatography (HPLC) (Cadel-Six et al., 2014), liquid chromatography-mass spectrometry (LC-MS) (Li et al., 2014), and whole cell bioassays (Sangolkar et al., 2006). However, these methods call for complex sample preparation, expensive equipment, high professional skills and massive time.
Recently, while single-layer MoS2 has found widespread applications in different fields (Zhang et al., 2016), to the best of our knowledge, biological application of MoS2 for MC-LR detection has not been sufficiently explored until now. Herein, for the first time, we report a simple and homogenous assay format for MC-LR using the quenching property of single-layer MoS2, specific recognition of aptamer and enhanced fluorescence of NaYF4:Yb,Tm@NaYF4:Yb nanoparticles (CS-UCNPs). The proposed method was subsequently applied in detecting MC-LR in real samples, which demonstrated it a sensitive, specific and stable assay.
Section snippets
Materials and regents
Yttrium chloride hexahydrate (YCl3·6H2O), Ytterbium (III) chloride hexahydrate (YbCl3·6H2O), Thulium (III) chloride hexahydrate (TmCl3·6H2O) were purchased from J&K Scientific Ltd. Octadecene (ODE), Ethyl-3-(3′-dimethylaminopropyl) carbodiimide (EDC), N-hydroxysulfosuccinimide sodium salt (sulfo-NHS), polyacrylic acid (PAA.M.W.2000) were obtained from Sigma Aldrich Co., Ltd. (Shanghai, China). Ammonium fluoride (NH4F), sodium hydroxide (NaOH), oleic acid (OA), methanol, chloroform, toluene and
Characterization
Typically, NaYF4 nanoparticles co-doped with Yb and Tm were first fabricated and then used as seeds for epitaxial growth of NaYF4:Yb shells. The morphology and size of the as-prepared core and core-shell nanoparticles were characterized by transmission electron microscopy (TEM). The images showed morphology of the core and core-shell with an average diameter of 65±3 nm and 100±4 nm, respectively (Fig. 1A–C). To verify the size distribution of the nanoparticles, dynamic light scattering (DLS) was
Conclusions
In summary, a new label-free nanoplatform based on 2D MoS2 nanosheets and CS-UCNPs for homogeneous detection of MC-LR has been successfully developed. The feasibility of this aptasensor is confirmed by using tap water and Tai Lake water as real samples. The LOD is 0.002 ng/ml, which is much lower than those of previously methods. The low detection limit of this method benefits from the outstanding energy transfer efficiency between CS-UCNPs and MoS2. Moreover, this aptamer-based platform can be
Acknowledgments
This work was partly supported by the National S&T Support Program of China (2015BAD17B02), National Natural Science Foundation of China (21375049 and 31401576), and Synergetic Innovation Center of Food Safety and Quality Control of Jiangsu Province.
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2022, TalantaCitation Excerpt :Lv et al. prepared Yb and Tm co-doped core/shell UCNPs, which exhibited 7 times enhanced fluorescence compared with the only-core UCNPs. A FRET-based aptasensor for MC-LR detection was constructed by adsorbing aptamer-modified UCNPs onto MoS2 sheet via van der Waals force [90]. The addition of MC-LR caused detachment of UCNPs from MoS2 sheet, leading to the recovery of UCNPs fluorescence.