Bioconjugate functionalization of thermally carbonized porous silicon using a radical coupling reaction

Designing Electrochemical Biosensing Platforms Using Layered Carbon-Stabilized Porous Silicon Nanostructures

Porous silicon (pSi) is an established porous material that offers ample opportunities for biosensor design thanks to its tunable structure, versatile surface chemistry, and large surface area. Nonetheless, its potential for electrochemical sensing is relatively unexplored. This study investigates layered carbon-stabilized pSi nanostructures with site-specific functionalities as an electrochemical biosensor. A double-layer nanostructure combining a top hydrophilic layer of thermally carbonized pSi (TCpSi) and a bottom hydrophobic layer of thermally hydrocarbonized pSi (THCpSi) is prepared. The modified layers are formed in a stepwise process, involving first an electrochemical anodization step to generate a porous layer with precisely defined pore morphological features, followed by deposition of a thin thermally carbonized coating on the pore walls via temperature-controlled acetylene decomposition. The second layer is then generated beneath the first by following the same two-step process, but the acetylene decomposition conditions are adjusted to deposit a thermally hydrocarbonized coating. The double-layer platform features excellent electrochemical properties such as fast electron-transfer kinetics, which underpin the performance of a TCpSi-THCpSi voltammetric DNA sensor. The biosensor targets a 28-nucleotide single-stranded DNA sequence with a detection limit of 0.4 pM, two orders of magnitude lower than the values reported to date by any other pSi-based electrochemical DNA sensor.

Porous Silicon Optical Devices: Recent Advances in Biosensing Applications

This review summarizes the leading advancements in porous silicon (PSi) optical-biosensors, achieved over the past five years. The cost-effective fabrication process, the high internal surface area, the tunable pore size, and the photonic properties made the PSi an appealing transducing substrate for biosensing purposes, with applications in different research fields. Different optical PSi biosensors are reviewed and classified into four classes, based on the different biorecognition elements immobilized on the surface of the transducing material. The PL signal modulation and the effective refractive index changes of the porous matrix are the main optical transduction mechanisms discussed herein. The approaches that are commonly employed to chemically stabilize and functionalize the PSi surface are described.

Crystallisation Behaviour of Pharmaceutical Compounds Confined within Mesoporous Silicon

The poor aqueous solubility of new and existing drug compounds represents a significant challenge in pharmaceutical development, with numerous strategies currently being pursued to address this issue. Amorphous solids lack the repeating array of atoms in the structure and present greater free energy than their crystalline counterparts, which in turn enhances the solubility of the compound. The loading of drug compounds into porous materials has been described as a promising approach for the stabilisation of the amorphous state but is dependent on many factors, including pore size and surface chemistry of the substrate material. This review looks at the applications of mesoporous materials in the confinement of pharmaceutical compounds to increase their dissolution rate or modify their release and the influence of varying pore size to crystallise metastable polymorphs. We focus our attention on mesoporous silicon, due to the ability of its surface to be easily modified, enabling it to be stabilised and functionalised for the loading of various drug compounds. The use of neutron and synchrotron X-ray to examine compounds and the mesoporous materials in which they are confined is also discussed, moving away from the conventional analysis methods.

Stable surface functionalization of carbonized mesoporous silicon

A new method to produce functional surfaces on porous silicon allow long term use of the material in aqueous environments.

Harnessing the Aqueous Chemistry of Silicon: Self-Assembling Porous Silicon/Silica Microribbons

The synthesis of microribbons based on the assembly of porous silicon nanoparticles (pSiNPs) in a silica matrix is reported. The formation of these structures is driven by dissolution and reprecipitation of silica derived from the NPs upon drying of an aqueous colloidal dispersion. The process generates composite films that fracture into filaments due to geometric stresses associated with drying of the film on a curved surface. By controlling NP concentration, solvent, and temperature during the evaporation process, well-defined microribbons with a rectangular cross section of ∼25 × 100 microns and lengths on the order of 1 cm are formed. Partial thermal oxidation of the ribbons generates luminescent Si-SiO₂ core-shell composites, and complete oxidation generates porous SiO₂ ribbons with retention of the mesoporous nanostructure. The pores can be infiltrated with daunorubicin as a model drug, and the resulting material shows sustained release of the chemotherapeutic for more than 70 days.

Differential functionalisation of the internal and external surfaces of carbon-stabilised nanoporous silicon

A versatile strategy to differentiate the surface chemistry of the internal and external pore walls of highly-stable nanoporous silicon.

Photoluminescent and biodegradable porous silicon nanoparticles for biomedical imaging

A set of unique properties including biodegradability, intrinsic photoluminescence, and mesoporous structure allows porous silicon nanoparticles to address current challenges of translational nanomedicine, especially in biomedical imaging.

Thermally Carbonized Porous Silicon and Its Recent Applications

Recent progress in research on thermally carbonized porous silicon (TCPSi) and its applications is reported. Despite a slow start, thermal carbonization has now started to gain interest mainly due to new emerging areas for applications. These new areas, such as optical sensing, drug delivery, and energy storage, require stable surface chemistry and physical properties. TCPSi is known to have all of these desired properties. Herein, the above-listed properties of TCPSi are summarized, and the carbonization processes, functionalization, and characterization of TCPSi are reviewed. Moreover, some of the emerging fields of TCPSi applications are discussed and recent advances in the fields are introduced.

Physicochemical properties and in vitro cytotoxicity of iron oxide-based nanoparticles modified with antiangiogenic and antitumor peptide A7R

Superparamagnetic iron oxide-based nanoparticles (SPIONs) are promising carriers as targeted drug delivery vehicles, because they can be guided to their target with the help of an external magnetic field. Functionalization of nanoparticles' surface with molecules, which bind with high affinity to receptors on target tissue significantly facilitates delivery of coated nanoparticles to their targeted site. Here, we demonstrate conjugation of an antiangiogenic and antitumor peptide ATWLPPR (A7R) to SPIONs modified with sebacic acid (SPIONs-SA). Successful conjugation was confirmed by various analytical techniques (FTIR, SERS, SEM-EDS, TEM, TGA). Cell cytotoxicity studies, against two cell lines (HUVEC and MDA-MB-231) indicated that SPIONs modified with A7R reduced HUVEC cell viability at concentrations higher than 0.01 mg Fe/mL, in comparison to cells that were exposed to either the nanoparticles modified with sebacic acid or A7R peptide solely, what might be partially caused by a process of internalization.

Preparation, characterization and antibiotic properties of silver–silicon nanocomposites

Ag nanoparticles supported on porous silicon showing excellent antibiotic properties against both E. coli and S. aureus were presented.

Oral hypoglycaemic effect of GLP-1 and DPP4 inhibitor based nanocomposites in a diabetic animal model

Glucagon-like peptide-1 (GLP-1), an incretin hormone, is used for type 2 diabetes mellitus (T2DM) treatment because of its ability to stimulate insulin secretion and release in a glucose-dependent manner. Despite of its potent insulinotropic effect, oral GLP-1 delivery is greatly limited by its instability in the gastrointestinal tract, poor absorption efficiency and rapid degradation by dipeptidylpeptidase-4 (DPP4) enzyme leading to a short half-life (~2min). Thus, a multistage dual-drug delivery nanosystem was developed to deliver GLP-1 and DPP4 inhibitor simultaneously. The system comprised of chitosan-modified porous silicon (CSUn) nanoparticles, which were coated by an enteric polymer, hydroxypropylmethylcellulose acetate succinate MF, using aerosol flow reactor technology. A non-obese T2DM rat model induced by co-administration of nicotinamide and streptozotocin was used to evaluate the in vivo efficacy of the nanosystem. The oral administration of H-CSUn nanoparticles resulted in 32% reduction in blood glucose levels and ~6.0-fold enhancement in pancreatic insulin content, as compared to the GLP-1+DPP4 inhibitor solution. Overall, these results present a promising system for oral co-delivery of GLP-1 and DPP4 inhibitor that could be further evaluated in a chronic diabetic study.

Recent Advances on Luminescent Enhancement-Based Porous Silicon Biosensors

Luminescence-based detection paradigms have key advantages over other optical platforms such as absorbance, reflectance or interferometric based detection. However, autofluorescence, low quantum yield and lack of photostability of the fluorophore or emitting molecule are still performance-limiting factors. Recent research has shown the need for enhanced luminescence-based detection to overcome these drawbacks while at the same time improving the sensitivity, selectivity and reducing the detection limits of optical sensors and biosensors. Nanostructures have been reported to significantly improve the spectral properties of the emitting molecules. These structures offer unique electrical, optic and magnetic properties which may be used to tailor the surrounding electrical field of the emitter. Here, the main principles behind luminescence and luminescence enhancement-based detections are reviewed, with an emphasis on europium complexes as the emitting molecule. An overview of the optical porous silicon microcavity (pSiMC) as a biosensing platform and recent proof-of-concept examples on enhanced luminescence-based detection using pSiMCs are provided and discussed.

Applications of zero-valent silicon nanostructures in biomedicine

Zero-valent, or elemental, silicon nanostructures exhibit a number of properties that render them attractive for applications in nanomedicine. These materials hold significant promise for improving existing diagnostic and therapeutic techniques. This review summarizes some of the essential aspects of the fabrication techniques used to generate these fascinating nanostructures, comparing their material properties and suitability for biomedical applications. We examine the literature in regards to toxicity, biocompatibility and biodistribution of silicon nanoparticles, nanowires and nanotubes, with an emphasis on surface modification and its influence on cell adhesion and endocytosis. In the final part of this review, our attention is focused on current applications of the fabricated silicon nanostructures in nanomedicine, specifically examining drug and gene delivery, bioimaging and biosensing.

Porous silicon nanoparticles for nanomedicine: preparation and biomedical applications

The research on porous silicon (PSi) materials for biomedical applications has expanded greatly since the early studies of Leigh Canham more than 25 years ago. Currently, PSi nanoparticles are receiving growing attention from the scientific biomedical community. These nanostructured materials have emerged as promising multifunctional and versatile platforms for nanomedicine in drug delivery, diagnostics and therapy. The outstanding properties of PSi, including excellent in vivo biocompatibility and biodegradability, have led to many applications of PSi for delivery of therapeutic agents. In this review, we highlight current advances and recent efforts on PSi nanoparticles regarding the production properties, efficient drug delivery, multidrug delivery, permeation across biological barriers, biosafety and in vivo tracking for biomedical applications. The constant boost on successful preclinical in vivo data reported so far makes this the ‘golden age’ for PSi, which is expected to finally be translated into the clinic in the near future.

Highly stable porous silicon-carbon composites as label-free optical biosensors

A stable, label-free optical biosensor based on a porous silicon-carbon (pSi-C) composite is demonstrated. The material is prepared by electrochemical anodization of crystalline Si in an HF-containing electrolyte to generate a porous Si template, followed by infiltration of poly(furfuryl) alcohol (PFA) and subsequent carbonization to generate the pSi-C composite as an optically smooth thin film. The pSi-C sensor is significantly more stable toward aqueous buffer solutions (pH 7.4 or 12) compared to thermally oxidized (in air, 800 °C), hydrosilylated (with undecylenic acid), or hydrocarbonized (with acetylene, 700 °C) porous Si samples prepared and tested under similar conditions. Aqueous stability of the pSi-C sensor is comparable to related optical biosensors based on porous TiO(2) or porous Al(2)O(3). Label-free optical interferometric biosensing with the pSi-C composite is demonstrated by detection of rabbit IgG on a protein-A-modified chip and confirmed with control experiments using chicken IgG (which shows no affinity for protein A). The pSi-C sensor binds significantly more of the protein A capture probe than porous TiO(2) or porous Al(2)O(3), and the sensitivity of the protein-A-modified pSi-C sensor to rabbit IgG is found to be ~2× greater than label-free optical biosensors constructed from these other two materials.

Amine modification of thermally carbonized porous silicon with silane coupling chemistry

Thermally carbonized porous silicon (TCPSi) microparticles were chemically modified with organofunctional alkoxysilane molecules using a silanization process. Before the silane coupling, the TCPSi surface was activated by immersion in hydrofluoric acid (HF). Instead of regeneration of the silicon hydride species, the HF immersion of silicon carbide structure forms a silanol termination (Si-OH) on the surface required for silanization. Subsequent functionalization with 3-aminopropyltriethoxysilane provides the surface with an amine (-NH(2)) termination, while the SiC-type layer significantly stabilizes the functionalized structure both mechanically and chemically. The presence of terminal amine groups was verified with FTIR, XPS, CHN analysis, and electrophoretic mobility measurements. The overall effects of the silanization to the morphological properties of the initial TCPSi were analyzed and they were found to be very limited, making the treatment effects highly predictable. The maximum obtained number of amine groups on the surface was calculated to be 1.6 groups/nm(2), corresponding to 79% surface coverage. The availability of the amine groups for further biofunctionalization was confirmed by successful biotinylation. The isoelectric point (IEP) of amine-terminated TCPSi was measured to be at pH 7.7, as opposed to pH 2.6 for untreated TCPSi. The effects of the surface amine termination on the cell viability of Caco-2 and HT-29 cells and on the in vitro fenofibrate release profiles were also assessed. The results indicated that the surface modification did not alter the loading of the drug inside the pores and also retained the beneficial enhanced dissolution characteristics similar to TCPSi. Cellular viability studies also showed that the surface modification had only a limited effect on the biocompatibility of the PSi.

Thermally promoted addition of undecylenic acid on thermally hydrocarbonized porous silicon optical reflectors

: Thermally promoted addition of undecylenic acid is studied as a method for modifying porous silicon optical reflectors that have been pre-treated with thermal hydrocarbonization. Successful derivatization of undecylenic acid is demonstrated and confirmed with Fourier transform infrared and X-ray photoelectron spectroscopies. The results indicate that the hydrocarbonization pre-treatment considerably improves stability against oxidation and chemical dissolution in basic environments. The two-step treatment also does not cause an appreciable change on sample reflectance spectra, which enables the use of the functionalized structures in optical sensing applications.

Switching of fluorescence mediated by a peroxynitrite-glutathione redox reaction in a porous silicon nanoreactor

A nanostructured porous silicon chip functionalized with dichlorofluorescein is employed as a nanoreactor to respond to Reactive Oxygen Species (ROS) and to real-time studying redox reactions.