Shuyun Zhu

Single-walled carbon nanohorns and their applications

Single-walled carbon nanohorns (SWCNHs) are horn-shaped single-walled tubules with a conical tip. They are generally synthesized by laser ablation of pure graphite without using metal catalyst with high production rate and high yield, and typically form radial aggregates. SWCNHs are essentially metal-free and very pure, which avoids cumbersome purification and makes them user-friendly and environmentally benign. Currently, SWCNHs have been widely studied for various applications, such as gas storage, adsorption, catalyst support, drug delivery system, magnetic resonance analysis, electrochemistry, biosensing application, photovoltaics and photoelectrochemical cells, photodynamic therapy, fuel cells, and so on. This review outlines the research progress on SWCNHs, including their properties, functionalization, applications, and outlook.

Simultaneous electrochemical determination of uric acid, dopamine, and ascorbic acid at single-walled carbon nanohorn modified glassy carbon electrode

Single-walled carbon nanohorn modified glassy carbon electrode (SWCNH-modified GCE) was first employed for the simultaneous determination of uric acid (UA), dopamine (DA), and ascorbic acid (AA). The SWCNH-modified GCE displayed excellent electrochemical catalytic activities. The oxidation overpotentials of UA, DA, and AA decrease significantly and their oxidation peak currents increase dramatically at SWCNH-modified GCE. Linear sweep voltammetry (LSV) was used for the simultaneous determination of UA, DA, and AA in their ternary mixture. The peak separations between UA and DA, and DA and AA are large up to 152mV and 221mV, respectively. The calibration curves for UA, DA, and AA were obtained in the range of 0.06-10 microM, 0.2-3.8microM, and 30-400microM, respectively. The detection limits (S/N=3) were 20nM, 60nM, and 5microM for UA, DA, and AA, respectively. The proposed method improved sensitivity for the determination of UA by more than one order of magnitude. The present method was applied to the determination of UA, DA, and AA in urine sample by using standard adding method and the results were satisfactory.

Single-walled carbon nanohorn as new solid-phase extraction adsorbent for determination of 4-nitrophenol in water sample.

Single-walled carbon nanohorn (SWCNH) was developed as new adsorbent for solid-phase extraction using 4-nitrophenol as representative. The unique exoteric structures and high surface area of SWCNH allow extracting a large amount of 4-nitrophenol over a short time. Highly sensitive determination of 4-nitrophenol was achieved by linear sweep voltammetry after only 120s extraction. The calibration plot for 4-nitrophenol determination is linear in the range of 5.0x10(-8) M-1.0x10(-5) M under optimum conditions. The detection limit is 1.1x10(-8) M. The proposed method was successfully employed to determine 4-nitrophenol in lake water samples, and the recoveries of the spiked 4-nitrophenol were excellent (92-106%).

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.

Novel turn-on fluorescent detection of alkaline phosphatase based on green synthesized carbon dots and MnO2 nanosheets

Using sterculia lychnophora seeds as precursors for the first time, fluorescent carbon dots (CDs) were synthesized by simple hydrothermal treatment. The quantum yield of as-synthesized CDs was 6.9% by using quinine sulfate as the reference. The fluorescence of CDs could be effectively quenched by a MnO2 nanosheet based on fluorescence resonance energy transfer (FRET). Ascorbic acid (AA) could reduce MnO2 to Mn2+ and result in the destruction of the MnO2 nanosheets, which could induce the fluorescence recovery of the CDs. In particular, alkaline phosphatase (ALP) could bio-catalyze acid 2-phosphate (AAP) hydrolysis to AA. Here, an efficient fluorescence probe based on a CDs-MnO2 nanosheet for rapid and selective detection of ALP was reported for the first time. Excellent performance for the detection of ALP was observed with high sensitivity and a detection limit of 0.4U/L owing to the low background. The detection of ALP in human serum was conducted with satisfactory results, demonstrating its potential applications in clinical diagnosis.

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)

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.

Functionalized single-walled carbon nanohorns for electrochemical biosensing

Single-walled carbon nanohorns (SWNHs), distinguished by their high purity and distinct structure, were noncovalently functionalized with poly(sodium 4-styrenesulfonate). The functionalized SWNHs were characterized by scanning electron microscopy, atomic force microscopy, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetry. Heme protein myoglobin was adsorbed onto surface of functionalized SWNHs to prepare electrochemical biosensor. Surface assembly process and direct electrochemistry of immobilized myoglobin were investigated by electrochemical impedance spectroscopy and cyclic voltammetry, respectively. The proposed biosensor exhibited good electrocatalysis to the reduction of hydrogen peroxide. The response was linear over the range 3-350 microM with a detection limit of 0.5 microM. Good reproducibility and stability of the biosensor were obtained toward hydrogen peroxide detection.

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.

In situ derivatization-ultrasound-assisted dispersive liquid-liquid microextraction for the determination of neurotransmitters in Parkinson's rat brain microdialysates by ultra high performance liquid chromatography-tandem mass spectrometry.

Simultaneous monitoring of several neurotransmitters (NTs) linked to Parkinsons disease (PD) has important scientific significance for PD related pathology, pharmacology and drug screening. A new simple, fast and sensitive analytical method, based on in situ derivatization-ultrasound-assisted dispersive liquid-liquid microextraction (in situ DUADLLME) in a single step, has been proposed for the quantitative determination of catecholamines and their biosynthesis precursors and metabolites in rat brain microdialysates. The method involved the rapid injection of the mixture of low toxic bromobenzene (extractant) and acetonitrile (dispersant), which containing commercial Lissamine rhodamine B sulfonyl chloride (LRSC) as derivatization reagent, into the aqueous phase of sample and buffer, and the following in situ DUADLLME procedure. After centrifugation, 50μL of the sedimented phase (bromobenzene) was directly injected for ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) detection in multiple reaction monitoring (MRM) mode. This interesting combination brought the advantages of speediness, simpleness, low matrix effects and high sensitivity in an effective way. Parameters of in situ DUADLLME and UHPLC-MS/MS conditions were all optimized in detail. The optimum conditions of in situ DUADLLME were found to be 30μL of microdialysates, 150μL of acetonitrile containing LRSC, 50μL of bromobenzene and 800μL of NaHCO3-Na2CO3 buffer (pH 10.5) for 3.0min at 37°C. Under the optimized conditions, good linearity was observed with LODs (S/N>3) and LOQs (S/N>10) of LRSC derivatized-NTs in the range of 0.002-0.004 and 0.007-0.015 nmol/L, respectively. It also brought good precision (3.2-12.8%, peak area CVs%), accuracy (94.2-108.6%), recovery (94.5-105.5%) and stability (3.8-8.1%, peak area CVs%) results. Moreover, LRSC derivatization significantly improved chromatographic resolution and MS detection sensitivity of NTs when compared with the reported studies through the introduction of a permanent charged moiety from LRSC into NTs. Taken together, this in situ DUADLLME method was successfully applied for the simultaneous determination of six NTs in biological samples.