Double enzyme mimetic activities of multifunctional Ag nanoparticle-decorated Co_(3)V_(2)O_(8)hollow hexagonal prismatic pencils for application in colorimetric sensors and disinfection

Since the catalytic activity of most nanozymes is still far lower than the corresponding natural enzymes,there is urgent need to discover novel highly efficient enzyme-like materials.In this work,Co_(3)V_(2)O_(8)with hollow hexagonal prismatic pencil structures were prepared as novel artificial enzyme mimics.They were then decorated by photo-depositing Ag nanoparticles(Ag NPs)on the surface to further improve its catalytic activities.The Ag NPs decorated Co_(3)V_(2)O_(8)(ACVPs)showed both excellent oxidase-and peroxidase-like catalytic activities.They can oxidize the colorless 3,3’,5,5’-tetramethylbenzidine rapidly to induce a blue change.The enhanced enzyme mimetic activities can be attributed to the surface plasma resonance(SPR)effect of Ag NPs as well as the synergistic catalytic effect between Ag NPs and Co_(3)V_(2)O_(8),accelerating electron transfer and promoting the catalytic process.ACVPs were applied in constructing a colorimetric sensor,validating the occurrence of the Fenton reaction,and disinfection,presenting favorable catalytic performance.The enzyme-like catalytic mechanism was studied,indicating the chief role of⋅O_(2)-radicals in the catalytic process.This work not only discovers a novel functional material with double enzyme mimetic activity but also provides a new insight into exploiting artificial enzyme mimics with highly efficient catalytic ability.

Enhancement of Toxic Gas Detecting Ability of Film Type Colorimetric Sensor

In this study, we tried to develop the in situ coating methods of hydrophilic polymer solution containing water soluble dye on nonwoven sheet for the colorimetric film sensor. And color change of coated dye according to contact various gas samples (as strong acid and base, chloroform, ammonia and HF) of this dye-coated nonwoven film was examined for the application of chemically toxic materials detecting tools in the actual site of working place without aid of any kinds of detecting devices. By the addition of electron transfer agent (quinone derivatives), quick color change behaviors were observed within 10 seconds under the contact of various toxic gases in general condition(room temperature, 50% humidity).

A pH-Regulated Colorimetric Sensor Array for Discrimination of Biothiols Based on Two Different-Sized β-Cyclodextrin-Functionalized AuNPs

The abnormal changes of biothiols are directly related to health condition of human body,and the effective identification and quantification of biothiols is of great significance for screening and diagnosis of disease.This study described the development of a p H-regulated colorimetric sensor array for discrimination of five kinds of biothiols including cysteine(Cys),glutathione(GSH),homocysteine(Hcy),cysteamine(CA)and N-acetylcysteine(NAC).The proposed sensor array was established using 5-nm-and 20-nm-sizedβ-cyclodextrin-functionalized gold nanoparticles(β-CD@Au NPs)as nonspecific receptor and signal transduction elements.Due to the different binding affinity between biothiols andβ-CD@Au NPs in various p H environments,the different aggregation behaviors of nanoparticles produced unique colorimetric response patterns,which were able to be distinguished by bare eyes and UV-vis spectrophotometer.Accordingly,principal component analysis(PCA)and hierarchical cluster analysis(HCA)were employed for pattern recognition and generated a clustering map for a clear differentiation of biothiols at the level ofμmol/L.Furthermore,it can be proved that the method was successfully applied to the analysis of biothiols in human urine samples.

Novel colorimetric sensor for mercury (Ⅱ) based on layer-by-layer assembly of unmodified silver triangular nanoplates

A simple layer-by-layer deposition technique was used to fabricate the multilayer thin films of unmodified silver triangular nanoplates （AgTNPs）. The multilayer of AgTNPs thin films were fabricated by alternate deposition of each anionic sodium citrate stabilized AgTNPs and cationic poly（diallyldimethylammonium chloride）. All prepared AgTNPs multilayer thin films were exhibited a strong plasmon band at the wavelength of 667 rim, which confirmed the formation of AgTNPs onto the substrate. The characteristics of the multilayer thin films were investigated using contact angle measurement, UV-visible spectroscopy, X-ray diffraction analysis （XRD）, atomic force microscope （AFM） and field emission scanning electron microscope （FESEM）. As these films are to be used as a mercury （Ⅱ） colorimetric sensor, the changes in optical properties of the films were evaluated for various mercury （Ⅱ） concentrations. AgTNPs assembled into thin films showed a strong color shift from blue to mauve and colorless when exposed to mercury （Ⅱ）. The constructed multilayer thin films exhibited excellent color changes of mercury （Ⅱ） with a linear range between 0.5 and 20 ppm. The limit of detection （LOD） and limit of quantitation （LOQ） were 0.45 ± 0.002 and 1.52 - 0.002 ppm, respectively. The recovery values of AgTNPs multilayer thin films are satisfactory in the range of 100.1%-106.4% when applied to determining mercury （Ⅱ） in water samt）les.

A Highly Selective Colorimetric Sensor for Cu^2＋ Based on Phenolic Group Biscarbonyl Hydrazone

A novel copper selective sensor 2 based on hydrazide and salicylaldehyde has been designed and prepared. Sensor 2 behaves a single selectivity and sensitivity in the recognition for Cu2＋ over other metal ions such as Fe3＋, Hg2＋, Ag＋, Ca2＋, Zn2＋, Pb2＋, Cd2＋, Ni2＋, Co2＋, Cr3＋ and Mg2＋ in DMSO. The distinct color change and the rapid changement of fluorescence emission provide naked-eyes detection for Cu2＋. The UV-vis data indicate that 1 ： 2 stoichiometry complex is formed by sensor 2 and Cu2＋. The association constant Ks was 3.51 × 104 mol 1%. The detection limitation of Cu2＋ with the sensor 2 was 2.2 × 10.7 mol·L^-1. The sensing of Cu2＋ by this sensor was found to be reversible, with the Cu2＋-induced color being lost upon addition of EDTA.

A highly selective colorimetric sensor for Hg^(2+) based on a copper (Ⅱ) complex of thiosemicarbazone in aqueous solutions

By applying an indirect strategy, a new copper （II） complex of a thiosemicarbazone L has been successfully developed as a colorimetric cbemosensor for the sensitive detection of mercury （II） ions. In the presence of copper （II） ions, the colorless so- lution of L became yellow; however, upon the addition of traces of mercury （II） ions, the yellow color faded to colorless im- mediately. Other ions, including Fe3＋, Ag＋, Ca2＋, Zn2＋, Pb2＋, Cd2＋, Ni2＋, Co2＋, Cr3＋ and Mg2＋ had a negligible influence on the probe behavior. The detection limits were 5.0×10^-6 M and 3.0×10^-7 M of Hg2＋ using the visual color changes and UV-vis changes respectively. Test strips based on Cu-L were fabricated, which could act as a convenient and efficient Hg2＋ test kits.

Quinoline-based colorimetric chemosensor for Cu^(2+): Cu^(2+)-induced deprotonation leading to color change

A quinoline-based colorimetric chemosensor （QDB） for Cu2＋ was synthesized by coupling quinoline-2- carbaldehyde with 4-（dimethylamino）benzohydrazide. Although most transition metal cations can cause redshiffs in the UV-vis spectrum of QDB, the response of the chemosensor for Cu2＋ can be easily distinguished because it exhibits the largest redshift together with a color change from colorless to red in response to Cu2＋. Other metal ions have no effect on the specific response of QDB to Cu2＋. The significant redshift and color change were attributed to Cu2＋-induced deprotonation of NH in the sensor.

A highly selective turn-on colorimetric and luminescence sensor based on a triphenylamine-appended ruthenium(Ⅱ) dye for detecting mercury ion

A dual colorimetric and luminescent sensor based on a heteroleptic ruthenium dye [Ru（Hipdpa）（Hdcb- py）（NCS）2]^-.0.5H^＋ 0.5[N（C4H9）4]＋ Ru（Hipdpa） {where Hdcbpy = monodeprotonted-4,4＇-dicarboxy-2,2＇- bipyridine and Hipdpa = 4-（1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl）-N,N-diphenylaniline} for selective detection of Hg2. is presented. The results of spectrophotometric titrations revealed an evident luminescence intensity enhancement （I/Io = 11 ） and a considerable blue shift in visible absorption and luminescence maxima with the addition of rig2.. The sensitive response of the optical sensor on Hg^2＋ was attributed to the binding of the electron-deficient Hg^2＋ to the electron-rich sulfur atom of the thiocyanate （NCS） ligand in the Ru（Hipdpa）, which led to an increase in the energy gap between the highest occupied molecular orbital （HOMO） and the lowest unoccupied molecular orbital （LUMO）. Accordingly, the blue shift in the absorption spectrum of Ru（Hipdpa） due to the binding of Hg2. was obtained. Ru（Hipdpa） was found to have decreased Hg2~ detection limit and improved linear region as compared to di（tetrabutylammonium） cis-bis（isothiocyanato）bis（2,2＇-bipyridine-4-carboxylic acid-4＇- carboxylate）ruthenium（ll） N719. Moreover, a dramatic color change from pink to yellow was observed, which allowed simple monitoring of Hg^2＋ by either naked eyes or a simple colorimetric reader. Therefore, the proposed sensor can provide potential applications for Hg2＊ detection.

A Simple Detection of Hg （11） down to ppm Level Employing Rhodamine Hydrazine Impregnated on a Solid-Phase Membrane

In the methanolic solution, the selectivity of rhodamine hydrazide （RhH） was simply switched from Cu2＋ to Hg2＋ ions. For the optimal absorption of RhH onto a solid-phase membrane, pure methanol was used to dissolve RhH prior to the impregnation. Of solid-phase membranes tested, the filter paper was chosen due to its cost-effectiveness and good detection limit of Hg2＋ ion. The detection limit of the RhH impregnated filter paper for the detection of Hg2＋ ion was determined to be under 2 ppm both fluorescent and colorimetric detection.

Novel Hydrazone-Based Tripodal Sensors： Single Selective Colorimetric Chemosensor for Acetate in Aqueous Solution

A series of novel tripodal colorimetric anion sensors based on hydrazone CH=N--NH groups have been synthesized and their recognition behavior with anionic guests has been studied. In DMSO solutions, sensors 1 and 2 show colorimetric responses for F^-, H2PO4 and AcO^-, while in DMSO/H20 （9 ： 1, V/V） solutions, sensor 1 shows single selectivity for AcO^-. ^1H NMR titration confirms that the tripodal sensors could bind anions through the collaboration of three hydrazone groups and anions residing in the central cavity of the sensors.

Synthesis of a Phenylhydrazone-based Colorimetric Anion Sensor with Complementary IMP/INH Logic Functions

A dinitrophenyl hydrazone colorimetric anion sensor （receptor 1） was synthesized and its recognition properties towards various anions were investigated by naked eye observation and spectroscopic methods, namely UV-vis and 1H NMR titrations in DMSO. The addition of AcO？, F？ and H2PO4？ to receptor 1 resulted in marked red shift of the charge-transfer absorbance band （Δλ=91 nm, 407 nm to 498 nm） concomitant with a ＇naked-eye＇ detectable colour change from yellow to pink. However, both the colour and spectral changes were reversible by the addition of cations （MII） of 3d5-10 as well as CdII, HgII, MgII and CaII. Subsequently, complementary IMP/INH logic functions based on colour and spectral switching （ON/OFF） were affirmed. The sensor can, thus be utilized as a colorimetric molecular switch modulated by F？/MII.

A novel colorimetric and ratiometric NIR fluorescent sensor for glutathione based on dicyanomethylene-4H-pyran in living cells

Glutathione(GSH)plays a critical role in maintaining oxidation-reduction homeostasis in biological systems.Considering the detection of GSH by fluorescence sensors is limited by either the short wavelength emission or the poor photostability,a highly stable colorimetric and ratiometric NIR fluorescent sensor(DCM-S)for GSH detection has been constructed on the basis of dicyanomethylene-4H-pyran(DCM)chromophore.The specific disulfide bond is incorporated via a carbamate linker as the GSH responsive group,which simultaneously blue-shifts and quenches the fluorescence.Upon addition of GSH,DCM-S exhibits outstanding colorimetric(from yellow to red)and ratiometric fluorescent response with the 6-fold enhancement of NIR fluorescence at 665 nm in quantum yield.More importantly,the GSH-treated DCM-S(DCM-NH_2 actually)possesses 20-fold longer fluorescence half-life period as well as much better photostability than the FDA-approved ICG.Finally,the ratiometric detection of GSH is also successfully operated in the living cell imaging,exhibiting NIR fluorescence and large Stokes shift(215 nm)with nearly no background fluorescence interference.As a consequence,DCM-S can be utilized as colorimetric and ratiometric NIR fluorescent sensor for GSH,with a great potential in the development of GSH-induced drug delivery system.

A new Keggin-type polyoxometallate-based bifunctional catalyst for trace detection and pH-universal photodegradation of phenol

The widespread application of phenolic substances in the field of food,medicine and industry,is harmful to the environment and human health.Therefore,it is very important to develop a con-venient and effective method to detect and degrade phenolic compounds.Herein,we report a new keggin-type polyoxometallate-based metal-organic complex self-assembled under solvothermal condition,{[Cu(dap)(3-PA)]4(SiW_(12)O_(40))(H_(2)O)_(2)}·2H_(2)O(1,dap=1,2-diaminopropane,3-HPA=3-pyridineacrylic acid).1 shows an interesting 1D ladder-like structure.As a bifunctional catalyst,1 can be employed as a colori-metric sensor toward phenol with the relatively low detection limit(LOD)of 0.36μmol/L(S/N=3)in the wide range(0.001-0.1 mmol/L).The title colorimetric sensor is applied to determine phenol in various water environment with good recoveries ranging from 95%-105%.In addition,1 also exhibits excellent photocatalytic degradation toward phenol under visible light with the highest removal efficiency at 96%for 100 min and wide pH universality.The selectivity,stability and reliability of the detection of 1 towards phenol,as well as the detection for 4-chlorophenol,o-cresol,4-nitrophenol and phloroglucinol were stud-ied.Furthermore,the photocatalytic reaction kinetics and the mechanisms of photodegradation of phenol were also investigated in detail.

A selective, sensitive and label-free visual assay of fructose using anti-aggregation of gold nanoparticles as a colorimetric probe

A new convenient colorimetric sensor for fructose based on anti-aggregation of citrate-capped gold nanoparticles（Au NPs） is presented. 4-Mercaptophenylboronic acid（MPBA） induces the aggregation of Au NPs, leading to a color change from red to blue. Fructose as a potent competitor has strong affinity for MPBA and a borate ester is formed between MPBA and fructose. There is an obvious color change from blue to red with increasing the concentration of fructose. The anti-aggregation effect of fructose on Au NPs was seen by the naked eye and monitored by UV–vis spectra. Our results showed that the absorbance ratio（A（519）/A（640）） was linear with fructose concentration in the range of 0.032–0.96 μmol/L（R^2= 0.996）, with a low detection limit of 0.01 μmol/L（S/N = 3）. Notably, a highly selective recognition of fructose was shown against other monosaccharide and disaccharide（glucose, mannose, galactose,lactose and saccharose）. With anti-aggregation assays higher selectivity is achievable. The results of this work provide a rapid method for evaluating the quantitative analysis of fructose in human plasma at physiologically meaningful concentrations and at neutral pH. The proposed procedure can be used as an efficient method for the precise and accurate determination of fructose.

A bifunctional rhodamine derivative as chemosensor for recognizing Cu^2+ and Hg^2+ ions via different spectra

A new simple bifunctional chemosensor 1 based on rhodamine was synthesized by hydrazide and formylformic acid,which could detect Cu^2+and Hg^2+via dif ferent detecting methods in CH3 CN-HEPES buffer solution(20 mmol/L,pH 7.4)(1:9,v/v)respectively.When sensor 1 bound with Cu^2+,it showed a colorimetric change,while a selective enhancement in fluorescence occurred upon 1 binding with Hg^2+,resulting from the spirolatam-ring opening process.The binding modes of 1 with Cu^2+and Hg^2+were investigated based on UV,fluorescence change,ESI-Mass and Job’s Plot data.Moreover,sensor 1 could selectively detect target ion in a mixed solution of Cu^2+and Hg^2+,and the two metal ions do not inte rfere with each other in the process of detecting Cu^2+or Hg^2+with 1.

Highly sensitive colorimetric detection of NH3 based on Au@Ag@AgCl core-shell nanoparticles

Abstract:As an important component of the atmosphere,ammonia(NH_(3))plays a very important role in maintaining the balance of environment.However,it is also one of the most toxic gases that can cause damage to the human respiratory system and mucous membranes even at low concentrations.As such,development of highly sensitive and selective NH_(3)sensors is of high significance for environmental monitoring and health maintenance.Herein,we have synthesized Au@Ag@Ag Cl core-shell nanoparticles(NPs)by oxidative etching and precipitating Au@Ag core-shell NPs using FeCl3 and further used them as optical probes for the colorimetric detection of NH_(3).The sensing mechanism is based on the fact that the etching of NH_(3)on AgCl and Ag shell leads to the variations of ingredients and core-to-shell ratio of the Au@Ag@AgCl NPs,thereby inducing noticeable spectral and color changes.By replacing the outmost layer of Ag with AgCl,not only is the stability of the sensor against oxygen significantly enhanced,but also is the sensitivity of the method improved.The method exhibits good linear relationship for the detection of NH_(3)from 0 to 5000 mmol/L with the limit of detection of 6.4 mmol/L.This method was successfully applied to the detection of simulated air polluted by NH_(3),indicating its practical applicability for environmental monitoring.This method shows great potential for on-site NH_(3)detection particularly in remote area,where a simple,fast,low-cost,and easy-to-handle method is highly desirable.

COLORIMETRIC DETECTION OF CARBENICILLIN USING CATIONIC POLYTHIOPHENE DERIVATIVES

A water-soluble, polythiophene-based colorimetric sensor was designed for selective and sensitive detection of carbenicillin in HEPES buffer solution. Quaternized quinine was linked to thiophene through bis-functionality benzyl group, which can interact with carbenicillin via electrostatic interaction and geometric match effect. The sensor exhibited a colorimetric signal change upon the addition of carbenicillin because of the formation of more nonplanar structures. However, the addition of other beta-lactarn antibiotics or dicarboxylic acids into the sensor solution caused no obvious changes in absorbance intensity ratio. This result may be attributed to the cavity formed by the semi-rigid framework of PTQ2, which is suitable for the special binding with carbenicillin. This novel sensor can effectively distinguish carbenicillin from other beta-lactam antibiotics and has a wide linear range response in HEPES buffer solution. Linear calibration curves are obtained with 0 to 18 μmol/L of HEPES buffer solution, with a limit of detection of 0.54μmol/L.

A Rhodamine-based fluorescent sensor for chromium ions and its application in bioimaging

A rhodamine-based sensor（1） has been developed for the detection of chromium ions.Cr-（3＋）-induced opening of the rhodamine spirocycle in sensor（1） led to the distinct colorimetric and fluorescence responses.Among all the tested ions,only Cr-（3＋） generated a significant fluorescence enhancement of up to13-fold,which indicated the high selectivity of 1.Sensor（1） was successfully applied in the in vivo fluorescence imaging of Cr-（3＋） in C.elegans.The results provided solid evidences for the future estimation of Cr-（3＋） in environmental applications and tobacco samples.

Synergistic Lewis acid-base sites of ultrathin porous Co_(3)O_(4)nanosheets with enhanced peroxidase-like activity

Surface Lewis acid-base sites in crystal structure may influence the physicochemical properties and the catalytic performances in nanozymes.Understanding the synergistic effect mechanism of Co_(3)O_(4)nanozymes towards substances(3,3’,5,5’-tetramethylbenzidine(TMB)and hydrogen peroxide(H2O2))induced by surface Lewis acid-base sites is important to enhance the efficiency for peroxidase-like reaction.Herein,ultrathin porous Co_(3)O_(4)nanosheets with abundant Lewis acid-base sites were prepared by sodium borohydride(NaBH4)reduction treatment,which exhibited high-efficiency peroxidase-like activity compared with original Co_(3)O_(4)nanosheets.The Lewis acid-base sites for ultrathin porous Co_(3)O_(4)nanosheets nanozyme were owing to the coordination unsaturation of Co ions and the formation of defect structure.Ultrathin porous Co_(3)O_(4)nanosheets had 18.26-fold higher catalytic efficiency(1.27×10^(-2)s^(-1)·mM^(-1))than that of original Co_(3)O_(4)(6.95×10^(-4)s^(-1)·mM^(-1))in oxidizing TMB substrate.The synergistic effect of surface acid and base sites can enhance the interfacial electron transfer process of Co_(3)O_(4)nanosheets,which can be a favor of absorption substrates and the generation of reactive intermediates such as radicals.Furthermore,the limit of detection of hydroquinol was 0.58μM for ultrathin porous Co_(3)O_(4)nanosheets,965-fold lower than original Co_(3)O_(4)(560μM).Besides,the linear range of ultrathin porous Co_(3)O_(4)nanosheets was widely with the concentration of 5.0-1,000μM.Colorimetric detection of hydroquinol by agarose-based hydrogel membrane was provided based on excellent peroxidase-like properties.This study provided insights into designing high-performance nanozymes for peroxidase-like catalysis via a strategy of solid surface acid-base sites engineering.

Functional photonic structures for external interaction with flexible/ wearable devices

In addition to vital functions,more subsidiary functions are being expected from wearable devices.The wearable technology thus far has achieved the ability to maintain homeostasis by continuously monitoring physiological signals.The quality of life improves if,through further developments of wearable devices to detect,announce,and even control unperceptive or noxious signals from the environment.Soft materials based on photonic engineering can fulfil the abovementioned functions.Due to the flexibility and zero-power operation of such materials,they can be applied to conventional wearables without affecting existing functions.The achievements to freely tailoring a broad range of electromagnetic waves have encouraged the development of wearable systems for independent recognition/manipulation of light,pollution,chemicals,viruses and heat.Herein,the role that photonic engineering on a flexible platform plays in detecting or reacting to environmental changes is reviewed in terms of material selection,structural design,and regulation mechanisms from the ultraviolet to infrared spectral regions.Moreover,issues emerging with the evolution of the wearable technology,such as Joule heating,battery durability,and user privacy,and the potential solution strategies are discussed.This article provides a systematic review of current progress in wearable devices based on photonic structures as well as an overview of possible ubiquitous advances and their applications,providing diachronic perspectives and future outlook on the rapidly growing research field of wearable technology.