Tyrosine-Reactive Cross-Linker for Probing Protein Three-Dimensional Structures.

Cross-linking mass spectrometry (XL-MS) has made significant progress in understanding the structure of protein and elucidating architectures of larger protein complexes. Current XL-MS applications are limited to targeting lysine, glutamic acid, aspartic acid, and cysteine residues. There remains a need for the development of novel cross-linkers enabling selective targeting of other amino acid residues in proteins. Here, a novel simple cross-linker, namely, [4,4'-(disulfanediylbis(ethane-2,1-diyl)) bis(1,2,4-triazolidine-3,5-dione)] (DBB), has been designed, synthesized, and characterized. This cross-linker can react selectively with tyrosine residues in protein through the electrochemical click reaction. The DBB cross-links produced the characteristic peptides before and after electrochemical reduction, thus permitting the simplified data analysis and accurate identification for the cross-linked products. This is the first time a cross-linker is developed for targeting tyrosine residues on protein without using photoirradiation or a metal catalyst. This strategy might potentially be used as a complementary tool for XL-MS to probe protein 3D structures, protein complexes, and protein-protein interaction.

Colorimetric determination of cysteine based on Au@Pt nanoparticles as oxidase mimetics with enhanced selectivity.

A H2O2-free colorimetric protocol based on urchin-like Au@Pt nanoparticles (Au@Pt NPs) has been developed for the sensitive and selective determination of cysteine (Cys). We verified the intrinsic oxidase-like activity of the Au@Pt NPs. They can act as artificial mimic oxidases to catalyse the oxidization of 3,3',5,5'-tetramethylbenzidine (TMB) with the assistance of dissolved oxygen, avoiding the use of H2O2 in the colorimetric determination of Cys. In addition, the discrimination of Cys from the other two biothiol analogues, homocysteine and glutathione, can be easily realized through a simple ageing process. HNO3 is added to this colorimetric system to terminate the reaction by oxidizing ox-TMB (oxidized form of TMB) to diphenoquinone (DPQ), thus generating a characteristic absorption peak of DPQ at 450 nm. By recording the absorbance at 450 nm, interference from the aggregated Au@Pt NPs (absorption peak at 670 nm) when 650 nm (the characteristic absorption peak of ox-TMB) is used as the absorption wavelength can be eliminated. We investigated this H2O2-free colorimetric protocol and obtained high sensitivity, with a detection limit of 1.5 nM and relatively high selectivity. The analytical performance for real samples was further explored. The Au@Pt NP-based H2O2-free colorimetric protocol is of great significance for the sensitive and selective determination of Cys in practical samples in different scenarios.

A turn-on fluorescent probe based on quinoline and coumarin for rapid, selective and sensitive detection of hypochlorite in water samples.

A fluorescent probe L-Cu2+ based on quinoline, coumarin and Cu2+ has been synthesized and characterized for hypochlorite determination. After copper ion was added to the solution of ligand L, the fluorescence quenching at 490 nm might result from a ligand-metal charge transfer (LMCT) process and its strong coordination ability for Cu2+ . In the presence of hypochlorite, the structure of ligand L was destroyed to form 7-(diethylamino)-coumarin-3-carboxylic acid, and the fluorescence was restored at 460 nm. In this case, L-Cu2+ complex could be used as a fluorescent probe to detect hypochlorite, with the advantages of rapid, selective, wide linear range and low detection limit.

Colorimetric sensing of iodide ions based on unmodified gold nanoparticles and the distinctive antiaggregation-to-aggregation process.

A highly sensitive and selective colorimetric analysis method based on unmodified gold nanoparticles (AuNPs) to detect iodide ions (I- ) in solution in the presence of hexadecyl trimethyl ammonium bromide (CTAB) and mercury ions (Hg2+ ) has been successfully developed. Hg2+ could form a gold amalgam with AuNPs to protect AuNPs from CTAB-induced aggregation caused by the electrostatic attraction between CTAB and citrate ion-covered AuNPs. When a mixture of Hg2+ and I- was added to the solution of AuNPs, the formation of the HgI2 complex destroyed the protection of Hg2+ for AuNPs, which led to the aggregation of AuNPs accompanied with the change in colour of the solution from red to grey black and decrease in the absorbance of AuNPs at 520 nm. There was a good linear relationship between A520nm and I- concentration from 0 to 800 nM with a low limit of detection (LOD) of 4.2 nM. Furthermore, this simple and reliable colorimetric sensor has been applied successfully to the detection of I- in practical samples.

A selective and sensitive fluorescent sensor for cysteine detection based on bi-8-carboxamidoquinoline derivative and Cu2+ complex.

In this paper, a novel fluorescent sensor 1 for selective and sensitive detection of cysteine was developed based on a complex between bi-8-carboxamidoquinoline derivative ligand (L) and Cu2+ . The interaction of Cu2+ with the ligand causes a dramatic fluorescence quenching most likely due to its high affinity towards Cu2+ and a ligand-metal charge transfer (LMCT) process. The in situ generated L-Cu2 complex was utilized as a chemosensing ensemble for cysteine. In the presence of cysteine, the fluorophore, L, was released from L-Cu2 complex because of the strong affinity of cysteine to Cu2+ via the Cu-S bond, leading to the fluorescence recovery of the ligand. The proposed displacement mechanism was confirmed by the results of mass spectrometry (MS) study. Under optimized conditions, the recovered fluorescence intensity is linear with cysteine concentrations in the range 1 × 10-6  mol/l to 8 × 10-6  mol/l. The detection limit for cysteine is 1.92 × 10-7  mol/l. Furthermore, the established method showed a highly sensitive and selective response to cysteine among the 20 fundamental α-amino acids used as the building blocks of proteins, after Ni2+ was used as a masking agent to eliminate the interference of His. The proposed sensor is applicable in monitoring cysteine in practical samples with good recovery rate.

Study of Fluorescent Imaging of Se (IV) in Living Cells Using a Turn-on Fluorescent Probe Based on a Rhodamine Spirolactame Derivative.

A highly selective fluorescent probe 2-(2-(2-aminoethylamino)ethyl)-3',6'-bis(ethylamino)-2',7'-dimethylspiro[isoindoline-1,9'-xanthen]-3-one (ABDO) for Se (IV) had been synthesized in our earlier report. In this study, this fluorescent sensor is applied on analysis fluorescent imaging of Se (IV) in Hela cells. The experiment conditions, such as the MTT assay, different concentration of saline, incubated time of Hela cells with ABDO and Se (IV), and intracellular action position of Se (IV), are investigated. Through a series of experiments, the fluorescent image of Se (IV) in Hela cells can be observed when the cells cultured by 2 µM ABDO and 2 µM Se (IV) for 210 min. And the intracellular action position of Se (IV) is verified after the co-localization experiments are done. It is mitochondria. These experimental results show that ABDO will be an eagerly anticipated sensor for fluorescent imaging analysis of selenium ion in living cells. Besides, we also can use the complexes of ABDO-Se to observe morphology and distribution of mitochondria in cells like JG-B.

A novel fluorescent 'off-on-off' probe for relay recognition of Zn2+ and Cu2+ derived from N,N-bis(2-pyridylmethyl)amine.

A metal-to-metal relay recognition was discovered with sequence specificity via a fluorescence 'off-on-off' phenomenon. We present here the synthesis of a new N,N-bis(2-pyridylmethyl)amine-based fluorescent sensor termed NBPA and its application as a selective relay probe for sensing of free trace zinc and copper ions. The addition of Zn(2+) to NBPA causes a drastic enhancement of fluorescent intensity by the formation of a 1 : 1 NBPA-Zn(2+) complex whereas other cations have no response. Moreover, Cu(2+) can induce fluorescence quenching in the NBPA-Zn(2+) system by the formation of a 1 : 1 NBPA-Cu(2+) complex confirmed by Job's Plot. The signal change of the sensor is based on the chelation-enhanced fluorescence (CHEF) effect of NBPA-Zn(2+) with the inhibition of the photoinduced electron transfer (PET) effect and the paramagnetic nature of Cu(2+) to the NBPA-Zn(2+) system. Under optimized conditions, the fluorescence intensity is linear to the concentration of Zn(2+) and Cu(2+) separately, exhibiting good linearities from 1.0 × 10(-6) M to 8.0 × 10(-6) M and 1.0 × 10(-6) M to 1.0 × 10(-5) M (R(2) = 0.9996 and R(2) = 0.9914) with detection limits of 7.89 × 10(-7) M and 1.27 × 10(-7) M, respectively. Furthermore, the rapid, selective feature enables the proposed sensor to be promising in monitoring Zn(2+) and Cu(2+) in biological and environmental research with good accuracy and precision.

Spontaneous aggregation-enhanced electrochemiluminescence via galvanic strategy.

Researchers unremittingly strive to develop innovative luminophores to enhance intrinsic electrochemiluminescence (ECL) performance. However, the potential to harness facile strategies, such as manipulating the physical properties of luminophores while retaining functional chemical properties to fabricate cost-effective ECL complexes, remains underexplored. Herein, we reported a novel and efficient one-step galvanic technique to actualize aggregation-enhanced ECL (AEECL) of ruthenium complexes. It marked the first instance of the galvanic process being employed to synthesize aggregate luminophores through electrostatic attraction. The ECL intensity and efficiency of the prepared ruthenium complexes with AEECL properties surpassed traditional ruthenium complexes by 8.9 and 13.6 times, respectively, outperforming most reported luminophores. Remarkably, the target luminophore exhibited high stability across varied scan rates and temperatures. Furthermore, a binder-free and carbon paper-based AEECL analytical device for lidocaine detection was fabricated, achieving a satisfactory detection limit (0.34 nM) and selectivity. The convenient modulation strategy of aggregate structure, along with the transformative leap from insufficient ECL to AEECL, bring forth a new revenue in aggregate science. This research also promises a universally applicable and versatile protocol for future biological analysis and bioimaging applications.

A target-induced fluorescent nanoparticle for in situ monitoring of Zn(II).

A target-induced fluorescent silica nanoparticle has been developed for the identification, enrichment and in situ determination of trace amounts of zinc(II). The nanoparticle combines the advantages of target-induced fluorescent compounds and the small size of the nanomaterial to produce a new, smarter nanosignaling material that is capable of selectively enriching a target and detecting a specific binding process in one step. As the target analyte, Zn(II), changes the fluorescence characteristics of the nanoparticle and effectively 'turns on' the fluorescence signal, no separation step is needed to confirm or quantify the binding process. The designed nanoparticle was characterized by several aspects prior to monitoring of Zn(II) in situ. The interferences from common metal ions were studied in detail. The photostability and reversibility of the sensing materials were investigated as well. The ability of this nanoparticle to detect the target Zn(II) provides a great advantage for in situ monitoring targets in biological samples under the fluorescence microscope.

Determination of lignans in Wuweizi by using magnetic bar microextraction and HPLC.

In this paper, a magnetic bar microextraction was developed to extract schisandrin A, schisantherin A, and deoxyschizandrin from Wuweizi. The analytes were determined by HPLC. A stainless-steel wire was inserted into the hollow of the hollow fiber to make the magnetic bar. The bar can be used to stir the extraction system and extract the analytes, and was isolated from the extract system by magnetic force. Several experimental parameters, including type and volume of extraction solvent, the number of magnetic bars, extraction temperature and time, stirring speed and NaCl concentration were investigated and optimized. The LODs for schisandrin A, schisantherin A, and deoxyschizandrin were 0.14, 0.06, and 0.10 g/mL, respectively. The recoveries were in the range of 70.90-106.67% and the RSDs were < 8.84%. Compared with ultrasound-assisted and Soxhlet extraction, when the present method was applied, the extraction time was shorter, the sample amount was smaller, and the consumption of organic solvent was lower.

Cu/Au nanoclusters with peroxidase-like activity for chemiluminescence detection of α-amylase.

Herein, a novel chemiluminescence method was developed for efficient and sensitive detection of α-amylase activity. α-Amylase is closely related to our life, and α-amylase concentration is a marker for the diagnosis of acute pancreatitis. In this paper, Cu/Au nanoclusters with peroxidase-like activity were prepared using starch as a stabilizer. Cu/Au nanoclusters can catalyze H2O2 to generate reactive oxygen species and increase the CL signal. The addition of α-amylase makes the starch decompose and causes the nanoclusters to aggregate. The aggregation of the nanoclusters caused them to increase in size and decrease in the peroxidase-like activity, resulting in a decrease in the CL signal. α-Amylase was detected by the CL method of signal changes caused by dispersion-aggregation in the range of 0.05-8 U mL-1 with a low detection limit of 0.006 U mL-1. The chemiluminescence scheme based on the luminol-H2O2-Cu/Au NC system is of great significance for the sensitive and selective determination of α-amylase in real samples, and the detection time is short. This work provides new ideas for the detection of α-amylase based on the chemiluminescence method and the signal lasts for a long time, which can realize timely detection.

Fluorescence quenching amplification in silica nanosensors for Au3+.

In this study silica nanoparticles (SiNPs) were covalently modified by the fluorescence ligand 2-((7-oxo-7H- furo [3, 2-g] chromen-9-yl) oxy)-N-(3-(triethoxysilyl) propyl) acetamide (CTPA) and provided an optical sensor allowing highly sensitive and selective detection for Au(3+). The probe exhibited a dynamic response range for Au(3+) from 5.0 × 10(-7) to 1.0 × 10(-4) M, with a detection limit of 2.3 × 10(-8) M. Other alkali, earth alkali and transition metal ions, even those that exist in high concentration, had no significant interference with Au(3+) determination.

A FeS2NPs-Luminol-MnO2NSs system based on chemiluminescence resonance energy transfer platform for sensing glutathione.

In this work, ferrous disulfide nanoparticles (FeS2NPs) with oxidase properties were synthesized, and a FeS2NPs-Luminol-MnO2 nanosheets (MnO2NSs) chemiluminescence resonance energy transfer (CRET) system was successfully established. Because of reaction with MnO2NSs, glutathione (GSH) can inhibit CRET between Luminol and MnO2NSs and recover the luminescence intensity of FeS2NPs-Luminol. Consequently, we developed a GSH sensor based on this chemiluminescence resonance energy transfer (CRET) system. Under optimal conditions, the FeS2NPs-Luminol-MnO2NSs sensing system showed very sensitive response to GSH in the range of 1 µM-500 µM. The limit of detection of GSH reached as low as 0.15 µM. Finally, the sensor was successfully used for the detection of GSH in serum.

A Fast Dual-responsive OFF-ON Fluorescent Probe for Cysteine and Glutathione without Interference from Homocysteine.

Abnormal levels of biothiols, such as cysteine (Cys), homocystine (Hcy), and glutathione (GSH), are generally known to result in various diseases. A fast dual-responsive OFF-ON fluorescent probe HBO-AC was synthesized and developed. Non-fluorescent HBO-AC can sense Cys by regaining fluorescence at 444 nm within 10 min and a response to GSH by restoring fluorescence at 349 nm within 20 min. There is no mutual interference with Δλ ca. 100 nm. A novel method was developed by utilizing a low reaction rate between HBO-AC and Hcy to eliminate common interference from Hcy. A successful determination of Cys and GSH in fetal bovine serum (FBS) indicated that the probe had potential application for clinical diagnosis. Moreover, it was confirmed that HBO-AC can resist interference from protein to some extent, since FBS was not pretreated before use.

Correction: Determination of sulfonamides in blood using acetonitrile-salt aqueous two-phase extraction coupled with high-performance liquid chromatography and liquid chromatography-tandem mass spectrometry.

Correction for 'Determination of sulfonamides in blood using acetonitrile-salt aqueous two-phase extraction coupled with high-performance liquid chromatography and liquid chromatography-tandem mass spectrometry' by Wei Yu et al., Anal. Methods, 2013, 5, 5983-5989, DOI: 10.1039/C3AY40902C.

A colorimetric sensor for detecting thiourea based on inhibiting peroxidase-like activity of gold-platinum nanoparticles.

In this study, gold-platinum nanoparticles (Au@PtNPs) with peroxidase-like activity were synthesized. In the absence of thiourea (TU), the Au@PtNPs can catalyze the decomposition of hydrogen peroxide, and oxidize 3,3',5,5'-tetramethylbenzidine dihydrochloride (TMB, colorless) into oxidized 3,3',5,5'-tetramethylbenzidine dihydrochloride (oxTMB, blue). The peroxidase-like activity of the Au@PtNPs is inhibited in the presence of TU, and TMB cannot be oxidized to oxTMB effectively, and no blue color could be observed. Based on this finding, a novel colorimetric sensor for detecting TU is proposed. The absorbance response curve showed a good linearity for the concentration of TU in the range of 10 nmol L-1 to 10 µmol L-1 with a correlation coefficient of R2 = 0.999, and the limit of detection is 9.57 nmol L-1. The colorimetric sensor possesses excellent selectivity, anti-interference ability, and application value in actual samples.

Extractive electrospray ionization mass spectrometry for sensitive detection of uranyl species in natural water samples.

Ambient mass spectrometry has been increasingly applied for sensitive detection of trace organic compounds present in complex matrixes. In the real world, detection of trace amounts of inorganic species, particularly with speciation information, is of great significances. Herein a method based on extractive electrospray ionization (EESI) tandem mass spectrometry (MS/MS) has been established for rapid detection of radioactive inorganic species in natural water samples. Negatively charged uranyl acetate undergoes characteristic fragmentation in the gas phase, providing the fundamental chemistry for specific detection of uranyl species in complex matrixes without sample pretreatment. Under the optimized experimental conditions, uranyl species in various natural water samples were rapidly detected using multiple-stage EESI mass spectrometry. The mean time for each sample analysis was about 10 s. The limit of detection was about a few 10(-3) ng/L of uranium by utilizing the characteristic fragments obtained in the EESI-MS(3) experiments. The typical relative standard deviation (RSD) of this method was 6.9-8.1% for 8 measurements (S/N = 3). The dynamic response range was 10(-1)-10(3) ng/L for uranium in water samples. The isotope ratio of uranyl species was quantitatively detected using EESI-MS experiments. The results show that EESI-MS, a typical method initially developed for organic compound analysis, has promising perspectives for real time, online monitoring of inorganic species such as uranyl species in natural water samples.

Carboxylate-modified squaraine dye doped silica fluorescent pH nanosensors.

Novel carboxylate-modified fluorescent silica pH nanosensors were synthesized using a reverse microemulsion method with a pH sensitive squaraine dye used as pH indicator. This pH sensitive squaraine dye was simply doped inside SiNPs without any complicated procedures. To avoid aggregation among the particles and to increase the water solubility of the pH nanosensors, the SiNPs were surface modified with a carboxyl group. This pH probe exhibits a good linear dynamic response between pH 3.01 and 5.72. Many alkali, alkaline earth, and transitional metal ions including Li( + ), Na( + ), K( + ), Rb( + ), Cs( + ), Mg(2 + ), Ca(2 + ), Sr(2 + ), Al(3 + ), V(5 + ), Cr(3 + ), Cr(6 + ), Mn(2 + ), Fe(2 + ), Fe(3 + ), Co(2 + ), Ni(3 + ), Cu(2 + ), Zn(2 + ), As(3 + ), Se(4 + ), Mo(6 + ), Ag( + ), Cd(2 + ), La(3 + ), Er(3 + ), Ir(3 + ), Hg( + ), Hg(2 + ), and Pb(2 + ) had no significant interference on pH value determination. Artificial sample determination showed that the pH nanosensors developed in this work possess a very promising applicability in biological and biomedical fields.

A highly sensitive and selective fluorescent Cu2+ sensor synthesized with silica nanoparticles.

A novel fluorescent nanosensor for the determination of Cu(2+) was synthesized with N-(quinoline-8-yl)-2-(3-triethoxysilyl-propylamino)-acetamide (QlOEt) grafted onto the surface of silica nanoparticles (SiNPs) using the reverse microemulsion method. Spherical SiNPs were used as substrate and QlOEt was used simultaneously as the binding and readout system for Cu(2+). This sensor has been realized as a highly sensitive and selective technique for the detection and quantification of trace amounts of Cu(2+). The probe exhibits a dynamic response range for Cu(2+) from 2.0 x 10(-6) to 2.0 x 10(-5) M, with a detection limit of 3.8 x 10(-7) M. Other alkali, alkaline earth, and transitional metal ions including Li(+), K(+), Mg(2+), Ca(2+), Sr(2+), Mn(2+), Zn(2+), Mo(6+), Pb(2+), Ag(+) had no significant interference on Cu(2+) determination. Poisonous and flammable reagents are avoided during the synthesis of this nanosensor. Therefore the strategy explored in this work can be extended to the synthesis of other chemo- and biosensors for direct detection of specific targets in an intracellular environment.

Core-shell Au@Pt Nanoparticles Catalyzed Luminol Chemiluminescence for Sensitive Detection of Thiocyanate.

In this study, core-shell Au@Pt nanoparticles (Au@Pt NPs) with peroxidase catalytic activity were synthesized by the seed-mediated method, and were used to catalyze the reaction of luminol-H2O2 to enhance the chemiluminescence (CL) intensity. It was found that thiocyanate (SCN-) can effectively inhibit the catalytic activity of Au@Pt NPs. Based on this phenomenon, a method to detect SCN- by using the Au@Pt NPs-catalytic luminol-H2O2 CL system was established, which has an ultra-low detection limit and an ultra-wide linear range, as well as the advantages of being simple and having low-cost and convenient operation. The research mechanism indicated that SCN- could be adsorbed on the surface of Au@Pt NPs and occupies the active sites of Pt nanostructures, which led to a decrease in the amount of Pt0 and a loss of the excellent catalytic activity of Au@Pt NPs. After optimizing the experimental conditions, this assay for detecting SCN- exhibited a good linear range from 5 to 180 nM, and the low detection limit was 2.9 nM. In addition, this approach has been successfully applied to the detection of SCN- in tap-water samples, which has practical application value and embodies good development prospects.