[Show abstract][Hide abstract] ABSTRACT: Noble metal nanoparticles are currently of great interest because of their unique optical properties and potential applications in disease diagnostics and cancer treatment. In the present work, a discovery was reported that dsDNA with terminal thiols at its two ends could lie easily flat onto the gold nanoparticle (GNP) surface rather than cross linked different GNPs, indicating an unique self-assembly behavior of newly-designed molecules on GNPs. This could intensively stabilize gold nanoparticles against aggregation even at a high salt concentration. On the basis of this discovery, a novel light-up colorimetric sensing strategy was developed for the detection of p53 gene by combining with the cyclical nucleic acid strand-displacement polymerization (CNDP). For the described colorimetric system, GNPs require no any surface functionalization, and target recognition reaction and CNDP amplification could be conducted under the optimized conditions to achieve a high efficiency. The high detection sensitivity and desirable selectivity are achieved, and the potential practical application was demonstrated. Besides, this sensing system can function in a wide range of salts, making it a suitable platform to cooperate with many biological processes.
[Show abstract][Hide abstract] ABSTRACT: DNA strand displacement cascades have been engineered to construct various fascinating DNA circuits. However, biological applications are limited by the insufficient cellular internalization of naked DNA structures, as well as the separated multicomponent feature. In this work, these problems are addressed by the development of a novel DNA nanodevice, termed intelligent layered nanoflare, which integrates DNA computing at the nanoscale, via the self-assembly of DNA flares on a single gold nanoparticle. As a "lab-on-a-nanoparticle", the intelligent layered nanoflare could be engineered to perform a variety of Boolean logic gate operations, including three basic logic gates, one three-input AND gate, and two complex logic operations, in a digital non-leaky way. In addition, the layered nanoflare can serve as a programmable strategy to sequentially tune the size of nanoparticles, as well as a new fingerprint spectrum technique for intelligent multiplex biosensing. More importantly, the nanoflare developed here can also act as a single entity for intracellular DNA logic gate delivery, without the need of commercial transfection agents or other auxiliary carriers. By incorporating DNA circuits on nanoparticles, the presented layered nanoflare will broaden the applications of DNA circuits in biological systems, and facilitate the development of DNA nanotechnology.
[Show abstract][Hide abstract] ABSTRACT: A novel liquid crystal (LC) biosensor was developed for the detection of platelet-derived growth factor BB (PDGF-BB) based on the orientation changes of liquid crystals. One glass slide of the LC cell was first modified with the APTES/DMOAP ((3-aminopropyl)trimethoxysilane/N,N-dimethyl-N-octadecyl(3-aminopropyl) trimethoxysilyl chloride) self-assembled monolayer (SAM) to trigger the homeotropic alignment of LC molecules and thereby produced a black background optical image under the crossed polarized light, and then the specific aptamer of PDGF-BB was immobilized on SAM through glutaraldehyde crosslinking to construct a LC sensing substrate. In the presence of PDGF-BB, the stable triple helix structure of PDGF-BB aptamer was formed by the specific binding event and thus led to the target PDGF-BB was captured to the sensing substrate, making a visible optical change which could be observed under the crossed polarized light via the huge steric effect of the PDGF-BB on disrupting the LC alignment. However, in the absence of PDGF-BB, the low packing density of the PDGF-BB aptamer had little effect on disrupting the ordered alignment to the LC and caused the black background optical image which could also be observed under the crossed polarized light. An obvious optical change was observed when the concentration of target PDGF-BB was 5 nM. The proposed LC biosensing method permits the label-free detection of PDGF-BB with good selectivity and high sensitivity, making them sufficiently simple and particularly useful for low-cost screening bioassay performed away from central laboratories.
Chinese Journal of Analytical Chemistry 05/2014; 42(5):629–635. DOI:10.1016/S1872-2040(13)60729-X · 0.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The water-soluble CP was conjugated with a rhodamine spirolactam for the first time to develop a new FRET-based ratiometric fluorescence sensing platform () for intracellular metal-ion probing. exhibits excellent water-solubility with two well-resolved emission peaks, which benefit ratiometric intracellular imaging applications.
Chemical Communications 01/2014; 50(16). DOI:10.1039/c3cc48649d · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work, by combining the enzymatic recycling reaction with the DNA functionalized gold nanoparticles (AuNPs)-based signal amplification, we have developed an electrochemical biosensor for label-free detection of DNA with high sensitivity and selectivity. In the new designed biosensor, a hairpin-structured probe HP was designed to hybridize with target DNA first, and an exonuclease ExoIII was chosen for the homogeneous enzymatic cleaving amplification. The hybridization of target DNA with the probe HP induced the partial cleavage of the probe HP by ExoIII to release the enzymatic products. The enzymatic products could then hybridize with the hairpin-structured capture probe CP modified on the electrode surface. Finally, DNA functionalized AuNPs was further employed to amplify the detection signal. Due to the capture of abundant methylene blue (MB) molecules by both the multiple DNAs modified on AuNPs surface and the hybridization product of capture DNA and enzymatic products, the designed biosensor achieved a high sensitivity for target DNA, and a detection limit of 0.6pM was obtained. Due to the employment of two hairpin-structured probes, HP and CP, the proposed biosensor also exhibited high selectivity to target DNA. Moreover, since ExoIII does not require specific recognition sequences, the proposed biosensor might provide a universal design strategy to construct DNA biosensor which can be applied in various biological and medical samples.
[Show abstract][Hide abstract] ABSTRACT: Aptamer-based fluorescence anisotropy (FA) assays have attracted great interest in recent years. However, a key factor that determines FA value is molar mass, thus limiting the utility of this assay for the detection of small molecules. To solve this problem, streptavidin, as a molar mass amplifier, was used in a hybridization chain reaction (HCR) to construct a target-triggered cyclic assembly of DNA-protein hybrid nanowires for highly sensitive detection of small molecules by fluorescence anisotropy. In this assay, one blocking DNA strand is released by target-aptamer recognition. The DNA then serves as an initiator to trigger enzyme-free autonomous cross-opening of hairpin probes via HCR to form a DNA nanowire for further assembly of streptavidin. Using adenosine triphosphate (ATP) as the small molecule target, this novel dual-amplified, aptamer-based FA assay affords high sensitivity with a detection limit of 100 nM. This LOD is much lower than that of the disassembly approach without HCR amplification or the assembly strategy without streptavidin. In contrast to the previous turn-off disassembly approaches based on nonspecific interactions between the aptamer probe and amplification moieties, the proposed aptamer-based FA assay method exhibits a turn-on response to ATP, which can increase sensing reliability and reduce the risk of false hits. Moreover, because of its resistance to environmental interferences, this FA assay has been successfully applied for direct detection of 0.5 μM ATP in complex biological samples, including cell media, human urine, and human serum, demonstrating its practicality in real complex biological systems.
[Show abstract][Hide abstract] ABSTRACT: An indirect competitive electrochemical immunosensor based on gold colloid-mediated hapten assembly was developed for the determination of clenbuterol (CLB), a beta-agonist drug that has been proved to be very toxic to human beings. The sensing substrate was prepared using a gold electrode modified with a self-assembled monolayer of 1, 6-hexanedithiol that mediated the assembly of a gold colloid layer, which adsorbed clenbuterol and bovine serum albumin conjugates onto the electrode surface. After competition for the limited anti-CLB mouse monoclonal antibody between immobilized hapten and CLB analyte in sample solution, alkaline phosphatase (ALP)-labeled horse anti-mouse IgG antibody reacted selectively with the primary antibodies captured on the electrode surface. Electrochemical response was produced by the oxidation of enzymatic product of 1-naphthyl phosphate. Under the optimal conditions, the ALP-mediated redox signals were inversely correlated to the concentration of the CLB analyte in the range of 0.1 mu g/L to 1000 mu g/L. The regression equation was I( A) = 8.79 X 10(-7) 2.66 X 10(-7) logC (mu g/L) with a correlation coefficient of 0.9960. The detection limit was estimated to be 20 pg/mL. Furthermore, the proposed electrochemical immunosensor was used to detect the content of clenbuterol in pork tissues with an average relative standard of 7.0%, and the recoveries were in the range from 89.1% to 105.6%. The statistical results for the same concentration level obtained by the proposed method and traditional indirect competitive ELISA were comparable, proving the feasibility of the electrochemical immunosensor for accurate determination of CLB in real samples.
CHINESE JOURNAL OF ANALYTICAL CHEMISTRY 08/2013; 40(8):1147-1152. DOI:10.3724/SP.J.1096.2012.20055 · 0.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work, we developed a multiple amplification-based electrochemical sensor for ultra-sensitive detection of nucleic acids, using a disease-related sequence of p53 gene as the model target. A capture probe (CP) with hairpin structure is immobilized on the electrode surface via thiol-gold bonding, while its stem is designed to contain a restriction site for EcoRI. In the absence of target DNA, the probe keeps a closed conformation and forms a cleavable region. After treated with EcoRI, the target binding portion (loop) plus the biotin tag can be peeled off, suppressing the background current. In contrast, the CP is opened by the target hybridization, deforming the restriction site and forcing the biotin tag away from the electrode. Based on the biotin-streptavidin complexation, gold nanoparticles (GNPs) modified with a large number of ferrocene-signaling probes (Fc-SPs) are captured by the resulting interface, producing an amplified electrochemical signal due to the GNP-based enrichment of redox-active moieties. Furthermore, Fc tags can be dragged in close proximity to the electrode surface via hybridization between the signaling probes and the CP residues after EcoRI treatment, facilitating interfacial electron transfer and further enhancing the signal. With combination of these factors, the present system is demonstrated to achieve an ultrahigh sensitivity of zeptomole level and a wide dynamic response range of over seven orders of magnitudes.
[Show abstract][Hide abstract] ABSTRACT: H2S is the third endogenously generated gaseous signaling compound, and has also been known to involve in a variety of physiological processes. To better understand its physiological and pathological functions, efficient methods for direct monitoring of H2S in living systems are desired. Although quite a few one photon fluorescence probes have been reported for H2S, two-photon (TP) probes are more favorable for intracellular imaging. In this work, by employing a Donor--Acceptor-structured naphthalene derivative as the two-photon fluorophore and an azide group as the recognition unit, we reported a new two-photon bio-imaging probe 6-(benzo[d]thiazol-2-yl)-2-azidonaphthalene (NHS1) for H2S with improved sensitivity. The probe shows very low background fluorescence in the absence of H2S. In the presence of H2S, however, a significant enhancement for both one photon and TP excited fluorescence were observed, resulting in a high sensitivity to H2S in aqueous solutions with a detection limit of 20 nM observed, much lower than previously reported TP probe. The probe also exhibits a wide linear response concentration range （0-5 μM）to H2S with high selectivity. All these features are favorable for direct monitoring of H2S in complex biological samples. It was then applied for direct TP imaging of H2S in living cells with satisfactory sensitivity, demonstrating its value of practical application in biological systems.
[Show abstract][Hide abstract] ABSTRACT: A novel fluorometric assay method based on target-induced signal on was developed for acetylcholinesterase (AChE) inhibitor with obviously improved detection sensitivity. In this method, the AChE molecules catalyzed the hydrolysis of acetylthiocholine (ATCl) to form thiocholine, which in turn can specifically react with fluorescent squaraine derivative, a specific chemodosimeter for thiol-containing compounds, resulting in fluorescence quenching and offering a low fluorometic background for the further detection of AChE inhibitor. In the presence of AChE inhibitor, the catalytic hydrolysis of ATCl is blocked, and then the squaraine derivative remains intact and shows signal-on fluorescence. The amount of the remaining fluorescent squaraine derivative is positively correlated with that of the AChE inhibitor in solution. This new designed sensing system shows an obviously improved sensitivity towards target with a detection limit of 5 pg mL-1 (0.018 nM) for the AChE inhibitor, compared favorably with previously reported fluorometric methods. To our best knowledge, this new method is the first example of fluorometric enzymatic assay for AChE inhibitors based on such a signal-on principle and using a specific reaction, which has potential to offer an effective strategy for the detection of AChE inhibitors.
[Show abstract][Hide abstract] ABSTRACT: Gold nanoparticles-based colorimetric assay possesses several unique advantages, and has been applied for a wide range of targets, varying from nucleic acids to different metal ions. However, due to the lack of proper coordinating ligand, gold nanoparticles-based colorimetric sensing system for Au(3+) has not been developed so far. It is well-known that Au(3+) could induce the oxidation transition of thiol compounds to disulfide compounds. In this article, for the first time we converted such thiol masking reaction into colorimetric sensing system for label-free detection of Au(3+) via a target-controlled aggregation of nanoparticles strategy. In the new proposed sensing system, fluorosurfactant-capped gold nanoparticles were chosen as signal reporter units, while an Au(3+)-triggered oxidation of cysteine (Cys), which inhibited the aggregation of gold nanoparticles, acted as the recognition unit. By varying the amount of Cys, a tunable response range accompanied with different windows of color change could be obtained for Au(3+), illustrating the universality of the sensing system for Au(3+) samples with different sensitivity requirements. Under optimized condition, the proposed sensing system exhibits a high sensitivity towards Au(3+) with a detection limit of 50nM, which is lower than previously reported spectroscopic methods. It has also been applied for detection of Au(3+) in practical water samples with satisfactory result.
[Show abstract][Hide abstract] ABSTRACT: A new and facile strategy using double-stranded DNA-copper nanoparticles (dsDNA-Cu NPs) as fluorescence reporters for the highly sensitive and selective detection of l-histidine was demonstrated. In the dsDNA-Cu NPs-based sensing system, the fluorescence was quenched considerably upon the addition of l-histidine. Under the optimized experimental conditions, the probe exhibits excellent performance (e.g., a satisfactory detection limit of 5μM and high specificity). Our in situ method requires no covalent attachment of DNA to a fluorophore, which could significantly reduce the cost and simplify the procedure for l-histidine detection. Moreover, the proposed sensing system could be applicable for the detection of target biomolecule in complex biological samples. These striking properties make it an attractive platform for the direct detection of l-histidine.
[Show abstract][Hide abstract] ABSTRACT: A novel template-dependent extension based isothermal amplification (TEIA) system with high single-base discrimination capability is developed, where the interference caused by non-specific reaction in isothermal strand displacement amplification (SDA) technique is substantially avoided via using a functionalized template probe, showing potential value in the development and application of SDA based detection devices.
Chemical Communications 02/2013; 49(24):2448-50. DOI:10.1039/c3cc38358j · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The self-assembly of cyclodextrin (CD) functionalized graphene (GR) and adamantane-modified horseradish peroxidase (HRP-ADA) by host-guest supramolecular interaction into novel nanostructures in aqueous solution is reported in the present study. Electrochemical impedance spectroscopy and cyclic voltammetry were applied to characterize the self-assembly process and study the electrochemical behaviors of the immobilized proteins. UV-vis spectra indicated that the native structure of HRP was maintained after the assembly, implying good biocompatibility of CD-functionalized GR (CD-GR). Furthermore, the HRP-ADA/CD-GR composites were utilized for the fabrication of enzyme electrodes (HRP-ADA/CD-GR electrodes). The proposed biosensor showed good reproducibility and high sensitivity to H2O2 with the detection limit of 0.1μM. In the range of 0.7-35μM, the catalytic reduction current of H2O2 was proportional to H2O2 concentration.
[Show abstract][Hide abstract] ABSTRACT: The development of autonomous DNA machines and their use for specific sensing purpose have recently attracted considerable research attention. In existing autonomous machines, the target recognition process and signal transduction are separated from each other. This results in misunderstanding of the operation behavior, and the assay capability is compromised when serving as a sensing tool. In this communication, the integrated signal transduction-based autonomous aptameric machine, in which the recognition element and signal reporters are integrated into a DNA strand, is developed. This new machine can execute the in situ amplification of target binding-induced signal. The authentic operation behavior of autonomous DNA machine is discovered: the machine's products directly hybridize to the "track" rather than to the signaling probes. Along this line, the machine is employed to detect the cocaine in a more straightforward fashion, and improved assay characteristics (for example, the dynamic response range is widened by more than 500-fold) are achieved. Our efforts not only clarify the concept described in traditional autonomous DNA machines but also have made technological advancements that are expected to be especially valuable in designing nucleic acid-based machines employed in basic research and medical diagnosis.
[Show abstract][Hide abstract] ABSTRACT: The generation of 8-oxo-7,8-dihydroguanine (8-oxoG) in DNA is a common type of DNA damage after exposure to reactive oxygen species or drugs. Human 8-oxoG DNA glycosylase/AP lyase (hOGG1) is a kind of base excision repair enzyme specifically used to repair the base excision of 8-oxoG. In this paper, we develop a novel, simple and sensitive strategy for the detection of hOGG1 activity based on the self-assembly of the active HRP-mimicking DNAzyme coupled with lambda exonuclease (λ exo) cleavage. We designed two DNA oligonucleotides that are fully complementary to each other. One is modified with 8-oxoG, the other contains the G-quadruplex DNAzyme sequence. The two single-stranded DNA (ssDNA) firstly hybridize to form a DNA duplex containing an 8-oxoG. In the presence of hOGG1, the formed DNA duplex is selectively cleaved at the 8-oxoG site, yielding a new DNA duplex with a recessed 5′-phosphate terminus. Upon treatment with λ exo, the 5′-phosphoryl ssDNA of the new DNA duplex is digested by λ exo, releasing the G-quadruplex DNAzyme sequence. After addition of hemin, the G-quadruplex–hemin complex is used as a peroxidase-mimicking DNAzyme, catalyzing H2O2-mediated oxidation of 2,2′-azinobis(3-ethylbenzothiozoline)-6-sulfonic acid (ABTS2−) to generate a colorimetric signal. The activity of hOGG1 is directly related to UV/Vis absorption intensity. The results revealed that the method allowed a sensitive quantitative assay of the hOGG1 concentration with a wide range from 0.05–32 U mL−1 and a low detection limit of 0.01 U mL−1.
[Show abstract][Hide abstract] ABSTRACT: In this study, to surmount the dependence of LC biosensor on the geometrical dimension of responsing molecules, we designed a new label-free LC biosensor for the highly selective and sensitive detection of heavy metal ions. This strategy takes use of the target-induced DNA conformational change to enhance the disruption of target molecules for the orientation of LC leading to an amplified optical signal. The Hg2+ ion, which possesses a unique property to bind specifically to two DNA thymine base (T), is used as a model heavy metal ions. In the presence of Hg2+, the specific oligonucleotide probes form a conformational reorganization of the oligonucleotide probes from hairpin structure to duplex-like complexes. The duplex-like complexes are then bound on the TEA/DMOP-coated substrate modified with capture probes, which can greatly distort the orientational profile of LC, making the optical image of LC cell birefringent as a result. The optical signal of LC sensor has a visible change at the Hg2+ concentration low to 0.1 nM, showing good detection sensitivity. The cost-effective LC sensing method can translate the concentration signal of heavy metal ions in solution into the presence of DNA duplexes, and is expected to be a sensitive detection platform for heavy metal ions and other small molecule monitor.
[Show abstract][Hide abstract] ABSTRACT: FRET strategy has been widely applied in designing ratiometric probes for bio-imaging applications. Unfortunately, for FRET systems, sufficiently large spectral overlap is necessary between the donor emission and the acceptor absorption, which would limit the resolution of double-channel images. Through-bond energy transfer (TBET) system does not need spectral overlap between donor and acceptor, and could afford large wavelength difference between the two emissions with improved imaging resolution and higher energy transfer efficiency than that of classic FRET system. It seems to be more favorable for designing ratiometric probes for bio-imaging applications. In this paper, we have designed and synthesized a coumarin-rhodamine (CR) TBET system, and demonstrated that TBET is a convenient strategy to design efficient ratiometric fluorescent bio-imaging probe for metal ions. Such TBET strategy is also universal, since no spectral overlap between the donor and the acceptor is necessary, and much more dye pairs than that of FRET could be chosen for probe design. As a proof-of-concept, Hg2+ was chosen as a model metal ion. By combining TBET strategy with dual-switch design, the proposed sensing platform shows two well-separated emission peaks with a wavelength difference of 110 nm, high energy transfer efficiency and a large signal-to-background ratio, which affords a high sensitivity for the probe with a detection limit of 7 nM for Hg2+. Moreover, by employing an Hg2+-promoted desulfurization reaction as recognition unit, the probe also shows a high selectivity to Hg2+. All these unique features make it particularly favorable for ratiometric Hg2+ sensing and bioimaging applications. It has been preliminarily used for ratiometric image of Hg2+ in living cells and practical detection of Hg2+ in river water samples with satisfying results.