Zhongyuan Liu

Oligonucleotide-stabilized fluorescent silver nanoclusters for turn-on detection of melamine.

Fluorescence nanoclusters have been used for the determination of melamine for the first time. The method is based on the fluorescence turn-on of oligonucleotide-stabilized silver nanoclusters (DNA-Ag NCs) by melamine. The enhancement factors (I-I(0))/I(0) increase linearly with melamine concentrations over the range 5.0×10(-8)-7.0×10(-6) M (R(2)=0.998). The detection limit is 1.0×10(-8) M, which is approximately 2000 times lower than the US Food and Drug Administration estimated melamine safety limit of 20.0 μM. Furthermore, the milk samples spiked with melamine are analyzed with excellent recoveries.

Label-free and signal-on electrochemiluminescence aptasensor for ATP based on target-induced linkage of split aptamer fragments by using [Ru(phen)3]2+ intercalated into double-strand DNA as a probe.

Aptamers are specific nucleic acids (DNA or RNA) selected from random sequence libraries using SELEX (systemic evolution of ligands by exponential enrichment) with high affinity and specificity in the binding to small molecules, proteins and other macromolecules. Owing to their simple synthesis, good stability, easy storage, and simple modification for further immobilization procedure, aptamers have attracted increasing interest as the ideal recognition elements for biosensor applications. Sandwich-type assays have been widely used in biosensors for their specificity and low detection limits. However, the approach largely excluded aptamer-based sensors due to the requirement that the target exposes two distinct epitopes. Hence, rather few aptamer-based sandwich-type assays have been reported for proteins, much less small molecules. Recently, the construction of aptasensors for small molecules based on linkage of split-aptamer fragments, in the presence of the analyte-substrate, creating a “sandwich assay”, was introduced as a general platform for aptasensors. However, most aptasensors need chemical labeling procedures, which are usually complex, timeconsuming, and labor-intense. Therefore it is desirable to establish a label-free aptamer-based sandwich-type assay with high specificity and low detection limit for small molecules. It has been reported that the double-strand DNA (dsDNA) has the capacity to be intercalated with some small molecules into its grooves with high affinity; some aptamer-based sensors have been developed based on the intercalation of small molecule probes into the DNA structures. Nevertheless, most of these sensors are based on the competing reaction between the analytes and complementary strands, which might be more difficult than only target–aptamer interaction. The factor could lead to relatively slow response to the target compared with some noncompetition assays. Recently, electrochemiluminescence (ECL) aptasensors, which integrate the advantages of electrochemical detection and chemiluminescent techniques, have received particular attention due to their high sensitivity and selectivity, wide linear ranges, as well as low production cost. As a popular ECL reagent with high ECL emission efficiency for bioassays, RuACHTUNGTRENNUNG(phen)32+ (phen =1,10-phenanthroline) can intercalate into the grooves of dsDNA. In comparison to the commonly used DNA-binding fluorescing intercalator ethidium bromide, Ru ACHTUNGTRENNUNG(phen)32+ is more expensive, but has the advantages of lower toxicity, better stability, and easy use. Moreover, RuACHTUNGTRENNUNG(phen)32+ can be used not only in fluorescence study but also ECL studies, which do not require expensive light source as in fluorescence study. Herein, a label-free sandwich-type ECL sensing system based on target-induced conjunction of split aptamer fragments has been developed by the use of Ru ACHTUNGTRENNUNG(phen)32+ intercalated into ds-DNA as the ECL probe. ATP was selected as the model target to demonstrate the principle of the present ECL aptamer-based assay. The design concept of the sensing system and the ATP detection are displayed in Scheme 1. To assemble the aptasensor, the 27-mer anti-ATP DNA aptamer was divided into two different fragments which do not interact with each other in the absence of ATP. One of them, modified with thiol at 5’ terminus (1), was immobi[a] M. Sc. Z. Liu, M. Sc. W. Zhang, B. Sc. L. Hu, B. Sc. H. Li, M. Sc. S. Zhu, Prof. Dr. G. Xu State Key Laboratory of Electroanalytical Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences, Changchun, Jilin 130022 (China) Fax: (+86) 431-85262747 E-mail : guobaoxu@ciac.jl.cn [b] B. Sc. L. Hu, B. Sc. H. Li, M. Sc. S. Zhu Graduate University of the Chinese Academy of Sciences Chinese Academy of Sciences, Beijing 100864 (China)

Ultrasensitive Glutathione Detection Based on Lucigenin Cathodic Electrochemiluminescence in the Presence of MnO2 Nanosheets

Glutathione (GSH) is a crucial antioxidant produced endogenously and plays key roles in biological systems. It is vitally important to design simple, selective, and sensitive methods to sense GSH and monitor changes of GSH concentration. In this work, the cathodic electrochemiluminescence (ECL) of lucigenin in the presence of MnO2 nanosheets at a glassy carbon electrode was utilized for GSH detection. GSH can reduce MnO2 nanosheets into Mn(2+) which can obviously inhibit the ECL of lucigenin. The ECL inhibition efficiencies increase linearly with the concentrations of glutathione in the range of 10 to 2000 nM. The detection limit for GSH measurement is 3.7 nM. This proposed method is highly sensitive, selective, simple, fast, and cost-effective. Moreover, this approach can detect GSH in human serum samples with excellent recoveries, which indicates its promising application under physiological conditions.

Nucleic acid detection using single-walled carbon nanohorns as a fluorescent sensing platform.

In this communication, we demonstrate for the first time the proof of concept that single-walled carbon nanohorns can be used as an effective fluorescent sensing platform for nucleic acid detection with a high selectivity down to single-base mismatch.

Turn-On Fluorescence Sensor Based on Single-Walled-Carbon-Nanohorn-Peptide Complex for the Detection of Thrombin

Proteases play a central role in several widespread diseases. Thus, there is a great need for the fast and sensitive detection of various proteolytic enzymes. Herein, we have developed a carbon nanotube (CNT)-based protease biosensing platform that uses peptides as a fluorescence probe for the first time. Single-walled carbon nanohorns (SWCNHs) and thrombin were used to demonstrate this detection strategy. SWCNHs can adsorb a fluorescein-based dye (FAM)-labeled peptide (FAM-pep) and quench the fluorescence of FAM. In contrast, thrombin can cleave FAM-pep on SWCNHs and recover the fluorescence of FAM, which allows the sensitive detection of thrombin. This biosensor has a high sensitivity and selectivity toward thrombin, with a detection limit of 100 pM.

Electrochemiluminescence Detection of TNT by Resonance Energy Transfer through the Formation of a TNT-Amine Complex

2,4,6-Trinitrotoluene (TNT) is a widely used nitroaromatic explosive with significant detrimental effects on the environment and human health. Its detection is of great importance. In this study, both electrochemiluminescence (ECL)-based detection of TNT through the formation of a TNT-amine complex and the detection of TNT through electrochemiluminescence resonance energy transfer (ECRET) are developed for the first time. 3-Aminopropyltriethoxysilane (APTES)-modified [Ru(phen)3](2+) (phen=1,10-phenanthroline)-doped silica nanoparticles (RuSiNPs) with uniform sizes of (73±3) nm were synthesized. TNT can interact with APTES-modified RuSiNPs through charge transfer from electron-rich amines in the RuSiNPs to the electron-deficient aromatic ring of TNT to form a red TNT-amine complex. The absorption spectrum of this complex overlaps with the ECL spectrum of the APTES-modified RuSiNPs/triethylamine system. As a result, ECL signals of the APTES-modified RuSiNPs/triethylamine system are turned off in the presence of TNT owing to resonance energy transfer from electrochemically excited RuSiNPs to the TNT-amine complex. This ECRET method has been successfully applied for the sensitive determination of TNT with a linear range from 1×10(-9) to 1×10(-6) M with a fast response time within 1 min. The limit of detection is 0.3 nM. The method exhibits good selectivity towards 2,4-dinitrotoluene, p-nitrotoluene, nitrobenzene, phenol, p-quinone, 8-hydroxyquinoline, p-phenylenediamine, K3[Fe(CN)6], Fe(3+), NO3(-), NO2(-), Cr(3+), Fe(2+), Pb(2+), SO3(2-), formaldehyde, oxalate, proline, and glycine.

Synthesis and electrochemical applications of nitrogen-doped carbon nanomaterials

Abstract Nitrogen doping is an effective way to tailor the properties of the shaped carbon materials, including the nanotubes, nanocups, nanofibers, as well as the nanorods, and render their potential use for various applications. The common bonding configurations obtained on the N insertion is the pyridinic N and pyrrolic N, which impart the characteristic properties to these carbon materials. This review will focus on the nitrogen-doped carbon materials, the doping effect on the electrochemistry of the doped nanomaterials, and the various synthetic methods to introduce N into the carbon network. The potential applications of the N-doped materials are also reviewed on the basis of the experimental and theoretical studies in electrochemistry.

Stainless Steel Electrode for Sensitive Luminol Electrochemiluminescent Detection of H2O2, Glucose, and Glucose Oxidase Activity

Electrogenerated chemiluminescence (ECL) application of stainless steel, a robust and cost-effective material, has been developed for the first time. Type 304 stainless steel electrode shows appealing ECL performance in the luminol-H2O2 system. It enables the detection of H2O2 with a linear range from 1 to 1000 nM and a limit of detection of 0.456 nM [signal-to-noise ratio (S/N) = 3]. The ECL method based on type 304 stainless steel electrode is more sensitive, more cost-effective, and much simpler than other ECL methods reported before. Because the stainless steel electrode has excellent performance for H2O2 detection and H2O2 participates in many important enzymatic reactions, applications of stainless steel electrode-based ECL for detection of enzyme activities and enzyme substrates were further investigated by use of glucose oxidase (GODx) and glucose as representative enzyme and substrate. The concentrations of glucose and the activity of GODx were directly proportional to ECL intensities over a range of 0.1-1000 μM and 0.001-0.7 units/mL with limits of detection of 0.076 μM and 0.00087 unit/mL (S/N = 3), respectively. This method was successfully used for determining glucose in honey. Because of their remarkable performance and user-friendly features, stainless steel electrodes hold great promise in various electroanalytical applications, such as biosensing, disposable sensors, and wearable sensors.

One-pot synthesis of gold nanorods using binary surfactant systems with improved monodispersity, dimensional tunability and plasmon resonance scattering properties

A facile seedless growth method for high-yield synthesis of monodisperse gold nanorods using binary surfactant mixtures is reported for the first time. In comparison with other seedless methods, the present method enables the preparation of gold nanorods with much better monodispersity. Moreover, the present seedless growth method enables the preparation of not only thin gold nanorods but also thick gold nanorods which cannot be prepared by other reported seedless methods. Dark-field microscopy measurements of a single gold nanorod indicate that the thicker gold nanorod shows enhanced scattering properties.

Detection of ozone based on its striking inhibition of tris(1,10-phenanthroline)ruthenium(II)/glyoxal electrochemiluminescence

Ozone unexpectedly dramatically suppresses the electrochemiluminescence (ECL) of Ru(phen)3(2+)/glyoxal at an ozone/glyoxal ratio of less than 0.5%. Moreover, a sensitive, simple and fast ECL method for ozone detection is developed, with a detection time within 1 min and a limit of detection of 20 nM.