Luminescent Porous Silicon Research Articles

Hybrid luminescent porous silicon for efficient drug loading and release

In recent decades, biocompatible and light emitting porous silicon (pSi) showed the possibility for use in biomedical applications.

Domino-Like Intercellular Delivery of Undecylenic Acid-Conjugated Porous Silicon Nanoparticles for Deep Tumor Penetration.

Improving the intratumoral distribution of anticancer agents remains the critical challenge for developing efficient cancer chemotherapy. Luminescent porous silicon nanoparticles (PSiNPs) have attracted considerable attention in the biomedical field especially in drug delivery. Here, we described the lysosomal exocytosis-mediated domino-like intercellular delivery of undecylenic acid-conjugated PSiNPs (UA-PSiNPs) for deep tumor penetration. UA-PSiNPs with significantly improved stability in physiological conditions were internalized into tumor cells by macropinocytosis-, caveolae-, and clathrin-mediated endocytosis and mainly colocalized with Golgi apparatus and lysosomes. Substantial evidence showed that UA-PSiNPs was excreted from cells via lysosomal exocytosis after cellular uptake. The exocytosed UA-PSiNPs induced a domino-like infection of adjacent cancer cells and allowed encapsulated doxorubicin (DOX) to deeply penetrate into both three-dimensional tumor spheroids and in vivo tumors. In addition, DOX-loaded UA-PSiNPs exhibited strong antitumor activity and few side effects in vivo. This study demonstrated that UA-PSiNPs as a drug carrier might be applied for deep tumor penetration, offering a new insight into the design of more efficient delivery systems of anticancer drugs.

Porous silicon-graphene oxide core-shell nanoparticles for targeted delivery of siRNA to the injured brain.

We report the synthesis, characterization, and assessment of a nanoparticle-based RNAi delivery platform that protects siRNA payloads against nuclease-induced degradation and efficiently delivers them to target cells. The nanocarrier is based on biodegradable mesoporous silicon nanoparticles (pSiNPs), where the voids of the nanoparticles are loaded with siRNA and the nanoparticles are encapsulated with graphene oxide nanosheets (GO-pSiNPs). The graphene oxide encapsulant delays release of the oligonucleotide payloads in vitro by a factor of 3. When conjugated to a targeting peptide derived from the rabies virus glycoprotein (RVG), the nanoparticles show 2-fold greater cellular uptake and gene silencing. Intravenous administration of the nanoparticles into brain-injured mice results in substantial accumulation specifically at the site of injury.

Porous silicon nanoparticles as efficient sensitizers for sonodynamic therapy of cancer

Luminescent porous silicon nanoparticles with mean size of about 100 nm were covered by biodegradable polymer (dextran) and were investigated as potential sensitizers for ultrasound-assisted therapy. Luminescent confocal microscopy revealed an efficient uptake of the nanoparticles by cancer cells in vitro. The nanoparticles were found to be almost nontoxic up to the concentration of 0.1 mg/mL and doses of 30 mg/kg as it was confirmed by in vitro and in vivo experiments, respectively. A strong suppression of the cancer cell proliferation was observed after a combined treatment by the nanoparticles and therapeutic ultrasound irradiation with frequencies of 1–3 MHz and intensities of 1–2 W/cm2. The obtained results are discussed in view of potential applications of biocompatible and biodegradable silicon-based nanoparticles in sonodynamic therapy of cancer.

Colloidal solutions of luminescent porous silicon clusters with different cluster sizes.

Silicon nanocrystals (Si-ncs) are promising for biological studies due to their supposed low cytotoxicity, good biocompatibility and biodegradability in living organisms. However, the bioresearchers' focus on Si-ncs has lasted only for a few recent years, and detailed studies of the interaction of various types of Si-ncs with biological environment are still rare. Suitable size and solubility of the Si-ncs in water-based isotonic solutions are important towards bringing the nanocrystals inside the living cells. We have prepared colloidal solutions of luminescent porous silicon of different cluster sizes in methanol, water and phosphate-buffered saline (PBS). By combination of ultrasonic treatment with filtration, we have obtained two different silicon cluster sizes in methanol (120 and 525 nm) and three different cluster sizes (85, 210 and 1,500 nm) in PBS. Nanoclusters of heavily oxidized porous silicon are hydrophilic and well soluble in water and/or PBS. They can be further used for studies on the biocompatibility of these materials and may be potentially employed as luminescent markers in living cells in biological research.PACS78.67.Rb; 78.67.-n; 87.85.Qr; 87.85.Rs; 81.07.-b

Luminescent porous silicon prepared by reactive ion etching

Realization of luminescent porous silicon structures by a sequential reactive ion etching is reported. The process is composed of one etching and two passivation subsequences. The impact of substrate resistivity, plasma power and the duration of the etching subsequence on the porosity and thickness of the fabricated porous silicon layer are investigated, as are the roles of two passivation subsequences. The porous silicon layer shows stable photoluminescence in the blue portion of the spectrum. Luminescence stability is due to the stable passivating oxyfluoride layer formed in the two passivation subsequences. Formation of the stable passivating layer is due to the controlled oxidation of the porous silicon surface and the passivation of the dangling bonds in the fluorination subsequence. Since the fabrication process is performed at room temperature, it can be used as a post-fabrication treatment to integrate light-emitting structures with microelectronic circuits.

Photoluminescent Porous Si/SiO2 Core/Shell Nanoparticles Prepared by Borate Oxidation

A systematic study on the activation of photoluminescence from luminescent porous silicon nanoparticles (LPSiNPs) by oxidation in aqueous media containing sodium tetraborate (borax) is presented. The treatment promotes surface oxidation of the porous silicon skeleton and consequently generates an electronically passivated material. Photoluminescence is ascribed to quantum confinement effects and to defects localized at the Si‐SiO2 interface, and the strong photoluminescence is attributed to passivation of nonradiative surface defects. The oxidation treatment (carried out at 20 °C) generates a gradual blue shift of the photoluminescence peak wavelength (from 800 nm to 630 nm), while the bandwidth remains relatively constant (≈210 nm). During the treatment period, the external quantum yield (λex = 365 nm) of photoluminescence increases to a maximum value of 23% after 200 min, and then it decreases at longer treatment times. The decrease in photoluminescence intensity at longer times is attributed to degradation and dissolution of the nanoparticles, which is inhibited at higher nanoparticle concentrations or by addition of free silicic acid.

Formation of Luminescent Silicon Nanowires and Porous Silicon by Metal-Assisted Electroless Etching

Metal-assisted etching of silicon in HF/H2O2 aqueous solutions has been used to fabricate luminescent silicon nanowires (SiNWs) and porous silicon. The impact of the gold catalyst layer thickness and the etching solution on the morphology of the synthesized nanostructures and the diameter of the obtained nanowires were systematically investigated. Scanning electron microscopy (SEM) analyses reveal that the morphology of the fabricated structures strongly depends on the composition of the solution and the thickness of the catalyst layer. It has been observed that SiNWs are formed in solutions with H2O2 ratios (ξ) below 10 %; increasing the H2O2 concentration above this critical value leads to mesoporous (10 % < ξ < 14 %) and macroporous (14 % < ξ < 17 %) structures. Photoluminescence measurements show that SiNWs emit light at about 430 nm. Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) analyses were utilized to determine the origin of the emission in the silicon nanostructures. TEM imaging demonstrates that SiNWs are covered by a thin layer of porous silicon, which is assumed to be responsible for their light emission.

Radiative and nonradiative relaxation phenomena in hydrogen- and oxygen-terminated porous silicon

Using time-resolved photoluminescence spectroscopy over a wide range of temperatures, we were able to probe both radiative and nonradiative relaxation processes in luminescent porous silicon. By comparing the photoluminescence decay times from freshly prepared and oxidized porous silicon, we show that radiative processes should be linked with quantum confinement in small Si nanocrystallites and are not affected by oxidation. In contrast, nonradiative relaxation processes are associated with the state of oxidation where slower relaxation times characterize hydrogen-terminated porous silicon. These results are in a good agreement with the extended vibron model for small Si nanocrystallites.PACS78.55.Mb; 78.67.Rb; 78.47.jd

Comparative Study on Electronic, Emission, Spontaneous Property of Porous Silicon in Different Solvents

Luminescent porous silicon (Psi) fabricated by simple chemical etching technique in different organic solvents was studied. By quantifying the silicon wafer piece, optical properties of the Psi in solutions were investigated. Observation shows that no photoluminescence light of Psi in all solvents is emitted. Morphology of Psi in different solvents indicates that the structure and distribution of Psi are differently observed. Particles are uniformly dispersive with the sizes around more or less 5–8 nm. The crystallographic plane and high crystalline nature of Psi is observed by selected area diffraction (SED) and XRD. Electronic properties of Psi in solutions are influenced due to the variation of quantity of wafer and nature of solvent. Influence in band gaps of Psi calculated by Tauc’s method is obtained due to change of absorption edge of Psi in solvents. PL intensities are observed to be depending on quantity of silicon wafer, etched cross‐section area on wafer surface. Effects on emission peaks and bands of Psi under temperature annealing are observed. The spontaneous signals of Psi measured under high power Pico second laser 355 nm source are significant, influenced by the nature of solvent, pumped energy, and quantity of Si wafer piece used in etching process.

Optical and electrical properties of porous silicon impregnated with Congo Red dye

Incorporation of molecules into porous silicon (PS) matrix is of particular interest for potential utilization in hybrid organic-semiconductor devices. In this study, the incorporation of Congo Red molecules inside luminescent PS layers was investigated. The resulting structures have been characterized by Fourier Transformer Infrared (FTIR) and photoluminescence (PL) techniques. Based on these characterizations, the infiltration of dye molecules into the porous matrix has been proved. The recuperated PL signal was more important than that of porous silicon alone. A nonradiative excitation transfer due to dipolar interactions was evidenced from the effect of the CR concentration on the PL emission which was also confirmed by FTIR spectroscopy. It was found that the formed composite displays an efficient and stable PL. Preliminary characterizations of the electrical properties of the resulting nanocomposite structure have been also performed. The current–voltage (I–V) characteristics of CR-PS/p-Si were measured at the room temperature (300 K). To study the effect of illumination on CR-PS/p-Si composites, the measurement has been performed in dark and under illumination, at room temperature. The diode characteristics including zero-bias barrier height (ΦB0), ideality factor (n), and series resistance (Rs) were calculated at room temperature in dark and under illumination. The obtained results have shown that these characteristics are largely affected by illumination. The incorporation of dye molecules in porous silicon matrix enhanced photovoltaic properties of resulting structures.

Engineered Stealth Porous Silicon Nanoparticles via Surface Encapsulation of Bovine Serum Albumin for Prolonging Blood Circulation in Vivo

Luminescent porous silicon nanoparticles (PSiNPs) have been widely used as drug delivery. However, fast biodegradation and short blood circulation have been major challenges for their biomedical applications. Herein, bovine serum albumin was readily encapsulated onto alkyl-terminated PSiNPs surfaces via hydrophobic interaction, which could significantly improve their water-dispersibility and long-term stability under physiological conditions. Furthermore, compared with PSiNPs alone, PSiNPs coated with bovine serum albumin remarkably reduced nonspecific cellular uptake in vitro and prolonged blood circulation in vivo.

Porous silicon photoluminescence modification by colloidal gold nanoparticles: Plasmonic, surface and porosity roles

Metal nanoparticles on semiconductors are of interest because of the tunable effect of the surface plasmon resonance on the physical properties of the semiconductor. In this work, colloidal gold nanoparticles obtained by two different methods, with an average size of 6.1±2.0nm and 5.0±2.0nm, were added to luminescent porous silicon by drop casting. The gold nanoparticles interact with porous silicon by modifying its optical properties such as photoluminescence. That being said, plasmon effects are not the only to be taken into account; as shown in this work, surface chemical modification and porosity also play a key role in the final performance of photoluminescence of a porous silicon–gold nanoparticle hybrid system.

In vivo time-gated fluorescence imaging with biodegradable luminescent porous silicon nanoparticles

Fluorescence imaging is one of the most versatile and widely used visualization methods in biomedical research. However, tissue autofluorescence is a major obstacle confounding interpretation of in vivo fluorescence images. The unusually long emission lifetime (5-13 μs) of photoluminescent porous silicon nanoparticles can allow the time-gated imaging of tissues in vivo, completely eliminating shorter-lived (< 10 ns) emission signals from organic chromophores or tissue autofluorescence.Here, using a conventional animal imaging system not optimized for such long-lived excited states, we demonstrate improvement of signal to background contrast ratio by > 50-fold in vitro and by > 20-fold in vivo when imaging porous silicon nanoparticles. Time-gated imaging of porous silicon nanoparticles accumulated in a human ovarian cancer xenograft following intravenous injection is demonstrated in a live mouse. The potential for multiplexing of images in the time domain by using separate porous silicon nanoparticles engineered with different excited state lifetimes is discussed.

Optical and structural characterization of tungsten oxide electrodeposited on nanostructured porous silicon: Effect of annealing atmosphere and temperature

Optical and structural properties of tungsten oxide (WO3), electrodeposited on luminescent nanostructured porous silicon (PS) have been investigated as a function of annealing atmosphere and temperature. Physical and optical properties of WO3/PS hybrid structures were analyzed using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and photoluminescence (PL) spectroscopy. Our experimental results reveal that evolution of PL peak, corresponding to band edge emission of WO3, increases with annealing temperature under nitrogen atmosphere in contrast with air atmosphere. Rectifying behavior of WO3/PS structures exhibits a decrease by a factor of approximately 7 in the annealed sample as compared to as deposited samples under nitrogen conditions. Such composites have potential applications in diodes technology as well as in improving sensing/catalytic performance of WO3.

Hydrogen in porous silicon — A review

a b s t r a c t This review is devoted to summarising the hydrogen-assisted properties and applications of porous silicon (PS). The role of hydrogen as an intermediate product in silicon porosification technology is accentuated. The regularities of hydrogen bonding in PS and its applications for hydrogen storage are listed. The models of hydrogen influence on luminescence and electrical properties of PS are analysed. The corresponding applications of PS for H2 gas sensors and pH metres are illustrated. Hydrogen-assisted explosion and grafting of PS are discussed. Such a review can be useful for the tailoring of PS properties.

Photoluminescence From Oxidized Macroporous Silicon: Nanoripples and Strained Silicon Nanostructures

We report synthesis of luminescent porous silicon (Si) having uniform macromorphology by sequential oxidation and etching of macroporous Si formed in a hydrofluoric acid and dimethylformamide solution. The macroporous template exhibits room-temperature photoluminescence (PL) with peaks in the blue/green region. Structural investigations reveal the formation of nanoripples and other strained nanostructured Si inside the pores of the oxidized samples. The room-temperature PL disappears, and the structure of the macropores changes on treating the oxidized templates with an alkaline solution. Based on these findings, we explicitly show that the origin of luminescence is due to the presence of nanoripples and strained Si nanostructures. Luminescent macroporous Si therefore reveals interesting physics but are untenable for application of light sources in optoelectronic devices.

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.

Fluorescence quenching in luminescent porous silicon nanoparticles for the detection of intracellular Cu2+

After microwave-induced hydrosilylation reaction with 10-undecenoic acid, luminescent porous silicon nanoparticles (LPSiNPs) showed excellent fluorescence stability under physiological conditions. Fluorescence quenching in as-prepared LPSiNPs was highly sensitive with the concentration of Cu(2+) at μmol L(-1) level, which could be further applied to the detection of intracellular Cu(2+).

Photoluminescence enhancement of porous silicon particles by microwave‐assisted activation

AbstractPhotoluminescence (PL) of porous silicon (PSi) particles can be significantly enhanced in some organic solvents (i.e., ethanol or dimethyl sulfoxide) under microwave irradiation. Fourier transform infrared spectra, dynamic‐light‐scattering measurements, and scanning electron microscopy had been adopted to explore the mechanism of PL enhancement of PSi particles under microwave irradiation, which is attributed to the formation of higher porosity and the growth of silicon oxide by microwave‐assisted wet etching. Compared with that fabricated by ultrasonication, smaller luminescent PSi nanoparticles (average size ∼60 nm) with stronger orange‐red fluorescence (PL quantum yield ∼14.8%) and higher dispersibility can be large‐scale prepared for cellular imaging and drug delivery in biomedical applications.