Conjugations between Cysteamine-Stabilized CdTe Quantum Dots and Single Stranded DNA

Abstract

Cysteamine-stabilized CdTe quantum dots were used to directly conjugate with single stranded DNA through electrostatic attraction between positive amino function groups on the surface of CdTe quantum dots and negatively charged DNA. The conjugates exhibited different optical properties from that of CdTe quantum dots, for example, the fluorescence intensity was enhanced obviously with maximum emission peaks gradually red-shifting, and the conjugates were more stable. Under the optimum conditions, the fluorescence intensity was proportional to concentration of DNA over the range 0.16–0.48 µg/mL. This proposed method demonstrated a versatile tool for the fluorescence probing of target DNA and fluorescence labeling.     

Specific Detection of Vibrio Parahaemolyticus by Fluorescence Quenching Immunoassay Based on Quantum Dots

In this study, anti-Vibrio parahaemolyticus polyclonal and monoclonal antibodies were prepared through intradermal injection immune and lymphocyte hybridoma technique respectively. CdTe quantum dots (QDs) were synthesized at pH 9.3, 98 °C for 1 h with stabilizer of 2.7:1. The fluorescence intensity was 586.499, and the yield was 62.43 %. QD probes were successfully prepared under the optimized conditions of pH 7.4, 37 °C for 1 h, 250 μL of 50 mg/mL EDC?·?HCl, 150 μL of 4 mg/mL NHS, buffer system of Na₂HPO₄-citric acid, and 8 μL of 2.48 mg/mL polyclonal antibodies. As gold nanoparticles could quench fluorescence of quantum dots, the concentration of V. parahaemolyticus could be detected through measuring the reduction of fluorescence intensity in immune sandwich reaction composed of quantum dot probe, gold-labeled antibody, and the sample. For pure culture, fluorescence intensity of the system was proportional with logarithm concentration of antigen, and the correlation coefficient was 99.764 %. The fluorescence quenching immunoassay based on quantum dots is established for the first time to detect Vibrio parahaemolyticus. This method may be used as rapid testing procedure due to its high simplicity and sensitivity.     

Selective recognition of Fe3+ and Cr3+ in aqueous medium via fluorescence quenching of graphene quantum dots

Graphene quantum dots (GQDs) have been prepared from graphene oxide (GO) and characterized by standard analytical techniques. The size of the prepared GQDs ranges from 2-10?nm. Aqueous dispersion of GQDs exhibited excitation-dependent emission behavior. Emission intensity of the aqueous dispersion found stable for the examined duration of about four months. GQDs exhibited selective recognition of Fe³⁺ and Cr³⁺ out of various common ions such as alkali, alkaline-earth and transition metal ions in aqueous medium through fluorescence quenching. The lower limit of detection of Fe³⁺ is 1?µM and that of Cr³⁺ is 4?µM.     

Direct electrochemistry and electrochemical biosensing of glucose oxidase based on CdSe@CdS quantum dots and MWNT-modified electrode

The direct electron transfer of glucose oxidase (GOx) was achieved based on the immobilization of CdSe@CdS quantum dots on glassy carbon electrode by multi-wall carbon nanotubes (MWNTs)-chitosan (Chit) film. The immobilized GOx displayed a pair of well-defined and reversible redox peaks with a formal potential (E ^θ’) of ?0.459 V (versus Ag/AgCl) in 0.1 M pH 7.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (k _s) of GOx confined in MWNTs-Chit/CdSe@CdS membrane were evaluated as 1.56 s^?1 according to Laviron's equation. The surface concentration (Γ*) of the electroactive GOx in the MWNTs-Chit film was estimated to be (6.52?±?0.01)?×?10^?11?mol?cm^?2. Meanwhile, the catalytic ability of GOx toward the oxidation of glucose was studied. Its apparent Michaelis–Menten constant for glucose was 0.46?±?0.01 mM, showing a good affinity. The linear range for glucose determination was from 1.6?×?10^?4 to 5.6?×?10^?3?M with a relatively high sensitivity of 31.13?±?0.02 μA?mM^?1?cm^?2 and a detection limit of 2.5?×?10^?5?M (S/N=3).     

A Novel Method for the Detection of Chlorpyrifos by Combining Quantum Dot-labeled Molecularly Imprinted Polymer with Flow Cytometry

Uniform-sized fluorescent molecularly imprinted polymers were prepared by one-step swelling and suspension polymerization, while chlorpyrifos, methacrylic acid, ethylene glycol dimethacrylate, and oil-soluble CdSe/ZnS quantum dots were used as the carrier, template molecule, functional monomer, cross-linker, and fluorophor, respectively. The morphology, adsorption dynamics, binding ability, and selectivity of quantum dot-labeled molecularly imprinted polymers were evaluated. The dosage of quantum dots for labeling the molecularly imprinted polymers was optimized. The results showed that the optimized dose of quantum dots was 200?µL using a concentration of 8.0?µM. The microsphere size was approximately 10?µm with a honeycombed surface. The quantum dot-labeled molecularly imprinted polymers had an even brightness and a high selectivity. In the presence of different concentrations of chlorpyrifos, a decrease in the fluorescence intensity of the quantum dot-labeled molecularly imprinted polymer was clearly identified by flow cytometry. The whole detection process was accomplished within 2?h including pretreatment. This method was used for the determination of chlorpyrifos in tap water samples.     

Synthesis,characterization, molecular modeling,and DNA interaction studies of a Cu(II) complex containing drug of chronic hepatitis B: adefovir dipivoxil

A new copper(II) complex [Cu(adefovir)₂Cl₂], where adefovir = adefovir dipivoxil drug, was synthesized and characterized by using different physicochemical methods. Binding interaction of this complex with calf thymus DNA (ct-DNA) has been investigated by multi-spectroscopic techniques and molecular modeling study. The complex displays significant binding properties of ct-DNA. The results of fluorescence and UV–vis absorption spectroscopy indicated that, this complex interacted with ct-DNA in a groove-binding mode, and the binding constant was 4.3(±0.2) × 10⁴ M^?1. The fluorimeteric studies showed that the reaction between the complex and ct-DNA is exothermic (ΔH = 73.91 kJ M^?1; ΔS = 357.83 J M^?1 K^?1). Furthermore, the complex induces detectable changes in the CD spectrum of ct-DNA and slightly increases its viscosity which verified the groove-binding mode. The molecular modeling results illustrated that the complex strongly binds to the groove of DNA by relative binding energy of the docked structure ?5.74 kcal M^?1. All experimental and molecular modeling results showed that the Cu(II) complex binds to DNA by a groove-binding mode.     

Cellular biosensor based on red blood cells immobilized on Fe3O4 Core/Au Shell nanoparticles for hydrogen peroxide electroanalysis

A core/shell Fe₃O₄/gold nanocomposite was prepared for immobilizing of red blood cells on a gold electrode via conjugation to a cysteamine monolayer. The hemoglobin in the film undergoes direct electron transfer at a formal potential of ?330 mV and displays excellent electrocatalytic response to hydrogen peroxide, with a linear range from 9.6 µM to 2.6 mM. The limit of detection is 4.4 µM (S/N?=?3). The Michaelis–Menten constant is 120 µM. Owing to its good biocompatibility, the biosensor exhibits good stability and acceptable reproducibility. The nanocomposite film provided a good matrix for the immobilization of cells and for the preparation of cellular biosensors.     

Doping-induced emission of infrared light from Co2+-doped ZnSe quantum dots

ZnSe quantum dots doped with Co²⁺ have been prepared in aqueous solution by a one-pot method using thioglycolic acid as stabilizer. The quantum dots were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV?Cvisible spectrophotometry, and spectrofluorimetry. The results confirmed the quantum dots formed a single cubic phase with zinc blende structure. The average particle size of the quantum dots was approximately 5 nm. Co²⁺ ions were doped into ZnSe lattice sites by substitution. As a result, infrared (IR) emission of Co^{2+ 4}T₂(F) ?? ⁴A₂(F) at approximately 3.5 ??m was detected on excitation with 755 nm radiation.     

Interaction of E6 Gene from Human Papilloma Virus 16 (HPV-16) with CdS Quantum Dots

The aim of this study was to analyze the interactions of blue and yellow fluorescent CdS quantum dots (CdS-QDs) with human papillomavirus 16 (HPV-16) oncogene E6. The interactions were investigated using chip capillary electrophoresis, spectrophotometry and square wave voltammetry (SWV). Using chip capillary electrophoresis we proved that blue fluorescent CdS-QDs (0.5 mM) caused an increase of the migration time of the E6 HPV-16 DNA–CdS-QDs complex by 42 s compared to control DNA (E6 HPV-16). The same concentration of yellow fluorescent CdS-QDs caused an increase in the migration time of the DNA–CdS-QDs complex by 108 s compared to the control DNA (E6 HPV-16). The difference in the migration times between both complexes was 66 s. Using square wave voltammetry (SWV), the reduction signal of cytosine and adenine (peak CA) was observed, after the complex with 2.5 µg mL^?1 DNA was formed. A decrease of the peak CA reduction signal of the complex DNA–CdS-QDs by 90 % was caused when yellow fluorescent CdS-QDs (0.03 mM) were used. The same concentration of blue fluorescent CdS-QDs caused only a 50 % decrease of the C and A reduction signal of the DNA–CdS-QDs complex. The difference between both CdS-QDs was 40 %. Electrochemical measurements and chip electrophoresis analyses confirmed that the yellow fluorescent CdS-QDs show higher affinity to the DNA (E6 HPV-16) compared to blue ones.     

Synthesis,characterization, and DNA binding of two copper(II) complexes as DNA fluorescent probes

[Cu(DAPT)₂Cl]Cl·H₂O and [Cu(DBM)(DAPT)Cl] [DAPT = 2,4-diamine-6-(pyrazin-2-yl)-1,3,5-triazine] were synthesized and characterized by IR and UV spectroscopy, elemental analysis, TG–DTA, molar conductivity, and LC–MS. The interaction with calf thymus DNA (ct-DNA) of the two complexes has been studied using UV spectra, fluorescent spectra, cyclic voltammetry, and viscosity measurements. The complexes interact with ct-DNA through classical intercalation. Fluorescence intensity changes of 1 and 2 in the absence and presence of ct-DNA have been investigated for quantitative determination of ct-DNA with the limit of detection of 3.8 and 7.7 ng mL^?1, respectively. From the result, the two complexes are potentially sensitive DNA fluorescent probes.     

Interaction of E6 Gene from Human Papilloma Virus 16 (HPV-16) with CdS Quantum Dots

The aim of this study was to analyze the interactions of blue and yellow fluorescent CdS quantum dots (CdS-QDs) with human papillomavirus 16 (HPV-16) oncogene E6. The interactions were investigated using chip capillary electrophoresis, spectrophotometry and square wave voltammetry (SWV). Using chip capillary electrophoresis we proved that blue fluorescent CdS-QDs (0.5 mM) caused an increase of the migration time of the E6 HPV-16 DNA–CdS-QDs complex by 42 s compared to control DNA (E6 HPV-16). The same concentration of yellow fluorescent CdS-QDs caused an increase in the migration time of the DNA–CdS-QDs complex by 108 s compared to the control DNA (E6 HPV-16). The difference in the migration times between both complexes was 66 s. Using square wave voltammetry (SWV), the reduction signal of cytosine and adenine (peak CA) was observed, after the complex with 2.5 µg mL⁻¹ DNA was formed. A decrease of the peak CA reduction signal of the complex DNA–CdS-QDs by 90 % was caused when yellow fluorescent CdS-QDs (0.03 mM) were used. The same concentration of blue fluorescent CdS-QDs caused only a 50 % decrease of the C and A reduction signal of the DNA–CdS-QDs complex. The difference between both CdS-QDs was 40 %. Electrochemical measurements and chip electrophoresis analyses confirmed that the yellow fluorescent CdS-QDs show higher affinity to the DNA (E6 HPV-16) compared to blue ones.

     

Quantum Dot-Based Biosensor for the Detection of Human T-Lymphotropic Virus-1

A method was developed to identify human T-lymphotropic virus-1 (HTLV-1) using cadmium–tellurium quantum dots. Two probes including the biotin-labeled acceptor and NH2-reporter probes with target DNA were hybridized. The resulted sandwich complex was immobilized on a well containing streptavidin. The quantum dot solution was added to the sandwich complex, conjugated with the amine group of reporter probe, and emission spectra of the quantum dots were recorded. The biosensor response was linear with HTLV-1 concentrations from 10 pg/µl to 0.24?ng/µl, with a detection limit of 19.5 pg/µl. The assay may be successfully used for detection of long nucleic acids.     

Electrodeposition of silver nanoparticles on a zinc oxide film: improvement of amperometric sensing sensitivity and stability for hydrogen peroxide determination

A strategy to fabricate a hydrogen peroxide (HP) sensor is developed by electrodepositing silver nanoparticles (Ag NPs) on a modified glassy carbon electrode (GCE) with a zinc oxide (ZnO) film. The Ag NPs/ZnO/GCE has been characterized by scanning electron microscopy, cyclic voltammetry, and chronoamperometry. It has been found that the Ag NPs synthesized in the presence of ZnO film provide an electrode with enhanced sensitivity and excellent stability. The sensitivity to HP is enhanced 3-fold by using Ag NPs/ZnO/GCE compared to Ag NPs/GCE. The HP sensor exhibits good linear behavior in the concentration range 2 µM to 5.5 mM for the quantitative analysis of HP with a detection limit of 0.42 µM (S/N?=?3).     

Dextran-coated CdSe quantum dots for the optical detection of monosaccharides by resonance light-scattering technique

A resonance light-scattering (RLS) detection method for saccharides was developed using dextran-coated CdSe quantum dots (dextran-CdSe-QDs) optical probes. The dextran-CdSe-QDs can be aggregated with concanavalin A (Con A), and the change in RLS intensity is used to monitor the extent of aggregation. The presence of glucose competitively binds with Con A, dissociating the Con A/dextran-CdSe-QDs complexes, affording the RLS intensity change and hence determining glucose concentrations in the range from a few to about 90 mM. Transmission electron microscopy was used to investigate the competitive interaction between glucose and dextran-CdSe-QDs with Con A. The competitive strategy could also be used to detect similar types of saccharides and the affinities of various monosaccharides for Con A increased in the order galactose?glucose < fructose < mannose. The proposed method was successfully applied to determine glucose in the human serum.

A resonance light-scattering (RLS) detection method for saccharides was developed using dextran-coated CdSe quantum dots (dextran-CdSe-QDs) optical probes. The dextran-CdSe-QDs were coupled to concanavalin A (Con A) to facilitate the aggregation of nanoparticles. The presence of glucose competitively binds with Con A, dissociating the Con A/dextran-CdSe-QDs complexes affording the RLS intensity change and hence determining glucose in the range from a few millimolar to about 90 mM. The proposed method was applied to the determination of glucose in human serum samples with satisfactory results.

     

Fluorescent cellulose aerogels containing covalently immobilized (ZnS)x(CuInS2)1−x/ZnS (core/shell) quantum dots

Photoluminiscent (PL) cellulose aerogels of variable shape containing homogeneously dispersed and surface-immobilized alloyed (ZnS)_x(CuInS₂)_1?x/ZnS (core/shell) quantum dots (QD) have been obtained by (1) dissolution of hardwood prehydrolysis kraft pulp in the ionic liquid 1-hexyl-3-methyl-1H-imidazolium chloride, (2) addition of a homogenous dispersion of quantum dots in the same solvent, (3) molding, (4) coagulation of cellulose using ethanol as antisolvent, and (5) scCO₂ drying of the resulting composite aerogels. Both compatibilization with the cellulose solvent and covalent attachment of the quantum dots onto the cellulose surface was achieved through replacement of 1-mercaptododecyl ligands typically used in synthesis of (ZnS)_x(CuInS₂)_1?x/ZnS (core–shell) QDs by 1-mercapto-3-(trimethoxysilyl)-propyl ligands. The obtained cellulose—quantum dot hybrid aerogels have apparent densities of 37.9–57.2 mg cm^?3. Their BET surface areas range from 296 to 686 m² g^?1 comparable with non-luminiscent cellulose aerogels obtained via the NMMO, TBAF/DMSO or Ca(SCN)₂ route. Depending mainly on the ratio of QD core constituents and to a minor extent on the cellulose/QD ratio, the emission wavelength of the novel aerogels can be controlled within a wide range of the visible light spectrum. Whereas higher QD contents lead to bathochromic PL shifts, hypsochromism is observed when increasing the amount of cellulose at constant QD content. Reinforcement of the cellulose aerogels and hence significantly reduced shrinkage during scCO₂ drying is a beneficial side effect when using α-mercapto-ω-(trialkoxysilyl) alkyl ligands for QD capping and covalent QD immobilization onto the cellulose surface.     

γ-Fe2O3 Nanoparticles Covered with Glutathione-Modified Quantum Dots as a Fluorescent Nanotransporter

The present paper describes the synthesis, characterization, and utilization of multi-functional magnetic conjugates that integrate optical and magnetic properties in a single structure for use in many biomedical applications. Spontaneous interaction with eukaryotic cell membrane (HEK-239 cell culture) was determined using fluorescence microscopy, and fluorescence analyses. Both, differences in excitation, and emission wavelength were observed, caused by glutathione intake by cells, resulting in disintegration of core–shell structure of quantum dots, as well as adhesion of conjugate onto cell surface. When compared with quantum dots fluorescent properties, HEK-239 cells with incorporated nanoconjugate exhibited two excitation maxima (λ _ex = 430 and 390 nm). Simultaneously, application of ideal λ _ex for quantum dots (λ _ex = 430 nm), resulted in two emission maxima (λ = 740 and 750 nm). This nanoconjugate fulfills the requirements of term theranostics, because it can be further functionalized with biomolecules as DNA, proteins, peptides or antibodies, and thus serves as a tool for therapy in combination with simultaneous treatment.     

Determination of DNA based on fluorescence quenching of terbium doped carbon dots

This work describes the preparation of carbon dots doped with terbium(III) (Tb-CDs) via a hydrothermal method, starting from terbium ion and ethylenediamine. The size, composition and spectral properties of the Tb-CDs were characterized by transmission electron microscopy, infrared spectra, and fluorescence spectra. The results show that doping of the CDs with Tb(III) reduces the particle size and results in more uniform particles, while fluorescence (at excitation/emission peaks of 380/475 nm) is strongly enhanced. The interaction between Tb-CDs and ct-DNA results in fluorescence quenching of Tb-CDs. The findings were exploited to design a quenchometric method for the determination of ct-DNA. The signal drops linearly in the 80 ng·mL^?1 to 50 μg·mL^?1 ct-DNA concentration range, and the detection limit is 53 ng·mL^?1. The method was applied to the determination of ct-DNA in spiked samples and gave satisfactory results. The possible fluorescence quenching mechanism (which is mainly static) was investigated using the Stern–Volmer equation and thermodynamic equations.

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Graphical abstract A kind of carbon dots doped with terbium(III) (Tb-CDs) were prepared via a hydrothermal method, using terbium ion and ethylenediamine as precursor. Doping with Tb(III) reduced the particle size of CDs and results in uniform particle size and stronger fluorescence. The interaction between the Tb-CDs and dsDNA results in quenching of the fluorescence of Tb-CDs and can be applied to determination of dsDNA.

     

Direct electrochemical behavior of hemoglobin at surface of Au@Fe3O4 magnetic nanoparticles

Nanoparticles (NPs) consisting of an Fe₃O₄ core and a thin gold shell (referred to as Au@Fe₃O₄ NPs) were self-assembled on the surface of a glassy carbon electrode modified with ethylenediamine. Following adsorption of hemoglobin, its interaction with the NPs was studied by UV–Vis spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. Stable and well-defined redox peaks were observed at about ?350 mV and ?130 mV in pH 6.0 buffer. The modified electrode was used as a mediator-free sensor for hydrogen peroxide (H₂O₂), with a linear range from 3.4 µM to 4.0 mM of H₂O₂, and with a 0.67 µM detection limit (at an S/N of 3). The apparent Michaelis-Menten constant is 2.3 mM.     

Optical Determination of Cholesterol in Milk with Molecularly Imprinted Polymer-Coated Quantum Dots

Fluorescent molecularly imprinted polymer-coated CdSe/ZnS quantum dots were prepared in an efficient one-step synthesis. Their application as fluorescent nanoparticles for the direct quantification of cholesterol in milk was characterized. The quantum dots were used as cores to produce fluorescence. The molecularly imprinted polymer shells provided specific binding sites for cholesterol. The system exhibited good linearity for cholesterol from 0.5 to 150?µg?mL^?1, a low detection limit of 0.15?µg?mL^?1, and acceptable reproducibility with a relative standard deviation of 4.2% for six replicates. The molecularly imprinted polymer-coated quantum dots were used to determine cholesterol in fortified milk. Recoveries were from 87.0 to 105.2% and a possible mechanism is proposed. The fluorescent molecularly imprinted polymer-coated quantum dots exhibited excellent selectivity and provide a simple, rapid, selective, and effective analytical approach.     

Determination of tetracycline using imprinted polymethacrylates along with fluorescent CdTe quantum dots on plastic substrates

Molecular imprints (MIPs) composed of CdTe quantum dots and tetracycline-imprinted polymethacrylates were synthesized on the surface of flexible plastic polyimide sheets from methacrylic acid, allyl mercaptan, and ethylene glycol dimethacrylate. The amount of aqueous CdTe solution, ethanol diluent, the reaction time and temperature of the radical-initiated polymerization were optimized. The MIP-QD composites were then copolymerized on the methacrylated polyimides. The resulting films were then immersed into a supersonic water-ethanol bath to strip off the tetracycline (Tc) templates. The fluorescence quenching intensity measured at 565 nm under 315 nm excitation before and after dropping a Tc sample on the film was used to optimize the processes. The calibration plot is linear in the 70 μM to 2.2 mM Tc concentration range at pH 7.5, and the LOD is 8.8 μM. The relative standard deviation is 8.2% (for n = 10). The method was applied to the determination of Tc in spiked samples of bovine serum albumin and fetal bovine serum and gave recoveries of 98% (at 200 μg?mL^?1) and 97% (at 1.0 ppt), respectively.

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Graphical abstract Flexible polyimide substrates were chemically modified with methacrylate groups for anchoring the composites (MIP-QD) of tetracycline-imprinted polymers and CdTe quantum dots. The fluorescence of the integrated substrates is quenched by tetracycline but not by methacycline and steroids.