4-(dimethylamino)butyric acid@PtNPs as enhancer for solid-state electrochemiluminescence aptasensor based on target-induced strand displacement

A solid-state electrochemiluminescence (ECL) aptasensor based on target-induced aptamer displacement for highly sensitive detection of thrombin was developed successfully using 4-(dimethylamino)butyric acid (DMBA)@PtNPs labeling as enhancer. Such a special aptasensor included three main parts: ECL substrate, ECL intensity amplification and target-induced aptamer displacement. The ECL substrate was made by modifying the complex of Pt nanoparticles (PtNPs) and tris(2,2-bipyridyl) ruthenium (II) (Ru(bpy)(3)(2+)) (Ru-PtNPs) onto nafion@multi-walled carbon nanotubes (nafion@MWCNTs) modified electrode surface. A complementary thrombin aptamer labeled by DMBA@PtNPs (Aptamer II) acted as the ECL intensity amplification. The thrombin aptamer (TBA) was applied to hybridize with the labeled complementary thrombin aptamer, yielding a duplex complex of TBA-Aptamer II on the electrode surface. The introduction of thrombin triggered the displacement of Aptamer II from the self-assembled duplex into the solution and the association of inert protein thrombin on the electrode surface, decreasing the amount of DMBA@PtNPs and increasing the electron transfer resistance of the aptasensor and thus resulting large decrease in ECL signal. With the synergistic amplification of DMBA and PtNPs to Ru(bpy)(3)(2+) ECL, the aptasensor showed an enlarged ECL intensity change before and after the detection of thrombin. As a result, the change of ECL intensity has a direct relationship with the logarithm of thrombin concentration in the range of 0.001-30 nM. The detection limit of the proposed aptasensor is 0.4 pM. Thus, the approach is expected to open new opportunities for protein diagnostics in clinical as well as bioanalysis in general.     

Label-free and sensitive electrogenerated chemiluminescence aptasensor for the determination of lysozyme

A novel label-free electrogenerated chemiluminescence (ECL) aptasensor for the determination of lysozyme is designed employing lysozyme binding aptamer (LBA) as molecular recognition element for lysozyme as a model analyte and Ru(bpy)(3)(2+) as an ECL signal compound. This ECL aptasensor was fabricated by self-assembling the thiolated LBA onto the surface of a gold electrode. Using this aptasensor, sensitive quantitative detection of lysozyme is realized on basis of the competition of lysozyme with Ru(bpy)(3)(2+) cation for the binding sites of LBA. In the presence of lysozyme, the aptamer sequence prefers to form the LBA-lysozyme complex, the less negative environment allows Ru(bpy)(3)(2+) cations to be less bound electrostatically to the LBAs on the electrode surface, in conjunction with the generation of a decreased ECL signal. The integrated ECL intensity versus the concentration of lysozyme was linear in the range from 6.4×10(-10) M to 6.4×10(-7) M. The detection limit was 1.2×10(-10) M. This work demonstrates that using the competition of target protein with an ECL signal compound Ru(bpy)(3)(2+) for binding sites of special aptamer confined on the electrode is promising approach for the design of label-free ECL aptasensors for the determination of proteins.     

In-situ produced ascorbic acid as coreactant for an ultrasensitive solid-state tris(2,2'-bipyridyl) ruthenium(II) electrochemiluminescence aptasensor

Herein, an ultrasensitive solid-state tris(2,2'-bipyridyl) ruthenium(II) (Ru(bpy)(3)(2+)) electrochemiluminescence (ECL) aptasensor using in-situ produced ascorbic acid as coreactant was successfully constructed for detection of thrombin. Firstly, the composite of Ru(bpy)(3)(2+) and platinum nanoparticles (Ru-PtNPs) were immobilized onto Nafion coated glass carbon electrode, followed by successive adsorption of streptavidin-alkaine phosphatase conjugate (SA-ALP) and biotinylated anti-thrombin aptamer to successfully construct an ECL aptasensor for thrombin determination. In our design, Pt nanoparticles in Ru(bpy)(3)(2+)-Nafion film successfully inhibited the migration of Ru(bpy)(3)(2+) into the electrochemically hydrophobic region of Nafion and facilitated the electron transfer between Ru(bpy)(3)(2+) and electrode surface. Furthermore, ALP on the electrode surface could catalyze hydrolysis of ascorbic acid 2-phosphate to in-situ produce ascorbic acid, which co-reacted with Ru(bpy)(3)(2+) to obtain quite fast, stable and greatly amplified ECL signal. The experimental results indicated that the aptasensor exhibited good response for thrombin with excellent sensitivity, selectivity and stability. A linear range of 1 × 10(-15)-1 × 10(-8) M with an ultralow detection limit of 0.33 fM (S/N=3) was obtained. Thus, this procedure has great promise for detection of thrombin present at ultra-trace levels during early stage of diseases.     

A simple electrochemical aptasensor for ultrasensitive protein detection using cyclic target-induced primer extension

A simple electrochemical aptasensor was developed for ultrasensitive protein detection by combining a novel strategy of cyclic target-induced primer extension (CTIPE) with an aptamer-hairpin probe and enzyme-amplified electrochemical readout. In the presence of protein target, the immobilized aptamer-hairpin probe recognized the protein to trigger primer extension reaction by target-induced conformational transition, which released the protein from replicated DNA duplex. The released target could cyclically bind with other aptamer-hairpin probes and trigger new primer extension, leading to formation of numerous biotin-tagged DNA duplex, which significantly amplified the protein recognition event and facilitated the subsequent enzymatic signal enhancement, leading to an ultrasensitive electrochemical aptasensor. Using human vascular endothelial growth factor as a model protein, the designed aptasensor could detect protein down to 0.82 pg mL(-1) with a linear range from 1 pg mL(-1) to 1 ng mL(-1). The proposed aptasensor was amenable to quantification of protein in complex biological matrixes, and would become a simple and powerful tool for bioanalysis and clinic diagnostic application.     

Determination of glucose and uric acid with bienzyme colorimetry on microfluidic paper-based analysis devices

An aptamer is an artificial functional oligonucleic acid, which can interact with its target molecule with high affinity and specificity. Enzyme linked aptamer assay (ELAA) is developed to detect cocaine using aptamer fragment/cocaine configuration based on the affinity interaction between aptamer fragments with cocaine. The aptasensor was constructed by cleaving anticocaine aptamer into two fragments: one was assembled on a gold electrode surface, while the other was modified with biotin at 3'-end, which could be further labelled with streptavidin-horseradish peroxidase (SA-HRP). Upon binding with cocaine, the HRP-labelled aptamer fragment/cocaine complex formed on the electrode would increase the reduction current of hydroquinone (HQ) in the presence of H(2)O(2). The sensitivity and the specificity of the proposed electrochemical aptasensor were investigated by differential pulse voltammetry (DPV). The results indicated that the DPV signal change could be used to sensitively detect cocaine with the dynamic range from 0.1 μM to 50 μM and the detection limit down to 20 nM (S/N=3). The proposed aptasensor has the advantages of high sensitivity and low background current. Furthermore, a new configuration for ELAA requiring only a single aptamer sequence is constructed, which can be generalized for detecting different kinds of targets by cleaving the aptamers into two suitable segments.     

Highly amplified electrochemiluminescence of peroxydisulfate using bienzyme functionalized palladium nanoparticles as labels for ultrasensitive immunoassay

An immunosensor based on the electrochemiluminescence (ECL) of peroxydisulfate was firstly proposed by coupling the cooperation of two enzymes to in situ generate coreactant with palladium nanoparticles (PdNPs) as catalyst for the ECL reaction. PdNPs were previously synthesized, which successfully attached to functional carbon nanotubes (FCNTs), to bind the secondary antibody and bienzyme (horseradish peroxidase and glucose oxidase). Then the prepared bioconjugates were introduced to the electrode via sandwich immunoreactions. Accordingly, a dramatically amplified ECL signal was obtained for that GOD catalyzed glucose to produce H(2)O(2) which was subsequently reduced by HRP to in situ generate O(2), then PdNPs as catalyst for the ECL reaction of peroxydisulfate/O(2). The present immunosensor was used to detect α-1-fetoprotein (AFP) and showed a wide linear range of 1×10(-5)-100ngmL(-1), with a low detection limit of 3.3fgmL(-1)(S/N=3). This new signal amplification strategy for preparation of the ECL immunosensor could be easily realized and has a potential application in ultrasensitive bioassays.     

Sensitive and antifouling impedimetric aptasensor for the determination of thrombin in undiluted serum sample

A highly sensitive and attractive antifouling impedimetric aptasensor for the determination of thrombin in undiluted serum sample was developed. The aptasensor was fabricated by co-assembling thiol-modified anti-thrombin binding aptamer, dithiothreitol and mercaptohexanol on the surface of gold electrode. The performance of aptasensor was characterized by atomic force microscopy, contact angle and electrochemical impedance spectroscopy. In the measurement of thrombin, the change in interfacial electron transfer resistance of aptasensor was monitored using a redox couple of Fe(CN)(6)(3-/4-). The increase in the electron transfer resistance was linearly proportional to the concentration of thrombin in the range from 1.0 to 20ng/mL and a detection limit of 0.3ng/mL thrombin was achieved. The fabricated aptasensor displayed attractive antifouling properties and allowed direct quantification of extrinsic thrombin down to 0.08ng/mL in undiluted serum sample. This work provides a promising strategy for clinical application with impressive sensitivity and antifouling characteristics.     

Development of a membrane strip immunosensor utilizing ruthenium as an electro-chemiluminescent signal generator

A photometric immunosensor that can be used for on-site diagnosis has been constructed. The sensor system was assembled by partially superimposing a nitrocellulose membrane strip (the lower) containing an immobilized antigen on the surface with a glass fiber membrane strip (the upper) including two electrodes on the opposite surfaces. To amplify the signal, we introduced a liposome, containing ruthenium molecules trapped in the core, chemically coupled to an antibody specific to the analyte (e.g. Legionella antigen). In the presence of the analyte, immune complexes were formed by antigen-antibody reactions upon addition of the immuno-liposome into a sample. This mixture was then absorbed by the capillary action from the bottom of the membrane strip. The liposome particles in the complexes were carried by a medium through the antigen pad without interaction, while free immuno-liposome was trapped by immune reactions on the pad surfaces. The aqueous medium influx into the glass pad dissolved a detergent pre-located within the compartment and the liposome rupture thereby released ruthenium molecules into the solution. The molecules were oxidized on the electrode surfaces and produced an electro-chemiluminescence (ECL) in proportion to the analyte concentration. The signal generation based on ECL resulted in an exponential dose-response pattern and the analyte detection limit of 2 ng/ml was approximately 10-fold more sensitive than that obtained from a conventional system.     

Signal-enhanced electrochemiluminescence immunosensor based on synergistic catalysis of nicotinamide adenine dinucleotide hydride and silver nanoparticles

A new metal-organic nanocomposite with synergistic catalysis function was prepared and developed to construct an electrochemiluminescence (ECL) immunosensor for ultrasensitive detection of tumor biomarker CA125. Silver nanoparticles (AgNPs) and nicotinamide adenine dinucleotide hydride (NADH) that can participate and catalyze the ECL reaction of Ru(bpy)(3)(2+) were employed as the metal component and the organic component to synthesize the metal-organic nanocomposite of NADH-AgNPs (NA). The novel ECL immunosensor was assembled via Ru(bpy)(3)(2+)-doped silica nanoparticles (Ru-SiO(2)) modified electrode with the NA as immune labels. First, the chitosan-suspended Ru-SiO(2) nanoparticles were cast on the gold electrode surface to immobilize the ECL probes of Ru(bpy)(3)(2+) and link gold nanoparticles. Then, the primary antibodies were loaded onto the modified electrode via the gold sulfhydryl covalent binding. After immunobinding the analytes of antigen, NA-attached secondary antibodies could be captured as a sandwich type on the electrode. Finally, based on the circularly synergistic catalysis by the silver and NADH for the solid-phase ECL of Ru(bpy)(3)(2+), the proposed immunosensor sensed the concentration of antigen. The synergistic ECL catalysis of metal-organic nanocomposite amplified response signal and pushed the detection limit down to 0.03 U ml(-1), which initiated a new ECL labeling field and has great significance for ECL immunoassays.     

Electrogenerated chemiluminescence detection of adenosine based on triplex DNA biosensor

A novel electrogenerated chemiluminescence (ECL) biosensor based on the construction of triplex DNA for the detection of adenosine was designed. The ECL biosensor employs an aptamer as a molecular recognition element, and quenches ECL of tris(2,2'-bipyridine) ruthenium (Ru(bpy)(3)(2+)) by ferrocenemonocarboxylic acid (FcA). Through self-assembly technology, the ECL probe of thiolated hairpin adenosine aptamer tagged was self-assembled onto the surface of a gold electrode with an ECL signal producer Ru(bpy)(3)(2+) derivative (Ru-DNA-1). The adenosine aptamer, including a section of triplex characteristic chain, formatted triplex DNA with two other DNAs (DNA-2, Fc-DNA-3) in the presence of triplex DNA binder coralyne chloride (CORA). Fc-DNA-3 was tagged with an ECL quencher ferrocenemonocarboxylic acid (FcA), a quenching probe. In the presence of adenosine, the aptamer sequence (Ru-DNA-1) prefers to form the aptamer-adenosine complex with hairpin configuration and the switch of the DNA-1 occurs in conjunction with the generation of a strong ECL signal owing to the dissociation of a quenching probe. Meanwhile, a control experiment was performed; the ECL-duplex biosensor was designed to detect adenosine. The detection limits were 2.7×10(-10) mol L(-1) and 2.3×10(-9) mol L(-1) for the ECL-triplex DNA biosensor and ECL-duplex DNA biosensor, respectively, which demonstrated that the ECL-triplex DNA biosensor improved the sensitivity and specificity greatly.     

A label-free electrochemiluminescence aptasensor for thrombin based on novel assembly strategy of oligonucleotide and luminol functionalized gold nanoparticles

In the work, a label-free electrochemiluminescence (ECL) aptasensor for the sensitive and selective detection of thrombin was constructed based on target-induced direct ECL signal change by virtue of a novel assembly strategy of oligonucleotide and luminol functionalized gold nanoparticles (luminol-AuNPs). It is the first label-free ECL biosensor based on luminol and its analogs functionalized AuNPs. Streptavidin AuNPs coated with biotinylated DNA capture probe 1 (AuNPs-probe 1) were firstly assembled onto an gold electrode through 1,3-propanedithiol. Then luminol-AuNPs co-loaded with thiolated DNA capture probe 2 and thiolated thrombin binding aptamer (TBA) (luminol-AuNPs-probe 2/TBA) were assembled onto AuNPs-probe 1 modified electrode through the hybridization between capture probes 1 and 2. The luminol-AuNPs-probe 2/TBA acted as both molecule recognition probe and sensing interface. An Au/AuNPs/ds-DNA/luminol-AuNPs/TBA multilayer architecture was obtained. In the presence of target thrombin, TBA on the luminol-AuNPs could capture the thrombin onto the electrode surface, which produced a barrier for electro-transfer and influenced the electro-oxidation reaction of luminol, leading to a decrease in ECL intensity. The change of ECL intensity indirectly reflected the concentration of thrombin. Thus, the approach showed a high sensitivity and a wider linearity for the detection of thrombin in the range of 0.005-50nM with a detection limit of 1.7pM. This work reveals that luminol-AuNPs are ideal platform for label-free ECL bioassays.     

A perovskite-based electrochemiluminescence aptasensor for tetracycline screening

Tetracyclines are currently the most commonly used class of antibiotics, and their residue issue significantly impacts public health safety. In this study, a surface modification of perovskite with cetyltrimethylammonium bromide led to the generation of stable electrochemiluminescence (ECL) emitters in aqueous systems and improved the biocompatibility of perovskite. A perovskite quantum dot-based ECL sensing strategy was developed. Utilizing the corresponding aptamer of the antibiotics, strain displacement reactions were triggered, disrupting the ECL quenching system composed of perovskite and Ag nanoclusters (Ag NCs) on the electrode surface, generating a signal to achieve quantitative detection of several common tetracycline antibiotics. The perovskite quantum dot provided a strong and stable initial signal, while the efficient catalytic activity of the silver cluster enhanced the recognition sensitivity. Tetracycline, chlortetracycline, and oxytetracycline were used as examples to demonstrate the differentiation and quantitative detection through this method. In addition, the aptasensor exhibited analytical performance with the linear range (0.1–10 μM OTC) and good recovery rates of 94.7% to 101.6% in real samples. This approach has the potential to become a sensitive and practical approach for assessing antibiotic residues.     

Electrochemiluminescence of peroxydisulfate enhanced by L-cysteine film for sensitive immunoassay

A novel label free electrochemiluminescence (ECL) immunosensor based on the ECL of peroxydisulfate solution for detection of α-1-fetoprotein (AFP) has been developed. For this proposed immunosensor, L-cysteine was firstly electrodeposited on the gold electrode surface, which promoted the electron transfer and largely enhanced the ECL of peroxydisulfate solution. Subsequently, gold nanoparticles (nano-Au) were assembled onto the L-cysteine film modified electrode to improve the absorption capacity of antibody and further amplify the ECL signal. Then, antibody was immobilized onto the electrode through nano-Au. At last bovine serum albumin (BSA) was employed to block the nonspecific binding sites. As a result, a novel ECL immunosensor was firstly obtained by applying the ECL of peroxydisulfate solution without conventional luminescent reagents. The AFP was determined in the range of 0.01-100 ng mL(-1), with a low detection limit of 3.3 pg mL(-1) (S/N=3). The proposed ECL immunosensor provides a rapid, simple, and sensitive immunoassay protocol for protein detection, which might hold a promise for clinical application. Moreover, this work would open up a new field in the application of peroxydisulfate solution ECL for highly sensitive bioassays.     

Homogeneous electrogenerated chemiluminescence immunoassay for the determination of digoxin employing Ru(bpy)(2)(dcbpy)NHS and carrier protein.

A highly sensitive homogeneous electrogenerated chemiluminescence (ECL) immunoassay for the determination of anti-digoxin antibody and digoxin hapten was developed employing Ru(bpy)(2)(dcbpy)NHS (bpy = 2,2'-bipyridyl; dcbpy = 2,2'-bipyridine-4,4'-dicarboxylic acid; NHS = N-hydroxysuccinimide ester) as an electrochemiluminescent label and bovine serum albumin (BSA) as a carrier protein. A digoxin hapten was indirectly heavily labelled with Ru(bpy)(2)(dcbpy)NHS through BSA to form Ru(bpy)(2)(dcbpy)NHS-BSA-digoxin conjugate. The ECL intensity of the immunocomplex of the conjugate with anti-digoxin antibody markedly decreased when the immunoreaction between Ru(bpy)(2)(dcbpy)NHS-BSA-digoxin conjugate and anti-digoxin antibody took place. Two formats, direct homogeneous immunoassay for anti-digoxin antibody and competitive immunoassay for digoxin, were developed to determine anti-digoxin antibody and digoxin, respectively. The anti-digoxin antibody concentration in the range 7.6 x 10(-8)-7.6 x 10(-6) g/mL was determined by direct homogeneous format. Digoxin hapten was determined throughout the range 4.0 x 10(-10)-1.0 x 10(-7) g/mL with a detection limit of 1.0 x 10(-10) g/mL by competitive format. The relative standard derivation for 6.0 x 10(-9) g/mL was 4.3%. The method has been applied to assaying digoxin in control human serum.     

Electrochemiluminescent biosensing of carbohydrate-functionalized CdS nanocomposites for in situ label-free analysis of cell surface carbohydrate

A facile electrochemiluminescent (ECL) strategy for in situ label-free monitoring of carbohydrate expression on living cells was designed by integrating the specific recognition of lectin to carbohydrate with a carbohydrate-functionalized CdS nanocomposite. The mercaptopropionic acid-capped CdS quantum dots were firstly immobilized on carbon nanotubes modified electrode and then functionalized with carbohydrate using mannan as a model on the surface. The carbohydrate-functionalized CdS nanocomposite showed high ECL sensitivity and good stability, and could be used for competitive recognition to concanavalin A with the target cells in solution, which led to a change of ECL intensity due to the resistance of concanavalin A. The change depended on both the cell number and the expression level of cell surface carbohydrate. A wide linear response to cells ranging from 2×10(3) to 1×10(7) cells mL(-1) with a detection limit of 1.2×10(3) cells mL(-1) was obtained. The proposed biosensor could be used to in situ evaluate cell surface glycan, and the average number of mannose moieties on single living BGC cell was detected to be 8.7×10(7). This sensitive strategy was further used for facile monitoring of dynamic carbohydrate expression on living cells in response to drugs. The proposed method could be further expanded to high-throughput detection with the addition of more specific glycan-lectin pairs to the repertoire.     

Highly sensitive electrochemical detection of cocaine on graphene/AuNP modified electrode via catalytic redox-recycling amplification

We demonstrated a new strategy for highly sensitive electrochemical detection of cocaine by using two engineered aptamers in connection to redox-recycling signal amplification. The graphene/AuNP nanocomposites were electrochemically deposited on a screen printed carbon electrode to enhance the electron transfers. The cocaine primary binding aptamers were self-assembled on the electrode surface through sulfur-Au interactions. The presence of the target cocaine and the biotin-modified secondary binding aptamers leads to the formation of sandwich complexes on the electrode surface. The streptavidin-conjugated alkaline phosphatases (ALPs) were used as labels to generate quantitative signals. The addition of the ALP substrate and the co-reactant NADH results in the formation of a redox cycle between the enzymatic product and the electrochemically oxidized species and the signal is thus significantly amplified. Because of the effective modification of the sensing surface and signal amplification, low nanomolar (1 nM) detection limit for cocaine is achieved. The proposed aptamer-based sandwich sensing approach for amplified detection of cocaine thus opens new opportunities for highly sensitive determination of other small molecules.     

A folding-based electrochemical aptasensor for detection of vascular endothelial growth factor in human whole blood

We herein report a folding-based electrochemical DNA aptasensor for the detection of vascular endothelial growth factor (VEGF) directly in complex biological samples, including blood serum and whole blood. The electrochemical signal generation is coupled to a large, target-induced conformational change in a methylene blue-modified and surface immobilized anti-VEGF aptamer. The sensor is sensitive, selective and essentially reagentless: we can readily detect VEGF down to 5 pM (190 pg/mL) directly in 50% blood serum. Similar to other aptasensors of this class, the VEGF sensor is also regenerable and reusable. In addition, the sensor performs comparably well even when fabricated on a gold-plated screen-printed carbon electrode and can potentially be implemented as a cost-effective, single-use biosensor for diseases diagnosis and therapy monitoring. The exceptional sensitivity, selectivity, and reusability of this electrochemical aptasensor platform suggest it may be a promising strategy for a wide variety of sensing applications.     

Ultrasensitive one-step rapid visual detection of bisphenol A in water samples by label-free aptasensor

A simple, one-step, rapid method to detect bisphenol A (BPA) using a label-free aptasensor is presented. A high selective anti-BPA aptamer was added to gold nanoparticles (GNPs) to prepare the label-free aptasensor for BPA, which maintains good tolerance of GNPs under aqueous conditions with high salt concentrations. With the presence of BPA in the aptasensor system, the GNPs would aggregate by competitive binding of BPA and aptamer. Detection results can be visualized by the aggregation-induced color change of GNPs without the use of any instrumentation. The limit of visual detection (LOD) was found to be 0.1ng/mL by naked-eye observation, which was competitive to some current rapid BPA detection methods, even some instrumental based methods. Besides the obvious advantages, including reduced detection time and operation procedures, the results of this method meet the various detection requirements for BPA and are comparable to the traditional ELISA and instrument-based methods. The proposed one-step, label-free method was successfully used to determine BPA in actual water samples.     

A signal-on electrochemiluminescence aptamer biosensor for the detection of ultratrace thrombin based on junction-probe

A novel signal-on junction-probe electrogenerated chemiluminescence (ECL) aptamer biosensor has been developed for the detection of ultratrace thrombin based on a structure-switching ECL-quenching mechanism. The ECL aptamer biosensor comprises two main parts: an ECL substrate and an ECL intensity switch. The ECL substrate was made by modifying the complex of Au nanoparticle and ruthenium (II) tris-bipyridine (Ru(bpy)(3)(2+)-AuNPs) on the surface of gold electrode (GE), and the ECL intensity switch contains three probes designed according to the "junction-probe" strategy. The first probe is capture probe (Cp) which was functionalized with a thiol group at one end and covalently attached to Ru(bpy)(3)(2+)-AuNPs modified GE through S-Au bonding. The second probe is aptamer probe (Ap), which containing 15-base anti-thrombin DNA aptamer. The third one is ferrocene-labeled probe (Fp), which was functionalized with ferrocene tag at one end. We demonstrated that, in the absence of thrombin, Cp, Ap and Fp will hybridize to form a ternary "Y" junction structure and resulted in a quenching of ECL of Ru(bpy)(3)(2+). Whereas, in the presence of thrombin, the Ap prefers to form the G-quadruplex aptamer-thrombin complex and lead to an obvious recovery of ECL of Ru(bpy)(3)(2+), which provided a sensing platform for the detection of thrombin. Using this reusable sensing platform, a simple, rapid and selective signal-on ECL aptamer biosensor for the detection of thrombin with a detection limit of 8.0×10(-15) M has been developed. The success in the present biosensor served as a significant step towards the development of monitoring ultratrace thrombin in clinical detection.     

Determination of erythromycin in rat plasma with capillary electrophoresis-electrochemiluminescence detection of tris(2,2'-bipyridyl) ruthenium(II)

A fast and sensitive approach for determination of erythromycin in rat plasma was described. The method used capillary electrophoresis coupled with end-column electrochemiluminescence (ECL) detection of Ru(bpy)(3)(2+). The separation column used had an inner diameter of 75 microm. The running buffer was 15 mmol/L sodium phosphate (pH=7.5). The solution in the detection cell was 50 mmol/L sodium phosphate (pH=8.0) and 5 mmol/L Ru(bpy)(3)(2+). ECL intensity varied linearly with erythromycin concentration from 1.0 ng/mL to 10 microg/mL. The detection limit (S/N=3) was 0.35 ng/mL. The relative standard deviations, of ECL intensity and migration time for eight consecutive injections of 1.0 microg/mL erythromycin (n=8), were 1.3% and 1.8%, respectively. The method was successfully applied to erythromycin determination in rat plasma. The recovery ranged from 92.5 to 97.5%.