Hydroxylated graphene quantum dots as fluorescent probes for sensitive detection of metal ions

Highly sensitive methods are important for monitoring the concentration of metal ions in industrial wastewater.Here,we developed a new probe for the determination of metal ions by fluorescence quenching.The probe consists of hydroxylated graphene quantum dots(H-GQDs),prepared from GQDs by electrochemical method followed by surface hydroxylation.It is a non-reactive indicator with high sensitivity and detection limits of 0.01μM for Cu2+,0.005μM for Al3+,0.04μM for Fe3+,and 0.02μM for Cr3+.In addition,the low biotoxicity and excellent solubility of H-GQDs make them promising for application in wastewater metal ion detection.

Silicon quantum dots-based fluorescent sensor for the detection of cobalt with high sensitivity and selectivity

Fluorescent silicon quantum dots(Si QDs)were hydrothermally synthesized from a mixture of 3(2-aminoethylamino)propyl(dimethoxymethylsilane)(AEAPDMMS)and poly(vinylpyrrolidine)(PVP).The resulting Si QDs exhibited good water solubility and high stability.Under the optimized conditions,the probe revealed an excellent linear fluorescence quenching effect on Co2+ranging from 1μmol/L to 120μmol/L with a limit of detection of 0.37μmol/L(based on 3 s/k).The quenching mechanism was studied,showing that static quenching(SQE)causes the main effect.Furthermore,the test paper based on Si QDs was prepared,which is cost-effective,high sensitivity,good selectivity,easy to use and show excellent anti-interference capability.This method was applied to analyze the content of Co2+in environmental water samples with satisfying results.

Enhanced fluorescence sensing of tetracycline with Ti_(2)C quantum dots

Ti_(2)C quantum dots(QDs)with rich surface functional groups have been synthesized using a hydrothermal method,and used to detect tetracycline(Tc)based on enhanced fluorescence.The interaction between the surface functional groups of Ti_(2)C QDs and Tc enhanced the fluorescence of Tc at 514 nm,which is used to detect Tc quickly and accurately.Under optimal conditions,the fluorescence intensity was linear to the concentration of Tc in the range of 50.0–30.0μM,with a detection limit of 21.6 nM.Furthermore,the Tc-Ti_(2)C QDs detection system was evaluated for detection of Tc in milk and artificial urine.This study demonstrates a new and simple strategy for Tc detection,which is important for food safety and human health.

Preparation of a Novel Green Fluorescent Carbon Quantum Dots and Application in Fe^(3+)-Specific Detection in Biological System

Trace ferric ion(Fe^(3+))detection has attracted increasing attention as an essential and indispensable role in many physiological and pathological research.The green-emitting carbon quantum dots(Green-CQDs)were obtained through a green and facile one-step hydrothermal method for the specific recognition and trace detection of Fe^(3+)in this paper.The optimal excitation and emission wavelengths of the CQDs were 395 nm and 490 nm,respectively.The stokes shift was up to 95 nm,which can effectively reduce the background fluorescence interference.In addition,it also exhibited good water solubility,stability,and high biocompatibility.The fluorescence intensity of Green-CQDs was linearly related to the concentration of Fe^(3+)(range of 0-80μmol/L),and the detection limit was as low as 59 nmol/L.These good properties were favorable and successful for Fe^(3+)detection in tap water,human serum samples and living cells.In addition,a fluorescence visual test paper(FP@CQDs)was prepared utilizing filter paper as carrier,which can quickly identify Fe^(3+)in real time,and is suitable for the visualization analysis of Fe^(3+)in environment.As an efficient nanoprobe,the Green-CQDs held great promise and bright prospects in practical application in prevention and early clinical diagnosis of Fe^(3+)-associated diseases.

Optical detection of acetylcholine esterase based on CdTe quantum dots

In this study, we have constructed a simple, sensitive and rapid biosensor for detection of acetylcholine esterase (AChE) based on CdTe quantum dots (QDs). The detection limit of AChE by one-step enzyme reaction based on the thiolglycolic acid (TGA) stabilized QDs (TGA-QDs) was 10 U/L and the linear range was 10-100 and 100-1200 U/L, respectively. The detection limit of AChE by two-step enzyme reaction based on the 3-mercaptopropionic acid (MGA) stabilized QDs (MGA-QDs) was found to be 20 U/L and the linear range was 100-2500 U/L. The experimental conditions of biosensors were optimized, and the detection mechanism was studied. We also detected AChE in serum samples based on TGA-QDs or MGA-QDs. The linear range was 10-140 and 50-1000 U/L, respectively. The excellent performance of this novel biosensor demonstrated that this strategy has prodigious potential to be applied in practice detection of AChE.

Ultrastable and ultrasensitive pH-switchable carbon dots with high quantum yield for water quality identification,glucose detection,and two starch-based solid-state fluorescence materials

It is attractive and encouraging to develop new fluorescent carbon dots(CDs)with excellent optical properties and promising applications prospects.Herein,highly-efficient green emissive CDs(m-CDs)with a high quantum yield(QY)of 71.7%in water are prepared through a facile solvothermal method.Interestingly,the m-CDs exhibit excellent fluorescence stability in the pH range of 1–9.However,the fluorescence intensity of the m-CDs is almost completely quenched as the pH is increased from 9 to 10.The mechanism of the unique pH-responsive behavior is discussed in detail and a plausible mechanism is proposed.Owing to the unique pH-responsive behavior,the m-CDs are used as a on-off fluorescent probe for water quality identification.By combining the reversible pH-ultrasensitive optical properties of the m-CDs in the pH range of 9–10 with the glucose oxidase-mimicking(GOx-mimicking)ability of Au nanoparticles(AuNPs),glucose can be quantitatively detected.Finally,two environment-friendly starch-based solid-state fluorescence materials(powder and film)are developed through green preparation routes.

Detection of Staphylococcus Aureus using quantum dots as fluorescence labels

Staphylococcus aureus(S.aureus)has been identified as one of the major foodborne pathogenic bacteria.The development of rapid detection methods for S.aureus is needed for assuring food safety.In this study,quantum dots were used as fluorescent labels in an immunoassay for quantitative detection of S.aureus.Firstly,biotin-labeled anti-S.aureus antibody was conjugated with streptavidin-coated magnetic nanobeads(180 nm diameter)and used to separate S.aureus cells.Then streptavidin coated quantum dots(QDs)were conjugated with biotin-labeled anti-S.aureus antibody and used as the fluorescence labels to mix with the separated S.aureus.Finally the fluorescence intensity of the bead-cell-QD complexes was measured at a wavelength of 620 nm.A linear relationship between S.aureus cell number(X)and fluorescence intensity(Y)was found for cell numbers ranging from 10^(3) to 10^(6) CFU(Colony Forming Unit)/mL,and the detection limit was 10^(3) CFU/mL.The regression model can be expressed as Y=7.68X+35.06 with R^(2)=0.94.The detection of S.aureus in food sample was explored initially.The fluorescence intensity of food sample was close to the background,so it was not satisfied.Further study will focus on the application of the method for detection of S.aureus in food sample.

Temperature-dependent photoluminescence of highly luminescent water-soluble CdTe quantum dots

Highly luminescent water-soluble CdTe quantum dots （QDs） have been synthesized with an electrogenerated precursor. The obtained CdTe QDs can possess good crystallizability, high quantum yield （QY） and favorable stability. Furthermore, a detection system is designed firstly for the investigation of the temperature-dependent PL of the QDs. ？2009 Yu Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Highly stable aqueous phase black phosphorus quantum dots with enhanced fluorescence property

Black phosphorus quantum dots(BPQDs)are a kind of outstanding optical material due to the tunable band structure.However,their fluorescence property and stability are obviously weakened in the aqueous phase,which extremely restricts the development of BPQDs.Here,we propose a new method to prepare stable BPQDs in an aqueous solution directly with high absolute fluorescence quantum yield.Aqueous phase BPQDs are synthesized by liquid exfoliation and hydrothermal with NH_(2)-polyethylene glycol(PEG)-NH_(2) as the modification agent to protect the BPQDs,which have high stability more than six months.In addition,NH_(2)-PEG-NH_(2) is also a surface passivation agent to enhance the emission of BPQDs by forming P-N bonds,which is confirmed by an absolute fluorescent quantum yield of 11.5%.Moreover,BPQDs show excellent resistance to a strong acid environment and high ionic strengths except for Fe^(3+).Therefore,the BPQDs are a kind of highly selective and linear response fluorescence probe for Fe^(3+).Considering the good biocompatibility of BPQDs,they are employed as cell fluorescent label probes and show excellent fluorescence imaging contrast.Based on the unique structural stability and fluorescence performance in the aqueous phase,BPQDs are potential candidates for Fe^(3+)detection and optical bio-imaging.

Thiourea functionalized CdSe/CdS quantum dots as a fluorescent sensor for mercury ion detection

CdSe/CdS quantum dots （QDs） functionalized by thiourea （TU） were synthesized and used as a fluorescent sensor for mercury ion detection. The TU-functionalized QDs were prepared by bonding TU via electrostatic interaction to the core/shell CdSe/CdS QDs after capping with thioglycolic acid （TGA）. It was observed that the fluorescence of the functionalized QDs was quenched upon the addition of Hg^2＋. The quantitative detection of Hg^2＋ with this fluorescent sensor could be conducted based on the linear relationship between the extent of quenching and the concentration of Hg^2＋ added in the range of 1-300 μg.L^-1, A detection limit of 0.56 μg.L^-1 was achieved. The sensor showed superior selectivity for Hg^2＋ and was successfully applied to the determination of mercury in environmental samples with satisfactory results

N-doped carbon quantum dots as fluorescent probes for highly selective and sensitive detection of Fe^3+ ions

To investigate the effect of nitrogen on the photoluminescence properties of carbon quantum dots (CO Ds), N-doped carbon quantum dots (N-CQDs)were synthesized by one-step hydrothermal treatment using biomass tar as the carbon precursor.As an inevitable organic pollutant,the unsaturated bonds in biomass tar,such as carboxylic acids,aldehydes,and aromatics,are favorable for formation of the graphitic carbon lattice.The obtained N-CQDs are spherical with an average particle size of 2.64nm and the crystal lattice spacing is 0.25nm,corresponding to the (100)facet of graphitic carbon.The N-CQDs emit bright blue photoluminescence under 365nm ultraviolet light,and they have excellent water solubility and stability with a high quantum yield of 26.1%.Coordination between the functional groups on the N-CQD surface and Fe^3+ ions is promoted because of the improved electronic properties and surface chemical reactivity caused by N atoms,leading to a significant fluorescence quenching effect of the N-CQDs in the presence of Fe^3+ions with high selectivity and sensitivity.There is a linear relationship between In (Fo/F)and the Fe^3+ concentration in the N-CQD concentration range 0.06-1400μmol/L with a detection limit of 60nmol/L, showing that the N-CQ.Ds have great potential as a fluorescent probe for Fe^3+detection.

Incorporation of Fluorescent Carbon Quantum Dots into Metal-Organic Frameworks with Peroxidase-Mimicking Activity for High-Performance Ratiometric Fluorescent Biosensing

A new ratiometric fluorescent sensor based on the bifunctional carbon quantum dots(CQDs)@metal-organic framework(MOF)nanocomposite possessing peroxidase-mimicking catalytic and luminescent characteristics was developed for hydrogen peroxide(H_(2)O_(2))and cholesterol detection.The incorporation of fluorescent CQDs into the cavities of MIL-101(Fe)MOF with peroxidase-like activities endows the nanocomposite with bifunctional properties.The CQDs@MOF can oxidize o-phenylene-diamine to 2,3-diaminophenolazine by H_(2)O_(2)with yellow fluorescence(556 nm).Meantime,the intrinsic fluorescence signal(455 nm)of CQDs@MOF is inhibited due to the inner filter effect.Therefore,the ratio of the fluorescent intensity is employed as the signal output to construct the H_(2)O_(2)ratiometric biosensor.In addition,the cholesterol can be determined by the ratiometric sensor with high sensitivity.In addition,the total cholesterol in human serum is determined with high accuracy using our ratiometric biosensor.This ratiometric fluorescent platform based on the bifunctional CQDs@MOF provides new insights in the field of bio-sensing.

Functional groups assisted-photoinduced electron transfer-mediated highly fluorescent metal-organic framework quantum dot composite for selective detection of mercury(Ⅱ) in water

The presence of toxic mercury (Ⅱ) in water is an ever-growing problem on earth that has various harmful effect on human health and aquatic living organisms.Therefore,detection of mercury (Ⅱ) in water is very much crucial and several researches are going on in this topic.Metal-organic frameworks (MOFs) are considered as an effective device for sensing of toxic heavy metal ions in water.The tunable functionalities with large surface area of highly semiconducting MOFs enhance its activity towards fluorescence sensing.In this study,we are reporting one highly selective and sensitive luminescent sensor for the detection of mercury (Ⅱ) in water.A series of binary MOF composites were synthesized using in-situ solvothermal synthetic technique for fluorescence sensing of Hg^(2+)in water.The welldistributed graphitic carbon nitride quantum dots on porous zirconium-based MOF improve Hg^(2+)sensing activity in water owing to their great electronic and optical properties.The binary MOF composite (2) i.e.,the sensor exhibited excellent limit of detection (LOD) value of 2.4 nmol/L for Hg^(2+).The sensor also exhibited excellent performance for mercury (Ⅱ)detection in real water samples.The characterizations of the synthesized materials were done using various spectroscopic techniques and the fluorescence sensing mechanism was studied.

Detection of Bacteria Based on Quantum Dots by Using a Laboratory-Made System

This study investigated a method that simultaneously detects three bacteria, Salmonella typhimurium, Escherichia coli, and Staphylococcus aureus via an approach that uses antibody-conjugated quantum dots(QDs) as fluorescence markers,by using a laboratory-made system. QDs with different emission wavelenghs were immobilized with antibody. Antibody conjugated QDs capture the bacteria selectively and specifically so that "sandwich" complex were formed. The suspension of the labeled bacteria was trickled onto a microporous membrane. A 450 nm semiconductor laser was used as a part of the laboratory-made system to excite the QDs. Three PMT detectors were utilized to detect the fluorescence intensity. This method, of which the detection procedures are completed within 1 h, can be applied to the cost-effective and rapid detecting of bacterial contamination.

Signal-on bimodal sensing glucose based on enzyme product-etching MnO_(2)nanosheets for detachment of MoS_(2)quantum dots

The sensitive and rapid detection of blood glucose is very important for monitoring and managing diabetes.Herein,a fluorescent/magnetic bimodal sensing strategy is proposed for glucose detection using a multifunction-responsive nanocomposite(MoS_(2)QDs-MnO_(2)NS).MoS_(2)QDs act as fluorescent probes,and MnO_(2)nanosheets are used as both quenchers and recognizers in this sensing platform.In the presence of glucose-mediated enzyme product(H_(2)O_(2)),MnO_(2)nanosheet is etched,thus releasing MoS_(2)QDs and Mn^(2+)ions,which causes the significantly enhancement of fluorescent and magnetic signals.Furthermore,MoS_(2)QDs-MnO_(2)NS-based fluorescent test paper is constructed for H_(2)O_(2)sensing with the naked eyes.Under optimal conditions,the dual linear ranges of 20-300μmol/L and 40-250μmol/L toward glucose detection are obtained for the fluorescent and magnetic mode,respectively.Furthermore,this bimodal assay exhibits good reproducibility and acceptable accuracy in glucose detection of clinical samples,demonstrating great versatility and flexibility of multifunctional probes in glucose detection.

Advances in single-particle detection for DNA sensing

Rapid, accurate and sensitive detection of particular DNA sequence is critical in fundamental biomedical research and clinical diagnostics. However, conventional approaches for DNA assay often suffer from cumbersome procedures, long analysis time and insufficient sensitivity. Recently, single-particle detection technology has emerged as a powerful tool in the biosensing area due to its significant advantages of ultrahigh sensitivity, low sample-consumption and rapid analysis time. Especially, the introduction of novel nanomaterials has greatly promoted the development of single-particle detection and its applications for DNA sensing. In this review, we summarize the recent advance in single-particle detection strategies for DNA sensing, and focus mainly on metallic nanoparticle-and semiconductor quantum dot-based single-particle detection. We highlight the emerging trends in this field as well.

双硅源硅量子点荧光探针的合成及检测Cr(Ⅵ)应用

Cr(Ⅵ)在水中溶解性很强,超过0.1 mg/L的Cr(Ⅵ)会对环境和生命健康产生毒害作用,因此开发灵敏度高的六价铬离子的检测方法就显得尤为重要。采用N-[3-(三甲氧基硅基)丙基]乙二胺,三甲基硅基咪唑作为双硅源前驱体,柠檬酸钠为还原剂,通过水热法可制备水分散性良好的球形双硅源硅量子点(D-Si QDs)。研究结果表明,D-Si QDs为球结构且表面含有大量氨基与咪唑基团。在最优条件下制备的D-Si QDs最佳激发波长为359 nm,最大发射波长为451 nm,有着较好的光稳定性。D-Si QDs的荧光可被Cr(Ⅵ)选择性猝灭,且荧光猝灭程度与Cr(Ⅵ)浓度在0.5~100μmol/L的范围内呈良好的线性关系,检测限为0.056μmol/L;对自来水样中检测Cr(Ⅵ)回收率在100.37%~105.83%,相对标准偏差均小于2.36%。研究为开发高灵敏度Cr(Ⅵ)检测的D-Si QDs荧光探针提供了思路。

氮掺杂碳量子点荧光法检测猪肉中的四环素

四环素(TC)作为一种广谱抗生素,用于预防和治疗细菌性疾病,以及作为饲料添加剂促进动物生长。本文旨在建立一种菠萝皮来源的氮掺杂碳量子点(N-CQDs)荧光猝灭法快速检测TC。以菠萝皮和二乙烯三胺为原料,通过水热法制备高量子产率的蓝色荧光N-CQDs。通过透射电子显微镜、傅里叶红外光谱、X射线光电子能谱对N-CQDs进行结构表征。结果表明,N-CQDs的平均粒径为3.53 nm,主要由C、N、O 3种元素组成,表面具有含氧和含氮基团。主要猝灭机理为静态猝灭和内滤效应。在最优试验条件下,该方法在0.3~40μg/mL范围线性良好,检出限为89.26μg/L。该检测方法被用于猪肉中四环素的检测,回收率在98.40%~106.02%之间,相对标准偏差1.29%~3.88%。

猪流行性腹泻病毒荧光免疫层析检测试纸条的研制和应用

为了建立一种快速、高效且灵敏的猪流行性腹泻病毒(PEDV)的现场快速检测技术,本研究以荧光量子点标记鼠抗PEDV单克隆抗体并喷涂到结合垫上,将鼠抗PEDV单克隆抗体和羊抗鼠IgG多克隆抗体固定到NC膜上,分别作为检测线和质控线制备荧光免疫层析试纸条,并对其敏感性、特异性及临床样品检测性能进行考察。结果:所制备的荧光试纸条可在20 min内完成临床样品中PEDV的现场检测,最低检测限为3.3×103 TCID50/mL,与猪轮状病毒、猪丁型冠状病毒、猪圆环病毒、伪狂犬病病毒、沙门菌、金黄色葡萄球菌等常见病原无交叉反应,对50份粪便、粪便拭子和肠道组织等临床样品进行检测,与RT-PCR检测结果的符合率为84.0%。本试验表明该试纸条具有较高的灵敏度和较强的特异性,检测时间短,操作简便,可用于PEDV的现场快速筛查。

N掺杂碳量子点的制备及在Hg^(2+)快速检测中的应用

以柠檬酸和丙烯酰胺为原料,通过一步水热合成法,合成了一种对Hg^(2+)具有单一且快速响应机制的新型蓝色荧光碳量子点(CDs)。通过傅里叶红外光谱仪和透射电子显微镜对其结构进行表征,发现该CDs平均粒径约为3.6nm,且表面有丰富的酰胺和羟基基团。探究了CDs的荧光性能,测试其对重金属离子的选择性、检测灵敏度、pH稳定性和猝灭响应时间。研究结果表明,该CDs对Hg^(2+)有优异的单一选择性,并能够在5min内实现快速响应。Hg^(2+)的检出限低至10.0nmol/L,并在0.1~25μmol/L较宽的浓度范围内具有线性响应,且猝灭率达到65%。制备的新型CDs可方便快速地实现对不同pH水样中Hg^(2+)的特异性识别和检测。