Photoluminescent Silicon Nanoparticles Research Articles

Determination of Fe(Ⅲ) ion and cellular bioimaging based on a novel photoluminescent silicon nanoparticles

The determination approaches of Fe (Ⅲ) in biological samples were developed by a novel water-soluble silicon nanoparticles (SiNPs). The SiNPs were synthesized by a facile microwave-assisted method, and simultaneously featured strong blue fluorescence (photoluminescence quantum yield: 25.2%), long lifetime (~13.29 ns) and good photo-stability. The fluorescence intensities of SiNPs were gradually quenched with Fe (Ⅲ) concentration increasing from 2.0 to 50 μmol/L. The detection limit of the established method was 0.56 μmol/L and the precision for eleven replicate detections of 20 μmol/L Fe (Ⅲ) was 3.2% (relative standard deviation, RSD). The spiked recoveries were 99.0%–104.5%. Results of the lifetime decay and cyclic voltammetry (CV) evidenced that the electron transfer was responsible for the fluorescence quenching mechanism of SiNPs and Fe (Ⅲ). Moreover, the SiNPs were successfully applied in the determination of Fe(Ⅲ) in different environmental waters and human serum. Finally, the resulting SiNPs exhibited the green fluorescence in HeLa cells as the optical probe.

Photoluminescence of silicon nanoparticles under the action of infrared femtosecond laser pulses

We present the experimental results for the absorption spectra and photoluminescence of silicon nanoparticles synthesized by femtosecond laser ablation in distilled water under action of femtosecond laser pulses at a wavelength of 1048 nm with intensities in the range from 1010 to 1012 W/cm2.

Organic coating of 1–2-nm-size silicon nanoparticles: Effect on particle properties

Photoluminescent silicon nanoparticles 1–2 nm in size were synthesized by a wet chemical procedure and derivatized with propylamine (NH2SiNP). Surface NH2 groups were used as linkers for additional poly(ethylene glycol) (PEG) and folic acid (Fo) attachment (PEG-NHSiNP and Fo-NHSiNP, respectively) to enable efficient targeting of the particles to tumors and inflammatory sites. The particles were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, ζ potential, dynamic light scattering, and time-resolved anisotropy.The photophysical properties and photosensitizing capacity of the particles and their interaction with proteins was dependent on the nature of the attached molecules. While PEG attachment did not alter the photophysical behavior of NH2SiNP, the attachment of Fo diminished particle photoluminescence. Particles retained the capacity for 1O2 generation; however, efficient 1O2 quenching by the attached surface groups may be a drawback when using these particles as 1O2 photosensitizers. In addition, Fo attachment provided particles with the capacity to generate the superoxide anion radical (O −2 ).The particles were able to bind tryptophan residues of bovine serum albumin (BSA) within quenching distances. NH2SiNP and PEG–NHSiNP ground state complexes with BSA showed binding constants of (3.1 ± 0.3) × 104 and (1.3 ± 0.4) × 103 M−1, respectively. The lower value observed for PEG-NHSiNP complexes indicates that surface PEGylation leads to a reduction in protein adsorption, which is required to prevent opsonization. An increase in particle luminescence upon BSA binding was attributed to the hydrophobic environment generated by the protein. NH2SiNP-BSA complexes were also capable of resonance energy transfer.

Highly sensitive and selective detection of dopamine using one-pot synthesized highly photoluminescent silicon nanoparticles.

A simple and highly efficient method for dopamine (DA) detection using water-soluble silicon nanoparticles (SiNPs) was reported. The SiNPs with a high quantum yield of 23.6% were synthesized by using a one-pot microwave-assisted method. The fluorescence quenching capability of a variety of molecules on the synthesized SiNPs has been tested; only DA molecules were found to be able to quench the fluorescence of these SiNPs effectively. Therefore, such a quenching effect can be used to selectively detect DA. All other molecules tested have little interference with the dopamine detection, including ascorbic acid, which commonly exists in cells and can possibly affect the dopamine detection. The ratio of the fluorescence intensity difference between the quenched and unquenched cases versus the fluorescence intensity without quenching (ΔI/I) was observed to be linearly proportional to the DA analyte concentration in the range from 0.005 to 10.0 μM, with a detection limit of 0.3 nM (S/N = 3). To the best of our knowledge, this is the lowest limit for DA detection reported so far. The mechanism of fluorescence quenching is attributed to the energy transfer from the SiNPs to the oxidized dopamine molecules through Förster resonance energy transfer. The reported method of SiNP synthesis is very simple and cheap, making the above sensitive and selective DA detection approach using SiNPs practical for many applications.

Optical Properties of Silicon Nanoparticles Prepared by Laser Ablation Method in Various Media

Bright photoluminescent silicon nanoparticles were successfully fabricated from porous silicon target in air and n-hexane using 532 nm line of YAG:Nd pulsed laser. The whole procedure was carried out at room temperature, in atmosphere. The morphology and composition of as-synthesized nanoparticles were characterized by SEM and EDS measurements. Their optical properties were investigated. The PL peak position of the as-synthesized Si nanoparticle ablated in air is slightly blue-shifted in comparison with those ablated in n-hexane, while it was almost no change of peak position of Si nanoparticles fabricated from p-Si in hexane and original p-Si wafer target. In contrast to PL intensity quenching of original p-Si sample and particles produced in air, those produced in n-hexane solvent exhibited an enhancement. The presence of dangling bonds or energy transfer from excited Si particles to oxygen molecules on the surface can be the cause of the quenching effect.

Fabrication and Characterization of Photoluminescent Silicon Nanoparticles for Drug Delivery Applications

Photoluminescent silicon nanoparticles containing camptothecin (CPT) were fabricated by using a CPT-derivatized porous silicon (PSi). PSi samples displaying red photoluminescence (PL) were prepared by an electrochemical etch of n-type silicon under the illumination with a 300 W tungsten filament bulb for the duration of etch. For the drug-derivatized PSi, luminescent PSi was oxidized and derivatized with CPT. Silicon nanoparticles containing CPT were obtained by fracturing of luminescent PSi with ultrasono-method. Optical characteristic of drug-derivatized silicon particles were investigated in aqueous buffer solution. The release of CPT was measured by UV-vis spectrometer. The intensity of fluorescence of the silicon nanoparticles was measured with a drug release. The concentration of released drug exhibited non-linear relationship with a release time.

Synthesis of water-dispersible photoluminescent silicon nanoparticles and their use in biological fluorescent imaging

Water-dispersible silicon nanoparticles (Si-NPs) are desirable for applications in biological techniques. A simplified method to synthesize such particles is reported here. The resulting Si-NPs are water-dispersible and luminescent. Under the excitation of UV light, the Si-NPs emit strong red light with a peak maximum at 606 nm and a quantum yield of 6%. They are highly stable, and remain so over several weeks. Fourier Transform Infrared (FTIR) spectroscopy shows a visible Si–CH2 scissoring vibration mode. Furthermore, the surface chemical bondings were confirmed by X-ray photoelectron spectroscopy (XPS). In the Si2p and C1s core levels, Si–C components are observed. The diameters of the synthesized Si-NPS as measured by atomic force microscope (AFM) are approximately 5 nm. Furthermore, the nanoparticles can be taken up by cultured cells. Fluorescence images of Si-NPs within MCF-7 human breast cancer cells show they are distributed throughout the cell tissue.

脉冲激光烧蚀法制备硅纳米颗粒及其光致发光特征

脉冲激光烧蚀法制备硅纳米颗粒及其光致发光特征

脉冲激光烧蚀法制备硅纳米颗粒及其光致发光特征

脉冲激光烧蚀法制备硅纳米颗粒及其光致发光特征

Comparison of cytotoxic and inflammatory responses of photoluminescent silicon nanoparticles with silicon micron‐sized particles in RAW 264.7 macrophages

Photoluminescent silicon nanoparticles have a bright and stable fluorescence and are promising candidates for bio-imaging, cell staining and drug delivery. With increasing development of nanotechnology applications for biomedicine, an understanding of the potential toxicity of nanoparticles is needed to assess safety concerns for clinical applications. The objective of this study was to compare biological responses of silicon nanoparticles (SNs, 3 nm diameter) with silicon microparticles (SMs, approximately 100-3000 nm diameter) in cultured murine macrophages (RAW 264.7) using standard protocols for assessing cytotoxicity/cell viability and inflammatory responses developed for micron-sized particles. SNs and SMs were exposed to macrophages with and without addition of endotoxin lipopolysaccharide (LPS), a positive inducer of tumor necrosis factor-alpha (TNF-alpha), interleukin 6 (IL-6), and nitric oxide (NO). Cytotoxicity was assayed using the dye exclusion and MTT assays. Cell supernatants were assayed for production TNF-alpha, IL-6 and NO. SNs at concentrations < or = 20 microg ml(-1) exhibited no cytotoxicity or inflammatory responses; however, SNs and SMs >20 and 200 microg ml(-1), respectively, increased cytotoxicity compared with controls. SMs induced concentration-related increases in TNF-alpha and IL-6 production; in contrast, the production of these cytokines was shown to decrease with increasing concentrations of SNs. NO production was not induced by SNs or SMs alone. Fluorescence microscopy demonstrated that SNs were associated with the macrophages, either internalized or attached to cell membranes. In conclusion, evaluating differences in biological responses for nanoparticles compared with microparticles of the same material may help improve tests to assess biological responses of nanoparticles that may be used in biomedical applications.

Luminescent Silicon Nanoparticles Formed in Solution

This review focuses on the preparation of Si nanoparticles by wet-chemical routes. The methods described include dispersion from porous silicon, etching and surface functionalization of Si/SiO2 powders and direct chemical reaction of Si precursors. Photoluminescence of silicon nanoparticles can be tuned to cover the whole visible spectrum depending on particle size. The excitonic origin or nature of PL has been generally accepted. Some researchers observed exciton recombination across the direct band-gap, i.e., gamma-gamma transitions, while others evidenced indirect nature of excitonic radiative recombination, which becomes direct in very small particles of 1-2 nm. A large redshift of photoluminescence from these small silicon nanoparticles has been explained by a localized surface states model. Others argue that no localized states are found in the band-gap if a complete oxide shell is formed, and the photoluminescence redshift is due to modification of band-edge states.

Conjugation of the Photoluminescent Silicon Nanoparticles to Streptavidin

We have covalently attached multiple photoluminescent silicon nanoparticles (SNs) to streptavidin molecules. Conjugation of SNs to a target protein is achieved using the multistage photoassisted procedure. In a first step, the terminal hydrogen in the freshly prepared SNs is substituted with an alkane monolayer that serves as a platform for chemical linkage to a heterobifunctional cross-linker: 4-azido-2,3,5,6-tetrafluorobenzoic acid, succinimidyl ester. A resulting surface coating stabilizes nanoparticles against oxidation and aggregation. Next, an open end of bifunctional cross-linker-diazirine succinimidyl ester is reacted with carboxyl moieties of streptavidin and forms an amide bond. Gel and capillary electrophoresis of the SN-streptavidin complex demonstrated separate elution of the conjugation product and unreacted protein. Then, the number of SNs per protein molecule was determined by measuring complex charge variation by capillary electrophoresis. Conjugate functionality was tested by allowing it to interact with biotinylated polystyrene microbeads. Intense photoluminescence at carefully washed microbeads demonstrated selective binding of silicon nanoparticle bearing streptavidin to biotinylated microbeads. The high quantum yield of streptavidin-SN conjugate in combination with the small size and biocompatibility of silicon nanoparticles presents an attractive platform for the fluorescence labeling in diverse bioassays.

Propionic-Acid-Terminated Silicon Nanoparticles: Synthesis and Optical Characterization

Photoinitiated hydrosilylation was used to attach acrylic acid to the surface of photoluminescent silicon nanoparticles, thereby producing water-dispersible, propionic-acid-terminated particles. From transmission electron microscope (TEM) observations, the average diameters of the synthesized nanocrystals were 1.9−2.4 nm. It is likely that smaller particles (<1.5 nm) were also present but could not be imaged. As the nanocrystal size decreased, both the optical absorption edge and photoluminescence (PL) emission peak blue-shifted, whereas the photoluminescence excitation (PLE) spectrum changed very little and showed a sharp onset indicative of direct interband absorption at Γ. After prolonged ultrasonication in water, the Si nanoparticles showed strong blue PL. This can tentatively be attributed to the formation of radiative centers related to incomplete oxidation of the nanocrystals. The silicon nanocrystals could be transferred into water or methanol by dialysis without inducing this oxidation. The PA-terminated Si nanoparticles were stably dispersed in acrylic acid, water, and methanol and showed essentially the same optical properties in all three solvents. The approach used here provides a general means of producing water-dispersible silicon nanocrystals with size-dependent photoluminescence tunable over a wide range of the visible spectrum.

Efficient Surface Grafting of Luminescent Silicon Quantum Dots by Photoinitiated Hydrosilylation

We suggest a method for efficient (high-coverage) grafting of organic molecules onto photoluminescent silicon nanoparticles. High coverage grafting was enabled by use of a modified etching process that produces a hydrogen-terminated surface on the nanoparticles with very little residual oxygen and by carefully excluding oxygen during the grafting process. It had not previously been possible to produce such a clean H-terminated surface on free silicon nanoparticles or, subsequently, to produce grafted particles without significant surface oxygen. This allowed us to (1) prepare air-stable green-emitting silicon nanoparticles, (2) prepare stable dispersions of grafted silicon nanoparticles in a variety of organic solvents from which particles can readily be precipitated by addition of nonsolvent, dried, and redispersed, (3) separate these nanoparticles by size (and therefore emission color) using conventional chromatographic methods, (4) protect the particles from chemical attack and photoluminescence quenching, and (5) provide functional groups on the particle surface for further derivatization. We also show, using 1H NMR, that the photoinitiated hydrosilylation reaction does not specifically graft the terminal carbon atom to the surface but that attachment at both the first and second atom occurs.

Discovery of a Huge Young Stellar Object Interaction Region in Camelopardalis

During the course of a wide-field VI survey of galaxies in the IC 342/Maffei Group, a large nebula, which looks like an inclined disk with a jetlike plume emerging from it, was discovered in Camelopardalis. The object is most prominent in I. The predominating disk component is 68 across, which corresponds to 4.0 ± 1.6 pc at the estimated distance of 2.0 ± 0.8 kpc (the Perseus Arm). The plume extends 38 (2.2 pc) outward from the core along a direction that is about 20° from the minor axis of the disk. The disk lies along the edge of a filament of dust and molecular gas in the Milky Way. The plume points toward the core of the filament. No large-scale emission is seen at Hα, and the nebula is invisible in Two Micron All Sky Survey (2MASS) images. About 30'' from the center of the disk is IRAS 04261+6339, which is a pair of unresolved Hα sources whose IRAS colors and spectra reveal them to be young stellar objects (YSOs). The northern of the two exhibits a near-infrared tail, which is 15'' (0.15 pc) long in H and directed 66° away from the plume. Although the stars are exposed, as in Class II YSOs, the spectral energy distribution of the pair rises beyond 2 μm, typical of Class I systems. It appears that they are transitional YSOs, with characteristics similar to those of Holoea (IRAS 05327+3404). The total brightness of the plume plus disk exceeds that of the stars by 1.6 mag in I, yet the V-I color is bluer by only 0.50 mag. Thus, the nebula cannot be a consequence of reflection, even allowing for differential extinction. It is tentatively identified as a remnant of an outflow from a binary YSO, glowing from the photoluminescence of silicon nanoparticles.

Process for Preparing Macroscopic Quantities of Brightly Photoluminescent Silicon Nanoparticles with Emission Spanning the Visible Spectrum

Silicon nanoparticles with bright visible photoluminescence have been prepared by a new combined vapor phase and solution phase process, using only inexpensive commodity chemicals. CO2 laser induced pyrolysis of silane was used to produce Si nanoparticles at high rates (20−200 mg/h). Particles with an average diameter as small as 5 nm were prepared directly by this vapor phase (aerosol) synthesis. Etching these particles with mixtures of hydrofluoric acid (HF) and nitric acid (HNO3) reduced the size and passivated the surface of these particles such that after etching they exhibited bright visible luminescence at room temperature. The wavelength of maximum photoluminescence (PL) intensity was controlled from above 800 nm to below 500 nm by controlling the etching time and conditions. Particles with blue emission (maximum PL intensity at 420 nm) were prepared by rapid thermal oxidation of orange-emitting particles. The particle synthesis methods; steady-state photoluminescence spectra; results of their characterization using TEM, XRD, FTIR absorption spectroscopy, and XPS; and preliminary assessments of the stability of the photoluminescence properties with time are presented here. Preparation of macroscopic quantities by the methods described here opens the door to chemical studies of free silicon nanoparticles that could previously be carried out only on porous silicon wafers, as well as to potential commercial applications of silicon nanoparticles.