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Prostate-specific antigen (PSA), one of the indications of possible prostate malignancy, is used as a biomarker for the diagnosis and prognosis of prostate cancer. Herein, we develop a new homogeneous potentiometric immunoassay for sensitive detection of low-concentration PSA without the need of sample separation and washing step. Two nanostructures including positively charged polyethyleneimine-poly(styrene-co-acrylic acid) (PEI-PSAA) nanospheres and negatively charged gold nanoparticles conjugated with anti-PSA antibody (Ab-AuNP) were first synthesized by using mulsifier-free emulsion copolymerization and wet chemistry method, respectively. Thereafter, the as-prepared PEI-PSAA was used as a pseudo hapten for the construction of immunosensing probe based on an electrostatic interaction between PEI-PSAA and Ab-AuNP. Upon target introduction, the added PSA competed with PEI-PASS for Ab-AuNP based on a specific antigen–antibody interaction, and displaced Ab-AuNP from PEI-PASS. The dissociated PEI-PASS was captured through the negatively charged Nafion- modified electrode, thereby resulting in the change of membrane potential. The fabrication process was characterized by using high-resolution transmission electron microscope (HRTEM), scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDX), surface plasmon resonance (SPR) and dynamic laser scattering (DLS) technique. Under optimal conditions, the output signal was indirectly proportional to the concentration of target PSA in the sample and exhibited a dynamic range from 0.1 to 50 ng/mL with a detection limit (LOD) of 0.04 ng/mL. Intra- and inter-assay coefficients of variation (CVs) were 6.8 and 7.5%, respectively. In addition, the methodology was evaluated for analysis of 12 clinical serum samples and showed good accordance between the results obtained by the developed immunosensing protocol and a commercialized enzyme-linked immunosorbent assay (ELISA) method.

An amplified colorimetric detection of Hg 2+ is proposed by combining T–Hg 2+ –T base pairs and hybridization chain reaction (HCR). Two hairpins consisting of three-fourths and one-fourth of the horseradish peroxidase (HRP)-mimicking DNAzyme in inactive configuration are used as functional elements. In the presence of Hg 2+ , one of the hairpins is opened by an assistant probe with the help of T–Hg 2+ –T base pairs and this triggers an autonomous cross-opening of the two hairpins using the strand displacement principle, resulting in the formation of DNA nanowires consisting of numerous reunited Q-quadruplex DNAzyme units. The resulting catalytically active hemin/G-quadruplex HRP-mimicking DNAzymes catalyze the oxidation of ABTS 2− by H 2 O 2 into a green-colored cationic radical ABTS •+ for the colorimetric readout. This “turn-on” sensing system enables the high sensitive and selective detection of aqueous Hg 2+ with a detection limit of 9.7 pM.

A simple and sensitive DNAzyme-based colorimetric sensor for detecting Hg2+ based on T–Hg2+-T base pair and magnetic beads (MBs) is proposed. In the presence of Hg2+, capture probes (CPs) immobilized on MBs are hybridized with the signal probes (SPs) consisting of G-quadruplex sequences with the help of T–Hg2+-T base pairs. The SPs are separated by MBs and used to bind hemin for the formation of catalytically active hemin/G-quadruplex DNAzymes, which catalyzes the H2O2-mediated oxidation of ABTS to produce a blue-green-colored product. A linear relationship between the absorbance and Hg2+ concentration is observed over a range of 10–200 nM with a limit of detection 5 nM. Taking advantage of MBs separation/collection process, the sensing system can be regenerated by using EDTA as the chelator.

A new coreactant electrochemiluminescence (ECL) system including single-layer graphene quantum dots (GQDs) and L-cysteine (L-Cys) was found to be able to produce strong cathodic ECL signal. The ECL signal of GQD/L-Cys coreactant system was revealed to be mainly dependent on some key factors, including the oxidation of L-Cys, the presence of dissolved oxygen and the reduction of GQDs. Then, a possible ECL mechanism was proposed for the coreactant ECL system. Furthermore, the ECL signal of the GQD/L-Cys system was observed to be quenched by lead(II) ions (Pb(2+)). After optimization of some important experimental conditions, including concentrations of GQDs and L-Cys, potential scan rate, response time, and pH value, an ECL sensor was developed for the detection of Pb(2+). The new methodology can offer a rapid, reliable, and selective detection of Pb(2+) with a detection limit of 70 nM and a dynamic range from 100 nM to 10 μM.

Three new mononuclear copper(II) complexes, [Cu(L2)](2+) (1), [Cu(acac)(L)](+) (2), and [Cu(acac-Cl)(L)](+) (3) (L = 2-(4-pyridine)oxazo[4,5-f]1,10-phenanthroline (4-PDOP); acac = acetylacetone; acac-Cl = 3-chloroacetylacetone), have been synthesized and characterized by elemental analysis, high resolution mass spectrometry (Q-TOF), and IR spectroscopy. Two of the complexes were structurally characterized by single-crystal X-ray diffraction techniques. Their interactions with DNA were studied by UV-vis absorption and emission spectra, viscosity, thermal melting, DNA unwinding assay and CD spectroscopy. The nucleolytic cleavage activity of the compounds was carried out on double stranded pBR322 circular plasmid DNA by using a gel electrophoresis experiment in the presence and absence of an oxidant (H2O2). Active oxygen intermediates such as hydroxyl radicals and hydrogen peroxide generated in the presence of L and complexes 1-3 may act as active species for the DNA scission. The cytotoxicity of the complexes against HepG2 cancer cells was also studied.

A novel signal-on fluorescence biosensor for detection of adenosine triphosphate (ATP) based on the target induced recombination of split aptamer fragments and click chemistry is proposed. The CuS NPs modified on the streptavidin magnesphere paramagnetic particles (PMPs) can be destroyed by acid to form Cu(II). In the presence of sodium ascorbate, Cu(II) can be reduced to Cu(I) which in turn catalyzes the reaction between a weak-fluorescent 3-azido-7-hydroxycoumarin and propargyl alcohol to form strongly fluorescent 1,2,3-triazole compounds. The proposed sensor has been applied to the detection of ATP in human serum samples with satisfactory results.

Molybdenum disulfide (MoS2) has attracted increasing research interest recently due to its unique physical, optical and electrical properties, correlated with its 2D ultrathin atomic-layered structure. Until now, however, great efforts have focused on its applications such as lithium ion batteries, transistors, and hydrogen evolution reactions. Herein, for the first time, MoS2 nanosheets are discovered to possess an intrinsic peroxidase-like activity and can catalytically oxidize 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to produce a color reaction. The catalytic activity follows the typical Michaelis-Menten kinetics and is dependent on temperature, pH, H2O2 concentration, and reaction time. Based on this finding, a highly sensitive and selective colorimetric method for H2O2 and glucose detection is developed and applied to detect glucose in serum samples. Moreover, a simple, inexpensive, instrument-free and portable test kit for the visual detection of glucose in normal and diabetic serum samples is constructed by utilizing agarose hydrogel as a visual detection platform.

A simple, sensitive, rapid fluorescence (FL) sensor has been developed to detect cyanide ions (CN−) based on the branched polyethylenimine-capped carbon quantum dots (BPEI-GQDs). The amino groups at the surfaces of BPEI-GQDs can selectively and sensitively capture copper ions (Cu2+) to form absorbent cupric amine, which can quench the FL of BPEI-GQDs through an inner filter effect. CN− can combine strongly with Cu2+ to [Cu(CN)x]n− species, preventing Cu2+ from being captured by the amino groups of BPEI-GQDs. As a result, Cu2+ can't quench the FL of BPEI-GQDs anymore in the presence of CN−. In other words, CN− can “turn on” the FL signal of BPEI-GQDs/Cu2+ system, producing a “recovered” FL signal. After optimizing experimental conditions, we demonstrated that this easy methodology could offer a sensitive, selective, simple and rapid method for detection of CN− with a detection limit of 0.65 μM (S/N = 3) and a linear response range of 2 to 200 μM.

In this work, a portable immunosensor was developed using a personal glucose meter (PGM) as the signal transducer. In this system, the anti-alpha-fetoprotein (anti-AFP) is immobilized on the screen-printed gold electrode (SPGE) surface. The presence of a target brought in the fixation of invertase–anti-AFP on anti-AFP modified SPGE; then, invertase catalyzed sucrose to glucose, which was detected using the PGM. The reading of the PGM exhibited a linear relationship with the AFP concentration. The detection limit is 0.18 ng mL−1. After one test, this immunosensor can be reused at least 5 times using an easy treatment. Moreover, the assay results of the clinical serum samples are satisfactory.

Hybrid nanoflowers were synthesized by a novel approach. The nanoflowers exhibited an enhanced enzymatic activity and can be used as an immobilized enzyme reactor (IMER) for highly efficient protein digestion.

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).

Heavy metal ion pollution poses severe risks in human health and environmental pollutant, because of the likelihood of bioaccumulation and toxicity. Driven by the requirement to monitor trace-level mercury ion (Hg 2+ ), herein we construct a new DNA-based sensor for sensitive electrochemical monitoring of Hg 2+ by coupling target-induced formation of gold amalgamation on DNA-based sensing platform with gold amalgamation-catalyzed cycling signal amplification strategy. The sensor was simply prepared by covalent conjugation of aminated poly-T (25) oligonucleotide onto the glassy carbon electrode by typical carbodiimide coupling. Upon introduction of target analyte, Hg 2+ ion was intercalated into the DNA polyion complex membrane based on T–Hg 2+ –T coordination chemistry. The chelated Hg 2+ ion could induce the formation of gold amalgamation, which could catalyze the p -nitrophenol with the aid of NaBH 4 and Ru(NH 3 ) 6 3+ for cycling signal amplification. Experimental results indicated that the electronic signal of our system increased with the increasing Hg 2+ level in the sample, and has a detection limit of 0.02 nM with a dynamic range of up to 1000 nM Hg 2+ . The strategy afforded exquisite selectivity for Hg 2+ against other environmentally related metal ions. In addition, the methodology was evaluated for the analysis of Hg 2+ in spiked tap-water samples, and the recovery was 87.9–113.8%.

A heterojunction with excellent photocatalytic performance based on graphene-like carbon nitride (g-C3N4) nanosheets and dendritic zinc(II) phthalocyanine was proposed. Herein, the g-C3N4 with excellent photo-activity and high nitrogen content was readily available as a functional material. The g-C3N4 acted as an electron pair donor for dendritic zinc(II) phthalocyanine through axial coordination, forming the p–n heterojunction. Then by taking advantage of the distortion of dendritic zinc(II) phthalocyanine, the spatial charge separation of photo-generated charge carriers in this metal macrocycle achieved high efficiency, resulting in the enhanced photo-to-electric conversion efficiency. Therefore, the optoelectronic sensing device based on the heterojunction led to an enhanced photocurrent, and made it a promising candidate for establishing photoelectrochemical biosensors. Moreover, the p–n heterojunction was successfully applied to the detection of choline with a wide linear range from 10 nM to 5 μM, which could be oxidized by the photo-generated holes. Along with these attractive features, the as-proposed biosensor also displayed a remarkable specificity against other interferents and could be successfully used for detecting choline in real samples. The heterojunction with enhanced photoelectronic properties provides a promising format for the future development of photoelectrochemical biosensors.

A novel imprinting strategy using reversible covalent complexation of glycoprotein was described for creating glycoprotein-specific recognition cavities on boronate-functionalized monolithic column. Based on it, a molecularly imprinted monolithic column was prepared by self-polymerization of dopamine (DA) on the surface of 4-vinylphenylboronic acid (VPBA)-based polymeric skeletons after reversible immobilization of horseradish peroxidase (HRP). Due to the combination of boronate affinity and surface imprinting of DA, the stable and accessible recognition sites in the as-prepared imprinted monolith could be obtained after the removal of the template, which facilitated the rebinding of the template and provided good reproducibility and lifetime of use. The recognition behaviors of proteins on the bare VPBA-based, HRP-imprinted and nonimprinted monolithic columns were evaluated in detail and the results showed that the HRP-imprinted monolith exhibited higher recognition ability toward the template than another two monolithic columns. Not only nonglycoproteins but also glycoproteins can be well separated with the HRP-imprinted monolith. In addition, the feasibility of the HRP-imprinted monolith, adopted as an in-tube solid phase microextraction (in-tube SPME), was further assessed by selective extraction and enrichment of HRP from human serum. The good results demonstrated its potential in glycoproteome analysis.

A simple and sensitive electrochemical sensor which was constructed with alkoxy silane and carbon nanohorns was first utilized to detect some food borne contaminants, including malachite green, sudans, triclosan, bisphenol A. Due to the large surface area, good conductivity, admirable electrochemical activity of carbon nanohorns and excellent immobility of alkoxy silane, the synergistic effect root from the easily controlled composition of organic–inorganic hybrid film was achieved. The present work demonstrated this functional film brings advantageous features such as stable and strong adherence to electrode matrix and excellent electrochemical catalysis, to electrochemical sensor to achieve advanced application. By choosing triclosan and malachite green as object, their kinetic parameters on this modified electrode were calculated and the relative quantitive protocols were established. Compared with previous reports, the designed sensor presented lower detection limit, higher sensitivity and more broad linear range. This electrochemical platform offered a useful tool for the on-site determination of food born contamination.

Herein, we report a versatile solid phase synthesis approach for partial functionalization of gold nanoparticles (AuNPs) via the assistance of surfactant. Hexadecyl trimethyl ammonium bromide (CTAB) is used as the bifunctional ligand to link the solid substrate and the AuNPs. This brings at least two advantages comparing to other bifunctional ligands: first, the thickness of the CTAB bilayer is flexible. During the “catch” process, the bilayer bound on different sites of the AuNPs could shrink or extend to a total thickness difference of ∼2.5 nm, which protects a spherical cap of the AuNPs with the height of ∼2.5 nm from chemical modification; second, after chemical modification, the “release” of the AuNPs from the substrate is quite simple. Not any second ligand, but only sonication is enough to release the AuNPs. As a result, the proposed approach produces partially functionalized AuNPs with a large surface area (80–95%) covered with unreactive ligands, while keeps the other small spatially limited region of the surface unmodified. This small unmodified surface can be directly used for further chemistry. Finally, the partially modified AuNPs is demonstrated for a one-step synthesis of AuNP dimers.

A facile and selective fluorescence sensor for laccase determination has been proposed depending on the interaction between 3-azidocoumarin and trametes versicolor (Tv) laccase in this paper. The azido group of 3-azidocoumarin that is electron-rich α-nitrogen can directly interact with histidines that coordinate to three copper sites through hydrogen bonds and forms a new complex, which decreases the electron-donating ability of the azido group, leading to enhance the fluorescence intensity of the sensing system. Also, other common proteins have no significant interference for the proposed laccase sensor. Additionally, the proposed fluorescence sensor is extended to demonstrate the conformational flexibility of Tv laccase by the urea denaturant. A good consistency of the results obtained with the presented laccase sensor and CD spectra is performed. Furthermore, the relationship between the catalytic activity and the unfolding percentage of the unfolded Tv laccase through the proposed laccase sensor is also elucidated well.

We report on a protocol for a simultaneous competitive immunoassay for tetracycline (TC) and chloramphenicol (CAP) on the same sensing interface. Conjugates of TC and of CAP with bovine serum albumin were first co-immobilized on a glassy carbon electrode modified with gold nanoparticles. In parallel, monoclonal anti-TC and anti-CAP antibodies were conjugated onto CdS and PbS nanoclusters, respectively. In a typical assay, the immobilized haptens and the added target analytes competed for binding to the corresponding antibodies on the nanoclusters. Subsequently, Cd(II) and Pb(II) ions are released from the surface of the corresponding nanoclusters by treatment with acid and then were detected by square wave anodic stripping voltammetry. The currents at the peak potentials for Cd(II) and Pb(II) were used as the sensor signal for TC and CAP, respectively. This multiplex immunoassay enables the simultaneous determination of TC and CAP in a single run with dynamic ranges from 0.01 to 50 ng mL−1 for both analytes. The detection limits for TC and for CAP are 7.5 pg mL−1 and 5.4 pg mL−1, respectively. No obvious nonspecific adsorption and cross-reactivity was observed in a series of analyses. Intra-assay and inter-assay coefficients of variation were less than 10 %. The method was evaluated by analyzing TC and CAP in spiked samples of milk and honey. The recoveries range from 88 % to 107 % for TC, and from 91 % to 119 % for CAP.

Epidermal growth factor receptor (EGFR) that has been over-expressed in many different types of cancers has become logical targets for both diagnosis and therapy. Herein, we report an electrochemical peptide-based biosensor for the detection of EGFR, in which ferrocene moiety modified peptide ligands that are specific to EGFR were immobilized on gold electrode through Au–S interaction. Upon the binding of peptide ligands with EGFR, complex formation changes occurred on the electrode surface, which resulted in current increase. The amplitude of the current increase displayed a linear relationship with logarithm of the EGFR concentrations in the range of 1.0 × 10−6–1.0 × 10−10 g L−1, with a detection limit of 3.7 × 10−11 g L−1. The proposed method has been applied for determination of EGFR in diluted human serum samples with satisfied results.

Two convenient, effective, and reproducible methods using microemulsion electrokinetic chromatography (MEEKC)-normal stacking mode (NSM) and reversed electrode polarity stacking mode (REPSM) were developed for the on-line sample stacking of phthalate esters (PAEs). REPSM coupled with MEEKC increased the sensitivity of 937.5 to 7,143 times for four PAEs compared to the conventional MEEKC. The separating conditions in the MEEKC method were studied, and many factors influencing the two sample stacking processes were investigated in detail. The optimum sample matrices for the two stacking methods were as follows: 30 mmol/L sodium cholate (SC) and 30.0 mmol/L borate (pH 8.5). Additionally, sample injections as large as 3.45 kPa x 40 s and 3.45 kPa x 90 s were applied for NSM-MEEKC and REPSM-MEEKC, respectively. The linear relationship and reproducibility were also examined. Under the optimum conditions, the detection limits (S/N = 3) of the PAEs were in the ranges of 0.021 - 0.33 mg/L and 0.7 - 4 microg/L for NSM-MEEKC and REPSM-MEEKC, respectively. The proposed REPSM-MEEKC has been successfully applied to determine PAEs in plastic-packaging bags, and the spiked recoveries were in the range of 89.1% - 105.6% with satisfactory results.

A new signal amplification strategy for sensitive electrochemical determination of tetracycline (TC) was developed by using platinum-catalyzed hydrogen evolution reaction (HER) on an anti-TC antibody-modified immunosensor. To construct such a HER, platinum nanoparticles were initially deposited to graphene nanosheets, and the as-synthesized platinum/graphene nanosheets (PtGN) were then used for the labeling of tetracycline-bovine serum albumin conjugates (TC–BSA). With a competitive immunoassay format, the resulting immunosensor was immersed into a platinum developer solution containing 1.0 mM PtCl 4 2 - , 0.1 M formate (reductant) and 0.5% Tween 80 (pH 6.5) to promote the platinum growth. The amplified electrochemical signal mainly derived from the platinum-catalyzed HER in an acidic medium containing 10 mM HCl and 1.0 M KCl. Two labeling methods and assay protocols including Pt-labeled TC–BSA and PtGN-labeled TC–BSA with or without the platinum enhancement were investigated for determination of target TC, respectively, and improved analytical features were obtained with graphene nanosheets and platinum growth mechanism. With PtGN-labeled TC–BSA, the effects of incubation time for antigen–antibody reaction and deposition time of platinum on the currents of the immunosensors were also studied. The strong attachment of TC–BSA to the PtGN resulted in a good repeatability and intermediate precision down to 9.8%. The dynamic concentration range spanned from 0.05 ng/mL to 100 ng/mL tetracycline with a low detection limit of 6 pg/mL at the 3sblank level. In addition, the methodology was further validated with tetracycline spiked samples including honey, milk and peanut, and the recoveries were 86–118%.

Chiral recognition based on enantioselective sensors is superior to conventional chromatographic enantioseparation techniques in terms of simplicity and rapidity. Normally, highly specific enantioselective receptors are used for the fabrication of enantioselective sensors. However, to date there only limited number of highly specific chiral selectors are reported, which greatly confines the development of enantioselective sensors. Herein, we demonstrate the feasibility of using relatively weak chiral selectors to construct an enantioselective biosensor for accurate chiral discrimination of enantiomers. The detection of racemic mixture of ( R )- and ( S )-1,2,3,4-Tetrahydro-1-naphthylamine (TNA) was demonstrated as an example. The sensor was made up of a dual-channel microfluidic chip. One channel of the chip was modified with human serum albumin (HSA), which was reported to be a weak chiral selector for TNA; while the other channel was modified with a monoclonal anti-TNA antibody, which was a non-enantioselective TNA receptor. A portable localized surface plasmon resonance (LSPR) detection system was integrated with the microfluidic chip to accomplish the signal collection. Our investigation revealed that the combination of LSPR responses obtained from the two channels can be used for quantitative discrimination of the ( R )- and ( S )-TNA. The limit of detection was found to be 150 nM for ( R )-TNA and 100 nM for ( S )-TNA. The feasibility of use relatively weak chiral selectors could potentially promote the development of various enantioselective sensors.

The four heteronuclear clusters [Ag2Au2(μ-dpppy)3(C≡CC6H4R-4)2](ClO4)2 (R = H (1) CH3 (2), COOCH3 (3), CHO (4)) were prepared by the self-assembly reaction between (AuC≡C6H4R-4)n (R = H, CH3, COOCH3, CHO) and [Ag2(μ-dpppy)3]2+ (dpppy = 2,6-bis(diphenylphosphino)pyridine) and characterized by elemental analyses, electrospray ionization mass spectrometry (ESI-MS), and 1H NMR and 31P{1H} NMR spectroscopy and by X-ray crystallography for 1, 3, and 4. It is revealed that the complexes exhibit bright blue (1–3) and green (4) luminescence in the solid state and in solution with the luminescent lifetimes in the microsecond range, indicating that the luminescence is most likely associated with a spin-forbidden triplet parentage. Interestingly, only complex 4 displays distinctly mechanical grinding responsive emission switching. The recognition interactions of complex 4 containing aldehyde groups with homocysteine (Hcy) and cysteine (Cys) have been studied by UV–vis and emission titrations. A strong luminescence qu...

A novel and general strategy is developed to design selective artificial enzyme inhibitor based on nanoparticleenzyme inter actions and molecular imprinting. Due to the creation of specific binding cavities, the resulting artificial inhibitor has high inhibition efficiency for the target enzyme, and shows great target-selectivity over other enzymes of similar function and proteins of compaable mole cular weight.

Silica aerogels functionalized with strongly fluorescent carbon quantum dots were first prepared and used for simple, sensitive, and selective sensing of NO2 gas. In the presence of ethanol, homemade silica aerogels with a large specific surface area of 801.17 m(2)/g were functionalized with branched polyethylenimine-capped quantum dots (BPEI-CQDs) with fluorescence quantum yield higher than 40%. The prepared porous CQD-aerogel hybrid material could maintain its excellent fluorescence (FL) activity in its solid state. The FL of CQD-aerogel hybrid material could be selectively and sensitively quenched by NO2 gas, suggesting a promising application of the new FL-functionalized aerogels in gas sensing.

The electrogenerated chemiluminescence (ECL) of two water-insoluble iridium(III) complexes (pq)2Ir(acac)(pq = 2-phenyl quinolone anion, acac = acetyl acetonate) and (ppy)2Ir(acac)(ppy = 2-phenylpyridine anion) in carbon nanotube (CNT)/Nafion composite films was investigated at a glassy carbon (GC) electrode. CNT and Nafion play significant roles in the iridium(III) complexes immobilization. The excellent chemical stability and electrical conductivity of CNT promote electron transfer. The experimental conditions, such as potential, pH, concentrations of CNT and various coreactants were investigated. The iridium(III) complexes modified electrode had good stability and reproducibility. In our work, the (pq)2Ir(acac)/DBAE (2-(dibutylamino)ethanol) system was used to detect the codeine, one of the many narcotics, and the detection limit was 0.05 μM (S/N = 3). This method enabled the two water-insoluble iridium(III) complexes to be used for the determination of the analyte in aqueous solution.

The preparative-scale separation of chiral compounds is vitally important for the pharmaceutical industry and related fields. Herein we report a simple approach for rapid preparative separation of enantiomers using functional nucleic acids modified gold nanoparticles (AuNPs). The separation of DL-tryptophan (DL-Trp) is demonstrated as an example to show the feasibility of the approach. AuNPs modified with enantioselective aptamers were added into a racemic mixture of DL-Trp. The aptamer-specific enantiomer (L-Trp) binds to the AuNPs surface through aptamer-L-Trp interaction. The separation of DL-Trp is then simply accomplished by centrifugation: the precipitate containing L-Trp bounded AuNPs is separated from the solution, while the D-Trp remains in the supernatant. The precipitate is then redispersed in water. The aptamer is denatured under 95 °C and a second centrifugation is then performed, resulting in the separation of AuNPs and L-Trp. The supernatant is finally collected to obtain pure L-Trp in water. The results show that the racemic mixture of DL-Trp is completely separated into D-Trp and L-Trp, respectively, after 5 rounds of repeated addition of fresh aptamer-modified AuNPs to the DL-Trp mixture solution. Additionally, the aptamer-modified AuNPs can be repeatedly used for at least eight times without significant loss of its binding ability because the aptamer can be easily denatured and renatured in relatively mild conditions. The proposed approach could be scaled up and extended to the separation of other enantiomers by the adoption of other enantioselective aptamers. Chirality 25:751–756, 2013. © 2013 Wiley Periodicals, Inc.

A sensitive and feasible multiplexed immunoassay protocol for simultaneous electrochemical determination of carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP) was developed using multifunctionalized graphene nanotags on a cyclodextrin-modified immunosensor. The sensor was fabricated via the guest–host chemistry between the immobilized cyclodextrin and anti-CEA/anti-AFP antibodies. Two nanotags including cyclodextrin-thionine-graphene and cyclodextrin-ferrocene-graphene nanostructures were synthesized based on a wet chemistry method. The synthesized nanotags were employed for the labelling of horseradish peroxidase (HRP)–anti-AFP and HRP–anti-CEA conjugates, respectively. With a sandwich-type assay format, the signal was monitored through the labelling of HRP toward catalytic reduction of H2O2 at various peak potentials in the presence of thionine and ferrocene, respectively. Under optimal conditions, the multiplexed immunoassay enabled the simultaneous determination of CEA and AFP with wide working ranges of 0.001–60 ng mL−1 for AFP and 0.003–40 ng mL−1 for CEA. The detection limits were 0.5 pg ml−1 for AFP and 0.8 pg ml−1 for CEA (at 3 sB). No obvious nonspecific adsorption and cross-talk were observed during a series of analyses to detect target analytes. Intra- and inter-assay coefficients of variation (CV) were below 9.5 %. Importantly, the methodology was also evaluated for the analysis of AFP and CEA in the clinical human serum specimens, receiving a good relationship between the developed immunoassay and a commercialized electrochemiluminescence enzyme-linked immunoassay.

Non-invasive early diagnosis of HIV is an important and effective means to reduce death from this disease. In this manuscript, we describe a method using a novel label-free electrochemical DNA biosensor for HIV related gene diagnosis with ultrahigh sensitivity and selectivity. The DNA biosensor was based on the interaction of hybrid double-stranded DNA and protein. In the presence of target DNA, the target/probe hybridization encountered the NF-kB protein. Upon addition of HRP, they formed the sandwich-like DNA sensor. The formed sandwich-like ds/NF-κB/HRP complex effectively catalyzed the H2O2-mediated oxidation of TMB, accompanied by a changed color of the reaction solution and an increased electrochemical current signal. However, in the absence of target DNA, no duplex DNA could bind NF-kB protein or HRP to form the DNA sensor. By employing the above strategy, the DNA biosensor was able to gain an amplified electrochemical signal and thus detected as low as 7.05 pM target DNA. Due to the high selectivity of the method, the developed biosensor also exhibited high discrimination ability even against single-base mismatch. Combined with the advantages of electrochemical detection and its ready integration with microelectronics, the proposed electrochemical DNA biosensor might represent a promising path toward direct HIV detection at the point of care.

A novel magneto-controlled electrochemical DNA biosensor is designed for the ultrasensitive detection of lead coupling a lead-specific DNAzyme with DNA-based hybridization chain reaction (HCR). To construct such a magnetic lead sensor, DNAzyme-based molecular beacons, selective to cleavage in the presence of Pb 2+ , are initially immobilized onto magnetic beads, which were used as the recognition elements. Upon addition of target lead, catalytic cleavage of substrate DNA segments in the double-stranded DNAzymes results in the capture of the initiator strands via the conjugated catalytic strands on magnetic beads. The captured DNA initiator strands trigger the hybridization chain reaction between two alternating hairpin DNA structures labeled with ferrocene to form a nicked double-helix on the magnetic beads. Numerous ferrocene molecules are formed on the neighboring probes, each of which produces an electrochemical signal within the applied potential. Under optimal conditions, the electrochemical signal of the magnetic lead sensor increases with the increasing lead level in the sample, and exhibits a linear response over a Pb 2+ concentration range of 0.1–75 nM with a detection limit of 37 pM. Quantitative measurement of Pb 2+ in the complex sample demonstrates the selectivity of the sensor scheme and points favorably to the application of such technologies to the analysis of environmental samples. The unique combination of a DNAzyme with hybridization chain reaction makes it possible to change the DNAzyme to select for other compounds of interest. This work represents the initial steps toward the creation of a robust field sensor for lead in groundwater or drinking water.

A new electrochemiluminescence (ECL) system consisting of carbon quantum dots (CQDs) and sulfite SO 3 2 - has been reported. In the ECL system, SO 3 2 - is a new ECL coreactant that can significantly enhance the cathodic ECL signal of CQDs. When cycling the potential between −1.300 and +1.400 V, SO 3 2 - is firstly electrochemically oxidized to sulfur trioxide anion free radical ( SO 3 - ) in the anodic polarization process. Then the electrogenerated SO 3 - is involved in a three-step auto-catalytic reaction in the presence of dissolved oxygen, producing sulfate radical ( SO 4 - ). In the subsequent cathodic polarization process, CQDs are electrochemically reduced to negatively charged CQDs (C −). Finally, the electrogenerated C − species react with the SO 4 - to form excited-state CQDs (C∗), emitting light (575 nm) when they come back to their ground states.

Enzyme-linked immunosorbent assay (ELISA) methods based on natural enzyme-labeled probes have been applied in the immunoassays, but most have some inevitable limitations (e.g. harsh preparation, purification and storage) and are unsuitable for routine use. Herein we synthesized a new class of irregular-shaped platinum nanoparticles (ISPtNP) with a mean length of 7.0 nm and a narrowing width from 2.0 to 5.0 nm along the longitudinal axes, which were utilized as peroxidase-like mimics for the development of colorimetric immunoassays. Compared with bioactive horseradish peroxidase (HRP), the synthesized ISPtNP exhibited a low Km value (~0.12 mM) and a high Kcat value (~2.27×10(4)s(-1)) for 3,3',5,5'-tetramethylbenzidine (TMB) with strong thermal stability and pH tolerance. The catalytic mechanism of the ISPtNP toward TMB/H2O2 was for the first time discussed and deliberated in this work. Based on a sandwich-type assay format, two types of colorimetric immunoassay protocols were designed and developed for the detection of rabbit IgG (RIgG, as a model) by using the synthesized ISPtNP and conventional HRP as the labeling of detection antibodies, respectively. Similar detection limits (LODs) of 2.5 ng mL(-1) vs. 1.0 ng mL(-1) were obtained toward RIgG with the ISPtNP labeling compared to HRP format. Intra- and inter-assay coefficients of variation were less than 13%. Importantly, the ISPtNP-based assay system could be suitable for use in a mass production of miniaturized lab-on-a-chip devices and open new opportunities for protein diagnostics and biosecurity.

A sensitive and selective fluorescent probe for histidine has been designed by taking the advantages of the click chemistry reaction (copper(I)-catalyzed azides and alkynes cycloaddition) and the inhibition of copper(II)-induced ascorbate oxidation by histidine. The fluorescence intensity decreases with the increasing of histidine concentration, and the value of F₀/F shows a good linear relationship with the concentration of histidine over the range of 0.5-100 μM with a detection limit of 76 nM, which is lower than those of many other fluorescent sensors. Moreover, the sensor has high specificity for histidine compared to some potential interferents, such as other amino acids and metal ions. In addition, the proposed sensor has been applied to determine histidine in cellular homogenate and ovalbumin samples with satisfactory results. The preferable simplicity, sensitivity and specificity for the detection of histidine indicate that the proposed sensor have potential prospect in environmental and biomedical analysis.

In this paper, a novel strategy of protein molecularly-imprinted electrochemical sensor was proposed to determine Bovine Hemoglobin selectively. Gold microdendrites and prussian blue particles were electrodeposited on the surface of glassy carbon electrode respectively to improve the sensitivity of MIECS. The molecularly imprinted polymers film is synthesized by electrochemically induced redox polymerization of acrylamide in the presence of template protein. The surface feature of the modified electrode was characterized by cyclic voltammetry. The reduced electrochemical intensity which was produced by prussian blue is related to the concentration of Bovine Hemoglobin. The times of washing and incubation of modified electrode were investigated and optimized. The MIECS with improved conductivity and electrochemical performances showed good response in the range of low concentrations from 0.1 to 1.0×10³ μg/mL and the detection limit (LOD, 3σ, RSD≤4.31 %) is 0.05 μg/mL. The result demonstrates significant specific recognition toward the template protein via selective test and a reasonable regeneration in five recyclings. The proposed sensor exhibited high sensitivity and selectivity, acceptable reproducibility, and could be extended to recognize other protein.

In this paper, we reported a convenient fluorescence method for the detection of genetically modified organisms (GMOs). As it is known that the cauliflower mosaic virus (CaMV) 35S promoter is widely used in most transgenic plants ( Schnurr and Guerra, 2000 ), we thus design a simple method based on the detection of a section target DNA (DNA-T) from the transgene CaMV 35S promoter. In this method, the full-length guanine-rich single-strand sequences were split into fragments (Probe 1 and 2) and each part of the fragment possesses two GGG repeats. In the presence of K+ ion and berberine, if a complementary target DNA of the CaMV 35S promoter was introduced to hybridize with Probe 1 and 2, a G-quadruplex–berberine complex was thus formed and generated a strong fluorescence signal. The generation of fluorescence signal indicates the presence of CaMV 35S promoter. This method is able to identify and quantify Genetically Modified Organisms (GMOs), and it shows wide linear ranges from 5.0×10−9 to 9.0×10−7 mol/L with a detection limit of 2.0×10−9 mol/L.

A novel fluorescent sensor for DNA sequence has been designed by taking advantages of copper nanoparticles (CuNPs) selectively formed on double stranded (ds) DNA template and Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) reaction. Copper(II) is derived from CuNPs which previously formed on the dsDNA template, and then copper(II) is reduced to copper(I) by ascorbate, which in turn induced CuAAC reaction between the weak-fluorescent compound (3-azido-7-hydroxycoumarin) and propargyl alcohol to form strong fluorescence compounds (1,2,3-triazole compounds). Since CuNPs are accumulated efficiently in the major groove of dsDNA and ssDNA has no groove, it indicates that the proposed sensor owns the merits of low detection limit, high sensitivity and selectivity for mutational p53 sequence detection. Additionally, the method has been successfully applied to recognize the sequence which contains a single-base mismatch in the short human p53 gene fragment. Furthermore, it has also been applied to detect DNA sequence in complex medium (hela cellular homogenate) with satisfactory results.

We have constructed a novel electrochemiluminescence (ECL) platform by functionalizing a poly(amidoamine) dendrimer (PAAD) with titanate nanotubes (TiNTs). The PAAD has an open spherical structure that possesses a high density of active groups and thus favors mass transport, while the TiNTs possess excellent electronic conductivity and thus can promote electron transfer on the surface of a glassy carbon electrode (GCE). A study on the intensity and stability of the ECL of luminol on the modified GCE revealed a substantial improvement compared to that of a bare GCE. The effects of the concentration of TiNTs, the pH value of the solution, and of electrochemical parameters on the intensity of the ECL of luminol were studied and resulted in a sensitive ECL sensor for hydrogen peroxide (H2O2) that works in the concentration range of 1 nM to 0.9 μM. The scavenging effect of superoxide dismutase (SOD) on the H2O2 electrode ECL was then exploited to design a biosensor for the determination of SOD in concentrations between 50 and 500 nM.

A simple and rapid capillary electrophoresis (CE) with an acidic potassium permanganate chemiluminescence (CL) detection method was developed to determine three alkaloids (curine, sinomenine and magnoflorine) simultaneously. A laboratory-built CE-CL detection interface was used. The field-amplified sample stacking technique was applied to the online concentration of alkaloids. Experimental conditions for CE separation and CL detection were investigated in detail to acquire optimum conditions. Under optimal conditions, the three alkaloids were baseline separated within 6 min, and the detection limits (S/N = 3) ranged from 0.03 µg/mL to 0.49 µg/mL. This method was successfully applied to determine the above three alkaloids in Sinomenium acutum, and the result of the determination of sinomenine was in good agreement with those given by high-performance liquid chromatography and CE methods. In addition, a possible CL reaction mechanism of sinomenine-KMnO4-H2SO4 was proposed.

The potential application of copper coordination polymer with dithiooxamide (H2dtoaCu), one of the metal-organic frameworks (MOFs) in the adsorption removal of crystal violet (CV) from aqueous solution was studied. Batch adsorption experiments were carried out as a function of initial pH, adsorbent concentration, contact time, initial dye concentration and temperature. The adsorption of CV on H2dtoaCu can be best described by the Langmuir isotherm model (R2 > 0.9983) with maximum monolayer adsorption capacity of 165.83, 185.87, and 204.50 mg g−1 at 298, 308, and 318 K, respectively. The kinetics of CV adsorption followed pseudo-second-order model (R2 > 0.9984) and the chemisorption was proved to be rate-limiting step. Thermodynamic parameters, the change of free energy (ΔG°), entropy (ΔS°) and enthalpy (ΔH°), showed that the adsorption of CV on H2dtoaCu was feasible, spontaneous and endothermic process. Here we concluded that H2dtoaCu is a promising adsorbent for the removal of harmful dyes from aqueous solution. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A new strategy for the construction of a sensitive and stable electrochemiluminescent platform based on titanate nanotubes (TNTs) and Nafion composite modified electrode for luminol is described, TNTs contained composite modified electrodes that showed some photocatalytic activity toward luminol electrochemiluminescence emission, and thus could dramatically enhance luminol light emission. This extremely sensitive and stable platform allowed a decrease of the experiment electrochemiluminescence luminol reagent. In addition, in luminol solution at low concentrations, we compared the capabilities of a bare glassy carbon electrode with the TNT composite modified electrode for hydrogen peroxide detection. The results indicated that compared with glassy carbon electrode this platform was extraordinarily sensitive to hydrogen peroxide. Therefore, by combining with an appropriate enzymatic reaction, this platform would be a sensitive matrix for many biomolecules. Copyright © 2013 John Wiley & Sons, Ltd.

We have designed a new molecularly imprinted co-polymer (MIP) for the sensitive detection of streptomycin (STR) in food using enzymes as signal amplification. The MIP was fabricated via co-polymerization of aniline and o-phenylenediamine on gold substrate in the presence of STR as template. The assay is based on competitive binding of free STR and glucose oxidase-labeled STR (GOx-STR) to the imprinters on the MIP. On addition of glucose, hydrogen peroxide is formed that is detected by differential pulse voltammetry. Under optimal conditions, the decrease of the catalytic current is proportional to the STR concentration in the range from 0.01 to 10 ng mL−1, with a detection limit (LOD) of 7.0 pg mL−1 STR (at 3sB). Intra- and inter-assay coefficients of variation (CVs) are

An HPLC system combining a chemiluminescence detector was applied to estimate the singlet oxygen (1O2) generation ability of di-sulfonic phthalocyanine zinc (ZnPcS2) isomers. As photosensitizers, ZnPcS2 produces 1O2 in air-saturated solutions under photoirradiation. The latter reacts with methyl Cypridina luciferin analogue (MCLA) to initiate chemiluminescence. This photoinduced chemiluminescence (PCL) of MCLA provides an easy method for evaluating the isomers' 1O2 generation ability during a simultaneous HPLC separation procedure. The cis-isomers and trans-isomers of ZnPcS2 show different 1O2 generation abilities, which are in accordance with differences in their absorption spectra. Copyright © 2013 John Wiley & Sons, Ltd.

An RP LC-ESI-MS/MS method for the determination of the migration of 16 primary phthalic acid esters from plastic samples has been developed using distilled water, 3% acetic acid, 10% alcohol, and olive oil as food simulants. Detection limits were 1.6-18.5 μg/kg in distilled water, 1.4-17.3 μg/kg in 3% acetic acid, 1.4-19.2 μg/kg in 10% alcohol, and 31.9-390.8 μg/kg in olive oil. The RSDs were in the range of 0.07-11.28%. The real plastic products inspection showed that only few analyzed samples were phthalates contaminated. Bis-2-ethylhexyl ester and dibutyl phthalate were the common items migrated from the plastic products into food and feeds, but the migration concentrations were far below the limits set by European Union (1.5 mg/kg for bis-2-ethylhexyl ester and 0.3 mg/kg for dibutyl phthalate).

In this paper, a sensitive graphite/poly(methyl methacrylate) (PMMA) composite electrode was firstly applied to the determination of o-sec -butylphenol ( os BP). This polymer carbon paste electrode (CPE) effectively improved the soft surface of traditional CPE, and enhanced the sensitivity and reproducibility. Factors influencing detection processes were optimized and kinetic parameters were calculated. Under the optimal conditions, the amperometric current density was linear with the concentration of os BP in the range from 2.50 × 10 −7 to 3.55 × 10 −5 mol L −1 and the detection limit was 3.48 × 10 −8 mol L −1 . The proposed method was successfully used to determine os BP in greengrocery samples and satisfactory results were obtained.

The preparation, characterization, fluorescence (FL) and electrochemiluminescence (ECL) of graphite-like carbon nitride nanoflake particles (g-C(3)N(4) NFPs) and nanoflake films (g-C(3)N(4) NFFs) have been reported. Highly water-dispersible g-C(3)N(4) NFPs with a height of ~5 to 35 nm and a lateral dimension of ~40 to 220 nm have been extracted from bulk g-C(3)N(4) materials by chemical oxidation. New, stable and defined g-C(3)N(4) NFFs can be easily obtained by drying NFPs on certain hydrophilic substrates such as glass or electrode surfaces. Both g-C(3)N(4) NFPs and g-C(3)N(4) NFFs have good FL activities, i.e. they can give strong blue light (435 nm) emission under UV light (365 nm) excitation. The as-prepared g-C(3)N(4) NFFs on a glassy carbon electrode exhibit strong non-surface state ECL activity in the presence of reductive-oxidative coreactants, including dissolved oxygen (O(2)), hydrogen peroxide (H(2)O(2)) and peroxydisulfate (S(2)O(8)(2-)) and give rise to blue light emission (435 nm), which is the same as the wavelength of FL. The non-surface state ECL mechanisms of the g-C(3)N(4) NFF-coreactant systems have been studied and discussed in detail.

A phenylboronic acid-silica hybrid monolithic column for capillary liquid chromatography (cLC) was prepared through one-pot process by using 4-vinylphenylboronic acid (VPBA) and alkoxysilanes simultaneously. The effects of the molar ratio of tetramethyloxysilane/γ-methacryloxypropyltrimethoxysilane (TMOS/γ-MAPS), amount of VPBA, and the volume of diethylene glycol (DEG) on the morphologies, permeabilities and pore properties of the prepared VPBA-silica hybrid monolithic columns were studied in detail. A relatively uniform monolithic structure with high porosity was obtained with optimized ingredients. A series of cis-diol-containing compounds, alkylbenzenes, amides, and anilines were utilized to evaluate the retention behaviors of the VPBA-silica hybrid monolithic column. The result demonstrated that the prepared VPBA-silica hybrid monolithic column exhibited multiple interactions including hydrophobicity, hydrophilicity, as well as cation exchange apart from the expected affinity interaction. The run-to-run, column-to-column and batch-to-batch reproducibility of the VPBA-silica hybrid monolith were satisfactory with the relative standard deviations (RSDs) less than 1.63% (n=5), 2.02% (n=3) and 2.90% (n=5), respectively, indicating the effectiveness and practicability of the proposed method. In addition, the VPBA-silica hybrid monolithic column was further applied to the separation of proteins and tryptic digest of bovine serum albumin (BSA), respectively. The successful applications suggested the potential of the VPBA-silica hybrid monolith in proteome analysis.

In this paper, a new niobate semiconductor photocatalyst Sr(0.4)H(1.2)Nb(2)O(6)·H(2)O (HSN) nanoparticle was applied to investigate the cathodic electrochemiluminescent (ECL) behavior of luminol for the first time. The results presented here demonstrated that there were two ECL peaks of luminol at the cathodic potential attributed to immobilization of HSN on the electrode surface. It is implied that HSN can be electrically excited and injected electrons into aqueous electrolytes from this electrode under a quite low potential that only excites luminol. A mechanism for this luminol-ECL system on HSN/GCE has been proposed. Additionally, this HSN/GCE has lots of advantages, such as high stability, good anti-interference ability, simple instrumentation, rapid procedure and ultrasensitive ECL response. It is envisioned that this HSN/GCE has further applications in biosensors.

Development of simple but sensitive biosensor for influenza detection is highly important in immediate and effective clinical treatment. In this study, a sensitive colorimetric immunosensor which combines the advantages of high selectivity of immunoassay and simplicity of colorimetric detection has been developed to detect influenza virus H5N1 based on enzyme-encapsulated liposome. Biotin-tagged liposome encapsulated with large amount of horseradish peroxidase (HRP) was firstly synthesized. In the presence of H5N1, H5N1 co-bound with the capture antibody and the biotinylated detection antibody to form sandwich immunocomplex. Subsequently, the HRP-encapsulated liposome was introduced to conjugate with the detection antibody through biotin-avidin-biotin linkage. Upon the addition of substrate (mixture of 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2), the liposome was directly lysed to release large amount of HRP by TMB. The released HRP catalyzed the H2O2-mediated oxidation of TMB, resulting in color change of the system, which was observed by naked eyes or UV-vis spectra. The result showed that the absorption intensity enhanced with the increase of H5N1 concentration ranging from 0.1 to 4.0 ng/mL, and the detection limit was calculated to be 0.04 ng/mL. The sensitivity of the proposed biosensor is much higher than that of conventional enzyme-linked immunosorbent assay method. The proposed immunosensor is relatively simple, low-cost, sensitive, and selective without using any sophisticated instruments, therefore it may have a promising prospect for detecting targets in clinical medicine, food safety analysis, and environmental monitoring.

Direct visual detection of circulating microRNAs could be a big challenge due to the ultralow concentration of microRNAs in real samples. Herein, we combine the techniques of nuclease amplification and oriented assembly of gold nanoparticle dimers to realize visual detection of microRNAs in human serum with the naked eye.

In this work, 3,3′,5,5′-tetramethylbenzidine(II) (TMB2+), derived from H2O2-horseradish peroxidase (HRP)-3,3′,5,5′-tetramethylbenzidine (H2O2-HRP-TMB) reaction system, was used to etch AuNRs to generate different colors of solution. Many enzyme reactions are involved in the production of H2O2 (e.g., glucose can react with the dissolved oxygen in the presence of glucose oxidase (GOx) to produce H2O2). Given this information, a simple visual biosensor was developed in this study, with glucose as the example target. The detection range of the proposed system varied with the experimental conditions, such as the concentration of GOx and HRP, and enzymatic reaction time. Under the optimized conditions, the longitudinal shift of localized surface plasmon resonances (LSPR) had a linear correlation with the glucose concentration in the range of 0.1~1.0 mM. Meanwhile, the solution displayed a specific color in response to the glucose concentration, thus enabling the visual quantitative detection of glucose at a glance. Compared with the traditional monochromic colorimetry, this multicolor glucose sensor generates various vivid colors, which can be easily distinguished by naked eyes without any sophisticated instrument. Notably, the proposed method has been successfully applied to detect glucose in serum samples with satisfied results.