Synchronous fluorescence determination of protein with functionalized CdS nanoparticles as a fluorescence probe

Nanometer-sized fluorescent particles have been successfully synthesized. A synchronous fluorescence method, with high sensitivity and selectivity, has been developed for rapid determination of protein with functionalized CdS as a fluorescence probe. When Δλ=260 nm, maximum synchronous fluorescence is produced at 274 nm at pH 7.0. Under optimal conditions, the calibration graphs are linear over the range 0.1-3.0 μg ml⁻¹ for bovine serum albumin (BSA), 0.1-11.0 μg ml⁻¹ for γ-globulin (γ-G) and 0.1-1.4 μg ml⁻¹ for human serum albumin (HSA), respectively. Limits of determination were 0.01 μg ml⁻¹ for BSA, 0.019 μg ml⁻¹ for γ-G and 0.021 μg ml⁻¹ for HSA, respectively. The relative standard deviations of seven replicate measurements were 1.8% for 1.0 μg ml⁻¹ BSA, 2.2% for 1.0 μg ml⁻¹ γ-G and 2.3% for 1.0 μg ml⁻¹ HSA.     

Preparation and application of functionalized nanoparticles of CdS as a fluorescence probe

CdS nanoparticles have been prepared and modified with mercaptoacetic acid. The functionalized nanoparticles are water-soluble and biocompatible. They could be used as a fluorescence probe in the determination of bovine serum albumin (BSA), which was proved to be a simple, rapid and specific method. In comparison with single organic fluorophores, these nanoparticle probes are brighter, more stable against photobleaching, and do not suffer from blinking. Under the optimum conditions, the response is linearly proportional to the concentration of BSA between 0.1 and 3.2 μg ml⁻¹, and the limit of detection is 0.08 μg ml⁻¹.     

Application of magdala red as a fluorescence probe in the determination of nucleic acids

A fluorescence quenching method was developed for the rapid determination of DNA and RNA using magdala red as fluorescence probe. In weakly acidic ¶medium, the fluorescence of magdala red (λex>lem = 54055 nm) can be largely quenched by DNA or RNA. The calibration graphs are linear over the range 0.01–¶1.2 μg/mL for both calf thymus DNA (CT DNA) and salmon DNA (SM DNA), and 0.015–1.0 μg/mL for yeast RNA, respectively. The corresponding detection limits are ¶6.0 ng/mL for CT DNA, 7.0 ng/mL for SM DNA and ¶15.0 ng/mL for yeast RNA, respectively. CT DNA could be determined in the presence of 20% (w/w) yeast RNA, and the relative standard deviation of six replicate measurements is 3.18% for 400 ng/mL of CT DNA. Interference from coexisting substances in the determination of DNA was also examined. Real samples were determined with satisfactory results.     

Preparation and application of cysteine-capped ZnS nanoparticles as fluorescence probe in the determination of nucleic acids

Cysteine-capped ZnS nanometer-sized fluorescent particles were produced by a colloidal aqueous synthesis. The functionalized nanoparticles are water-soluble and suitable for biological application. A synchronous fluorescence method has been developed for the rapid determination of DNA with functionalized nano-ZnS as a fluorescence probe, based on the synchronous fluorescence enhancement of cysteine-capped nano-ZnS in the presence of DNA. When Deltalambda =190 nm, maximum synchronous fluorescence is produced at 267 nm at pH 5.12. Under optimum conditions, the synchronous fluorescence intensity is proportional to the concentration of nucleic acids in the range 0.1-1.2 microg ml(-1) for calf thymus DNA, 0.1-0.6 microg ml(-1) for fish sperm DNA. The corresponding detection limit is 32.9 ng ml(-1) for calf thymus DNA and 24.6 ng ml(-1) for fish sperm DNA. This method is simple, inexpensive, rapid and sensitive. The recovery and relative standard deviation are satisfactory.     

Application of magdala red as a fluorescence probe in the determination of nucleic acids

A fluorescence quenching method was developed for the rapid determination of DNA and RNA using magdala red as fluorescence probe. In weakly acidic medium, the fluorescence of magdala red (lambdaex/lambdaem = 540/555 nm) can be largely quenched by DNA or RNA. The calibration graphs are linear over the range 0.01-1.2 microg/mL for both calf thymus DNA (CT DNA) and salmon DNA (SM DNA), and 0.015-1.0 microg/mL for yeast RNA, respectively. The corresponding detection limits are 6.0 ng/mL for CT DNA, 7.0 ng/mL for SM DNA and 15.0 ng/mL for yeast RNA, respectively. CT DNA could be determined in the presence of 20% (w/w) yeast RNA, and the relative standard deviation of six replicate measurements is 3.18% for 400 ng/mL of CT DNA. Interference from coexisting substances in the determination of DNA was also examined. Real samples were determined with satisfactory results.     

应用水相合成的CdTePCdS核壳型量子点荧光探针测定DNA

以巯基丙酸（HS-CH2CH2COOH）为稳定剂水相合成了核壳型CdTePCdS量子点（QDs）。CdTePCdSQDs具有宽而连续的激发光谱和狭窄对称的发射光谱,最大发射波长位于578nm。与DNA作用后荧光强度显著降低。基于DNA对量子点荧光的猝灭效应,将CdTePCdS量子点作为荧光探针建立了一种简便快速测定DNA的荧光分析法,详细研究了pH、量子点浓度、离子强度、温度等备件对量子点荧光及DNA测定的影响。该方法测定ctDNA线性范围为50．0—750．0ng／mL,检出限为20ng／mL．7次重复测定O．5ttg／mLctDNA的相对标准偏差为2．0％。方法可用于合成样品的测定。     

Fluorescence enhancement method for the determination of nucleic acids using cationic cyanine as a fluorescence probe

A fluorescence enhancement method with a cationic cyanine as a probe was developed for the determination of nucleic acids. Under the experimental conditions, the fluorescence enhancement of cyanine (lambda(ex)/lambda(em)= 524/591.5 nm) was observed in the presence of DNA. The calibration graphs were linear over the range of 0.01-15 microg mL(-1) for both calf thymus DNA (CT DNA) and fish sperm DNA (FS DNA). The limits of detection were 0.005 and 0.007 microg mL(-1) for CT DNA and FS DNA, respectively. The method was applied to the determination of DNA in synthetic and real samples and satisfactory results were obtained. A possible fluorescence enhancement mechanism was also studied.     

Determination of ciprofloxacin with functionalized cadmium sulfide nanoparticles as a fluorescence probe

A novel assay of ciprofloxacin with a sensitivity at the microgram level is proposed based on the measurement of enhanced fluorescence intensity signals resulting from the interaction of functionalized nano-CdS with ciprofloxacin. The CdS nanoparticles was synthesized by thioacetamide (TAA) and cadmium nitrate (Cd(NO(3))(2)) in the alkaline solution. At pH 7.4, the fluorescence signals of functionalized nano-CdS were greatly enhanced by ciprofloxacin with the increase concentration of ciprofloxacin. Linear relationship can be established between the enhanced fluorescence intensity and ciprofloxacin concentration in the range of (1.25-8.75)x10(-4) mg mL(-1) ((3.77-26.4) x 10(-4)mmol L(-1)) or (8.75-1200) x 10(-4)mg mL(-1) ((26.4-3625) x 10(-4) mmol L(-1)). The limit of detection is 7.64 x 10(-6) mg mL(-1) (2.31 x 10(-5)mmol L(-1)). Based on this, a new direct quantitative determination method for ciprofloxacin in human serum samples without separation of foreign substances was established. The contents of ciprofloxacin in human serum samples were determined with recovery of 95-105% and relative standard deviation (R.S.D.) of 1.5-2.5%. This method was proved to be very sensitive, rapid, simple and tolerance of most interfering substances.     

Determination of nucleic acids using calcein-neodymium complex as a fluorescence probe.

A novel fluorometric method has been developed for rapid determination of DNA and RNA with calcein-neodymium complex as a fluorescence probe. The method is based on the fluorescence enhancement of calcein-Nd(III) complex in the presence of DNA or RNA, with maximum excitation and emission wavelength at 489 nm and 514 nm, respectively. Under optimal conditions, the calibration graphs are linear over the range 0.5 - 3.0 microg/ml for both DNA and yeast RNA, 0.4 - 2.0 microg/ml for fish sperm DNA (FS DNA) and 0 - 3.0 microg/ml for calf thymus DNA (CT DNA). The corresponding detection limits are 15.1 ng/ml for DNA, 21.2 ng/ml for yeast RNA, 10.5 ng/ml for FS DNA and 8.9 ng/ml for CT DNA. The interaction mechanism for the binding of calcein-Nd(III) complex to DNA is also studied. The results of absorption spectra, fluorescence polarization measurements and thermal denaturation experiments, suggested that the interaction between calcein-Nd(III) complex and DNA is an electrostatic interaction.     

Cationic cyanine as a near-infrared fluorescent probe for the determination of nucleic acids

A new method with a cationic near-IR cyanine as fluorescent probe was developed for the determination of nucleic acids. The near-IR cyanine shows maximum excitation and emission wavelengths at 765 and 790 nm, respectively, in aqueous solution. The method is based on the fluorescence decrease of near-IR cyanine in the presence of nucleic acids. Under optimal conditions, the ratio of fluorescence intensity in the absence and presence of nucleic acids was proportional to the concentration of ¶nucleic acids over the range 0.10–1.2 μg/mL for CT (calf thymus) DNA or SM (salmon sperm) DNA, and 0.10–¶1.6 μg/mL for yeast RNA. The detection limits were ¶30 ng/mL for CT DNA, 25 ng/mL for SM DNA and ¶70 ng/mL for yeast RNA. The relative standard deviation (n = 6) was 2.1% for 500 ng/mL CT DNA, 2.4% for ¶500 ng/mL SM DNA and 2.7% for 500 ng/mL yeast RNA, respectively.     

Cationic cyanine as a near-infrared fluorescent probe for the determination of nucleic acids

A new method with a cationic near-IR cyanine as fluorescent probe was developed for the determination of nucleic acids. The near-IR cyanine shows maximum excitation and emission wavelengths at 765 and 790 nm, respectively, in aqueous solution. The method is based on the fluorescence decrease of near-IR cyanine in the presence of nucleic acids. Under optimal conditions, the ratio of fluorescence intensity in the absence and presence of nucleic acids was proportional to the concentration of nucleic acids over the range 0.10-1.2 microg/mL for CT (calf thymus) DNA or SM (salmon sperm) DNA, and 0.10-1.6 microg/mL for yeast RNA. The detection limits were 30 ng/mL for CT DNA, 25 ng/mL for SM DNA and 70 ng/mL for yeast RNA. The relative standard deviation (n = 6) was 2.1% for 500 ng/mL CT DNA, 2.4% for 500 ng/mL SM DNA and 2.7% for 500 ng/mL yeast RNA, respectively.     

Application of linear-sweep voltammetry to the determination of nucleic acids using crystal violet as an electrochemical probe

A new linear-sweep voltammetric assay of nucleic acids (NAs) based on their interaction with crystal violet (CV) is proposed. In a pH 3.5 Britton—Robinson (B-R) buffer solution, CV had an irreversible voltammetric reductive peak at −0.77 V and the peak current greatly decreased by the addition of NAs. Under the experimental conditions, the decrease in the peak current was used for the NAs assay 0.5–18.0 μg/mL of fish sperm DNA, 0.6–15.0 μg/mL of calf thymus DNA, and 0.8–12.0 μg/mL of yeast RNA. The detection limits (3σ) were 0.32, 0.47, and 0.61 μg/mL for fsDNA, ctDNA, and yRNA, respectively. The binding reaction can be completed after mixing DNA with CV within 10 min and the electrochemical response is stable for 2 h. There are seldom interferences in this method and three synthetic samples were analyzed with satisfactory results. The stoichiometry of the supramolecular complex with the binding number 3 and the binding constant 2.78 × 10¹⁴ is calculated using electrochemical data. The text was submitted by the authors in English.     

Terbium fluorescence as a sensitive,inexpensive probe for UV-induced damage in nucleic acids

Much effort has been focused on developing methods for detecting damaged nucleic acids. However, almost all of the proposed methods consist of multi-step procedures, are limited, require expensive instruments, or suffer from a high level of interferences. In this paper, we present a novel simple, inexpensive, mix-and-read assay that is generally applicable to nucleic acid damage and uses the enhanced luminescence due to energy transfer from nucleic acids to terbium(III) (Tb³⁺). Single-stranded oligonucleotides greatly enhance the Tb³⁺ emission, but duplex DNA does not. With the use of a DNA hairpin probe complementary to the oligonucleotide of interest, the Tb³⁺/hairpin probe is applied to detect ultraviolet (UV)-induced DNA damage. The hairpin probe hybridizes only with the undamaged DNA. However, the damaged DNA remains single-stranded and enhances the intrinsic fluorescence of Tb³⁺, producing a detectable signal directly proportional to the amount of DNA damage. This allows the Tb³⁺/hairpin probe to be used for sensitive quantification of UV-induced DNA damage. The Tb³⁺/hairpin probe showed superior selectivity to DNA damage compared to conventional molecular beacons probes (MBs) and its sensitivity is more than 2.5 times higher than MBs with a limit of detection of 4.36 ± 1.2 nM. In addition, this probe is easier to synthesize and more than eight times cheaper than MBs, which makes its use recommended for high-throughput, quantitative analysis of DNA damage.     

Determination of nucleic acids using fluorescence probe sensitized by microemulsion

Because the fluorescence of azur A can be quenched by adding nucleic acid, a sensitive fluorometric method for determination of nucleic acids at nanogram levels was established. Using optimal conditions, the calibration curves were linear in the range of 0-6.0 microg/mL for calf thymus deoxyribonucleic acid (ct DNA) and 0-7.0 microg/mL for herring sperm DNA (hs DNA). The limits of determination were 3.5 and 3.8 ng/mL, respectively, which shows the high sensitivity of this method. Triton X-100 microemulsion was applied as a sensitive media to enhance the sensitivity. The binding mode concerning the interactions of azur A with nucleic acids was also studied and the association constant with different binding numbers was obtained. The method has been applied to the determination of nucleic acid in both synthetic and real samples, such as cauliflower and pork liver, with satisfactory results.     

Silver nanoparticles fluorescence enhancement effect for determination of nucleic acids with kaempferol-Al(III)

Nucleic acids can greatly enhance fluorescence intensity of the kaempferol (Km)-Al(III) system in the presence of silver nanoparticles (AgNPs). Based on this, a novel method for the determination of nucleic acids is proposed. Under studied conditions, there are linear relationships between the extent of fluorescence enhancement and the concentration of nucleic acids in the range of 5.0 × 10⁻⁹ to 2.0 × 10⁻⁶ g mL⁻¹ for fish sperm DNA (fsDNA), 7.0 × 10⁻⁹ to 2.0 × 10⁻⁶ g mL⁻¹ for salmon sperm DNA (smDNA) and 2.0 × 10⁻⁸ to 3.0 × 10⁻⁶ g mL⁻¹ for yeast RNA (yRNA), and their detection limits are 2.5 × 10⁻⁹ g mL⁻¹, 3.2 × 10⁻⁹ g mL⁻¹ and 7.3 × 10⁻⁹ g mL⁻¹, respectively. Samples were satisfactorily determined. And the system of Km-Al(III)-AgNPs was used as a fluorescence staining reagent for sensitive DNA detection by DNA pattern of agarose gel electrophoresis analysis. The results indicate that the fluorescence enhancement should be attributed to the formation of Km-Al(III)-AgNPs-nucleic acids aggregations through electrostatic attraction and adsorption bridging action of Al(III) and the surface-enhanced fluorescence effect of AgNPs.     

Sensitive determination of nucleic acids using organic nanoparticle fluorescence probes

This paper describes the preparation of organic nanoparticles by reprecipitation method under sonication and vigorous stirring. Transmission electron microscopy (TEM) was used to characterize the size and size distribution of the luminescent nanoparticles. Their average diameter was about 25 nm with a size variation of +/-18%. The fluorescence decay lifetime of the nanoparticles also was determined on a self-equipped fluorospectrometer with laser light source. The lifetime (approximately 0.09 micros) of nanoparticles is about three times long as that of the monomer. The nanoparticles were in abundant of hydrophilic groups, which increased their miscibility in aqueous solution. These organic nanoparticles have high photochemical stability, excellent resistance to chemical degradation and photodegradation, and a good fluorescence quantum yield (25%). The fluorescence can be efficiently quenched by nucleic acids. Based on the fluorescence quenching of nanoparticles, a fluorescence quenching method was developed for determination of microamounts of nucleic acids by using the nanoparticles as a new fluorescent probe. Under optimal conditions, maximum fluorescence quenching is produced, with maximum excitation and emission wavelengths of 345 and 402 nm, respectively. Under optimal conditions, the calibration graphs are linear over the range 0.4-19.0 microgml(-1) for calf thymus DNA (ct-DNA) and 0.3-19.0 microgml(-1) for fish sperm DNA (fs-DNA). The corresponding detection limits are 0.25 microgml(-1) for ct-DNA and 0.17 microgml(-1) for fs-DNA. The relative standard deviation of six replicate measurements is 1.3-2.1%. The method is simple, rapid and sensitive with wide linear range. The recovery and relative standard deviation are very satisfactory.     

Preparation and application of functionalized nanoparticles of CdSe capped with 11-mercaptoundecanoic acid as a fluorescence probe

A new fluorescence probe, CdSe nanocrystal has been prepared and modified with 11-mercaptoundecanoic acid [HS-(CH₂)₁₀-COOH]. The functionalized nanoparticles were characterized using transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) spectroscopy. The results demonstrate that CdSe is dispersed homogeneously in aqueous solution and well protected from the environmental oxygen. They can be used as a new fluorescence probe for lysozyme, which was simple, rapid and specific. Under the optimum condition, the response is linearly proportional to the amount of lysozyme from 0.20 to 26.0 μg ml⁻¹, and the limit of detection is 0.115 μg ml⁻¹. The proposed method has been applied to the determination of lysozyme in egg white, with the recovery of 96-105%.     

Brilliant cresyl blue as a new red region fluorescent probe for determination of nucleic acids

A fluorescence quenching method was developed for determination of microamounts of nucleic acids by using brilliant cresyl blue (BCB) as a new red region fluorescent probe. In aqueous hexylmethylene tetramine solution, BCB showed maximum excitation and emission wavelengths at 626 and 670 nm, respectively, and the fluorescence of BCB could be greatly quenched by DNA (or RNA). Under optimal conditions, the calibration graphs are linear over the range of 0.02–0.80 μg/ml for SM DNA and 0.25–1.5 μg/ml for yeast RNA. The corresponding detection limits are 7 ng/ml for SM DNA and 25 ng/ml for yeast RNA, respectively. SM DNA can be determinated in the presence of 40% (w/w) RNA, and the relative standard deviation of six measurements is 2.5% for 500 ng/ml SM DNA. The result of the determination of golden staphylococcus DNA by this method was satisfactory.     

Application of l-cysteine-capped nano-ZnS as a fluorescence probe for the determination of proteins

Nanometer-sized l-cysteine-capped ZnS particles have been synthesized and used as a fluorescence probe to investigate the effect of proteins on fluorescent intensity. With =190 nm, maximum and constant synchronous fluorescence enhancement was produced at 267 nm and pH 5.12 in the presence of proteins. A highly sensitive synchronous fluorescence method for the rapid determination of proteins has been developed. Under optimum conditions, calibration graphs are linear over the range 0.03–8.0 g mL^–1 for bovine serum albumin (BSA), 0.01–6.0 g mL^–1 for human serum albumin (HSA), 0.05–8.0 g mL^–1 for -globulin (-G), and 0.04–4.0 g mL^–1 for ovalbumin, respectively. The relative standard deviations of seven replicate measurements were 1.75% for 1.0 g mL^–1 BSA, 1.90% for 1.0 g mL^–1 HSA, 1.65% for 1.0 g mL^–1 -G, and 2.32% for 1.0 g mL^–1 ovalbumin.     

L-Cysteine-coated CdSe/CdS core-shell quantum dots as selective fluorescence probe for copper(II) determination

Quantum dots (QDs) or semiconductor nanocrystals have been receiving great interest in the last few years. In this paper, L-cysteine-coated CdSe/CdS core-shell QDs (λ_em = 585 nm) have been prepared, which have excellent water-solubility. The full width at half maximum (FWHM) of the photoluminescence of these nanocrystals is very narrow (about 30 nm), and the quantum yield (QY) is 15% relative to Rhodamine 6G in ethanol (QY = 95%). With excess free L-cysteine in the solution, the fluorescence intensity of L-cysteine-coated CdSe/CdS QDs showed improved stability. It was found that the fluorescence of L-cysteine-capped CdSe/CdS QDs could be quenched only by copper (II) ions and was insensitive to other physiologically important cations, such as Ca²⁺, Mg²⁺, Zn²⁺, Al³⁺, Fe³⁺, Mn²⁺ and Ni²⁺ etc. Based on this finding, the quantitative analysis of Cu²⁺ with L-cysteine-capped CdSe/CdS QDs has been established. The linear range was from 1.0 × 10^− 8 to 2.0 × 10^− 7 mol L^− 1 and the limit of detection (LOD) was 3.0 × 10^− 9 mol L^− 1 (S/N = 3). The proposed method has first been applied to the determination of Cu²⁺ in vegetable samples with recoveries of 99.6–105.8%.