Doped Zinc Sulfide Quantum Dots Research Articles

“Turn-on” fluorescence sensing of cardiac troponin I based on MnO2 nanosheet quenched mercaptopropionic acid capped Mn2+ doped zinc sulphide quantum dots

Acute Myocardial Infarction (AMI) is the persisting serious threat among all cardiovascular diseases due to its highest mortality rates. Clinicians resort to biomarker levels pertinent to AMI in triaging patients. Among the several cardiac biomarkers, by virtue of the specificity and sensitivity, cardiac troponin I (cTnI) was recognized as the gold standard for AMI diagnosis. Immunosensors that have been developed for cTnI detection are limited by multistep process and long diagnostic time which makes them unadaptable in primary healthcare centres. Recently, Fluorescence Resonance Energy Transfer (FRET) based immunosensors have found wide applicability in biomolecule detection. Among the evolving nanomaterials, Quantum dots (QDs) have been emerged as attractive donors in FRET based sensors for biomolecules. In the present work, we report a simple and sensitive fluorescence immunosensor for cTnI detection using Mercaptopropionic acid (MPA) capped Mn2+ doped ZnS QDs and MnO2 nanosheet as the FRET couple. For the specific detection of cTnI antigen, we have coupled cTnI antibody on the surface of MPA capped Mn2+ doped ZnS QDs. cTnI can be detected linearly with a low Limit of Detection (LoD) of 0.05 ng/mL. Furthermore, the selectivity of the developed probe has also been evaluated in the presence of other potential interferants and other cardiac biomarkers. In real serum samples, good recovery percentage was obtained proving that the probe is adaptable for Point of care detection of cTnI.

Synthesis, feasibility study of production of singlet oxygen and hydroxyl radical and performance in antibacterial activity of ZnS:Eu QDs

 ZnS:Eu nanoparticles also have the ability to produce reactive oxygen species that can be used to treat cancers. Eu doped zinc sulfide quantum dots (QDs) were prepared by the chemical Co-precipitation method. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and infrared Fourier transform (FT-IR) analysis were used to characterize the quantum dots. The photoluminescence spectrum (PL) of ZnS:Eu QD in excitation wavelength of 280 nm shows two emission peaks at 384 and 715 nm. In order to use these QDs as photosensitizer in photodynamic therapy, anthracene and methylene blue chemical detectors were used for detection of singlet oxygen and hydroxyl radical, respectively. The significant point for these quantum dots is that, in addition to production of hydroxyl radical, they also have the ability to produce singlet oxygen with UV-C radiation. The antimicrobial effect of ZnS:Eu QDs was also investigated using a disc diffusion method on 11 microbial strains. Zinc sulfide nanoparticles with Europium impurities can have good medical application due to their good antibacterial activity and ability to produce reactive oxygen species.

Fluorescent sensor based on thiourea capped Mn doped ZnS quantum dots for the sensing of Cu2+ ions in water

In the present study the utilization of a simple, rapid, and highly effective “turn-off” fluorescent sensor based on thiourea capped manganese doped zinc sulphide quantum dots for the detection of Cu2+ ions in water is described for the first time. The quantum dots are prepared by a simple and facile chemical precipitation method. The developed quantum dots are characterized by UV–vis., FT-IR, photoluminescence, XRD, and TEM techniques. The doping by manganese is confirmed by a peak at 598 nm in the PL spectrum. The sensor exhibit high sensitivity and selectivity towards copper ion at pH 9 with a limit of detection of 20.75 nM. The obtained results are also reasonable in real sample analysis.

Copper doped zinc sulfide quantum dots as ratiometric fluorescent probes for rapid and specific detection of tetracycline residues in milk

In this work, copper-doped zinc sulfide quantum dots (ZnS:Cu QDs) were developed as ratiometric fluorescent probes to detect tetracycline (TC) in milk. With the increasing of TC concentration, the fluorescence at 578 nm of ZnS:Cu QDs was quenched, while a new fluorescence at 520 nm was significantly enhanced due to the formation of a green-emitting complex of Zn2+ and TC on the surface of probes. The fluorescence intensity ratio (I520/I578) have a good linear relationship (R2 = 0.98) with the concentration of TC in the range of 0.2–2.0 μM. The detection limit was calculated to 149 nM, which is lower than the allowable level of TC (about 180 μM) in milk set by the US Food and Drug Administration (FDA). Finally, the fluorescent test papers have been also prepared using ZnS:Cu QDs as ink by painting on a piece of filter paper. With the addition of TC, the orange test paper produced green spots that became more and more obvious with a dose-discerning ability as low as 2 μM. This work demonstrated a great potential of ratiometric fluorescent probe for the easy and visual detection of TC in complicated real samples.

One-pot synthesis of color-tunable copper doped zinc sulfide quantum dots for solid-state lighting devices

Color-tunable semiconductor quantum dots (QDs) are highly attractive for a wide range of applications including imaging, sensing, and lighting. Herein, we reported a facile synthesis of copper-doped zinc sulfide quantum dots (ZnS:Cu QDs) with tunable emission colors, using a microwave-assisted one-pot reaction. 3-mercaptopropionic acid (MPA) was used as a stabilizer agent and sulfide source for the formation of ZnS:Cu QDs. The photoluminescence of ZnS:Cu QDs showed a clear red-shift as increasing Cu concentration, which can be controlled by microwave irradiation time. As increasing the irradiation time, the emission color (peak) of ZnS:Cu QDs changed from blue (500 nm) to green (540 nm), yellow (580 nm), and to orange-red (595 nm). The obtained ZnS:Cu QDs were highly luminescent, as evidenced by their high quantum yields. The potential utility of ZnS:Cu QDs as a novel lighting source was demonstrated in a near-UV chip-based white light-emitting diode.

Synthesis, characterization and photovoltaic applications of noble metal—doped ZnS quantum dots

Un-doped zinc sulphide (ZnS) and noble metal-doped ZnS quantum dots were synthesized by chemical method. The synthesized nanomaterial was characterized by UV-Visible, Fourier Transformed Infra-red Spectrometer (FTIR), Fluorescence, High Resolution Transmission Electron Microscope (HRTEM) and X-ray Diffraction (XRD). Scanning electron microscope complemented with energy dispersive X-ray was used to study particle size and chemical composition of un-doped and metal-doped ZnS QDs. A significant red shift in absorption band was observed in metal doped ZnS sample having concentration of impurity 0.05 M with respect to the un-doped ZnS with increasing the size of nanocrystals. Such red shift of the absorption bands are attributed due to quantum confinement effect. As un-doped and noble metal-doped ZnS QDs are direct band gap materials. The band gap energy of ZnS, Ag-doped, and Au-doped ZnS quantum dots is found to 2.5 eV, 2.4 eV and 2.2 eV, respectively. PL spectrum of the un-doped zinc sulphide nanocrytals witnessed two bands, first at 418 nm and second at 468 nm. However, PL spectrum of Ag-doped ZnS nanocrystals shows no green light emission band while a broad emission ranging up to 700 nm in Au-doped ZnS sample. XRD spectra of synthesized QDs exhibited that the material was in cubic phase. X-ray Photoelectron Spectroscopy (XPS) was used for comparative study of surfaces of zinc sulphide and noble metal zinc sulphide nanocrystals. The effects of inserting ZnS and noble metal doped ZnS nanocrystals in the active layer on the performance of organic solar cells were studied. The active layer mainly comprises of electron acceptor [6,6] phenyl-C61-butyric acid methyl ester (PCBM) and organic electron donor poly (3-hexylthiophene (P3HT) with quantum dots dissolved in dichlorobenzene. The cell conversion efficiency improved by embedding the doped QDs in the active layer blend. The cells fabricated with ZnS QDs exhibited cell conversion efficiency of 1.46%. By doping with silver and gold, the cell conversion efficiency was increased about 1.85% and 2.01%, respectively. The morphology of blend of nanocrystals with P3HT:PCBM were studied using atomic force microscopy.

Manganese Doped Zinc Sulfide Quantum Dots as Efficient Photocatalyst for Dye Decolorization

A simple aqueous based synthesis technique at room temperature was performed for preparation of pure and manganese (Mn2+) doped ZnS quantum dots in the presence of glutathione as the capping agent. Under UV-excitation quantum dots show photoluminescence bands at 2.13 and 3.0 eV corresponded to Mn2+ and intrinsic ZnS emission respectively. ZnS quantum dots were used as the photocatalyst to remove organic dyes in aqueous solution, with methylene blue as a model dye. The influence of the Mn2+ concentration on the dye degradation efficiency was studied. The highest photocatalytic degradation rate of methylene blue was obtained for ZnS quantum dots in glutathione shell doped with 0.125 at % of Mn2+.

Photoluminescence sensing of bilirubin in human serum using l-cysteine tailored manganese doped zinc sulphide quantum dots

Bilirubin (BR) is a protective antioxidant generated as end-product of heme catabolism in human. However, BR accumulation in biological tissues in connection with neonatal and hereditary jaundice causes severe hyperbilirubinemia and neurotoxicity. Herein, a fluorescence turn-off sensor for the detection of BR, a major biomarker for jaundice, is designed based on l-cysteine capped manganese doped zinc sulphide quantum dots (Mn:ZnS QDs). The QDs were synthesized by a microwave assisted chemical co-precipitation method. Under optimum conditions, the luminescence quenching response of Mn:ZnS QDs can be effectively used for detection of BR in the linear range of 10.99 μM - 63.84 μM BR. The limit of detection (LOD) is as low as 1.8 μM and limit of quantification (LOQ) is 6 μM. The plausible mechanism behind BR induced luminescence quenching is reductive photo-induced electron transfer (PET) in which Mn:ZnS QDs act as electron acceptor and BR act as electron donor. The developed sensor show good selectivity for BR over other co-existing biomolecules such as creatine, cholesterol, bisphenol, glutathione, uric acid, urea, hemoglobin, fructose, galactose and glucose. The developed sensor was validated by the detection of BR in spiked human serum and urine samples. For practical applications, a paper strip based sensor was also developed.

Sensing and photocatalytic activity of zinc sulfide quantum dots based on charge transfer process to analyte molecule

We demonstrated the efficientcharge transfer between manganese doped zinc sulfide quantum dots (QDs)and an analyte molecule, methaneor methylene blue dye, by means of photoluminescence properties of ZnS QDs. In the presenceof methane QDs arefound to exhibit non-uniform increasing of luminescence intensity due to specific charge transfer from analyte to QD defect states. It is revealed that charge transfer leads to destruction of methylene blue dye molecule which makes possible to use the QDs for organic dye removal in aqueous solution. The limit of methane detection is 100 ppm. The photocatalytic rate of methylene blue degradation is 0.033 s−1 which is almost two orders higher than Degussa P25 rate.

Fast sonochemically-assisted synthesis of pure and doped zinc sulfide quantum dots and their applicability in organic dye removal from aqueous media

In this research, a sono-assisted chemical precipitation method was developed for a quick and efficient water-based synthesis of zinc sulfide (ZnS) quantum dots (QDs), in room temperature. ZnS QDs as pure and doped with some transition metal ions (such as Cu2+, Mn2+, Ag+) were prepared in the presence of l-cysteine, as capping agent. In comparison with the previous conventional methods, applying the ultrasonic irradiation provides a significant decrease in the reaction time. In comparison with previous reported conventional chemical QD synthesis methods, the required time for a complete synthesis in the presence of ultrasonic irradiations was significantly reduced to a period as short as 15 min, in a temperature of 40 °C. The sono-synthesized QDs were characterized with various techniques such as colorimetry, UV–Vis absorption spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). A broad absorption band between 270 and 290 nm was observed for colloidal ZnS QDs with the optical band gap larger than 3.68 eV. From the XRD and TEM results, the average particle size below 5 nm was estimated for the prepared QDs. After characterization, the samples were employed as nanophotocatalysts during a UV-derivate photocatalytic process for the degradation of Victoria blue R (VBR), as a pollutant dye. To obtain the optimal operating conditions, the influence of the affecting parameters such as the initial pH of the dye solution, irradiation time, initial dye concentration, type, electrolyte salt concentration and dosage of the nanophotocatalyst samples on the degradation efficiency (DE % was comprehensively studied, all in batch mode. Taking the optimum conditions into account, the maximum removal of VBR dye (>95%) can be obtained by spectrophotometric measurements at alkaline pH of 10.5, in the presence of low amounts of QDs (3 mg) and after 30 min of being exposed to UV irradiations. The results demonstrate that despite the removal of VBR, the QDs prepared by sonochemically method can be reused for at least six more times; without a significant decrease in their photocatalytic properties.

Investigations on photoluminescence enhancement of poly(vinyl alcohol)-encapsulated Mn-doped ZnS quantum dots

In our work, we focused on the photoluminescence (PL) enhancement of poly(vinyl alcohol) (PVA)-encapsulated Mn2+-doped zinc sulfide quantum dots (ZnS:Mn2+ QDs) synthesized at 80°C in basic aqueous solutions. The structural, morphological and optical properties were investigated using characterization techniques such as X-ray powder diffraction (XRD), Transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), UV–vis absorption and photoluminescence (PL) spectroscopy. According to the results of UV–vis absorption spectra, the optical bandgap of the quantum dots was higher than that of the bulk ZnS due to the quantum confinement effect. The studied result showed that the Mn2+ 4T1 → 6A1 emission intensity at the wavelength of 600nm significantly increased with the increase of Mn2+ doping content and reached its maximum value at the Mn2+ concentration of 4.5%. In addition, the effect of PVA/Zn2+ molar ratio on the PL enhancement of PVA-encapsulated Mn2+-doped ZnS quantum dots also was systematically investigated and explained in this paper. The studied results indicated the energy transfer process from the ZnS host lattice and PVA capping molecules to Mn2+ centers is more efficient at the optimal PVA/Zn2+ molar ratio of 3 × 10−4. Furthermore, a mechanism for the formation of the PVA-encapsulated Mn2+-doped ZnS quantum has also been suggested in this study.

A two-dimensional sensing device based on manganese doped zinc sulfide quantum dots for discrimination and identification of common sugars

A Mn-doped ZnS QD 2D sensor for identification and separation of common sugars.

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 1.25–30μM and a detection limit of 0.74μM. The relative standard deviation for eleven repeat detections of 20μM 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%.

Melamine-modulated mercaptopropionic acid-capped manganese doped zinc sulfide quantum dots as a room-temperature phosphorescence sensor for detecting clenbuterol in biological fluids

A turn-off room-temperature phosphorescence (RTP) sensor for clenbuterol (CB) based on melamine (MA)-modulated mercaptopropionic acid (MPA)-capped Mn-doped ZnS quantum dots (QDs) was described in this paper. Due to the hydrogen-bonding interaction between CB and MA, introduction of CB into the solution of MPA-capped Mn-doped QDs in the presence of MA could increase the surface defects of the QDs and lead to their reaction aggregation. So that the MA-induced RTP could be enhanced and subsequent CB-induced RTP quenching could be observed. This phenomenon could build a solid base for us to develop a QDs-based turn-off RTP sensor for detecting CB. Under the optimal conditions, the detection limit for CB was 3.2ngmL−1, the relative standard deviations was 2.9% while the recovery of the method was in the range of 97–104%. The coexisting substances which includes 2000-fold excesses of Na+ and K+, 1500-fold excesses of lysine, cysteine, ascorbic acid, uric acid, Vitamin B1, Vitamin B2, Mn2+, Mg2+, Ca2+, Zn2+ and Al3+, 500-fold excesses Cu2+ and Ag+ did not affect the determination of CB. The proposed method was successfully applied to biological fluids with satisfactory results.

Room-temperature phosphorescence sensor based on manganese doped zinc sulfide quantum dots for detection of urea

In this work, a simple scheme was proposed to prepare a urea-sensing system, which was composed of water-soluble Mn-doped ZnS phosphorescent QDs and urease. It allows for effective and quantitative detection of urea. The phosphorescence properties of MPA-capped Mn-doped ZnS QDs were explored to develop an RTP method for facile, rapid, cost-effective and selective detection of urea. This method does not need any deoxidant or other inducers and detects urea in biological fluids without being interfered from autofluorescence or the scattering light of the matrix. The new RTP sensor for urea detection has a detection limit of 0.014mM and two linear ranges from 0 to 10mM and from 10 to 60mM. The precision for 11 replicate detections of 0.1mM urea was 4.7%. The recoveries on spiked urine samples are 95–103%. It was successfully applied to the determination of urine without any complicated sample pretreatment.

Recovering hidden quanta of Cu2+-doped ZnS quantum dots in reductive environment

We report that photoluminescence of doped quantum dots (Qdots)-which was otherwise lost in the oxidized form of the dopant-could be recovered in chemical or cellular reducing environment. For example, as-synthesized Cu(2+)-doped zinc sulfide (ZnS) Qdots in water medium showed weak emission with a peak at 420 nm, following excitation with UV light (320 nm). However, addition of reducing agent led to the appearance of green emission with a peak at 540 nm and with quantum yield as high as 10%, in addition to the weak peak now appearing as a shoulder. The emission disappeared in the presence of an oxidizing agent or with time under ambient conditions. X-Ray photoelectron spectroscopic (XPS) and electron spin resonance (ESR) measurements suggested the presence of Cu(2+) in the as-synthesized Qdots, while formation of its reduced form was indicated (by ESR results) following treatment with a reducing agent. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) studies confirmed the formation of ZnS nanocrystals, the size and shape of which did not undergo any change in the presence of a reducing or oxidizing agent. Nanoparticulate forms of the Qdots and chitosan (a biopolymer) composite exhibited similar emission characteristics. Interestingly, when mammalian cancer cells or non-cancerous cells were treated with the composite nanoparticles (NPs), characteristic green fluorescence was observed. Further, the intensity of the fluorescence diminished when the cells were treated later with pyrogallol-a known reactive oxygen species generator. Overall, the results indicated a new way of probing the reducing nature of mammalian cells using the emission properties of the Qdot based on the redox state of its dopant.

Redox-Tuned Three-Color Emission in Double (Mn and Cu) Doped Zinc Sulfide Quantum Dots.

The photoluminescence characteristics of colloidal Mn(2+) and Cu(2+) (double) doped zinc sulfide (ZnS) quantum dots (Qdots) could be drastically influenced by reactions with redox reagents. Importantly, experiments revealed Cu(+) in ZnS nanocrystals rather than Cu(2+), in conjunction with Mn(2+), as the emitting dopant. Thus, as-synthesized aqueous Qdots emitted orange (with peaks at 460 and 592 nm) due to the host and Mn(2+) dopant emissions. However, upon treatment with a reducing agent, the color changed to yellow with dual peaks positioned at 520 and 590 nm due to Cu(+) and Mn(2+) dopant emissions. The characteristics could be changed reversibly with appropriate redox reagents. Further, treatment with excess of an oxidizing agent led to blue emission with a single peak at 450 nm.

Functionalized Mn2+ Doped Zinc Sulfide Quantum Dots as a Metal Ion Sensor for Industrial Wastes

L-cysteine capped Mn2+-doped ZnS quantum dots are prepared as a fluorescence probe for the detection of heavy metal contaminants, such as As2O42-, Cd2+, CrO42-, Ni2+, Zn2+, Ca2+, Fe2+, Cu2+, Pb2+, Co2+ and Mn2+ ions. The results show L-cysteine capped Mn2+-doped ZnS quantum dots exhibit good sensitivity and selectivity for the detection of copper ions. The relationship between the detection limit, linear range and the concentration of quantum dots are examined. The optimum fluorescence sensor is obtained at the L-cysteine-ZnS QDs concentration of 2 mg/mL and pH 7.0 in phosphate buffer. The limit of detection for this sensor system is 0.2 ppm with the linear range between 0.5 and 20 ppm. The effect of foreign ions from Mn2+, Fe2+, Co2+ and Ni2+ for the detection of Cu2+ solution is also evaluated. The results show there is no significant difference on the measurement of quenching effect.

Functionalized Mn2+-Doped Zinc Sulfide Quantum Dots as a Metal Ion Sensor for Industrial Wastes

Functionalized Mn2+-Doped Zinc Sulfide Quantum Dots as a Metal Ion Sensor for Industrial Wastes

Synthesis and characterizations of ultra-small ZnS and Zn (1− x) Fe xS quantum dots in aqueous media and spectroscopic study of their interactions with bovine serum albumin

This work reports a new experimental methodology for the synthesis of ultra small zinc sulfide and iron doped zinc sulfide quantum dots in aqueous media. The nanoparticles were obtained using a simple procedure based on the precipitation of ZnS in aqueous solution in the presence of 2-mercaptoethanol as a capping agent, at room temperature. The effect of Fe 3+ ion concentration as dopant on the optical properties of ZnS was studied. The size of quantum dots was determined to be about 1 nm, using scanning tunneling microscopy. The synthesized nanoparticles were characterized by X-ray diffraction, UV–Vis absorption and photoluminescence emission spectroscopies. The presence and amount of iron impurity in the structure of Zn (1− x) Fe x S nanocrystals were confirmed by atomic absorption spectrometry. A blue shift in band-gap of ZnS was observed upon increasing incorporation of Fe 3+ ion in the iron doped zinc sulfide quantum dots. The photoluminescence investigations showed that, in the case of iron doped ZnS nanoparticles, the emission band of pure ZnS nanoparticles at 427 nm shifts to 442 nm with appearance of a new sharp emission band around 532 nm. The X-ray diffraction analysis indicated that the iron doped nanoparticles are crystalline, with cubic zinc blend structure, having particle diameters of 1.7 ± 022 nm. Finally, the interaction of the synthesized nanoparticles with bovine serum albumin was investigated at pH 7.2. The UV–Vis absorption and fluorescence spectroscopic methods were applied to compare the optical properties of pure and iron doped ZnS quantum dots upon interaction with BSA. It was proved that, in both cases, the fluorescence quenching of BSA by the quantum dots is mainly a result of the formation of QDs–BSA complex in solution. In the steady-state fluorescence studies, the interaction parameters including binding constants ( K a ), number of binding sites ( n), quenching constants ( K ′ S V ), and bimolecular quenching rate constants ( k q ) were determined at three different temperatures and the results were then used to evaluate the corresponding thermodynamic parameters Δ H, Δ S and Δ G.