Fluorescence-detecting cationic surfactants using luminescent CdTe quantum dots as probes

A novel fluorescence quenching method for the determination of cationic surfactants (CS), specifically cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), and cetylpyridinium chloride (CPC), has been developed using water-soluble luminescent CdTe quantum dots (QDs) modified with thioglycolic acid (TGA). The possible interference from heavy and transition metals (HTM) has been efficiently eliminated through simple sample treatment with mercapto cotton made in-house. Under optimum conditions, the extent of fluorescence quenching of CdTe QDs is linearly proportional to the concentration of CS from 2.0 × 10⁻⁷ to 7.0 × 10⁻⁶ mol L⁻¹ with a detection limit of 5.0 × 10⁻⁸ mol L⁻¹. The relative standard deviation for 1.0 × 10⁻⁶ mol L⁻¹ CTAB is 2.5% (n = 6). The proposed method exhibits high sensitivity and selectivity and furthermore avoided the use of toxic organic solvents and tedious solvent extraction procedures. It has been applied to the determination of trace CS in natural river water and commodity samples with satisfactory results. Potential interference from heavy and transition metals is eliminated during photoluminescence detection of CS through simple sample pre-treatment with mercapto cotton     

CdTe量子点荧光法测定阳离子表面活性剂

合成了巯基乙酸(TGA)保护的水溶性发光CdTe量子点,并考察了此探针在阳离子表面活性剂十六烷基三甲基溴化铵(CTMAB)中的发光行为。根据观察到的发光猝灭效应,建立了一种简单的测定阳离子表面活性剂的方法。考察了CdTe量子点的浓度、体系酸度、反应时间及共存物质等对测定的影响。在最佳条件下,CdTe量子点发光强度与CTMAB的浓度分别在6×10-7~9.0×10-6mol/L和1.2×10-5~3.8×10-5mol/L范围内分段成线性关系。该方法用于水样的阳离子表面活性剂的测定,回收率为97%~102%。     

A novel enhancement assay for immunochromatographic test strips using gold nanoparticles

The immunochromatographic assay is a well-known and convenient diagnostic system. In this report, the development of a novel enhancement assay for the test strips is described. Additionally, this highly sensitive immunochromatographic assay was applied to detect human chorionic gonadotropin hormone (HCG) as the model case. The primary antibody-conjugated gold nanoparticles were used as the enhancer of the standard method. The primary antibodies were immobilized within a defined detection zone (test line) on the diagnostic nitrocellulose membrane. The secondary antibodies were conjugated with colloidal gold nanoparticles. In combination with an effective sample pretreatment, the gold-conjugated antibodies and the primary antibodies formed a sandwich complex with the target protein. Within the test line, the sandwich complex was immobilized, and furthermore, concentrated by the enhancer resulting in a localized surface plasmon resonance (LSPR) phenomenon and a distinct red color on the test line. The intensity of color of the red test line (signal intensity), which correlated directly with the concentration of the target protein in the standard or spiked samples, was assessed visually and by computer image analysis using a three-determination analysis. Under optimum conditions, the limit of detection (LOD) for HCG assay was 1 pg/mL. When using human serum, 10 pg/mL of HCG could be detected. We have also spiked total prostate-specific antigen (TPSA) in female serum. The LOD for TPSA was determined as 0.2 ng/mL. With this method, the quantitative determination of the target protein could be completed in less than 15 min. Our novel immunochromatographic strips using the enhancing method based on LSPR of gold nanoparticles are useful as a rapid and simple screening method for the detection of important analytes for medical applications, environmental monitoring, food control, and biosecurity.      

An immunochromatographic assay for rapid and simultaneous detection of levonorgestrel and methylprednisolone in water samples

Synthetic contraceptive levonorgestrel (LNG) and glucocorticoid methylprednisolone (MP) residues are eventually discarded to environmental water system and function as environmental hormones, displaying potential risk to humans and ecosystems, thus there is an urgent need for fast, sensitive and simultaneous detection of these compounds in water samples. In this study, a competitive immunochromatographic assay (ICA) using colloidal gold-labeled polyclonal antibodies as probes for rapid and simultaneous detection of LNG and MP in water samples was developed. The visual detection limits of LNG and MP in water samples were 10 ng/mL. The detection process could be completed within 10 min. There was no cross-reactivity of the ICA with other seven compounds. The strips could be stored at 4℃ for 10 weeks without significant loss of activity. The assay is a suitable tool for rapid and semiquantitative detection of LNG and MP in water samples on site.     

胶体金免疫层析法快速检测三聚氰胺

采用戊二醛法制备三聚氰胺-BSA偶联抗原,胶体金标记三聚氰胺单克隆抗体,建立了检测三聚氰胺的胶体金免疫层析试验。结果显示,该试验具有良好的敏感性,胶体金免疫层析试验对鲜奶、奶粉和饲料样品中三聚氰胺的最低检测量分别为1.0、2.0和2.5μg/g,该法适合现场快速检测三聚氰胺。     

A novel immunochromatographic assay based on a time-resolved chemiluminescence strategy for the multiplexed detection of ractopamine and clenbuterol

A novel multiplexed immunochromatographic assay (ICA) based on a time-resolved chemiluminescence (CL) strategy was developed for quantitative detection of β-agonists, by utilizing ractopamine (RAC) and clenbuterol (CLE) as the models. Different from conventional multiplexed ICA methods which usually require two or more test lines, this strategy was developed for detection of two β-agonists by using only one test line on the nitrocellulose membrane. In this study, horseradish peroxidase and alkaline phosphatase were used as the signal probes to label RAC antibody and CLE antibody, respectively. The two CL reactions with flash type and glow type kinetics characteristics were triggered simultaneously by injecting the coreactants, then the signals for RAC and CLE detections were recorded at 3 s and 300 s after coreactants injection, respectively. Owing to the utilization of CL detection, this protocol showed ideal sensitivity for quantitation. Under the optimal conditions, the detection limits for RAC and CLE were 0.17 ng mL⁻¹ and 0.067 ng mL⁻¹ (S/N = 3), respectively. The whole assay process can be accomplished within 20 min without complicated sample pretreatment. The proposed method was successfully applied for the detection of RAC and CLE in spiked swine urine. It opens up a new pathway for designing a low cost, time-efficiency and multiplexed strategy for rapid screening and field assay.     

A bare-eye based one-step signal amplified semiquantitative immunochromatographic assay for the detection of imidacloprid in Chinese cabbage samples

A novel bare-eye based one-step signal amplified semi-quantitative immunochromatographic assay (SAS-ICA) was developed for detection of the pesticide imidacloprid. This method was based on competitive immunoreactions. Signal amplification was achieved by dual labeling of the test lines (TLs) on the strip using high affinity nanogold-biotinylated anti-imidacloprid mAb (BAb) and nanogold-streptavidin (Sa) probes. The relative color intensities of three TLs (TL-I, TL-II and TL-III) on a nitrocellulose (NC) membrane were used for direct visual analysis of the SAS-ICA strips, and could be used for semi-quantitation of analyte concentrations by observing what TLs disappeared in the amplification zone. Under optimized conditions, the following imidacloprid concentration ranges would be detected by visual examination of the SAS-ICA strip: 0–5 ng mL⁻¹ (negative samples), and 5–25 ng mL⁻¹, 25–250 ng mL⁻¹, 250–1000 ng mL⁻¹ and >1000 ng mL⁻¹ (positive samples). The sensitivity (the visual detection limit (VDL) of TL-III) and semi-quantitative analytical capacity (when TL-III disappeared completely) of the SAS-ICA strip were 10-fold and 160-fold higher than those of traditional ICA, respectively. The developed SAS-ICA strip was applied to the analysis of spiked and authentic contaminated Chinese cabbage samples in the laboratory and under field conditions, and the results were validated by high-performance liquid chromatography (HPLC). This process could be adopted as a potential generous technique for all ICA-based detection methods.     

Pretreatment-free immunochromatographic assay for the detection of streptomycin and its application to the control of milk and dairy products

A rapid pretreatment-free immunochromatographic assay was developed for the control of the streptomycin (STR) content in milk and dairy products. The assay is based on the competition between an immobilized STR–protein conjugate and STR in a sample to be tested for the binding to monoclonal anti-STR antibodies conjugated to colloidal gold during the flow of the sample along a membrane strip with immobilized reactants. It is possible to improve the cut-off level of positive and negative samples distinguished by a change in the molar STR to protein ratio in the immobilized conjugate. The cut-off level (500 ng mL⁻¹) thus achieved corresponds to the stated MRL of STR in milk and dairy products. For STR concentrations in the range of 16–250 ng mL⁻¹ its content can be quantitatively measured based on the degree of binding of a colloidal gold label in the test strip zone with the immobilized STR–protein conjugate. The duration of the assay is 10 min. The selected sizes of membrane pores and colloidal gold particles allow the assay to be carried out at room temperature without additional reactants and pretreatment. The applicability of the assay for milk, whole milk, sour clotted milk, and kefir with different fat content (from 0.5% to 6%) was confirmed. The results of quantitative immunochromatographic assay show good correlation with traditional ELISA (r was equal to 0.935 and 0.940 for the series tested).     

Application of luminescent nanocrystals as labels for biological molecules

Luminescent semiconductor nanocrystals, so called quantum dots (QD), have attracted increasing interest for bioanalytical labeling applications in recent years. This review describes the major optical and (bio)chemical features of this class of label, compared with organic dyes. Different conjugation methods are also discussed and the most important recent applications are presented. An overview over the current state-of-the-art is given, as also is an outlook on possibilities and limitations.     

Development of a combined technique using a rapid one-step immunochromatographic assay and indirect competitive ELISA for the rapid detection of baicalin

A colloidal gold conjugated anti-baicalin monoclonal antibody (anti-BA MAb) was prepared and used in an immunochromatographic assay (ICA) for BA in Scutellariae Radix and Kampo medicines. This competitive ICA uses an anti-BA MAb which shows a high specificity for BA and baicalein. Its advantages include a short assay time (15 min), no dependence on any instrumental systems, and it can detect BA in plant materials and Kampo medicines. The limit of detection for the ICA was found to be around 0.6 μg mL⁻¹of baicalin. Moreover, the usefulness of the combination of indirect competitive ELISA and the ICA using anti-BA MAb as a quality control method was confirmed for analysis of BA in Scutellariae Radix and Kampo medicines with a sufficient sensitivity (200 ng mL⁻¹ to 2 μg mL⁻¹), obtainable in an easy and timely manner.     

Microtiter plate assay for phosphate using a europium-tetracycline complex as a sensitive luminescent probe

A new luminescent europium probe is presented for the determination of phosphate (P) in microtiter plate format. The assay is based on the quenching of the luminescence of the europium-tetracycline (EuTc) 1:1 complex by phosphate using a reagent concentration of 20.8 μmol/L. The probe is excited at 400 nm and displays a large Stokes’ shift of 210 nm. The emission maximum is located at 616 nm. The system works best at neutral pH 7 and is therefore suitable for phosphate determination in biological and biochemical systems. The linear range of the calibration plot is from 5 × 10⁻⁶ mol/L to 7.5 × 10⁻⁴ mol/L of phosphate, and the limit of detection is 3 μmol/L.     

Synthesis and characterization of magnetic and luminescent Fe_3O_4/CdTe nanocomposites using aspartic acid as linker

In this study,the preparation of a new kind of magnetic and luminescent Fe₃O₄/CdTe nanocomposites was demonstrated. Superparamagnetic Fe₃O₄ nanoparticles were first synthesized by hydrothermal coprecipitation of ferric and ferrous ions,followed by the modification of their surfaces with tetramethylammonium hydroxide（TMAOH） and the chemical activation with aspartic acid.The surface-modified Fe₃O₄ nanoparticles were then covalently coated with CdTe quantum dots（QDs）,which were modified with mercaptoacetic acid（MPA）,to form the Fe₃O₄/CdTe magnetic and luminescent nanocomposites through the coordination of the amino groups on the surfaces of Fe₃O₄ and the carboxyl groups on CdTe QDs.The structure and properties of as-synthesized nanocomposites were characterized.It was indicated that the nanocomposites possessed structure with an average diameter of 40- 50 nm,yellow-green emission feature and room temperature ferro-magnetism.Both the fluorescence and UV-vis absorption spectra of the nanocomposites showed a blue shift comparing with those of CdTe QDs.The mechanism of the blue shift was presented.The nanocomposites retained the ferromagnetic property with a saturation magnetization of 8.9 emu/g.     

CdTe量子点荧光探针测定氯霉素含量的研究

在水溶液体系中制备出了具有高质量荧光性能,巯基乙酸(TGA)修饰的CdTe量子点(QDs),基于量子点与氯霉素混合后发生荧光猝灭作用,建立CdTe量子点作为荧光探针测定氯霉素的新方法。在Tris-HCl缓冲液(pH 7.00,0.10 mol·L-1)中,反应时间为10min时,氯霉素浓度在10～70μg·mL-1范围内与CdTe量子点的荧光猝灭程度呈良好的线性关系,相关系数为0.9981,检出限为0.799μg.mL-1。方法简便快速,灵敏度高,可用于实际样品中氯霉素的检测。     

Using capillary electrophoresis mobility shift assay to study the interaction of CdTe quantum dots with bovine serum albumin

In this work, the capillary electrophoresis mobility shift assay （CEMSA） was first adopted to study the interaction of protein with quantum dots （QDs）. In this study, bovine serum albumin （BSA） and CdTe QDs were used as model samples. We observed that BSA was facilely adsorbed to CdTe QDs surface, and the QD-BSA complex was formed by a 1：1 stoichiometric ratio. A value of 2.17 4-0.27 × 10^6 mol^-1 L^-1 （at 25 ℃） for the association constant was obtained by CEMSA.     

Hydrothermal synthesis of highly luminescent CdTe quantum dots by adjusting precursors’ concentration and their conjunction with BSA as biological fluorescent probes

A study on hydrothermal synthesis of CdTe quantum dots, highly luminescent nanocrystals at a relatively lower temperature, via changing the concentration of the CdTe precursors, is described. The full width at half maximum ranged from 40 to 80 nm and quantum yield (QY) was detected to be 27.4% at room temperature. The as-prepared CdTe QDs were labeled with BSA for fluorescence probes without pretreatment. Conjunction experimental results suggested that the as-prepared CdTe QDs are suitable for the application of biotechnology.     

MnFe2O4 nanoclusters as labels for the quantitative detection of D‐dimer in a lateral‐flow immunochromatographic assay

In this study, MnFe₂O₄ nanoclusters were prepared as bioprobes to establish a lateral‐flow immunochromatographic assay (LFIA) for the rapid and quantitative detection of D‐dimer for the first time. The magnetic properties of the magnetic labels play a key role in the quantitative detection of biomolecules. The 47.3‐nm MnFe₂O₄ magnetic nanoclusters (MNCs) with good dispersion and high saturation magnetization (76 emu/g) were fabricated via thermal decomposition of Fe(acac)₃ with Mn(acac)₂. The prepared MnFe₂O₄ MNCs were well dispersed in water because the surfaces were fully covered with 3,4‐dihydroxyhydrocinnamic acid (DHCA) molecules by ligand exchange. Anti‐D‐dimer antibodies were coupled on the surface of MnFe₂O₄ MNCs, and the target protein, D‐dimer, was detected, in the range 0.05–6 μg/mL. This assay provides a promising platform for D‐dimer detection for point‐of‐care diagnosis.     

谷胱甘肽稳定的高性能CdTe/CdS核壳型量子点制备及应用于荧光免疫检测米醋中痕量黄曲霉毒素B1

谷胱甘肽作稳定剂水相合成CdTe/CdS核壳型量子点,以EDC/NHS为活化剂对黄曲霉毒素B1(AFB1)抗体进行量子点标记,然后用牛血清蛋白封闭抗体。通过对量子点和标记抗体性能的研究发现,CdTe/CdS核壳型量子点荧光的强度和稳定性较裸壳的CdTe量子点分别提高了4倍和2倍以上。由于谷胱甘肽碳链较长,量子点对抗体尤其是活性位点处的空间构型影响减少,从而改善了量子点标记抗体的稳定性和活性,CdTe/CdS标记的AFB1抗体与AFB1免疫前后荧光强度变化显示抗体至少可以稳定6 d。基于谷胱甘肽稳定的高性能CdTe/CdS量子点,建立了一种荧光免疫检测黄曲霉毒素B1的新方法。AFB1浓度在0.68～40 pmol/L之间荧光强度与浓度呈线性关系,相关系数(R2)为0.9914,检出限为0.3 pmol/L。方法已成功应用于米醋样品中痕量黄曲霉毒素B1的测定。     

Chemiluminescence of CdTe quantum dots using K3Fe(CN)6 as oxidant and its capping ligand-dependent effect

Water-soluble CdTe quantum dots (QDs) capped with three different thioalkyl acids (mercaptoacetic acid, cysteine and glutathione) were synthesized in aqueous solution. In basic media, K₃Fe(CN)₆ could directly oxidize the water-soluble CdTe QDs to produce strong CL emission. It was found that the CL intensity depended on the capping ligand and size of CdTe QDs. CL spectra and fluorescence spectra of the system were measured to investigate the CL reaction mechanism. Moreover, the effects of 17 metal ions on the CL system were carefully investigated. Ca²⁺, Co²⁺, Mn²⁺, Hg²⁺, Mg²⁺, Cu²⁺, Ni²⁺, Cr³⁺ and Fe³⁺ could markedly inhibit the CL signal of the K₃Fe(CN)₆–CdTe QDs system, which makes it applicable for the detection of such ions. This work is of importance for gaining a better understanding of the unique optical and physical chemistry properties of QDs, and it is also helpful to find more practical applications of QDs.     

Development of a competitive format sorbent assay for the determination of parathion in water using molecular imprinted polymer as specific sorbent carrier

<正>A rapid,simple,and reliable competitive molecular imprinted polymer sorbent assay(MIPSA) was developed and validated for measurement of parathion in water samples.This assay employed a molecular imprinted polymer(MIP) that was synthesized with non-covalent imprinting method as capture reagent and p-aminoparathion conjugate of horseradish peroxidase(para-HRP) as an enzyme label.The assay depended on a competitive binding reaction between the enzyme conjugate and analyte for the binding sites of the MIP.The optimized analysis conditions of 10 ng mL~(-1) para-HRP and 10 mg mL~(-1) polymer were found.The assay was acceptable to detect parathion in water samples under the optimized conditions,with a limit of detection of 50 ng mL~(-1).Mean analytical recoveries of added parathion in water samples ranged from 101.2%to 105%.The precision of the assay was satisfactory; relative standard deviation ranged from 4.3%to 6%.     

Study the property of double-ended fluoroalkyl poly(ethylene glycol) hydrogel as a depot for hydrophobic drug delivery using electron paramagnetic resonance technique and cell proliferation assay

Hydrogel formed by fluoroalkyl double-ended polyethylene glycol (R_f-PEG) micelles was studied to assess its properties to encapsulate a hydrophobic electron spin labeled drug, Chlorambucil–Tempol adduct (CT), and to control and sustain the drug release. The drug loaded hydrogel samples were characterized with variable-temperature dependent EPR experiment, and EPR theoretical lineshape analysis. It was found that CT molecules reside in the hydrophobic R_f-cores/IPDU shells of the R_f-PEG micelles and the maximum molecular-level loading capacity was estimated to be 18.8 mg per gram of the R_f-PEG. It has been known that R_f-PEG hydrogel with certain molecular masses for the fluoroalkyl group and the PEG chain shows properties of sol/gel phase coexistence and surface erosion, which represent the favorable condition for a pharmaceutical depot to control the kinetics of drug release. To evaluate the R_f-PEG’s biocompatibility and kinetics of the drug release, a cell proliferation assay was carried out on human oropharyngeal carcinoma (KB) cells. The results show that R_f-PEG is biocompatible and able to release CT to the cell media with a constant equilibrium concentration independent of the amount of CT loaded hydrogel.