Synthesis, Characterization, and Bio-conjugation of Silicon Nanocrystal

Bulk silicon is unable to emit fluorescence because of its indirect band gap nature. However, it has been reported that nano-structured silicon can be fluorescent when properly excited. Silicon nanocrystals (SN) have gathered scientific attention not only because of their uncertain fluorescence origin, but also because of their advantages over fluorescent dyes. This thesis summarizes studies on the synthesis, characterization and bio applications of fluorescent SN. Size control of SN provided size dependent tuning of the fluorescence. Higher quantum yield and narrower size distribution of SN have been achieved. HrTEM, SANS, light scattering, photoluminescence and optical transmission spectroscopy on the size measurements of SN helped determine the average size accurately. Fuctionalization of surface prepares silicon nanocrystals as a platform for bio conjugating applications

Silicon nanocrystals: Biocompatible fluorescent nanolabel

This study discusses a synthesis, characterization, bioconjugation, and biological responses of fluorescent silicon nanocrystals (SiNCs). First, the efficient method of synthesizing fluorescent SiNCs is presented employing an electrochemical reduction of trichloro(octyl)silane. Miligram amount of bright fluorescent SiNCs is obtained with well-defined nanocrystalline structures. Octyl passivation of the surface provides SiNCs a monodispersity, hydrophobicity and physical stability. Second, physical and chemical characteristics of synthesized SiNCs are described based on the nanoparticle size and surface chemistry information measured by different techniques: transmission electron microscopy (TEM), X-ray energy dispersive spectroscopy (EDX), X-ray powder diffraction (XRD), dynamic light scattering (DLS), UV-VIS absorption spectroscopy (Abs), photoluminescence spectroscopy (PL), and Fourier Transform Infrared spectroscopy (FT-IR). Next, potential applications of SiNCs as a fluorescent nanolabel are highlighted by studying the covalent, multiple attachments of fluorescent SiNCs to the target biomolecules. Streptavidin is tagged by several SiNCs through covalent linkage while it retains its characteristic affinity to biotin molecules. SiNCs-Streptavidin-biotin complexes are characterized by FT-IR spectroscopy for each step of conjugation. SiNCs retain their brightness of blue fluorescence after the final conjugation with biotinylated microbeads. Finally, biological responses of SiNCs are assessed by in vitro assay experiments with murine macrophages. Cytotoxicity of SiNCs is not pronounced until their concentration reaches up to 20 µg/ml. Inflammatory responses of SiNCs are not activated because of their small size (< 5nm in diameter) which allows them pass through the macrophage's defense mechanism. SiNCs penetrate the macrophage cells by pinocytosis and are observed by fluorescence microscopy and optical Z-stacks. Presented studies on the synthesis, characterizations, bio-tagging, and biological responses of SiNCs will benefit research in broad areas of nano-bio science and facilitate the development of small, bright, biocompatible, and multifunctional nanolabels for biological applications

Assessment of Size-Dependent Antimicrobial and Cytotoxic Properties of Silver Nanoparticles

Nanoscale silver has been increasingly applied to commercial products for their antimicrobial function as antibiotics and disinfectants. In this work, the different sizes of silver nanoparticles (AgNPs) were studied not only in Methylobacterium spp. for their antimicrobial potential but also in human peripheral blood mononuclear cells (PBMCs) for their cytotoxicity in order to determine responses dependent on their particle size. Size controlled silver particles were prepared by chemical reduction of silver cations (Ag+) and then dispersed in water for their physicochemical characterization using transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta potential measurements. To ascertain antimicrobial response, water-soluble silver nanoparticles were mixed into Methylobacterium spp. cultured for two days and the sample from the broth was spread on the agar plate for colony counting. 10 nm nanoparticles showed more antimicrobial activity than 100 nm particles at which concentrations were equivalently controlled. Increased cytotoxic effect of smaller silver nanoparticles was also observed in PBMCs cocultured with particles. Silver ions released from 10 nm particles might be correlated with upregulated antimicrobial and cytotoxic properties of AgNPs

Poly (DL-lactide-co-glycolide) nanospheres with encapsulated selenium nanoparticles as a system with therapeutic functionality

Selenium (Se) is an essential trace element with important physiological functions and extensive pharmacological actions. The role of selenium as a chemopreventive and chemotherapeutic agent has been supported by a large number of epidemiological, preclinical, and clinical trials. Uniform, stable, amorphous selenium nanoparticles (SeNps) have been synthesized and additionally encapsulated within spherical PLGA particles (PLGA/SeNps). The morphology (size and shape) of the particles plays key role in their adhesion and interaction with the cell. Synthesized particles were characterized by FTIR spectroscopy, FESEM, TEM, HRTEM, and Zeta potential measurements. The influence of PLGA/SeNps on cell viability, ROS generation in HepG2 cells, as well as anticancer activity against epithelial tumor cells was investigated. As a part of this study, we have also performed in vivo dynamic imaging studies in normal mice, using SPECT imaging and a high resolution gamma camera. The PLGA/SeNps nanoparticles have been radiolabelled with Tc-99m, by applying the direct labeling method. Ex vivo biodistribution measurements, as well as in vivo dynamic studies up to 1h p.i. and at 24h were performed, showing increased concentration in liver and spleen

In vitro cell interaction and in vivo biodistribution of poly (dl-lactide-co-glycolide) nanospheres with encapsulated selenium nanoparticles for the treatment of liver diseases

The role of selenium as a chemopreventive and chemotherapeutic agent has been supported by a large number of epidemiological, preclinical, and clinical trials [1, 2] suggesting that anti-tumor effect mechanisms of selenium include induction of apoptosis, inhibition of cell proliferation, protection against oxidative stress, and stimulation of immune system. Herein we demonstrate a simple and quick synthesis of uniform, stable, amorphous selenium nanoparticles (SeNps), using ascorbic acid as the reduction agent. The choice of an appropriate stabilizer and reducing agent for preparation of stable selenium nanoparticles is very important. We used bovine serum albumin (BSA) as an organic layer for selenium nanoparticles, i.e., as a capping agent to make them more biocompatibile and protect them from agglomeration in the suspension medium. SeNps were additionally encapsulated within spherical PLGA particles (PLGA/SeNps). One of the most important requirements for the controlled and balanced release of the drug in the body is ideal spherical shape of the particles and narrow distribution of their sizes. The morphology (size and shape) of the particles plays key role in their adhesion and interaction with the cell. The influence of PLGA/SeNps on cell viability, ROS generation in HepG2 cells, as well as anticancer activity against epithelial tumor cells was investigated. Synthesized nanoparticles were characterized by FTIR spectroscopy, FESEM, TEM, HRTEM, and Zeta potential measurements. As a part of this study, we have also performed in vivo dynamic imaging studies in normal mice, using SPECT imaging and a high resolution gamma camera. The PLGA/SeNps nanoparticles have been radiolabelled with Tc-99m, by applying the direct labeling method [3]. Ex vivo biodistribution measurements, as well as in vivo dynamic studies up to 1h p.i. and at 24h were performed, showing increased concentration in liver and spleen. Acknowledgements This study was supported by the Ministry of Science and Technological Development of the Republic of Serbia, under Grant No. III45004: Molecular designing of nanoparticles with controlled morphological and physicochemical characteristics and functional materials based on them. Presented were the results of a study also supported by the COST Action TD1004. References 1. Popova, N. V. Cancer Lett. 2002, 179, 39–42. 2. Li, S.; Zhou, Y.; Wang, R.; Zhang, H.; Dong, Y.; Ip, C. Mol. Cancer Ther. 2007, 6, 1031–1038. 3. Psimadas, D.; Baldi, G.; Ravagli, C.; Bouziotis, P.; Xanthopoulos, S.; Francini, M.; Georgoulias, P.; Loudos, G.; J. Biom. Nan., 2012, 8, 4, 575-585

Mesoporous Silica-Coated Hollow Manganese Oxide Nanoparticles as Positive T1 Contrast Agents for Labeling and MRI Tracking of Adipose-Derived Mesenchymal Stem Cells

Mesoporous silica-coated hollow manganese oxide (HIVInO@ mSiO(2)) nanoparticles were developed as a novel T-1 magnetic resonance imaging (MRI) contrast agent. We hypothesized that the mesoporous structure of the nanopartide shell enables optimal access of water molecules to the magnetic core, and consequently, an effective longitudinal (R-1) relaxation enhancement of water protons, which value was measured to be 0.99 (mM(-1) s(-1)) at 11.7 T. Adipose-derived mesenchymal stem cells (MSCs) were efficiently labeled using electroporation, with much shorter T-1 values as compared to direct incubation without electroporation, which was also evidenced by signal enhancement on T-1-weighted MR images in vitro. Intracranial grafting of HMnO@mSiO(2)-labeled MSCs enabled serial MR monitoring of cell transplants over 14 days. These novel nanopartides may extend the arsenal of currently available nanoparticie MR contrast agents by providing positive contrast on T-1-weighted images at high magnetic field strengths.