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

Nanostructured materials for electrochemiluminescence (ECL)-based detection methods: recent advances and future perspectives

This review presents a general picture of the last advances and developments (2003-2008) related to novel nanostructured materials for electrochemiluminescence-based biosensors using. It briefly covers the basic mechanisms of ECL detection, and the recent developments in fabrication of solid-state ECL sensors using nanostructured materials such as carbon nanotubes, metal nanoparticles, quantum dots, thin films of metallopolymers and of inorganic metal complexes. Finally, challenges and perspectives of the use of such materials for biomedical diagnostics are discussed.

Applications of nanomaterials in electrogenerated chemiluminescence biosensors

Electrogenerated chemiluminescence (also called electrochemiluminescence and abbreviated ECL) involves the generation of species at electrode surfaces that then undergo electron-transfer reactions to form excited states that emit light. ECL biosensor, combining advantages offered by the selectivity of the biological recognition elements and the sensitivity of ECL technique, is a powerful device for ultrasensitive biomolecule detection and quantification. Nanomaterials are of considerable interest in the biosensor field owing to their unique physical and chemical properties, which have led to novel biosensors that have exhibited high sensitivity and stability. Nanomaterials including nanoparticles and nanotubes, prepared from metals, semiconductor, carbon or polymeric species, have been widely investigated for their ability to enhance the efficiencies of ECL biosensors, such as taking as modification electrode materials, or as carrier of ECL labels and ECL-emitting species. Particularly useful application of nanomaterials in ECL biosensors with emphasis on the years 2004-2008 is reviewed. Remarks on application of nanomaterials in ECL biosensors are also surveyed.

Electrogenerated chemiluminescence

In electrogenerated chemiluminescence, also known as electrochemiluminescence (ECL), electrochemically generated intermediates undergo a highly exergonic reaction to produce an electronically excited state that then emits light. These electron-transfer reactions are sufficiently exergonic to allow the excited states of luminophores, including polycyclic aromatic hydrocarbons and metal complexes, to be created without photoexcitation. For example, oxidation of [Ru(bpy)(3)](2+) in the presence of tripropylamine results in light emission that is analogous to the emission produced by photoexcitation. This review highlights some of the most exciting recent developments in this field, including novel ECL-generating transition metal complexes, especially ruthenium and osmium polypyridine systems; ECL-generating monolayers and thin films; the use of nanomaterials; and analytical, especially clinical, applications.

Ultra-sensitive detection of mutated papillary thyroid carcinoma DNA using square wave stripping voltammetry method and amplified gold nanoparticle biomarkers

This study presents an ultra-sensitive technique for the electrochemical detection of the mutated BRAF gene associated with papillary thyroid carcinomas (PTC). In the proposed approach, a biotinylated 30-nucleotides probe DNA was immobilized in a streptavidin-modified 96-well microtiter plate and the free active sites of the streptavidin were blocked using biotinylated bovine serum albumin (BSA). The biotinylated target DNA was then added and allowed to hybridize with the immobilized probe DNA for 30min. Subsequently, streptavidin-labeled gold nanoparticles were added, and a nanoparticle enlargement process was performed using gold ion solution and formaldehyde reductant. The gold particles were then dissolved in bromide and DNA hybridization detection process was performed using a square wave stripping voltammetry (SWSV) technique. The results indicated a stable SWSV response in differential detection between blank solution and target DNA solution with a concentration of 130aM. Moreover, the coefficient of determination (R(2)) of the semi-log plot of the SWSV response current against the target DNA concentration (0.52-1300aM) was found to be 0.9982. The detection limit was estimated to be 0.35aM (based on a signal-to-noise ratio of 3:1). This value was approximately three orders of magnitude lower than that obtained using the same method but without gold amplification process. Finally, the proposed approach is successful in differentiating between the mutant and wildtype BRAF sequences that are present in genuine 224-nucleotides DNA.

Developments and Applications of Electrogenerated Chemiluminescence Sensors Based on Micro- and Nanomaterials

A variety of recent developments and applications of electrogenerated chemiluminescence (ECL) for sensors are described. While tris(2,2′-bipyridyl)-ruthenium(II) and luminol have dominated and continue to pervade the field of ECL-based sensors, recent work has focused on use of these lumophores with micro- and nanomaterials. It has also extended to inherently luminescent nanomaterials, such as quantum dots. Sensor configurations including microelectrode arrays and microfluidics are reviewed and, with the recent trend toward increased use of nanomaterials, special attention has been given to sensors which include thin films, nanoparticles and nanotubes. Applications of ECL labels and examples of label-free sensing that incorporate nanomaterials are also discussed.

[Ru(bpy)3]2+-doped silica nanoparticles within layer-by-layer biomolecular coatings and their application as a biocompatible electrochemiluminescent tag material

[Ru(bpy)3]2+-doped silica (RuSi) nanoparticles were synthesized by using a water/oil microemulsion method. Stable electrochemiluminescence (ECL) was obtained when the RuSi nanoparticles were immobilized on a glassy carbon electrode by using tripropylamine (TPA) as a coreactant. Furthermore, the ECL of the RuSi nanoparticles with layer-by-layer biomolecular coatings was investigated. Squential self-assembly of the polyelectrolytes and biomolecules on the RuSi nanoparticles gave nanocomposite suspensions, the ECL of which decreased on increasing the number of bilayers. Moreover, factors that affected the assembly and ECL signals were investigated. The decrease in ECL could be assigned to steric hindrance and limited diffusion of the coreactant molecules in the silica matrix after they were attached to the biomolecules. Since surface modification of the RuSi nanoparticles can improve their biocompatibility and prevent leaking of the [Ru(bpy)3]2+ ions, the RuSi nanoparticles can be readily used as efficient and stable ECL tag materials in immunoassay and DNA detection.

Nanostructures as analytical tools in bioassays

We critically evaluate the usefulness of different nanostructures described as labels, nanoscaffolds or separation media in immunoassays and nucleic-acid hybridization assays. Many of the great number of publications describe only theoretical aspects of using these nanostructures or nanoparticles, but do not verify their applicability in the presence of potential interferents that can be present in the sample matrix. We attempt a systematic study of the advantages and the limitations of using these new reagents in bioassays, the different assay formats for individual and multiplexed detection, and the capability of these assays in analyzing real samples.

Bifunctional Nanostructure of Magnetic Core Luminescent Shell and Its Application as Solid-State Electrochemiluminescence Sensor Material

Bifunctional nanoarchitecture has been developed by combining the magnetic iron oxide and the luminescent Ru(bpy)32+ encapsulated in silica. First, the iron oxide nanoparticles were synthesized and coated with silica, which was used to isolate the magnetic nanoparticles from the outer-shell encapsulated Ru(bpy)32+ to prevent luminescence quenching. Then onto this core an outer shell of silica containing encapsulated Ru(bpy)32+ was grown through the Stöber method. Highly luminescent Ru(bpy)32+ serves as a luminescent marker, while magnetic Fe3O4 nanoparticles allow external manipulation by a magnetic field. Since Ru(bpy)32+ is a typical electrochemiluminescence (ECL) reagent and it could still maintain such property when encapsulated in the bifunctional nanoparticle, we explored the feasibility of applying the as-prepared nanostructure to fabricating an ECL sensor; such method is simple and effective. We applied the prepared ECL sensor not only to the typical Ru(bpy)32+ co-reactant tripropylamine (TPA), but also to the practically important polyamines. Consequently, the ECL sensor shows a wide linear range, high sensitivity, and good stability.

Detection of thrombin using electrogenerated chemiluminescence based on Ru(bpy)3(2+)-doped silica nanoparticle aptasensor via target protein-induced strand displacement

A sensitive and selective aptasensor using tri(2,2'-bipyridyl)ruthenium(II)-doped silica nanoparticles (Ru(bpy)3(2+)-doped SNPs) as DNA tags for detection of thrombin is developed based on the target protein-induced strand displacement of the DNA probe. For the proposed aptasensor, the aptamer was assembled on the surface of the Au electrode through Au-S binding. The hybridization event between the DNA probe labeled by the Ru(bpy)3(2+)-doped SNPs and the aptamer was evaluated by electrogenerated chemiluminescence (ECL) measurements. Then, the DNA probe was displaced by thrombin and the binding event between the thrombin and the aptamer was monitored by ECL measurements again. The difference of ECL intensity (deltaI(ECL)) of the two events could be used to quantify the thrombin. Other proteins, such as bovine serum albumin and bovine hemoglobin, had almost negligible deltaI(ECL). Under the optimal conditions, the deltaI(ECL) was linearly related to the concentration of the thrombin in the range of 10 fM to 10 pM and the detection limit was down to 1.0 fM since SNPs containing a large number of Ru(bpy)3(2+) molecules were labeled on the DNA probe.