pSi Surface Research Articles

Novel development of laser synthesized double orthogonal PSi surface NH3 gas sensors

Novel development of laser synthesized double orthogonal PSi surface NH3 gas sensors

Biomimetic Inorganic Nanovectors as Tumor-Targeting Theranostic Platform against Triple-Negative Breast Cancer.

Mesoporous silicon nanoparticles (PSi NPs) are promising platforms of nanomedicine because of their good compatibility, high payload capacities of anticancer drugs, and easy chemical modification. Here, PSi surfaces were functionalized with bisphosphonates (BP) for radiolabeling, loaded with doxorubicin (DOX) for chemotherapy, and the NPs were coated with cancer cell membrane (CCm) for homotypic cancer targeting. To enhance the CCm coating, the NP surfaces were covered with polyethylene glycol prior to the CCm coating. The effects of the BP amount and pH conditions on the radiolabeling efficacy were studied. The maximum BP was (2.27 wt%) on the PSi surfaces, and higher radiochemical yields were obtained for 99mTc (97% ± 2%) and 68Ga (94.6% ± 0.2%) under optimized pH conditions (pH = 5). The biomimetic NPs exhibited a good radiochemical and colloidal stability in phosphate-buffered saline and cell medium. In vitro studies demonstrated that the biomimetic NPs exhibited an enhanced cellular uptake and increased delivery of DOX to cancer cells, resulting in better chemotherapy than free DOX or pure NPs. Altogether, these findings indicate the potential of the developed platform for cancer treatment and diagnosis.

Porous silicon surface modification via a microwave-induced in situ cyclic disulfide (S-S) cleavage and Si-S bond formation

Porous silicon (pSi) materials have gained a great deal of attention from various research fields, and their surface-functionalization is one of the critical points for their applications. In this study, a new surface modification method of Si-H-terminated pSi materials via microwave-induced Si-S bond formation is disclosed. The silicon hydride (Si−H) functionality on the pSi surface could react with the 5-membered cyclic disulfide (S-S) compound (DL-α-lipoic acid in this study) by microwave-induced in situ S-S bond cleavage and Si-S bond formation. This surface chemistry is fast responsive (<10 min) and more efficient than other methods such as vortexing, heating stirring, or ultrasonication. The reaction maintains the primary porous structure of pSi materials including pSi wafer, pSi rugate filer, and pSi nanoparticles. An additional functional group such as carboxylic acid is demonstrated to be readily introducible on the pSi surface for further applications. Overall, this study has successfully demonstrated the porous silicon surface modification via a microwave-induced in situ cyclic disulfide (S-S) cleavage and Si-S bond formation.

Nanostructured Silicon Enabled HR-MS for the Label-Free Detection of Biomarkers in Colorectal Cancer Plasma Small Extracellular Vesicles

Despite improvements in treatment options for advanced colorectal cancer (CRC), survival outcomes are still best for patients with non-metastasised disease. Diagnostic tools to identify blood-based biomarkers and assist in CRC subtype classification could afford a means to track CRC progression and treatment response. Cancer cell-derived small extracellular vesicles (EVs) circulating in blood carry an elevated cargo of lipids and proteins that could be used as a signature of tumour suppressor/promoting events or stages leading up to and including metastasis. Here, we used pre-characterised biobanked plasma samples from surgical units, typically with a low volume (~100 µL), to generate and discover signatures of CRC-derived EVs. We employed nanostructured porous silicon (pSi) surface assisted-laser desorption/ionisation (SALDI) coupled with high-resolution mass spectrometry (HR-MS), to allow sensitive detection of low abundant analytes in plasma EVs. When applied to CRC samples, SALDI-HR-MS enabled the detection of the peptide mass fingerprint of cancer suppressor proteins, including serine/threonine phosphatases and activating-transcription factor 3. SALDI-HR-MS also allowed the detection of a spectrum of glycerophospholipids and sphingolipid signatures in metastatic CRC. We observed that lithium chloride enhanced detection sensitivity to elucidate the structure of low abundant lipids in plasma EVs. pSi SALDI can be used as an effective system for label-free and high throughput analysis of low-volume patient samples, allowing rapid and sensitive analysis for CRC classification.

Preparation high quality ethanol gas sensor by modifying porous silicon (PS) surface with carbon nanotube (CNTs)

In the study, the high-quality gas sensor for ethanol was prepared by modified porous silicon (PS) with a thin layer of carbon nanotube. The PSi samples have been prepared by using the photoelectrochemical etching (PECE) process at various current densities J = 12, 24, and 30 mA/cm2 with 10 min etching time and Hydrofluoric acid concentration (HFC) of 40%. All samples (PSi and MWCNTs/PSi) were analyzed using X-ray diffraction (XRD), field emission Scanning electron microscopy (FE-SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Atomic Force Microscopic (AFM), to determine the structural, morphological, and surface bond configuration. As a result, the Photoluminescence (PL) test was performed on all samples using the PL system in order to calculate the energy band gap for all samples. Then the PSi and MWCNTs/PSi samples were applied as ethanol gas sensor at room temperature (RT). The results showed that the best sensitivity of ethanol gas was about (2.1912349) at a concentration of 500 parts per million (ppm) for MWCNTs/PSi sample compared to PSi surface, it was about (1.709) under the same used conditions at etching current density 30 mA/cm2. The MWCNTs/PSi layers serve as low-cost and high-quality ethanol gas sensors. The carbon nanotube used to replace expensive materials used in gas sensors that function at low temperatures, including room temperature. The materials have an exceptionally high surface-to-volume ratio (increasing surface area), ease of fabrication, and compatibility with silicon microelectronics manufacturing processes.

Trace level detection of explosives and pesticides using robust, low-cost, free-standing silver nanoparticles decorated porous silicon.

We report results from our extensive studies on the fabrication of ultra-thin, flexible, and cost-effective Ag nanoparticle (NP) coated free-standing porous silicon (FS-pSi) for superior molecular sensing. The FS-pSi has been prepared by adopting a simple wet-etching method. The deposition time of AgNO3 has been increased to improve the number of hot-spot regions, thereby the sensing abilities are improved efficiently. FESEM images illustrated the morphology of uniformly distributed AgNPs on the pSi surface. Initially, a dye molecule [methylene blue (MB)] was used as a probe to evaluate the sensing capabilities of the substrate using the surface-enhanced Raman scattering (SERS) technique. The detection was later extended towards the sensing of two important explosive molecules [ammonium nitrate (AN), picric acid (PA)], and a pesticide molecule (thiram) clearly demonstrating the versatility of the investigated substrates. The sensitivity was confirmed by estimating the analytical enhancement factor (AEF), which was ∼107 for MB and ∼104 for explosives and pesticides. We have also evaluated the limit of detection (LOD) values in each case, which were found to be 50 nM, 1 µM, 2 µM, and 1 µM, respectively, for MB, PA, AN, and thiram. Undeniably, our detailed SERS results established excellent reproducibility with a low RSD (relative standard deviation). Furthermore, we also demonstrate the reasonable stability of AgNPs decorated pSi by inspecting and studying their SERS performance over a period of 90 days. The overall cost of these substrates is attractive for practical applications on account of the above-mentioned superior qualities.

Influence of magnetic field on the characteristics of n-type PSi prepared by photo-electro-chemical etching process

The surface uniformity of porous silicon (PSi) morphologies will enhance the overall properties of the PSi layer. In this study, the role of perpendicular magnetic field (MF) on structural, optical, and electrical properties of (PSi) substrates are reported. The (PSi) is prepared with a photo-electrochemical etching process in the front-side illumination pathway with and without a perpendicular magnetic field (MF). The application of (MF) on the path of the electric charge carrier leads to modify the morphologies of PSi surface. The pores shape, sizes, orientation, and homogeneity, and electrical properties will vary with the (MF). The role of (MF) will contribute to an increase in the number of pores and decrease the overlapping process. And also, promotes the orientation of the relatively more defined pores across the Psi surface. The observed noticeable changes in PL spectra, electrical properties, and charge carrier transport mechanisms may be owing to the surface reconstruction process. The influence of (MF) on the characteristics of Au thin layer / PSi/c-Si/Al structures will lead to converting its behavior from the resistor to Schottky-like junction.

Recent advances in surface engineering of porous silicon nanomaterials for biomedical applications

Surface engineering of the nanomaterials opens a new era of their biomedical applications. To date, various kinds of nanoparticles and their surface engineering techniques have been developed and applied to drug-delivery systems, bio-imaging, sensors, disease diagnosis, and therapy. Among them, nanostructured porous silicon (pSi) materials have been highlighted due to their unique properties in the biological system. This review focuses on the recent advances in surface engineering of porous silicon nanoparticles (pSiNPs) from a chemistry viewpoint. Conventional surface functionalization strategies and fabrication methods for pSiNPs are outlined with a schematic map, followed by the recently developed new techniques to maximize the properties of pSiNPs and overcome the drawbacks of known methods. New chemical reagents and chemical reactions for the surface engineering of pSiNPs are the main focus covered in this review. We also described the new approaches of polymer hybridization. Finally, the current status of pSi surface engineering, its future prospects, and challenges in biomedical applications are discussed. Conventional and recent advances in surface engineering methods of porous silicon nanomaterials are summarized. • A general overview of porous silicon nanoparticles and a brief introduction of surface engineering are introduced. • Conventional and recent advances in surface engineering methods of porous silicon nanomaterials with their representative biomedical applications are comprehensively summarized. • Promising porous silicon nanoparticles' prospects and their potential within biomedical fields (targeted DDS, controlled drug release, multi-functional ability) are covered.

Impact of Mesoporous Silicon Template Pore Dimension and Surface Chemistry on Methylammonium Lead Trihalide Perovskite Photophysics

AbstractIn influencing fundamental properties—and ultimately device performance—of lead halide perovskites, interfacial interactions play a major role, notably with regard to carrier diffusion and recombination. Here anodized porous Si (pSi) as well as porous silica particles are employed as templates for formation of methylammonium lead trihalide nanostructures. This allows synthesis of relatively small perovskite domains and comparison of associated interfacial chemistry between as‐prepared hydrophobic hydrideterminated functionalities and hydrophilic oxide‐terminated surfaces. While physical confinement of MAPbBr3 has a uniform effect on carrier lifetime, pore size (7–18 nm) of the silicon‐containing template has a sensitive influence on perovskite photoluminescence (PL) wavelength maximum. Furthermore, identity of the surface functionality of the template significantly alters the PL quantum efficiency, with lowest PL intensity associated with the H‐terminated pSi and the most intense PL affiliated with the oxideterminated pSi surface. These effects are explored for green‐emitting MAPbBr3 as well as infrared‐emitting MAPbI3. In addition, the role of silicon surface chemistry on the time‐dependent stability of these perovskites packaged within a given mesoporous template is also evaluated, specifically, a lack of miscibility between MAPbI3 and the H‐terminated pSi template results in a diffusion of this specific perovskite composition eluting from this porous matrix over time.

Dark and photocurrent response of porous Si/GO-PANI and Si/rGO-PANI heterojunctions for photovoltaics applications

Abstract Porous silicon (pSi) surface enhances light trapping in which improves the silicon solar cell performance. Metal assisted chemical etching (MaCE) technique was used to synthesize pSi. The pSi heterojunction with graphene oxide (GO), reduced graphene oxide (rGO), GO-polyaniline(PANI) and rGO-PANI was fabricated and characterized with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) to investigate chemical bonding, structural and morphological properties respectively. The FTIR signature at around 1300, 1500, and 1600 cm−1 confirmed the signature of C–C stretching vibrations, C = C stretching of the benzenoid ring, and C = N stretching for the quinoid ring in pSi/rGO-PANI heterojunction. The dark and photocurrent of current–voltage (IV) characteristics showed the Schottky behavior was highest for Si/rGO-PANI. Moreover, pSi/rGO-PANI heterojunction showed the highest photosensitivity and photoresponsivity values of 58.92 and 1.25 mAW−1 respectively.

Porous Silicon Fabrication and Surface Cracking Behavior Research Based on Anodic Electrochemical Etching▴

AbstractPorous silicon (PSi) was fabricated based on anodic electrochemical etching, and the relationship between preparation conditions, nanostructure and PSi surface crack behavior were systematically studied. The effects of silicon wafer resistivity (doping concentration), etching time, and etching current density on nanostructure of PSi were investigated. Results indicated that lower resistivity was beneficial to etching process and led to higher porosity with uniform nano‐channels, and surface crack was more intense during drying process. Thickness and porosity of the porous layer are both initially increased and then decreased with increasing etching time. Direction of capillary stress depended on pore geometry, which further affected crack shape (shrinkage or crimp) of surface layer of PSi. Cracking extent was controlled by porosity, that the surface cracking layer began to peel off when the porosity exceeded 70%. Finally, a geometry and porosity‐controlled model was proposed to describe the cracking behaviors of PSi surface layer.

Controlling and Predicting the Dissolution Kinetics of Thermally Oxidised Mesoporous Silicon Particles: Towards Improved Drug Delivery

Porous silicon (pSi) continues to receive considerable interest for use in applications ranging from sensors, biological scaffolds, therapeutic delivery systems to theranostics. Critical to all of these applications is pSi degradation and stabilization in biological media. Here we report on progress towards the development of a mechanistic understanding for the dissolution behavior of native (unoxidized) and thermally oxidized (200–600 °C) pSi microparticles. Fourier transform infrared (FTIR) spectroscopy was used to characterize the pSi surface chemistry after thermal oxidation. PSi dissolution was assessed using a USP method II apparatus by monitoring the production of orthosilicic acid, and the influence of gastro-intestinal (GI) fluids were examined. Fitting pSi dissolution kinetics with a sum of the exponential model demonstrated that the dissolution process strongly correlates with the three surface hydride species and their relative reactivity, and was supported by the observed FTIR spectral changes of pSi during dissolution. Finally, the presence of GI proteins was shown to hamper pSi dissolution by adsorption to the pSi surface acting as a barrier preventing water attack. These findings are significant in the optimal design of pSi particles for oral delivery and other controlled drug delivery applications.

Long duration stabilization of porous silicon membranes in physiological media: Application for implantable reactors.

The natural biodegradabilty of porous silicon (pSi) in physiological media limits its wider usage for implantable systems. We report the stabilization of porous silicon (pSi) membranes by chemical surface oxidation using RCA1 and RCA2 protocols, which was followed by a PEGylation process using a silane-PEG. These surface modifications stabilized the pSi to allow a long period of immersion in PBS, while leaving the pSi surface sufficiently hydrophilic for good filtration and diffusion of several biomolecules of different sizes without any blockage of the pSi structure. The pore sizes of the pSi membranes were between 5 and 20 nm, with the membrane thickness around 70 μm. The diffusion coefficient for fluorescein through the membrane was 2 × 10-10 cm2 s-1, and for glucose was 2.2 × 10-9 cm2 s-1. The pSi membrane maintained that level of glucose diffusion for one month of immersion in PBS. After 2 months immersion in PBS the pSi membrane continued to operate, but with a reduced glucose diffusion coefficient. The chemical stabilization of pSi membranes provided almost 1 week stable and functional biomolecule transport in blood plasma and opens the possibility for its short-term implantation as a diffusion membrane in biocompatible systems.

Efficient SnO2/CuO/porous silicon nanocomposites structure for NH3 gas sensing by incorporating CuO nanoparticles

In this paper, a porous silicon (Psi) surface modification process, including the incorporating of pure and CuO mixed SnO2 within a Psi layer, was investigated. A Psi layer with a pore-like structure prepared via laser-assisted etching process with a laser illumination intensity of (40) mW/cm2 was employed as a substrate for materialization SnO2/CuO/Psi nanocomposites for gas sensing application. Pure SnO2 and SnO2:CuO nanoparticles were synthesized via a chemical spray pyrolysis process on the Psi surface at 350 °C. The materialization of SnO2:CuO/Psi nanocomposites were recognized through Field-Emission Scanning Electron Microscopy, X-ray Diffraction, Atomic Force Microscopy, and Energy-dispersive X-ray Analysis. The results displayed that the morphological properties of SnO2:CuO nanoparticles were definitely controlled by varying the CuO contents. Different shapes (nearly cubic shape and spherical shape) with various sizes of SnO2 and SnO2:CuO within the Psi surface were achieved by increasing the CuO content. SnO2:CuO/Psi nanocomposites, plans, grain size, average surface roughness, homogeneity and specific surface area of SnO2:CuO nanoparticles were considerably influenced by CuO content. The lower grain size and higher average surface roughness and specific surface area were attained when the percentage of CuO was about 30% within the structure of 70% SnO2:30% CuO, and the performance of the NH3 gas sensor revealed a short response time with a high sensitivity of (88%).

Oral Curcumin via Hydrophobic Porous Silicon Carrier: Preparation, Characterization, and Toxicological Evaluation In Vivo.

Curcumin has antioxidant, anti-inflammatory, antimicrobial, and anticarcinogenic activities. However, the clinical application of curcumin has been restricted by the poor water solubility and low bioavailability of this molecule. In this work, hydrophobic porous silicon (pSi) particles were prepared by electrochemical etching method and grafted with the different hydrophobic groups on their surfaces. The loading efficiency of curcumin in pSi has been investigated. The properties of pSi particles have been characterized by scanning electron microscopy (SEM) and Fourier transform-infrared spectroscopy (FTIR). The highest loading efficiency of curcumin can be obtained with pSi surface modified with the octadecyl silane group. The release properties of curcumin in hydrophobic pSi have been researched in vitro and in vivo. The curcumin in the hydrophobic pSi surface keeps a high antioxidant bioactivity. The toxicological evaluation of the hydrophobic pSi particles indicates they have a high in vivo biocompatibility within the observed dose ranges. The hydrophobic pSi particles could provide an effective and controlled release delivery carrier for curcumin, which may provide a new tool platform for the further development of curcumin.

Spatially Controlled Surface Modification of Porous Silicon for Sustained Drug Delivery Applications

A new and facile approach to selectively functionalize the internal and external surfaces of porous silicon (pSi) for drug delivery applications is reported. To provide a surface that is suitable for sustained drug release of the hydrophobic cancer chemotherapy drug camptothecin (CPT), the internal surfaces of pSi films were first modified with 1-dodecene. To further modify the external surface of the pSi samples, an interlayer was applied by silanization with (3-aminopropyl)triethoxysilane (APTES) following air plasma treatment. In addition, copolymers of N-(2-hydroxypropyl) acrylamide (HPAm) and N-benzophenone acrylamide (BPAm) were grafted onto the external pSi surfaces by spin-coating and UV crosslinking. Each modification step was verified using attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, water contact angle (WCA) measurements, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). In order to confirm that the air plasma treatment and silanization step only occurred on the top surface of pSi samples, confocal microscopy was employed after fluorescein isothiocyanate (FITC) conjugation. Drug release studies carried out over 17 h in PBS demonstrated that the modified pSi reservoirs released CPT continuously, while showing excellent stability. Furthermore, protein adsorption and cell attachment studies demonstrated the ability of the graft polymer layer to reduce both significantly. In combination with the biocompatible pSi substrate material, the facile modification strategy described in this study provides access to new multifunctional drug delivery systems (DDS) for applications in cancer therapy.

Porous Silicon Carrier Delivery System for Curcumin: Preparation, Characterization, and Cytotoxicity in Vitro.

A novel carrier delivery system for curcumin based on porous silicon (pSi) has been developed. The pSi film was prepared by electrochemical etching method and the microparticles of pSi were obtained by ultrasonication. The pSi film and particles of pSi were characterized by scanning electron microscopy (SEM). Sodium nitrite can induce curcumin into pSi and improve the drug loading (DL) and encapsulation efficiency (EE) of curcumin in double-distilled water loading buffer solution. Curcumin on the pSi surface was confirmed by Fourier transform infrared spectroscopy (FTIR) and UV-spectroscopy. The optimal loading conditions of curcumin in pSi are investigated. The curcumin in pSi keeps more than 95% bioactivity for 3 h and good repeatability. The cumulative release ratio of curcumin from PSi can reach 35% after 10 h. The in vitro cytotoxicity of curcumin loaded pSi was evaluated with HT-29 and NCM460 cell lines. The pSi delivery carrier can provide a controlled release and efficacy system for curcumin.

Two-Dimensional Electrochemiluminescence on Porous Silicon Platform for Explosive Detection and Discrimination.

This work established a rapid and sensitive explosive detection and recognition technique. We report a two-dimensional electrochemiluminescence (2-D ECL) method based on porous silicon (pSi) by monitoring the dynamic change in peak position and peak intensity of pSi-ECL. Gold nanoparticles (AuNPs) were deposited on the pSi surface to promote the electrochemical reaction and electron transfer efficiency at the pSi-electrolyte interface. The 2-D ECL can effectively detect and discriminate different classes of explosives including nitro compounds, peroxides with nitrogen atoms, and peroxides without nitrogen atoms due to their different oxidation and electron transfer ability.

Functionalized p-silicon photocathodes for solar fuels applications: Insights from electrochemical impedance spectroscopy

In this contribution we report on an in-depth electrochemical impedance spectroscopy (EIS) study of the interfaces and processes involved in the photoelectrochemical hydrogen production by efficient p-type silicon (pSi) photocathodes, designedly functionalized with protective and catalytic layers.In particular, we have optimized the thermal evaporation of compact and conformal ultra-thin (5 nm) Ti films on pSi, with the double aim of (i) protecting the pSi surface from passivation and photocorrosion, as well as of (ii) introducing platforms with improved adhesion properties for the further functionalization with co-catalysts (in the specific, Pt nanoparticles). The best performing electrodes (labelled as pSi-5Ti-Pt) display an improved photocurrent onset (ca. 200 mV positive shift in 1 M H2SO4), as well as a more than doubled saturation photocurrent (up to −27 mA/cm2) when compared to the unmodified pSi photocathodes. As evidenced by the EIS analysis, the proposed modifications of pSi surface led to an enhancement of the charge extraction from the semiconductor, most likely due to surface dipole effects able to reduce the resistance associated to the transport through the space charge layer. With respect to unmodified silicon, the presence of the Ti overlayer, partially oxidized to TiO2, also allows for a denser surface coverage of the electrodeposited Pt nanoclusters, resulting in decreased interfacial charge transfer resistance for hydrogen evolution.The proposed functionalization strategy relies on common fabrication methods (already applied at industrial level) and can be easily extended to other photoelectrode materials prone to passivation/photocorrosion and/or difficult to functionalize, thus introducing more flexibility in the choice of materials for photoelectrochemical cells.

Correlation between structural and optical properties of porous silicon treated with Erbium(III)

This paper highlights a novel passivation approach of porous silicon (pSi) surface through a simple spin coating Erbium (Er) (III) treatment. The effects of Er(III) concentration and annealing temperature on the structural and optical properties of pSi have been investigated. XRD measurements show a significant improvement in the crystallinity of the Er(III) layer and a decrease in the silicon (Si) crystalline size with temperature. Atomic force microscopy (AFM) was used to estimate the surface roughness of the Er-doped pSi layer. Changes of surface chemical composition and spatial distribution of elements in the pSi/Er(III) layer were inspected using Fourier-transform infrared (FTIR) and energy-dispersive X-ray (EDX) spectroscopies. FTIR analysis exhibit a steady enhancing of SiO2 bands accompanied by a dwindling of SiHx bands and the appearance of new bands related to Er–O–Si. Photoluminescence (PL) spectroscopy reveals a sixfold increase in the intensity with the Er(III) concentration and a shift toward the higher energy with the temperature.