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Covalent Binding of Antibodies to Cellulose Paper Discs and Their Applications in Naked-eye Colorimetric Immunoassays

This report presents two methods for the covalent immobilization of capture antibodies on cellulose filter paper grade No. 1 (medium-flow filter paper) ...

Temasek Polytechnic

The reaction of corresponding cadmium salts with the flexible ligand 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene (bbtz) affords the 3D coordination network [Cd3(bbtz)6(H2O)6](BF4)(6.1.75H2O (1), containing ribbons of rings and planar 2D (4,4) networks polycatenated with each other, the undulating 2D (4,4) network [Cd(bbtz)2(H2O)2](ClO4)2.2H2O (2), and ribbons of rings [Cd(bbtz)2(H2O)2](BF4)2.3DMF (3) and [Cd(bbtz)2(H2O)2](ClO4)2.3DMF (4).

Supramolecular isomers in the same crystal: a new type of entanglement involving ribbons of rings and 2D (4,4) networks polycatenated in a 3D architecture.

In this report, an electrical detection scheme for the quantification of DNA using a nanogap sensor array is detailed. The prime objective is to develop a novel sensing procedure, based on the electronic transduction mechanism, which would mitigate the problems intrinsic to nanostructure-based biosensing devices. Design considerations of the sensor array take into account the feasibility of mass production in a cost-effective way by using standard silicon microfabrication technologies. The sensing mechanism relies on bridging the nanogap upon hybridization of the two termini of a target DNA with two different surface-bound capture probes, followed by a simple metallization step. About 2 orders of magnitude enhancement in conductance, as referred to a clean background (<1.0 pS) observed at a control sensor, was obtained in the presence of as little as 1.0 fM target DNA. This sensitivity is comparable to the best of electrochemical/electrical biosensors. A linear relationship between the conductance and the DNA concentration was obtained from 1.0 fM to 1.0 pM with an exceptional signal intensity of 2.1 x 10(4)% change per unit concentration. This change in conductivity is so large that it can unambiguously detect the concentration of DNA quantitatively and may obviate the need for target amplification used in current DNA tests. Moreover, the sensor array exhibited excellent single-base mismatch discrimination due to its unique vertically aligned nanostructure and the two-probe configuration.

Mass-produced nanogap sensor arrays for ultrasensitive detection of DNA.

A simple and sensitive electrical sensor array for polymerase chain reaction-free (PCR-free) messenger RNA (mRNA) expression profiling is described in this work. The sensor array, consisting of vertically aligned gold microband electrode/SiO(2)/gold microband electrode sandwich structures (nanogap sensors) in orthogonal configurations, was fabricated on a 1 cm x 1 cm silicon chip. A target mRNA was first hybridized with its specific capture probes (CP) on the bottom side of the nanogap, followed by a second hybridization (annealing) of its poly(A) tail with poly(T) annealing probes (AP) on the top side of the nanogap, holding the hybridized mRNA strands vertically across the nanogap. A subsequent metallization of the hybridized mRNA strands bridged the nanogap and consequently produced a substantial change in conductance, allowing ultrasensitive detection of mRNA without any amplification. Noticeable conductance changes were observed in the presence of as little as 0.10 fM mRNA. A linear relationship between the conductance and mRNA concentration was obtained from 0.50 fM to 1.0 pM with exceptional signal intensity. As little as a 50% difference in mRNA expression was successfully detected. The sensor array also exhibited excellent mismatch discrimination due to its unique vertically aligned nanostructure and the two-step hybridization.

Electrical sensor array for polymerase chain reaction-free messenger RNA expression profiling.

This work reports a highly sensitive procedure for the determination of trace amounts of mercury, based on fluorescence quenching of thenoyltrifluoroacetone (TTA) capped hierarchically nanostructured europium oxide (cHN-Eu(2)O(3)). The HN-Eu(2)O(3) consisted of nanometer-thick Eu(2)O(3) sheets self-organized into nano- and micro-sized monoliths with a hierarchical architecture while retaining its desirable fluorescence properties. The fluorescence intensity of the cHN-Eu(2)O(3) was 1000 times higher than that of commercial Eu(2)O(3) nanoparticles (equivalent weight) when it was capped with TTA, suggesting that a synergetic effect, confining the longtime Eu(3+) excitation within the nanostructure and light-harvesting effect of the capping agent, is responsible for this fluorescence enhancement. Excellent interaction between the cHN-Eu(2)O(3) and solution species is expected owing to its large surface area, high surface-to-bulk ratio, and ultrahigh fluorescence intensity. As an example, aqueous suspensions of the cHN-Eu(2)O(3) were used as sensing agent for the determination of trace amounts of mercury. A linear relationship between the concentration of mercury and fluorescence quenching was observed from 10 ppb to 10 ppm with a correlation coefficient of 0.997 and a detection limit of 5.0 ppb. Mercury in various samples was analyzed using the cHN-Eu(2)O(3) suspension.

Determination of trace amounts of mercury using hierarchically nanostructured europium oxide.

Well-defined voltammetric current peaks of polyaniline were observed at biosensors hybridized with ruthenium oxide nanoparticle-tagged microRNAs and incubated in a mixture of aniline/H(2)O(2), which can be used for direct microRNA expression profiling with excellent sensitivity.

A highly sensitive microRNA biosensor based on ruthenium oxide nanoparticle-initiated polymerization of aniline.

A highly sensitive microRNA (miRNA) biosensor that employs ruthenium oxide nanoparticle (RuO(2) NP)-initiated polymerization of 3,3'-dimethoxybenzidine (DB) and miRNA-templated deposition of an insulating poly(3,3'-dimethoxybenzidine) (PDB) film is described in this work. The biosensor was made of a mixed monolayer of oligonucleotide capture probes (CPs) and 4-mercaptoaniline on a gold electrode. Following hybridization with a RuO(2) NP-tagged target miRNA, a mixture of DB/H(2)O(2) in pH 5.0 0.10 M acetate buffer was applied to the biosensor. The RuO(2) NPs serve as polymerization initiator/catalyst for the polymerization of DB. And the hybridized anionic miRNA strands and free CPs serve as templates, guiding the deposition of PDB. The amount of the deposited PDB and its insulating power directly correlated to the concentration of the target miRNA in solution. Electrochemical impedance spectroscopic tests showed that a linear charge-transfer resistance-concentration relationship from 6.0 fM to 2.0 pM was attained after 60 min of incubation in the DB/H(2)O(2) mixture. There was no cross-hybridization between pre-miRNA and mature miRNA and very little cross-hybridization among closely related miRNA family members even at single-base-mismatched levels. This impedance-based biosensor offers an attractive alternative for miRNA expression profiling and may enable the development of a portable multiplexing miRNA profiling system.

Amplified detection of microRNA based on ruthenium oxide nanoparticle-initiated deposition of an insulating film.

A detailed mechanistic study reveals that instead of being postulated as oxidase-like, nanoceria is a plain nanoparticulate oxidant and dissolves completely after being reduced.

Mechanism of the oxidation of organic dyes in the presence of nanoceria.

A highly sensitive microRNA (miRNA) biosensor for both ligation- and PCR-free detection of miRNAs is described in this work. The biosensor was made of a monolayer of long oligonucleotide capture probes (CPs) comprising of miRNA capturing segments at the top (3' termini) and detection probe capturing segments at the bottom (5' termini). Following hybridization with a target miRNA, a cocktail of Surveyor(®) and exonuclease I in pH 7.4 phosphate buffered saline was applied to the biosensor. Unhybridized CP strands and mismatched miRNA/CP duplexes were digested while complementarily hybridized ones remained intact. Thereafter, electrochemically activated glucose oxidase-tagged peptide nucleic acid detection probes (GOx-DP) were hybridized to the bottom segments of the CPs on the biosensor. The number of GOx molecules found at the biosensor surface coincides with the number of miRNA strands hybridized and therefore correlates directly to the concentration of the target miRNA. A detection limit of 10 fM and a linear current-concentration relationship up to 10 pM were attained under optimized conditions. The biosensor effectively eliminated the needs for chemical/biological ligation and PCR. It was showed that there is little cross-hybridization among closely related miRNA family members even at single-base-mismatched levels. Successful attempts were made in applying the biosensor to the detection of miRNAs in total RNA extracted from cell lines.

A highly sensitive and specific biosensor for ligation- and PCR-free detection of microRNAs.

Ru sitting comfortably: Ruthenium oxide nanoparticles show bienzyme-like activities, and are capable of catalyzing H(2)O(2) disproportionation at pH 7.0 and peroxidation at pH 4.0 in aqueous solutions (see scheme). Their specific activities are better than many natural catalases and peroxidases and far better than bifunctional catalase/peroxidases.

Article	Year
Supramolecular isomers in the same crystal: a new type of entanglement involving ribbons of rings and 2D (4,4) networks polycatenated in a 3D architecture. Chemical communications (Cambridge, England)\| PubMed ID: 15877119	2005
Mass-produced nanogap sensor arrays for ultrasensitive detection of DNA. Journal of the American Chemical Society\| PubMed ID: 19655794	2009
Electrical sensor array for polymerase chain reaction-free messenger RNA expression profiling. Analytical chemistry\| PubMed ID: 20578701	2010
Determination of trace amounts of mercury using hierarchically nanostructured europium oxide. Talanta\| PubMed ID: 20875597	2010
A highly sensitive microRNA biosensor based on ruthenium oxide nanoparticle-initiated polymerization of aniline. Chemical communications (Cambridge, England)\| PubMed ID: 21042626	2010
Amplified detection of microRNA based on ruthenium oxide nanoparticle-initiated deposition of an insulating film. Analytical chemistry\| PubMed ID: 21207998	2011
Mechanism of the oxidation of organic dyes in the presence of nanoceria. Chemical communications (Cambridge, England)\| PubMed ID: 21264416	2011
A highly sensitive and specific biosensor for ligation- and PCR-free detection of microRNAs. Biosensors & bioelectronics\| PubMed ID: 21420848	2011
Nanoparticulate peroxidase/catalase mimetic and its application. Chemistry (Weinheim an der Bergstrasse, Germany)\| PubMed ID: 22733717	2012

Yanfen Peng

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