FloDots: luminescent nanoparticles

Bright and Stable Nanomaterials for Imaging and Sensing

This review covers strategies to prepare high-performance emissive polymer nanomaterials, combining very high brightness and photostability, to respond to the drive for better imaging quality and lower detection limits in fluorescence imaging and sensing applications. The more common approaches to obtaining high-brightness nanomaterials consist of designing polymer nanomaterials carrying a large number of fluorescent dyes, either by attaching the dyes to individual polymer chains or by encapsulating the dyes in nanoparticles. In both cases, the dyes can be covalently linked to the polymer during polymerization (by using monomers functionalized with fluorescent groups), or they can be incorporated post-synthesis, using polymers with reactive groups, or encapsulating the unmodified dyes. Silica nanoparticles in particular, obtained by the condensation polymerization of silicon alcoxides, provide highly crosslinked environments that protect the dyes from photodegradation and offer excellent chemical modification flexibility. An alternative and less explored strategy is to increase the brightness of each individual dye. This can be achieved by using nanostructures that couple dyes to plasmonic nanoparticles so that the plasmon resonance can act as an electromagnetic field concentrator to increase the dye excitation efficiency and/or interact with the dye to increase its emission quantum yield.

Dye-sensitized lanthanide containing nanoparticles for luminescence based applications

Due to their exceptional luminescent properties, lanthanide (Ln) complexes represent a unique palette of probes in the spectroscopic toolkit. Their extremely weak brightness due to forbidden Ln electronic transitions can be overcome by indirect dye-sensitization from the antenna effect brought by organic ligands. Despite the improvement brought by the antenna effect, (bio)analytical applications with discrete Ln complexes as luminescent markers still suffers from low sensitivity as they are limited by the complex brightness. Thus, there is a need to develop nano-objects that cumulate the spectroscopic properties of multiple Ln ions. This review firstly gives a brief introduction of the spectral properties of lanthanides both in complexes and in nanoparticles (NPs). Then, the research progress of the design of Ln-doped inorganic NPs with capping antennas, Ln-complex encapsulated NPs and Ln-complex surface functionalized NPs is presented along with a summary of the various photosensitizing ligands and of the spectroscopic properties (excited-state lifetime, brightness, quantum yield). The review also emphasizes the problems and limitations encountered over the years and the solutions provided to address them. Finally, a comparison of the advantages and drawbacks of the three types of NP is provided as well as a conclusion about the remaining challenges both in the design of brighter NPs and in the luminescence based applications.

Optical Sensing and Imaging of pH Values: Spectroscopies, Materials, and Applications

This is the first comprehensive review on methods and materials for use in optical sensing of pH values and on applications of such sensors. The Review starts with an introduction that contains subsections on the definition of the pH value, a brief look back on optical methods for sensing of pH, on the effects of ionic strength on pH values and pKa values, on the selectivity, sensitivity, precision, dynamic ranges, and temperature dependence of such sensors. Commonly used optical sensing schemes are covered in a next main chapter, with subsections on methods based on absorptiometry, reflectometry, luminescence, refractive index, surface plasmon resonance, photonic crystals, turbidity, mechanical displacement, interferometry, and solvatochromism. This is followed by sections on absorptiometric and luminescent molecular probes for use pH in sensors. Further large sections cover polymeric hosts and supports, and methods for immobilization of indicator dyes. Further and more specific sections summarize the state of the art in materials with dual functionality (indicator and host), nanomaterials, sensors based on upconversion and 2-photon absorption, multiparameter sensors, imaging, and sensors for extreme pH values. A chapter on the many sensing formats has subsections on planar, fiber optic, evanescent wave, refractive index, surface plasmon resonance and holography based sensor designs, and on distributed sensing. Another section summarizes selected applications in areas, such as medicine, biology, oceanography, bioprocess monitoring, corrosion studies, on the use of pH sensors as transducers in biosensors and chemical sensors, and their integration into flow-injection analyzers, microfluidic devices, and lab-on-a-chip systems. An extra section is devoted to current challenges, with subsections on challenges of general nature and those of specific nature. A concluding section gives an outlook on potential future trends and perspectives.

Confinement of Dyes inside Boron Nitride Nanotubes: Photostable and Shifted Fluorescence down to the Near Infrared

Fluorescence is ubiquitous in life science and used in many fields of research ranging from ecology to medicine. Among the most common fluorogenic compounds, dyes are being exploited in bioimaging for their outstanding optical properties from UV down to the near IR (NIR). However, dye molecules are often toxic to living organisms and photodegradable, which limits the time window for in vivo experiments. Here, it is demonstrated that organic dye molecules are passivated and photostable when they are encapsulated inside a boron nitride nanotube (dyes@BNNT). The results show that the BNNTs drive an aggregation of the encapsulated dyes, which induces a redshifted fluorescence from visible to NIR-II. The fluorescence remains strong and stable, exempt of bleaching and blinking, over a time scale longer than that of free dyes by more than 10⁴ . This passivation also reduces the toxicity of the dyes and induces exceptional chemical robustness, even in harsh conditions. These properties are highlighted in bioimaging where the dyes@BNNT nanohybrids are used as fluorescent nanoprobes for in vivo monitoring of Daphnia Pulex microorganisms and for diffusion tracking on human hepatoblastoma cells with two-photon imaging.

Tumor Targeting Strategies of Smart Fluorescent Nanoparticles and Their Applications in Cancer Diagnosis and Treatment

Advantages such as strong signal strength, resistance to photobleaching, tunable fluorescence emissions, high sensitivity, and biocompatibility are the driving forces for the application of fluorescent nanoparticles (FNPs) in cancer diagnosis and therapy. In addition, the large surface area and easy modification of FNPs provide a platform for the design of multifunctional nanoparticles (MFNPs) for tumor targeting, diagnosis, and treatment. In order to obtain better targeting and therapeutic effects, it is necessary to understand the properties and targeting mechanisms of FNPs, which are the foundation and play a key role in the targeting design of nanoparticles (NPs). Widely accepted and applied targeting mechanisms such as enhanced permeability and retention (EPR) effect, active targeting, and tumor microenvironment (TME) targeting are summarized here. Additionally, a freshly discovered targeting mechanism is introduced, termed cell membrane permeability targeting (CMPT), which improves the tumor-targeting rate from less than 5% of the EPR effect to more than 50%. A new design strategy is also summarized, which is promising for future clinical targeting NPs/nanomedicines design. The targeting mechanism and design strategy will inspire new insights and thoughts on targeting design and will speed up precision medicine and contribute to cancer therapy and early diagnosis.

Multimodality Imaging of Silica and Silicon Materials In Vivo

Recent progress in the development of silica- and silicon-based multimodality imaging nanoprobes has advanced their use in image-guided drug delivery, and the development of novel systems for nanotheranostic and diagnostic applications. As biocompatible and flexibly tunable materials, silica and silicon provide excellent platforms with high clinical potential in nanotheranostic and diagnostic probes with well-defined morphology and surface chemistry, yielding multifunctional properties. In vivo imaging is of great value in the exploration of methods for improving site-specific nanotherapeutic delivery by silica- and silicon-based drug-delivery systems. Multimodality approaches are essential for understanding the biological interactions of nanotherapeutics in the physiological environment in vivo. The aim here is to describe recent advances in the development of in vivo imaging tools based on nanostructured silica and silicon, and their applications in single and multimodality imaging.

Nanodiagnostics for tuberculosis detection

INTRODUCTION

Tuberculosis (TB) is a leading killer worldwide. End TB strategy aims at ending the TB epidemic by 2030. Early, accurate, and affordable diagnosis represents a cornerstone to achieve this goal. Innovative strategies for TB diagnostics have been introduced. However, the ideal assay is yet unavailable and conventional methods remain necessary for diagnosis. Unique properties of nanoparticles (NPs) have allowed their utilization in TB detection via targeting disease biomarkers. Area covered: Until now, around thirty-five TB NP-based assays have been partially or fully characterized. Accuracy, low-cost, and short time-to-result represent the common properties of proposed platforms. TB nanodiagnostics now encompass almost all clinical aspects of the disease including active TB, non-tuberculous mycobacteria, rifampicin resistant TB, TB/HIV co-infection, latent TB, and extra-pulmonary TB. This review summarizes state-of-the-art knowledge of TB nanodiagnostics for the last 10 years. Special consideration is given for fabrication concepts, detection strategies, and clinical performance using various clinical specimens. The potential of TB nanodiagnostics to fulfill the need for ideal MTB testing is assessed. Expert commentary: TB nanodiagnostics show promise to be ideal detection tools that can meet the rigorous demands to end the TB epidemic by 2030.

Synthesis and stability of IR-820 and FITC doped silica nanoparticles

Fluorescent silica nanoparticles (NPs) have potential in biomedical applications as diagnostics and traceable drug delivery agents. In this study, we have synthesized fluorescent dye grafted silica NPs in two step process. First, a stable method to synthesize various sizes of silica NPs ranging from 20 to 52, 95, 210 and 410nm have been successfully demonstrated. Secondly, as-synthesized silica NPs are readily grafted with some fluorescent dyes like IR-820 and fluorescein isothiocyanate (FITC) dyes by simple impregnation method. IR-820 and FITC dyes are 'activated' by (3-mercaptopropyl)trimethoxysilane (MPTMS) and (3-aminopropyl)triethoxysilane (APTS) respectively prior to the grafting on silica NPs. UV-vis spectroscopy is used to test the stability of dye grafted silica NPs. The fluorescent dye grafted silica NPs are quite stable in aqueous solution. Also, a new type of dual dye-doped hybrid silica nanoparticles has been developed. The combination of microscopic and spectroscopic techniques shows that the synthesis parameters have significant effects on the particle shape and size and is tuneable from a few nanometers to a few hundred nanometers. The ability to create size controlled nanoparticles with associated (optical) functionality may have significant importance in bio-medical imaging.

Prolonged Dye Release from Mesoporous Silica-Based Imaging Probes Facilitates Long-Term Optical Tracking of Cell Populations In Vivo

Nanomedicine is gaining ground worldwide in therapy and diagnostics. Novel nanoscopic imaging probes serve as imaging tools for studying dynamic biological processes in vitro and in vivo. To allow detectability in the physiological environment, the nanostructure-based probes need to be either inherently detectable by biomedical imaging techniques, or serve as carriers for existing imaging agents. In this study, the potential of mesoporous silica nanoparticles carrying commercially available fluorochromes as self-regenerating cell labels for long-term cellular tracking is investigated. The particle surface is organically modified for enhanced cellular uptake, the fluorescence intensity of labeled cells is followed over time both in vitro and in vivo. The particles are not exocytosed and particles which escaped cells due to cell injury or death are degraded and no labeling of nontargeted cell populations are observed. The labeling efficiency is significantly improved as compared to that of quantum dots of similar emission wavelength. Labeled human breast cancer cells are xenotransplanted in nude mice, and the fluorescent cells can be detected in vivo for a period of 1 month. Moreover, ex vivo analysis reveals fluorescently labeled metastatic colonies in lymph node and rib, highlighting the capability of the developed probes for tracking of metastasis.

Human mesenchymal stem cells labelled with dye-loaded amorphous silica nanoparticles: long-term biosafety, stemness preservation and traceability in the beating heart

BACKGROUND

Treatment of myocardial infarction with mesenchymal stem cells (MSCs) has proven beneficial effects in both animal and clinical studies. Engineered silica nanoparticles (SiO2-NPs) have been extensively used as contrast agents in regenerative medicine, due to their resistance to degradation and ease of functionalization. However, there are still controversies on their effective biosafety on cellular systems. In this perspective, the aims of the present study are: 1) to deeply investigate the impact of amorphous 50 nm SiO2-NPs on viability and function of human bone marrow-derived MSCs (hMSCs); 2) to optimize a protocol of harmless hMSCs labelling and test its feasibility in a beating heart model.

RESULTS

Optimal cell labelling is obtained after 16 h exposure of hMSCs to fluorescent 50 nm SiO2-NPs (50 µg mL(-1)); interestingly, lysosomal activation consequent to NPs storage is not associated to oxidative stress. During prolonged culture hMSCs do not undergo cyto- or genotoxicity, preserve their proliferative potential and their stemness/differentiation properties. Finally, the bright fluorescence emitted by internalized SiO2-NPs allows both clear visualization of hMSCs in normal and infarcted rat hearts and ultrastructural analysis of cell engraftment inside myocardial tissue.

CONCLUSIONS

Overall, 50 nm SiO2-NPs display elevated compatibility with hMSCs in terms of lack of cyto- and genotoxicity and maintenance of important features of these cells. The demonstrated biosafety, combined with proper cell labelling and visualization in histological sections, make these SiO2-NPs optimal candidates for the purpose of stem cell tracking inside heart tissue.

Investigating the colloidal stability of fluorescent silica nanoparticles under isotonic conditions for biomedical applications

Fluorescent silica nanoparticle (NP) labels are of great interest in biomedical diagnostics, however, when used in bioassays under physiological conditions they rapidly agglomerate and precipitate from solution leading to high levels of non-specific binding. In this work, using size and zeta-potential data obtained from Dynamic and Electrophoretic Light Scattering analysis, the improvement in colloidal stability of silica NPs under physiological conditions was correlated with an increase in the concentration of three additives: (1) a protein, bovine serum albumin (BSA); (2) a neutral surfactant, Tween 20®; and (3) a charged surfactant, sodium dodecyl sulfate (SDS). The number of BSA molecules present in the NP corona at each concentration was calculated using UV-Vis spectroscopy and a bicinchoninic acid protein assay (BCA). The optimal concentration of each additive was also effective in stabilizing antibody labeled fluorescent nanoparticles (αNPs) under physiological conditions. Using a fourth additive, trehalose, the colloidal stability of αNPs after freeze-drying and long-term storage also significantly improved. Both as-prepared and freeze-dried αNPs were tested in a standard fluorescence immunoassay for the detection of human IgG. The as-prepared assay showed a higher sensitivity at low concentration and a lower limit of detection when compared to a free dye assay. Assays performed with freeze dried αNPs after 4 and 22 days also showed good reproducibility.

Photosensitive fluorescent dye contributes to phototoxicity and inflammatory responses of dye-doped silica NPs in cells and mice

Dye-doped fluorescent silica nanoparticles provide highly intense and photostable fluorescence signals. However, some dopant dye molecules are photosensitive. A widely-used photosensitive fluorescent dopant, RuBpy, was chosen to systematically investigate the phototoxicity of the dye-doped silica nanoparticles (NPs). We investigated cell viability, DNA damage, and Reactive Oxygen Species (ROS) levels in alveolar macrophages using the dye-doped NPs with or without irradiation. Our results showed that the RuBpy-doped silica NPs could induce significant amount of ROS, DNA damage, apoptosis and impaired proliferation in MH-S cells. In vivo studies in mice showed that RuBpy-doped silica NPs induced significant inflammatory cytokine production and lowered expression in signaling proteins such as ERK1/2 and NF-κB as well as increased lung injury determined by myeloperoxidase and lipid peroxidation. Strikingly, we also found that both RuBpy alone and NPs induced systemic signaling activation in the kidney compared to the liver and lung where showed highly selective signaling patterns, which is more pronounced than RuBpy-doped silica NPs. Moreover, we discovered a critical biomarker (e.g., HMGB1) for silica NPs-induced stress and toxicity and demonstrated differentially-regulated response patterns in various organs. Our results indicate for the first time that the RuBpy-doped silica NPs may impose less inflammatory responses but stronger thermotherapeutic effects on target cells in animals than naked NPs in a time- and dose-dependent manner.

Signal amplification systems in immunoassays: implications for clinical diagnostics

Biomarkers in physiological specimens serve as useful sensors for clinical diagnosis. Accurate detection of specific markers is crucial for the diagnosis of disease, monitoring drug therapy and patient screening. In vitro immunoassays are probably the most common, simple and relatively inexpensive serological tools used in clinical laboratories for the diagnosis and management of disease. Despite continued efforts to improve the performance of immunoassays in the past three decades, there is a need for highly sensitive assays that can detect the lowest levels of disease markers with greater accuracy. This review summarizes recent advances made towards increasing the sensitivity of immunoassays by amplifying detection signals, with implications for the development of highly sensitive diagnostic systems; it also discusses the principles of related methodologies.

Volume labeling with Alexa Fluor dyes and surface functionalization of highly sensitive fluorescent silica (SiO2) nanoparticles

A new synthesis approach is described that allows the direct incorporation of fluorescent labels into the volume or body of SiO2 nanoparticles. In this process, fluorescent Alexa Fluor dyes with different emission wavelengths were covalently incorporated into the SiO2 nanoparticles during their formation by the hydrolysis of tetraethoxysilane. The dye molecules were homogeneously distributed throughout the SiO2 nanoparticles. The quantum yields of the Alexa Fluor volume-labeled SiO2 nanoparticles were much higher than nanoparticles labeled using conventional organic dyes. The size of the resulting nanoparticles was controlled using microemulsion reaction media with sizes in the range of 20-100 nm and a polydispersity of <15%. In comparison with conventional surface tagged particles created by post-synthesis modification, this process maintains the physical and surface chemical properties that have the most pronounced effect on colloidal stability and interactions with their surroundings. These volume-labeled nanoparticles have proven to be extremely robust, showing excellent signal strength, negligible photobleaching, and minimal loss of functional organic components. The native or "free" surface of the volume-labeled particles can be altered to achieve a specific surface functionality without altering fluorescence. Their utility was demonstrated for visualizing the association of surface-modified fluorescent particles with cultured macrophages. Differences in particle agglomeration and cell association were clearly associated with differences in observed nanoparticle toxicity. The capacity to maintain particle fluorescence while making significant changes to surface chemistry makes these particles extremely versatile and useful for studies of particle agglomeration, uptake, and transport in environmental and biological systems.

Synthesis and Characterization of Dye-Labeled Poly(methacrylic acid) Grafted Silica Nanoparticles

The synthesis of dye-labeled poly(methacrylic acid) (PMAA) grafted silica nanoparticles was studied. Surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization of tert-butylmethacrylate (tBuMA) was conducted on dye-labeled CPDB coated silica nanoparticles followed by sequential removal of the thiocarbonylthio end groups and the tert-butyl moieties. Additionally, as a more straightforward strategy, direct polymerization of methacrylic acid on silica nanoparticles with a diameter size as small as 15 nm was conducted via the RAFT polymerization technique. A variety of PMAA brushes with different lengths and densities were prepared on nanoparticle surfaces via surface-initiated RAFT polymerization with excellent control and surface grafting densities as high as 0.65 chains/nm². The grafted PMAA was methylated by trimethylsilyldiazomethane to conduct organic phase GPC characterization. The dye-labeled PMAA grafted nanoparticles provide a platform to bind biomolecules and to track the movement of the nanoparticles in biological systems.

Sulfonates-PMMA nanoparticles conjugates: a versatile system for multimodal application

We report herein the viability of a novel nanoparticles (NPs) conjugated system, namely the attachment, based on ionic and hydrophobic interactions, of different sulfonated organic salts to positively charged poly(methylmethacrylate) (PMMA)-based core-shell nanoparticles (EA0) having an high density of ammonium groups on their shells. In this context three different applications of the sulfonates@EA0 systems have been described. In detail, their ability as cytotoxic drugs and pro-drugs carriers was evaluated in vitro on NCI-H460 cell line and in vivo against human ovarian carcinoma IGROV-1 cells. Besides, 8-hydroxypyrene-1,3,6-trisulfonic acid, trisodium salt (HPTS) was chosen for NPs loading, and its internalization as bioimaging probe was evaluated on Hep G2 cells. Overall, the available data support the interest for these PMMA NPs@sulfonates systems as a promising formulation for theranostic applications. In vivo biological data strongly support the potential value of these core-shell NPs as delivery system for negatively charged drugs or biologically active molecules. Additionally, we have demonstrated the ability of these PMMA core-shell nanoparticles to act as efficient carriers of fluorophores. In principle, thanks to the high PMMA NPs external charge density, sequential and very easy post-loading of different sulfonates is achievable, thus allowing the preparation of nanocarriers either with bi-modal drug delivery behaviour or as theranostic systems.

Novel luminescent silica nanoparticles (LSN): p53 gene delivery system in breast cancer in vitro and in vivo

OBJECTIVES

Mutations in the p53 tumor suppressor gene are one among the most common genetic abnormalities to be described in breast cancer. However, there are a few recant reports on non-viral vector-mediated p53 gene delivery in breast cancer.

METHODS

A new formulation of luminescent silica nanoparticles (LSNs) for gene delivery was produced by the two-step method with slight modification.

KEY FINDINGS

The pp53 plasmid constructs (p53-EGFP)/LSNs complexes were transfected into human breast cancer cell (MCF-7) and transfection efficiency was determined by FACS analysis. The gene expression was determined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis respectively. Further the growth inhibition through induced apoptosis with pp53-EGFP/LSNs complex were assessed by trypan blue exclusion assay and annexin V staining, respectively. Interestingly the in vivo biodistribution of plasmid DNA study revealed the occurrence was investigated by PCR and RT-PCR. The transfection efficiency of LSNs showed the highest transfection efficiency among the LSN formulation was higher than that of commercially available Lipofectin®. The LSNs-mediated transfection of the p53 gene resulted in efficient high level of wild-type p53 mRNA and protein expression levels in MCF-7 cells. Selected tissues were analyzed for any potential toxicity by histological analysis the efficient reestablishment of wild-type p53 function in breast cancer cells restored the p53 dependent apoptotic pathway.

CONCLUSIONS

Taken together, our results reveal that cationic LSN-mediated p53 gene delivery may have potential application as a non-viral vector-mediated breast cancer gene therapy due to its effective induction of apoptosis and tumor growth inhibition.

Fabrication of glyconanoparticle microarrays

We report a new type of microarray, based on glyconanoparticles (GNPs), to study glycan-lectin interactions. GNPs, synthesized by conjugating carbohydrate ligands on silica nanoparticles, were printed on a photoactive surface followed by covalent immobilization by light activation. The GNP microarrays could be probed by lectins labeled with fluorescein as well as fluorescein-doped silica nanoparticles (FSNPs). Results showed that FSNP as the label enhanced the signals for the higher affinity ligands than the lower ones.

Luminescent nanoparticles and their use for in vitro and in vivo diagnostics

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.

Calcium phosphate ceramic systems in growth factor and drug delivery for bone tissue engineering: a review

Calcium phosphates (CaPs) are the most widely used bone substitutes in bone tissue engineering due to their compositional similarities to bone mineral and excellent biocompatibility. In recent years, CaPs, especially hydroxyapatite and tricalcium phosphate, have attracted significant interest in simultaneous use as bone substitute and drug delivery vehicle, adding a new dimension to their application. CaPs are more biocompatible than many other ceramic and inorganic nanoparticles. Their biocompatibility and variable stoichiometry, thus surface charge density, functionality, and dissolution properties, make them suitable for both drug and growth factor delivery. CaP matrices and scaffolds have been reported to act as delivery vehicles for growth factors and drugs in bone tissue engineering. Local drug delivery in musculoskeletal disorder treatments can address some of the critical issues more effectively and efficiently than the systemic delivery. CaPs are used as coatings on metallic implants, CaP cements, and custom designed scaffolds to treat musculoskeletal disorders. This review highlights some of the current drug and growth factor delivery approaches and critical issues using CaP particles, coatings, cements, and scaffolds towards orthopedic and dental applications.

Dye doped Eosin yellowish silica nanoparticles as novel fluorophore for a peroxyoxalate chemiluminescence system

In this work, we report the preparation and characterization of novel dye doped fluorophore Eosin yellowish silica nanoparticles (ESNPs). We synthesized ESNPs by the Stöber method via encapsulation of Eosin Yellowish in silica particles by the condensation of tetraethyl orthosilicate under alkaline condition at room temperature. The resulted ESNPs were characterized by transmission electron microscopy, atomic force microscopy; UV-Visible, fluorescence and Fourier transform infrared spectroscopy. The sizes of the nanoparticles have been found to be 300.0 (±1.0), 400.0 (±1.1) and 500.0 (±5.2) nm depending the reaction conditions under which they were synthesized. Furthermore, because of intense light emission, the ESNPs were used as fluorophore in a peroxyoxalate chemiluminescence system. The effect of solvent and concentrations of necessary reagents, bis(2,4,6-trichlorophenyl)oxalate, sodium salicylate, hydrogen peroxide and the effects of size of the ESNP and temperature on the luminescence efficiency of the system were examined. The activation kinetic parameters of the system were also evaluated from the temperature investigation.

Silica nanoparticles for the layer-by-layer assembly of fully electro-active cytochrome c multilayers

BACKGROUND

For bioanalytical systems sensitivity and biomolecule activity are critical issues. The immobilization of proteins into multilayer systems by the layer-by-layer deposition has become one of the favorite methods with this respect. Moreover, the combination of nanoparticles with biomolecules on electrodes is a matter of particular interest since several examples with high activities and direct electron transfer have been found. Our study describes the investigation on silica nanoparticles and the redox protein cytochrome c for the construction of electro-active multilayer architectures, and the electron transfer within such systems. The novelty of this work is the construction of such artificial architectures with a non-conducting building block. Furthermore a detailed study of the size influence of silica nanoparticles is performed with regard to formation and electrochemical behavior of these systems.

RESULTS

We report on interprotein electron transfer (IET) reaction cascades of cytochrome c (cyt c) immobilized by the use of modified silica nanoparticles (SiNPs) to act as an artificial matrix. The layer-by-layer deposition technique has been used for the formation of silica particles/cytochrome c multilayer assemblies on electrodes. The silica particles are characterized by dynamic light scattering (DLS), Fourier transformed infrared spectroscopy (FT-IR), Zeta-potential and transmission electron microscopy (TEM). The modified particles have been studied with respect to act as an artificial network for cytochrome c and to allow efficient interprotein electron transfer reactions. We demonstrate that it is possible to form electro-active assemblies with these non-conducting particles. The electrochemical response is increasing linearly with the number of layers deposited, reaching a cyt c surface concentration of about 80 pmol/cm2 with a 5 layer architecture. The interprotein electron transfer through the layer system and the influence of particle size are discussed.

CONCLUSIONS

This study demonstrates the ability to construct fully electro-active cyt c multilayer assemblies by using carboxy-modified silica nanoparticles. Thus it can be shown that functional, artificial systems can be build up following natural examples of protein arrangements. The absence of any conductive properties in the second building block clearly demonstrates that mechanisms for electron transfer through such protein multilayer assemblies is based on interprotein electron exchange, rather than on wiring of the protein to the electrode.The construction strategy of this multilayer system provides a new controllable route to immobilize proteins in multiple layers featuring direct electrochemistry without mediating shuttle molecules and controlling the electro-active amount by the number of deposition steps.

Poly(ethyl cyanoacrylate) colloidal particles tagged with Rhodamine 6G: preparation and physicochemical characterization

This paper describes the preparation and characterization of poly(ethyl cyanoacrylate) colloidal particles loaded with the organic fluorophore Rhodamine 6G. We studied the physicochemical properties of the colloidal particles: morphology, size-distribution, ζ-potential, fluorescent properties and photobleaching upon UV-light illumination. The properties of the obtained colloidal particles, as well as the dye loading efficiency, were found to depend on the concentrations of ethyl cyanoacrylate monomer and Rhodamine 6G in the polymerization medium. The fluorophore release from the colloidal particles in aqueous buffer is also studied.

Surface-enhanced Raman scattering-active nanostructures and strategies for bioassays

Surface-enhanced Raman scattering (SERS) techniques offer a number of advantages in molecular detection and analysis, particularly in terms of the multiplex detection of biomolecules. So far, many new SERS-based substrates and analytical techniques have been reported. For easy understanding, various SERS techniques are classified into the following four categories: adsorption-mediated direct detection; antibody- or ligand-mediated direct detection; binding catalyzed indirect detection; and tag-based indirect detection. Among these, recent successes of SERS tagging/encoding (nano/micro) materials and detection methods are highlighted, including our recent works. Some novel SERS-based strategies for the detection of several biological molecules are also introduced.

Nanotechnology: emerging tool for diagnostics and therapeutics

Nanotechnology is an emerging technology which is an amalgamation of different aspects of science and technology that includes disciplines such as electrical engineering, mechanical engineering, biology, physics, chemistry, and material science. It has potential in the fields of information and communication technology, biotechnology, and medicinal technology. It involves manipulating the dimensions of nanoparticles at an atomic scale to make use of its physical and chemical properties. All these properties are responsible for the wide application of nanoparticles in the field of human health care. Promising new technologies based on nanotechnology are being utilized to improve diverse aspects of medical treatments like diagnostics, imaging, and gene and drug delivery. This review summarizes the most promising nanomaterials and their application in human health.

Enriching PMMA nanospheres with adjustable charges as novel templates for multicolored dye@PMMA nanocomposites

Multicolored fluorescent dye loaded PMMA nanospheres were synthesized by the electrostatic adsorption of dye molecules on the charged PMMA nanospheres, whose charges were adjusted by choosing different initiators. The charged PMMA nanospheres have a wider capacity and advantage for combining the charged dyes. The fluorescent dye@PMMA composite nanospheres possess the advantages of higher brightness, longer lifetime and stronger resistance to photobleaching relative to dye molecules. Dye leakage remained lower than 5% over one week. These fluorescent nanospheres have been used in biological labels in cell imaging. They can easily stain blood cancer cells without further surface modification.

Label-free biosensing based on multilayer fluorescent nanocomposites and a cationic polymeric transducer

This study describes the preparation and characterization of a DNA sensing architecture combining the molecular recognition capabilities of a cationic conjugated polymer transducer with highly fluorescent core-shell nanoparticles (NPs). The very structure of the probe-labeled NPs and the polymer-induced formation of NP aggregates maximize the proximity between the polymer donor and acceptor NPs that is required for optimal resonant energy transfer. Each hybridization event is signaled by a potentially large number of excited reporters following the efficient plasmon-enhanced energy transfer between target-activated polymer transducer and fluorophores located in the self-assembled core-shell aggregates, resulting in direct molecular detection of target nucleic acids at femtomolar concentrations.

Dye-doped silica nanoparticles as efficient labels for glycans

We report that dye-doped fluorescent silica nanoparticles (FSNPs) are highly efficient labels for glycans. Mono- and oligo-saccharides were conjugated to FSNPs using a general photocoupling chemistry. FSNP-labeled glycans were applied to image and detect bacteria, and to study carbohydrate-lectin interactions on a lectin microarray.

Near infrared imaging with nanoparticles

Near infrared imaging has presented itself as a powerful diagnostic technique with potential to serve as a minimally invasive, nonionizing method for sensitive, deep tissue diagnostic imaging. This potential is further realized with the use of nanoparticle (NP)-based near infrared (NIR) contrast agents that are not prone to the rapid photobleaching and instability of their organic counterparts. This review discusses applications that have successfully demonstrated the utility of nanoparticles for NIR imaging, including NIR-emitting semiconductor quantum dots (QDs), resonant gold nanoshells, and dye-encapsulating nanoparticles. NIR QDs demonstrate superior optical performance with exceptional fluorescence brightness stability. However, the heavy metal composition and high propensity for toxicity hinder future application in clinical environments. NIR resonant gold nanoshells also exhibit brilliant signal intensities and likewise have none of the photo- or chemical-instabilities characteristic of organic contrast agents. However, concerns regarding ineffectual clearance and long-term accumulation in nontarget organs are a major issue for this technology. Finally, NIR dye-encapsulating nanoparticles synthesized from calcium phosphate (CP) also demonstrate improved optical performances by shielding the component dye from undesirable environmental influences, thereby enhancing quantum yields, emission brightness, and fluorescent lifetime. Calcium phosphate nanoparticle (CPNP) contrast agents are neither toxic, nor have issues with long-term sequestering, as they are readily dissolved in low pH environments and ultimately absorbed into the system. Though perhaps not as optically superior as QDs or nanoshells, these are a completely nontoxic, bioresorbable option for NP-based NIR imaging that still effectively improves the optical performance of conventional organic agents.

Multicolor dye-doped silica nanoparticles independent of FRET

Multicolor particles were prepared by incorporating two dyes, one fluorescent (fluorescein isothiocyanate) and one phosphorescent (tris(1,10-phenanathroline) ruthenium ion), into the silica matrix. Colors of the particles can be easily tuned by either varying the doping ratios of the two dyes or changing the excitation wavelength while fixing the ratios. The multicolor character of the particles is less sensitive to the location of the two dyes in the silica, since the luminescence of the particles is independent of Förster resonance energy transfer (FRET).