Sensitive turn-on fluorescent detection of melamine based on fluorescence resonance energy transfer

We here report a novel fluorescent method for the detection of melamine based on the high fluorescence quenching ability of gold nanoparticles. The fluorescence was significantly quenched via fluorescence resonance energy transfer when fluorescein molecules were attached to the surface of gold nanoparticles by electrostatic interaction. Upon addition of melamine, the fluorescence was enhanced due to the competitive adsorption of gold nanoparticles between melamine and fluorescein. Under the optimum conditions, the fluorescence enhancement efficiency [(I-I(0))/I(0)] showed a linear relationship with the concentration of melamine in the range of 1.0 × 10(-7) mol L(-1)~4.0 × 10(-6) mol L(-1), and the detection limit was calculated to be 1.0 × 10(-9) mol L(-1). The proposed method showed several advantages such as high sensitivity, short analysis time, low cost and ease of operation.     

Ultrasensitive endonuclease activity and inhibition detection using gold nanoparticle-enhanced fluorescence polarization

We have developed a highly sensitive and selective fluorescence polarization assay method based on the specificity of the DNA cleavage reaction with the enhancement of gold nanoparticles (AuNPs) for assaying endonuclease activity and inhibition. This assay can detect EcoRI endonuclease down to 5.0×10(-4) U mL(-1) with a detection range from 5.0×10(-4) to 10 U mL(-1).     

金纳米粒子比色探针检测牛奶及鸡蛋中的三聚氰胺

三聚氰胺能诱导金纳米粒子(AuNPs)团聚,溶液颜色由酒红色变为紫色或蓝灰色.以AuNPs作为比色探针,建立了快速检测牛奶和鸡蛋中三聚氰胺的方法.实验优化得最佳反应条件为:AuNPs粒径13 min、pH=7、反应时间10 min和温度为室温.对样品中常见物质进行了干扰实验.样品经10％三氯乙酸和氯仿提取、离心分离后可...     

Determination of 6-mercaptopurine based on the fluorescence enhancement of Au nanoparticles

A novel method for the determination of 6-mercaptopurine (6MP) has been developed based on fluorescence enhancement of Au nanoparticles (AuNPs). The fluorescent AuNPs with mean diameter of ∼15 nm were synthesized in aqueous solution, exhibiting the stable maximum emission at 367 nm, under the excitation at wavelength of 264 nm. The AuNPs self-assembly with 6MP were characterized with transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) absorption, fluorescence and surface-enhanced Raman scattering (SERS) spectroscopy. The results revealed that the surface attachment through versatile binding sites of S10, N3, N9 and N7 atoms in 6MP produced the interparticle coupling and formed aggregates of AuNPs. As a result, the fluorescence emission enhancement was significantly observed upon AuNPs self-assembly with 6MP. The fluorimetric determination under optimal conditions indicated that 6MP could be quantified in good linearity range of 6.35 × 10⁻⁸ to 3.05 × 10⁻⁷ M, with a low detection limit of 4.82 × 10⁻¹⁰ M. The relative standard deviation (n = 11) was 1.8% at 2.54 × 10⁻⁸ M 6MP concentration level. The proposed method was successfully applied for the determination of 6MP in spiked human urine. The probable fluorescence enhancement mechanism was also discussed there.     

Colorimetric detection of Cd2+ using gold nanoparticles cofunctionalized with 6-mercaptonicotinic acid and L-cysteine

We have developed a colorimetric assay for the highly sensitive and selective detection of Cd(2+) using gold nanoparticles (AuNPs) cofunctionalized with 6-mercaptonicotinic acid (MNA) and L-Cysteine (L-Cys) through the formation of an Au-S bond. In the presence of Cd(2+), the aggregation of functionalized AuNPs occurred by means of a metal-ligand interaction that led to visible color changes. Most importantly, cofunctionalized AuNPs had better responses for Cd(2+) than that functionalized by either MNA or L-Cys. Cd(2+) could be detected by the colorimetric response of AuNPs that could be detected by the naked eye or a UV-vis spectrophotometer. The absorbance ratio (A(620)/A(523)) was linear with the Cd(2+) concentration in the range of 2.0 × 10(-7) to 1.7 × 10(-6) M. Under optimum conditions (2.0 × 10(-5) M MNA, 2.0 × 10(-6) M L-Cys and 0.020 M NaCl at pH 10.0), the detection limit (3σ) of Cd(2+) could be as low as 1.0 × 10(-7) M. Interference experiments showed that Pb(2+) and Cu(2+) caused a slight interference for Cd(2+) determination while other metal ions caused no interference. The proposed method was successfully applied to determine the concentration of Cd(2+) in environmental samples (lake water).     

Nickel(II)-induced excimer formation of a naphthalene-based fluorescent probe for living cell imaging

Ni(2+)-induced intramolecular excimer formation of a naphthalene-based novel fluorescent probe, 1-[(naphthalen-3-yl)methylthio]-2-[(naphthalen-6-yl)methylthio]ethane (L), has been investigated for the first time and nicely demonstrated by excitation spectra, a fluorescence lifetime experiment, and (1)H NMR titration. The addition of Ni(2+) to a solution of L (DMSO:water = 1:1, v/v; λ(em) = 345 nm, λ(ex) = 280 nm) quenched its monomer emission, with subsequent enhancement of the excimer intensity (at 430 nm) with an isoemissive point at 381 nm. The fluorescence lifetime of free L (0.3912 ns) is much lower than that of the nickel(2+) complex (1.1329 ns). L could detect Ni(2+) as low as 1 × 10(-6) M with a fairly strong binding constant, 2.0 × 10(4) M(-1). Ni(2+)-contaminated living cells of plant origin could be imaged using a fluorescence microscope.     

碳纳米管负载纳米金-石墨烯量子点修饰电极电化学检测过氧化氢

采用过氧化氢刻蚀法制备石墨烯量子点(GQDs),再采用原位化学还原法制备金纳米粒子-石墨烯量子点纳米复合物(Au NPs-GQDs),最后以聚二甲基二烯丙基氯化铵(PDDA)为交联剂将上述纳米复合物组装于多壁碳纳米管表面,制得金纳米粒子-石墨烯量子点-PDDA-多壁碳纳米管复合材料(Au NPs-GQDsPDDA-MWCNTs)。通过荧光光谱法、紫外-可见吸收光谱法和透射电子显微镜对上述复合材料进行表征。采用滴涂法制得该复合材料修饰的玻碳电极,研究了过氧化氢在该电极上的电化学行为。结果表明:在石墨烯量子点、金纳米粒子和多壁碳纳米管三者的协同作用下,该电极对过氧化氢的电氧化表现出强的催化活性。在优化条件下,安培法检测H_2O_2的线性范围为2.0×10~(-8)~1.5×10~(-3)mol/L,检出限(3sb)为8.0×10~(-9)mol/L,灵敏度为61.6μA/(mmol·L~(-1))。     

Fluorescence "Turn-On" chemosensor for the selective detection of beryllium

A new fluorogenic method for selective and sensitive determination of beryllium using 2,6-diphenyl-4-benzo-9-crown-3-pyrane (DBCP) was developed. The proposed fluorescent probe undergoes fluorescent emission intensity enhancement upon binding to beryllium ions in MeOH/H(2)O (70:30, v/v) solution. The fluorescence enhancement of DBCP is attributed to a 1:1 complex formation between DBCP and Be(2+) ion, which has been utilized as the basis for selective detection of Be(2+) ion. With the optimum condition described, the fluorescence enhancement at 531 nm was linear to the concentration of beryllium in the range of 1.6×10(-8)-1.6×10(-7) M and a detection limit of 1.5×10(-9) M. The fluorescent probe exhibits high selectivity for Be(2+) ion over the other common mono, di- and trivalent cations.     

巴比妥酸衍生物荧光增强法快速测定牛奶中的三聚氰胺

建立了一种简单快速测定三聚氰胺的方法. 在pH=7.0的磷酸盐缓冲溶液中, 三聚氰胺与巴比妥酸衍生物(DBA)形成稳定的氢键, 使三聚氰胺的荧光强度显著增强, 由此建立了巴比妥酸衍生物荧光增强测定牛奶中三聚氰胺的新方法. 在优化的条件下, 该方法的线性范围为12.5~1250 μg/L, 检出限为7.5 μg/L, 相对标准偏差为2.06%, 样品平均加标回收率为96.62%. 本方法简便、快速、准确, 可用于大量牛奶样品中三聚氰胺的快速检测.     

Determination of melamine based on electrochemiluminescence of Ru(bpy)3(2+) at bare and single-wall carbon nanotube modified glassy carbon electrodes

The electrochemiluminescence (ECL) of Ru(bpy)(3)(2+) at bare and single-wall carbon nanotube (SWNT) modified glassy carbon (GC) electrodes has been employed for the determination of melamine for the first time, giving a linear response (R(2) = 0.99682) for melamine concentration from 1.0 × 10(-10) to 1.0 × 10(-5) M at a bare GC electrode in pH 10 borate buffer, and the detection limit is 1.0 × 10(-10) M. However, the detection limit can be reduced further to 1.0 × 10(-13) M after modification of the GC electrode by SWNTs. This is much lower compared to other detection methods. The proposed method was applied to the determination of melamine added to a commercial milk sample; the recovery is quite satisfactory with good reproducibility and stability. All of these results provide the possibility of developing a novel ECL detection method for melamine.     

利用salen型荧光探针测定Cr3+

研究了salen型席夫结构的荧光探针N,N’-二(2-羟基-1-萘甲醛)-l,2-苯二胺(NAPPDIH)对Cr3+的响应。Cr3+能够使该探针的荧光猝灭。研究表明,在pH3.5(乙酸胺-盐酸)和DMSO/H2O(V/V,8:2)的条件下,8.0×10-6 mol/L的Cr3+可以导致NAPPDIH 65%的荧光猝灭。并且,Cr3+的浓度在5.0×10-7～8.0×10-6 mol/L的范围内,与荧光强度的变化值呈良好的线性关系,检出限为3.7×10-7 mol/L。方法可用于直接检测水样中的Cr3+。     

Enhancing fluorescence intensity of Ellagic acid in Borax-HCl-CTAB micelles

Ellagic acid (C(14)H(6)O(8)), a naturally occurring phytochemical, found mainly in berries and some nuts, has anticarcinogenic and antioxidant properties. It is found that fluorescence of Ellagic acid (EA) is greatly enhanced by micelle of cetyltrimethylammonium bromide (CTAB) surfactant. Based on this effect, a sensitive proposed fluorimetric method was applied for the determination of Ellagic acid in aqueous solution. In the Borax-HCl buffer, the fluorescence intensity of Ellagic acid in the presence of CTAB is proportional to the concentration of Ellagic acid in range from 8.0×10(-10) to 4.0×10(-5) mol L(-1); and the detection limits are 3.2×10(-10) mol L(-1) and 5.9×10(-10) mol L(-1) excited at 266 nm and 388 nm, respectively. The actual samples of pomegranate rinds are simply manipulated and satisfactorily determined. The interaction mechanism studies argue that the negative EA-Borax complex is formed and solubilized in the cationic surfactant CTAB micelle in this system. The fluorescence intensity of EA enhances because the CTAB micelle provides a hydrophobic microenvironment for EA-Borax complex, which can prevent collision with water molecules and decrease the energy loss of EA-Borax complex.     

基于聚苯胺纳米纤维复合膜界面构建电化学细胞传感器及其对癌细胞的识别检测

合成了聚苯胺纳米纤维,直径在50～70 nm之间;基于静电作用构建聚苯胺纳米纤维-纳米金复合膜界面,并在此界面上层层组装修饰叶酸分子,构建叶酸功能化传感界面,基于叶酸分子与癌细胞表面过量表达的叶酸受体之间的特异性识别作用,将此传感界面应用于对癌细胞的识别和捕获。结果表明:叶酸功能化传感界面能够特异性识别和捕获叶酸受体过量表达的癌细胞。采用电化学阻抗技术,以HeLa细胞为模型,应用于对癌细胞的识别和检测,细胞在1.0×104～6.4×106cells/mL浓度范围内与阻抗变化值ΔRct呈良好的线性关系;检出限为2000 cells/mL。本方法简单、快速灵敏、重现性和稳定性良好;制备的传感器可以再生使用。     

The interaction between some diamines and CdSe quantum dots

The interaction of some diamines (ethylenediamine (EDA), 1,6-hexanediamine (HDA), o-phenylenediamine (OPD)) with CdSe quantum dots (QDs) is reported. With increasing concentration of EDA from 0 to 2.0 x 10(-6) mol l(-1), slight fluorescence enhancement is observed. However, the CdSe QDs fluorescence quenching is seen at relatively higher concentration of EDA. There is a red-shift of 0-7 nm in fluorescence emission spectra of CdSe QDs when the concentration of EDA is changed from 2.0 x 10(-6) to 8.0 x 10(-6) mol l(-1). The resonance light scattering (RLS) spectra of CdSe QDs have little change when the concentration of EDA is less than 5.0 x 10(-6) mol l(-1). It indicates there are little large particles formed in the solution. However, a significant increase of the RLS is observed in the 300-500 nm wavelength range after adding higher concentration than 5.0 x 10(-6) mol l(-1) EDA, which could be attributed to the large particles formed. The interaction between HDA and CdSe QDs is similar to that of EDA. However, with the OPD, it is found that the interaction is much different from those of EDA, HDA, and that the quenching, even at low concentration, is effective for CdSe QDs emission. The quenching phenomenon could be explained by a surface bound complexation equilibrium model.     

Selective determination of 3,4-dihydroxyphenylacetic acid in the presence of ascorbic acid using 4-(dimethylamino)pyridine capped gold nanoparticles immobilized on gold electrode

4-(Dimethylamino)pyridine capped gold nanoparticles (DMAP-AuNPs) were synthesized in aqueous medium and then immobilized on 1,6-hexanedithiol (HDT) modified Au electrode for the selective determination of 3,4-dihydroxyphenylacetic acid (DOPAC) in the presence of ascorbic acid (AA). The synthesized DMAP-AuNPs were characterized by UV-visible spectroscopy and high resolution-transmission electron microscopy (HR-TEM). The HR-TEM images showed that the nanoparticles are spherical in shape with a diameter of ～12 nm. The DMAP-AuNPs immobilized on HDT modified electrode was characterized by cyclic voltammetry and impedance spectroscopy. Impedance spectra show that the electron transfer reaction was more facile at the AuNPs modified electrode when compared to bare and HDT modified Au electrodes. The application of DMAP-AuNPs modified electrode was demonstrated by selective determination of DOPAC in the presence of high concentration of AA at pH 4. Using amperometry method, 40 nM detection of each AA and DOPAC was achieved. The current response was increased linearly with increasing AA and DOPAC in the concentration range of 40×10(-9) to 10×10(-5) M and a detection limit was found to be 5.6×10(-10) M and 3.7×10(-10) M (S/N=3) for AA and DOPAC, respectively. The present modified electrode was also successfully used for the determination of 40 nM DOPAC in the presence of 2500-fold excess of common interferents such as Na(+), Mg(2+), Cu(2+), Ca(2+), NH(4)(+) urea and glucose.     

Nitrate enhanced electrochemiluminescence determination of tris(2,3-dibromopropyl) isocyanurate with a gold nanoparticles-modified gold electrode

Tris(2,3-dibromopropyl) isocyanurate (TBC) is a heterocyclic hexabrominated flame retardant, which cannot be degraded even over a long time and may be a potential environmental pollutant. In this paper, TBC is for the first time as far as we know determined by silver nitrate-enhanced electrochemiluminescence (ECL) using a gold nanoparticles (AuNPs)-modified gold electrode. In our experiments, TBC was found to have the characteristics of increasing the ECL intensity of Ru(bpy)(3)(2+), and the ECL signal was proportional to the concentration of TBC. Based on this, we have successfully developed a novel, fast and sensitive method for the analysis of TBC. The main influencing factors including the volume ratio of acetonitrile and water, and the concentration of Ru(bpy)(3)(2+) were investigated in detail. Compared with using a bare gold electrode in MeCN without AgNO(3), the limit of detection is remarkably lowered by 20 times and the linear range is expanded by 5 times by using the AuNPs-modified gold electrode and AgNO(3). Under the optimal conditions, a limit of detection of 5.0 × 10(-8) M (S/N = 3) is achieved with a linear range of 1.0 × 10(-7) to 5.0 × 10(-5) M. The mechanism of the ECL enhancement of the system is also investigated.     

Determination of acetamiprid by a colorimetric method based on the aggregation of gold nanoparticles

A method was developed for the detection of the insecticide acetamiprid based on the strong interaction of the cyano group of acetamiprid with gold nanoparticles (AuNPs). The interaction results in the aggregation of gold nanoparticles and is accompanied by a color change from red to purple. The concentration of acetamiprid can be determined qualitatively and quantitatively by visually monitoring the color change or by using a spectrometer. Transmittance electron microscopy and UV-vis spectroscopy have been used to characterize the process. The experimental parameters were optimized with regard to the size of the AuNPs, pH, and incubation time. Under optimal experimental conditions, linear relationships between the logarithm of the concentration of acetamiprid and the absorbance were found over the range of 0.66 to 6.6???M for AuNPs with diameters of 22.0?±?1.0?nm and of 6.6?C66???M for AuNPs with diameters of 15.0?±?1.0?nm. This method was successfully applied to detect acetamiprid in vegetables.

Determination of melamine in food contact materials using an electrode modified with gold nanoparticles and reduced graphene oxide

We describe an electrochemical sensor for melamine based on a glassy carbon electrode (GCE) modified with reduced graphene oxide that was decorated with gold nanoparticles (AuNP/rGO). The AuNPs/rGO nanocomposite was synthesized by co-reduction of Au(III) and graphene oxide and characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The response of the modified GCE to melamine was investigated by using hexacyanoferrate as an electrochemical reporter. It is found that the electrochemical response to hexacyanoferrate is increasingly suppressed by increasing concentration of melamine. This is attributed to competitive adsorption of melamine at the AuNP/rGO composite through the interaction between the amino groups of melamine and the AuNPs. The presence of rGO, in turn, provides a platform for a more uniform distribution of the AuNPs and enhances the electron transfer rate of the redox reaction. The findings were used to develop a sensitive method for the determination of melamine. Under optimized conditions, the redox peak current of hexacyanoferrate at a working voltage of 171 mV (vs. SCE) is linearly related to the concentration of melamine in 5.0 to 50 nM range. The method was successfully applied to the determination of melamine in food contact materials.

A simple electrochemical sensor based on gold nanoparticles decorated reduced graphene oxide was developed for highly sensitive measurement of melamine in food contact materials.

     

Al(III)- CTMAB增敏酸性降解荧光法测定土霉素

The fluorescence characteristics of acid degraded product of oxytetracycline with aluminium(III) in micellar system has been studied.The experiment indicated that oxytetracycline reacts with hydrochloric acid and produces more strong fluorescent species.After CTMAB and aluminium(III)are added in this species,its fluorescence intensity can be enhanced greatly in pH 7.20 Na2HPO4-KH2PO4 buffer solution.Based on this,a new fluorimetric method involving acidic degradation and enhancement by surfactant and aluminium(III)is proposed for the determination of oxytetracyline.The maximum excitation and emission wavelengths are 392nm and 492nm,respectively.The fluorescence intensity is proportional to the concentration of oxytetracycline over the range of 2.01×10-8mol/L～2.10×10-6mol/L with the detection limit of 1.0×10-8 mol/L.The method has been used to the determination of oxytetracycline in tablets with satisfacoty results.     

Gold nanoparticles for enhanced chemiluminescence and determination of 2,4-dichlorophenol in environmental water samples

Gold nanoparticles (AuNPs) of different sizes were synthesized by the citrate reduction method. It was found that AuNPs could enhance the chemiluminescence (CL) of the luminal-NaOH system and 2,4-dichlorophenol (2,4-DCP) could inhibit AuNPs-luminal-NaOH CL signals in alkaline solution. CL spectra, UV-visible spectra, and transmission electron microscopy (TEM) were used to investigate the CL mechanism. On the basis of the inhibition, a flow-injection CL method has been established for determination of 2,4-DCP in water samples. Under the optimized conditions, the linear range for determination of the 2,4-DCP was 0.1 × 10(-6) to 20 × 10(-6) g mL(-1), LOD (limit of detection, S/N = 3) was 1.36 × 10(-8) g mL(-1), with RSD of 1.8% (n = 11). This method has been successfully used for analysis of 2,4-DCP in environmental water samples.