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.

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.

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.

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 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.

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.

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.

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.

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 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.

An acidic residue reactive and disulfide bond-containing cleavable cross-linker for probing protein 3D structures based on electrochemical mass spectrometry.

Cross-linking mass spectrometry (XL-MS) has attracted broad attention because of the capability to probe three-dimensional structure of proteins. Up to now, several amine-reactive cross-linkers have been developed for characterization of proteins and protein complexes. However, spatial information retrieved by XL-MS is still limited, partly because the strategies using an acidic residue reactive cross-linker have been rarely reported. In this paper, an acidic residue (e.g. aspartic acid, glutamic acid)-specific, disulfide bond-containing, cleavable cross-linker with a length of 13.1 Å, named 3,3'-dithiobis(propanoic dihydrazide), was presented for the first time. In addition, a novel approach using the cross-linker was proposed for unambiguous characterization of peptides and proteins with disulfide bonds. After cross-linked, the peptides could be electrochemically reduced, then characterized by high performance liquid chromatography mass spectrometry. For demonstration, the approach has been adopted to characterize the emideltide, insulin, and myoglobin, of which four pairs of intrachain cross-links have been successfully identified in myoglobin. The results showed that the cross-links displayed predictable fragmentation pattern upon collision induced dissociation (CID), thus admitting simplifying data analysis. In summary, this work introduces a novel type of cross-linker utilized for cross-linking and a new strategy to XL-MS technology for comprehensively understanding the three-dimensional structure of proteins.

Colorimetric Sensor for Thiocyanate Based on Anti-aggregation of Gold Nanoparticles in the Presence of 2-Aminopyridine.

Based on the anti-aggregation mechanism of citrate stabilized gold nanoparticle (AuNPs), a new specific and sensitive colorimetric sensor for thiocyanate (SCN-) was developed. In this scheme, the AuNPs were aggregated in the presence of the aggregating agent 2-aminopyridine (2-AP) due to electrostatic attraction. The solution color changed from red to blue. When SCN- was present, SCN- formed a sulfur-gold bond with the AuNPs to protect the AuNPs from aggregation. Thiocyanate can be detected by the color change of the solution from blue to red. The results showed that the absorbance ratio A675/A520 was linear with the concentration of SCN- in the range of 0.4 - 1.2 µmol L-1 by UV-Vis spectroscopy. The limit of detection (LOD) of this assay was 0.37 µmol L-1. The system also had excellent selectivity and anti-interference ability. In addition, this method was successfully used for the detection of SCN- in actual water samples and achieved good results.

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.

Water-soluble Hemin-mPEG-enhanced Luminol Chemiluminescence for Sensitive Detection of Hydrogen Peroxide and Glucose.

In the present study, we synthesized a water-soluble substance (Hemin-mPEG) at room temperature by using hemin and poly(ethylene glycol) methyl ether (mPEG). It was found that the Hemin-mPEG maintained the excellent catalytic activity inherited from hemin, and was first used to catalyze a luminol-H2O2 chemiluminescence (CL) system to generate an intense and slow CL signal. The results of a mechanism research showed that the presence of Hemin-mPEG could promote the production of oxygen-relative radicals from H2O2 and dissolved oxygen in solution. Based on this mechanism, an ultra-sensitive, cheap and simply practical sensor for detecting glucose and H2O2 was developed. Under the most optimal experimental conditions, H2O2 and glucose detection results exhibited a good linear range from 0.002 to 3 µM and from 0.02 to 4 µM, respectively, and the detection limits were 1.8 and 10 nM, respectively. This approach has been successfully used to detect glucose in actual biological samples, and achieved good results.

Disulfide linkage assignment based on reducing electrochemistry and mass spectrometry using a lead electrode.

The study of disulfide linkage is a crucial part of the quality assessment of biopharmaceutical products because disulfide bonds stabilize the tertiary structure of proteins and maintain protein functions. Therefore, a suitable method is highly required for disulfide linkage assignment when nested disulfide bonds formed with closely spaced cysteine residues. A novel approach for disulfide linkage assignment of disulfide-rich peptides and proteins via electrochemical reduction on a lead electrode with mass spectrometry is presented in this paper. The method features partial electrochemical reduction and alkylation of peptides followed by alkylated peptide sequencing based on tandem mass spectrometry. Lead was chosen for the first time as an electrode material for disulfide bond reduction, because it has the advantages of maintenance free (only infrequent polishing needed), easy operation in DC mode, and reusability. Without any special sample preparation and any chemical reduction agents, disulfide bond in peptides can be cleaved rapidly. The new method was successfully tested with two peptides and one protein containing nested disulfide bonds.

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.

Residue analysis of tetracyclines in milk by HPLC coupled with hollow fiber membranes-based dynamic liquid-liquid micro-extraction.

A novel hollow fiber membranes-based dynamic liquid-liquid micro-extraction (HF-DLLME) coupled with HPLC-UV detection has been developed for the residue analysis of tetracyclines in milk samples without deproteinization and degreasing. The influences of experimental parameters were investigated and optimized. The method showed a good performance. The limits of detection (LOD) are in the range of 0.95-3.6µg/L. The recoveries in spiked samples range from 92.38 to 107.3%. The relative standard deviations (RSDs) are lower than 8.66%. The advantages of this method are simple operation, high efficiency, absence of sample carryover and low cost.

Conjugated polymer with carboxylate groups-Hg2+ system as a turn-on fluorescence probe for label-free detection of cysteine-containing compounds.

In this work, a turn on fluorescent sensor, based on Hg2+ coordination conjugated polymer, was developed to detect cysteine-containing compounds. The fluorescence of conjugated polymer (poly(2,5-bis (sodium 4-oxybutyrate) -1,4 - phenylethynylene-alt-1,4-phenyleneethynylene; PPE-OBS) would be quenched by Hg2+ because of the coordination-induced aggregation and electron transfers of PPE-OBS toward Hg2+. When there were some cysteine-containing compounds in PPE-OBS-Hg2+ system, the fluorescence of PPE-OBS would be recovered. It indicated that the PPE-OBS-Hg2+ system could be used to detect cysteine-containing compounds. Under the optimized conditions, the experiment results showed that there were particularly linear range, high sensitivity and selectivity over other amino acids. The limit of detection (LOD) of cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) were 0.725µmolL-1, 0.982µmolL-1 and 1.21µmolL-1 by using this sensor. In addition, Cys standard recovery in several green tea drink and honey samples was also demonstrated. The recovery of Cys was range from 96.3 to 105.0% and RSD was less than 3.25%. The satisfactory results demonstrated that the proposed method could be as a potential fluorescent method for determining cysteine-containing compounds in real samples.

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.

Highly Sensitive Fluorescence Detection of Hg2+ Based on a Water-soluble Conjugated Polymer with Carboxylate Groups.

A label-free, highly selective, and highly sensitive fluorescent sensor to detect Hg2+ was developed using a water-soluble conjugated polymer with carboxylate groups (poly(2,5-bis(sodium 4-oxybutyrate)-1,4-phenylethynylene-alt-1,4-phenyleneethynylene, PPE-OBS) in this work. The fluorescence of PPE-OBS would be quenched because of the effect among the unique coordination-induced aggregation and electron transfers of PPE-OBS toward Hg2+. The linear relationship between the fluorescence intensity and concentration of Hg2+ was observed within the range from 6 × 10-8 to 8 × 10-5 mol L-1 (R2 = 0.9985), and the limit of detection was 2.10 × 10-9 mol L-1. The proposed method was applied to detect Hg2+ in environmental water samples, and satisfactory results were obtained.