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Effect of pH on the Synthesis and Properties of Luminescent SiO2/Calcium Phosphate:Eu3+ Core-Shell Nanoparticles
Abstract
A novel method for the synthesis of luminescent SiO(2)/calcium phosphate (CaP):Eu(3+) core-shell nanoparticles (NPs) was developed via a sol-gel route followed by annealing at a temperature of 800 °C. The object of this study was the investigation of the effect of pH on the formation of a CaP shell around the silica core. The resulting annealed NPs exhibited an amorphous SiO(2) core and a crystalline luminescent shell. The formation of a CaP layer was possible at pH below 4.5 and above 6.5 during the coating step. The crystal structure of the shell was studied by X-ray diffraction analysis. Hydroxyapatite (HAp) and α-tricalcium phosphate were detected as crystal phases of the surrounding layer. However, NPs produced under basic conditions exhibited a higher crystallinity of the CaP layer than did samples coated at pH below 4.5. In the pH interval between 4.5 and 6.5, no shell growth but the formation of secondary NPs containing CaO and Ca(OH)(2) was observed. Furthermore, SiO(2)/CP:Eu(3+) core-shell NPs were investigated by transmission electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, inductively coupled plasma optical emission spectrometry, and photoluminescence spectroscopy. The resulting HAp-coated NPs were successfully tested by a cell-culture-based viability assay with respect to a later application as a luminescent marker for biomedical applications.
... Many researchers have prepared a variety of core-shell-structured fluorescent powders [9,10]. For example, the Lin's research group prepared a series of core-shell structures of spherical luminous materials and studied the influence of the annealing temperature and SiO 2 core particle size on the luminescence intensity [9]. ...
... For example, the Lin's research group prepared a series of core-shell structures of spherical luminous materials and studied the influence of the annealing temperature and SiO 2 core particle size on the luminescence intensity [9]. Sofia Dembski's team also studied the effect of pH on luminescent core-shell nanoparticles [10]. These studies showed that the annealing temperature, SiO 2 particle size, and pH value all had important impacts on the luminescent performance. ...
... These studies showed that the annealing temperature, SiO 2 particle size, and pH value all had important impacts on the luminescent performance. Increasing the annealing temperature and SiO 2 particle size and maintaining the pH value within a suitable range can grant property-enhanced luminescent materials [9,10]. However, few studies have reported on the effects of annealing temperature on the synthesis of SiO 2 @LaPO 4 :Ce 3+ /Tb 3+ green phosphors. ...
Enhanced luminescent SiO2@LaPO4:Ce³⁺/Tb³⁺ phosphors were prepared using a homogeneous precipitation method followed by a subsequent heat-treatment process. The products were characterized by XRD, SEM, TEM, HRTEM, XPS, and photoluminescence (PL).The XRD results demonstrated that all of the diffraction peaks can be well indexed to the pure monoclinic phase. The SEM and TEM images indicated that the phosphors have perfect spherical shapes with a narrow size distribution and no agglomeration. The EDS and XPS analysis revealed that LaPO4:Ce³⁺/Tb³⁺ layers have been deposited successfully on SiO2 particles. The PL results demonstrated the samples annealed at 800 °C have the strongest green emission.
... Silica-MB was synthesized by a modified Stöber method [27,28]. Typically, 0.10 g of methylene blue (MB) was dissolved in 92 ml of ethanol, 13.8 ml of deionized water and 2.38 ml of aqueous ammonia (NH 3 •H 2 O) under stirring. ...
... The coating of OCP on silica-MB was carried out by a modified Pechini sol-gel process [27,29], which was illustrated in Scheme 1. In a typical reaction, 4.50 g of citric acid monohydrate (CiA), 2.48 g of tetrahydrate calcium nitride and 0.85 g of diammonium hydrogen phosphate were dissolved in 46.1 ml of ethanol and 138.3 ml of deionized water. ...
... Phases of silica-MB and silica-MB@OCP were identified by XRD as shown in Fig. 1. For silica-MB, the broad peak centered at 22 • was a typical diffraction peak of amorphous silica [27]. In solutions containing water, ethanol, MB and NH 3 •H 2 O, TEOS was firstly hydrolyzed to reactive silanol group, and then condensed to the Si-O-Si network, finally precipitated as amorphous silica. ...
Methylene blue-loaded silica (silica-MB) was coated by a shell of polyethylene glycol (PEG), citrate ions and octacalcium phosphate (OCP) through a facile sol–gel method. The influences of molecular weight of PEG, addition amount of PEG and citric acid on the phase, morphology and chemical composition of samples were characterized by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. Compared with that of silica-MB, the sustained-release behavior of MB from silica-MB@OCP was sensitive to the shell structure and the pH value of culture solution. At each time interval, the ratio of absorbance of MB monomers over that of MB dimers released from silica-MB@OCP was higher than that from silica-MB, indicating that the significant influence of interaction density among the network of PEG, citrate ions and OCP on the release behavior of MB. Silica-MB and silica-MB@OCP were degraded when MB molecules diffused to the culture solution from solid silica matrix, which would shed light on the self-destruction investigation of drug/drug carrier systems in the biological system.
... HA has three sites of Ca 2+ , PO4 3-, and OHthat can be easily replaced by many cations and anions such as Sr 2+ , Na + , RE 3+ , CO3 2-, VO4 3-, F -, Cl - [8][9][10][11]. The structure, morphology, optical properties, as well as application areas of the RE doped HA, depend on the many synthesis conditions such as synthesis method, Ca/P ratio, dopant ions, pH of the solution, and initial materials, etc. [5,[12][13][14]. Xie et al. [12] observed the energy transfer from Gd 3+ to Eu 3+ of the HA: Eu, Gd phosphor as imaging agents in vitro and in vivo. ...
... Xie et al. [12] observed the energy transfer from Gd 3+ to Eu 3+ of the HA: Eu, Gd phosphor as imaging agents in vitro and in vivo. Dembski et al. [13] reported that the luminescence properties of Eu 3+ -doped SiO2/Calcium phosphate core-shell depend on the pH, where they indicate that the formation of a calcium phosphate shell is possible at pH below 4.5 and above 6.5. Furthermore, the cell proliferation test shows that the phosphor can be used in various biological and medical diagnostic applications, particularly as labels for imaging experiments on living cells. ...
This paper reported the impact of pH on the structure, morphology, and the green upconversion (UC) emission of Er/Yb/Mo tri-doped hydroxyapatite (HA) synthesized through hydrothermal method. X-ray diffraction confirmed that the pH of the solution strongly influenced the phase composition of the phosphors, and HA single phase was obtained at a high pH value. Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images of the phosphor exhibited rod-like morphology, and their length increased with increased of the pH values. Under laser-diode excitation wavelength of 975 nm, the phosphor showed typical upconversion emission bands of the ion: strong green emission bands around 510-535/540-560 nm and weak red emission bands around 630-680 nm. The green and red emission intensity as a function of pH reached its maximum value at pH8. Finally, the emission intensity of
... A modified Stöber method was used to synthesize silica-MB in the following sequence [25,26]. Briefly, 92 ml of ethanol, 17.20 ml of water and 2.48 ml of NH 3 ÁH 2 O were mixed and followed by addition of 0.10 g of MB under stirring. ...
... Phases of silica-MB and silica-MB@TA were identified by XRD as shown in Fig. 1. A broad diffraction peak centered at 2h = 22°is a characteristic diffraction peak of amorphous silica [25]. After hydrolysis of TEOS in reaction solution, reactive silanol groups with negative charge were attached to the electropositive groups of MB and then condensed to SiAOASi network of silica [29] (Scheme 1). ...
To avoid multidrug resistance and tumour recurrence, photodynamic therapy (PDT) was emerging as an alternative therapy and its efficiency was related to photosensitizer (PS) efficiency, oxygen concentration and light characteristic. Methylene blue (MB) molecules as PSs were loaded in silica (silica-MB) and followed by encapsulation by coordination complexes of tannic acid (TA) and Fe(III) ions. In comparison with those of silica-MB, decreased condensation of Si-O-Si, shifted infrared absorbance frequencies of chemical bands, delayed thermal degradation and modulated release behavior of MB were observed for [email protected] with a core-shell structure. Although MB dimers were dominantly released from silica-MB, release of MB monomers from [email protected] was significantly promoted, which was described by the Higuchi model. The promotion of release of MB monomers from [email protected] indicated the well control of aggregate states of MB by the encapsulation of TA and Fe(III) ions complexes. Through monitoring the oxidation of uric acid, generation efficiency of singlet oxygen (¹O2) by MB released from [email protected] was fairly higher than that from silica-MB. A facile method to encapsulate silica-MB with complexes of TA and Fe(III) ions was herein demonstrated to raise the generation efficiency of singlet oxygen.
... Although previous work demonstrated co-precipitation reactions under an inert atmosphere [20] and used multiple surfactants [16][17][18] to prevent oxidation, the approach is still cost-effective and time consuming. Another approach to co-precipitation is to control the pH of the reactant solution [22,23] by controlling the addition of reducing agent, usually a basic solution. Nevertheless, controlling pH neither avoids oxidation nor determines the size and homogeneity of the particles. ...
This work demonstrates the synthesis and characterization of Fe nanoparticles surrounded by a citrate (CIT) matrix prepared at various temperatures and concentrations of metal, capping agent and reducing agent at standard conditions. We study the effect of reactant ratio and reaction temperature on the magnetization of the produced nanoparticles and their crystal structure. We found that for optimal metal concentrations, magnetic saturation increases with increase in the concentration of capping and reducing agents but decreases as the temperature of the reaction increases. Synthesis conditions were tailored to reveal nucleation of particles with average sizes ranging from 24 to 105 nm and a spherical shape. The ultra-high saturation magnetization of 228 emu g⁻¹ obtained for samples prepared at a metal precursor concentration of 27.8 mol l⁻¹ was attributed to the formation of small magnetic domains. Energy band gap measurements revealed a band gap energy for the Fe nanoparticles in the CIT matrix which is associated with CIT concentration and/or possible formation of a few thin layers of iron oxide shell and does not have a significant effect on the magnetic properties of the samples. Herein, we demonstrate that the synthesis parameters are crucial for the nucleation of Fe-CIT nanoparticles tailoring their magnetizatic properties as well as their potential for different applications.
... It is more chemically stable against an irritant environment (e.g. heat, pH, UV, and γ-ray) compared to organic molecules, and it exhibits a large Stokes shift of over 250 nm [17]. Studies have also shown that small amounts of Eu have no biologically harmful effects; therefore, Eu-doped HAp (EuHAp) nanocrystals are excellent candidates for biological fluorescent probes [12,18]. ...
... It was shown that Tf/RGD-MSCNs delivered the anti-tumor drug doxorubicin more efficiently into lysosomes and the resulting DOX-loaded nanoparticles (DOX-Tf/RGD-MSCNs) showed a stronger inhibitory effect towards tumor cell growth than free DOX and DOX delivered by unmodified MSNs. Besides, to explore the effect of pH on the synthesis and properties of SiO 2 /calcium phosphate core-shell nanoparticles, SiO 2 cores with a particle diameter of 46 nm were successfully coated with an approximately 6-nm-thick Eu 3þ -doped calcium phosphate shell [176]. It has been established that the formation of a calcium phosphate shell is possible at pH below 4.5 and above 6.5. ...
Calcium phosphate nanoparticles represent promising materials for drug delivery because of its favorable properties, including biocompatibility, biodegradability and strong affinity for binding to nucleic acids (pDNA, siRNA, miRNA, etc.) and therapeutic drugs (cisplatin, carboplatin, paclitaxel, gefitinib, doxorubicin, etc.). Various strategies to prepare the size-controllable, stable, targeting and pH-responsive CaP nanocarriers have been extensively developed as the potential candidates in clinic. This review discusses the mostly recent developments in the design of calcium phosphate nanocarriers as drug delivery systems and therapeutic agents. Additionally, the advantage is unquestionably demonstrated and the obstacles are thoroughly examined in order to overcome future clinical issues.
... This may be due to the adsorption of the dye further weakening the diffraction signal of some very fine crystalline nanoparticles in the SiO 2 sample. 33 This speculation is further confirmed by Raman spectroscopy data. This speculation is further confirmed by Raman spectra. ...
Purpose
Worldwide water contamination treatment and water security are essential for all living organisms. Among various water contaminants, dye, and bacteria pollution needs to be solved urgently.
Methods and Results
In this work, a ceramic sheet from monodisperse, porous silica nanospheres (SiO2 NSs) with an average diameter of 220 was prepared. The prepared SiO2 ceramic sheets were investigated as a “filtration” material in removing dyes (alcian blue, AB; and methylene blue, MB) and bacteria (E. coli and S. aureus). The obtained sheets had efficient adsorption efficiency of 98.72% (for AB) and 97.35% (for MB), and a high adsorption capacity for AB is 220 (mg/g), for MB is 176 (mg/g). Furthermore, these SiO2 ceramic sheets had a high recycling capability for removing dyes by calcination. Being modified by Ag nanoclusters, the ceramic sheets present a strong bactericidal function.
Conclusion
Our results demonstrated that the obtained SiO2 non-sintered ceramic sheets is rapid and efficient in the filtration of dyes and bacteria from polluted water.
... Such type of composites was also fabricated using ammonium dihydrogen phosphate, or ammonium phosphate, or P 2 O 5 and calcium nitrate as staring materials [266][267][268][269][270]. The sol-gel derived CHAp blocks were mixed with TEOS in ethanol-water system for 1 min and sintered at 1200°C for 2 h to get an outer coating over CHAp. ...
In this review article the available results about application of sol–gel synthesis method for the preparation of different calcium phosphates and composite materials are summarized. The attention is paid to calcium phosphate-containing compounds which show the biological properties and could be used as potential phosphate bioceramics in medicine. It was demonstrated that the sol–gel synthesis method is a powerful tool for the synthesis of calcium hydroxyapatite and other phosphates, and different calcium phosphate-based composites at mild synthetic conditions resulted in high reproducibility, high phase purity, and desired morphology. Thus, the sol–gel synthesis method enables the researchers to develop biomaterials with superior features in terms of biomedical applications.
For the synthesis of calcium phosphate biomaterials an effective sol–gel chemistry approaches have been developed. KI, EG, and AK. “Sol–gel synthesis of calcium phosphate-based biomaterials—A review of environmentally benign, simple, and effective synthesis routes”.
... The monoclinic GdPO 4 : Nd 3+ nanoparticles were coated with calcium phosphate (CaPO) using a modified sol gel-based Pechini method to prepare a core/shell-type structure [37]. A small amount (0.0483 g) of citric acid (CA) was dissolved in a mixed solution of 75 cm 3 of deionized water and 25 cm 3 of ethanol (water/ethanol = 3/1 in volume). ...
Core/shell-type nanoparticles composed of GdPO4: x mol% Nd³⁺/calcium phosphate (CaPO) (0 ≤ x ≤ 5) were synthesized by a precipitation method, as nontoxic bio imaging phosphors that can emit near-infrared (NIR) light under NIR excitation. The GdPO4: x mol% Nd³⁺ core, obtained in a single-phase form of the monoclinic rare-earth orthophosphate structure, exhibited characteristic emissions attributed to the f–f transitions of Nd³⁺. The strongest emission peak was observed at 1061 nm under excitation at 800 nm in a sample containing 3 mol% of Nd³⁺. The average particle size of GdPO4: 3 mol% Nd³⁺ was 42 nm, indicating that nano-sized particles were successfully obtained. Although the average particle size of the core/shell-type GdPO4: 3 mol% Nd³⁺/CaPO nanophosphor was slightly increased to 54 nm by a second calcination in the surface coating process, the CaPO shell was well formed with a thickness of 3 nm around the GdPO4: 3 mol% Nd³⁺ core. With surface coating with the CaPO4 shell, the NIR emission intensity increased to 4.2 times higher than that of GdPO4: 3 mol% Nd³⁺. This emission intensity was significantly higher than that of indocyanine green, moreover, which is used in practice as an organic bioimaging reagent.
... 10 But, QDs possess several disadvantages, which include their cytotoxicity, lack of chemical stability, low light-penetration ability, blinking effects, and oxidation in the presence of oxygen or water; as a result limiting their application in in vivo imaging. 11 Silica or silica doped QDs and carbon nanotubes are demonstrated as promising luminescent materials for in vivo imaging owing to their unique optical properties. 12,13 Several studies describe the poor biocompatibility of silica and carbon nanotubes since the silica particles interact with cells and cause inflammatory responses. ...
... In this process, the adsorption of one component onto the core is affected by the surface charge, the solution pH, and the precursor concentrations. The thickness of the shell and the size of the core are strongly pH-dependent [35][36][37]. This chemical makeup method can also be used to prevent iron NPs from oxidation and agglomeration [23]. ...
In these recent years, magnetite (Fe3O4) has witnessed a growing interest in the scientific community as a potential material in various fields of application namely in catalysis, biosensing, hyperthermia treatments, magnetic resonance imaging (MRI) contrast agents and drug delivery. Their unique properties such as metal-insulator phase transitions, superconductivity, low Curie temperature, and magnetoresistance make magnetite special and need further investigation. On the other hand, nanoparticles especially gold nanoparticles (Au NPs) exhibit striking features that are not observed in the bulk counterparts. For instance, the mentioned ferromagnetism in Au NPs coated with protective agents such as dodecane thiol, in addition to their aptitude to be used in near-infrared (NIR) light sensitivity and their high adsorptive ability in tumor cell, make them useful in nanomedicine application. Besides, silver nanoparticles (Ag NPs) are known as an antimicrobial agent. Put together, Put together, the Fe3O4AuxAgy ((x, y) = (0, 1)) nanocomposites with tunable size can therefore display important demanding properties for diverse applications. In this review, we try to examine the new trend of magnetite-based nanomaterial synthesis and their application in catalysis and nanomedicine.
... Research on nanostructured materials is important from the viewpoint of understanding their varied physical properties in comparison to the bulk counterparts. Experimental parameters such as solution pH [1,2], precursors [3,4] and stabilizing agent [5] influence the luminescence, size and morphology of the synthesized nanomaterials. Zutz et al. demonstrated the influence of Cd/Se precursor ratio on the efficiency of the CdSe/polymer hybrid solar cells [6]. ...
ZnS nanoparticles have been synthesized using the amino acid histidine as a stabilizing agent. The syntheses were carried out by varying the starting pH and histidine/Zn2+ ratio. The as-prepared ZnS nanoparticles were characterized by various analytical techniques. The photocatalytic activity of the ZnS nanoparticles was determined by studying the degradation of methyl orange. The ZnS nanoparticles synthesized with 1:1 histidine/Zn2+ ratio and starting pH of 10.3 were found to exhibit the highest photocatalytic activity. Nearly 95% of methyl orange was degraded in 30 min of irradiation using the photocatalyst. Particle size was not the main factor in determining the photocatalytic activity of the ZnS nanoparticles. Fluorescence lifetime measurements indicated that photocatalytic activity of the ZnS nanoparticles was enhanced with increase in their fluorescence lifetime.
Counterfeit electronic products not only cause financial losses but also come with safety risks. The worst‐case failure scenario certainly is a fire event. Since manufacturers are liable for damages and suffer image loss, fire‐proof postmortem taggants are needed, enabling differentiation between originals and counterfeits even after a fire incident. This work presents such taggants: optomagnetic supraparticles (SPs), i.e., complex microscale particles composed of luminescent and magnetic nanoparticles (NPs) are generated. Their hybrid nature is pivotal, as magnetic separation can effectively remove the tags from light‐absorbing fire debris, and a fire‐proof identification (ID) fingerprint is based on ratiometric luminescence signals. To achieve thermally stable magnets, iron oxide (IO) NPs are wet‐chemically coated with a SiO2‐3‐aminopropyltriethoxysilane (APTES) shell. Subsequently, these magnetic NPs are assembled with luminescent nanophosphors (lanthanide‐doped calcium phosphate NPs with a SiO2‐core) and SiO2‐APTES spacer NPs by spray‐drying to form hybrid SPs. The careful choice of type and ratios of the NPs and process parameters make it possible to achieve and precisely tune the desired functionality of the resulting fire‐proof taggants. A proof‐of‐concept is demonstrated, in which the taggants are incorporated as additives into coatings and subjected to real fire simulations.
Biologically, effectively regulated light with a wavelength of about 485 nm can support physiological processes in the body and has a positive impact on the human sleep–wake rhythm. However, the application of common light therapy devices is not always practicable and sometimes difficult to integrate into everyday life. Here, miniaturization of therapy devices, for example, in the form of contact lenses, can reduce the handling disadvantages. Especially, contact lenses modified with phosphorescence materials offer this benefit. Herein, a method to prepare phosphorescent Eu2+, Dy3+‐doped strontium aluminate nanoparticles (NPs) by laser vaporization of macroscopic Eu2+, Dy3+‐doped Sr4Al14O25 particle powder and their integration into polymer‐based contact lenses is provided. NPs with a diameter of about 34 nm emit light in the desired therapeutic wavelength region. These novel NPs are biocompatible and do not show any negative effects during the testing of eye irritation safety in a 3D in vitro cornea model. Phosphorescent lanthanide‐doped strontium aluminate nanoparticles (NPs) are prepared by laser vaporization of a macroscopic powder and integrated into contact lenses to apply for the light therapy of winter depression or sleep disorders. Novel NPs are biocompatible and do not show any negative effects during the testing of eye irritation safety in a 3D in vitro cornea model.
As a kind of near-infrared dye, methylene blue (MB) molecule is proneness to form excimers in solid powder or solution at high concentration, which results in weak photoluminescence intensity during clinic diagnostic and cell labeling applications. Aiming to improve the quantum yield of MB, silica-MB particles are herein prepared and treated hydrothermally (HT) to synthesize silica-MB-HT and [email protected] carbon with glucose as carbon source ([email protected]). Significantly, hydrothermal treatment causes destruction of Si-O-Si network, modulation of aggregation state, variations of energy gap and release behavior of MB. In comparison with that of silica-MB, emission intensities of both silica-MB-HT and [email protected] increase greatly and their photoluminescence peaks are blue-shifted, which are closely related with Raman-active vibration modes of MB in a locally-excited state. Enhanced emissions of both silica-MB-HT120 and [email protected] are observed with increased intensities of Raman peaks assigned to in-plane bending vibrations of CH bond during skeletal deformation of CC in ring. In contrast, the in-plane bending vibration for CH bonds at end group of MB is considered as a way of radiation decay, and strong vibration of this Raman-active mode causes weak emission intensities of silica-MB-HT180 and [email protected] The stabilities of photophysical properties are compared after 72 h of incubation in buffered mediums or 5 h of illumination under ultraviolet light. The photoluminescence intensity of [email protected] fluorophore increase remarkably after illumination, meeting the requirements of reduced photobleaching, minized solvatochromic shift and increased fluorescent efficiency during versatile applications.
Three kinds of novel [email protected] complex core-shell composites were synthesized with 2-chlorobenzoic acid, 4-chlorobenzoic acid, and 2,4-dichlorobenzoic acid as the ligand, respectively. The XRD, UV/vis absorption and FT-IR results show that terbium ions are coordinated with ligands and the corresponding complexes are successfully included into composites. SEM and EDS results reveal that Tb complexes are fully and homogenously coated on the surface of hydroxyapatite (HAP) microspheres consisting of a large number of nanosized crystals. The strongest luminescence properties are obtained when 2,4-dichlorobenzoic acid is used as ligand. The study on fluorescence lifetime of composites shows that the lifetime is inversely related to emission intensity. TGA-DSC results indicate that the core-shell composites have an excellent thermal stability. Therefore, the current core-shell structure provides a cost-effective route to manufacture of biocompatible and heat-resistant highly luminescent materials.
Photodynamic therapy (PDT) is a promising alternative to traditional chemotherapy for cancer treatment. The photodynamic efficiency of PDT is closely related to the generation of singlet oxygen, which is greatly dependent on the aggregation state of photosensitizer (PS). Herein, methylene blue (MB) molecules as PSs were loaded in silica-MB via electrostatic interactions, and silica-MB was subsequently incubated in acetate (Ac) buffer solution to obtain silica-MB-Ac. [email protected] with a core-shell structure was finally prepared with an assembly of coordination complexes of tannic acid (TA) and Fe(III) ions. Compared with those values for silica-MB, cumulative amount and absorbance ratio of monomer versus dimer of MB released from both silica-MB-Ac and [email protected] increased remarkably as a result of significant decrease of MB self-aggregations with aromatic-aromatic interactions. Sustained and pH-dependent release behaviors of monomeric MB were well simulated by the theoretical Higuchi model based on the Fickian diffusion. The generation of singlet oxygen, photodynamic efficiency and stability against in vitro reduction of monomeric MB released from [email protected] were significantly higher than those for silica-MB-Ac, due to the effective control of aggregation state of MB molecules during outward diffusion through the complexes of TA and Fe(III) ions. The present investigation demonstrated a facile route to obtain high photodynamic efficiency by finely controlling the aggregation state of MB molecules.
Highly dispersed core–shell α′′-Fe16N2/SiO2 particles were prepared using hydroxyapatite (HAp) as the sintering prevention layer. HAp was effective as anti-sintering agent, and could be dissolved by solutions with wide pH range. The α′′-Fe16N2 phase was formed by reduction and nitridation, in spite of the presence of SiO2 and HAp. HAp was effective to prevent the aggregation of the core–shell α′′-Fe16N2/SiO2 particles resulted from the elimination of the surface Si–OH of silica shell layer. The HAp was successfully removed using the citric acid without the degeneration of the SiO2 shell layer and α′′-Fe16N2 core particles.
This article reports a novel category of coating structure SiO2@Eu(MABA-Si) luminescence nanoparticles (NPs) consisting of a unique organic shell, composed of perchlorate europium(III) complex, and an inorganic core, composed of silica. The binary complex Eu(MABA-Si)3·(ClO4)3·5H2O was synthesized using HOOCC6H4N(CONH(CH2)3Si(OCH2CH3)3)2 (MABA-Si) and was used as a ligand. Furthermore, the as-prepared silica NPs were successfully coated with the -Si(OCH2CH3)3 group of MABA-Si to form Si–O–Si chemical bonds by means of the hydrolyzation of MABA-Si. The binary complexes were characterized by elemental analysis, molar conductivity and coordination titration analysis. The results indicated that the composition of the binary complex was Eu(MABA-Si)3·(ClO4)3·5H2O. Coating structure SiO2@Eu(MABA-Si) NPs were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and infrared (IR) spectra. Based on the SEM and TEM measurements, the diameter of core-SiO2 particles was ~400 and 600 nm, and the thickness of the cladding layer Eu(MABA-Si) was ~20 nm. In the binary complex Eu(MABA-Si)3·(ClO4)3·5H2O, the fluorescence spectra illustrated that the energy of the ligand MABA-Si transferred to the energy level for the excitation state of europium(III) ion. Coating structure SiO2@Eu(MABA-Si) NPs exhibited intense red luminescence compared with the binary complex. The fluorescence lifetime and fluorescence quantum efficiency of the binary complex and of the coating structure NPs were also calculated. The way in which the size of core-SiO2 spheres influences the luminescence was also studied. Moreover, the luminescent mechanisms of the complex were studied and explained.
Scaffolds for bone tissue engineering (BTE) must be mechanically competent and chemically compatible with bone tissue to repair defects. Polymeric materials exhibit suitable mechanical and processing abilities but lack the bioactivity of inorganic ceramics. Composites of these materials are being developed to combine and improve their properties. It has become evident that cells respond to the topography of the surrounding extracellular matrix, specifically to nano-sized features; and reproducing these physical characteristics on the surface of scaffolds improves cell spread and attachment. Electrospinning can produce thin fibres with wide-ranging diameters and offers the possibility of fabricating nanocomposite fibrous scaffolds. This chapter focuses on ascertaining the impact of an inorganic phase on the mechanical properties, bioactivity and cell behaviour of electrospun composite structures.
Nano-sized spherical hydroxyapatite (HAp) particles were prepared via a wet chemical precipitation method after the solutions comprising calcium and phosphate precursors were mixed at a slow addition rate. According to the high adsorption capacity for drug (methylene blue, MB) and the standard deviation, the optimal experimental condition of sol-gel route was determined via the orthogonal experiment design method. The HAp/mesoporous silica (HAp/mSiO2) powder was fabricated through the deposition of mSiO2 on HAp at low silanophilic activity under the optimal experimental condition. The adsorption capacity of MB onto HAp/mSiO2 in solutions containing MB at a concentration of 0.10 g/L is 79.26 mg/g. The adsorption isotherm of methylene blue onto HAp/mSiO2 is a type II isotherm, i.e., the monomer and dimmers of drug molecules are adsorbed on HAp/mSiO2. The sustained-release behavior of drugs from HAp/mSiO2 is related to the pH value of the buffers (pH=7.2~7.4 in phosphate buffered saline and pH=4.7 in lysosome-like buffers) due to the influence of solution properties on the microstructures of drug carriers and interaction mechanisms between drug molecules and powders.
Silica particle as core material was prepared by a modified Stöber method, and then core-shell structured silica@hydroxyapatite was prepared through a modified Pechini process. The phase and structure of the samples were characterized by scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectrometer. The formation mechanism of core-shell structured powder is that hydroxyapatite shell is deposited on the surface of amorphous silica with assist of polyethylene glycol and citric acid. The sustained-release behaviors of drug from silica@hydroxyapatite powders with drug storage are seriously depended on core-shell structure and pH value of phosphate buffered saline (pH=7.2-7.4) or lysosome-like buffer (pH=4.7). ©, 2015, Rengong Jingti Xuebao/Journal of Synthetic Crystals. All right reserved.
Hydroxyapatite (HAp) is the most important constituent of biological tissues such as bone and teeth and exhibits several characteristic features. HAp nanoparticles (NPs) are good host materials and can be functionalized with various kinds of dopants and substrates. By endowing HAp NPs with desired properties in order to render them suitable for biomedical applications including cellular imaging, non-invasive and quantitative visualisation of molecular process occurring at cellular and subcellular levels becomes possible. Depending on their functional properties, HAp based nanoprobes can be divided into three classes, i.e., luminescent HAp NPs (for both downconversion and upconversion luminescence), magnetic HAp NPs, and luminomagnetic HAp NPs. Luminomagnetic HAp NPs are particularly attractive in terms of bimodal imaging and even multimodal imaging by virtue of their luminescence and magnetism. Functionalised HAp NPs are potential candidates for targeted drug delivery applications. This review (with 166 references) spotlights the cellular imaging applications of three types of HAp NPs. Specific sections cover aspects of molecular imaging and the various imaging modes, a comparison of the common types of nanoprobes for bioimaging, synthetic methods for making the various kinds of HAp NPs, followed by overviews on fluorescent NPs for bioimaging (such as quantum dots, gold nanoclusters, lanthanide-doped or fluorophore-doped NPs), magnetic HAp NPs for use in magnetic resonance imaging (MRI), luminomagnetic HAp NPs for bimodal imaging, and sections on drug delivery as well as cellular imaging applications of HAp based nanoprobes (including targeted imaging).
Methylene blue-loaded silica (silica-MB) was coated by octacalcium phosphate (silica-MB@OCP) through a facile sol–gel method. Both MB monomers and dimers were released from silica-MB, while release of MB dimers from silica-MB@OCP was predominant in phosphate-buffered saline and lysosome-like buffer as an indicative of the influence of the molecular weight of polyethylene glycol (PEG) on the interaction density of shell network consisted of PEG, citric acid, ethylenediaminetetraacetic acid and OCP. The ratio evolution of absorbance of dimers over that of monomers was caused by the radical distribution of MB molecules in silica-MB and silica-MB@OCP. The investigation of MB dimers/carrier system would shed light on the investigation of MB dimers in photodynamic therapy for the specific treatment to outgrowing solid tumors with the disproportion between oxygen supply and consumption.
Graphical Abstract
We synthesized composites of Eu(3+)-doped calcium apatite (CaAp:Eu(3+)) nanoparticles and silica particles via two methods: (i) in situ synthesis of CaAp:Eu(3+) in the presence of silica particles; and (ii) electrostatic adsorption of CaAp:Eu(3+) nanoparticles on silica particle surfaces. In both methods, submicrometer spherical silica particles were covered with CaAp:Eu(3+) nanoparticles without forming any impurity phases, as confirmed by X-ray diffractometry, Fourier-transform infrared spectroscopy, and scanning electron microscopy. In method (i), part of the silica surface acted as a nucleation site for apatite crystals and silica particles were inhomogeneously covered with CaAp:Eu(3+) nanoparticles. In method (ii), positively charged CaAp:Eu(3+) nanoparticles were homogeneously adsorbed on the negatively charged silica surface through electrostatic interactions. The bonds between the silica surface and CaAp:Eu(3+) nanoparticles are strong enough not to break under ultrasonic irradiation, irrespective of the synthetic method used. The composite particles showed red photoluminescence corresponding to 4f → 4f transitions of Eu(3+) under near-UV irradiation. Although the absorption coefficient of the forbidden 4f → 4f transitions of Eu(3+) was small, the red emission was detectable with a commercial fluorescence microscope because the CaAp:Eu(3+) nanoparticles accumulated on the silica particle surfaces.
Yttrium aluminum garnet Y3Al5O12 (YAG):Ce3+ nanoparticles prepared by glycothermal method are modified with poly(acrylic acid) (PAA). This surface modification enables YAG:Ce3+ nanoparticles to be well dispersed in phosphate-buffered saline (PBS) without any serious aggregation. YAG:Ce3+ nanoparticles emit yellowish green light under the excitation of blue light. This fluorescent property does not change after the modification of PAA. Streptavidin (SA) is immobilized on the surface of PAA-modified YAG:Ce3+ nanoparticles by using carboxyl groups of PAA as cross-linking sites. We demonstrate the quantitative analysis of bovine serum albumin in PBS by SA-immobilized YAG:Ce3+ nanoparticles.
Uniform spherical core–shell structured SiO2@CaMoO4:Eu3+,Li+ phosphors were prepared by a combined homogeneous precipitation approach and combustion synthesis. CaMoO4:Eu3+,Li+ layer was grown onto submicrometer amorphous SiO2 particles, which were synthesized by the Stöber method, via a homogeneous precipitation technique. The following combustion reaction at 600 °C and simply post-annealing resulted in uniform spherical SiO2@CaMoO4:Eu3+,Li+ core–shell structured phosphors. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectra (EDS), and photoluminescence (PL). The results show that the amorphous SiO2 submicrospheres were coated by crystalline CaMoO4:Eu3+,Li+ nanoparticles, forming spherical core–shell structure with uniform size of ∼260 nm. The powder samples showed strong red emission corresponding to 5D0 → 7F2 transitions of Eu3+ ions under near ultraviolet (UV) or blue light. Their color coordinate (0.63, 0.36) is close to the standard of national television standards committee (NTSC) (0.67, 0.33).
In this work, the availability of calcium phosphates for the light emitting layer of a thin-film electroluminescent (TFEL) device was investigated. The goal of this work was to develop an electronic device with ordinary materials such as a calcium phosphate, the principal ingredient of the skeleton of the vertebrate. Compositions of 2CaO·P2O5 (Ca2P2O7), 3CaO·P2O5 (Ca3(PO4)2) and 4CaO·P2O5 (Ca4O(PO4)2) were examined as the candidates for the light emitting layer. Before composing the TFEL device, the photoluminescence (PL) properties of the three compositions were investigated in the powder form to evaluate the performance as the light emitting layer. Among the examined calcium phosphates, Eu-doped β-Ca3(PO4)2 showed the best PL properties. It showed typical red-emission from Eu3+. The PL intensity was enhanced with the heat-treatment temperature and the optimal temperature was 1250 °C. Then, a TFEL device was prepared by a spray pyrolysis method with the β-Ca3(PO4)2:Eu3+ phosphor layer on a BaTiO3 disk. The TFEL device exhibited the red emission originating in Eu3+ at 610 nm under applying alternating voltage. Different from the power sample, the intensity of EL decreased with the heat-treatment temperature from 1000 to 1250 °C. The deterioration of EL at the higher temperatures was attributed to chemical interaction between the phosphor layer and the BaTiO3 disk.
In 550 °C and H2 current, the mesoporous nickel–silica composite core–shell microspheres with tunable chamber structures have been successfully prepared by reduction of Ni3Si2O5(OH)4 microspheres, which are synthesized by the reaction between Ni(Ac)2·4H2O and SiO2 microspheres via a self-template approach. The chamber (SiO2 core sizes) and shell thickness (40–150 nm) of the nickel–silica microspheres can be controlled by adjusting the synthetic parameters of Ni3Si2O5(OH)4, such as the reaction time. After reduction, these microspheres still have the same sizes, morphologies, and core–shell structures with porous shell as before. These mesoporous nickel–silica microspheres with large BET surface area, exhibit good catalytic activity in m-dinitrobenzene (m-DNB) and high selectivity of m-phenylenediamine (m-PDA) after 3.5 h, but different selectivity of m-PDA in the progress, showing good potential in the catalyst industry.
Luminescent core–shell particles are structures widely applied to biomedical purposes with the potential of combining multiple features within one single particle. The development of particles that are easily synthesised and tunable for each application, combining biocompatibility, easy bioconjugation and a high detection signal as a label, is highly desired. In this work, we describe a one-step synthesis of poly[styrene-co-(2-hydroxyethyl methacrylate)], PSHEMA, core–shell particles containing [Ru(4,4′-dicarboxilate-2,2′-bpy)3] luminescent complexes. These particles show monodispersity, biocompatibility, easy functionalization and dye incorporation to focus on bioapplications, such as cell-tracking and diagnostics. The monomers assemble during the polymerization and produce core–shell structures with hydrophilic-hydrophobic character. This allows the concentration of hydrophilic ruthenium complexes onto the shell and incorporation of hydrophobic molecules (e.g. diphenylanthracene) due to the hydrophobic character of styrene. The incorporation of the Ru complex resulted in higher photostability compared to the free dye. Furthermore, carboxylic groups on the particle surface originated from carboxylated ligands of Ru complexes were used to immobilize biomolecules. The particles were successfully used as a diagnostic label for dengue fever (DF) infection. Using the complexes in the immunospot assay the test provided a detection limit (DL) of 187 ng mL−1 for the viral non-structural glycoprotein NS1. The particles showed a considerable decrease in the DL and allowed the diagnosis of the infection 24 hours earlier compared to common available assays based on gold nanoparticles. In addition, the particles were tested with an adherent grown fibroblast cell line and showed potential biocompatibility.
Europium-doped fluorine-substituted hydroxyapatite (Eu:FHAp) nanoparticles with different morphologies were synthesized by a simple hydrothermal method. The structure, composition, morphology, and luminescence of the products were investigated by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and fluorescence spectroscopy. The prepared Eu:FHAp had a nanorod-like shape and their aspect ratios dropped when the pH of the solution was increased from 3.0 to 11.0. The luminescence intensity of the products increased significantly with increasing substitution of OH− with F−. The nanoparticles did not adversely affect the growth of hela cells, which indicates that they have potential applications as fluorescent cell labeling agents.
Summary Due to exceptional photo-physical properties, up-converting nanoparticles (UCNPs) are promising and advantageous alternative to conventional fluorescent labels used in many bio-medical applications. The first part of this review aims at presenting these properties as well as the current state-of-the-art in the up-conversion enhancement, NPs surface functionalization and bioconjugation. In the second part of the paper, the applications of UCNPs and currently available detection instrumentation are discussed in the view of the distinctive properties of these markers. Because the growing widespread use of the biofunctionalized NPs, scarce instrumentation for up-conversion detection is reviewed. Finally, the challenges and future perspectives of the UCNPs are discussed.
Fluorescence spectroscopy has been shown to be a useful tool for a broad variety of biological and medical applications. Many of the analytical methods, as used for tumor marker and gene mutation detection, recognition of pathogens or monitoring of cell-related processes, are based on the labeling of the investigating object with luminescent nanoparticles. Owing to their size, which is comparable to that of biomolecules, and to their extraordinary optical properties, luminescent nanoparticles could well improve the sensitivity and flexibility of current detection techniques. This article provides a general overview of the synthesis, properties and application of luminescent semiconductor, metal and inorganic nanoparticles for in vitro and in vivo diagnostics, also reflecting the aspect of biocompatibility.
Blend membranes of chitosan and poly (ethylene oxide) with different molecular weights of 100,000 and 600,000 were prepared by the solution cast technique. The Chitosan-PEO blend membranes were produced to study their water adsorptions capacity and characteristics of the haemodialysis membrane application. An increase in the water adsorption capacity of chitosan-PEO blend membranes compared to the pure chitosan was due to the porous structure as evident from the scanning electron micrograph. Addition of PEO with higher molecular weight had reduced the percentage of water adsorption of the chitosan-PEO blend membranes. XRD results revealed that chitosan-PEO blend membrane with higher water adsorption ability shows lesser degree of amorphosity. Intermolecular interactions between chitosan and higher molecular PEO chains in the blend contributed to important alteration in chitosan structure as observed in the infrared spectroscopy which lessens the permeability of the membrane.
The sections in this article are
Introduction
Nano‐Calcium Phosphates in Hard Tissues
Bone
Tooth
Other Biological Organisms
Biological Formation of Calcium Phosphates
Characteristic Mechanical Properties
Stability of Nano‐Calcium Phosphates
Demineralization of Biominerals
Dissolution of Pure HAP
Nanosize Effects in Biomaterials
Synthesis of Nano‐Calcium Phosphates
Synthesis of Nano‐Calcium Phosphate Particles
Biomimetic Construction using HA Nanoparticles
Nano‐ HA –Collagen Composites
Nano‐ HA Coating
Nano‐Calcium Phosphate in Biomedical Engineering
Bone Repair
Bone‐Related Cells
Enamel Repair
Other Applications
Summary
Acknowledgments
A simple route to the production of high-quality CdE (E = S, Se, Te) semiconductor nanocrystallites is presented. Crystallites from approximately 12 angstrom to approximately 115 angstrom in diameter with consistent crystal structure, surface derivatization, and a high degree of monodispersity are prepared in a single reaction. The synthesis is based on the pyrolysis of organometallic reagents by injection into a hot coordinating solvent. This provides temporally discrete nucleation and permits controlled growth of macroscopic quantities of nanocrystallites. Size selective precipitation of crystallites from portions of the growth solution isolates samples with narrow size distributions (<5% rms in diameter). High sample quality results in sharp absorption features and strong ''band-edge' emission which is tunable with particle size and choice of material. Transmission electron microscopy and X-ray powder diffraction in combination with computer simulations indicate the presence of bulk structural properties in crystallites as small as 20 angstrom in diameter.
Nanocrystalline CaWO4 and Eu3+ (Tb3+)-doped CaWO4 phosphor layers were coated on non-aggregated, monodisperse and spherical SiO2 particles by the Pechini sol–gel method, resulting in the formation of SiO2@CaWO4, SiO2@CaWO4:Eu3+/Tb3+ core–shell structured particles. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), time-resolved PL spectra and lifetimes were used to characterize the core–shell structured materials. Both XRD and FT-IR indicate that CaWO4 layers have been successfully coated on the SiO2 particles, which can be further verified by the FESEM and TEM images. The PL and CL demonstrate that the SiO2@CaWO4 sample exhibits blue emission band with a maximum at 420 nm (lifetime = 12.8 µs) originated from the WO42− groups, while SiO2@CaWO4:Eu3+ and SiO2@CaWO4:Tb3+ show additional red emission dominated by 614 nm (Eu3+:5D0–7F2 transition, lifetime = 1.04 ms) and green emission at 544 nm (Tb3+:5D4–7F5 transition, lifetime = 1.38 ms), respectively. The PL excitation, emission and time-resolved spectra suggest that there exists an energy transfer from WO42− to Eu3+ and Tb3+ in SiO2@CaWO4:Eu3+ and SiO2@CaWO4:Tb3+, respectively. The energy transfer from WO42− to Tb3+ in SiO2@CaWO4:Tb3+ is more efficient than that from WO42− to Eu3+ in SiO2@CaWO4:Eu3+.
n molecular biology, the production of proteins can be effectively inhibited by introducing specific oligonucleotides into a living cell (gene silencing or antisense strategy; important for gene therapy). Calcium phosphate nanoparticles can serve as carriers for biomolecules in such therapeutic applications due to their high biocompatibility and biodegradability. Stable colloids were prepared by coating the inorganic nanoparticles with single- and double-stranded oligonucleotides. The dispersions were analysed by dynamic light scattering, zeta potential measurements, transmission electron microscopy, and scanning electron microscopy. Particles with a diameter of about 100 nm were obtained under optimized conditions. The efficiency of such nanoparticles to specifically inhibit protein synthesis was tested on HeLa-EGFP cells whose green fluorescence was turned off by the coated nanoparticles (gene silencing with siRNA). If siRNA was incorporated into the calcium phosphate particle and thereby protected from intracellular degradation, the transfection efficiency was significantly increased. The dispersions were stable and could be stored at 4C without loss of activity for several weeks, making them available as biochemical reagents.
Calcium phosphate nanoparticles were prepared by precipitation and stabilized as colloids by coating with DNA. They were doped with europium or terbium during this precipitation (about 2.5 wt%) and showed good fluorescence in the visible part of the spectrum. The fluorescence efficiency depended strongly on the internal crystallinity, i.e. amorphous nanoparticles of the same composition showed much weaker fluorescence. These particles are biocompatible and are easily taken up by cells (T-HUVEC), i.e. they can be used as fluorescing markers. Different colours can be realized by doping with different lanthanides.
Blend membranes of chitosan and poly (ethylene oxide) with different molecular weights of 100,000 and 600,000 were prepared by the solution cast technique. The chitosan-PEO blends membranes were produced to study their water adsorptions capacity and characteristics for haemodialysis membrane application. An increase in the water adsorption capacity of chitosan-PEO blend membranes compared to the pure chitosan was due to the porous structure as evident from the scanning electron micrograph. Addition of PEO with higher molecular weight had reduced the percentage of water adsorption of the chitosan-PEO blend membranes. XRD results revealed that chitosan-PEO blend membrane with higher water adsorption ability shows lesser degree of amorphosity. Intermolecular interactions between chitosan and higher molecular PEO chains in the blend contributed to important alteration in chitosan structure as observed in the infrared spectroscopy which lessens the permeability of the membrane.
Calcium phosphate is the most important inorganic constituent of biological tissues, and synthetic calcium phosphate has been widely used as biomaterials. In this study, a facile method has been developed for the fabrication of amorphous calcium phosphate (ACP)/polylactide-block-monomethoxy(polyethyleneglycol) hybrid nanoparticles and ACP porous nanospheres. Europium-doping is performed to enable photoluminescence (PL) function of ACP porous nanospheres. A high specific surface area of the europium-doped ACP (Eu3+:ACP) porous nanospheres is achieved (126.7 m2/g). PL properties of Eu3+:ACP porous nanospheres are investigated, and the most intense peak at 612 nm is observed at 5 mol% Eu3+ doping. In vitro cytotoxicity experiments indicate that the as-prepared Eu3+:ACP porous nanospheres are biocompatible. In vitro drug release experiments indicate that the ibuprofen-loaded Eu3+:ACP porous nanospheres show a slow and sustained drug release in simulated body fluid. We have found that the cumulative amount of released drug has a linear relationship with the natural logarithm of release time (ln(t)). The Eu3+:ACP porous nanospheres are bioactive, and can transform to hydroxyapatite during drug release. The PL properties of drug-loaded nanocarriers before and after drug release are also investigated.
Quantum dots (QDs) are being investigated as novel in vivo imaging agents. The leaching of toxic metals from these QDs in biological systems is of great concern. This study compared the cytotoxic mechanisms of two QD species made of different core materials (cadmium selenide [CdSe] vs. indium gallium phosphide [InGaP]) but similar core sizes (5.1 vs. 3.7 nm) and surface compositions (both ZnS capped, lipid-coated and pegylated). The CdSe QD was found to be 10-fold more toxic to porcine renal proximal tubule cells (LLC-PK1) than the InGaP QD on a molar basis, as determined by MTT assay (48 h IC(50) 10nM for CdSe vs. 100nM for InGaP). Neither of the QD species induced appreciable oxidative stress, as determined by lipid peroxide and reduced glutathione content, suggesting that toxicity was not metal associated. In agreement, treatment of cells with CdSe QDs was not associated with changes in metallothionein-IA (MT-IA) gene expression or Cd-associated caspase 3 enzyme activation. By contrast, incubation of the LLC-PK1 cells with the InGaP QD resulted in a dramatic increase in MT-IA expression by 21- and 43-fold, at 8 and 24 h, respectively. The most remarkable finding was evidence of extensive autophagy in QD-treated cells, as determined by Lysotracker Red dye uptake, TEM, and LC3 immunobloting. Autophagy induction has also been described for other nanomaterials and may represent a common cellular response. These data suggest that QD cytotoxicity is dependent upon properties of the particle as a whole, and not exclusively the metal core materials.
The inorganic part of hard tissues (bones and teeth) of mammals consists of calcium phosphate, mainly of apatitic structure. Similarly, most undesired calcifications (i.e. those appearing as a result of various diseases) of mammals also contain calcium phosphate. For example, atherosclerosis results in blood-vessel blockage caused by a solid composite of cholesterol with calcium phosphate. Dental caries result in a replacement of less soluble and hard apatite by more soluble and softer calcium hydrogenphosphates. Osteoporosis is a demineralization of bone. Therefore, from a chemical point of view, processes of normal (bone and teeth formation and growth) and pathological (atherosclerosis and dental calculus) calcifications are just an in vivo crystallization of calcium phosphate. Similarly, dental caries and osteoporosis can be considered to be in vivo dissolution of calcium phosphates. On the other hand, because of the chemical similarity with biological calcified tissues, all calcium phosphates are remarkably biocompatible. This property is widely used in medicine for biomaterials that are either entirely made of or coated with calcium phosphate. For example, self-setting bone cements made of calcium phosphates are helpful in bone repair and titanium substitutes covered with a surface layer of calcium phosphates are used for hip-joint endoprostheses and tooth substitutes, to facilitate the growth of bone and thereby raise the mechanical stability. Calcium phosphates have a great biological and medical significance and in this review we give an overview of the current knowledge in this subject.
The relation between single particle and ensemble measurements is addressed for semiconductor CdSe nanocrystals. We record their fluorescence at the single molecule level and analyze their emission intermittency, which is governed by unusual random processes known as Lévy statistics. We report the observation of statistical aging and ergodicity breaking, both related to the occurrence of Lévy statistics. Our results show that the behavior of ensemble quantities, such as the total fluorescence of an ensemble of nanocrystals, can differ from the time-averaged individual quantities, and must be interpreted with care.
Ultrafine individualised mono crystalline Ca(10-x)(PO4)(6-x)(HPO4)x(OH)(2-x) deficient calcium hydroxyapatite nanocrystals displaying fluorescence under visible excitation are proposed for utilisation as biocompatible biological probes.
Focusing on the basic principles of mineral formation by organisms, this comprehensive volume explores questions that relate to a wide variety of fields, from biology and biochemistry, to paleontology, geology, and medical research. Preserved fossils are used to date geological deposits and archaeological artifacts. Materials scientists investigate mineralized tissues to determine the design principles used by organisms to form strong materials. Many medical problems are also associated with normal and pathological mineralization. Lowenstam, the pioneer researcher in biomineralization, and Weiner discuss the basic principles of mineral formation by organisms and compare various mineralization processes. Reference tables listing all known cases in which organisms form minerals are included.
Brushite is one of the most frequently formed products of the electrochemical deposition. It has shown excellent biological behaviour of calcium phosphate coatings on carbon composites. Calcium phosphate coatings were obtained by the electrochemical deposition from the solution of calcium and phosphate ions at pH = 2.4 and with 0.2 or 1 wt.% gelatine addition. Graphite substrate was used as cathode and Pt basket as anode. Electrochemical deposition of brushite/gelatine composite layer was carried out at current densities from 5 to 20 mA/cm2. Coatings were examined before and after annealing at 850 °C in Ar. The large channels were observed in coatings at higher concentrations of gelatine and high current densities in microstructure. The adhesive strength of thin brushite/gelatine coating was around 7 MPa. Linear dependence of deposit weight increase with electrolysis time was observed. Similarly, the gelatine content in coating rose linearly with gelatine concentration in electrolyte. After annealing of coatings at 850 °C in argon, the brushite was transformed to hydroxyapatite and CaO, the size of the needle-like brushite particles decreased and small spherical or regular shaped particles of CaO were formed. The weak bonding of thermal treated brushite/gelatine deposits to graphite was found.
Lanthanide-doped fluorescent hydroxyapatite/silica core–shell nanorods, 50–100 nm in length and 30 nm in width, were prepared by precipitation of calcium phosphate in the presence of Eu3+ and Y3+ ions at 60 °C, followed by hydrothermally enhanced crystallization, stabilization with poly(ethyleneimine), and reaction with tetraethyl orthosilicate. The fluorescence intensity of the Eu3+-doped hydroxyapatite nanorods was enhanced threefold by co-doping with Y3+ and doubled after hydrothermal treatment. Significantly, fluorescence quenching by water was reduced in the presence of the thin silica nanoshell to give a further doubling of the fluorescence intensity compared with lanthanide-doped hydroxyapatite nanoparticles prepared in the absence of tetraethyl orthosilicate. Our results suggest that a combination of lanthanide doping, controlled crystallization and core–shell fabrication is a promising route to the preparation of biocompatible calcium phosphate nanoparticles with enhanced fluorescence for potential use in biomedical applications.
Excitation and emission spectra of Pb(2+) ions in Ca(10-x)Pb(x)(PO(4))(6)Cl(2) (0≤x≤10) compounds are investigated for various activator concentrations at different temperatures. A calcium-lead chlorapatite system shows a common apatitic structure and occurs as a continuous solid solution. An attempt to identify the pure electronic transitions between the ground and the excited levels of Pb(2+) is made. As a consequence of the two different sites in the apatite, two emission bands due to the [Formula: see text] (at room temperature) and [Formula: see text] (at low temperature) transitions of the Pb(2+) ions are observed. Decay times of Pb(2+) emission have been measured. Experimental data point out thermalization between (3)P(1) and (3)P(0) levels, for example, at very low temperature, the forbidden transition [Formula: see text] is the most intense. The overlap between the emission band of one site and the excitation band of the other site corresponds to an energy transfer phenomenon. Correlations between the luminescence results and the structural data are discussed.
A europium-doped apatitic calcium phosphate was synthesized at low temperature (37°C) in water–ethanol medium. This apatite was calcium-deficient, rich in hydrogen phosphate ions, and poorly crystallized with nanometric sized crystallites. It is similar to the mineral part of calcified tissues of living beings and is thus a biomimetic material. The substitution limit of Eu3+ for Ca2+ ions in this type of bioapatite ranged about 2–3%. The substitution at this temperature was facilitated by vacancies in the calcium-deficient apatite structure. As the luminescence of europium is photostable, the doped apatite could be employed as a biological probe. Internalization of these nanoparticles by human pancreatic cells in culture was observed by luminescence confocal microscopy.
The crystal-field (CF) spectra of Eu3+ in various inorganic crystalline phases are summarized based on previous investigations. A majority of experimental results can be well interpreted using a standard CF model. However, there are cases in which the spectroscopic properties and fluorescence dynamics of Eu3+ cannot be interpreted within the framework of the standard model. A particularly interesting system is Eu3+ doped into microcrystals of a charge-unbalanced host such as BaFCl. For Eu3+:BaFCl, one Eu3+ site (Site I) exhibits normal CF splitting and its energy levels and fluorescence intensity are similar to most other normal systems ever reported. A standard CF fitting has been performed for Site I. However, Eu3+ at a distorted site (Site II) is of anomalous fluorescence dynamics and CF splitting which are significantly different from those of Site I. In the metastable state of 5D0, Eu3+ ions at Site II also exhibit unusual temperature-dependent lifetime.
Solubility of tricalcium citrate has been determined at 21 and 95° C. by dissolution in water and by precipitation from supersaturated solutions containing various proportions of calcium to citrate and at pH 4.4 to 8.8. Solubility product in solutions at equilibrium varied with ionic strength, according to the relation pks=17.63−10.84μ, but was unaffected by variations in pH and temperature and by the presence of magnesium or phosphate ions. Milk ultrafiltrates were shown to be saturated with tricalcium citrate, i.e., the calculated pks values agreed with the solubility product in all but two of the 15 samples tested, and composition of two ultrafiltrates was unaffected by agitation with crystals of tricalcium citrate.
Nanophosphors have been extensively investigated during the last decade due to their application potential for various high-performance displays and devices. These act as a strategic component in almost all displays. Synthesis of nanophosphors can be accomplished in two ways namely, chemical and physical methods. Under chemical methods, different routes such as colloidal, capping, cluster formation, sol–gel, electrochemical, etc., are being followed. Physical methods widely used are molecular beam epitaxy, ionised cluster beam, liquid metal ion source, consolidation, sputtering and gas aggregation of monomers. Chemical precipitation in presence of capping agents, reaction in microemulsions, sol–gel reaction and autocombustion are commonly used techniques for synthesis of nanophosphors. However, the particle size has to be restricted to 3–5nm to get the real advantage of quantum confinement. In other words, the particle size must be less than twice of Bohr radii of exciton as quantum confinement regime is limited to that size. A brief review of different synthesis techniques employed all over the world for the development of industrially important nanophosphors and extent of particle size reduction achieved is discussed.
The morphology and size of hydroxyapatite Ca10(PO4)6(OH)2 (denoted HAP) can be controlled under hydrothermal treatment assisted with different dendrimers, such as carboxylic terminated poly(amidoamine) (PAMAM) and polyhydroxy terminated PAMAM. The structure and morphology were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR) and transmission electron microscopy (TEM). IR spectra were also used to investigate the complexation of Ca2+ with PAMAM. The results revealed that the inner cores of the PAMAM dendrimers are hydrophilic and potentially open to calcium ions, since interior nitrogen moieties serve as complexation sites, especially in case of the polyhydroxy terminated PAMAM. And the reasonable mechanism of crystallization was proposed that it can be attributed to the localization of nucleation site: external or interior PAMAM. Additionally, the PAMAM dendrimer with carboxylic and polyhydroxy groups has an effective influence on the size and shape of hydroxyapatite (HAP) nanostructures. Different crystal morphology was accomplished by adsorption of different dendrimers onto specific faces of growing crystals, altering the relative growth rates of the different crystallographic faces and leading to different crystal habits.
Silicon-substituted hydroxyapatite (Si-HA) was prepared successfully by hydrothermal method. The crystalline phase, microstructure, chemical composition, morphology and thermal stability of Si-HA were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The results show that the substitution of the silicate groups for the phosphate groups causes some OH- loss to maintain the charge balance and changes the lattice parameters of HA. Furthermore, the substitution of the silicate groups restrains the growth of Si-HA crystal. DSC analysis shows that the small amount of silicon incorporates into HA lattice does not influence the thermal stability of HA.
Monodisperse, core-shell-structured Si O2 @NaGd (W O4) 2: Eu3+ particles were prepared by the sol-gel method. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence (PL), and low-voltage cathodoluminescence (CL) as well as time-resolved PL spectra and lifetimes. PL and CL study revealed that the core-shell-structured Si O2 @NaGd (W O4) 2: Eu3+ particles show strong red emission dominated by the D05 - F27 transition of Eu3+ at 614 nm with a lifetime of 0.74 ms. The PL and CL emission intensity can be tuned by the coating number of NaGd (W O4) 2: Eu3+ phosphor layers on Si O2 and by accelerating voltage and the filament current, respectively.
The synthesis and characterization of Zn2SiO4:Mn phosphor layers on spherical silica spheres, i.e., core-shell particles of Zn2SiO4:Mn@SiO2 are described in this paper. First, monodisperse silica spheres with an average size around 750 nm have been obtained via the Stöber method by the hydrolysis and condensation of tetraethoxysilane Si(OC2H5)4 under base condition (using NH4OH as the catalyst). Second, the silica spheres are coated with Zn2SiO4:Mn phosphor layers by a sol-gel process. The resulting core-shell particles are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscope, energy-dispersive X-ray spectroscopy, transmission electron microscopy, photoluminescence, low-voltage cathodoluminescence, as well as kinetic decay. The results confirm that the 1000°C-annealed sample consists of crystalline Zn2SiO4:Mn shells and amorphous SiO 2 cores with spherical morphology and narrow size distribution. The Zn2SiO4:Mn@SiO2 particles show the green emission at 521 nm corresponding to 4T1( 4G)-6A1(6S) transition of Mn 2+ under the excitation of UV (250 nm), vacuum UV (172 nm), and electron-beams (1-6 kV). The luminescence intensity has been studied as a function of coating number, accelerating voltage, and filament current, respectively.
Functionalised nanoparticles of calcium phosphate were prepared by controlled precipitation from aqueous solution, followed by coating with DNA. A successful transfection of transformed human endothelial cells was accomplished by adding the dispersion of nanoparticles to the cell culture. The functionalised nanoparticles formed a stable colloid and did not lose their ability for cell transfection during 2–3 weeks of storage. The nanoparticles were approximately spherical with diameters of 10 to 20 nm and covered and stabilised by a hull of DNA.
The compounds 10CaO·(6–x)PO2.5·xBO1.5·tH2O (x=0, 0.3, 0.5) doped with 1% Ce3+ ions have been synthesized and investigated for the first time. They have been prepared by a solid state reaction under reducing atmosphere.X-ray diffraction and IR spectroscopy show that these three compounds have an apatite structure. The environments of boron, phosphorus and hydrogen were investigated by MAS (magic angle spinning) NMR experiments and discussed in comparison with non-doped compounds.Steady state and laser induced excitation and emission spectra of Ce3+ doped borohydroxyapatites were measured either at room temperature or at 77 K showing that borate groups enhance the emission intensity and induce a shift of the emission bands to higher wavelengths.
Calcium phosphates deposited by an electrochemical deposition process (ECD) have been prepared in the 0.04M Ca(H2PO4)2H2O (MCPM) solution at 10V, 60°C and 80Torr for 1h. Subsequently, the deposits have been treated in various concentrations of NaOH(aq) solutions at different temperatures for 1h. When excess OH− is present in the ECD process, hydroxyapatite (HAP) referred to as pre-HAP is deposited on the Ti–6Al–4V substrate. After NaOH(aq) treatment, all deposits are converted to the HAP phase. The treatment in 1–2.5M NaOH(aq) solution at over 60°C offers a more proper environment for the HAP conversion, referred to as post-HAP, and has an average crystallite size of about 21nm. For more than 5M NaOH(aq) treatment, both pre- and post-HAP show a reduction of 5–20nm in particle size.
The crystal structure of poly(ethylene oxide) was analyzed by X-ray diffraction method. Four (7/2) helical molecules pass through a unit cell with parameters, a = 8.05 Å, b = 13.04 Å, c(fiber axis) = 19.48 Å, and β = 125.4°, and the space group, P21/a-C2h5. The molecule was found to be appreciably distorted from the molecular model proposed in a previous paper1 whose symmetry was isomorphous to the point group D7. For the present analysis, the constrained least-squares method and the least-squares method for helical molecules were utilized.
LaPO4:Ce3+ and LaPO4:Ce3+, Tb3+ phosphor layers have been deposited successfully on monodispersed and spherical SiO2 particles of different sizes (300, 500, 900 and 1200 nm) through a sol–gel process, resulting in the formation of core–shell structured SiO2@LaPO4:Ce3+/Tb3+ particles. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microcopy (SEM), transmission electron microscopy (TEM), and general and time-resolved photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting SiO2@LaPO4:Ce3+/Tb3+ samples. The XRD results demonstrate that the LaPO4:Ce3+, Tb3+ layers begin to crystallize on the SiO2 templates after annealing at 700 °C, and the crystallinity increases on raising the annealing temperature. The obtained core–shell phosphors have perfectly spherical shape with a narrow size distribution, non-agglomeration, and a smooth surface. The doped rare-earth ions show their characteristic emission in the core–shell phosphors, i.e. Ce3+ 5d–4f and Tb3+ 5D4–7FJ (J = 6–3) transitions, respectively. The PL intensity of the Tb3+ increased on increasing the annealing temperature and the SiO2 core particle size. The energy transfer process from Ce3+ to Tb3+ in SiO2@LaPO4:Ce3+, Tb3+ core–shell particles was studied using the time-resolved emission spectra.
Polymer blending is an effective method for providing desirable polymeric materials with properties useful for the packaging industry. In the study reported, blends of chitosan/poly(ethylene oxide) (PEO) were prepared in various weight ratios with and without glycerol. Line profile analysis of the X‐ray diffraction patterns of these blended films was carried out. Microstructural parameters such as crystallite size and lattice strain were determined using paracrystalline modelling of X‐ray data. These values were correlated with physico‐mechanical and optical properties of the chitosan/PEO blends with and without glycerol to understand the holistic behaviour of the blends. Two prominent Bragg reflections at 2 ≈ 19° and 23° were observed in the wide‐angle X‐ray diffraction patterns of the glycerol‐based chitosan/PEO blended films of various ratios. Interruption of PEO crystallization with chitosan results in an amorphous polymer network and hence a reduction in crystallite size by almost 97.7%. For glycerol‐based blends, the crystallite size/area decreases to 94.4% of the virgin crystallite size. The X‐ray profile analysis supports the results for the physico‐mechanical properties of the blends. The results show that the addition of 20 wt% of glycerol results in an increase of the elongation at break by more than 150%, meaning that these chitosan/PEO films could be applied in flexible packaging. Copyright © 2010 Society of Chemical Industry
Long Si nanowires were tried to form using a thermal gradient evaporation method. Amorphous SiO2/Si nanowires longer than 6 mm were formed at 1403–1433 K. The long nanowires consist of a silicon single core of 50–100 nm in diameter and an amorphous SiO2 outer layer of 10–15 nm in thickness. The growth direction of the long Si nanowires was 〈1 1 1〉. The nanowires showed IR absorption peaks at 1130, 1160 and 1200 cm−1 due to the disordered structure of SiO2/Si nanowires.
The time-resolved luminescence of the Eu3+ ion in calcium hydroxyapatite Ca5(PO4)3OH prepared by a precipitation reaction is reported. The emission principally arises from the 5D0 level. Site-selective excitation of the 5D1 and 5D2 levels was needed to distinguish very similar sites, labelled A, B and C. The 20 K luminescence decay times of these three sites were measured for the 5D0 emitting level of Eu3+. The spectroscopic results are considered in relation to the existence of different crystallographic sites for Eu3+ in this material and in terms of possible charge compensation mechanisms.
A novel procedure for Zn2SiO4:Mn2+ phosphor powder synthesis based on a combination of sol–gel and combustion methods is presented. The procedure utilizes Zn-nitrate, Mn-nitrate, tetraethylorthosilicate and polyethylene glycol to produce gel, which is then combusted in a microwave oven to form Zn2SiO4:Mn2+ powder and further annealed to crystallize in desired structure. The material has been investigated by X-ray diffraction, scanning electron microscopy, infrared and photoluminescence spectroscopy. These investigations showed well-crystallized powder particles exhibiting intense green light emission.
The Pechini based liquid-mix technique has been applied to prepare either single phases of hydroxyapatite –Ca10(PO4)6OH2– (OHAp), α and β-tricalcium phosphate –Ca3(PO4)2–, (α-TCP, β-TCP) or biphasic calcium phosphates (BCP). Compositions with a Ca/P molar ratio between 1.5 and 1.667 were synthesized and subjected to a thermal treatment up to 1400 °C. α and β-TCP were both prepared from a Ca/P ratio of 1.5, but while β-TCP is isolated at 900 °C and remains stable up to 1100 °C, it is necessary to anneal at 1400 °C for 72 h to obtain pure α-TCP. OHAp is obtained as a single phase from a 1.667 Ca/P ratio after annealing at 1000 °C for 24 h and starts to decompose at 1400 °C. Between these two extremes a whole range of biphasic calcium phosphates can be prepared by using this technique with an accurate control of the starting reactants. These materials have been characterized by FTIR, XRF, BET, XRD and, based on this technique, a phase quantification determination (QXRD). The solubility of these products was tested in a buffered solution at 37 °C and pH=7.4.
In apatitic structures such as Ca10(PO4)6(OH)2, borate groups are introduced as planar and regular BO33− and substitute phosphate and hydroxyl groups. In order to study the influence in the change of the coordination environment of the cationic sites on the luminescent properties of RE ions doping calcium borohydroxyapatite, the time-resolved luminescence of the Eu3+ ion in this new compound is reported. Site-selective excitation of the 5D0 level was performed and luminescence decay times of each Eu3+ site were measured at 77 K. By comparison with Eu-doped boron free apatites, it is shown that borate groups induce perturbations in the Eu3+ luminescence features. The spectroscopic results are discussed in terms of possible charge compensation mechanisms correlated with the structural data.
We describe the synthesis of water-soluble semiconductor nanoparticles and discuss and characterize their properties. Hydrophobic CdSe/ZnS core/shell nanocrystals with a core size between 2 and 5 nm are embedded in a siloxane shell and functionalized with thiol and/or amine groups. Structural characterization by AFM indicates that the siloxane shell is 1-5 nm thick, yielding final particle sizes of 6-17 nm, depending on the initial CdSe core size. The silica coating does not significantly modify the optical properties of the nanocrystals. Their fluorescence emission is about 32-35 nm fwhm and can be tuned from blue to red with quantum yields up to 18%, mainly determined by the quantum yield of the underlying CdSe/ZnS nanocrystals. Silanized nanocrystals exhibit enhanced photochemical stability over organic fluorophores. They also display high stability in buffers at physiological conditions (>150 mM NaCl). The introduction of functionalized groups onto the siloxane surface would permit the conjugation of the nanocrystals to biological entities.
Terbium doped calcium phosphate (Tb-doped CaP) nanocrystalline powders were synthesized by the citric acid sol–gel combustion
method. The phase composition, morphology and luminescent property of Tb-doped CaP nanocrystalline powders were characterized
by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, fluorescence spectrophotometer
and fluorescence microscopy. At 700°C, Tb-doped CaP nanocrystalline powders are composed of HAP (main phase) and β-TCP (minor
phase) with Tb doping content of 0.5–4%. SEM and TEM observations show that the 4% Tb-doped CaP nanocrystalline powders are
about 50–150nm spherical particles. The 4% Tb-doped CaP nanocrystalline powders exhibit the strongest emission at 548nm
(λexcitation=240nm) and show strong green fluorescence under fluorescence microscopy.
A system of chemical reactions has been developed which permits the controlled growth of spherical silica particles of uniform size by means of hydrolysis of alkyl silicates and subsequent condensation of silicic acid in alcoholic solutions. Ammonia is used as a morphological catalyst. Particle sizes obtained in suspension range from less than 0.05 μ to 2 μ in diameter.
Mn-doped willemite (Zn2SiO4:Mn), which is a zinc silicate green phosphor, is synthesized in an aqueous medium at as low temperature as 250°C. Zn2SiO4:Mn samples showed acicular and spherical shaped particles ranging in size from ∼50 to 2400 nm. The microstructures of the nanocrystalline products were characterized by XRD, TEM, SEM, and light scattering. The results indicated the formation of solid crystalline structures. The optical emission of 1% and 3% Mn-doped Zn2SiO4 was measured by fluorescence spectroscopy, which give further evidence for the incorporation of Mn within the lattice. This procedure provides an easy and contamination-free method for synthesis of willemite, which commonly is prepared at very high temperatures.
The Eu3+ fluorescence in the continous solid solution Ca10-xEux(PO4)601+x/2□1-x/2, with 0.05⩽x⩽ , is studied at 300 and 77 K. The emission mainly arises from the 5D0 level. The dependence upon the composition shows that Eu3+ ions occupy preferentially the calcium site II of the apatite structure. Eu3+ ions occupy site I only for x>1. The emission lines are broadened as a result of anion vacancies. Site-selective laser excitation of Eu3+ in site II reveals the presence of two types of centers, whose structural model is proposed. The emission spectra present the following unusual features for Eu3+: (a) high value of the splitting; and (c), the very strong intensity of the emission line. The covalent character of the Eu3+-02- bond correlated to a strong crystal field of nearly C∞v symmetry allows as to propose the assignement of the lines. Discussion of this exceptional behavior of Eu3+ is given in terms of J-mixing.
SiO(2)/Zn(2)SiO(4):Mn(2+) core-shell nanoparticles with mean diameters in the range of 55-220 nm were prepared by a modified Pechini sol-gel method followed by lyophilization and annealing at temperatures of 800-1100°C. The as-synthesized nanoparticles were characterized by transmission electron microscopy, X-ray diffraction analysis, and photoluminescence spectroscopy. The results demonstrate that the crystal structure of the shell and the optical properties can be tuned by the annealing temperature and a variation of the concentration of doping ions. Under UV excitation, the samples emit green luminescence with its maximum at 525 nm, typical for the Mn(2+) ions in α-Zn(2)SiO(4). The resulting nanoparticles were successfully modified with amine and carboxyl functions with respect to a later attachment of biological moieties.
In a search for new luminescent biological probes, we synthesized calcium pyrophosphates doped with europium up to an atomic Eu/(Eu+Ca) ratio of 2%. They were prepared by coprecipitating a mixture of calcium and europium salts with phosphate. After heating at 900°C in air, two phases coexisted, identified as the β calcium pyrophosphate form and EuPO4. Heating near 1250°C in air, during the β→ transformation, europium ions substitute for calcium ions in the * calcium pyrophosphate structure as demonstrated by the spectroscopic study. Europium ions with both valence states (divalent and trivalent) were observed in the samples. Following the synthesis procedure, partial reduction of Eu3+ took place even in an oxidizing atmosphere. The 0.5%-doped compound could serve as a sensitive probe in biological applications. Depending on the excitation wavelength, the luminescence occurs either in the red or in the blue regions, which discriminates it from parasitic signals arising from other dyes or organelles in live cells.
Encapsulation of imaging agents and drugs in calcium phosphate nanoparticles (CPNPs) has potential as a nontoxic, bioresorbable vehicle for drug delivery to cells and tumors. The objectives of this study were to develop a calcium phosphate nanoparticle encapsulation system for organic dyes and therapeutic drugs so that advanced fluoresence methods could be used to assess the efficiency of drug delivery and possible mechanisms of nanoparticle bioabsorption. Highly concentrated CPNPs encapsulating a variety of organic fluorophores were successfully synthesized. Well-dispersed CPNPs encapsulating Cy3 amidite exhibited nearly a 5-fold increase in fluorescence quantum yield when compared to the free dye in PBS. FCS diffusion data and cell staining were used to show pH-dependent dissolution of the particles and cellular uptake, respectively. Furthermore, an experimental hydrophobic cell growth inhibitor, ceramide, was successfully delivered in vitro to human vascular smooth muscle cells via encapsulation in CPNPs. These studies demonstrate that CPNPs are effective carriers of dyes and drugs for bioimaging and, potentially, for therapeutic intervention.
In this review, we examine numerous applications of the green fluorescent protein (GFP) marker gene in environmental microbiology research. The GFP and its variants are reviewed and applications in plant-microbe interactions, biofilms, biodegradation, bacterial-protozoan interactions, gene transfer, and biosensors are discussed. Methods for detecting GFP-marked cells are also examined. The GFP is a useful marker in environmental microorganisms, allowing new research that will increase our understanding of microorganisms in the environment.
Colloidal semiconductor quantum dots are attractive fluorophores for multicolor imaging because of broad absorption and narrow emission spectra, and they are brighter and far more photostable than organic dyes. However, severe intermittence in emission (also known as blinking) has been universally observed from single dots and has been considered an intrinsic limitation difficult to overcome. This is unfortunate because growing applications in spectroscopy of single biological molecules and quantum information processing using single photon sources could greatly benefit from long-lasting and nonblinking single-molecule emitters. For instance, in a recent application of single-dot imaging, the tracking of membrane receptors was interrupted frequently due to the stroboscopic nature of recording. Blinking can also reduce the brightness in ensemble imaging via signal saturation. Here we show that the quantum dot blinking can be suppressed with the emission duty cycle approaching 100% while maintaining biocompatibility.
Calcium phosphate nanoparticles can be prepared in almost uniform size and shape by a continuous precipitation process that also allows their functionalisation by organic molecules (DNA, surfactants).