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We describe a screening method for DNA-targeted anticancer drugs in vitro by using DNA-templated silver nanoclusters (DNA/AgNCs) as a fluorescent probe. It was found that the fluorescence of DNA/AgNCs decreases during the transition of AgNCs from the dispersed to the aggregated state which is the case if the DNA/AgNC-drug complex is formed. The formation of this complex was studied by resonance light scattering (RLS) spectroscopy. The method was applied to a series of organometallic iridium (III) compounds (IrC). Sensitive detection of IrC with the detection limit of 10 mol·L was achieved. The dependence of RLS intensity on IrC amount was successfully utilized to investigate the interactions between IrC and DNA. In addition, assays on cell toxicity and cell apoptosis revealed the anticancer activity of IrC. Specifically, it is found that the iridium (III) bis[2-(4,6-difluorophenyl)pyridinato-N,C]-picolinate complex is a promising candidate for further evaluation as a chemotherapeutic agent. This strategy is reliable, sensitive, and may form the basis for rapid screening of libraries for anti-cancer drugs. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A DNA-templated copper nanoparticle (CuNP) probe has been developed for the determination of the human immunodeficiency virus oligonucleotide (HIV-DNA). The function of the probe relies on affinity binding-induced DNA hybridization associated with the use of double G-quadruplexes. Double-stranded DNA (dsDNA) with poly(AT-TA) bases was used as a template for synthesis of dsDNA-CuNPs. These have weak fluorescence. In the next step, two G-rich sequences that are linked to both sides of the ds-DNA are locked by HIV complementary DNA (cDNA). If HIV-DNA is introduced, it will hybridize with cDNA, thereby transforming the two G-rich sequences into G-quadruplexes. This enhances the fluorescence of the adjacent dsDNA-CuNPs. Fluorescence increases linearly in the 1 to 200 and 250-1000 nM HIV-DNA concentration range, and the detection limit is 13 pM. This enzyme-free fluorometric assay is time-saving, easily operated, and therefore has large potential in biosensing because it may be extended to various other DNA targets.Double-strand DNA-templated copper nanoparticles (DNA-CuNPs) have weak fluorescence. When Human Immunodeficiency Virus oligonucleotide (HIV-DNA) is added, it completely hybridized with HIV complementary DNA (cDNA). As a result, the two exposed G-rich sequences are transformed into G-quadruplexes, and an apparent increase in the fluorescence intensity can be observed. (AA: ascorbic acid). [ABSTRACT FROM AUTHOR]

A molecular beacons (MBs) loaded on molybdenum disulfide (MoS 2) nanosheets as fluorescence probes for sensitive and versatile detection of microRNAs (miRNAs) through hybridization chain reaction (HCR) has been designed. MoS 2 was used as a adsorbent to capture the MBs and a selective fluorescence quencher to reduce the background signal. In the absence of miRNAs, HCR could not be triggered due to the stability of MB probes. The probes attached to the MoS 2 surface, efficiently quenching fluorescence of the G-quadruplex/Thioflavin T. However, the presence of target miRNAs triggers the HCR process to generate large amount of HCR products. Meanwhile, the HCR products of long nanowires chain with abundant G-quadruplexes could not be adsorbed on the surface of MoS 2 , and therefore detach from the MoS 2. Consequently, Thioflavin T could be embedded in G-quadruplexes and produced strong fluorescence signal. This fluorescence emission signal could achieve detection of miRNA as low as 4.2 pM and a wide linear ranges from 0.1 to 100 nM. In addition, a versatile fluorescence probe has been developed for detection of miRNA-21 by changing the miRNA-recognition domain of MB. Thus, the fluorescent probe would be a potential alternative tool for biomedical research and clinical molecular diagnostics. MB1 and MB2 hairpins DNA can absorb onto MoS 2 nanosheets without target miRNA. In the presence of target, it can opened the hairpin structure of MB1 and caused the rest sequence of MB1 to bind with parts of MB2. Similarly, after MB2 was opened, the exposed parts of MB1 hybridized with the complementary sequences of another MB2. Such HCRs can generate a long MB1-MB2 duplex chain which desorbed from MoS 2 nanosheets and the fluorescence intensity of G-quadruplex/ThT was recoveried. Image 1 • A low-background MoS 2 nanosheets-loaded molecular beacon probe with signal amplification by HCR technology for different miRNAs detection. • This lable-free and enzyme-free, high selectivity, cost-saving miRNAs detection assay with the limit of detection as low as 4.2 pM. • MiRNAs detection in cell lysates with satisfactory results. [ABSTRACT FROM AUTHOR]

Abstract A rapid, label-free, and multifunctional fluorescent probe for simultaneous detection of multiple targets was fabricated based on G-quadruplexes and DNA-templated silver nanoclusters (AgNCs). In this work, a probe with two capitated recognized regions was coupled with a locked G-quadruplex at the 5′-terminus and dark AgNC at the 3′-terminus. Upon the addition of the virus subtype H5N1 gene or microRNA-141, only the sequence of the G-quadruplex was released and bound with Thioflavin T (ThT) for a specific fluorescent response. On the contrary, with the presence of the influenza virus subtype H1N1 gene or microRNA-21, the fluorescence intensity was enhanced because of two split AgNCs approaching closely to produce a nanocluster dimer. Subsequently, with multiple target addition, fluorescence signals were produced for both G-quadruplexes and AgNCs. Moreover, this single and duplex detection for virus DNAs and microRNAs, which provides a versatile platform for different targets, was sufficiently sensitive for the expected detection limit, and still possessed unique selectivity with similar oligonucleotides. The simultaneous detection of targets in biological fluids indicated that there is great opportunity for this strategy to be further applied in biomedical research and clinical diagnosis. Graphical abstract Image 1 Highlights • A rapid, label-free and multifunctional fluorescent probe was fabricated to overcome cumbersome labeling procedures. • The system based on G-quadruplexes and DNA-templated silver nanoclusters (AgNCs) was designed for improving the sensitivity for simultaneous detection of virus DNA and microRNA. • The proposed strategy exhibited special selectivity in similar oligonucleotides and could be well applied in biological fluids. • The detection limit for H5N1 and H1N1 was estimated to be 0.45 nM and 10 nM respectively, and for miRNA-141 and miRNA-21was 1 nM and 10 nM respectively. [ABSTRACT FROM AUTHOR]

Abstract A fluorescent biosensing strategy based on three helix molecular beacons (tMBs) for simultaneous simple and rapid detection of HIV related genes was developed. This tMBs contain outer loop sequences and fluorescent probes. The outer loop sequences consist of target capture sequences (cDNA) and the stems can lock the fluorescent probes (P). Initially, the probes were tethered to display weak fluorescence signals in the tMBs. Once the target DNAs opened loops, the stems of tMBs were dehybridized which resulted in turning on the fluorescence. By applying tMBs fluorescent switch detection strategy, the fluorescence response at 484 nm and 367 nm were corresponding to thioflavin (THT) and 2-aminopurine (2-AP) respectively with high selectivity and sensitivity. The detection limits were calculated to be 227 pM for HIV-1 and 352 pM for HIV-2, respectively. As a general detection model for multiple species, the proposed strategy exhibits outstanding analytical performance such as simple, low-cost, and high anti-interference capability, which provides a new and ultrasensitive biosensing platform for multiple DNAs simultaneous detection in biomedical research and early clinical diagnosis. [ABSTRACT FROM AUTHOR]

An efficient dual-amplification system based on catalyzed hairpin assembly (CHA) amplification and hybridization chain reaction (HCR) circuits is developed for G-quadruplex-based and non-enzymatic fluorescence detection of microRNA. Four hairpin probes, namely, H1, H2, H3, and H4, are excellently designed to coexist metastably without a target. Upon the addition of the target, H1 recognizes the target and releases the G-quadruplexes. Meanwhile, H2 fully hybridizes with H1 to form stable H1/H2 duplex that leads to the replacement of the target for participating in another cycle. Moreover, the newly formed product of CHA cycles, H1/H2 duplex, hybridizes with H3 and frees the trigger to open HCR circuits, resulting in the cross-opening of H3 and H4 and self-assembling into a long DNA nanowire with abundant G-quadruplexes. Consequently, many G-quadruplex structures are formed and further combined with thioflavin T for significant fluorescence enhancement. The proposed system can detect miRNA in a wide concentration range with the detection limit as low as 36 fM and can exhibit special selectivity in homologous miRNA sequences. Moreover, this detection assay can be well applied in cancer cell samples, which possesses enormous potential to show novel perspectives in the analysis of biomarkers, clinical diagnostics, and biomedical applications. [ABSTRACT FROM AUTHOR]

The simultaneous detection of two important microRNAs (miRNAs) can potentially evaluate pathological states. The simultaneous detection of miRNA-26a and miRNA-122 is proposed in this study using a cleverly designed single-labeled, dual-functional fluorescent probe with a 2-aminopurine as a fluorophore, which is a G-quadruplex single-stranded DNA. The probe can partly complement cDNA-1 and cDNA-2. cDNA-1 and cDNA-2 are complementary strands of miRNA-26a and miRNA-122, respectively. When the target miRNAs are added simultaneously, these cDNA (cDNA-1 and cDNA-2) can be competed off from the cDNA∖probe duplex to form a cDNA∖RNA heteroduplex. The probe is released and the fluorescent signal is increased. The detection limits of miRNA-26a and miRNA-122 are both 2.5 nM, and their wide linear which ranges from 2.5 to 500 nM are achieved using the assay. This method has potential practical applications. [ABSTRACT FROM AUTHOR]

Here we reported a method for the early diagnosis of ovarian cancer that is respective and simultaneous detection of tumour marker cancer antigen 125 (CA125) and stress-induced phosphoprotein 1 (STIP1) using aptamer-based fluorescent and RLS sensors. The fluorescent sensor was fabricated by Carboxyfluorescein (FAM)-labelled CA125 aptamer and cyanine-5-modified STIP1 aptamer onto the surface of RGO, thereby quenching the fluorescence of fluorophores. When STIP1 was introduced, the fluorescence recovered. When CA125 was added, the specific binding of aptamer and CA125 triggered the release of the FAM-labeled CA125 aptamer under the effect of formaldehyde, and adsorbed on the surface of RGO which lead to fluorescence quenching of FAM. This fluorescence signals change could be used to detect CA125 and STIP1 with the lowest detectable concentration down to 0.05 U mL −1 and 1 ng mL −1 respectively. The RLS sensor was fabricated by methyl violet interact with dsDNA which is obtained by CA125 aptamer hybridized to STIP1 aptamer. The dependence of RLS intensity on targets amount was successfully utilized for simultaneous detection of CA125 and STIP1, which provide robust evidences for the presence of ovarian cancer in the early stage. This strategy is reliable, sensitive, and may form the basis for rapid screening of ovarian cancer. [ABSTRACT FROM AUTHOR]

Herein, a metal-organic framework (UiO-66-NH 2) with two functions (intrinsic fluorescence and fluorescence quenching ability) is designed to establish a ratiometric fluorescent platform for high-performance miRNA detection. The use of a fluorescent organic ligand endows the MOF material with a strong intrinsic fluorescence at 440 nm. In the presence of target miRNA, the fluorescence signal of the FAM is restored with the triple helix molecular beacons bind to the target. Using the I FAM /I MOF signal as the output, the prepared ratiometric probe was able to eliminate disturbance caused by the sensing environment. Under the optimal reaction conditions, including buffer pH of 7.4, temperature of 37 °C, and response time of 1 h, the best detection results can be obtained. The ratiometric fluorescence probe presented showed good sensitivity and selectivity for detecting miRNA-203 and the limit of detection was 400 pM with a wide linear range from 1 nM to 160 nM. In addition, this method was applied to diluted human serum and cell lysates, and good detection effect was realized. In the absence of miRNA-203, the FAM-modified P2 was closed to the UiO-66-NH 2 due to the formation of triple helix molecular beacon, so that the fluorescence of FAM was quenched. In the presence of miRNA-203, the P2 was hybridized with miR-203 and release the long strand DNA P1. Thus, FAM went away from UiO-66-NH 2 , resulting in significant fluorescence enhancement. [Display omitted] • UiO-66-NH 2 can apply to miRNA-203 detection at picomolar level as a new fluorescence quencher and fluorescence output signal. • This UiO-66-NH 2 has a larger surface area, unique resistance to enzyme digestion, and efficient endocytosis. • The proposed fluorescent probe can be further applied to actual samples such as cell lysates and human serum samples. [ABSTRACT FROM AUTHOR]