Dual-channel optical sensing platform for detection of diminazene aceturate based on thioglycolic acid-wrapped cadmium telluride/cadmium sulfide quantum dots.

A dual-channel optical sensing platform which combines the advantages of dual-wavelength overlapping resonance Rayleigh scattering (DWO-RRS) and fluorescence has been designed for the detection of diminazene aceturate (DA). It is based on the use of thioglycolic acid-wrapped CdTe/CdS quantum dots (Q-dots). In the absence of DA, the thioglycolic acid-wrapped CdTe/CdS Q-dots exhibit the high fluorescence spectrum and low RRS spectrum, so are selected to develop an easy-to-get system. In the presence of DA, the thioglycolic acid-wrapped CdTe/CdS Q-dots and DA form a complex through electrostatic interaction, which result in the RRS intensity getting enhanced significantly with new RRS peaks appearing at 317 and 397 nm; the fluorescence is powerfully quenched. Under optimum conditions, the scattering intensities of the two peaks are proportional to the concentration of DA in the range of 0.0061-3.0 µg mL(-1). The detection limits for the two single peaks are 4.1 ng mL(-1) and 3.3 ng mL(-1), while that of the DWO-RRS method is 1.8 ng mL(-1), indicating that the DWO-RRS method has high sensitivity. Besides, the fluorescence also exhibits good linear range from 0.0354 to 10.0 µg mL(-1) with a detection limit of 10.6 ng mL(-1). In addition, the system has been applied to the detection of DA in milk samples with satisfactory results.

Reaction analysis on Yb(3+) and DNA based on quantum dots: The design of a fluorescent reversible off-on mode.

Even though various strategies have reported for DNA detection, development of a simple, time-saving and specific fluorescent sensing platform still remains a desired goal. In this work, a quantum dots (QDs) based fluorescent reversible "off-on" mode was developed for sensitively recognition of herring sperm DNA (hsDNA). Firstly, in the "turn off" stage, the fluorescence of glutathione (GSH) capped CdTe QDs could be effectively quenched by ytterbium ion (Yb(3+)) was due to the occurrence of the electron transfer between Yb(3+) and the photoexcited QDs. And then, in the following "turn on" stage, with the effective binding reaction of Yb(3+) to hsDNA, the fluorescence intensity of GSH-capped CdTe QDs enhanced. Under the optimal conditions, the linear range of fluorescence versus the concentration of hsDNA was 0.010-12 µg/mL, and the detection limit was 3.033 ng/mL. In addition, the reaction mechanism among GSH-capped CdTe QDs, Yb(3+) and hsDNA were investigated by fluorescence spectroscopy, UV-vis spectrophotometry, fluorescence lifetime measurement and viscosity measurements. This analytical fluorescent reversible "off-on" pattern offered a way with good sensitivity and selectivity for the detection of hsDNA.

Detection of DNA utilizing a fluorescent reversible change of a biosensor based on the electron transfer from quantum dots to polymyxin B sulfate.

A fluorescent "turn off-on" pattern for the detection of herring sperm DNA (hsDNA) had been designed through utilizing the interaction between polymyxin B sulfate (PMBS) and hsDNA as an inherent performance and the fluorescent transformation of glutathione (GSH)-capped CdTe quantum dots (QDs) as an external manifestation. Due to the occurrence of the photoinduced electron transfer from the QDs to PMBS, the fluorescence of GSH-capped CdTe QDs could be effectively quenched by PMBS, causing the system into "off" state. With the addition of hsDNA, the quenched fluorescence of GSH-capped CdTe QDs could be restored for the reason that PMBS embedded into hsDNA double helix structure to form new complex and peeled off from the surface of GSH-capped CdTe QDs, leading the system into "on" condition. Corresponding experimental results illustrated that the relative recovered fluorescence intensity of GSH-capped CdTe QDs-PMBS system was near proportional to the concentration of hsDNA within the range of 0.059-15.0 µg mL(-1). This proposed method demonstrated a good linear correlation coefficient of 0.9937 and a detection limit (3 σ/K) of 0.018 µg mL(-1) for hsDNA. This dual-directional fluorescent biosensor overcame the selectivity problem commonly existed in the traditional mono-directional fluorescence detection mode and owned perfect analysis applications in biochemical DNA monitoring.

Sensitive detection of sodium cromoglycate with glutathione-capped CdTe quantum dots as a novel fluorescence probe.

A sensitive and simple analytical strategy for the detection of sodium cromoglycate (SCG) has been established based on a readily detectable fluorescence quenching effect of SCG for glutathione-capped (GSH-capped) CdTe quantum dots (QDs). The fluorescence of GSH-capped CdTe QDs could be efficiently quenched by SCG through electron transfer from GSH-capped CdTe QDs to SCG. Under optimum conditions, the response was linearly proportional to the concentration of SCG between 0.6419 and 100 µg/mL, with a correlation coefficient (R) of 0.9964; the detection limit (3δ/K) was 0.1926 µg/mL. The optimum conditions and the influence of coexisting foreign substances on the reaction were also investigated. The very effective and simple method reported here has been successfully applied to the determination of SCG in synthetic and real samples. It is believed that the established approach could have good prospects for application in the fields of clinical diseases diagnosis and treatment.

Highly sensitive fluorescence biosensors for sparfloxacin detection at nanogram level based on electron transfer mechanism of cadmium telluride quantum dots.

A sensitive fluorescence biosensor for determining sparfloxacin (SPF) based on the electron transfer mechanism and the fluorescence quenching effect of SPF to cadmium telluride quantum dots (CdTe QDs) was developed. The mechanism of the interaction between SPF and CdTe QDs was investigated by UV/Vis absorption and fluorescence spectroscopy. The biosensor could be used for the determination of SPF with a high sensitivity. Under optimum conditions, the linear range was from 0.28 to 40 µg SPF ml(-1) with a correlation coefficient of 0.9983, and the detection limit (3δ/k) was 83.7 ng SPF ml(-1). Furthermore, this method has been applied to the determination of SPF in the synthetic environmental water samples and the spiked human serum samples with good results.

Fluorescent reversible regulation based on the interactions of topotecan hydrochloride, neutral red and quantum dots.

The interactions of topotecan hydrochloride (THC), neutral red (NR) and thioglycolic acid (TGA) capped CdTe/CdS quantum dots (QDs) built a solid base for the controlling of the fluorescent reversible regulation of the system. This study was developed by means of ultraviolet-visible (UV-vis) absorption, fluorescence (FL), resonance Rayleigh scattering (RRS) spectroscopy and transmission electron microscopy (TEM). Corresponding experimental results revealed that the fluorescence of TGA-CdTe/CdS QDs could be effectively quenched by NR, while the RRS of the QDs enhanced gradually with the each increment of NR concentration. After the addition of THC, the strong covalent conjugation between NR and THC which was in carboxylate state enabled NR to be dissociated from the surface of TGA-CdTe/CdS QDs to form more stable complex with THC, thereby enhancing the fluorescence of the TGA-CdTe/CdS QDs-NR system. What is more, through analyzing the optical properties and experimental data of the reaction between TGA-CdTe/CdS QDs and NR, the possible reaction mechanism of the whole system was discussed. This combination of multiple spectroscopic techniques could contribute to the investigation for the fluorescent reversible regulation of QDs and a method could also be established to research the interactions between camptothecin drugs and dyes.

Molecular spectroscopic studies on the interactions of rhein and emodin with thioglycolic acid-capped core/shell CdTe/CdS quantum dots and their analytical applications.

Water-soluble thioglycolic acid (TGA)-capped core/shell CdTe/CdS quantum dots (QDs) were synthesized. The interactions of rhein and emodin with TGA-CdTe/CdS QDs were evaluated by fluorescence and ultraviolet-visible absorption spectroscopy. Experimental results showed that the high fluorescence intensity of TGA-CdTe/CdS QDs could be effectively quenched in the presence of rhein (or emodin) at 570 nm, which may have resulted from an electron transfer process from excited TGA-CdTe/CdS QDs to rhein (or emodin). The quenching intensity was in proportion to the concentration of both rhein and emodin in a certain range. Under optimized conditions, the linear ranges of TGA-CdTe/CdS QDs fluorescence intensity versus the concentration of rhein and emodin were 0.09650-60 µg/mL and 0.1175-70 µg/mL with a correlation coefficient of 0.9984 and 0.9965, respectively. The corresponding detection limits (3σ/S) of rhein and emodin were 28.9 and 35.2 ng/mL, respectively. This proposed method was applied to determine rhein and emodin in human urine samples successfully with remarkable advantages such as high sensitivity, short analysis time, low cost and easy operation. Based on this, a simple, rapid and highly sensitive method to determine rhein (or emodin) was proposed.

Detection of DNA using an "off-on" switch of a regenerating biosensor based on an electron transfer mechanism from glutathione-capped CdTe quantum dots to nile blue.

Although various strategies have been reported for double-stranded DNA (DNA) detection, development of a time-saving, specific, and regeneratable fluorescence sensing platform still remains a desired goal. In this study, we proposed a new DNA detection method that relies on an "off-on" switch of a regenerated fluorescence biosensor based on an electron transfer mechanism from glutathione (GSH)-capped CdTe quantum dots (QDs) to nile blue (NB). Initially, the high fluorescence of GSH-capped CdTe QDs could be effectively quenched by NB due to the binding of NB to the GSH on the surface of the QDs and the electron transfer from the photoexcited GSH-capped CdTe QDs to NB. Then, the high affinity of DNA to NB enabled the NB to be dissociated from the surface of GSH-capped CdTe QDs to form a more stable complex with DNA and suppress the electron transfer process between GSH-capped CdTe QDs and NB, thereby restoring the fluorescence of NB surface modified GSH-capped CdTe QDs (QDs-NB). In addition, we have testified the regenerability of the proposed DNA senor. The corresponding result shows that this DNA sensor is stable for two reuses. This fluorescence "off-on" signal was sensitive to the concentration of DNA in the range from 0.0092 to 25.0 µg mL(-1) with a good correlation coefficient of 0.9989, and the detection limit (3σ/S) was 2.78 ng mL(-1). To further investigate for perfect analysis performance, the developed biosensor was applied for the determination of DNA in human fresh serum samples with satisfactory results.

Quantum dots (QDs) based fluorescence probe for the sensitive determination of kaempferol.

In this work, using the quenching of fluorescence of thioglycollic acid (TGA)-capped CdTe quantum dots (QDs), a novel method for the determination of kaempferol (KAE) has been developed. Under optimum conditions, a linear calibration plot of the quenched fluorescence intensity at 552nm against the concentration of KAE was observed in the range of 4-44µgmL(-1) with a detection limit (3σ/K) of 0.79µgmL(-1). In addition, the detailed reaction mechanism has also been proposed on the basis of electron transfer supported by ultraviolet-visible (UV-vis) absorption and fluorescence (FL) spectroscopy. The method has been applied for the determination of KAE in pharmaceutical preparations with satisfactory results. The proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation.

Characterization of the interaction of a mono-6-thio-ß-cyclodextrin-capped CdTe quantum dots-methylene blue/methylene green system with herring sperm DNA using a spectroscopic approach.

Novel, water-soluble CdTe quantum dots (QDs) capped with ß-cyclodextrin (ß-CD) and ~ 4.0 nm in diameter were synthesized in aqueous solution, and characterized using transmission electron microscopy (TEM). A fluorescence-sensing system based on the photoinduced electron transfer (PET) of (mono-6-thio-ß-CD)-CdTe QDs was then designed to measure the interaction of phenothiazine dyes [methylene blue (MB) and methylene green (MG)] with herring sperm DNA (hsDNA). This fluorescence-sensing system was based on a fluorescence "OFF-ON" mode. First, MB/MG adsorbed on the surface of (mono-6-thio-ß-CD)-CdTe QDs effectively quenches the fluorescence of (mono-6-thio-ß-CD)-CdTe QDs through PET. Then, addition of hsDNA restores the fluorescence intensity of (mono-6-thio-ß-CD)-CdTe QDs, because hsDNA can bind with MB/MG and remove it from the as-prepared (mono-6-thio-ß-CD)-CdTe QDs. In addition, detailed reaction mechanisms of the (mono-6-thio-ß-CD)-CdTe QDs-MB/MG-hsDNA solution system were studied using optical methods, by comparison with the TGA-CdTe QDs-MB/MG-hsDNA solution system.

Fluorescence quenching investigation on the interaction of glutathione-CdTe/CdS quantum dots with sanguinarine and its analytical application.

Water-soluble glutathione (GSH)-capped core/shell CdTe/CdS quantum dots (QDs) were synthesized. In pH5.4 sodium phosphate buffer medium, the interaction between GSH-CdTe/CdS QDs and sanguinarine (SA) was investigated by spectroscopic methods, including fluorescence spectroscopy and ultraviolet-visible absorption spectroscopy. Addition of SA to GSH-CdTe/CdS QDs results in fluorescence quenching of GSH-CdTe/CdS QDs. Quenching intensity was in proportion to the concentration of SA in a certain range. Investigation of the quenching mechanism, proved that the fluorescence quenching of GSH-CdTe/CdS QDs by SA is a result of electron transfer. Based on the quenching of the fluorescence of GSH-CdTe/CdS QDs by SA, a novel, simple, rapid and specific method for SA determination was proposed. The detection limit for SA was 3.4 ng/mL and the quantitative determination range was 0.2-40.0 µg/mL with a correlation coefficient of 0.9988. The method has been applied to the determination of SA in synthetic samples and fresh urine samples of healthy human with satisfactory results.

Fluorescence quenching studies on the interaction of riboflavin with tryptophan and its analytical application.

The ineraction between riboflavin (RBF) and tryptophan (Trp) was investigated using fluorescence spectroscopy and UV-vis absorption spectroscopy under physiological conditions. The fluorescence of Trp was quenched by RBF via dynamic quenching, which was analyzed using the Stern-Volmer relation. The value of the Forster distance R0 (2.31 nm) was obtained according to the Forster's theory of nonradiative energy transfer. Under physiological conditions, a linear relationship could be established between the quenched fluorescence intensity of Trp and the concentration of RBF in the range of 5.8 × 10(-7) -2.0 × 10(-5) mol/L. The detection limit was 1.8 × 10(-7) mol/L. The method was successfully applied to determine riboflavin concentrations in pharmaceutical samples.

Fluorescence enhancement of CdTe/CdS quantum dots by coupling of glyphosate and its application for sensitive detection of copper ion.

A novel fluorescent probe for Cu(2+) determination based on the fluorescence quenching of glyphosate (Glyp)-functionalized quantum dots (QDs) was firstly reported. Glyp had been used to modify the surface of QDs to form Glyp-functionalized QDs following the capping of thioglycolic acid on the core-shell CdTe/CdS QDs. Under the optimal conditions, the response was linearly proportional to the concentration of Cu(2+) between 2.4×10(-2)µg mL(-1) and 28µg mL(-1), with a detection limit of 1.3×10(-3)µg mL(-1) (3δ). The Glyp-functionalized QDs fluorescent probe offers good sensitivity and selectivity for detecting Cu(2+). The fluorescent probe was successfully used for the determination of Cu(2+) in environmental samples. The mechanism of reaction was also discussed.

Study on the interaction of CdTe quantum dots with coumaric acid and caffeic acid based on fluorescence reversible tune.

This paper describes the synthesis of CdTe quantum dots (QDs) together capped by glutathione and thioglycolic acid (GSH and TGA) in aqueous solution. The narrow photoluminescence (fwhm ≤ 40 nm) CdTe QDs, whose emission spans most of the visible spectrum from green through red, has a quantum yield (QY) of 68% at room temperature. GSH/TGA-CdTe QDs are characterized by various experimental techniques such as optical absorption, photoluminescence and AFM measurements. Coumaric acid and caffeic acid is able to quench the fluorescence of GSH/TGA-CdTe QDs, and the fluorescence intensity is linearly proportional to the concentration of quenchers. The addition of bovine serum albumin (BSA) restores the fluorescence intensity of GSH/TGA-CdTe QDs-coumaric acid system and GSH/TGA-CdTe QDs-caffeic acid system. The fluorescence recovery was due to the interaction of BSA with coumaric acid and caffeic acid, leading to the freeing of the GSH/TGA-CdTe QDs. The fluorescence quenching mechanism of GSH/TGA-CdTe QDs was discussed. The binding constant and thermodynamics parameters of BSA-coumaric acid and BSA-caffeic acid during the binding process were calculated in the paper.

Studying the interaction between CdTe quantum dots and Nile blue by absorption, fluorescence and resonance Rayleigh scattering spectra.

Thioglycolic acid (TGA) capped CdTe quantum dots (QDs) with the diameter of 2-3nm were synthesized. The interaction between CdTe QDs and Nile blue (NB) was investigated by ultraviolet-visible (UV-vis) absorption, resonance Rayleigh scattering (RRS) and fluorescence spectroscopy. UV-vis absorption spectrum of CdTe QDs and NB obviously changed, showing that CdTe QDs could associate with NB to form a new complex. At pH 6.8, NB effectively quenched the fluorescence of CdTe QDs. It was proved that the fluorescence quenching of CdTe QDs by NB was mainly result of the formation of CdTe QDs-NB complex, electrostatic attraction and hydrophobic forces played a major role in stabilizing the complex. The binding molar ratio of CdTe QDs and NB was 5:1 by a mole-ratio method. The interaction between CdTe QDs and NB lead to the remarkable enhancement of RRS and the enchantments were in proportional to the concentration of NB in a certain range. The mechanism of the interaction between CdTe QDs and NB, reasons for the enhancement of RRS intensity were also discussed. The obtained results suggested the more satisfactory mechanism for the interaction between CdTe QDs and NB.

Resonance Rayleigh-scattering spectral method for the determination of some aminoglycoside antibiotics using CdTe quantum dots as a probe.

A novel method is used for the determination of some aminoglycoside antibiotics (AGs) such as etimicin (ETM), isepamicin (ISP) and amikacin (AMK). It is based on the resonance Rayleigh scattering (RRS) intensities enhanced by AGs-induced CdTe quantum dots aggregation. Under the optimum conditions, the increments in RRS intensity were directly proportional to the concentration of AGs in certain ranges. At the same time, the second-order scattering, the frequency-doubling scattering and the frequency-trebling scattering intensities were also enhanced and their increments were proportional to the concentration of AGs. Among them, the RRS method had the highest sensitivity; the linear ranges and detection limits for ETM, ISP and AMK were 0.085-7.2, 0.0067-1.2, 0.017-6.0 and 0.025, 0.0051, 0.0020 µg mL(-1) . This method was applied to the measurement of AGs in human serum and urine with satisfactory results. In addition, the reaction mechanism and the reasons for the enhancement of RRS are discussed using fluorescence, RRS, transmission electron microscope technology and quantum chemistry method.

Resonance Rayleigh scattering and resonance non-linear scattering method for the determination of aminoglycoside antibiotics with water solubility CdS quantum dots as probe.

In pH 6.6 Britton-Robinson buffer medium, the CdS quantum dots capped by thioglycolic acid could react with aminoglycoside (AGs) antibiotics such as neomycin sulfate (NEO) and streptomycin sulfate (STP) to form the large aggregates by virtue of electrostatic attraction and the hydrophobic force, which resulted in a great enhancement of resonance Rayleigh scattering (RRS) and resonance non-linear scattering such as second-order scattering (SOS) and frequency doubling scattering (FDS). The maximum scattering peak was located at 310 nm for RRS, 568 nm for SOS and 390 nm for FDS, respectively. The enhancements of scattering intensity (DeltaI) were directly proportional to the concentration of AGs in a certain ranges. A new method for the determination of trace NEO and STP using CdS quantum dots probe was developed. The detection limits (3 sigma) were 1.7 ng mL(-1) (NEO) and 4.4 ng mL(-1) (STP) by RRS method, were 5.2 ng mL(-1) (NEO) and 20.9 ng mL(-1) (STP) by SOS method and were 4.4 ng mL(-1) (NEO) and 25.7 ng mL(-1) (STP) by FDS method, respectively. The sensitivity of RRS method was the highest. The optimum conditions and influence factors were investigated. In addition, the reaction mechanism was discussed.

Study on the interaction between CdSe quantum dots and chitosan by scattering spectra.

Two different stabilizing agents thioglycolic acid (TGA) and L-cysteine (L-Cys) capped CdSe QDs with the diameter of 2 nm were synthesized, large amounts of stabilizing agents connected to CdSe QDs surface through Cd-S bond. The interaction between chitosan and QDs had been investigated, respectively. The interaction lead to the remarkable enhancement of RRS, RNLS and the enchantments were in proportional to the concentration of chitosan in a certain range. Under the optimal conditions, compared with TGA-CdSe QDs, the interaction between L-Cys-CdSe QDs with chitosan owned more broad linear range 0.042-3.0 microg mL(-1) and lower detect limits 1.2 ng mL(-1). The influences of factors on the interaction between chitosan with QDs and some foreign substances were all examined, which showed that the methods had a good sensitivity and selectivity. Based on this, it is hoped to build a method for the determination of chitosan using CdSe QDs as probes. Through Fourier transform infrared spectroscopy (FTIR) transmission electron microscopy (TEM), it was speculated that CdSe QDs interacted with chitosan to form a network structure aggregates through electrostatic attraction and hydrophobic forces. The reasons for the enhancement of RRS intensity were assumed as follows: resonance enhanced Rayleigh scattering effect, increase of the molecular volume, and hydrophobic effect.

[Classification of Panax quinquefolium L. and Panax ginseng C. A. Mey. based on FTIR analysis with SVM].

The support vector machine (SVM) is a new learning technique based on the statistical learning theory. In the present paper, forty Panax quinquefolium L. samples were used as experimental materials. The classification models were established using Fourier transform infrared spectra(FTIR)-SVM training method with the intention of identifying whether the Panax quinquefolium L. samples are genuine or they are just Panax ginseng C. A. Mey. samples. The thirty samples in training set were identified by the classifying models with an accurate rate of 100%, while the ten estimate samples had an accurate rate of 90%. The research result shows the feasibility of establishing the models with FTIR-SVM method to identify Panax quinquefolium L. samples and Panax ginseng C. A. Mey.

[Photochemical preparation of Au nanoparticles with polyethyelene glycol and its resonance scattering spectral study].

The nano-photochemical reaction of polyethyelene glycol (PEG)-Au3+ was studied by resonance scattering and absorption spectrophotometry, and transmission electron microscopy. Influence of various factors on the preparation of gold nanoparticles was considered. There is a correlation between the molecular mass of PEG and the size of gold nanoparticles. A new photochemical method was proposed for the preparation of gold nanoparticles in size of 6-60 nm, using different molecular mass of PEG. The cause of obtaining gold nanoparticle with different size is the different space effect and hydrophobic property of PEG. A reasonable nano-reaction mechanism was developed.