A novel fluorescence sensor for milk clotting enzyme chymosin using peptide as substrate and covalent organic framework nanosheet as fluorescence quencher

Chymosin is one of the critical enzymes in cheese making.Herein,we proposed a novel fluorometric assay for chymosin determination.Firstly,covalent organic frameworks(COF)were synthesized and exfoliated to 2-dimensional COF nanosheets(COF NS)by ultrasound treatment.Gold nanoparticles(Au NPs)were loaded with COF NS to prepare AuNPs/COF NS(Au@COF NS).Secondly,rhodamine B(RhB)modified substrate peptide(Pep)for chymosin was linked with Au@COF NS to construct a Pep-Au@COF NS nanocomposite.For the sensing principle,fluorescence of RhB was quenched by Au@COF NS and the fluorescence intensity was weak due to the fluorescence resonance energy transfer between COF NS and RhB of Pep.However,in the presence of chymosin,the RhB was released by specific cleavage of the substrate peptide by chymosin and resulted in the recovery of fluorescence.The increased fluorescence intensity was proportional to the increase of chymosin concentration and thus a“turn on”fluorescent sensor for chymosin was constructed.The sensor showed a linear range in the concentration of 0.05-60.00μg/mL for the detection of chymosin with a detection limit of 20 ng/mL.The sensor was used to quantify chymosin in rennet product with good selectivity,which has the potential applications in cheese manufacturing.

Isomeric fluorescence sensors for wide range detection of ionizing radiations

In order to achieve a wider range of ionizing radiations detection,novel fluorescence sensing materials have been developed that utilize the fluorescence enhancement phenomenon caused by the intramolecular photoinduced electron transfer(PET)effect.Two perylene diimide isomers PDI-P and PDI-B were designed and synthesized,and their molecular structures were characterized by high-resolution Fourier transform mass spectrometry(HRMS),nuclear magnetic resonance hydrogen and carbon spectroscopy(~1H and~(13)C NMR).The interaction between ionizing radiation and fluorescent molecules was simulated by HCl titration.The results show that combining PDIs and HCl can improve fluorescence through the retro-PET process.Despite the similarities in chemical structures,the fluorescent enhancement multiple of PDI-B with aromatic amine as electron donor is much higher than that of PDI-P with alkyl amine.In the direct irradiation experiments of ionizing radiation,the emission enhancement multiples of PDI-P and PDI-B are 2.01 and 45.4,respectively.Furthermore,density functional theory(DFT)and time-dependent density functional theory(TDDFT)calculations indicate that the HOMO and HOMO-1 energy ranges of PDI-P and PDI-B are 0.54 e V and 1.13 e V,respectively.A wider energy range has a stronger driving force on electrons,which is conducive to fluorescence quenching.Both femtosecond transient absorption spectroscopy(fs-TAS)and transient fluorescence spectroscopy(TFS)tests show that PDI-B has shorter charge separation lifetime and higher electron transfer rate constant.Although both isomers can significantly reduce LOD during PET process,PDI-B with aromatic amine has a wider detection range of 0.118—240 Gy due to its larger emission enhancement,which is a leap of three orders of magnitude.It breaks through the detection range of gamma radiation reported in existing studies,and provides theoretical support for the further study of sensitive and effective new materials for ionizing radiation detection.

Benzo[4,5]imidazo[1,2-a]pyrimidine-based structure-inherent targeting fluorescent sensor for imaging lysosomal viscosity and diagnosis of lysosomal storage disorders

Benzo[4,5]imidazo[1,2-a]pyrimidine-based derivatives play crucial roles in medicines,pesticides,tracers and photoelectric materials.However,their synthesis approach still needs to be optimized,and their fluorescent properties in intracellular microenvironment are unclear.Here,a Cu(II)-catalyzed cascade coupling cyclization reaction was successfully developed to synthesize benzo[4,5]imidazo[1,2-a]pyrimidine scaffold with mild reaction conditions,broad substrate scopes and high yields.After a system study,we found that compound 4aa displayed an optimal viscosity-specific response with remarkable fluorescence enhancement(102-fold)for glycerol at 490 nm.Particularly,4aa possessed excellent structure-inherent targeting(SIT)capability for lysosome(P=0.95)with high p H stability and large Stokes shift.Importantly,4aa was validated for its effectiveness in diagnosing lysosomal storage disorders(LSD)in living cells.The 4aa also showed its potential to map the micro-viscosity and its metabolism process in zebrafish.This work not only affords an efficient protocol to fabricate benzo[4,5]imidazo[1,2-a]pyrimidine derivatives,reveals this skeleton has excellent SIT features for lysosome,but also manifests that 4aa can serve as a practical tool to monitor lysosomal viscosity and diagnose LSD.

CdTe quantum dots as fluorescence sensor for the determination of vitamin B6 in aqueous solution

A novel, rapid and simple CdTe quantum dots （QDs） based technology platform was established for selective and sensitive determination of vitamin B6 in aqueous solution. It can perform accurate and reproducible quantification of vitamin B6 in pharmaceutical with satisfactory results.

Highly sensitive ratiometric fluorescent fiber matrices for oxygen sensing with micrometer spatial resolution

Oxygen(O_(2))-sensing matrices are promising tools for the live monitoring of extracellular O_(2) consumption levels in long-term cell cultures.In this study,ratiometric O_(2)-sensing membranes were prepared by electrospinning,an easy,low-cost,scalable,and robust method for fabricating nanofibers.Poly(ε-caprolactone)and poly(dimethyl)siloxane polymers were blended with tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II)dichloride,which was used as the O_(2)-sensing probe,and rhodamine B isothiocyanate,which was used as the reference dye.The functionalized scaffolds were morphologically characterized by scanning electron microscopy,and their physicochemical profiles were obtained by Fourier transform infrared spectroscopy,thermogravimetric analysis,and water contact angle measurement.The sensing capabilities were investigated by confocal laser scanning microscopy,performing photobleaching,reversibility,and calibration curve studies toward different dissolved O_(2)(DO)concentrations.Electrospun sensing nanofibers showed a high response to changes in DO concentrations in the physiological-pathological range from 0.5%to 20%and good stability under ratiometric imaging.In addition,the sensing systems were highly biocompatible for cell growth promoting adhesiveness and growth of three cancer cell lines,namely metastatic melanoma cell line SK-MEL2,breast cancer cell line MCF-7,and pancreatic ductal adenocarcinoma cell line Panc-1,thus recreating a suitable biological environment in vitro.These O_(2)-sensing biomaterials can potentially measure alterations in cell metabolism caused by changes in ambient O_(2)content during drug testing/validation and tissue regeneration processes.

Elemental composition x-ray fluorescence analysis with a TES-based high-resolution x-ray spectrometer

The accurate analysis of the elemental composition plays a crucial role in the research of functional materials.The emitting characteristic x-ray fluorescence(XRF)photons can be used for precisely discriminating the specified element.The detection accuracy of conventional XRF methodology using semiconductor detector is limited by the energy resolution,thus posing a challenge in accurately scaling the actual energy of each XRF photon.We adopt a novel high-resolution x-ray spectrometer based on the superconducting transition-edge sensor(TES)for the XRF spectroscopy measurement of different elements.Properties including high energy resolution,high detection efficiency and precise linearity of the new spectrometer will bring significant benefits in analyzing elemental composition via XRF.In this paper,we study the Ledge emission line profiles of three adjacent rare earth elements with the evenly mixed sample of their oxide components:terbium,dysprosium and holmium.Two orders of magnitude better energy resolution are obtained compared to a commercial silicon drift detector.With this TES-based spectrometer,the spectral lines overlapped or interfered by background can be clearly distinguished,thus making the chemical component analysis more accurate and quantitative.A database of coefficient values for the line strength of the spectrum can then be constructed thereafter.Equipped with the novel XRF spectrometer and an established coefficient database,a direct analysis of the composition proportion of a certain element in an unknown sample can be achieved with high accuracy.

Palladium nanoparticles/wool keratin-assisted carbon composite-modified flexible and disposable electrochemical solid-state pH sensor

Several p H-dependent processes and reactions take place in the human body;hence,the p H of body fluids is the best indicator of disturbed health conditions.However,accurate and real-time diagnosis of the p H of body fluids is complicated because of limited commercially available p H sensors.Hence,we aimed to prepare a flexible,transparent,disposable,userfriendly,and economic strip-based solid-state p H sensor using palladium nanoparticles(Pd NPs)/N-doped carbon(NC)composite material.The Pd NPs/NC composite material was synthesized using wool keratin(WK)as a precursor.The insitu prepared Pd NPs played a key role in the controlled switching of protein structure to the N-doped carbon skeleton withπ–πarrangement at the mesoscale level,which mimics the A–B type polymeric structure,and hence,is highly susceptible to H+ions.The optimized carbonization condition in the presence of Pd NPs showed that the material obtained using a modified Ag/Ag Cl reference electrode had the highest p H sensitivity with excellent stability and durability.The optimized p H sensor showed high specificity and selectivity with a sensitivity of 55 m V/p H unit and a relative standard deviation of 0.79%.This study is the first to synthesize Pd NPs using WK as a stabilizing and reducing agent.The applicability of the sensor was investigated for biological samples,namely,saliva and gastric juices.The proposed protocol and material have implications in solid-state chemistry,where biological material will be the best choice for the synthesis of materials with anticipated performance.

Anthracylmethyl Benzoazacrown Ether as Selective Fluorescence Sensors for Zn^(2+)

A new benzoazacrown ether fluorescence sensor was synthesized with 9-anthrylmethyl chloride and benzoaza-15-crown-5 in CH3CN, which particularly shows a strong affinity for Zn2+. Its fluorescence quantum yield increase more than one order of magnitude and a red shift could be noticed when passing from the apolar to the polar solvent.

Terpyridine-derived Zn^(2+) Selective Fluorescence Sensor: Ratiometric Fluoroionophoric Behavior Study

A sensitive and selective zinc ion ratiometric fluorescence sensor has been synthesized and characterized. This material displays dual fluorescence. After the material was bonded to a closed-shell metal ion, such as Zn2＋, the recovery of the local excited fluorescence of the material-Zn2＋ complex, largely at the expense of the intramolecular charge transfer fluorescence, is consistent with the difference between selected orbital transitions of the free dye and the metal-chelated complex. For instance, the contribution of the πtpy→πtpy, transition becomes more prominent. This is also consistent with the results of the fluorescence decay behavior, measured via a time-correlated single photon counting setup. In contrast, the corresponding open shell Ni2＋ -bound complex quenches both kinds of photoluminescence, due to spin-orbit coupling.

A Fluorescence Optical Fiber Sensor for Amrinon Using a New Oxazole Compound

A new oxazole compound, 1,4 bis(naphtho[1,2 d][1,3]oxazol 2 yl)benzene(BNOB) was synthesized and incorporated into a thin plasticized polymeric membrane for sensing Amrinon. The sensor exhibits a linear response to Amrinon in the range of 7 98×10 -7 —1 52×10 -4 mol/L at pH 3 28—4 04. The response mainly originates from the Primary Inner Filter Effect, which causes a decrease in the fluorescence intensity of the sensor membrane. The distinct advantages of the proposed sensor are of full reversibility, high sensitivity and selectivity as well as short response time(<1 min), indicating that the sensor can be used to monitor Amrinon in serum samples.

Isolated Solid-State Packaging Technology of High-Temperature Pressure Sensor

The principle of miniature isolated solid-state encapsulation technology of high-temperature pressure sensor and the structure of packaging are discussed, including static electricity bonding, stainless steel diaphragm selection and rippled design, laser welding, silicon oil infilling, isolation and other techniques used in sensor packaging, which can affect the performance of the sensor. By adopting stainless steel diaphragm and high-temperature silicon oil as isolation materials, not only the encapsulation of the sensor is as small as 15 mm in diameter and under 1 mA drive, its full range output is 72 mV and zero stability is 0.48% F.S/mon, but also the reliability of the sensor is improved and its application is widely broadened.

A selective optical chemical sensor for the determination of iodine based on fluorescence quenching of LiTOE

An optical chemical sensor has been developed for the determination of iodine based on the reversible fluorescence quenching of 2, 2, 7, 7, 12, 12, 17, 17-octamethyl-21, 22, 23, 24-tetraoxaquaterene-Li （LiTOE） immobilized in a plasticized poly（vinyl chloride） （PVC） membrane. The optimum membrane of the sensor consists of 100 mg of PVC, 200 mg of bis （2-ethytbexyl） sebacate （BOS） and 3.0 mg of LiTOE. The maximum response of the optode membrane for iodine is obtained in Tris-HCl buffer solutlon （pH 8.0）. With the optimum conditions described, the proposed sensor responds linearly in the measuring range of 3.90×10^-2 to 3.90×10^-4 mol/L, and has a detection limit of 6.0×10^-8 mol/L. The response time of the sensor is less than I rain. In addition to high reproducibility and reversibility of the fluorescence signal, the sensor also exhibits good selectivity. It is not interfered by some common anions and cations. It is applied for the determination of iodine in table salt samples. The results agree with those obtained by another method.

Portable hydrogel-based tri-channel fluorescence sensor array for visual detection of multiple explosives

The identification and detection of various types of explosives are essential for human health and environmental monitoring.Array-based sensing approach offers significant advantages in detecting multi-analytes simultaneously,thereby holding great potential in identifying multiple explosives.Here,we report a tri-channel fluorescence array composed of three distinct fluorescence probes based on gold nanoclusters and nicotinamide adenine dinucleotide with well-separated emission colors.Through the specific interactions of explosives with different fluorescent probes and the yielded response patterns,seven explosives can be successfully distinguished with 100%accuracy.In particular,the sensor array exhibits excellent performance in the quantitative analysis of individual explosive and the differentiation of multiple explosive mixtures.To facilitate the field detection towards practical application,the tri-channel fluorescence array was further integrated with polymer hydrogels.The fabricated portable hydrogel-based array sensors can not only visually identify seven different explosives by their distinct fluorescence color change,but also enable quantitative detection based on linear discriminant analysis(LDA)together with a smartphone.This study illustrates the great potential of hydrogel-based fluorescence sensor array as robust sensors for explosives,which also holds significant promise for the development of portable explosive devices towards practical application.

1-Pyrenecarboxaldehyde thiosemicarbazone:A novel fluorescent molecular sensor towards mercury(Ⅱ) ion

A novel and simple fluorescent molecular sensor,1-pyrenecarboxaldehyde thiosemicarbazone（Hpytsc）,was synthesized.Its higher sensitivity and selectivity to mercury（Ⅱ） ion were studied through absorption and emission channels.The UV-vis spectra show that the increasing mercury（Ⅱ） ion concentrations result in the decreasing absorption intensity.The fluorescence monomer emission of Hpytsc is enhanced upon binding mercury（Ⅱ） ion,which should be due to the 1：1 complex formation between Hpytsc and metal ion.

Carbon Dots as“On–Off–On”Fluorescence Sensors for Selective and Consecutive Detection of 4-Nitrophenol and Cerium(IV)in Water Samples

An“on–off–on”fluorescence sensor was designed for rapidly and consecutively detecting 4-nitrophenol and cerium(IV)without the use of any labeling materials.The yellow carbon dots were synthesized by a simple one-step hydrothermal approach,and various techniques were applied to investigate the morphology,structure,and optical properties of the carbon dots.Under the optimal experimental conditions,4-nitrophenol rapidly quenched the fluorescence of carbon dots as a result of the inner filter eff ect(IFE).The fluorescence intensity of carbon dots was linear with the concentration of 4-nitrophenol(1–150μmol/L)and the limit of detection was 0.32μmol/L.The fluorescence was gradually recovered as the cerium(IV)concentration(0.5–100μmol/L)increased in CDs/4-NP,and the limit of detection was 0.16μmol/L.The sensor showed good selectivity and demonstrated high accuracy for the analysis of 4-nitrophenol and cerium(IV)in actual water samples.

A novel highly selective fluorescent chemosensor for Hg(Ⅱ) in fully aqueous media

A novel fluorescent Hg^2＋ chemosensor based on dithia-dioxa-monoaza crown ether was synthesized in four steps from inexpensive starting materials. This new sensor exhibited very strong fluorescence response to Hg^2＋ （FHg^2＋/Ffree 〉 130） and it was highly selective to Hg^2＋ over the other metal ions by more than 45-fold.

The Recent Advances of Fluorescent Sensors Based on Molecularly Imprinted Fluorescent Nanoparticles for Pharmaceutical Analysis

Fluorescent nanoparticles have good chemical stability and photostability,controllable optical properties and larger stokes shift.In light of their designability and functionability,the fluorescent nanoparticles are widely used as the fluorescent probes for diverse applications.To enhance the sensitivity and selectivity,the combination of the fluorescent nanoparticles with the molecularly imprinted polymer,i.e.molecularly imprinted fluorescent nanoparticles(MIFN),was an effective way.The sensor based on MIFN(the MIFN sensor)could be more compatible with the complex sample matrix,which was especially widely adopted in medical and biological analysis.In this mini-review,the construction method,detective mechanism and types of MIFN sensors are elaborated.The current applications of MIFN sensors in pharmaceutical analysis,including pesticides/herbicide,veterinary drugs/drugs residues and human related proteins,are highlighted based on the literature in the recent three years.Finally,the research prospect and development trend of the MIFN sensor are forecasted.

Real-time in situ visualization of internal relative humidity in fluorescence embedded cement-based materials

The transmission and distribution of moisture in cement-based materials are of great significance to the properties and durability of materials. Traditional macro-humidity monitoring equipment in civil engineering cannot capture the microscale humidity inside cement-based materials in situ. In this paper, a method of using rhodamine 6G fluorescence to characterize the change in relative humidity in cement-based materials is proposed. Two kinds of moulding processes are designed, which are premixed and smeared after moulding, and the optimal preparation concentration is explored. The results showed that rhodamine 6G can reflect the relative humidity of cement-based materials in situ by its fluorescence intensity and had little effect on the hydration heat release and hydration products of cement-based materials;the fluorescence intensity was much higher when the internal relative humidity was 63% and 75%. The research results lead the application of polymer materials in the field of traditional building materials, help to explore the performance evolution law of cement-based materials in micro scale, and have important significance for the evolution from single discipline to interdisciplinary.

Design and Synthetic Scheme of Water Dispersible Graphene Oxide-Coumarin Complex for Ultra-Sensitive Fluorescence Based Detection of Copper (Cu2+) Ion in Aqueous Environment

Copper oxides and its salts are now widely used as pesticides to control fungal and bacterial diseases of field crops. Copper toxicity is often a major contributor of human health problems caused through accumulation of excess copper ions in various organs via drinking water, fruits and vegetables. So, detection and estimation of cupric ions in biological organs, drinking water, fruits and vegetables are extremely important. Recently, a fluorescence based sensor using coumarin dye (high quantum yield) has been proposed to detect micromolar Cu++ ion in biological organs. But major problem with coumarin dye is that it is insoluble in water and undergoes dye-dye aggregation in organic solvents. We proposed here a synthetic scheme of preparation of graphene oxide conjugated coumarin dye derivative which would be water dispersible and expected to be an ideal candidate for Cu2+ ion estimation in biological organs and drinking water.