One stone two birds:electrochemical and colorimetric dual-mode biosensor based on copper peroxide/covalent organic framework nanocomposite for ultrasensentive norovirus detection

Norovirus(NoV)is regarded as one of the most common causes of foodborne diarrhea in the world.It is urgent to identify the pathogenic microorganism of the diarrhea in short time.In this work,we developed an electrochemical and colorimetric dual-mode detection for NoV based on the excellent dual catalytic properties of copper peroxide/COF-NH_(2)nanocomposite(CuO_(2)@COF-NH_(2)).For the colorimetric detection,NoV can be directly detected by the naked eye based on CuO_(2)@COF-NH_(2)as a laccase-like nonazyme using“peptide-NoV-antibody”recognition mode.The colorimetric assay displayed a wide and quality linear detection range from 1 copy/mL to 5000 copies/mL of NoV with a low limit of detection(LOD)of 0.125 copy/mL.For the electrochemical detection of NoV,CuO_(2)@COF-NH_(2)showed an oxidation peak of copper ion from Cu^(+)to Cu^(2+)using“peptide-NoV-antibody”recognition mode.The electrochemical assay showed a linear detection range was 1-5000 copies/mL with a LOD of 0.152 copy/mL.It's worthy to note that this assay does not need other electrical signal molecule,which provide the stable and sensitive electrochemial detection for NoV.The electrochemical and colorimetric dual-mode detection was used to detect NoV in foods and faceal samples,which has the potential for improving food safety and diagnosing of NoV-infected diarrhea.

Electrochemical and colorimetric dual-signal detection of Staphylococcus aureus enterotoxin B based on AuPt bimetallic nanoparticles loaded Fe-N-C single atom nanocomposite

Sensitive detection of Staphylococcus aureus enterotoxin B(SEB)is of importance for preventing food poisoning from threatening human health.In this work,an electrochemical and colorimetric dual-signal detection assay of SEB was developed.The probe(Ab2/AuPt@Fe-N-C)was bound to SEB captured by Ab1,where the Ab2/AuPt@Fe-N-C triggered methylene blue degradation and resulted in the decrease of electrochemical signal.Furthermore,the probe catalyzed the oxidation of 3,3’,5,5’-tetramethyl biphenyl to generate a colorimetric absorbance at 652 nm.Once the target was captured and formed a sandwich-like complex,the color changed from colorless to blue.SEB detection by colorimetric and electrochemical methods showed a linear relationship in the concentration ranges of 0.0002-10.0000 and 0.0005-10.0000 ng/mL,with limits of detection of 0.0667 and 0.1670 pg/mL,respectively.The dual-signal biosensor was successfully used to detect SEB in milk and water samples,which has great potential in toxin detection in food and the environment.

The effects of electrochemical oxidation on in-vivo fluorescence and toxin content in Microcystis aeruginosa culture

The increasing occurrence of cyanobacterial blooms in water bodies is a serious threat to the environment. Efficient in-lake treatment methods for the control of cyanobacteria proliferation are needed, their in-vivo detection to obtain a real-time response to their presence, as well as the information about their physiological state after the applied treatment. In-vivo fluorescence measurements of photosynthetic pigments have proved to be effective for quantitative and qualitative detection of phytoplankton in a water environment. In the experiment, chlorophyll and phycocyanin fluorescence sensors were used concurrently to detect stress caused by electrochemical oxidation applying an electrolytic cell equipped with borondoped diamond electrodes on a laboratory culture of cyanobacteria Microcystis aeruginosa PCC 7806. The inflicted injuries were reflected in a clear transient increase in the phycocyanin fluorescence signal(for 104 %? 43%) 24 h after the treatment, which was not the case for the chlorophyll fluorescence signal. In the next 72 h of observation, the fluorescence signals decreased(on 40% of the starting signal) indicating a reduction of cell number, which was confirmed by cell count(24% reduction of the starting concentration) and analysis of extracted chlorophyll and phycocyanin pigment. These results demonstrate the viability of the combined application of two sensors as a useful tool for in-vivo detection of induced stress, providing real-time information needed for the evaluation of the efficiency of the in-lake treatment and decision upon the necessity of its repetition. The electrochemical treatment also resulted in a lower free microcystins concentration compared to control.

Crystal Structure, Electrochemical and Fluorescent Properties of a New Copper(Ⅱ) Coordination Polymer with 2,3-Pyridinedi-carboxylic Acid

A new copper(Ⅱ)coordination polymer[Cu5(Hpt)5(H2O)2(2,3-PCA)2]n·12nH2O(1)has been successfully synthesized under hydrothermal conditions with copper hydroxide,3-(pyridin-2-yl)-1,2,4-triazole(Hpt)and 2,3-pyridinedi-carboxylic acid(2,3-PCA).The structure of the title compound was determined by X-ray diffraction analyses,elemental analyses and IR spectrum.The architecture of 1 consists of one-dimensional sandwich-like chains which are connected by extensive hydrogen bonding interactions.The solid-state photoluminescence displays an obvious emission band at 384 nm upon excitation at 340 nm.In addition,electrochemistry property has also been studied.

Crystal Structure,Electrochemical and Fluorescent Properties of a New Cadmium(II) Complex[Cd(C_(12)H_6O_4N_2)(Phen)_2(H_2O)]·3H_2O

A new Cd（II） complex [Cd（C12H6OaN2）（Phen）ffH2O）]＇3H2O with 2,2＂-bipyridine- 3,3＂-dicarboxylic acid as a ligand has been synthesized. Crystal data for the title complex are as follows： monoclinic, space group P2dn, a = 12.8458（5）, b = 17.9131（7）, c = 15.2960（6） A, β = 111.7430（10）°, V = 3269.3（2） A3, Dc = 1.581 g/cm3, Z = 4,/a（MoKa） = 0.731 mm-1, F（000） = 1580, the R = 0.0244 and wR = 0.0605. In the title complex, the central Cd（ll） ion is located in a distorted octahedral coordination environment. The electrochemical and fluorescent properties of the title complex were studied. The results show that the electron transfer of the title complex is irreversible in the electrode reaction and it has a broad emission peak in the range of 470-508 nm with the excitation wavelength of 488 nm.

Crystal Structure and Electrochemical, Fluorescent and Magnetic Properties of a New Complex [Ag(2,2ˊ-bipy)(C_(14)H_9O_3)]·(C_(14)H_(10)O_3)

A novel silver（I） complex [Ag（2,2ˊ-bipy）（C14H9O3）]·（C14H10O3） has been synthesized with 2-benzoylbenzoic acid as the ligand. Crystal data for the title complex： monoclinic, space group Cc, a = 27.4089（13）, b = 10.2897（5）, c = 12.0024（6）A, β = 111.864（4）°, Mr = 715.49, V = 3141.5（3） A3, Dc = 1.513 g/cm^3, Z = 4, μ（Mo Kα） = 0.694 mm^-1, F（000） = 1456, the final R = 0.0473 and w R = 0.1146. In the title complex, the central Ag（I） ion is located in a triangular coordination environment. The electron transfer is quasi-reversible in the electrode reaction and it shows a strong emission peak in the range of 495-520 nm under 502 nm excitation. In addition, it displays diamagnetic property from 3 to 300 K.

Multifunctional Ce-MOF@PdNPs with colorimetric fluorescent electrochemical activity for ultrasensitive and accurate detection of diethylstilbestrol

The development of biosensors is gaining tremendous attention in various fields due to their extraordinary advantages, however, their sensitivity and accuracy are still challenging. Herein, we proposed a novel multifunctional nanocomposite Ce-MOF@PdNPs (MOF = metal-organic framework, PdNPs = Pd nanoparticles)-mediated triple-readout aptasensor for accurate and reliable detection of diethylstilbestrol (DES), in which Ce-MOF@PdNPs exhibited excellent peroxidase (POD)-like activity, fluormetric, and electro conductive properties. In addition, enzymes-assisted target recycling amplification was utilized to improve the sensitivity, that is the specific binding of aptamer and DES triggered an Exo III enzyme-assisted recycling reaction. The generated F-DNA was captured by the H3 strand linked to Ce-MOF@PdNPs immobilized on the electrode, exposing cleavage sites and activating the Nt.BbvCI enzyme-assisted recycling reaction, leading to the dissociation of Ce-MOF@PdNPs and a significant reduced electrochemical signal. The collected Ce-MOF@PdNPs solution also induced a proportional change in the color and fluorescence, achieving a colorimetric and fluormetric detection functionality. The detection limit under colorimetric mode was 0.16 and 0.76 ng/mL under fluorescence mode, and 0.87 pg/mL under electrochemical mode. This triple-readout aptasensor exhibits high sensitivity, selectivity and accuracy, providing a new idea for designing novel biosensing platforms for veterinary drug residue detection.

Electrochemical, Photophysical, and Magnetic Properties of Green Emitting bis(2,5-Hexyloxy)-Phenylene-<i>alt</i>-Thiophene Fluorescent Conducting Oligomer Addended Fullerene-Diol Dyad

Towards the development of potential new organic photovoltaic and optoelectronic materials, a simple route to synthesize flexibly ether linked fullerene-bis[oligo-(phenylene-alt-thiophene)] and evaluation of electrochemical, photophysical and magnetic properties is presented. Flexible ether linking of oligo-phenylene-thiophene chain to 1, 2 C60(OH)2 is achieved employing Williamson’s ether synthesis. 7-chain phenylene-thiophene chain fluorescent conducting oligomer is synthesized using Grignard coupling reaction with preservation of bromo end groups. Oligomer is highly ordered and soluble in all organic solvents while on linking to fullerene-diol, solubility of adduct restricts only to dimethyl sulfoxide (DMSO). All the synthesized materials are characterized through spectroscopic techniques and molecular weight is determined by mass spectrometry and GPC. Properties of the material indicate the substantial effect of fullerene. High quenching in fluorescence intensity and strong paramagnetic property are observed in this material.

Recent advances in fluorescent and colorimetric sensing for volatile organic amines and biogenic amines in food

Volatile organic amines and biogenic amines produced by the amino acid degradation can undeniably affect the food quality and safety,and thus causes serious health problems.It is of great urgency to exploit reliable and sensitive detection methods for amines to ensure food safety and public health.The fluorescent and colorimetric sensors offer simple and robust means to monitor amines with high sensitivity and selectivity,quick response,facile operation and low cost.Herein,we briefly review the past five years’progress in fluorescent and colorimetric sensing for monitoring organic and biogenic amines in food.The architectures of sensing materials ranging from small molecules to frameworks to polymers or self-assembly materials have been highlighted.Moreover,the main challenges and perspective of various sensing materials are presented to inspire further research and development.In the end,the development trend of new sensing materials and devices for real-time monitoring of food quality is also forecasted.This review is expected spur more research interest in design of novel amine sensing materials for future application transformation research.

Development of a Label-Free Colorimetric Aptasensor with Rationally Utilized Aptamer for Rapid Detection of Okadaic Acid

Okadaic acid(OA)is a typical marine toxin with strong toxicity causing diarrheic shellfish poisoning(DSP).Aptamers show great advantages in toxin detection and attract increasing attentions in the field of food analysis.In this study,a label-free col-orimetric aptasensor was constructed for visual and rapid detection of OA in shellfish.To exploit the binding capability of the anti-OA aptamer,the inherent molecular recognition mechanism of aptamer and OA was studied,based on molecular docking,fluorescent assay,and biolayer interferometry.Consistent results showed that the stem-loop near the 3’terminal of the aptamer exhibit dominate binding capacity.Based on the revealed recognition information,the aptamer was thus rationally utilized and combined with AuNPs and cationic polymer polydiallyl dimethyl ammonium chloride(PDDA)for the development of the label-free colorimetric aptasensor,in which the 3’terminal was thoroughly exposed to OA.The aptasensor provided robust performance with a linear detection range of 100-1200 nmol L-1,a limit of detection of 41.30 nmol L-1,recovery rates of 91.6%-106.2%,as well as a high selectivity towards OA in shellfish samples.The whole detection process can be completed within 1 h.To our best knowledge,this is the first time that the anti-OA aptamer was thoroughly studied,and a label-free colorimetric aptasensor was rationally designed in this way.This study not only provides a rapid detection method for highly sensitive and specific detection of OA,but also serves as a reference for the design of efficient aptasensors in the future.

ELECTROCHEMICAL COPOLYMERIZATION OF DIBENZOFURAN AND 3-METHYLTHIOPHENE IN BORON TRIFLUORIDE DIETHYL ETHERATE

The copolymerization of dibenzofuran(DBF)and 3-methylthiophene(MET)was successfully achieved electrochemically by direct anodic oxidation of the monomer mixtures in boron trifluoride diethyl etherate.The effects of applied polymerization potential and the monomer concentration ratios on the copolymerization were investigated by linear sweep voltammetry and cyclic voltammetry(CV).The structure of copolymer films were investigated by UV-Vis,infrared spectroscopy,thermal analysis.As-formed novel copolymers own...

Nanocellulose-Based Biosensors: Design, Preparation, and Activity of Peptide-Linked Cotton Cellulose Nanocrystals Having Fluorimetric and Colorimetric Elastase Detection Sensitivity

Nanocrystalline cellulose is an amphiphilic, high surface area material that can be easily functionalized and is biocompatible and eco-friendly. It has been used singularly and in combination with other nanomaterials to optimize biosensor design. The attachment of peptides and proteins to nanocrystalline cellulose and their proven retention of activity provide a route to bioactive conjugates useful in designs for point of care biosensors. Elastase is a biomarker for a number of inflammatory diseases including chronic wounds, and its rapid sensitive detection with a facile approach to sensing is of interest. An increased interest in the use of elastase sensors for point of care diagnosis is resulting in a variety of approaches to elsastase sensors utilizing different detection technologies. Here elastase substrate peptide-celluose conjugates synthesized as colorimetric and fluorescent sensors on cotton cellulose nanocrystals are compared. The structure of the sensor peptide-nanocellulose crystals when modeled with computational crystal structure parameters demonstrates the spatio-stoichiometric features of the nanocrystalline surface that allows ligand to active site protease interacttion. An understanding of the structure/function relations of enzyme and conjugate substrate of the peptides covalently attached to nancellulose has implications for enhancing the biomolecular transducer. The potential applications of both fluorescent and colorimetric detection to markers like elastase using peptide cotton cellulose nanocrystals as a transducer surface to model point of care biosensors for protease detection are discussed.

Advances on ultra-sensitive electrospun nanostructured electrochemical and colori metric sensors for diabetes mellitus detection

Recent developments in the biochemical and medicinal industries have been heavily focused on producing affordable glucose biosensors due to the condi nuous annual increase of diabetic patients worldwide.The devel-opment of a fast,accurate,and reliable glucose sensor will increase confidence in controlling di abetes mellitus and its assoclated health complications among the diabetic community.Electraspinning is a versatile method that can produce complex nanofbrous assemblies with attractiwe and functional characteristics from varlous polymers.Electrospun nanofibers demonstrated high efficiency in the immobilization of biological molecules,which can improve the sensing performance further.Integr ation of polymer electrospun nanofibers with metal nanoparticles,metal oxde or transition metal in producing nanobiocomposites is also a highly popul ar approach in the past few years.This report presents the current progress and research trends of the technique,focusing on varous ma-terials and fabrication strategies used to produce biosensing interfaces.This helps readers decide the suitable approach in designing highly sensitive,selective,fast,and inexpensive glucose sensors.

Determination of hydroxyl radical in organic wastewater treatment by electrochemical oxidation

A method of detection hydroxyl radical （ · OH） produced by electrochemical oxidation in organic wastewater treatment was developed. Benzoic acid with weak fluorescence may reacted with hydroxyl radical to produce 3-hydroxybenzonic acid with intense fluorescence, whose characteristic fluorescence excitation and e- mission wavelength were at 305 nm and 410 nm. The 3-hydroxybenzonic acid was separated from electroehenaical oxidation system by HPLC. Two major hydroxylated products were quantified corresponding to 3-hydroxybenzonic, 4-hydroxybenzonic acid. Therefore the quantity of hydroxyl radical in the reactive system should be primarily calculated. The optimal experimental program was obtained by studying the determination conditions, which were benzoic acid of 1.0 mmol/L, electrolysis time of 60 min, current density of 39 mA/cm^2 , supporting electrolyte （Na2SO4 ） of 0. 02 mol/L, and the low rate of sparged-air of 25 mL/s. The results show that this method is stable, sinaple and rapid and can be used as a convenient method for the determination of hydroxyl radical.

Quick Fluorescence Method for the Distinguishing of Vegetable Oils

This paper presents the possibilities offered by fluorescence spectroscopy for the identification of vegetable oils such as soybean, sunflower, flax, walnut, corn, almond, sesame, olive and pumpkin oils. The probes under study have been excited with two types of sources： a laser diode （LD） and light-emitting diodes （LEDs） emitting in the UV and in the visible range. Total luminescence spectra were recorded by measuring the emission spectra in the range 350-720 nm at excitation wavelengths from 375 to 450 nm. The excitation-emission matrices have been obtained and two basic fluorescence regions in the visible have been outlined. On this basis the fluorescence spectra of the oils have been subdivided into three categories depending on the prevalence of the fluorescence maxima. The samples show differences in their fluorescence spectra. The latter fact shows that fluorescence spectroscopy can be used for the quick identification of edible oils. The fatty acid, the tocopherol, the beta-carotene and chlorophyll contents in the analyzed oils have been studied. It is shown that some of the types of oils differ significantly from each other by the first derivatives of their fluorescence spectra. There also exist color differences between the groups of vegetable oils under study.

A New Coumarin-Based Fluorescent pH Probe

A new iminocoumarin-derived colorimetric and fluorescent pH probe was developed for rapid and sensitive detection of pH changes in biological and environmental media. With the decrease of pH value( from 6. 24 to 3. 00),an obvious color change of the probe in ethanol-water solution from green to yellow was observed under nature light. The intensity of the maximum fluorescence emission peak of the probe decreased gradually with the acidity increase of the solution. While the fluorescence intensity of the emission peak of the probe did not exhibit distinct change when pH was less than 11. 00 and the fluorescence was almost quenched at pH 13. 50. Sensitivity of the fluorescent pH probe was not interfered by the presence of common metal cations and anions.

Colorimetric and electrochemical detection of ligase through ligation reaction-induced streptavidin assembly

We propose a concept for ligase detection by conversion of aggregation-based homogeneous analysis into surface-tethered electrochemical assay through streptavidin(SA)-biotin interaction.Sortase A(Srt A)served as the model analyte and two biotinylated peptides(bio-LPETGG and GGGK-bio)were used as the substrates.Srt A-catalyzed ligation of the peptide substrates led to the generation of bio-LPETGGGKbio.The ligation product(bio-LPETGGGK-bio)induced the aggregation and color change of SA-modified gold nanoparticles(Au NPs)through the SA-biotin interactions,which could be assayed by the colorimetric method.Furthermore,we found that the bio-LPETGGGK-bio could trigger the assembly of tetrameric SA proteins with the formation of the(SA-bio-LPETGGGK-bio)nassemblies through the same interactions.The above results were further confirmed by atomic force microscopy and fluorescent imaging.The insulated assemblies were in-situ fabricated at the SA-modified gold electrode,thus hindering the electron transfer of[Fe(CN)_(6)]^(3-/4-) and leading to an increase in the electron-transfer resistance.The capability of the method for the detection of Srt A both in vitro and Staphylococcus aureus(S.aureus)has been demonstrated.Srt A with a concentration down to 1 pmol/L has been determined by the electrochemical analysis,which is lower than that achieved by the colorimetric assay(50 pmol/L).By integrating the advantages of homogeneous reaction and heterogeneous detection,the strategy serves as an ideal means for the fabrication of various sensing platforms by adopting biotin-labeled and sequence-specific peptide or nucleic acid substrates.

Response of indigenous Cd-tolerant electrochemically active bacteria in MECs toward exotic Cr（VI） based on the sensing of fluorescence probes

Electrochemically active bacteria （EAB） on the cathodes of microbial electrolysis cells （MECs） can remove metals from the catholyte, but the response of these indigenous EAB toward exotic metals has not been examined, particularly from the perspective of the co-presence of Cd（II） and Cr（VI） in a wastewater. Four known indigenous Cd-tolerant EAB of Ochrobactrum sp X l, Pseudomonas sp X3, Pseudomonas delhiensis X5, and Ochrobactrum anthropi X7 removed more Cd（II） and less Cr（VI） in the simultaneous presence of Cd（II） and Cr（VI）, compared to the controls with individual Cd（II） or single Cr（VI）. Response of these EAB toward exotic Cr（VI） was related to the associated subcellular metal distribution based on the sensing of fluorescence probes. EAB cell membrane harbored more cadmium than chromium and cytoplasm located more chromium than cadmium, among which the imaging ofintracelluler Cr（III） ions increased over time, contrary to the decreased trend for Cd（II） ions. Compared to the controls with single Cd（II）, exotic Cr（VI） decreased the imaging of Cd（II） ions in the EAB at an initial 2 h and negligibly affected therealier. However, Cd（II） diminished the imaging of Cr （III） ions in the EAB over time, compared to the controls with individual Cr（VI）. Current accelerated the harboring of cadmium at an initial 2 h and directed the accumulation of chromium in EAB over time. This study provides a viable approach for simultaneously quantitatively imaging Cd（II） and Cr （III） ions in EAB and thus gives valuable insights into the response of indigenous Cd-tolerant EAB toward exotic Cr（VI） in MECs.

Novel colorimetric,photothermal and up-conversion fluorescence triple-signal sensor for rosmarinic acid detection

Rosmarinic acid(RA)is promising as a natural and nontoxic food additive.However,many analysis methods for RA generally depend on large instruments and single signals for quantitative detection.A new upconversion fluorescence,colorimetric and photothermal multi-modal sensing strategy is developed for the quantification of RA.β-cyclodextrin(CD)modified citric acid(Cit)wrapped NaYF_(4):Yb/Er-Cit-CD(Y:Yb/Er-Cit-CD)up-conversion nanocomposite has been synthesized,which emits green fluorescence at 550nm under 980nm near-infrared(NIR)excitation.In the presence of oxidized 3,3',5,5'-tetramethylbenzidine(oxTMB),the green fluorescence is significantly quenched attributed to the fluorescence inner filter effect(IFE)between oxTMB and Y:Yb/Er-Cit-CD.When RA is intervened,blue oxTMB is reduced to colorless 3,3',5,5'-tetramethylbenzidine(TMB)inducing the recovery of up-conversion fluorescence.At the same time,colorimetric and photothermal signals readout can be easily achieved thanks to the color indication and photothermal effect of the oxTMB.The constructed Y:Yb/Er-Cit-CD/oxTMB sensor displays high sensitivity,visibility and simplicity for RA,and the limits of detection(LOD)for fluorescence,colorimetric and photothermal were 0.004μmol/L,0.036μmol/L and 0.043μmol/L,respectively.This sensing system is successfully performed for the detection of RA in food samples.

Fluorescent Chemosensing Properties of New Isoindoline Based-Receptors towards F^-and Cu²⁺Ions

Two simple colorimetric and fluorescent anion chemosensors based on amide moieties, 4-nitro-N-[(1,3-dioxoisoindolin-2yl)benzamide (1), 3,5-dinitro-N-[(1,3-dioxoisoindolin-2yl)benzamide (2) have been synthesized and characterized. Comparing with other anions studied, the UV-visible absorption spectrum in DMSO shows significant response toward F- ion with high selectivity, and meanwhile color change is observed from colorless to pink and violet for 1 and 2 respectively in the presence of tetrabutylammonium fluoride (TBAF) (5 × 10-3 M). Moreover, F--induced color changes remain the same even in the large excess of Cl- , Br- and I-. In addition, the 1H NMR spectrum titration in DMSO-d6 shows deprotonation of the receptors 1 and 2 in the presence of basic F- ion. In particular, addition of F- to the receptors 1 and 2 resulted in an enhancement in fluorescence intensity at 770 nm. Both receptors 1 and 2 exhibit a fluorescent emission enhancement when addition of Zn2+, Ni2+, Co2+, Cu2+ and Mn2+ metal ions. The fluorescent enhancement values for the receptor 1 are 2.29 (Cu2+), 1.85 (Ni2+), 1.37 (Co2+), 1.27 (Mn2+), 1.25 (Zn2+) and for 2, 2.57 (Cu2+), 1.66 (Ni2+), 1.36 (Co2+), 1.15 (Mn2+), 1.09 (Zn2+). The selectivity of Cu2+ is higher for 1 and 2 than other metal ions such as Zn2+, Ni2+, Co2+ and Mn2+.