Luminescent Ag6Au6 heterometallic ethisterone cluster and probe for estrogen receptor α.

A heterometallic cluster [Ag6Au6(ethisterone)12] of an unprecedented topology was synthesized and characterized. A sensitive and specific probe for estrogen receptor α (ERα) has been developed for the first time based on the enhancement of the Ag6Au6 luminescence.

Ultrasensitive colorimetric carcinoembryonic antigen biosensor based on hyperbranched rolling circle amplification.

In this study, a hyperbranched rolling circle amplification (HRCA)-based colorimetric biosensor for carcinoembryonic antigen (CEA) is developed with high sensitivity and specificity. A CEA aptamer can bind with its target (CEA) to form a complex due to their high affinity, and the introduced CDNA cannot hybridize with the aptamer. Thus, free CDNA can propagate the HRCA reaction to form a large number of single-stranded DNA (ss-DNA). ss-DNA can be easily adsorbed onto AuNPs and prevent salt-induced AuNPs aggregation, which causes the change in the color of the system. It is found that the absorbance intensity ratio (A520/A660) has a linear relationship with the concentration of the target in the range of 5 pM-0.5 nM, and the detection limit is as low as 2 pM (S/N = 3).

Synthesis, characterization, and DNA binding of a novel ligand and its Cu (II) complex.

A novel naphthalene-2,3-diamine-2-salicylaldehyde (NS) ligand and its mononuclear copper(II) complex (CuNS) have been synthesized and structurally characterized. The UV­vis absorption and emission spectra of NS showed obvious changes on addition of Cu2+ solution. The interaction of the compounds with calf thymus DNA and G-quadruplex DNA were investigated by spectroscopic methods and thermal melting assay. The nucleolytic cleavage activity of the compounds was investigated on double-stranded circular pBR322 plasmid DNA and G-quadruplex DNA by electrophoretic mobility shift assay. The results show that CuNS has a greater ability to stabilize G-quadruplex DNA over calf-thymus DNA. The cytotoxicity of the compounds toward HpeG2 cancer cells was also studied, and they showed significant potential for antineoplastic effects.

Enzyme-free and label-free ultrasensitive electrochemical detection of human immunodeficiency virus DNA in biological samples based on long-range self-assembled DNA nanostructures.

Biosensors based on nanomaterials have been used for detection of various biological molecules with high sensitivity and selectivity. Herein, we developed a simple and ultrasensitive electrochemical DNA biosensor using long-range self-assembled DNA nanostructures as carriers for signal amplification, which can achieve an impressive detection limit of 5 aM human immunodeficiency virus (HIV) DNA even in complex biological samples. In this study, we designed two auxiliary probes. A cascade of hybridization events between the two auxiliary probes can lead to long-range self-assembly and form micrometer-long one-dimensional DNA nanostructures. In the presence of target DNA, each copy of the target can act as a trigger to connect a DNA nanostructure to a capture probe on the electrode surface. Then, a great amount of redox indicator [Ru(NH(3))(6)](3+) can be electrostatically bound to the DNA nanostructures and eventually result in significantly amplified electrochemical signals.

General colorimetric detection of proteins and small molecules based on cyclic enzymatic signal amplification and hairpin aptamer probe.

In this work, we developed a simple and general method for highly sensitive detection of proteins and small molecules based on cyclic enzymatic signal amplification (CESA) and hairpin aptamer probe. Our detection system consists of a hairpin aptamer probe, a linker DNA, two sets of DNA-modified AuNPs, and nicking endonuclease (NEase). In the absence of a target, the hairpin aptamer probe and linker DNA can stably coexist in solution. Then, the linker DNA can assemble two sets of DNA-modified AuNPs, inducing the aggregation of AuNPs. However, in the presence of a target, the hairpin structure of aptamer probe is opened upon interaction with the target to form an aptamer probe-target complex. Then, the probe-target complex can hybridize to the linker DNA. Upon formation of the duplex, the NEase recognizes specific nucleotide sequence and cleaves the linker DNA into two fragments. After nicking, the released probe-target complex can hybridize with another intact linker DNA and the cycle starts anew. The cleaved fragments of linker DNA are not able to assemble two sets of DNA-modified AuNPs, thus a red color of separated AuNPs can be observed. Taking advantage of the AuNPs-based sensing technique, we are able to assay the target simply by UV-vis spectroscopy and even by the naked eye. Herein, we can detect the human thrombin with a detection limit of 50 pM and adenosine triphosphate (ATP) with a detection limit of 100 nM by the naked eye. This sensitivity is about 3 orders of magnitude higher than that of traditional AuNPs-based methods without amplification. In addition, this method is general since there is no requirement of the NEase recognition site in the aptamer sequence. Furthermore, we proved that the proposed method is capable of detecting the target in complicated biological samples.

Electrochemiluminescence properties of [Pt2Ag4(C≡CC6H4R)8]n (R = CH3, n = 1; R = H, n = 1 and 2) with amine (TPrA and DBAE) as the coreactant and determination of Sudan I.

Two hexanuclear clusters, [Pt(2)Ag(4)(C≡CC(6)H(4)R)(8)] (R = CH(3), 1; R = H, 2), together with dimer [Pt(2)Ag(4)(C≡CC(6)H(5))(8)](2) (3), have been synthesized and characterized by elemental analyses, electrospray ionization mass spectrometry, and (1)H NMR spectroscopy and by X-ray crystallography for 1 and 3. A considerable enhancement of photoluminescence (PL) and a notable red shift in the emission maximum of 1 (λ(max) 600 nm) relative to 2 (λ(max) 545 nm) are observed. Electrogenerated chemiluminescence (ECL) of 1 and 2 in the absence or presence of coreactant tri-n-propylamine (TPrA) or 2-(dibutylamino)ethanol (DBAE) at different working electrodes in different solvents (CH(2)Cl(2), CH(2)ClCH(2)Cl, or CH(3)CN) has been studied. The ECL spectra are identical with the PL spectra, indicating that ECL emissions are also due to a MLM'CT [Pt(d)/π (C≡CC(6)H(4)R-4) → Pt(p(z))/Ag(sp)/π* (C≡CC(6)H(4)R-4)] state modified by Pt···Ag and Ag···Ag contacts. ECL of 1- and 2/amine systems in CH(2)ClCH(2)Cl was produced at the potentials of 1.14-1.19 V vs SCE, notably negatively shifted by about 0.38 V compared to those of the Ru(bpy)(3)(2+)/amine system. In all cases, ECL quantum efficiencies of 2 are higher than those of 1 and on the same order of magnitude as that of the [Ru(bpy)(3)](PF(6))(2)/amine system. It is noted that Sudan I tends to decrease the ECL intensity of the 1/DBAE system in CH(2)ClCH(2)Cl at a platinum working electrode. A new ECL method for the determination of Sudan I was developed with a linear range of 2.5 × 10(-5)-1.0 × 10(-3) M and a detection limit of 8.0 × 10(-6) M based on 3 times the ratio of signal-to-noise.

General approach for monitoring peptide-protein interactions based on graphene-peptide complex.

Peptide-protein interactions have critical roles in biology. Monitoring peptide-protein interactions plays an important role in investigating molecular recognition, screening drugs, and designing biosensors. In this paper, we develop a novel fluorescent approach to monitor peptide-protein interactions based on the assembly of pyrene-labeled peptide and graphene oxide (GO). The pyrene-labeled peptide is strongly adsorbed on the surface of GO via π-π interactions and hydrophobic interactions. As a result, the proximity of the GO to the pyrene moiety effectively quenches the fluorescence of pyrene. In the presence of target protein, the competitive binding of the target protein with GO for peptide results in the restoration of fluorescence signal. This signaling mechanism makes it possible to monitor the peptide-protein interactions in a homogeneous real-time format.

High electrochemiluminescence of a new water-soluble iridium(III) complex for determination of antibiotics.

A new water-soluble iridium(III) diimine complex with appended sugar was synthesized and characterized. The electrochemiluminescent behavior of the new complex in aqueous buffer was first studied and the ECL signal was found to be much higher than that of [Ru(bpy)(3)](2+) at a Pt working electrode. Tri-n-propylamine (TPA) and antibiotics were determined by the ECL of the iridium(III) complex in aqueous buffer at the Pt electrode and the method was found to show good sensitivity and reproducibility. The new iridium(III) complex was found to display good solubility in aqueous solution and a strong ECL signal at the Pt electrode, which might open up the possibility of its application in analysis.

Preparation and evaluation of a phenylboronate affinity monolith for selective capture of glycoproteins by capillary liquid chromatography.

A phenylboronate affinity monolith was prepared and applied to the selective capture of glycoproteins from unfractionated protein mixtures. The monolith was synthesized in a 100 µm i.d capillary by an in situ polymerization procedure using a pre-polymerization mixture consisting of 4-vinylphenylboronic acid (VPBA) as functional monomer, ethylene dimethacrylate (EDMA) as crosslinker, diethylene glycol and ethylene glycol as binary porogenic solvents, and azobisisobutyronitrile (AIBN) as initiator. The prepared monolith was characterized in terms of the morphology, pore property, and recognition property. The selectivity and dynamic binding capacity were evaluated by using standard glycoproteins and nonglycoproteins as model proteins. The chromatographic results demonstrated that the phenylboronate affinity monolith had higher selectivity and binding capacity for glycoprotein than nonglycoprotein. The resulting phenylboronate affinity monolith was used as the sorbent for in-tube solid phase microextraction (in-tube SPME), and the extraction performance of the monolith was assessed by capture of ovalbumin from egg white sample.

Label-free fluorescent sensor for mercury(II) ion by using carbon nanotubes to reduce background signal.

A simple, selective and sensitive turn-on fluorescent sensor for the detection of mercury(II) ion was developed using Sybr Green I as the signal reporter and SWCNTs as the quencher. Due to the affinity of SWCNTs towards ssDNA and organic dye, Sybr Green I, thymine-rich ssDNA and SWCNTs could form a self-assembly of three components, resulting in fluorescence quenching. Upon addition of another thymine-rich ssDNA and mercury(II) ion, formation of dsDNA via T-Hg(2+)-T base pairs enabled Sybr Green I to intercalate into the dsDNA, resulting in the restoration of fluorescence. SWCNTs were found to reduce the background signal and improve the analytical sensitivity. A linear relationship between the fluorescence intensity and the concentration of mercury(II) ion was observed in the range of 20-1250 nM (R = 0.9985) with a detection limit of 7.9 nM. The proposed method was applied to detect mercury(II) ion in tap water samples with good results.

Simple and selective sensing of cysteine using gold nanoparticles modified by ruthenium(II) complexes.

A simple and selective luminescence sensing method for the cysteine detection was developed based on gold nanoparticles modified by the new ruthenium(II) complexes. The intense emission of the modified ruthenium(II) complexes was quenched efficiently by gold nanoparticles due to the energy and charge transfer between the ruthenium(II) fluorophores and gold nanoparticles. Upon addition of cysteine, the emission of the ruthenium(II) complexes was enhanced significantly by the release of the ruthenium(ll) complexes from the surface of the gold nanoparticles. Therefore, cysteine could be detected by this gold nanoparticles-ruthenium(II) complexes based probes. The synthesis of gold nanoparticles and the modification based fluorophores probed could be accomplished successfully within one step, which simplified the preparation of luminescence sensors. Moreover, since metal-to-ligand charge transfer transition (3MLCT) emission band of the ruthenium(II) complexes was in the visible region, this approach was available for biomolecular sensing applications, and its relatively long life time made it suitable for the biological process studies.

Increasing the sensitivity and single-base mismatch selectivity of the molecular beacon using graphene oxide as the "nanoquencher".

Here, we report a novel, highly sensitive, selective and economical molecular beacon using graphene oxide as the "nanoquencher". This novel molecular beacon system contains a hairpin-structured fluorophore-labeled oligonucleotide and a graphene oxide sheet. The strong interaction between hairpin-structured oligonucleotide and graphene oxide keep them in close proximity, facilitating the fluorescence quenching of the fluorophore by graphene oxide. In the presence of a complementary target DNA, the binding between hairpin-structured oligonucleotide and target DNA will disturb the interaction between hairpin-structured oligonucleotide and graphene oxide, and release the oligonucleotide from graphene oxide, resulting in restoration of fluorophore fluorescence. In the present study, we show that this novel graphene oxide quenched molecular beacon can be used to detect target DNA with higher sensitivity and single-base mismatch selectivity compared to the conventional molecular beacon.

Cathodic electrochemiluminescence at C/CxO(1-x) electrodes for the fabrication of label-free biosensors.

Cathodic electrochemiluminescence (ECL) is firstly observed at a carbon oxide covered glassy carbon (C/C(x)O(1-x)) electrode as a large cathodic pulse polarization is applied. This insulating carbon oxide (C(x)O(1-x)) film is constructed on a glassy carbon (GC) substrate by electrochemical oxidization in basic media. The film properties, such as the composition of carbon and oxygen, and the thickness as well, can be controlled by the potential and the duration in the oxidizing process. X-Ray photoelectron spectroscopy (XPS) studies show that carbonyl and carboxyl dominate at the oxidized surface, to which antibodies can be covalently bound. The specific immunoreaction between antigen (Ag) and antibody (Ab) resulted in a decrease in the ECL intensity, thus creating an interesting basis for the development of a label-free cathodic ECL immunosensor. As an example, human IgG (hIgG) was sensitively determined in the concentration range of 0.01-100 ng mL(-1), and the detection limit was ca. 1.0 pg mL (-1) (S/N = 3). In addition, the content of hIgG in human serum has been assayed by the developed immunosensor and a commercially available immune turbidimetry method, respectively, and consistent results were obtained. The prepared immunosensor provides a promising approach for the clinical determination of IgG levels in human serum, because it is simple, rapid, highly sensitive, specific, and without the need of tedious labeling operations.

An extremely stable and sensitive end-column electrochemical detector based on heated copper microdisk electrode with direct current for CE and CE-Chip.

A heated copper microdisk electrode (HCME) was fabricated and successfully applied to capillary electrophoresis (CE) and CE-Chip as an electrochemical detector (ECD) for the detection of three carbohydrates and shikimic acid (SA) in Illicium verum Hook F., respectively. The temperature of HCME was heated by twin-wire-wound coil with direct current to reduce the magnetic interference. Coupled with CE and CE-chip, this detector exhibits both extremely stable and sensitive performance at elevated temperature compared with that at room temperature. In successive detection of three carbohydrates and shikimic acid (SA), the HCME exhibits very stable response with RSD of ca. 2% with elevated temperature without renewing the electrode, while at room temperature, RSD of ca. 20% is obtained. This is very important in practical applications that tedious works, such as polishing and re-fixing the electrode at each detection, can be therefore avoided. In addition, the sensitivity is about 2-6 time increased, and the linear range is about an order wider at elevated temperature (ca. 60 degrees C) than that at room temperature (ca. 25 degrees C).

Separation and detection of isoquinoline alkaloids using MEEKC coupled with field-amplified sample injection induced by ACN.

New methods based on MEEKC coupling with field-amplified sample injection (FASI) induced by ACN were proposed for five isoquinoline alkaloids (berberine, palmatine, jatrorrhizine, sinomenine and homoharringtonine) in no salt and high salt sample solution (HS). For the separation of five isoquinoline alkaloids, a running buffer composed of 18 mM sodium cholate, 2.4% v/v butan-1-ol, 0.6% v/v ethyl acetate, 10% v/v (or 30% v/v) methanol and 87.0% v/v (or 67% v/v) 5 mM Na2B4O7~10 mM NaH2PO4 buffer (pH 7.5) was developed. In order to improve the sensitivity, FASI induced by ACN was applied to increase the detection sensitivity. The detection limit was found to be as low as 0.0002 microg/mL in no salt sample solution and 0.062 microg/mL in HS. The method has been applied for the analysis of human urine spiked with analytes, and the assay results were proved to be satisfactory, and also the determination of berberine in urine sample after oral administration berberine.

Highly enhanced electrocatalytic oxidation of glucose and shikimic acid at a disposable electrically heated oxide covered copper electrode.

A heated oxide covered copper electrode (HOCE) was facilely fabricated for the first time, providing a highly enhanced electrocatalytic oxidation, and cost effective and sensitive determination for polyhydroxy compounds such as glucose and shikimic acid.

A graphene platform for sensing biomolecules.

Sensitive platform: The use of graphene oxide (GO) as a platform for the sensitive and selective detection of DNA and proteins is presented. The interaction of GO and dye-labeled single-stranded DNA leads to quenching of the dye fluorescence. Conversely, the presence of a target DNA or protein leads to the binding of the dye-labeled DNA and target, releasing the DNA from GO, thereby restoring the dye fluorescence (see picture).

Rapid hydrolysis and electrochemical detection of trace carbofuran at a disposable heated screen-printed carbon electrode.

A disposable heated screen-printed carbon electrode (HSPCE) is successfully fabricated. It demonstrates rapid responses to electrical heating and is easily elevated above the water boiling point by a high frequency alternating current. The temperature rise at the HSPCE was found to be strongly dependent on the square of the heating current and the electrode width. Carbofuran (CAF) could be rapidly hydrolyzed to carbofuran phenol at the HSPCE with raised temperature, and then determined at the same electrode at room temperature by differential potential voltammetry (DPV). The factors influencing the detection were examined, including pH, hydrolytic temperature and heating time. Under the optimum conditions, the detection linear range of CAF was from 4.0 x 10(-7) to 4.0 x 10(-4) mol L(-1) and the detection limit was 5.0 x 10(-8) mol L(-1) (S/N = 3). This method was successfully applied to the analysis of CAF residues in real samples (spiked water, soil and vegetables), and satisfactory recoveries were obtained.

[Ru (bpy)3(2+) electrochemi-luminescence of screen-printed electrodes for low cost disposable C2O4(2-) sensor].

The present paper reports the establishment of an electrochemi-luminescence (ECL) sensor by using screen-printed electrodes(SPE) which contain Ru(bpy)3(2+). The method of making the SPE and the fix of Ru(bpy)3(2+) were studiedin detail. The characters of the sensor were studied. The sensor has been applied to detect C2O4(2-) in solution. Under optimised conditions, at 1.55 V vs. Ag/AgCl, in 0.2 mol x L(-1) phosphate buffer solution (pH 6.0), the linger range extends from 3.0 x 10(-7) mol x L(-1) to 1.0 x 10(-5) mol x L(-1), the detection limit is 1.2 x 10(-7) mol x L(-1) (S/N=3). The sensors have good stability and reproductivity. It should be noted that based on the same principle, the sensors can be applied to detect many other compounds, such as amino acids, TprA and NAD. If the screen machine is used to make the SPE, the reproductivity and stability of the SPEs can be improved further.

[Research of Hg2+ sol-gel membrane made of organically modified silicates].

A photochemical sensor for the determination of Hg2+ consisting of organically modified silicates (ormosils) was developed. Hg(2+)-sensitive fluorescent sol-gel films were prepared by co-condensation of tetramethoxysilane (TMOS) and dimethyldimethoxysilane (DMOS), and the fluorescent indicator 5,10,15, 20-tetra (p-sulfonatophenyl) porphyrin sodium was embedded in sol-gel in the form of ion pairs with cetyltrimethyl ammonium bromide. The optimization condition of preparation and response performance of sol-gel membrane were investigated. The experimental results showed a linear range of Hg2+ concentrations from 1.0 x 10(-5) to 1.0 x 10(-4) mol x L(-1) in a Tris-HCl buffer at pH 8.0 with fast response and good repetition. The indicators in the sol-gel membrane did not leak out and the sensor showed good selectivity over other metal ions.