Folic acid capping Bi3+-doped Ag quantum dots for enzyme-like dual-mode recognition of toxic S2- and visual sensing of NO2.

BACKGROUND: NO2- and S2- are two kinds of common toxic anions widely distributed in environmental water, soil and food products. Human beings have suffered a lot of diseases from intake of excessive NO2- or S2-, i.e., infantile methemoglobin, cancer and even to death. Although tremendous efforts have been afforded to monitor NO2- and S2-, most were high instrument-depended with complex processing procedures. To keep food safety and to protect human health, it will be a huge challenge to develop a convenient and efficient way to monitor S2- and NO2- in practice. RESULTS: A kind of folic acid capping Bi3+-doped Ag quantum dots (FA@Bi3+-Ag QDs) was developed for the first time by one-pot homogeneous reduced self-assembly. Not only did FA@Bi3+-Ag QDs possess intrinsic fluorescent property, it expressed synergistic peroxidase-like activity to catalyze the redox of 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2 with Km/vmax of 0.087 mM/6.61 × 10-8 M s-1 and 6.42 mM/6.25 × 10-7 M s-1 respectively. Interestingly, trace S2- could exclusively alter its fluorescent property and peroxidase-like activity, exhibiting significant hypochromic and "turn-on" fluorescent effects. While trace NO2- could make FA@Bi3+-Ag QDs-TMB-H2O2 system hyperchromic. Under the optimized conditions, FA@Bi3+-Ag QDs were applied for dual-mode recognition of S2- and visual sensing of NO2- in real food samples with satisfactory recoveries, i.e., 100.7-107.9 %/95.8-104.7 % and 97.2-104.8 % respectively. The synergistic enzyme-mimic mechanism of FA@Bi3+-Ag QDs and its selective response mechanisms to S2- and NO2- were also proposed. SIGNIFICANCE: This represents the first nanozyme-based FA@Bi3+-Ag QDs system for dual-mode recognition of S2- and visual sensing of NO2-, well meeting the basic requirement in drinking water set by WHO. It will offer a promising way for multi-mode monitoring of different pollution using the same nanozyme-based sensor.

Poly-ß-cyclodextrin strengthen Pr6O11 porous oxidase mimic for dual-channel visual recognition of bioactive cysteine and Fe2.

To conveniently monitor bioactive cysteine (Cys) and Fe2+ in practice, a kind of poly-ß-cyclodextrin strengthen praseodymium oxide (Pr6O11) porous oxidase mimic (p-ß-CD@Pr6O11) was constructed by virtue of the strong coordination between nano Pr6O11 and poly-ß-cyclodextrin substrate. After its microstructure and physicochemical property were characterized in detail, it was noted that porous p-ß-CD@Pr6O11 exhibited excellent enzyme-like catalytic activity to accelerate the oxidation of 3,3',5,5,'-tetramethylbanzidine (TMB) and 2,2'-azinobis (3-ethylbenzo-thiazoline-6-sulfonic acid) ammonium salt (ABTS) with significant color-enhancement effect in the air. Based on the signal amplification, trace Cys could exclusively deteriorate the UV-vis absorbance at 653 nm of p-ß-CD@Pr6O11-TMB and Fe2+ alter the one at 729 nm of p-ß-CD@Pr6O11-ABTS with visual color changes. Under the optimized conditions, the proposed p-ß-CD@Pr6O11-TMB and p-ß-CD@Pr6O11-ABTS systems were successfully applied for dual-channel monitoring of Cys in Cys capsules and fetal bovine serum and Fe2+ in agricultural products with quite low detection limits, i.e., 7.8×10-9 mol·L-1 for Cys and 6.93×10-8 mol·L-1 (S/N=3) for Fe2+, respectively. The synergetic-enhancement detection mechanisms to Cys and Fe2+ were also proposed.

Biocompatible Folic-Acid-Strengthened Ag-Ir Quantum Dot Nanozyme for Cell and Plant Root Imaging of Cysteine/Stress and Multichannel Monitoring of Hg2+ and Dopamine.

To boost the enzyme-like activity, biological compatibility, and antiaggregation effect of noble-metal-based nanozymes, folic-acid-strengthened Ag-Ir quantum dots (FA@Ag-Ir QDs) were developed. Not only did FA@Ag-Ir QDs exhibit excellent synergistic-enhancement peroxidase-like activity, high stability, and low toxicity, but they could also promote the lateral root propagation of Arabidopsis thaliana. Especially, ultratrace cysteine or Hg2+ could exclusively strengthen or deteriorate the inherent fluorescence property with an obvious "turn-on" or "turn-off" effect, and dopamine could alter the peroxidase-like activity with a clear hypochromic effect from blue to colorless. Under optimized conditions, FA@Ag-Ir QDs were successfully applied for the turn-on fluorescence imaging of cysteine or the stress response in cells and plant roots, the turn-off fluorescence monitoring of toxic Hg2+, or the visual detection of dopamine in aqueous, beverage, serum, or medical samples with low detection limits and satisfactory recoveries. The selective recognition mechanisms for FA@Ag-Ir QDs toward cysteine, Hg2+, and dopamine were illustrated. This work will offer insights into constructing some efficient nanozyme sensors for multichannel environmental analyses, especially for the prediagnosis of cysteine-related diseases or stress responses in organisms.

Spindle-shaped Cu-Ru mesoporous nanospheres with enhanced enzyme-like activity for visual differentiation of toxic o-/m-aminophenol and recognition mechanisms.

To effectively differentiate toxic aminophenol isomers, a kind of spindle-shaped Cu-Ru bimetal mesoporous nanozyme (Cu-Ru MPNZ) with high specific surface was developed by one-pot homogeneous reduction method, directed by hexadecyl trimethyl ammonium bromide (CTAB) in this work. By virtue of the distinctive microstructure, Cu-Ru MPNZ expressed superior bi-functional oxidase- and peroxidase-mimic activity to catalyze the oxidation of 3,3',5,5,'-tetramethylbenzidine (TMB) and 2,2'-azinobis (3-ethylbenzothiazoline-6- sulfonic acid) ammonium salt (ABTS) with low Michaelis-Menten constants and quick reaction rates. Especially, toxic aminophenol isomers could exclusively react with the oxydates of TMB or ABTS to express differentiable signals in color. Under the optimal conditions, Cu-Ru MPNZ was successfully applied for visual differentiation of toxic aminophenol isomers in real aqueous, juices and medicinal samples with low detection limits (1.60 × 10-8 mol/L for o-aminophenol and 3.25 × 10-8 mol/L for m-aminophenol) and satisfactory recoveries (96.6-103.5%). The different recognition mechanisms of Cu-Ru MPNZ to toxic o- and m-aminophenol isomers were proposed for the first time as far as we known. This work will provide a potential way to monitor different organic isomer pollution in future.

A high-performance fluorescent and ratiometric colorimetric detection of Cu2+ in practice.

To monitor Cu2+ efficiently, a kind of D-π-A-π-D conjugated 3,5-di-(2-hydroxyl naphthaldehyde)-iminyl triazole (HNIT) was developed, using triazole as the electron acceptor, 2-hydroxyl naphthaline as the electron donor, and -CN- as the bridging group. The proposed HNIT possessed superior UV-vis and fluorescent spectral property with high molar absorption coefficient of 2.313 × 104 L mol-1 cm-1 and fluorescence quantum yield of 36.2%. Trace Cu2+ could exclusively alter its UV-vis and fluorescent property with clear color change. Under the optimized conditions, a high-performance fluorescent and ratiometric colorimetric detection of Cu2+ based on HNIT was efficient, with low detection limits of 3.3 × 10-8 mol L-1 (S/N = 3) and 9.6 × 10-8 mol L-1 (S/N = 3), respectively. It well satisfied with the safe value of 31.5 µM Cu2+ in drinking water recommended by World Health Organization (WHO). When applied for detection of Cu2+ in real environmental samples, the recovery was in the range of 97.5-105.2%. The recognition mechanism for HNIT to Cu2+ realized quite stable 6-membered rings between electron-deficient Cu2+ and electron-rich N and O atoms in HNIT with 1 : 2 chemical stoichiometry of HNIT to Cu2+.

Hybrid CuSn nanosphere-functionalized Cu/Sn co-doped hollow carbon nanofibers as anode materials for sodium-ion batteries.

To strengthen the electrochemical performance of anode materials for sodium-ion batteries, Cu/Sn co-doped hollow carbon nanofibers functionalized by hybrid CuSn nanospheres (CuSn/C@MCNF) were prepared by a simple electrospinning method. The microstructural characteristics of CuSn/C@MCNF confirmed the same doped elements and strong interactions in hybrid CuSn nanospheres and the hollow carbon nanofiber substrate. CuSn/C@MCNF has superior specific capacity, excellent conductivity and high cycling stability. In particular, the doped hollow carbon nanofiber substrate can facilitate Na+ transport and alleviate volume expansion during the process of sodium storage. When applied as an anode material for sodium-ion batteries, CuSn/C@MCNF can deliver a reversible capacity of 340.1 mA h g-1 at a large current density of 1 A g-1 for 1000 cycles and a high-rate capacity of 202.5 mA h g-1 at 4.0 A g-1, all superior to the corresponding Sn-SnOx@MCNF- and MCNF-based electrodes. This work provides a basic idea for future anode materials in high-performance sodium-ion batteries.

Silk fibroin based wearable electrochemical sensors with biomimetic enzyme-like activity constructed for durable and on-site health monitoring.

Flexible biomimetic sensors have encountered a bottleneck of sensitivity and durability, as the sensors must directly work within complex body fluid with ultra-trace biomarkers. In this work, a wearable electrochemical sensor on a modified silk fibroin substrate is developed using gold nanoparticles hosted into N-doped porous carbonizated silk fibroin (AuNPs@CSF) as active materials. Taking advantage of the inherent biocompatibility and flexibility of CSF, and the high stability and enzyme-like catalytic activity of AuNPs, AuNPs@CSF-based sensor exhibits durable stability and superior sensitivity to monitor H2O2 released from cancer cell (4T1) and glucose in sweat. The detection limits for H2O2 and glucose are low to be 1.88 µM and 23 µM respectively, and the sensor can be applied in succession within 30 days at room temperature. Further, physical cross-linking of polyurethane (PU) with SF well matches with the skin tissue mechanically and provides a flexible, robust and stable electrode-tissue interface. AuNPs@CSF is applied successfully for wearable electrochemical monitoring of glucose in human sweat.The present AuNPs@CSF will possess a potential application in clinical diagnosing of H2O2- or glucose-related diseases in future.

Convenient colorimetric-fluorescent dual-mode recognition of I- in agricultural products and visual determination of Hg2+ in drinking beverages using Ag-Pt bimetal quantum dot nanozyme.

Conveniently and efficiently monitoring I- and Hg2+ in agricultural products or drinking beverages for the protection of human health is currently a great challenge. With this aim, a Ag-Pt bimetal quantum-dot nanozyme boosted by bioactive folic acid (FA@Ag-Pt QDs) was first developed for multichannel monitoring of I- and Hg2+ in this work using a two-step liquid-phase reduction method. Not only did the present FA@Ag-Pt QDs possess superior peroxidase-like activity with Michaelis constant (Km) and maximal reaction rate (Vmax) of 0.01 mM/2.95 × 10-8 M·s-1 and 1.15 mM/3.88 × 10-8 M·s-1, respectively, trace Hg2+ or I- could exclusively alter their enzyme-mimic performance with obvious color changes from blue to colorless or dark blue. I- could also strengthen the inherent fluorescence property of FA@Ag-Pt QDs. When applied for visual monitoring of I- and Hg2+ in real beverages or iodine-containing agricultural products, the detection recoveries were 93.9 %-105.3 % and 96.8-104.3 % with low detection limits of 6.56 × 10-8 mol/L and 4.00 × 10-10 mol/L (S/N = 3), respectively. The recovery and detection limit for fluorescent detection of I- were 95.8 %-104.1 % and 1.75 × 10-8 mol/L (S/N = 3), respectively. The mechanisms driving the improved peroxidase-like activity of FA@Ag-Pt QDs and their selective monitoring of Hg2+ and I- were illustrated in detail. The proposed FA@Ag-Pt QDs will act as an efficient sensor for the practical multichannel monitoring of Hg2+ and I-, with superior catalytic signal amplification.

2D Co3O4 modified by IrO2 nanozyme for convenient detection of aqueous Fe2+ and intercellular H2O2.

A portable sensor for visual monitoring of Fe2+ and H2O2, two-dimensional Co3O4 modified by nano-IrO2 (IrO2@2D Co3O4) was prepared in this work, for the first time, with the help of microwave radiation at 140 °C, which was further stabilized onto common test strips. The present IrO2@2D Co3O4 possessed superior dual-function enzyme-like activity with low toxicity and excellent biocompatibility. Especially, trace Fe2+ and H2O2 could exclusively alter their enzyme-like catalytic activity with discriminating hyperchromic or hypochromic effect, i.e., from blue to colorless or to dark blue for both IrO2@2D Co3O4 dispersion and its functionalized test strips. The linear regression equations were A652 = 0.5940 - 0.00041 cFe2+ (10-8 M, R2 = 0.9927) for Fe2+ and ∆A652 = 0.0023 cH2O2 + 0.00025 (10-7 M, R2 = 0.9982) for H2O2, respectively. When applied to visual monitoring of aqueous Fe2+ and intercellular H2O2, the recoveries were 101.2 ~ 102.5% and 95.8 ~ 103.7% with detection limits of 1.25 × 10-8 mol/L and 1.02 × 10-7 mol/L, respectively, far below the permitted values in drinking water set by the World Health Organization. The mechanisms for the enhancing enzyme-mimetic activity of IrO2@2D Co3O4 and its selective responses to Fe2+ and H2O2 were investigated in detail.

Peroxidase-like activity of bimetal Cu-Zn oxide mesoporous nanospheres for the determination of o-aminophenol.

To enhance the peroxidase-like performance and its application in detection of toxic o-aminophenol (o-AP), a kind of bimetal Cu-Zn oxide-based mesoporous nanosphere (Cu2/3Zn1/3O PNPs) was constructed under microwave-radiation conditions. Its mesoporous microstructure and peroxidase-like catalytic activity were investigated in detail. The results showed that Cu2/3Zn1/3O PNPs possessed a high specific surface area of 34.89 m2g-1 and a well-distributed mesoporous size of approximate 6.07 nm, which endowed the superior peroxidase-like performance. The material catalyzes the oxidization of 3,3',5,5'-tetramethylbenzidine (TMB) with Km/Vmax of 0.104 mM/3.79 × 10-8 M·s-1 in the presence of H2O2. Especially o-AP could exclusively deteriorate the characteristic UV-Vis absorbance intensity at 653 nm (A653) of the Cu2/3Zn1/3O PNPs-TMB-H2O2 system with obvious color change from blue to colorless. Under the optimal conditions, the effect of some interfering substances was low and the limit of detection (LOD) for o-AP was 1.65 × 10-8 mol/L (S/N = 3). When applied to the colorimetric detection of o-AP in practice, the recovery was between 96.1 and 107.2% with R.S.D. less than 2.04%. The mechanism of synergic-enhancement peroxidase-mimic activity of Cu2/3Zn1/3O PNPs and its exclusive colorimetric response to o-AP were proposed as well.

Ag nanozyme strengthened by folic acid: Superior peroxidase-mimicking activity and application for visual monitoring of dopamine.

Dopamine (DA) is an important neurotransmitter; however, any excess or deficiency of DA will cause several diseases in humans. To monitor DA efficiently and conveniently, a Ag nanozyme strengthened by bioactive folic acid (FA@AgNPs) was developed by homogeneous redox assembly. After the microstructure and performance were characterized in detail, it was noted that the proposed FA@AgNPs possessed superior peroxidase-like activity due to the ultra-small Ag nanoparticles and multiple amino, hydroxyl, and aromatic rings in FA. FA@AgNPs accelerated the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with a low Michaelis constant (Km) and high maximal reaction rate (Vmax). Importantly, the characteristic absorbance intensity of FA@AgNPs-TMB-H2O2 at 652 nm (A652) was exclusively deteriorated in the presence of trace DA, accompanied by a visual color change from blue to colorless. Under the optimized conditions (pH 4.0, 300 µL 1.5 mM TMB, 300 µL 1.0 M H2O2 and incubated for 30 min at room temperature), there expressed an excellent linear relationship between lgA0/A652 and cDA from 1.0 ×10-8 to 6.67×10-6 mol/L with a low limit detection of 7.1×10-10 mol/L (S/N=3). When applied for monitoring of DA in real fruit juice and pharmaceutical samples, the recovery was between 96.6% and 104.9%, with RSD less than 2.2%. The enhanced peroxidase-like activity of the FA@AgNP system and its selective recognition mechanism for DA are also proposed.

Chloramphenicol-activated electro-chemiluminescent behavior of BNQDs-Ru(phen)32+ system for ultra-sensitive sensing of chloramphenicol in pharmaceutical and milk samples.

To improve the sensitivity for electro-chemiluminescent (ECL) detection of chloramphenicol (CAP), a common broad-spectrum antibiotic, boron nitride quantum dots (BNQDs) were prepared with excellent photoelectric property and low toxicity. After its structure and electrochemical property were investigated in detail, it was noted that the ECL signal of Ru(Phen)32+could be strengthened by the proposed BNQDs, which was further activated by ten's times in the presence of CAP. Under the optimized conditions, there was an excellent linear relationship between ΔECL and lgcCAPin a wide linear range from 1.0 × 10-10to 1.0 × 10-6mol l-1CAP. The detection limit was super-low to be 3.3 × 10-11mol l-1(S/N = 3). When applied for CAP detection in real pharmaceutical and food samples, the recoveries were between 97.8% and 105.7% with R.S.D. less than 3.3%. A possible CAP-activated ECL mechanism of BNQDs-Ru(phen)32+was also proposed. This work will offer a great potential for efficient monitoring of CAP pollution and clinical diagnosing of CAP-related diseases in future.

Chloramphenicol-activated electro-chemiluminescent behavior of BNQDs-Ru(phen)32+ system for ultra-sensitive sensing of chloramphenicol in pharmaceutical and milk samples.

To improve the sensitivity for electro-chemiluminescent (ECL) detection of chloramphenicol (CAP), a common broad-spectrum antibiotic, boron nitride quantum dots (BNQDs) were prepared with excellent photoelectric property and low toxicity. After its structure and electrochemical property were investigated in detail, it was noted that the ECL signal of Ru(Phen)32+ could be strengthened by the proposed BNQDs, which was further activated by ten's times in the presence of CAP. Under the optimized conditions, there was an excellent linear relationship between △ECL and lgcCAP in a wide linear range from 1.0×10-10 to 1.0×10-6 mol/L CAP. The detection limit was super-low to be 3.3×10-11 mol/L (S/N=3). When applied for CAP detection in real pharmaceutical and food samples, the recoveries were between 97.8 and 105.7 % with R.S.D. less than 3.3%. A possible CAP-activated ECL mechanism of BNQDs-Ru(phen)32+ was also proposed. This work will offer a great potential for efficient monitoring of CAP pollution and clinical diagnosing of CAP-related diseases in future.

A neoteric dual-channel spectral sensor for wide-range pH detection based on variables in UV-vis peak and intensity.

A water-soluble 2',4',6'-trihydroxy phenylazo luminol dye (THPL) with a D-π-A conjugated structure was developed for the first time for the dual-channel spectral sensing of a wide-range of pH values in aqueous solutions, using phloroglucinol as the electron-donating group, heterocycle amide luminol as the electron-accepting one and -NN- as the π-conjugated bridge. Its UV-vis absorption spectrum, especially its spectral response to pH, was investigated in detail. The results confirmed that the proposed THPL exhibited superior UV-vis spectral properties, a strong molar absorption coefficient (εmax = 3.35 × 104 L mol-1 cm-1) and a small half-band width of ca. 126 nm. In particular, either the absorption intensity (Abs) or peak (λmax) changed linearly with pH values from 3.0 to 10.0 under the optimized conditions. Notably, THPL expressed an exclusive dual-channel spectral response to pH, i.e., Abs (a.u.) = 0.1316 + 0.0278 pH (R2 = 0.9921), λmax = 441.5 - 6.64 pH (R2 = 0.9968, pH = 3.0-6.0) and λmax = 359.6 + 7.38 pH (R2 = 0.9879, pH = 6.0-10.0). Under the optimized conditions, THPL was applied to detect pH values in some aqueous and fruit juice samples with satisfactory results. The reversible recognition mechanism was deduced by UV-vis titration, 1H NMR titration and theoretical calculation.

One-dimensional nitrogen doped porous carbon nano-array arranged by carbon nanotubes for electrochemical sensing ascorbic acid, dopamine and uric acid simultaneously.

In this work, one-dimensional nitrogen doped porous carbon nano-arrays arranged by carbon nanotube (1D CNTs@NPC) were first constructed, using a coating technology at room temperature and followed by high temperature carbonization. It was expected that the resulting glassy carbon electrodes modified by 1D CNTs@NPC (CNTs@NPC/GCE) could express different electrochemical responses to ascorbic acid (AA), dopamine (DA), uric acid (UA), by virtue of the synergistic-improved effect between CNTs and NPC. Under the optimized conditions, there were excellent analytical parameters for CNTs@NPC/GCE to detect AA, DA and UA, i.e. a wide linear range of 40-2100µM for AA, 0.5-49µM for DA and 3-50µM for AA with low detection limits of 0.36µM, 0.02µmol l-1and 0.57µM respectively. Importantly, the proposed CNTs@NPC/GCE was efficiently applied to determine AA, DA and UA in some real samples with high stability, reproducibility and selectivity. This work will offer an efficient potential for diagnosing ascorbic acid, dopamine or uric acid-related diseases on clinical testing in future.

2D Co3O4 stabilizing Rh nano composites developed for visual sensing bioactive urea and toxic p-aminophenol in practice by synergetic-reinforcing oxidase activity.

To enlarge the perspective of nanozyme, 2-dimensional Co3O4 stabilizing Rh nano composite (2D Co3O4@Rh NC) was identified and developed first by one-pot surfactant-aided oxido-reduction. By virtue of the synergetic-reinforcing oxidase activity between 2D Co3O4 substrate and Rh nano particles, the obtained 2D Co3O4@Rh NC could catalyze the oxidation of chromogenic substrate 3,3',5,5,'-tetramethylbenzidine (TMB) to blue oxTMB with quite a low Michaelis-Menten constant (Km) of 0.018 mM and a quick vmax of 6.45 × 10-8 M s-1, expressing superior oxidase-like catalysis with a wide temperature range from 20 to 60 °C. Importantly, either bioactive urea or toxic p-aminophenol (p-Ap) could exclusively alter the existed state of oxTMB with differentiable color changes. Under the optimized conditions, 2D Co3O4@Rh NC was successfully applied for ratiometric colorimetric sensing urea and p-Ap in environmental water, soil and urine samples with low detection limits (1.1 µM for urea and 0.68 µM for p-Ap) and satisfactory recoveries (96.0-105.8%). The synergetic enhanced oxidase-like activity of 2D Co3O4@Rh NC and the different reaction mechanisms of the 2D Co3O4@Rh NC-TMB system to urea and p-Ap were investigated. Not only does the work provide an efficient way for sensing organic pollution of p-Ap, it will offer an efficient potential for diagnosing urea-related diseases on clinical medical testing in future.

Recent developments of nanoenzyme-based colorimetric sensors for heavy metal detection and the interaction mechanism.

Heavy metal contamination has posed a great threat to human survival and social development. For this, a series of nanoenzyme-based colorimetric sensors, e.g., metal nanoparticles, metal oxides, metal sulfides, graphene-based nanomaterials, G-quadruplex and so on, were developed for the rapid and efficient detection of toxic heavy metal ions, whose detection limit for heavy metal ions could be as low as the nmol L-1 level. The recognition mechanism was based on the catalysis and signal amplification of nanozymes, a new type of nanomaterial possessing specific catalytic activity towards certain chemical reactions such as the oxidation of colorless TMB to blue oxTMB. In this work, we are trying to present readers with a better understanding of this important colorimetric sensing material by illustrating its application in the detection of heavy metal ions using metal nanoparticles, metal oxides, metal sulfides, graphene-based nanomaterials, G-quadruplex, etc. respectively.

Efficient Polymer Pendant Approach toward High Stable Organic Fluorophore for Sensing Ultratrace Hg2+ with Improved Biological Compatibility and Cell Permeability.

A convenient and efficient method to eliminate the aggregation effect of organic photoelectric sensing materials and to improve biological compatibility and cell permeability as well was developed by hanging organic fluorophores on a polymer chain, for example, fluorescein fluorophores had been controllably hung on polyacrylamide main chains with a 1:2 stoichiometric ratio by a simple copolymerization strategy. The results showed that introduction of water-soluble bioactive polyacrylamide main chains into fluorescein fluorophores via covalent bonds could effectively improve their optical stability by deteriorating π-π stack and charge-transfer interactions among different fluorophores. More importantly, the resultant materials possessed low toxicity and excellent cell permeability ten times larger than their precursor fluorescein fluorophore, which made it express an especially turn-on fluorescent response to ultratrace Hg2+ both in aqueous and living cells by forming stable 5-member-ring complexes with Hg2+ with a correlation coefficient of 0.997 and a low detection limit of 4.0 × 10-10 mol·L-1. This work provides promising insight into constructing some practical sensing materials for environmentally-friendly biological analyses.

One-Pot Methylenation-Cyclization Employing Two Molecules of CO2 with Arylamines and Enaminones.

One-pot methylenation-cyclization employing two molecules of CO2 with enaminones and primary aromatic amines was discussed for the first time to access cyclized products. This 1,5,7-triazabicyclo[4.4.0]dec-5-ene and ZnCl2-catalyzed procedure was characterized by the selective conversion of two molecules of CO2 into methylene groups in a multicomponent cyclization reaction. According to the computational study and control experiments, the reaction might proceed through the generation of bis(silyl)acetal and condensation of arylamine and aza-Diels-Alder processes. Moreover, the resulting products will probably be potential organic building blocks with adjustable photophysical properties.

A multiple fluorescein-based turn-on fluorophore (FHCS) identified for simultaneous determination and living imaging of toxic Al3+ and Zn2+ by improved Stokes shift.

A multiple turn-on fluorophore (FHCS), combining fluorescein, hydrazone, cyanuric chloride and salicylaldehyde chromone into a molecule, was identified and developed based on density functional theoretical calculation. It was expected that FHCS could express exclusive fluorescent signals and improved Stokes shifts when chelating Al3+ or Zn2+. After it was synthesized and characterized in detail, it was noted that FHCS could turn-on fluorescently discriminate trace Al3+ and Zn2+ under the optimized conditions, i.e., from no-fluorescence to strong blue fluorescence for Al3+ and to green fluorescence for Zn2+ with low detection limits of 5.37 × 10-8 M and 7.90 × 10-8 M respectively. Owing to its low toxicity, FHCS was successfully applied for quantitative determination of Al3+ and Zn2+ in natural aqueous samples and toxicity evaluation of Al3+ and Zn2+ in living cells and bio-tissues with excellent linear relationships. The action mechanisms for FHCS with Al3+ and Zn2+ were confirmed to form stable 5-member-co-6-member condensed rings between Al3+/Zn2+ and N/O atoms in FHCS by both theoretic and experimental methods, which resulted in turn-on fluorescence with different dipolar moments and improved Stokes shifts.