Lianzhe Hu

Applications and trends in electrochemiluminescence.

Electrochemiluminescence (ECL) is chemiluminescence triggered by electrochemical techniques. More than 150 ECL assays with remarkably high sensitivity and extremely wide dynamic range are currently available, and accounts for hundreds of millions of dollars in sales per year. The recent development of ECL is particularly rapid. After a brief introduction to ECL, this critical review presents the active and/or emerging areas of ECL research as well as new applications and phenomena of ECL, such as light-emitting electrochemical cell, wireless electrochemical microarray using ECL as photonic reporter, high throughput analysis, aptasensors, immunoassays and DNA analysis, ECL of nanoclusters and carbon nanomaterials, ECL imaging techniques, scanning ECL microscopy, colorimetric ECL sensor, surface plasmon-coupled ECL, electrostatic chemiluminescence, soliton-like ECL waves, ECL investigation of molecular interaction, and single molecule detection. Finally, some perspectives on this rapidly developing field are discussed (322 references).

Highly sensitive fluorescent detection of trypsin based on BSA-stabilized gold nanoclusters

In this study, fluorescent metal nanoclusters are presented as novel probes for sensitive detection of protease for the first time. The sensing mechanism is based on trypsin digestion of the protein template of BSA-stabilized Au nanoclusters. The decrease in fluorescence intensity of BSA-Au nanoclusters caused by trypsin allows the sensitive detection of trypsin in the range of 0.01-100 μg/mL. The detection limit for trypsin is 2 ng/mL (86 pM) at a signal-to-noise ratio of 3. The present nanosensor for trypsin detection possesses red emission, excellent biocompatibility, high selectivity, and good stability. In addition, we demonstrated the application of the present approach in real urine samples, which suggested its potential for diagnostic purposes.

[Ru(bpy)2dppz]2+ Electrochemiluminescence Switch and Its Applications for DNA Interaction Study and Label-free ATP Aptasensor

[Ru(bpy)2dppz]2+ electrochemiluminescence (ECL) was studied, and it was used to investigate DNA interaction and develop a label-free ATP aptasensor for the first time. ECL of [Ru(bpy)2dppz]2+ is negligible in aqueous solution, and increases approximately 1000 times when [Ru(bpy)2dppz]2+ intercalates into the nucleic acid structure. The ECL switch behavior of [Ru(bpy)2dppz]2+ is ascribed to the intercalation that shields the phenazine nitrogens from the solvent and results in a luminescent excited state. The ECL switch by DNA was applied to investigate the interaction of [Ru(bpy)2dppz]2+ with herring sperm DNA. The calculated equilibrium constant (K) is 1.35 x 10(6) M(-1), and the calculated binding-site size (s) is 0.88 base pair, which is consistent with the reported values. Moreover, ATP can dramatically affect ECL of the [Ru(bpy)2dppz]2+/ATP aptamer complex. As a result, a label-free, sensitive, and selective [Ru(bpy)2dppz]2+ ECL method for ATP detection was developed. The detection limit is 100 nM for ATP (with a signal-to-noise ratio, S/N, of 3) with a linear range of 0-1 microM. The result demonstrates that [Ru(bpy)2dppz]2+ ECL holds great promise in aptasensors.

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)

Dual Switchable CRET-Induced Luminescence of CdSe/ZnS Quantum Dots (QDs) by the Hemin/G-Quadruplex-Bridged Aggregation and Deaggregation of Two-Sized QDs

The hemin/G-quadruplex-catalyzed generation of chemiluminescence through the oxidation of luminol by H2O2 stimulates the chemiluminescence resonance energy transfer (CRET) to CdSe/ZnS quantum dots (QDs), resulting in the luminescence of the QDs. By the cyclic K(+)-ion-induced formation of the hemin/G-quadruplex linked to the QDs, and the separation of the G-quadruplex in the presence of 18-crown-6-ether, the ON-OFF switchable CRET-induced luminescence of the QDs is demonstrated. QDs were modified with nucleic acids consisting of the G-quadruplex subunits sequences and of programmed domains that can be cross-linked through hybridization, using an auxiliary scaffold. In the presence of K(+)-ions, the QDs aggregate through the cooperative stabilization of K(+)-ion-stabilized G-quadruplex bridges and duplex domains between the auxiliary scaffold and the nucleic acids associated with the QDs. In the presence of 18-crown-6-ether, the K(+)-ions are eliminated from the G-quadruplex units, leading to the separation of the aggregated QDs. By the cyclic treatment of the QDs with K(+)-ions/18-crown-6-ether, the reversible aggregation/deaggregation of the QDs is demonstrated. The incorporation of hemin into the K(+)-ion-stabilized G-quadruplex leads to the ON-OFF switchable CRET-stimulated luminescence of the QDs. By the mixing of appropriately modified two-sized QDs, emitting at 540 and 610 nm, the dual ON-OFF activation of the luminescence of the QDs is demonstrated.

Switchable Catalytic DNA Catenanes

Two-ring interlocked DNA catenanes are synthesized and characterized. The supramolecular catenanes show switchable cyclic catalytic properties. In one system, the catenane structure is switched between a hemin/G-quadruplex catalytic structure and a catalytically inactive state. In the second catenane structure the catenane is switched between a catalytically active Mg(2+)-dependent DNAzyme-containing catenane and an inactive catenane state. In the third system, the interlocked catenane structure is switched between two distinct catalytic structures that include the Mg(2+)- and the Zn(2+)-dependent DNAzymes.

Immobilization of tris(1,10-phenanthroline)ruthenium with graphene oxide for electrochemiluminescent analysis

Electrochemiluminescence (ECL) of ruthenium complexes has broad applications and the immobilization of Ru(bpy)(3)(2+) has received extensive attention. In comparison with Ru(bpy)(3)(2+), Ru(phen)(3)(2+) can be immobilized more easily because of its better adsorbability. In this study, immobilization of Ru(phen)(3)(2+) for ECL analysis has been demonstrated for the first time by using graphene oxide (GO) as an immobilization matrix. The immobilization of Ru(phen)(3)(2+) is achieved easily by mixing Ru(phen)(3)(2+) with GO without using any ion exchange polymer or covalent method. The strong binding of Ru(phen)(3)(2+) with GO is attributed to both the π-π stacking interaction and the electrostatic interaction. The Ru(phen)(3)(2+)/GO modified electrode was characterized by using tripropylamine (TPA) as the coreactant. The linear range of TPA is from 3×10(-7) to 3×10(-2) mol L(-1) with the detection limit of 3×10(-7) mol L(-1). The ECL sensor demonstrates outstanding long-term stability. After the storage in the ambient environment for 90 days, the ECL response remains comparable with its original signal.

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.