Synthesis and properties of magnetic and luminescent Fe3O4/SiO2/Dye/SiO2 nanoparticles

A simple and reproducible method was developed to synthesize a novel class of Fe₃O₄/SiO₂/dye/SiO₂ composite nanoparticles. As promising candidates for use in bioassays, the obtained nanoparticles have an average diameter of 30 nm, and the thickness of the outer shell of silica could be tuned by changing the concentration of the silicon precursor tetraethyl orthosilicate during the synthesis. These multifunctional nanoparticles were found to be highly luminescent, photostable and superparamagnetic. The luminescence intensity of the nanoparticles was increased as the dye concentration was increased in the preparation process. The color of the luminescence was successfully tuned by incorporating different dyes into the nanoparticles. The measurements of the emission spectra indicated that relative to the dye molecules dissolved in ethanol, the emission of the dye-doped nanoparticles exhibited either a red shift or a blue shift, to which a tentative explanation was given.     

Relative Quantum Yield Measurements of Coumarin Encapsulated in Core-Shell Silica Nanoparticles

Fluorescent silica nanoparticles encapsulating organic fluorophores provide an attractive materials platform for a wide array of applications where high fluorescent brightness is required. We describe a class of fluorescent silica nanoparticles with a core-shell architecture and narrow particle size distribution, having a diameter of less than 20 nm and covalently incorporating a blue-emitting coumarin dye. A quantitative comparison of the scattering-corrected relative quantum yield of the particles to free dye in water yields an enhancement of approximately an order of magnitude. This enhancement of quantum efficiency is consistent with previous work on rhodamine dye-based particles. It provides support for the argument that improved brightness over free dye in aqueous solution is a more general effect of covalent incorporation of fluorescent organic dyes within rigid silica nanoparticle matrices. These results indicate a synthetic route towards highly fluorescent silica nanoparticles that produces excellent probes for imaging, security, and sensing applications.     

羧基修饰纳米SiO2荧光指印试剂的制备与应用

指印是一种重要的证据形式，它百年以来持续成为法庭科学领域的研究重点。在实践中，已经得到广泛推广的粉末法和熏显法对环境和工作人员的身体健康构成了重大威胁。近年来发展的纳米悬浮液显现指印的方法能够有效减少纳米粉尘在空气中的悬浮，降低对使用者健康和环境的侵害，并且规避了悬浮液制备过程中分散剂的使用以及有机染料溶液的处理等瓶颈。因此，关注纳米二氧化硅荧光指印显现试剂的制备与应用：首先，利用反相微乳液法制备了掺杂氯化三（2,2’-联吡啶）钌（Ⅱ）·六水化合物的荧光型纳米二氧化硅颗粒；随后，通过氨基硅烷偶联剂的氨基改性以及与丁二酸酐的氨解反应，使用两步法实现了表面羧基化阴离子修饰的荧光二氧化硅纳米材料的合成；此外，利用红外吸收光谱对纳米二氧化硅，以及目标产物的表面氨基、羧基等化学修饰基团进行表征，并测定了不同修饰产物在水相中的表面电性能以其水合半径；通过紫外可见光吸收光谱和分子荧光光谱仪对材料的荧光性能做了检测，测试了不同染料浓度产物的荧光强度；对新型纳米材料在指印显现中的应用条件进行了系统考察，通过正交试验设计法，全面探究了pH值、母液稀释倍数和显现时间等重要因素对于指印显现效果的综合影响，并最终确定了此种显现试剂的最佳显现条件；论文最后依据上述优化实验条件对捺印在玻璃非渗透性光滑客体表面的指印样品的显现效果进行了系统评价。实验结果表明：产物悬浮液与染料溶液的紫外可见吸收光谱之间并未发生明显的红移或蓝移，这意味着二氧化硅包覆对于荧光染料分子结构没有显著影响；根据染料浓度与产物荧光强度之间的变化关系可知，最佳染料掺杂浓度为15 mmol·L-1；纳米材料的表面氨基化和羧基化修饰已经成功，其最佳激发光源波长为375 nm；Zeta电位-DLS测试结果印证了氨基质子化带正电、羧基电离带负电的纳米材料电学性能，此外羧基化前后纳米二氧化硅颗粒负电荷密度的显著改变也为基于静电吸附作用的指印显现方法灵敏度的提升奠定了基础；使用悬浮液法对前述优化后的合成产物进行指印显现方面的应用，其最佳显现条件为溶液pH值为2.8、母液稀释倍数为2倍且显现时间5 min，其对非渗透性客体表面的新鲜指印及陈旧指印均具有良好的显现效果，部分情况下甚至可以实现三级指印特征的理想显现效果。     

Synthesis and characterisation of highly fluorescent core–shell nanoparticles based on Alexa dyes

Current and future developments in the emerging field of nanobiotechnology are closely linked to the rational design of novel fluorescent nanomaterials, e.g. for biosensing and imaging applications. Here, the synthesis of bright near infrared (NIR)-emissive nanoparticles based on the grafting of silica nanoparticles (SNPs) with 3-aminopropyl triethoxysilane (APTES) followed by covalent attachment of Alexa dyes and their subsequent shielding by an additional silica shell are presented. These nanoparticles were investigated by dynamic light scattering (DLS), transmission electron microscopy (TEM) and fluorescence spectroscopy. TEM studies revealed the monodispersity of the initially prepared and fluorophore-labelled silica particles and the subsequent formation of raspberry-like structures after addition of a silica precursor. Measurements of absolute fluorescence quantum yields of these scattering particle suspensions with an integrating sphere setup demonstrated the influence of dye labelling density-dependent fluorophore aggregation on the signaling behaviour of such nanoparticles.     

Synthesis of Fluorescent Silica Nanoparticles and Their Applications as Fluorescence Probes

This paper presents the synthesis of organic dye molecules embedded silica nanoparticles by Stöber method and their applications as fluorescence probes in cell imaging. By modifying the surface of fluorescent silica nanoparticles (FSNs) with amino, biologically functionalized and monodisperse FSNs can be obtained. In this work, FSNs were conjugated with monoclonal anti-Carcinoembryonic Antigen (anti-CEA) antibody via covalent binding. The antibody-conjugated FSNs can be used to label the SPCA-1 cells successfully, demonstrating that the application of FSNs as fluorescence probes in fluorescence imaging and bioassay would be feasible.     

One-step synthesis of dye-incorporated porous silica particles

Fluorescent nanoparticles have a variety of biomedical applications as diagnostics and traceable drug delivery agents. Highly fluorescent porous silica nanoparticles were synthesized in a water/oil phase by a microemulsion method. What is unique about the resulting porous silica nanoparticles is the combination of a single-step, efficient synthesis and the high stability of its fluorescence emission in the resulting materials. The key of the success of this approach is the choice of a lipid dye that functions as a surrogate surfactant in the preparation. The surfactant dye was incorporated at the interface of the inorganic silica matrix and organic environment (pore template), and thus insures the stability of the dye?Csilica hybrid structure. The resulting fluorescent silica materials have a number of properties that make them attractive for biomedical applications: the availability of various color of the resulting nanoparticle from among a broad spectrum of commercially dyes, the controllablity of pore size (diameters of ~5?nm) and particle size (diameters of ~40?nm) by adjusting template monomer concentration and the water/oil ratio, and the stability and durability of particle fluorescence because of the deep insertion of surfactant??s tail into the silica matrix.     

Controlled surface functionalization of silica-coated magnetic nanoparticles with terminal amino and carboxyl groups

General and versatile methods for the functionalization of superparamagnetic, silica-coated, maghemite nanoparticles by surface amino and/or carboxyl groups have been established. The nanoparticles were synthesized using co-precipitation from aqueous solutions and coated with a thin layer of silica using the hydrolysis and condensation of tetraethoxysilane (TEOS). For the amino functionalization, 3-(2-aminoethylamino)propylmethyldimethoxysilane (APMS) was grafted onto the nanoparticle surfaces in their aqueous suspensions. The grafting process was followed by measurements of the ζ-potential and a determination of the concentration of the surface amino groups with conductometric titrations. The surface concentration of the amino groups could be varied by increasing the amount of APMS in the grafting process up to approximately 2.3 –NH₂ groups per nm². The carboxyl functionalization was obtained in two ways: (i) by a ring-opening linker elongation reaction of the surface amines at the functionalized nanoparticles with succinic anhydride (SA) in non-aqueous medium, and (ii) by reacting the APMS and SA first, followed by grafting of the carboxyl-terminated reagent onto the nanoparticle surfaces. Using the first method, the SA only reacted with the terminal primary amino groups (–NH₂) of the surface-grafted APMS molecules. Infra-red spectroscopy (ATR FTIR) and mass spectrometry (HRMS) showed that the second method enables the bonding of up to two SA molecules per one APMS molecule, since the SA reacted with both the primary (–NH₂) and secondary amino (–NH–) groups of the APMS molecule. When using both methods, the ratio between the surface amino and carboxyl groups can be controlled.     

Quantum-chemical study of effect of conjugation on structure and spectral properties of C105 sensitizing dye

The structure and spectral properties of two organic ruthenium complexes used as sensitizing dyes for solar batteries (well-known N3 dye and its selenophene-conjugated analogue C105 ([Ru(bpy)(bpysef)(COOH)₂(NCS)₂] (bpy = 2,2′-bipyridine, bpysef = 4,4′-bis(5-hexylselenophene-2-yl)2,2′-bipyridine)) are comparatively studied within the density functional method. It is shown that the conjugation of the bipyridine ligand with selenophene affects the electronic structure of the C105 dye. A multilevel model for interpreting the electronic spectra of dyes is proposed based on the analysis of the shapes of molecular orbitals. The nature of the absorption bands of these ruthenium complexes in the region of 300–800 nm is explained. It is found that, in the polar acetonitrile solvent, these dyes are negatively solvatochromic, which agrees with the current classical views on the effect of the solvent on the shape of electronic absorption spectra of related compounds.     

Structural and luminescence properties of europium(III)-doped zirconium carbonates and silica-supported Eu3+-doped zirconium carbonate nanoparticles

The synthesis, morphology and luminescence properties of europium(III)-doped zirconium carbonates prepared as bulk materials and as silica-supported nanoparticles with differing calcination treatments are reported. Transmission electron microscopy and X-ray diffraction analyses have, respectively, been used to study the morphology and to quantify the atomic amount of europium present in the optically active phases of the variously prepared nanomaterials. Rietveld analysis was used to quantify the constituting phases and to determinate the europium content. Silica particles with an approximate size of 30 nm were coated with 2 nm carbonate nanoparticles, prepared in situ on the surface of the silica core. Luminescence measurements revealed the role of different preparation methods and of europium-doping quantities on the optical properties observed.     

Comparison of Eu(NO<Subscript>3</Subscript>)<Subscript>3</Subscript> and Eu(acac)<Subscript>3</Subscript> precursors for doping luminescent silica nanoparticles

In this study, we report the comparison between Eu³⁺-doped silica nanoparticles synthesized by Stöber method using Eu(NO₃)₃ or Eu(acac)₃ as precursors. The impact of different europium species on the properties of the final silica nanospheres is investigated in details in terms of size, morphology, reachable doping amount, and luminescence efficiency. Moreover, the results obtained for different thermal treatments are presented and discussed. It is shown that the organic complex modify the silica growing process, leading to bigger and irregular nanoparticles (500–800 nm) with respect to the perfectly spherical ones (400 nm) obtained by the nitrate salt, but their luminescence intensity and lifetime is significantly higher when 800–900 °C annealing is performed.     

Highly Sensitive Optical Biosensor for Thrombin Based on Structure Switching Aptamer-Luminescent Silica Nanoparticles

We describe here the construction of a sensitive and selective optical sensor system for the detection of human α-thrombin. The surface functionalized luminescent [Ru(dpsphen)₃]^4? (dpsphen-4,7-diphenyl-1,10-phenanthroline disulfonate) ion doped silica nanoparticles (SiNPs) with a size ~70 nm have been prepared. The DABCYL (2-(4-dimethylaminophenyl)diazenyl-benzoic acid) quencher labeled thrombin binding aptamer is conjugated to the surface of SiNPs using BS³ (bis(sulfosuccinimidyl) suberate) as a cross-linker, resulting in the conformational change of aptamer to form G-quadruplex structure upon the addition of thrombin. The binding event is translated into a change in the luminescence intensity of Ru(II) complex via FRET mechanism, due to the close proximity of DABCYL quencher with SiNPs. The selective detection of thrombin using the SiNPs-aptamer system up to 4 nM is confirmed by comparing its sensitivity towards other proteins. This work demonstrates the application of simple aptamer-SiNPs conjugate as a highly sensitive system for the detection of thrombin and also it is highly sensitive towards thrombin in the presence of other proteins and complex medium such as BSA.     

Surface functionalization of silica-coated magnetic nanoparticles for covalent attachment of cholesterol oxidase

A systematic approach towards the fabrication of highly functionalized silica shell magnetic nanoparticles, presently used for enzyme immobilization, is herein fully presented. The synthesis of bare maghemite (γ-Fe₂O₃) nanoparticles was accomplished by thermal co-precipitation of iron ions in ammonia alkaline solution at harsh reaction conditions, respectively. Primary surface engineering of maghemite nanoparticles was successfully performed by the proper deposition of silica onto nanoparticles surface under strictly regulated reaction conditions. Next, the secondary surface functionalization of the particles was achieved by coating the particles with organosilane followed by glutaraldehyde activation in order to enhance protein immobilization. Covalent immobilization of cholesterol oxidase was attempted afterwards. The structural and magnetic properties of magnetic silica nanocomposites were characterized by TEM and vibrating sample magnetometer (VSM) instruments. X-ray diffraction measurements confirmed the spinel structure and average size of uncoated maghemite nanoparticles to be around 20 nm in diameter. SEM-EDS spectra indicated a strong signal for Si, implying the coating procedure of silica onto the particles surface to be successfully accomplished. Fourier transform infrared (FT-IR) spectra analysis confirmed the binding of amino silane molecules onto the surface of the maghemite nanoparticles mediated Si-O-Si chemical bonds. Compared to the free enzyme, the covalently bound cholesterol oxidase retained 50% of its activity. Binding of enzyme onto chemically modified magnetic nanoparticles via glutaraldehyde activation is a promising method for developing biosensing components in biomedicine.     

Photophysical Properties of Luminescent Quaternary Lanthanide Molecular Hybrid Systems with Chemical Bonds from the Cooperative Design and Assembly of Structure and Function

Two long chain aliphatic acyl chlorides (dodecanoyl chloride (C₁₀H₁₉OCl, abbreviated as DC) and stearoyl chloride (C₁₈H₃₅Ocl, abbreviated as SC)) were modified by means of the amidation reaction with crosslinking molecules (N-aminopropyl-triethoxylsiliane, (APES, H₂N(CH₂)₃Si(OC₂H₅)₃)) and afford two kinds of structural molecular bridge DC (SC)− APES with double reactivity. Subsequently, according to the principle of coordination chemistry, ternary lanthanide (terbium and europium) molecular complex systems with two molecular bridges DC (SC)− APES and 1,10-phenanthroline (phen) of were successfully assembled. Then the modified molecular bridges behave as structural ligands to form the covalent bond Si− O network with matrix precursor (tetraethoxysilane, TEOS) through a sol-gel process (cohydrolysis and copolycondensation process), resulting in a novel quaternary molecular hybrid material (so called as phen-Tb(Eu)−DC(SC)− APES) with strong chemical bonds (N− Tb(Eu)− O coordination bonds and Si− O covalent bonds). And phen behaves as functional ligand to sensitize the luminescence of terbium or europium ions through the effective intramolecular energy transfer process, which gives rise to the characteristic emission of metal ion.     

Design and Synthesis of a Ruthenium(II) Complex-Based Luminescent Probe for Highly Selective and Sensitive Luminescence Detection of Nitric Oxide

Nitric oxide (NO) is one of the most important intercellular signaling molecules, and plays important roles in various biological systems. In this work, a unique Ru^II complex, tris[(5-(4-methylamino-3-aminobenzylamino)-1,10-phenanthroline)] ruthenium(II) hexafluorophosphate [Ru(MAA-phen)₃][PF₆]₂, has been designed and synthesized as a luminescent probe for the detection of NO in aqueous media. The complex itself is almost non-luminescent, but can specifically react with NO under the aerobic conditions to afford its highly luminescent triazole derivative in aqueous media, [Ru(MTA-phen)₃]²⁺ (MTA-phen: methyl-trazolebenzylamino-1,10-phenanthroline), accompanied by a 302-fold increase in luminescence intensity at 598 nm with a 130 nm Stokes shift. The luminescence response of [Ru(MAA-phen)₃]²⁺ to NO is rapid, highly specific without interferences of other reactive oxygen/nitrogen species, and highly stable against the pH changes in the range of pH 4.5–9.5. These features enable [Ru(MAA-phen)₃]²⁺ to be used as a probe for the highly selective and sensitive luminescence detection of NO in weakly acidic, neutral, and weakly basic media.     

Synthesis of Eu(III): naphtoyltrifluoroacetone:trioctylphosphineoxide complex-doped silica fluorescent nanoparticles through a new approach

In this study, a new approach for the preparation of a fluorescent europium(III) complex-doped silica nanoparticles has been developed. The synthesis process involved the following steps: (1) preparing silica nanoparticles by water-in-oil microemulsion method, (2) dyeing the spherical silica particles by europium(III): naphtoyltrifluoroacetone (NTA):trioctylphosphineoxide (TOPO), (3) adsorbing polyvinylpyrrolidone (PVP) onto the core structure and growing silica on PVP surface. The as-prepared nanoparticles exhibited stronger emission intensity, higher photo- and chemical stability. Despite the fact that europium(III) complex was doped into the nanoparticles, its fluorescence properties such as a wide Stokes shift, a narrow emission peak, and long fluorescence lifetime, were retained. The nanoparticles are uniform in shape and size (50 ± 5 nm in diameter). This study could provide new avenue for the fabrication of Eu: NTA:TOPO-based nanoparticles, facilitating their application in bioassay issues.     

Luminescence from copper nanoparticles

The presence of copper nanoparticles in alumina and silica modifies their luminescence, and the changes in spectra are influenced by variations in the nanoparticle size distributions. Luminescence signals are sensitive to the total defect population. Thus the luminescence not only reflects changes caused by thermal annealing, which can modify both intrinsic defects and the copper nanoparticles, but also responds to the method of preparation of thin film layers. Copper nanoparticle influence on luminescence is reported both for ion-implanted bulk silica and for copper in pulsed laser deposition within alumina. Luminescence thus potentially offers a non-destructive monitor of the layer quality, reproducibility and growth conditions, as well as the state and size of the copper nanoparticles. Received: 29 June 2001 / Published online: 10 October 2001     

FITC Labeled Silica Nanoparticles as Efficient Cell Tags: Uptake and Photostability Study in Endothelial Cells

The use of fluorescent nanomaterials has gained great importance in the field of medical imaging. Many traditional imaging technologies have been reported utilizing dyes in the past. These methods face drawbacks due to non-specific accumulation and photobleaching of dyes. We studied the uptake and internalization of two different sized (30 nm and 100 nm) FITC labeled silica nanoparticles in Human umbilical vein endothelial cell line. These nanomaterials show high biocompatability and are highly photostable inside live cells for increased period of time in comparison to the dye alone. To our knowledge, we report for the first time the use of 30 nm fluorescent silica nanoparticles as efficient endothelial tags along with the well studied 100 nm particles. We also have emphasized the good photostability of these materials in live cells.     

Study of transient luminescence of three kinds of Ru complexes bound to DNA

The transient luminescence of three kinds of ruthenium complexes [Ru(bpy)₂(7-CH₃-dppz)]²⁺, [Ru(bpy)₂(7-F-dppz)]²⁺ and [Ru(phen)₂(7-F-dppz)]²⁺ bound to calf thymus DNA (ctDNA) has been studied by using the time-resolved spectroscopy. The results show that the luminescence is due to the radiative decay from the charge-transfer states to the ground state. By the interaction with DNA, the radiativeless rate of the photoexcited Ru complex molecules decreases, which results in the increase of luminescence lifetime and efficiency. The structure of the Ru complex has an important impact on the interaction with DNA. The [Ru(bpy)₂(7-CH₃-dppz)]²⁺ shows the longest luminescence lifetime (about 382 ns), while the [Ru(bpy)₂(7-F-dppz)]²⁺ shows the shortest lifetime (about 65 ns). The possible origin of the luminescence dynamics is discussed. Supported by the National Natural Science Foundation of China (Grant Nos. 60478013 and 20571089), the Key Program of Natural Science Foundation of Guangdong Province of China (Grant No. 05101819), the Doctoral Program Foundation of Institutions of Higher Education of China (Grant No. 20040558031) and the Scientific Research Foundation of Maoming College (Grant No. 203346)     

Electronic state of ruthenium deposited onto oxide supports: An XPS study taking into account the final state effects

The electronic state of ruthenium in the supported Ru/EO_x (EO_x = MgO, Al₂O₃ or SiO₂) catalysts prepared by with the use of Ru(OH)Cl₃ or Ru(acac)₃ (acac = acetylacetonate) and reduced with H₂ at 723 K is characterized by X-ray photoelectron spectroscopy (XPS) in the Ru 3d, Cl 2p and O 1s regions. The influence of the final state effects (the differential charging and variation of the relaxation energy) on the binding energy (BE) of Ru 3d_5/2 core level measured for supported Ru nanoparticles is estimated by comparison of the Fermi levels and the modified Auger parameters determined for the Ru/EO_x samples with the corresponding characteristics of the bulk Ru metal. It is found that the negative shift of the Ru 3d_5/2 peak which is observed in the spectrum of ruthenium deposited onto MgO (BE = 279.5-279.7 eV) with respect to that of Ru black (BE = 280.2 eV) or ruthenium supported on γ-Al₂O₃ and SiO₂ (BE = 280.4 eV) is caused not by the transfer of electron density from basic sites of MgO, as considered earlier, but by the differential charging of the supported Ru particles compared with the support surface. Correction for the differential charging value reveals that the initial state energies of ruthenium in the Ru/EO_x systems are almost identical (BE = 280.5 ± 0.1 eV) irrespectively of acid-base properties of the support, the mean size of supported Ru crystallites (within the range of 2-10 nm) and the surface Cl content. The results obtained suggest that the difference in ammonia synthesis activity between the Ru catalysts supported on MgO and on the acidic supports is accounted for by not different electronic state of ruthenium on the surface of these oxides but by some other reasons.     

Photoluminescence effect of Ru dye on alumina membranes with ordered pore arrays

We have investigated the quenching luminescence and the luminescence mechanisms of self-assembled Ru(II)L₂X₂ (Ru(II)(4,4’-dicarboxyl-2,2’-bipyridyl)₂(SCN)₂) dye in porous anodic alumina. Porous anodic alumina can emit visible light due to numerous oxygen vacancies formed during anodic oxidation. Energy transfer from the porous anodic alumina to the dye molecules causes the quenching and red shift of the PL peak, which gives a fundamental understanding of the PL mechanism in porous anodic alumina. Received: 29 May 2001 / Accepted: 3 August 2001 / Published online: 30 October 2001