Highly selective localized surface plasmon resonance sensor for selenium diagnosis in selenium-rich soybeans.

It is a challenge to determine selenium in acid aqueous for environmental monitoring and selenium-rich agricultural diagnosis. Herein, we developed a novel localized surface plasmon resonance (LSPR) sensor to detect Se(IV) ions based on the extraordinary laterals etching of gold nanorods (AuNRs). The etching started from the laterals in the low amount of Se(IV) ions, and accompanied by an apparent red shift of the longitudinal plasmon band (LPB), and then transformed to the tips etching with the upward of Se(IV) ions, the LPB band immediately shifted to the shorter wavelength. The red shift change (Δλ) of LPB band was utilized to quantitative analysis instead of blue shift or absorbance intensity, which gave a high selectivity for the proposed sensor. More importantly, this sensor could be performed in 0.1 mol/L of HCl solution, which achieved the seamlessly jointing with the pretreatment of complex samples, without time-consuming pH adjustment.Successful selenium detection was demonstrated in complex soybean samples that collected from the maturity after spraying organic chelated selenium at full flower period. The sensor provided a promising way to monitor and diagnose selenium in complex environmental samples and selenium-rich crops.

Sensitive detection of cadmium ions based on a quantum-dot-mediated fluorescent visualization sensor.

A sensitive ratiometric fluorescent sensor for detecting cadmium ions (Cd2+) was constructed based on carbon quantum dots (CQDs)/CdTe quantum dots (CdTe QDs). Red fluorescence (from CdTe QDs) played the role of the signal response and blue fluorescence (from CQDs) served as a reference probe without a color change. The fluorescent sensor showed high selectivity and sensitivity to Cd2+ with a limit of detection (LOD) of 0.018 µM and a range from 0.1 µM to 23 µM. The proposed method was successfully applied to the determination of Cd2+ in real rice samples. In addition, a fluorescent sensor integrated with a smartphone platform was further designed for the visualized and quantitative detection of Cd2+. This work might extend the range of visualization analysis strategies and provide new insights into the rapid quantitative, portable and sensitive detection of Cd2+ in real-time and on-site applications.

A highly selective and simple fluorescent probe for salbutamol detection based on thioglycolic acid-capped CdTe quantum dots.

In this paper, a highly fluorescent water-soluble CdTe quantum dots (CdTe QDs) stabilized with thioglycolic acid (TGA) were synthesized for the quantitative and selective determination of salbutamol (SAL). When ten different of 2.09 × 10-6 mol L-1 alpha-2 adrenoceptor agonist were added to 4.38 × 10-4 mol L-1CdTe QDs solution, the fluorescence signal of the CdTe QDs quenched obviously by SAL with 57.32% and 0.815% - 7.00% for other nine kinds of veterinary medicine, such as tulobuterol, fenoterol, phenylethanamine A, simatero, penbutolol, clenbuterol, ractopamine, terbutaline and clorprenaline. The result shows that the CdTe QDs is highly sensitive sensor for SAL. The quenching mechanism has been investigated by absorption spectroscopy and KSV at different temperatures, and shew a static quenching process than dynamic quenching. Under the optimal conditions, respectively the straight line equation (F0/F = 0.1491 × 106 C + 1.3078) was found between the relative fluorescence intensity and the concentration of SAL was in the range of 6.27 × 10-8 to 2.09 × 10-7 mol L-1, and the limit of detection was 4.2 × 10-8 mol L-1. The proposed method has been applied to the determination of SAL in pig urine samples.

Triazole-stabilized fluorescence sensor for highly selective detection of copper in tea and animal feed.

A triazole-stabilized fluorescence sensor is developed for copper detection in the study. Tris-(benzyltriazolylmethyl)amine (TBTA) is used to improve the sensitivity and stability for the sensing system. A series of comparative experiments are performed with and without TBTA. In the presence of TBTA, the fluorescence decrease ratio is enhanced from 2.46 to 118.25; the detection limit is reduced from 67 nM to 3.6 nM; the higher selectivity toward copper compared to the other metal ions is verified, including K+, Ca2+, Cd2+, Zn2+, Mg2+, Mn2+, Pb2+, Hg2+, Fe3+ and Cr3+. Besides, the sensing system is successfully applied for copper determination in complex tea samples and chicken feed samples with the recovery range of 91.67-116.8%. A good consistency between the presented sensor and the flame atom absorbance spectrometry (FAAS) is confirmed by the low relative errors with the range from -2.39% to 7.02%.

DNA template-mediated click chemistry-based portable signal-on sensor for ochratoxin A detection.

A novel signal-on portable sensing system has been developed for OTA detection using personal glucose meter (PGM) as signal transducer. In the study, we explore the potential of using a short dsDNA as template to trigger the "click" ligation of two DNA strands, further improve the stability of DNA strand on the magnetic beads (MBs) surface, and thereby reduce the background signal. Compared with no "click" ligation, the background signal decreases 7.5 times. Both the sensitivity and selectivity are greatly promoted. A high sensitivity with OTA detection down to 72 pg/mL is achieved, which is comparable with several existing detectors, such as fluorescence-based detectors and electrochemical detectors. The feasibility of the strategy in real samples is well verified and evaluated by detecting OTA in feed samples, indicating the potential application in the food safety field.

Catalytic assembly of DNA nanostructures on a nanoporous gold array as 3D architectures for label-free telomerase activity sensing.

Telomerase, an enzyme known to catalyze telomere elongation by adding TTAGGG [thymine (T), adenine (A), and guanine (G)] repeats to the end of telomeres, is vital for cell proliferation. Overexpression of telomerase has been found in most tumor cells, resulting in telomere dysfunction and uncontrolled cellular proliferation. Thus, telomerase has been considered as a potential cancer biomarker, as well as a potential target in cancer therapy. In this study, telomerase-catalyzed growth of tandem G-quadruplex (G4) assembled on a nanoporous gold array (NPGA) resulted in the formation of three-dimensional hybrid nanoarchitectures. The generated nanostructure then captured malachite green (MG) (reporter molecule) without the need of a complicated labeling process. Upon laser irradiation, the captured MG molecules produced a surface-enhanced Raman scattering (SERS) signal that was generated by an abundant amount of plasmonic hot spots in the NPGA substrates. A limit of detection (LOD) of 10-10 IU along with a linear range, which was 3 orders of magnitude, was achieved, which was equivalent to the telomerase amount extracted from 20 HeLa cells. The LOD is 2 orders of magnitude better than that of the commercial enzyme-linked immunosorbent assay (ELISA), and it approaches that of the most sensitive technique, telomeric repeat amplification protocols (TRAP), which require a laborious and equipment-intensive polymerase chain reaction (PCR). In addition, X-ray photoelectron spectroscopy (XPS) was used to chemically identify and quantify the telomerase activity on the sensitized NPGA surface. Furthermore, the sensor was applied to screen the effectiveness of anti-telomerase drugs such as zidovudine, thus demonstrating the potential use of the sensor in telomerase-based diagnosis and drug development. Moreover, the framework represents a novel paradigm of collaborative plasmonic intensification and catalytic multiplication (c-PI/CM) for label-free biosensing.

Nanoporous Gold Disks Functionalized with Stabilized G-Quadruplex Moieties for Sensing Small Molecules.

We report label-free small molecule sensing on nanoporous gold disks functionalized with stabilized Guanine-quadruplex (G4) moieties using surface-enhanced Raman spectroscopy (SERS). By utilizing the unique G4 topological structure, target molecules can be selectively captured onto nanoporous gold (NPG) disk surfaces via π-π stacking and electrostatic attractions. Together with high-density plasmonic "hot spots" of NPG disks, the captured molecules produce a remarkable SERS signal. Our strategy represents the first example of the detection of foreign molecules conjugated to nondouble helical DNA nanostructures using SERS while providing a new technique for studying the formation and evolution of G4 moieties. The molecular specificity of G4 is known to be controlled by its unit sequence. Without losing generality, we have selected d(GGT)7GG sequence for the sensing of malachite green (MG), a known carcinogen frequently abused illegally in aquaculture. The newly developed technique achieved a lowest detectable concentration at an impressive 50 pM, two orders of magnitude lower than the European Union (EU) regulatory requirement, with high specificity against potential interferents. To demonstrate the translational potential of this technology, we achieved a lowest detectable concentration of 5.0 nM, meeting the EU regulatory requirement, using a portable probe based detection system.

Highly selective colorimetric bacteria sensing based on protein-capped nanoparticles.

A rapid and cost-effective colorimetric sensor has been developed for the detection of bacteria (Bacillus subtilis was selected as an example). The sensor was designed to rely on lysozyme-capped AuNPs with the advantages of effective amplification and high specificity. In the sensing system, lysozyme was able to bind strongly to Bacillus subtilis, which effectively induced a color change of the solution from light purple to purplish red. The lowest concentration of Bacillus subtilis detectable by the naked eye was 4.5 × 10(3) colony-forming units (CFU) mL(-1). Similar results were discernable from UV-Vis absorption measurements. A good specificity was observed through a statistical analysis method using the SPSS software (version 17.0). This simple colorimetric sensor may therefore be a rapid and specific method for a bacterial detection assay in complex samples.

Quantification of DNA through a fluorescence biosensor based on click chemistry.

A simple, sensitive and selective fluorescence biosensor for determination of DNA using CuS particles based on click chemistry is reported. Biotin-modified capture DNA was modified on Streptavidin MagneSphere Paramagnetic Particles (PMPs) and hybridized with target DNA (hepatitis B virus DNA had been chosen as an example), then bound target DNA was hybridized with DNA-CuS particles and formed a sandwich like structure. CuS particles on the sandwich structures can be destroyed by acid to form Cu(II), and Cu(II) can be reduced to Cu(I) by sodium ascorbate, which in turn catalyzes the reaction between a weak-fluorescent 3-azido-7-hydroxycoumarin and propargyl alcohol to form a fluorescent 1,2,3-triazole compound. Using this method, target DNA concentration can be determined by a change in the fluorescence intensity of the system. It is found that the fluorescence increase factor has a direct linear relationship to the logarithm of target DNA concentrations in the range of 0.1 to 100 nM, and the detection limit is 0.04 nM (S/N = 3). The proposed sensor not only allows high sensitivity and good reproducibility, but also has a good selectivity to single-nucleotide mismatches.

Label-free fluorometric method for monitoring conformational flexibility of laccase based on a selective laccase sensor.

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.

Colorimetric and fluorometric dual-readout sensor for lysozyme.

A novel, highly sensitive and selective dual-readout sensor (colorimetric and fluorometric) for the detection of lysozyme was proposed. The fluorescence of triazolylcoumarin molecules was quenched by Au nanoparticles (AuNPs) initially through the fluorescence resonance energy transfer (FRET), after the addition of lysozyme, the stronger binding of lysozyme onto the surfaces of AuNPs made triazolylcoumarin molecules remove from the AuNPs surface and led to the recovery of the fluorescence of triazolylcoumarin molecules, and accompanied by the discernable color change of the solution from red to purple. The lowest detectable concentration for lysozyme was 50 ng mL(-1) by the naked eye, and the limit of detection (LOD) was 23 ng mL(-1) by fluorescence measurements. In addition, satisfactory results for lysozyme detection in hen egg white were confirmed in the study. Moreover, the presented sensor provides a reliable option to determine lysozyme with high sensitivity and selectivity.

A fluorescent probe for detection of histidine in cellular homogenate and ovalbumin based on the strategy of click chemistry.

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.

A novel fluorescent sensor for mutational p53 DNA sequence detection based on click chemistry.

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.

Novel colorimetric molecular switch based on copper(I)-catalyzed azide-alkyne cycloaddition reaction and its application for flumioxazin detection.

A novel colorimetric switch based on the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction has been developed. G-quadruplex-hemin DNAzyme catalyzes the oxidation of 2,2'-azinobis(3-ethylbenzothiozoline)-6-sulfonic acid (ABTS) to form ABTS˙(+), the UV absorbance of the solution increased greatly and the color of the solution changed to dark green. However, in the presence of an azide complex, the absorbance signal decreased and the solution became light green since the catalytic ability of the hemin was inhibited by the azide groups. However, once propargylamine has been added into the above reaction system, which would react with azide groups through the CuAAC reaction, the solution becomes dark green again and the absorption intensity of the system is also increased. The proposed switch allows a good reversibility and can be identified clearly by the naked eye. In addition, the method has been applied to detect some pesticides, which have alkynyl groups (flumioxazin), with high sensitivity and selectivity, where the UV absorbance has a direct linear relationship with the logarithm of flumioxazin concentrations in the range of 0.14-14 nM, and the limit of detection was 0.056 nM (S/N = 3), which can meet the requirement of the maximum residue limits (MRLs) of United States of America (56 nM).

Determination of copper(II) in the dairy product by an electrochemical sensor based on click chemistry.

Herein, a novel sensitive electrochemical sensor for copper(II) based on Cu(I) catalyzed alkyne-azide cycloaddition reaction (CuAAC) is described. The catalyst of Cu(I) species is derived from electrochemical reduction of Cu(II) through bulk electrolysis (BE) with coulometry technique. The propargyl-functionalized ferrocene (propargyl-functionalized Fc) is covalently coupled onto the electrode surface via CuAAC reaction and forms propargyl-functionalized Fc modified gold electrode, which allows a good and stable electrochemical signal. The change of current at peak (dI), detected by differential pulse voltammetry (DPV), exhibits a linear response to the logarithm of Cu(II) concentration in the range of 1.0×10(-14)-1.0×10(-9) mol L(-1). It is also found that the proposed sensor has a good selectivity for copper(II) assay even in the presence of other common metal ions. Additionally, the proposed method has been applied to determine copper(II) in the dairy product (yoghurt) with satisfactory results.

An ultra-sensitive electrochemical sensor for ascorbic acid based on click chemistry.

A highly selective and sensitive electrochemical sensor for ascorbic acid (AA) assay has been prepared through Cu(I) catalyzed azide-alkyne cycloaddition reaction (CuAAC). The catalyst, Cu(I) species, is acquired from the reduction of Cu(II) by AA in situ. In the presence of Cu(I) catalyst, the azide modified Au electrode surface is shown to react quantitatively with terminal propargyl-functionalized ferrocene forming 1,2,3-triazoles. The electrochemical response of propargyl-functionalized ferrocene modified Au electrode surface can be monitored using differential pulse voltammetry (DPV) technique. Under optimal conditions, it is found that the current intensity has a linear relationship with the logarithm of AA concentration in the range of 5.0 × 10(-12) to 1.0 × 10(-9) M. Furthermore, the proposed electrochemical sensor shows a good stability (RSD 4.2%), high selectivity and low detection limit for AA detection. In addition, it also demonstrates that the proposed sensor can be applied to detect AA in real urine samples with satisfactory results.

Electrochemical impedance spectroscopy sensor for ascorbic acid based on copper(I) catalyzed click chemistry.

Copper(I) species can be acquired from the reduction of copper(II) by ascorbic acid (AA) in situ, and which in turn quantitative catalyze the azides and alkynes cycloaddition reaction. In this study, propargyl-functionalized ferrocene (propargyl-functionalized Fc) has been modified on the electrode through reacting with azide terminal modified Au electrode via copper(I) catalyzed azides and alkynes cycloaddition (CuAAC) reaction. The electrochemical impedance spectroscopy (EIS) measurement has been applied to test the electron transfer resistance of the Au electrode before and after click reaction. The changes of the fractional surface coverage (θ) with different AA concentrations are characterized. It is found that the θ value has a linear response to the logarithm of AA concentration in the range of 5.0 pmol/L to 1.0 nmol/L with the detection limits of 2.6 pmol/L. The sensor shows a good stability and selectivity. And it has been successfully applied to the AA detection in the real samples (urine) with satisfactory results.

Development of ultra-high sensitive and selective electrochemiluminescent sensor for copper(II) ions: a novel strategy for modification of gold electrode using click chemistry.

A promising and highly sensitive electrochemiluminescence (ECL) sensor for the detection of Cu(2+) based on Cu(+)-catalyzed click reaction is described in this paper. Firstly, 1-azidoundecan-11-thiol was assembled on the Au electrode surface via a simple thiol-Au reaction, then the propargyl-functionalized Ru(bpy)(3)(2+)-doped SiO(2) nanoparticles (Ru-SNPs) ECL probe was covalently coupled on the electrode surfaces via click chemistry. Cu(+), the catalyst for click chemistry, is derived from the electrolytic reduction of Cu(2+)via the Bulk Electrolysis with coulometry (BE) technique and without any reductants. It is found that the ECL intensity detected from the electrode surface has a linear relationship with the logarithm of Cu(2+) concentration in the range of 1.0 × 10(-15) to 1.0 × 10(-11) M with a detection limit of 1.0 × 10(-16) M. Also, the method is highly specific even in the presence of high concentrations of other metal cations. It has been applied to detect trace Cu(2+) in complex samples (hepatoma cell) without sample treatment.