Ru(bpy)32+-doped silica nanoparticle DNA probe for the electrogenerated chemiluminescence detection of DNA hybridization

An Ultrasensitive Voltammetric Genosensor for the Detection of Bacteria Vibrio cholerae in Vegetable and Environmental Water Samples

In view of the presence of pathogenic Vibrio cholerae (V. cholerae) bacteria in environmental waters, including drinking water, which may pose a potential health risk to humans, an ultrasensitive electrochemical DNA biosensor for rapid detection of V. cholerae DNA in the environmental sample was developed. Silica nanospheres were functionalized with 3-aminopropyltriethoxysilane (APTS) for effective immobilization of the capture probe, and gold nanoparticles were used for acceleration of electron transfer to the electrode surface. The aminated capture probe was immobilized onto the Si-Au nanocomposite-modified carbon screen printed electrode (Si-Au-SPE) via an imine covalent bond with glutaraldehyde (GA), which served as the bifunctional cross-linking agent. The targeted DNA sequence of V. cholerae was monitored via a sandwich DNA hybridization strategy with a pair of DNA probes, which included the capture probe and reporter probe that flanked the complementary DNA (cDNA), and evaluated by differential pulse voltammetry (DPV) in the presence of an anthraquninone redox label. Under optimum sandwich hybridization conditions, the voltammetric genosensor could detect the targeted V. cholerae gene from 1.0 × 10^-17-1.0 × 10^-7 M cDNA with a limit of detection (LOD) of 1.25 × 10^-18 M (i.e., 1.1513 × 10^-13 µg/µL) and long-term stability of the DNA biosensor up to 55 days. The electrochemical DNA biosensor was capable of giving a reproducible DPV signal with a relative standard deviation (RSD) of <5.0% (n = 5). Satisfactory recoveries of V. cholerae cDNA concentration from different bacterial strains, river water, and cabbage samples were obtained between 96.5% and 101.6% with the proposed DNA sandwich biosensing procedure. The V. cholerae DNA concentrations determined by the sandwich-type electrochemical genosensor in the environmental samples were correlated to the number of bacterial colonies obtained from standard microbiological procedures (bacterial colony count reference method).

Recent advances in the exonuclease III-assisted target signal amplification strategy for nucleic acid detection

The detection of nucleic acids has become significantly important in molecular diagnostics, gene therapy, mutation analysis, forensic investigations and biomedical development, and so on. In recent years, exonuclease III (Exo III) as an enzyme in the 3'-5' exonuclease family has evolved as a frequently used technique for signal amplification of low level DNA target detection. Different from the traditional target amplification strategies, the Exo III-assisted amplification strategy has been used for target DNA detection through directly amplifying the amounts of signal reagents. The Exo III-assisted amplification strategy has its unique advantages and characters, because the character of non-specific recognition of Exo III can overcome the limitation of a target-to-probe ratio of 1 : 1 in the traditional nucleic acid hybridization assay and acquire higher sensitivity. In this review, we selectively discuss the recent advances in the Exo III-assisted amplification strategy, including the amplification strategy integrated with nanomaterials, biosensors, hairpin probes and other nucleic acid detection methods. We also discuss the strengths and limitations of each strategy and methods to overcome the limitations.

A Comparison of Commercially Available Screen-Printed Electrodes for Electrogenerated Chemiluminescence Applications

We examined a series of commercially available screen-printed electrodes (SPEs) for their suitability for electrochemical and electrogenerated chemiluminescence (ECL) detection systems. Using cyclic voltammetry with both a homogeneous solution-based and a heterogeneous bead-based ECL assay format, the most intense ECL signals were observed from unmodified carbon-based SPEs. Three commercially available varieties were tested, with Zensor outperforming DropSens and Kanichi in terms of sensitivity. The incorporation of nanomaterials in the electrode did not significantly enhance the ECL intensity under the conditions used in this evaluation (such as gold nanoparticles 19%, carbon nanotubes 45%, carbon nanofibers 21%, graphene 48%, and ordered mesoporous carbon 21% compared to the ECL intensity of unmodified Zensor carbon electrode). Platinum and gold SPEs exhibited poor relative ECL intensities (16% and 10%) when compared to carbonaceous materials, due to their high rates of surface oxide formation and inefficient oxidation of tri-n-propylamine (TPrA). However, the ECL signal at platinum electrodes can be increased ∼3-fold with the addition of a surfactant, which enhanced TPrA oxidation due to increasing the hydrophobicity of the electrode surface. Our results also demonstrate that each SPE should only be used once, as we observed a significant change in ECL intensity over repeated CV scans and SPEs cannot be mechanically polished to refresh the electrode surface.

Advances in chemiluminescence and electrogenerated chemiluminescence based on silicon nanomaterials

Since 1950, when chemiluminescence (CL) of siloxane upon treatment with strong oxidants was discovered by Kurtz, many silicon-based nanomaterials with different elements, specific molecules, shapes and sizes have been developed as light emitters, energy acceptors, and catalyzers to provide valuable CL and electrogenerated CL (ECL) detection platforms in analytical chemistry fields. This review mainly focuses on the recent development of their mechanisms and sensing methodologies for small molecules, free radicals, ion, enzyme, protein, DNA, cancer cells, and metabolites based on specific reactions such as aptamer sensing and enzymatic reaction. Additionally, the future trend is discussed.

Graphene quantum dots mediated electron transfer in DNA base pairs

Graphene quantum dots (GQDs) were connected to [Ru(bpy)3]2+ to sense DNA-mediated charge transfer. Interaction between abasic site double stranded DNA (Abasic-DNA) and [Ru(bpy)3-GQD]2+ was investigated by absorption spectroscopy, gel electrophoresis, circular dichroism, and melting temperature measurements. The results indicate that [Ru(bpy)3-GQD]2+ could be intercalated into double stranded DNA. Using [Ru(bpy)3-GQD]2+ as a signal molecule, the charge transfer performance of DNA-intercalated [Ru(bpy)3-GQD]2+ was determined using electrochemical and electrochemiluminescence measurements. Various DNA types were immobilized on Au electrodes via Au-S bonds. Electrochemiluminescence and electrochemical measurements indicate that [Ru(bpy)3-GQD]2+ could enhance DNA-mediated charge transfer when intercalated into an abasic site of double stranded DNA. And comparing with [Ru(bpy)3]2+, it can be concluded that GQDs intercalate into the DNA duplex by acting as a base analog, thus enhancing DNA charge transfer. These findings suggest that the DNA-GQD structure could aid the development of molecular devices and electric drivers, and broaden the application of DNA charge transfer.

Effects of TiO2 crystal structure on the luminescence quenching of [Ru(bpy)2(dppz)]2+-intercalated into DNA

The intercalation of [Ru(bpy)₂(dppz)]²⁺ labeled as Ru(II) (bpy=2,2'-bipyridine and dppz=dipyrido[3,2,-a:2',3'-c]phenazine) into herring sperm DNA leads to the formation of emissive Ru(II)-DNA dyads, which can be quenched by TiO₂ nanoparticles (NPs) and sol-gel silica matrices at heterogeneous interfaces. The calcinations temperature exhibits a remarkable influence on the luminescence quenching of the Ru(II)-DNA dyads by TiO₂ NPs. With increasing calcinations temperature in the range from 200 to 850°C, the anatase-to-rutile TiO₂ crystal structure transformation increases the average particle size and hydrodynamic diameter of TiO₂ and DNA@TiO₂. The anatase TiO₂ has the stronger ability to unbind the Ru(II)-DNA dyads than the rutile TiO₂ at room temperature. The TiO₂ NPs and sol-gel silica matrices can quench the luminescence of the Ru(II) complex intercalated into DNA by selectively capturing the negatively DNA and positively charged Ru(II) complex to unbind the dyads, respectively. This present results provide new insights into the luminescence quenching and competitive binding of dye-labeled DNA dyads by inorganic NPs.

PAMAM dendrimers: A multifunctional nanomaterial for ECL biosensors

Polyamido amine (PAMAM) dendrimers have been shown to function as electrochemiluminescence (ECL) co-reactant and have the inherent capability of improving immobilization of molecules on surfaces due to their dendritic structure. Here, we investigated the combination of both of these properties as the basis for biosensor development. Dendrimers with 5, 8, 10 and 16 terminal amine groups, respectively, were used. These were covalently coupled to biotin as model recognition site, and tagged with Ru(bpy)₃²⁺ via adsorption. Due to their hydrophilicity, Ru-dendrimers showed significantly improved electrochemical activity in comparison to the standard tripropylamine (TPA) assisted ECL and similar luminescence yields even though 10 fold less dendrimer concentration was required in comparison to TPA. Best signals were obtained for D8 and D10 dendrimers. These Ru-dendrimers were subsequently used for the quantification of streptavidin, as its binding to the biotin-tag caused a proportional decrease in ECL signal with a dynamic range of 5nM to 1μM. These preliminary studies demonstrate that PAMAM dendrimers can function as responsive signal generators in solution-based ECL-bioassays with an assumed even higher impact when being immobilized directly on the electrode-surface.

A sensitive ratiometric electrochemical biosensor based on DNA four-way junction formation and enzyme-assisted recycling amplification

We develop a ratiometric electrochemical biosensor for DNA assay based on DNA four-way junction formation and enzyme-assisted recycling amplification.

Electrochemiluminescent Sensing for Caspase-3 Activity Based on Ru(bpy)3(2+)-Doped Silica Nanoprobe

Caspase-3 is one of the most frequently activated cysteine proteases during the apoptosis process and has been identified as a well-established cellular marker of apoptosis. In this study, a novel approach for the sensitive determination of caspase-3 activity was proposed using electrochemiluminescence (ECL) of Ru(bpy)3(2+)-doped silica (Ru@SiO2) with tripropylamine (TPA) as coreactant. A nanocomposite containing gold nanoparticles (AuNPs), poly(dimethyldiallyl ammonium chloride) (PDDA), and multiwalled carbon nanotubes (CNTs) was fabricated as an ECL platform. The biotinylated DEVD-peptide (biotin-Gly-Asp-Gly-Asp-Glu-Val-Asp-Gly-Cys) was immobilized on the nanocomposite surface via the strong bonding interaction between AuNPs and the thiol group. Then the streptavidin-modified Ru(bpy)3(2+)-doped silica (Ru@SiO2-SA) was immobilized on the ECL platform via the specific interaction between biotin and streptavidin to generate ECL signal. Caspase-3 can specifically recognize and cleave the N-terminus of DEVD, leading to the loss of the biotin label and the decrease of ECL intensity to determine the activity of caspase-3. The results revealed a new ECL avenue for the sensitive and specific monitor of caspase-3, and the platform could be utilized to evaluate anticancer drugs.

Interactions of DNA with graphene and sensing applications of graphene field-effect transistor devices: a review

Graphene field-effect transistors (GFET) have emerged as powerful detection platforms enabled by the advent of chemical vapor deposition (CVD) production of the unique atomically thin 2D material on a large scale. DNA aptamers, short target-specific oligonucleotides, are excellent sensor moieties for GFETs due to their strong affinity to graphene, relatively short chain-length, selectivity, and a high degree of analyte variability. However, the interaction between DNA and graphene is not fully understood, leading to questions about the structure of surface-bound DNA, including the morphology of DNA nanostructures and the nature of the electronic response seen from analyte binding. This review critically evaluates recent insights into the nature of the DNA graphene interaction and its affect on sensor viability for DNA, small molecules, and proteins with respect to previously established sensing methods. We first discuss the sorption of DNA to graphene to introduce the interactions and forces acting in DNA based GFET devices and how these forces can potentially affect the performance of increasingly popular DNA aptamers and even future DNA nanostructures as sensor substrates. Next, we discuss the novel use of GFETs to detect DNA and the underlying electronic phenomena that are typically used as benchmarks for characterizing the analyte response of these devices. Finally, we address the use of DNA aptamers to increase the selectivity of GFET sensors for small molecules and proteins and compare them with other, state of the art, detection methods.

Ruthenium polypyridine complexes combined with oligonucleotides for bioanalysis: a review

Ruthenium complexes are among the most interesting coordination complexes and they have attracted great attention over the past decades due to their appealing biological, catalytic, electronic and optical properties. Ruthenium complexes have found a unique niche in bioanalysis, as demonstrated by the substantial progress made in the field. In this review, the applications of ruthenium complexes coordinated with polypyridine ligands (and analogues) in bioanalysis are discussed. Three main detection methods based on electrochemistry, electrochemiluminescence, and photoluminscence are covered. The important targets, including DNA and other biologically important targets, are detected by specific biorecognition with the corresponding oligonucleotides as the biorecognition elements (i.e., DNA is probed by its complementary strand and other targets are detected by functional nucleic acids, respectively). Selected examples are provided and thoroughly discussed to highlight the substantial progress made so far. Finally, a brief summary with perspectives is included.

In situ hybridization chain reaction amplification for universal and highly sensitive electrochemiluminescent detection of DNA

In this work, we describe a new universal and highly sensitive strategy for electrochemiluminescent (ECL) detection of sequence specific DNA at the femtomolar level via in situ hybridization chain reaction (HCR) signal amplification. The DNA capture probes are self-assembled on a gold electrode. The presence of the target DNA and two hairpin helper DNAs leads to the formation of extended dsDNA polymers through HCR on the electrode surface. The in situ, HCR-generated dsDNA polymers cause the intercalation of numerous ECL indicators (Ru(phen)(3)(2+)) into the dsDNA grooves, resulting in significantly amplified ECL signal output. The proposed strategy combines the amplification power of the DNA HCR and the inherent high sensitivity of the ECL technique and enables low femtomolar detection of sequence specific DNA. The developed strategy also shows high selectivity against single-base mismatch sequences, which makes our new universal and highly sensitive HCR-based method a useful addition to the amplified DNA detection arena.

Signal-on electrochemiluminescent biosensor for ATP based on the recombination of aptamer chip

A novel signal-on electrochemiluminescent (ECL) biosensor based on adenosine triphosphate (ATP)-induced recombination of split aptamer chips is presented.

Highly sensitive electrochemiluminescent biosensor for adenosine based on structure-switching of aptamer

A highly sensitive and selective electrochemiluminescent (ECL) biosensor for the determination of adenosine was developed. Single DNA (capture DNA) was immobilized on the gold electrode through Au-thiol interaction at first. Another DNA modified with tris(2,2'-bipyridyl) ruthenium(II)-doped silica nanoparticles (Ru-SNPs) that contained adenosine aptamer was then modified on the electrode surface through hybridizing with the capture DNA. In the presence of adenosine, adenosine-aptamer complex is produced rather than aptamer-DNA duplex, resulting with the dissociation of Ru-SNPs-labeled aptamer from the electrode surface and the decrease in the ECL intensity. The decrease of ECL intensity has a direct relationship with the logarithm of adenosine concentration in the range of 1.0×10(-10) to 5.0×10(-6)molL(-1). The detection limit of the proposed method is 3.0×10(-11)molL(-1). The existence of guanosine, cytidine and uridine has little interference with adenosine detection, demonstrating that the developed biosensor owns a high selectivity to adenosine. In addition, the developed biosensor also demonstrates very good reusability, as after being reused for 30 times, its ECL signal still keeps 91% of its original state.

A novel electrochemiluminescence strategy for ultrasensitive DNA assay using luminol functionalized gold nanoparticles multi-labeling and amplification of gold nanoparticles and biotin-streptavidin system

Luminol functionalized gold nanoparticles were used as labels for electrochemiluminescence signal amplification and an ultrasensitive, highly selective, convenient, low cost DNA detection strategy was developed.

Signal-on electrochemiluminescence biosensor for thrombin based on target-induced conjunction of split aptamer fragments

A highly sensitive and selective electrochemiluminescence biosensor for detection of thrombin based on the strategy of target-induced conjunction of split aptamer fragments was developed.

Quantum dot-based DNA hybridization by electrochemiluminescence and anodic stripping voltammetry

Simple and convenient assays with quantum dots (QDs) as the labels for DNA detection are developed. The probe DNA modified with thiol was first immobilized on a pretreated Au electrode, and then the complementary DNA (cDNA) oligonucleotides were hybridized with the immobilized probes by immersing the probe-modified Au electrode into the cDNA oligonucleotide solution. Finally, the avidin-modified QDs were bound to the biosensor in the presence of biotin-modified cDNA. The fabrication process for the biosensor was monitored by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Different from the traditional sandwich-structure strategy, the QDs bind to the target DNA directly via the biotin-avidin-system. By observing the ECL signal and determination of the cadmium component in QDs, the DNA hybridization event was detected by ECL and square wave anodic stripping voltammetric technique (SWASV) respectively. For SWASV detection, the signal linearly increased with the increase of the logarithm of the cDNA concentration over the range of 50 nM-5 microM. The minimum detectable concentration is 50 pM. For ECL, it showed wider linearity range over 5 nM-5 microM and lower detectable concentration of 10 pM. This indicated that the ECL assay could be comparable to the conventional electrochemical assay. Furthermore, this biosensor possesses high selectivity over different sequences of target DNA oligonucleotides.

Ru(bpy)3(2+)-doped silica nanoparticles labeling for a sandwich-type electrochemiluminescence immunosensor

A new approach was established to construct a sandwich-type electrochemiluminescence (ECL) immunosensor by using Ru(bpy)(3)(2+)-doped silica (abbreviated as Ru-SiO(2)) nanoparticles to label secondary antibody. Firstly, carboxylate-terminated multi-walled carbon nanotubes (MWCNTs) were modified on the electrode to bond with avidin. Subsequently, biotinylated antibodies were immobilized on the surface of the electrode by employing the specific interaction of biotin/avidin and the non-covalent and covalent conjugation function of MWCNTs. Later, the electrode was incubated with antigen of mouse IgG and then reacted with the secondary antibody which was labeled by Ru-SiO(2). Accordingly, through the ECL response of Ru-SiO(2) and tripropylamine (TPA), a strong ECL signal was obtained and an amplification analysis of protein interaction was achieved. The present immunosensor showed a wide linear range of 0.05-200.00 ng mL(-1) for detecting mouse IgG, with a low detection limit of 17 pg mL(-1). There was a 4-300-fold improvement in detection limit compared with other similar studies. The morphologies of Ru-SiO(2) nanoparticles were characterized by using transmission electronic microscopy (TEM). The fabrication process of the immunosensor was studied by cyclic voltammetry (CV) and the performance of the immunosensor was monitored with an electrochemiluminescence analyzer. This new strategy for preparation of the ECL immunosensor could be easily realized and has potential application in ultrasensitive bioassays.

Chemiluminescence platforms in immunoassay and DNA analyses

Chemiluminescent (CL) detection techniques for DNA assays and immunoassays have become very popular in recent years. This review discusses recent advances in those CL assays that have occurred over the last few years. In the monoplex assay section, different classes of CL labels including nanoparticle, DNAzyme, acridinium ester, enzyme and luminol-based CL assays are reviewed concerning the detection of DNAs and proteins. In the multiplex assay section, both spatial resolution and substrate zone-resolved techniques are discussed.

Novel highly charged silica-coated Tb(III) nanoparticles with fluorescent properties sensitive to ion exchange and energy transfer processes in aqueous dispersions

Novel silica-coated Tb(III) nanoparticles with high luminecsence were synthesized using the reverse microemulsion procedure. The quenching of luminescent properties of these nanoparticles can be achieved by ion exchange and energy transfer mechanisms. The quenching through the ion exchange of Tb(III) by H+ or La(III) is time dependent, indicating that the ion exchange is probably diffusion controlled. The quenching by Co(III) complex cations is achieved by the energy transfer mechanism and thus is not time dependent. The analysis of quenching data in Stern-Volmer cooordinates reveal the negative charge of the silica-coated Tb(III)-TCAS nanoparticles and several types of luminophoric species, located within the core and close to the surface of silica nanoparticles.