Synthesis of Multifunctional Mn‐Doped CdTe/ZnS Core/Shell Quantum Dots

The synthesis of a novel water‐soluble Mn‐doped CdTe/ZnS core‐shell quantum dots using a proposed ultrasonic assistant method and 3‐mercaptopropionic acid (MPA) as stabilizer is descried. To obtain a high luminescent intensity, post‐preparative treatments, including the pH value, reaction temperature, reflux time and atmosphere, have been investigated. For an excellent fluorescence of Mn‐doped CdTe/ZnS, the optimal conditions were pH 11, reflux temperature 100°C and reflux time 3 h under N₂ atmosphere. While for phosphorescent Mn‐doped CdTe/ZnS QDs, the synthesis at pH 11, reflux temperature 100°C and reflux time 3 h under air atmosphere gave the best strong phosphorescence. The characterizations of Mn‐doped CdTe/ZnS QDs were also identified using AFM, IR, powder XRD and thermogravimetric analysis. The data indicated that the photochemical stability and the photoluminescence of CdTe QDs are greatly enhanced by the outer inorganic ZnS shell, and the doping Mn²⁺ ions in the as‐prepared quantum dots contribute to strong luminescence. The strong luminescence of Mn‐doped CdTe/ZnS QDs reflected that Mn ions act as recombination centers for the excited electron‐hole pairs, attributing to the transition from the triplet state (⁴T₁) to the ground state (⁶A₁) of the Mn²⁺ ions. All the experiments demonstrated that the surface states played important roles in the optical properties of Mn‐doped CdTe/ZnS core‐shell quantum dots.     

Ascorbic Acid Induced Enhancement of Room Temperature Phosphorescence of Sodium Tripolyphosphate‐Capped Mn‐Doped ZnS Quantum Dots: Mechanism and Bioprobe Applications

Although quantum dot (QD)‐based room temperature phosphorescence (RTP) probes are promising for practical applications in complex matrixes such as environmental, food and biological samples, current QD‐based‐RTP probes are not only quite limited but also exclusively based on the RTP quenching mechanism. Here we report an ascorbic acid (AA) induced phosphorescence enhancement of sodium tripolyphosphate‐capped Mn‐doped ZnS QDs, and its application for turn‐on RTP detection. The chelating ability allows AA to extract the Mn and Zn from the surface of the QDs and to generate more holes which are subsequently trapped by Mn²⁺, while the reducing property permits AA to reduce Mn³⁺ to Mn²⁺ in the excited state, thereby enhancing the excitation and orange emission of the QDs. The enhanced RTP intensity of the QDs increases linearly with the concentration of AA in the range of 0.05–0.8 μM . Thus, a QD‐based RTP probe for AA is developed. The proposed QD‐based turn‐on RTP probe avoids tedious sample pretreatment, and offers good sensitivity and selectivity for AA in the presence of the main relevant metal ions and other molecules in biological fluids. The limit of detection (3s) of the developed method is 9 nM AA, and the relative standard deviation is 4.8 % for 11 replicate detections of 0.1 μM AA. The developed method is successfully applied to the analysis of real samples of human urine and plasma for AA with quantitative recoveries from 96 to 105 %.     

Sensing during In Situ Growth of Mn‐Doped ZnS QDs: A Phosphorescent Sensor for Detection of H2S in Biological Samples

Monitoring the in situ growth of Mn‐doped ZnS quantum dots is shown to be a route to selectively detect H₂S, an important endogenously produced signalling molecule. The use of Mn²⁺ as a dopant resulted in orange phosphorescence, making it possible to avoid the background fluorescence from biological surroundings that can occur at other wavelengths. The choice of ZnS QDs as the host material ensured selectivity, since only sulfide can precipitate Zn²⁺ and Mn²⁺ from aqueous solution.     

Doped zinc sulfide quantum dots based phosphorescence turn-off/on probe for detecting histidine in biological fluid

We report a turn-on phosphorescence probe for detection of histidine based on Co²⁺-adsorbed N-acetyl-l-cysteine (NAC) capped Mn: ZnS quantum dots (QDs) which is directly synthesized by the hydrothermal method. The phosphorescence of NAC-Mn: ZnS QDs is effectively quenched by Co²⁺ attributing to the adsorption of Co²⁺ onto the surface of QDs with a concomitant in suppressing the recombination process of hole and electron of QDs. The phosphorescence of Co²⁺-adsorbed NAC-Mn: ZnS QDs can be recovered by binding of Co²⁺ with histidine. The quenching and regeneration of the phosphorescence of NAC-Mn: ZnS QDs have been studied in detail. The as-prepared QDs-based probe is applied to determine histidine with a linear range of 1.25–30 μM and a detection limit of 0.74 μM. The relative standard deviation for eleven repeat detections of 20 μM histidine is 0.65%. Co²⁺-adsorbed NAC-Mn: ZnS QDs show high sensitivity and good selectivity to histidine over other amino acids, metal ions and co-existing substances. The proposed QDs probe has been successfully applied to determination of histidine in human urine samples with good recoveries of 98.5–103%.     

Ratiometric two-photon excited photoluminescence of quantum dots triggered by near-infrared-light for real-time detection of nitric oxide release in situ

Probe-donor integrated nanocomposites were developed from conjugating silica-coated Mn²⁺:ZnS quantum dots (QDs) with MoS₂ QDs and photosensitive nitric oxide (NO) donors (Fe₄S₃(NO)₇⁻, RBS). Under excitation with near-infrared (NIR) light at 808 nm, the Mn²⁺:ZnS@SiO₂/MoS₂-RBS nanocomposites showed the dual-emissive two-photon excited photoluminescence (TPEPL) that induced RBS photolysis to release NO in situ. NO caused TPEPL quenching of Mn²⁺:ZnS QDs, but it produced almost no impact on the TPEPL of MoS₂ QDs. Hence, the nanocomposites were developed as a novel QDs-based ratiometric TPEPL probe for real-time detection of NO release in situ. The ratiometric TPEPL intensity is nearly linear (R² = 0.9901) with NO concentration in the range of 0.01∼0.8 μM, which corresponds to the range of NO release time (0∼15 min). The detection limit was calculated to be approximately 4 nM of NO. Experimental results confirmed that this novel ratiometric TPEPL probe possessed high selectivity and sensitivity for the detection of NO against potential competitors, and especially showed high detection performance for NIR-light triggered NO release in tumor intracellular microenvironments. These results would promote the development of versatile probe-donor integrated systems, also providing a facile and efficient strategy to real-time detect the highly controllable drug release in situ, especially in physiological microenvironments.     

基于Mn掺杂ZnS量子点室温磷光法检测盐酸巴马汀

本文以3-巯基丙酸(3-Mercaptopropionic Acid,MPA)为稳定剂,采用水相合成法制备了Mn掺杂ZnS量子点(Mn∶ZnS QDs),基于Mn∶ZnS QDs的室温磷光性质,盐酸巴马汀(Palmatine Hydrochloride,PaH)可与Mn∶ZnS QDs发生静电作用,使得Mn∶ZnS QDs发生室温磷光猝灭效应,从而发展了一种高效、快速检测人体体液中痕量PaH的新方法。实验结果表明,当PaH的浓度在0.75~30μmol/L范围时,其浓度与室温磷光猝灭强度(ΔIRTP)呈良好的线性关系,相关系数为0.996,检出限为0.35μmol/L,加标回收率为94.0%~103.3%。     

CdS/ZnS core-shell quantum dots capped with mercaptoacetic acid as fluorescent probes for Hg(II) ions

We have synthesised water soluble CdS/ZnS core-shell quantum dots (QDs) capped with mercaptoacetic acid (MAA). They were characterised by UV–vis absorption spectroscopy, fluorescence spectroscopy, FT-IR and transmission electron microscopy. Such QDs can be used as fluorescent probes for the determination of metal ions because they quench the fluorescence of the QDs. The QDs exhibit absorption and emission bands at 345?nm and 475?nm respectively, which is more longer wavelength compared to MAA-capped CdS QDs and obviously is the result of the larger particle size. The fluorescence intensity of CdS-based QDs is strongly enhanced by coating them with a shell of ZnS. In addition, such functionalised QDs are more sensitive to Hg(II) ions. Parameters such as pH, temperature and concentration of the QDs have been optimised. A high selectivity and sensitivity toward Hg(II) ions is obtained at pH 7.4 and a concentration of 12.0?mg of QDs per L. Under optimum conditions, the fluorescence intensity of CdS/ZnS QDs is linearly proportional to the concentration of Hg(II) in the range from 2.5 to 280?nM, with a detection limit of 2.2?nM. The effect of potentially interfering cations was examined and confirmed the high selectivity of this material.

Near‐Infrared Emission from Tin–Lead (Sn–Pb) Alloyed Perovskite Quantum Dots by Sodium Doping

Phase‐stable CsSn_xPb_1?xI₃ perovskite quantum dots (QDs) hold great promise for optoelectronic applications owing to their strong response in the near‐infrared region. Unfortunately, optimal utilization of their potential is limited by the severe photoluminescence (PL) quenching, leading to extremely low quantum yields (QYs) of approximately 0.3 %. The ultra‐low sodium (Na) doping presented herein is found to be effective in improving PL QYs of these alloyed QDs without alerting their favourable electronic structure. X‐ray photoelectron spectroscopy (XPS) studies suggest the formation of a stronger chemical interaction between I^? and Sn²⁺ ions upon Na doping, which potentially helps to stabilize Sn²⁺ and suppresses the formation of I vacancy defects. The optimized PL QY of the Na‐doped QDs reaches up to around 28 %, almost two orders of magnitude enhancement compared with the pristine one.     

Electrophoretic properties of BSA-coated quantum dots

Low toxic InP/ZnS quantum dots (QDs), ZnS:Mn²⁺/ZnS nanocrystals and CdSe/ZnS nanoparticles were rendered water-dispersible by different ligand-exchange methods. Eventually, they were coated with bovine serum albumin (BSA) as a model protein. All particles were characterised by isotachophoresis (ITP), laser Doppler velocimetry (LDV) and agarose gel electrophoresis. It was found that the electrophoretic mobility and colloidal stability of ZnS:Mn²⁺/ZnS and CdSe/ZnS nanoparticles, which bore short-chain surface ligands, was primarily governed by charges on the nanoparticles, whereas InP/ZnS nanocrystals were not charged per se. BSA-coated nanoparticles showed lower electrophoretic mobility, which was attributed to their larger size and smaller overall charge. However, these particles were colloidally stable. This stability was probably caused by steric stabilisation of the BSA coating.     

基于Mn掺杂ZnS量子点的室温磷光传感应用的研究进展

与一般有机染料分子相比,半导体材料量子点具有优异的光学性能,在多个领域得到了广泛的应用.量子点具有窄而对称且可调的发射波长、宽激发强吸收、抗光漂白能力强以及水溶性好等诸多优势,引起了研究者广泛关注.为了增加量子点的斯托克斯位移从而很好地避免量子点的自猝灭现象,引入掺杂物是一种很有效的方式.掺杂量子点不仅保留了量子点原有的优点,而且还赋予量子点额外的优异性能.如Mn掺杂ZnS量子点生物相容性好,不含Cd和Hg等有害元素,而且Mn2+的加入使其具有优异的室温磷光特性.磷光检测能很好地避开生物背景荧光的干扰,使得Mn掺杂ZnS量子点能够广泛应用于磷光生物分析.本文综述了Mn掺杂ZnS量子点在室温磷光分析中的研究进展,着重介绍了几种具有启发意义的设计策略,包括其发光机理以及应用于离子、分子以及生物大分子等的检测.     

Novel β-cyclodextrin modified quantum dots as fluorescent probes for polycyclic aromatic hydrocarbons （PAHs）

Water-soluble CdSe/ZnS quantum dots （QDs） were prepared via a simple sonochemical procedure using β-cyclodextrin （CD） as surface coating agent. The QDs displayed a sensitive emission enhancement for anthracene over other related polycyclic aromatic hydrocarbons, and the detection limit was around 1.6 × 10^-8 mol/L.     

Quantum dot-based "turn-on" fluorescent probe for detection of zinc and cadmium ions in aqueous media

Health or environmental issue caused by abnormal level of metal ions like Zn²⁺ or Cd²⁺ is a worldwide concern. Developing an inexpensive and facile detection method for Zn²⁺ and Cd²⁺ is in urgent demand. Due to their super optical properties, fluorescent quantum dots (QDs) have been developed as a promising alternative for organic dyes in fluorescence analysis. In this study, a CdTe QDs-based sensitive and selective probe for Zn²⁺ and Cd²⁺ in aqueous media was reported. The proposed probe worked in fluorescence “turn-on” mode. The initial bright fluorescence of CdTe QDs was effectively quenched by sulfur anions (S²⁻). The presence of Zn²⁺ (or Cd²⁺) can “turn-on” the weak fluorescence of QDs quenched by S²⁻ due to the formation of ZnS (or CdS) passivation shell. Under optimal conditions, a good linear relationship between the fluorescence response and concentration of Zn²⁺ (or Cd²⁺) could be obtained in the range from 1.6 to 35 μM (1.3–25 μM for Cd²⁺). The limit of detection (LOD) for Zn²⁺ and Cd²⁺ were found to be 1.2 and 0.5 μM, respectively. Furthermore, the present probe exhibited a high selectivity for Zn²⁺ and Cd²⁺ over other metal ions and was successfully used in the detection of Zn²⁺ or Cd²⁺ in real water samples.     

Two Recent Studies Involving Pressure Tuning Spectroscopy

In this paper we present two recent studies utilizing pressure tuning spectroscopy. In the first of these we use high pressure photoluminescence to characterize the large difference in luminescence efficiency at one atmosphere between [Ru(bpy)₃]²⁺ and [Ru(bpy)₂py₂]²⁺ ions. The lower efficiency of the latter ion is due to dissipation of excitation energy by motion of the pyridines. The second study involves a combination of photo-and thermoluminescence of doped ZnS phosphors of technical importance. In the phosphor doped with CI and Cu⁺ we demonstrate that the donors are pinned to the conduction band and the acceptors to the valence band. We invoke the presence of “deep levels” to describe the behavior of the traps. In the phosphor doped with Mn⁺² plus C1- and Cu⁺ a series of traps appeared as the pressure was increased. By comparison with ZnS doped only with Mn⁺² it was possible to assign some of the traps to C1- and others to Mn⁺².     

Long‐Lived Charge Carriers in Mn‐Doped CdS Quantum Dots for Photoelectrochemical Cytosensing

Photoelectrochemical (PEC) biosensing with semiconductor quantum dots (QDs) has received great attention because it integrates the advantages of both photo‐excitation and electrochemical detection. During the photon‐to‐electricity conversion in PEC processes, electron–hole (charge) separation competes with electron–hole recombination, and the net effect essentially determines the performance of PEC biosensors. Herein, we propose a new approach for slowing down electron–hole recombination to increase charge separation efficiency for PEC biosensor development. Through doping with Mn²⁺, a pair of d bands (⁴T₁ and ⁶A₁) is inserted between the conduction and valence bands of CdS QDs, which alters the electron–hole separation and recombination dynamics, allowing the generation of long‐lived charge carriers with ms‐scale lifetime that decay about 10⁴–10⁵‐fold more slowly than in the case of undoped QDs. Photocurrent tests indicated that Mn²⁺ doping resulted in an approximately 80 % increase in photocurrent generation compared with undoped CdS QDs. For application, the Mn‐doped CdS QDs were coated on the surface of a glassy carbon electrode and functionalized with a cell surface carbohydrate‐specific ligand (3‐aminophenylboronic acid). In this way, a sensitive cytosensor for K562 leukemia cells was constructed. Moreover, the sugar‐specific binding property of 3‐aminophenylboronic acid allowed the electrode to serve as a switch for the capture and release of cells. This has been further explored with a view to developing a reusable PEC cytosensing platform.     

Hue‐ and Chromaticity‐Based Exploration of Surface Complexation‐Induced Tunable Emission from Non‐Luminescent Quantum Dots

Herein we report the use of a hue parameter of HSV (Hue, Saturation and Value) color space—in combination with chromaticity color coordinates—for exploring the complexation‐induced luminescence color changes, ranging from blue to green to yellow to white, from a non‐luminescent Fe‐doped ZnS quantum dot (QD). Importantly, the surface complexation reaction helped a presynthesized non‐luminescent Fe‐doped ZnS QD to glow with different luminescence colors (such as blue, cyan, green, greenish‐yellow, yellow) by virtue of the formation of various luminescent inorganic complexes (using different external organic ligands), while the simultaneous blue‐ and yellow‐emitting complex formation on the surface of non‐luminescent Fe‐doped ZnS QD led to the generation of white light emission, with a hue mean value of 85 and a chromaticity of (0.28,0.33). Furthermore, the surface complexation‐assisted incorporation of luminescence properties to a non‐luminescent QD not only overcomes their restricted luminescence‐based applications such as light‐emitting, biological and sensing applications but also bring newer avenues towards unravelling the surface chemistry between QDs and inorganic complexes and the advantage of having an inorganic complex with QD for their aforementioned useful applications.     

Signal-on bimodal sensing glucose based on enzyme product-etching MnO_2 nanosheets for detachment of MoS_2 quantum dots

The sensitive and rapid detection of blood glucose is very important for monitoring and managing diabetes.Herein,a fluorescent/magnetic bimodal sensing strategy is proposed for glucose detection using a multifunction-responsive nanocomposite(MoS_2 QDs-MnO_2 NS).MoS_2 QDs act as fluorescent probes,and MnO_2 nanosheets are used as both quenchers and recognizers in this sensing platform.In the presence of glucose-mediated enzyme product(H_2 O_2),MnO_2 nanosheet is etched,thus releasing MoS_2 QDs and Mn~(2+)ions,which causes the significantly enhancement of fluorescent and magnetic signals.Furthermore,MoS_2 QDs-MnO_2 NS-based fluorescent test paper is constructed for H_2 O_2 sensing with the naked eyes.Under optimal conditions,the dual linear ranges of 20-300 μmol/L and 40-250 μmol/L toward glucose detection are obtained for the fluorescent and magnetic mode,respectively.Furthermore,this bimodal assay exhibits good reproducibility and acceptable accuracy in glucose detection of clinical samples,demonstrating great versatility and flexibility of multifunctional probes in glucose detection.     

Fluorescent turn-on detection of cysteine using a molecularly imprinted polyacrylate linked to allylthiol-capped CdTe quantum dots

CdTe quantum dots capped with thioglycolic acid (TGA) display a strong turn-on fluorescence response if exposed to solutions of cysteine (Cys). In order to exploit this effect, a molecularly imprinted polymer (MIP) for Cys was covalently linked to the QDs via allyl mercaptan. The resulting nanomaterials (QDs, MIP-coated QDs, and nonimprint-coated QDs) were characterized by FTIR and scanning electron microscopy. The adsorption of Cys was studied in phosphate buffer (pH 7.4) with respect to equilibration times (5, 15, and 40 min, respectively), binding constants [2.98, 2.42, and 0.96 (×10⁴ M^?1)], and Langmuir isotherms (R²?=?0.9995, 0.9999, and 0.9983) in the Cys concentration range between 3.33 μM to 500 μM. The method has a detection limit of 0.85 μM (3σ, blank, for n?=?10). The selectivity of the MIP-coated QDs for Cys over 19 other amino acids is similar to that of bare QDs, but MIP-QDs afford better recoveries of Cys from solutions also containing bovine serum albumin (90 %) and fetal bovine serum (97 %), respectively, when compared to the recoveries that are obtained with bare (non-imprinted) QDs (135 % and 120 %). This is probably due to the fact that the outer MIP shell largely reduces protein wrapping, dot aggregation, and matrix inclusion.

Highly sensitive detection of lead(II) ion using multicolor CdTe quantum dots

Multicolor and water-soluble CdTe quantum dots (QDs) were synthesized with thioglycolic acid (TGA) as stabilizer. These QDs have a good size distribution, display high fluorescence quantum yield, and can be applied to the ultrasensitive detection of Pb(II) ion by virtue of their quenching effect. The size of the QDs exerts a strong effect on sensitivity, and quenching of luminescence is most effective for the smallest particles. The quenching mechanism is discussed. Fairly selective detection was accomplished by utilizing QDs with a diameter of 1.6?nm which resulted in a detection limit of 4.7?nmol?L^?1 concentration of Pb(II). The method was successfully applied to the determination of Pb(II) in spinach and citrus leaves, and the results are in good agreement with those obtained with atomic absorption spectrometry.

Electochemiluminescence of CdTe/CdS Quantum Dots with Triproprylamine as Coreactant in Aqueous Solution at a Lower Potential and Its Application for Highly Sensitive and Selective Detection of Cu2+

Anodic electrochemiluminescence (ECL) of 3‐mercaptopropionic acid (MPA)‐ capped CdTe/CdS core‐shell quantum dots (QDs) with tripropylamine (TPrA) as the co‐reactant were studied in aqueous (Tris buffer) solution for the first time. The results suggest that the oxidation of TPrA at a glassy carbon electrode (GCE) surface participated in the ECL of QDs, and the onset potential and the intensity of ECL of CdTe/CdS QDs were affected seriously by TPrA, as the co‐reactant, in Tris buffer solution. The onset potential of ECL in this new system was about +0.5 V (vs. Ag/AgCl) and the ECL intensity greatly enhanced when TPrA was present. Various influencing factors, such as the electrolyte, pH, QDs concentration, potential range and scan rates on the ECL were studied. Based on the selective quenching by Cu²⁺ to the light emission from CdTe/CdS QDs/TPrA system, a highly sensitive and selective method for the determination of Cu²⁺ was developed. At the optimal conditions, the relative ECL intensity, I₀/I, was proportional to the concentration of Cu²⁺ from 14 nM to 0.21 μM with the detection limit of 6.1 nM based on the signal‐to‐noise ratio of 3. The possible ECL mechanism of QDs and the quenching mechanism of ECL were proposed.     

Facile synthesis of N-acetyl-L-cysteine capped ZnS quantum dots as an eco-friendly fluorescence sensor for Hg2+

This paper described an investigation of a novel eco-friendly fluorescence sensor for Hg²⁺ ions based on N-acetyl-l-cysteine (NAC)-capped ZnS quantum dots (QDs) in aqueous solution. By using safe and low-cost materials, ZnS QDs modified by NAC were easily synthesized in aqueous medium via a one-step method. The quantitative detection of Hg²⁺ ions was developed based on fluorescence quenching of ZnS QDs with high sensitivity and selectivity. Under optimal conditions, its response was linearly proportional to the concentration of Hg²⁺ ions in a range from 0 to 2.4 × 10⁻⁶ mol L⁻¹ with a detection limit of 5.0 × 10⁻⁹ mol L⁻¹. Most of common physiologically relevant cations and anions did not interfere with the detection of Hg²⁺. The proposed method was applied to the trace determination of Hg²⁺ ions in water samples. The possible quenching mechanism was also examined by fluorescence and UV-vis absorption spectra.