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  • In this work we constructed a versatile platform


    In this work, we constructed a versatile platform based on MoS2-loaded molecular beacon(MB) and HCR for miRNA detection with high sensitivity and low-background. In this method, the G-quadruplex/Thioflavin T (THT) as fluorescent signal output, which possesses a variety of advantages, such as label-free, low-cost, and stable fluorescence [23,24]. MoS2 nanosheets were used to reduce the background signal and control the ʺon" and ʺoff" of fluorescence. In the absence of miRNAs, HCR could not be triggered due to the stability of two MB probes. The probes attached to the MoS2 surface, efficiently quenching fluorescence of the G-quadruplex/THT. Upon the addition of target miRNAs, the process was continuously amplified through the HCR of two MBs during the operation. As a result, a long double-stranded phospholipase inhibitor with numerous G-quadruplex structures were generated, and it could not be adsorbed on the surface of MoS2, and therefore detach from the MoS2. Consequently, THT were embedded in G-quadruplexes and produced strong fluorescence signal. A sensitive strategy for miRNA detection accompanying with fluorescence “turn-on", signal amplification response can be achieved. This method has great potential for application in clinical diagnostics and cancer research.
    Results and discussion
    Conclusions In summary, a versatile and enzyme-free fluorescence detection method for sensitive analysis of multiple targets, miRNA-199a/b-3p and miRNA-21 was developed through combining HCR technology with MoS2-loaded G-quadruplex MB probes. In this sensing system, MoS2 was used as fluorescence quencher to reduce the background signal. The HCR products with numerous G-quadruplexes for enhanced fluorescence signal with the addition of THT, the resulting signal for sensitive determine multiple targets down to 4.2 pM. Additionally, the proposed strategy is simple and low-cost owing to no complicated labels were required. More noteworthy, it has been successfully used to detect miRNAs in different cell lysates, indicating the novel MoS2-based fluorescent sensing platform have huge potential for diagnosis of cancer.
    Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 21775132, 21305118), Scientific Research Foundation of Hunan Provincial Education Department (No. 16A204), and the National Natural Science Foundation of Hunan province (No.2018JJ2388). Hunan 2011 Collaborative Innovation Center of Chemical Engineering & Technology with Environmental Benignity and Effective Resource Utilization, the project of innovation team of the ministry of education (IRT_17R90), and “1515″academic leader team program of Hunan Agricultural University.
    Introduction The design of small molecule and anion sensors for high sensitively and selectively sensing has long been a focus because of the essential roles of the molecule and ions in medical, industrial and environmental processes [1,2]. Small molecule such as melamine (2, 4, 6-triamino-1, 3, 5-triazine), is widely used in industry for the production of formaldehyde resins [3]. Since the interference of nonprotein nitrogen (NPN) reagent can't be avoided by Kjeldahl method, some fraudulent merchants add melamine into the products to regard as the protein contents [4,5]. Therefore, the addition of melamine in dairy products caused many serious diseases [6]. Iodide (I−), as one of the biologically important anions, is essential for human growth and metabolism as a micronutrient [7,8]. Either the deficiency or abundance of iodide can lead to thyroid disease [9]. Hence, it is highly demanded to develop a simple and sensitive method for the determination of trace melamine and iodide. Until now, various assays have been developed for the determination of melamine, such as mass spectrometry (MS) [10,11], high performance liquid chromatography (HPLC) [12,13], enzyme linked immunosorbent assay (ELISA) [14,15], electrochemiluminescence (ECL) [[16], [17], [18]], electrochemical (EC) method [[19], [20], [21], [22]], atomic fluorescence spectrometry (AFS) [23], colorimetric [24,25], and fluorescence method [[26], [27], [28], [29], [30]]. Techniques used for determination of I− also have been developed, including gas chromatography mass spectrometry (GC–MS) [31], atomic absorption spectrometry (AAS) [32,33], ion chromatography inductively coupled plasma mass spectrometry (IC-ICP-MS) [34], chemiluminescence (CL) [35], capillary electrophoresis (CE) [36] and fluorescence and colorimetric analysis [[37], [38], [39], [40]]. Although these techniques can achieve high sensitivity and selectivity for melamine or I− detection, they are usually requiring expensive instruments, tedious sample treatment and extended times [1,2]. Compared with traditional instrumental methods, fluorescent sensors have attracted sustained interests due to their advantages of homogenous, simplicity, high sensitivity, and excellent selectivity [41]. However, most reported fluorescent aptasensors need laborious and time-consuming modification of aptamers with fluorophores, nanomaterials and quenchers [26,38,42]. And what's more, few probes were developed for small molecule (like melamine) and anions (like I−) detection in one method. Therefore, it is still a great challenge to detect melamine and I− with one strategy.