Iron-substituted SBA-15 microparticles: a peroxidase-like catalyst for H2O2 detection

In this communication, we demonstrate our recent finding that iron-substituted SBA-15 (Fe-SBA-15) microparticles possess intrinsic peroxidase-like activity and can catalyze the oxidation of peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) by H(2)O(2) to develop a blue color in aqueous solution, leading to a simple approach towards colorimetric detection of H(2)O(2) with a linear detection range from 0.4 μM to 15 μM (r = 0.997) and a detection limit of 0.2 μM.     

A sensitive, label-free, aptamer-based biosensor using a gold nanoparticle-initiated chemiluminescence system

We report a label-free, aptamer-based chemiluminescent biosensor. The biosensor relies upon the catalytic activity of unmodified gold nanoparticles (AuNPs) on the luminol-H(2)O(2) chemiluminescence (CL) reaction, and the interaction of unmodified AuNPs with the aptamer. The unmodified AuNPs can effectively differentiate unstructured and folded aptamer. The binding of the aptamer with the target can induce the AuNP aggregation in the presence of 0.5 M NaCl, and after aggregation the catalytic activity of the AuNPs on the luminol-H(2)O(2) CL reaction is greatly enhanced. During the assay, no covalent functionalization of the AuNPs or aptamer is required. The detection limit of thrombin was estimated to be as low as 26 fM, and the sensitivity was more than 4 orders of magnitude better than that of known AuNP-based colorimetric methods for the detection of thrombin. This aptamer-based biosensor offers the advantages of being simple, cheap, rapid, and sensitive.     

Aptamer functionalized microcantilever sensors for cocaine detection

A cocaine-specific aptamer was used as a receptor molecule in a microcantilever-based surface stress sensor for detection of cocaine molecules. An interferometric technique that relies on measuring differential displacement between two microcantilevers (a sensing/reference pair) was utilized to measure the cocaine/aptamer binding induced surface stress changes. Sensing experiments were performed for different concentrations of cocaine from 25 to 500 μM in order to determine the sensor response as a function of cocaine concentration. In the lower concentration range from 25 to 100 μM, surface stress values increased proportionally to coverage of aptamer/cocaine complexes from 11 to 26 mN/m. However, as the cocaine concentration was increased beyond 100 μM, the surface stress values demonstrated a weaker dependence on the affinity complex surface coverage. On the basis of a sensitivity of 3 mN/m for the surface stress measurement, the lowest detectable threshold for the cocaine concentration is estimated to be 5 μM. Sensing cantilevers could be regenerated and reused because of reversible thermal denaturation of aptamer.     

基于谷胱甘肽抑制纳米金催化3,3’,5,5’-四甲基联苯胺与过氧化氢反应比色检测谷胱甘肽

采用具有类似过氧化物酶活性的金纳米粒子(AuNPs)催化四甲基联苯胺(TMB)-H2O2反应,氧化产物(oxTMB)被谷胱甘肽(GSH)还原成TMB,导致吸光度下降,颜色由蓝色变为无色。利用上述现象,设计了一种超灵敏检测谷胱甘肽的比色传感器。在10 pmol/L~10μmol/L范围内,吸光度随GSH浓度呈良好的线性降低关系,检出限为7.5 pmol/L。该方法可以定量检测人血清中的谷胱甘肽。     

A novel colorimetric determination of reduced glutathione in A549 cells based on Fe3O4 magnetic nanoparticles as peroxidase mimetics

In this paper, a novel and simple colorimetric method for the determination of reduced glutathione (GSH) based on Fe(3)O(4) magnetic nanoparticles (MNPs) as peroxidase mimetics was developed. The Fe(3)O(4) MNPs prepared via a coprecipitation method, which possess intrinsic peroxidase-like activity, were used as a catalyst in the color development reaction of a peroxidase substrate 2,2'-azino-bis(3-thylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS) and H(2)O(2). The existence of GSH can consume H(2)O(2) and cause a color change of the reaction system which can be detected by the naked eye. Accordingly, the GSH can be detected by measuring the wastage of H(2)O(2). A good linear relationship was obtained from 3.0 to 30.0 μM for GSH. Good recoveries ranging from 96.7 to 107% were obtained. Furthermore, it was used to detect GSH in A549 cells.     

增强氯化血红素催化活性用于水胺硫磷比色检测研究

建立了一种基于增强氯化血红素(Hemin)过氧化物酶催化活性比色检测水胺硫磷的方法.在H2O2存在下, Hemin催化氧化底物3,3′,5,5′-四甲基联苯胺(TMB), 使其失去1个电子, 导致反应体系由无色变为蓝绿色.水胺硫磷的加入可提高Hemin对底物亲和力, 进一步增强其催化活性, 使底物氧化失去2个电子, 反应体系由蓝绿色变为黄色, 且颜色变化程度与水胺硫磷浓度成正比.在最优条件下, 本方法的动态检测范围为2～100 μg/L, 检出限为1.2 μg/L(3σ).其它有机磷农药对水胺硫磷检测无明显干扰, 实际样品中水胺硫磷的加标回收率为93.0％～113.0％. 本方法可应用于农产品中水胺硫磷残留的检测.     

Aptamer-functionalized magnetic nanoparticle-based bioassay for the detection of ochratoxin A using upconversion nanoparticles as labels

A sensitive luminescent bioassay for the detection of ochratoxin A (OTA), a small molecular mycotoxin, was developed using aptamer-conjugated magnetic nanoparticles (MNPs) as the recognition and concentration element and upconversion nanoparticles (UCNPs) as highly sensitive labels. The bioassay system was fabricated by immobilizing aptamer DNA 1 sequence onto the surface of Fe(3)O(4) MNPs, which were implemented to capture and concentrate OTA from bulk samples. The aptamer DNA 1 sequence then hybridized with UCNPs modified with DNA 2 sequence, which could dissociate from DNA 1 and result in a decreased luminescent signal when aptamer DNA 1 recognized and bound to target OTA. Under the optimal conditions, the decreased luminescent intensity (ΔI) is proportional to the concentration of OTA in the range of 1 × 10(-13) to 1 × 10(-9) g mL(-1) with a detection limit of 1 × 10(-13) g mL(-1). The proposed method then was successfully applied to measure OTA in naturally contaminated maize samples and validated by a commercially available enzyme-linked immunosorbent assay (ELISA) method. Benefiting from the magnetic separation and concentration effect of MNPs, the high sensitivity of UCNPs, as well as the selectivity and stability of the aptamer, the present upconversion luminescent bioassay offers a promising approach for the screening of small molecular mycotoxins because it is simple, rapid, highly sensitive, specific, does not require sample pre-concentration and lacks interference from autofluorescence of other biomolecules.     

Electrochemical Aptasensor for the Determination of Cocaine Incorporating Gold Nanoparticles Modification

A novel electrochemical aptasensor incorporating a signal enhancement for the determination of cocaine was designed. Gold nanoparticles were self‐assembled onto the surface of a gold electrode through 1,6‐hexanedithiol. A bifunctional derivative of the 32‐base cocaine‐binding aptamer with a redox‐active ferrocene moiety and a thiol linker group at the termini of the strand was self‐assembled onto the surface of gold nanoparticles. The oxidation peak current is linearly related to the concentration of cocaine from 1.0 to 15.0 μM with a detection limit of 0.5 μM. It was found that the sensitivity of the aptasensor with gold nanoparticles modification was ca. 10‐fold higher than that of the aptasensor without gold nanoparticles modification. This work demonstrates that gold nanoparticles‐assembled gold electrode provides a promising platform for immobilizing aptamer and enhancing the sensitivity.     

聚集诱导发光分子/适配体/外切酶Ⅰ体系对可卡因的检测

目前非法药物的滥用已经成为全球性的公共安全卫生问题之一[1~3].其中可卡因作为一种全球禁用的非法药物,长期滥用会对人体造成许多不良的影响,如精神疾病、失眠、抑郁和暴力倾向等,甚至威胁生命,同时,吸食可卡因还会导致出现各种社会问题[4,5].因此实现对可卡因的快速检测成为打击毒品犯罪、维护社会稳定的关键.目前对于可卡因的检测主要采用气相色谱/质谱(GC/MS)和液相色谱/质谱(LC/MS)等大型仪器.虽然能够实现对可卡因检测,但大多需要专业人员操作且耗时较长,因此开发一种简便、高效且可靠的可卡因检测方法成为研究的热点[6~8].其中,基于荧光探针的检测手段由于具有高效、灵敏及便捷等优势而备受关注,但传统的荧光探针面临聚集导致发光猝灭(ACQ)的难题[9,10],即这类分子在溶液中发光非常强,一旦聚集或在固体中发光显著减弱,非常不利于实际应用.     

Label-free Electrochemical Aptasensor for the Determination of Serotonin

A label-free electrochemical aptasensor was fabricated for the determination of serotonin (5-HT) by the employment of specific binding between 5-HT and aptamer and directly electrochemical measurement of 5-HT oxidation. The comparison between two aptasensors and two strategies was studied. An electrochemical aptasensor fabricated using 57-mer aptamer was facilely used to determine 5-HT in the range from 1 μM to 100 μM with detection limit of 0.3 μM via one step recognition and detection. This work demonstrates that electrochemical method combing aptamer recognition and 5-HT oxidation provides an alternative and promising method for the determination of 5-HT with good selectivity and simplicity.     

Aptamer enzymatic cleavage protection assay for the gold nanoparticle-based colorimetric sensing of small molecules

A label-free, homogeneous aptamer-based sensor strategy was designed for the facile colorimetric detection of small target molecules. The format relied on the target-induced protection of DNA aptamer from the enzymatic digestion and its transduction into a detectable signal through the length-dependent adsorption of single-stranded DNA onto unmodified gold nanoparticles (AuNPs). The proof-of-principle of the approach was established by employing the anti-tyrosinamide aptamer as a model functional nucleic acid. In the absence of target, the aptamer was cleaved by the phosphodiesterase I enzymatic probe, leading to the release of mononucleotides and short DNA fragments. These governed effective electrostatic stabilization of AuNPs so that the nanoparticles remained dispersed and red-colored upon salt addition. Upon tyrosinamide binding, the enzymatic cleavage was impeded, resulting in the protection of the aptamer structure. As this long DNA molecule was unable to electrostatically stabilize AuNPs, the resulting colloidal solution turned blue after salt addition due to the formation of nanoparticle aggregates. The quantitative determination of the target can be achieved by monitoring the ratio of absorbance at 650 and 520 nm of the gold colloidal solution. A limit of detection of ∼5 μM and a linear range up to 100 μM were obtained. The sensing platform was further applied, through the same experimental protocol, to the adenosine detection by using its DNA aptamer as recognition tool. This strategy could extend the potentialities, in terms of both simplicity and general applicability, of the aptamer-based sensing approaches.     

Reusable split-aptamer-based biosensor for rapid detection of cocaine in serum by using an all-fiber evanescent wave optical biosensing platform

A rapid, facile, and sensitive assay of cocaine in biological fluids is important to prevent illegal abuse of drugs. A two-step structure-switching aptasensor has been developed for cocaine detection based on evanescent wave optical biosensing platform. In the proposed biosensing platform, two tailored aptamer probes were used to construct the molecular structure switching. In the existence of cocaine, two fragments of cocaine aptamer formed a three-way junction quickly, and the fluorophore group of one fragment was effectively quenched by the quencher group of the other one. The tail of the three-way junction hybridized with the cDNA sequences immobilized on the optical fiber biosensor. Fluorescence was excited by evanescent wave, and the fluorescence signal was proportional to cocaine concentration. Cocaine was detected in 450 s (300 s for incubation and 150 s for detection and regeneration) with a limit of detection (LOD) of 165.2 nM. The proposed aptasensor was evaluated in human serum samples, and it exhibited good recovery, precision, and accuracy without complicated sample pretreatments.     

Ultrasensitive Detection and Binding Mechanism of Cocaine in an Aptamer‐based Single‐molecule Device

Aptamer serves as a potential candidate for the micro‐detection of cocaine due to its high specificity, high affinity and good stability. Although cocaine aptasensors have been extensively studied, the binding mechanism of cocaine‐aptamer interactions is still unknown, which limits the structural refinement in the design of an aptamer to improve the performance of cocaine aptasensors. Herein, we report a label‐free, ultrasensitive detection of single‐molecule cocaine‐aptamer interaction by using an electrical nanocircuit based on graphene‐molecule‐ graphene single‐molecule junctions (GMG‐SMJs). Real‐time recordings of cocaine‐aptamer interactions have exhibited distinct current oscillations before and after cocaine treatment, revealing the dynamic mechanism of the conformational changes of aptamer upon binding with cocaine. Further concentration‐dependent experiments have proved that these devices can act as a single‐molecule biosensor with at least a limit of detection as low as 1 nmol?L^–1. The method demonstrated in this work provides a novel strategy for shedding light on the interaction mechanism of biomolecules as well as constructing new types of aptasensors toward practical applications.     

Colorimetric Detection of Glucose Using WO3 Nanosheets as Peroxidase-mimetic Enzyme

In the present work, WO₃ nanosheets(WO₃ NSs) were prepared by a facile method at room temperature. The obtained WO₃ NSs showed peroxidase-like activity, which could catalyze 3,3',5,5'-tetramethylbenzidine(TMB) to form a blue oxidation product(ox TMB) in the presence of H₂O₂. Based on this, convenient and sensitive colorimetric methods for the detection of H₂O₂ and glucose were established. The linear ranges for detecting H₂O₂ and glucose were 1-200 μmol/L and 1-100 μmol/L, respectively. The limits of the detection of H₂O₂ and glucose were as low as 0.79 and 0.96 μmol/L, respectively. This method was also successfully applied to the detection of glucose in urine samples. The detection result was consistent with that of the value detected by the clinical method, indicating the potential in clinical diagnosis and biomedical detection.     

高灵敏检测葡萄糖的新型荧光纳米传感器

构建了一种用于高灵敏检测葡萄糖的新型荧光纳米传感器.在辣根过氧化物酶(HRP)的催化下,H2O2氧化3,3′,5,5′-四甲基联苯胺(TMB),生成具有强吸光性质的TMB多聚体,导致1-氧-1H-非那烯-2,3-二腈(1-Oxo-1H-phenalene-2,3-dicarbonitrile, OPD)分子的荧光发生淬灭,基于此实现H2O2的定量检测,线性范围分别为0.05~0.80 μmol/L和1~10 μmol/L,检出限(3σ)为0.02 μmol/L.由于葡萄糖氧化酶(Gox)可催化葡萄糖分解产生H2O2,基于此可以实现葡萄糖分子的定量检测,线性范围分别为0.1~3.0 μmol/L和4.0~30 μmol/L, 检出限(3σ)为0.02 μmol/L.将本方法用于实际血清样品中葡萄糖的定量检测,结果与临床检测结果相符.     

Electrochemical Conversion of Magnetic Nanoparticles Using Disposable Working Electrode in a 3D‐Printed Electrochemical Cell

Exploration of new property/function of nanomaterials is always a strong impetus in the nanoscience field. Here, a new method of electrochemical conversion (ECC) of magnetic nanoparticles (MNPs) is proposed to endow MNPs with signal generation ability for sensing. Briefly, high potential was applied to split H₂O to generate acid, while Fe₃O₄ MNPs reacted with H⁺ and produce ferric/ferrous ions, which further reacted with K₄Fe(CN)₆ to yield Prussian blue (PB) through potential cycling. The ECC method worked well on both home‐made and commercial MNPs with different sizes. The generated PB possessed strong electrochemical activity for further applications. Interestingly, an uneven deposition of PB on working electrode and undesired contamination of the reference and counter electrodes were found when using commercial integrated three‐electrode chip. A 3D‐printed electrochemical cell was designed to facilitate the ECC and avoid drawbacks of commercial integrated electrode. The 3D‐printed electrochemical cell was proven to solve the problem above through spatial separation of electrodes and thus facilitated the ECC process. An electrochemical sensor for H₂O₂ detection based on the catalysis ability of ECC‐based PB exhibited a linear response from 5 μM to 1 mM, a high sensitivity of 269 μA mM^?1 cm^?2 and a low detection limit of 0.16 μM (S/N=3), which suggests its promising application prospect in electrochemistry‐related analysis.     

Fabrication of nanoporous nanocomposites entrapping Fe3O4 magnetic nanoparticles and oxidases for colorimetric biosensing

A nanostructured multicatalyst system consisting of Fe(3)O(4) magnetic nanoparticles (MNPs) as peroxidase mimetics and an oxidative enzyme entrapped in large-pore-sized mesoporous silica has been developed for convenient colorimetric detection of biologically important target molecules. The construction of the nanocomposites begins with the incorporation of MNPs on the walls of mesocellular silica pores by impregnating Fe(NO(3))(3)·9H(2)O, followed by the immobilization of oxidative enzymes. Glutaraldehyde crosslinking was employed to prevent enzymes leaching from the pores and led to over 20 wt% loading of the enzyme. The oxidase in the nanocomposite generates H(2)O(2) through its catalytic action for target molecules and subsequently activates MNPs to convert selected substrates into colored products. Using this strategy, two different biosensing systems were constructed employing glucose oxidase and cholesterol oxidase and their analytical capabilities were successfully verified by colorimetrically detecting the corresponding target molecules with excellent selectivity, sensitivity, reusability, and stability. Future potential applications of this technology range from biosensors to multicatalyst reactors.     

Ionic liquids as recycling solvents for the synthesis of magnetic nanoparticles

This work describes an easy synthesis (one pot) of MFe(2)O(4) (M = Co, Fe, Mn, and Ni) magnetic nanoparticles MNPs by the thermal decomposition of Fe(Acac)(3)/M(Acac)(2) by using BMI·NTf(2) (1-n-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) or BMI·PF(6) (1-n-butyl-3-methylimidazolium hexafluorophosphate) ionic liquids (ILs) as recycling solvents and oleylamine as the reducing and surface modifier agent. The effects of reaction temperature and reaction time on the features of the magnetic nanomaterials (size and magnetic properties) were investigated. The growth of the MNPs is easily controlled in the IL by adjusting the reaction temperature and time, as inferred from Fe(3)O(4) MNPs obtained at 150 °C, 200 °C and 250 °C with mean diameters of 8, 10 and 15 nm, respectively. However, the thermal decomposition of Fe(Acac)(3) performed in a conventional high boiling point solvent (diphenyl ether, bp 259 °C), under a similar Fe to oleylamine molar ratio used in the IL synthesis, does not follow the same growth mechanism and rendered only smaller NPs of 5 nm mean diameter. All MNPs are covered by at least one monolayer of oleylamine making them readily dispersible in non-polar solvents. Besides the influence on the nanoparticles growth, which is important for the preparation of highly crystalline MNPs, the IL was easily recycled and has been used in at least 20 successive syntheses.     

Titanium silicalite-1 zeolite microparticles for enzymeless H2O2 detection

In this communication, we demonstrate for the first time that titanium silicalite-1 zeolite microparticles (TSZMs) can effectively catalyze the reduction of H(2)O(2), leading to an enzymeless H(2)O(2) sensor with a linear detection range from 100 μM to 40 mM (r = 0.994) and a detection limit of 0.5 μM at a signal-to-noise ratio of 3.     

Small-molecule-dependent split aptamer ligation

Here we describe the first use of small-molecule binding to direct a chemical reaction between two nucleic acid strands. The reported reaction is a ligation between two fragments of a DNA split aptamer using strain-promoted azide-alkyne cycloaddition. Utilizing the split aptamer for cocaine, we demonstrate small-molecule-dependent ligation that is dose-dependent over a wide range of cocaine concentrations and is compatible with complex biological fluids such as human blood serum. Moreover, studies of split aptamer ligation at varying salt concentrations and using structurally similar analogues of cocaine have revealed new insight into the assembly and small-molecule binding properties of the cocaine split aptamer. The ability to translate the presence of a small-molecule target into the output of DNA ligation is anticipated to enable the development of new, broadly applicable small-molecule detection assays.