Mn Quantum Dots Research Articles

Circular Dichroism Spectroscopy as a Powerful Tool for Unraveling Assembly of Chiral Nonluminescent Aggregates of Photosensitizer Molecules on Nanoparticle Surfaces.

Recent developments in nanoscience and nanotechnology significantly help improve the properties of traditional materials. A striking example of this is the formation of hybrid nanostructures based on nanoparticles and photosensitizer molecules, the potential range of applications of which extends from photovoltaics to biomedicine. However, the creation of new and effective hybrid nanomaterials of this form inevitably entails new challenges, one of which is a common and critical problem of aggregation of both nanoparticles and photosensitizer molecules. Therefore, a fundamental challenge is to determine the presence of these aggregates, which will produce a significant step toward creating a new generation of materials and devices of broad-spectrum applicability. Here we report on the key role of circular dichroism spectroscopy as a tool to detect the formation of nonluminescent aggregates of chlorin e6, a second-generation photosensitizer, in a hybrid nanostructure with ZnS:Mn quantum dots. These aggregates are active acceptors of photoexcitation energy from quantum dots and limit the photophysical properties of the whole nanostructure. It has been established that circular dichroism spectroscopy reveals the presence of nonluminescent molecule aggregates at chlorin e6 concentrations of ∼10-6 mol/L, which compares very favorably to absorption spectroscopy which does not show any direct indications of aggregation up to ∼10-5 mol/L. This result demonstrates the promise and importance of using circular dichroism spectroscopy in the study of organic/inorganic hybrid nanostructures.

Co-application of TiO2 nanoparticles and randomly directed TiO2 nanorods in the photoelectrode of the CdS:Mn quantum dots sensitized solar cells and optimization of the doping for the efficiency improvement

In this research double-layer photoelectrodes including TiO2 nanocrystals (NCs) and nanorods (NRs) were fabricated and applied in quantum dot sensitized solar cells (QDSCs). TiO2 mesoporous sub-layer was formed of hydrothermally grown TiO2 NCs with dominant size of 25 nm. The randomly directed inclined TiO2 NRs were also grown on the surface of the mesoporous layer through a second hydrotermal process. These could simultaneously create high surface area, enhanced light scattering and better electron transport for the double-layer photoelectrode. Mn doped CdS NCs were applied for light sensitization of the photoanode with apparent Mn/Mn + Cd molar ratio of 0–9%. Different photoelectrodes were fabricated and effect of Mn doping on sensitization and corresponding photovoltaic performance was investigated. According to the results, the optimized photoanode with Mn/Mn + Cd molar ratio of 7% represented the maximum power conversion efficiency of 3.04%. This efficiency was increased about 31% compared to the reference cell which was sensitized with undoped CdS NCs. The reason was attributed to the tunable mid-gap electron energy states created by Mn doping inside the band-gap energy of the CdS NCs and better electron transfer inside the cell.

Ultrasonic synthesis of Mn-doped CsPbCl3 quantum dots (QDs) with enhanced photoluminescence

Mn-doped CsPbCl3 (CsPbCl3:Mn) perovskite colloidal quantum dots (QDs) attract a great deal of interests, and have great potentials for various optoelectronics applications due to their outstanding optical and electrical properties. However, practical applications of CsPbCl3:Mn QDs are severely limited by the cumbersome preparation methods and low photoluminescence quantum efficiency (PLQY). Herein, we propose a single-step ultrasonic synthesis method to successfully synthesize CsPbCl3:Mn QDs with controlled size and morphology by changing the Mn:Pb ratio. Simultaneously, we introduce triethylamine (TETN) to passivate the surface of CsPbCl3:Mn QDs. The phase purity, microstructure, chemical composition and photoluminescence properties of the samples were investigated by means of various analytic techniques. The synthesized QDs exhibit dual emissions of 411 and 601 nm, ascribing to the excitonic emission of QDs and the characteristic Mn2+ emission, respectively. The quantum yield of the CsPbCl3:Mn QDs could therefore be significantly improved from 17.49 to 41.15%. We believe that the facial synthesis method and the surface passivation of TETN can also be applied to other transition metal or lanthanide ions doped lead halide perovskite QDs.

Four-Photon Absorption Properties of Mn-Doped ZnSe Quantum Dots

A multiphoton absorption is one of the main nonlinear optical characteristics of semiconductor quantum dots (QDs). In this paper, we report on four-photon absorption of ZnSe:Mn QDs. The four-photon excitation spectrum is characterized under 1350 nm excitation with 50 fs femtosecond laser pulses. The experimental results indicate that the highest absorption coefficient was 2.87 × 10 -5 cm 5 /GW 3 for Mn doping of 170 μl, and corresponding cross-section is 2.03 × 10 -79 cm 8 ·s 3 . We also proved that it has low biotoxicity. The results of our studies suggest that these QDs can potentially be used to detect electric fields, limit laser power, and for biosensing applications.

Quantum dot sensitized solar cell based on the different photoelectrodes for the enhanced performance

In this work, the TiO2 nanoparticles have been used for the fabrication of CdS/TiO2, CdSe/TiO2, ZnS/CdSe/CdS/TiO2, ZnS/CdSe:Cu/CdS/TiO2 and ZnS/CdSe:Mn/CdS/TiO2 quantum dot-sensitized solar cells. The TiO2 films are sensitized with consecutive layers of CdS, CdSe quantum dots. Further, Cu2+ or Mn2+ ions were doped on CdSe quantum dots by successive ion layer adsorption and reaction. The performance of the QDSSCs is examined in detail using polysulfide electrolyte with Cu2S counter electrode. The cells containing CdSe quantum dots doped with the these ions show an improved short circuit current density (∼20.01 mA/cm2) with a maximum power conversion efficiency of 4.31% under 1 sun illumination. This enhancement is mainly attributed due to the superior light harvesting ability of the CdSe:Cu or CdSe:Mn quantum dots and make large accumulation of photo-injected electrons in the conduction band of TiO2 nanoparticles. In addition, the combination of doped CdSe and the presence of CdS layers caused lower recombination of photo-injected electrons with the electrolyte. These changes are demonstrated in this studying by using photovoltaic and electrochemical impedance spectroscopy.

Synthesis and characterisation of functional manganese doped ZnS quantum dots for bio-imaging application

ABSTRACTFluorescent quantum dots (QDs) are potential candidates for bio-imaging but major problems in using them for bio-imaging applications are either bandgap lying in UV region or the cytotoxicity of the visible light-excited cadmium-based QDs. Keeping these things in mind, glutathione (GLT) functionalised Mn-doped ZnS QDs has been studied to make a desired fluorescent system for bioimaging application. XRD measurements show that grain size decreases at higher concentration of GLT capping on Mn-doped quantum dots. UV–visible studies show that the band gap shows a blue shift at higher GLT concentration. FTIR studies confirm GLT functionalisation on the surface of ZnS QDs. Both UV excited and IR excited photoluminescence spectrum of samples exhibited a tunable orange emission intensity with increase in GLT concentration however multiphoton infrared excited spectra was used to show the feasibility of GLT functionalised ZnS:Mn quantum dots for a real application in a biological window of 650–950 nm.

Quenched sandwich-type photoelectrochemical aptasensor for protein detection based on exciton energy transfer

This work proposes a quenched photoelectrochemical sensing method for highly selective and sensitive detection of protein via Energy Transfer (ET) effect between the AuNPs and CdS:Mn quantum dots. This detection was performed on a sandwich-type aptamer sensing interface. Chitosan modified CdS:Mn/TiO2/ITO electrode was used to immobilize capture DNA (S1) via -CONH- bond. In the presence of target protein, AuNPs labeled DNA (AuNPs-S2) was further bonded to the protein to fabricate sandwich sensing platform, which forced the AuNPs away from the electrode surface. In this state, the photocurrent was greatly depressed, mainly due to two factors: (a) the ET effect produced by interparticle distance between CdS:Mn and AuNPs; (b) the steric hindrance of AuNPs-S2 partly obstructs the diffusion of the electron donor. The photocurrent decreased with the increasing concentration of the target protein. Using thrombin as a target, this sensitized method showed a detectablerange of 0.1 pM to 8 nM and a detection limit of 30 fM. It possessed high selectivity and good stability for detection of thrombin. This method is extremely flexible and can be extended to varieties of protein targets.

Hydrothermal synthesis of ZnSe:Mn quantum dots and their optical properties

Water-soluble Mn2+-doped ZnSe quantum dots (QDs) were synthesized using a hydrothermal method. The characteristics of the precursor solutions greatly affected the photoluminescence (PL) properties of the ZnSe:Mn QDs. In QDs synthesized with alkaline precursor solutions, a PL band originating from the intra-3d shell transition of Mn2+ is clearly observed, indicating that Mn2+ ions are thoroughly doped inside the ZnSe QDs. The PL quantum yield of the ZnSe:Mn QDs synthesized under the optimum conditions reached 20%. By introducing a ZnS shell at the surface of the ZnS:Mn QDs, the PL properties were improved and the PL quantum yield was further increased to 30%.

Optimization of the doping process and light scattering in CdS:Mn quantum dots sensitized solar cells for the efficiency enhancement

In this work a double-layer photoanode composed of TiO2 nanocrystals (NCs) and hollow spheres (HSs) was applied in CdS:Mn sensitized solar cells. TiO2 NCs with dominant size of 25 nm were synthesized by a facile hydrothermal method. TiO2 HSs were also prepared through the liquid phase deposition (LPD) of TiO2 on carbon spheres followed by a calcination process. The double electron transport layer of quantum dot sensitized solar cells (QDSCs) was formed of a nanocrystalline TiO2 layer covered by a light scattering HSs film. The corresponding thicknesses were also controlled to be about 10 µm and 7 µm, respectively. The sensitization of photoanode with Mn doped CdS NCs were carried out by a successive ionic layer adsorption and reaction (SILAR) technique. The apparent $$\frac{\text{Mn}}{\text{Mn}+\text{Cd}}$$ molar ratio was altered in a wide range of 0–9%. The corresponding QDSCs were fabricated and the doping process was optimized for the improved power conversion efficiencies. According to the results, the QDSC with a double-layer photoanode sensitized with $$\frac{\text{Mn}}{\text{Mn}+\text{Cd}}$$ ratio of 7.0% showed the maximum efficiency of 3.26%. This value was increased about 61% and 18% compared to those of the reference cells with single nanocrystalline and double-layer photoanodes sensitized with un-doped CdS NCs. The reason was addressed due to the higher light scattering and Mn related electron energy states within the bandgap energy of CdS NCs and the improved electron transport property of the cell. A ZnS passivating layer was also utilized as the electron blocking layer on the surface of the optimized doped photoanode with different thicknesses. It was shown that the highest energy conversion efficiency of 3.55% was achieved for three cycles of ZnS SILAR deposition.

Hydrothermal preparation of ZnS: Mn quantum dots and the effects of reaction temperature on its structural and optical properties

In this paper, the structural and optical properties of ZnS: Mn (0.6 at.%) quantum dots (QDs) synthesized by hydrothermal method at different reaction temperature were reported. X-ray diffraction patterns indicated that the ZnS: Mn QDs had cubic structure, and the average grain size increased from 3.75 to 6.36 nm with rising reaction temperature. Scanning electron microscope and transmission electron microscopy images revealed that the small grain size made samples poor dispersion. Also, we provided Fourier transform infrared spectroscopy spectra of the ZnS: Mn QDs to investigate components information. Further, optical properties of ZnS: Mn QDs were found to be affected by quantum confinement effect and specific surface area. The optical energy gap increased from 3.2 to 3.5 eV with the decrease of reaction temperature. Moreover, photoluminescence emissions of all samples showed the blue shift of position and the increase of emissions intensity with decreasing reaction temperature.

Water-Soluble Conjugates of ZnS:Mn Quantum Dots with Chlorin e6 for Photodynamic Therapy

Water-soluble conjugates based on semiconductor quantum dots ZnS:Mn with chlorin e6 have been created. It has been established by optical spectroscopy that effective energy transfer (~35%) from quantum dots to chlorin e6 is observed in the resulting conjugates.

Phototoxicity free quantum dot-based niosome formulation for controlled drug release and its monitoring

A novel niosomes-based system composed of Hypromellose (HPMC) functionalized fluorescent, biocompatible ZnS:Mn quantum dots (QDs), and anti-HIV drug Tenofovir disoproxil fumarate (TDF) was designed. An appropriate ratio of surfactant Sorbitan Monostearate (SPAN-60) and cholesterol was used to obtain an optimal entrapment efficiency. Initially, after observing the successful interaction of HPMC with SPAN-60, the noisome formulation including (QDs + drug) and HPMC-coated QDs was synthesized by a wet chemical route and characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM) and Selected Electron Diffraction (SAED). Secondly, (QDs + drug) loaded niosome formulations were studied by varying the ratio of SPAN-60 and cholesterol. Multiple studies were done to characterize the shape, size, viscosity, colloidal stability, and entrapment efficiency of (QDs + drug) loaded niosomes. Lastly, pH-dependent (QDs + drug) release profiles were studied by a spectroscopic technique considering the pH of the human gastrointestinal region to obtain the formulation stability of (QDs + drug) release from the niosome vesicles. These studies also include pH-dependent photo-stability measurements based on laser-induced multiphoton excitation technique in the Infrared region. The multiphoton time-resolved studies were completed to avoid the UV induced phototoxicity in the drug delivery modules. Current studies on the formulation of niosomes-based (QDs + drug) system laid a foundation to make a complete phototoxicity free system for tracking controlled drug release and its imaging.

Tunable excitation properties of ZnCdS:Mn/ZnS quantum dots for cancer imaging.

Water-soluble ZnS:Mn quantum dots (QDs) were synthesized using a hydrothermal method with 3-mercaptopropionic acid as stabilizer. The optical properties of ZnS:Mn QDs were thoroughly investigated by tuning the doping concentration of Mn2+ and the Zn/S precursor ratio, to obtain an optimal parameter for QDs with excellent fluorescence characteristics. ZnS:Mn QDs excited at only one wavelength, however, which seriously limited their further application. Here, a trace Cd ion was doped into a ZnS host, resulting in QD excitation covering a wide adjustable waveband. Furthermore, when a ZnS shell was coated onto the surface of the ZnCdS:Mn QDs, photoluminescence intensity and stability were further enhanced. After coupling with an anti-CK 19 antibody, the ZnCdS:Mn/ZnS core/shell QDs were able to function by labeling cancer cells, indicating that they could be considered as a suitable bio-probe for cells and tissue imaging.

Photoluminescence of ZnS: Mn quantum dot by hydrothermal method

ZnS: Mn quantum dots (QDs) with the average grain size from 4.2 to 7.2 nm were synthesized by a hydrothermal method. All samples were cubic zinc blende structure (β-ZnS) measured using X-ray diffraction (XRD). And the main diffraction peaks of ZnS: Mn shifted slightly towards higher angle in comparison with the intrinsic ZnS because of the substitution of Mn2+ for Zn2+. Due to the small grain size (4-7 nm) effect, the poor dispersion and serious reunion phenomenon for the samples were observed from transmission electron microscopy (TEM). ZnS: Mn QDs had four peaks centered at 466, 495, 522, and 554 nm, respectively, in the photoluminescence (PL) spectra, in which the band at 554 nm absent in the intrinsic ZnS: Mn is attributed to the doping of Mn2+ in the lattice sites. As the concentration of Mn2+ increasing from 0% to 0.6 at%, the intensity of the PL emission also increased. But the concentration reached 0.9 at%, quenching of PL emission occurred. The peak in ZnS: Mn QDs observed at 490 cm-1 was originated from the stretching vibration of the Mn–O bonds in the Fourier transform infrared (FTIR) spectra. And the small changes about this peak compared with the previous reports at 500 cm-1 can be attributed to the formation of quantum dots. This method we utilized to synthesize ZnS: Mn QDs is very simple, low cost, and applicable for other semiconductor QD materials.

Influence of manganese doping on the luminescence characteristics of colloidal ZnxCd1−xS quantum dots in gelatin

Colloidal pure and Mn-doped mixed ZnxCd1−xS quantum dots were successfully prepared by aqueous synthesis in photographic inert gelatin. Quantum dots are formed in a cubic crystal lattice with the average size of about 2nm. Two emission bands in photoluminescence spectra of Mn-doped quantum dots are observed: trap state luminescence and Mn characteristic emission. The possibility of Mn-doped quantum dots spectral characteristics tuning by changing the synthesis conditions is shown. It is shown that value of trap state – Mn ion excitation transfer efficiency in mixed ZnxCd1−xS:Mn quantum dots is about 24–30%.

Ultrasensitive Electrochemiluminescence Biosensor for MicroRNA Detection by 3D DNA Walking Machine Based Target Conversion and Distance-Controllable Signal Quenching and Enhancing

In this study, an electrochemiluminescence (ECL) regenerated biosensor was reported to sensitively detect microRNA through 3D DNA walking machine and "on-off-super on" strategy. First, 3D DNA walking machine with higher efficiency of payload releasing and superior signal amplification than those of the traditional DNA walking machine was initially introduced in the ECL system for converting target microRNA to intermediate DNA and achieving significant signal amplification. Second, the distance between CdS:Mn quantum dots and Au nanoparticles was increased with the hybridization of intermediate DNA and Au nanoparticles modified S2, which weakened the energy transfer for ECL signal recovering and excited the surface plasma resonance for further enhancing the signal to construct the on-off-super on biosensor. Such an on-off-super on strategy not only reduced the ECL background signal but also increased the detection sensitivity. Impressively, the elaborately designed biosensor could be regenerated by Lambda exonuclease hydrolyzing the intermediate DNA to make Au nanoparticles modified S2 recover to their original hairpin structure. With the amazing signal amplification of 3D DNA walking machine and sensitive distance control of the on-off-super on strategy, the biosensor showed excellent performance for microRNA-141 detection with a low detection limit of 3.3 fM and could be applied to human prostate cancer cells analysis. Furthermore, this work established a foundation to apply 3D walker in ECL methodology and provided an effective way for analysis of other microRNA or cancer cells.

Enantioselective cytotoxicity of ZnS:Mn quantum dots in A549 cells.

Chirality strongly influences many biological properties of materials, such as cell accumulation, enzymatic activity, and toxicity. In the past decade, it has been shown that quantum dots (QDs), fluorescent semiconductor nanoparticles with unique optical properties, can demonstrate optical activity due to chiral ligands bound on their surface. Optically active QDs could find potential applications in biomedical research, therapy, and diagnostics. Consequently, it is very important to investigate the interaction of QDs capped with chiral ligands with living cells. The aim of our study was to investigate the influence of the induced chirality of Mn-doped ZnS QDs on the viability of A549 cells. These QDs were stabilized with D- and L-cysteine using a ligand exchange technique. The optical properties of QDs were studied using UV-Vis, photoluminescence (PL), and circular dichroism (CD) spectroscopy. The cytotoxicity of QDs was investigated by high content screening analysis. It was found that QDs stabilized by opposite ligand enantiomers, had identical PL and UV-Vis spectra and mirror-imaged CD spectra, but displayed different cytotoxicity: QDs capped with D-cysteine had greater cytotoxicity than L-cysteine capped QDs.

Green synthesis of white-light-emitting ZnSe:Eu2+, Mn2+ quantum dots in an aqueous solution

High-quality ZnSe:Eu, Mn quantum dots (QDs) with white light emitting were synthesized via a green preparation method in an aqueous solution using thioglycolic acid as a stabilizing agent. The composition of the QDs could be flexibly controlled by varying the amount of Eu or Mn cation. The effects of reflux time and Eu2+ ion dopant concentration on the luminescence properties were systematically investigated. The obtained QDs were characterized by photoluminescence spectrometry, X-ray powder diffraction, and high-resolution transmission electron microscopy. The proposed method formed cubic ZnSe:Mn2+, Eu2+ QDs with the maximum emission peak at 460 and 580 nm. In the optimal condition, the quantum yields of ZnSe:Mn2+, Eu2+ QDs could reach 27.68%. The CIE color coordinates were (0.328, 0.334), which agreed with those of pure white light (0.33, 0.33). The results verified that the ZnSe:Mn2+, Eu2+ QDs exhibited potential in light-emitting diode applications.

A novel electrochemiluminescence immunosensor based on Mn doped Ag2S quantum dots probe for laminin detection

In recent years, quantum dots (QDs) have been widely used as biological probes, however, most of the QDs used in electrochemiluminescence (ECL) studies have toxic heavy metals, which was an important road-block for QDs in bio-application. A novel low-toxic, water-dispersed Mn doped Ag2S quantum dots (Ag2S:Mn QDs) were firstly served as a kind of ECL materials, and applied to construct ECL biosensor for the detection of laminin (LN). Here, the Ag2S QDs were simply synthesized with 3-Mercaptopropionic acid (3-MPA) as growth template, and then Mn was doped into Ag2S QDs to improve the optical and electrical properties. Herein, the energy levels and electron transfer path were studied in detail to explain the ECL performance of Ag2S:Mn QDs with K2S2O8 as coreactant. Furthermore, the bovine serum albumin (BSA) containing amino groups (-NH2) could easily combine with Ag2S:Mn QDs via amide bond, and multiple QDs gathered to form a unit (BSA-Ag2S:Mn bioconjugates), which provided mass active area to immobilize antibody and possessed strong ECL emission to improve the detection sensitivity. Based on a sandwiched immunoassay method, this proposed immunosensor achieved a linear range from 10pg/mL to 100ng/mL with a relatively low detection limit of 3.2pg/mL for LN detection. Compared with traditional luminescent reagents, the Ag2S:Mn QDs could be served as a kind of promising luminescent materials for new types of ECL biosensors in the future due to its low toxicity, well photo-stability and easy surface functionalization.

Studies of hypro-mellose (HPMC) functionalized ZnS:Mn fluorescent quantum dots

Fluorescent ZnS:Mn quantum dots coated with hypro-mellose (HPMC) were synthesized by using simple and facile chemical precipitation technique in which HPMC acts as a novel organic surfactant to passivate the surface, to tune the optical properties and also to functionalize the surface of quantum dot for a futuristic controlled drug release applications. Morphological and optical characterizations were done to see the effect of HPMC coating on ZnS:Mn quantum dots. Structural and morphological studies was done by using XRD and TEM respectively. XRD studies confirms the pure zinc blende phase for all the samples. TEM studies shows that HPMC is efficiently doing the surface passivation in doped quantum dots. Optical studies were done by using UV–visible, FTIR and time resolved photoluminescence. UV–visible studies shows that quantum confinement effect is more prominent and also tunable in case of HPMC coated manganese doped ZnS quantum dots. FTIR studies confirms the functionalization of HPMC on the surface of doped ZnS quantum dots. Laser induced time resolved photoluminescence studies were also done to see the effect of HPMC on the photoluminescence intensity of doped quantum dots. Time resolved studies clearly shows the much desired luminescence stability of the HPMC coated quantum dots. It is observed that both the structural and optical characteristics have strong dependence on capping concentration. As HPMC is a very important viscoelastic polymer and organic surfactant used in various types of drug formulations, these studies opens a new way in the area of efficient drug delivery, controlled drug release and targeting.