Porous Silicon Nanostructures Research Articles

Novel Si nanostructures via Ag-assisted chemical etching route on single and polycrystalline substrates

Silicon is the most widely used semiconductor material for electronics and energy related applications. Herein, different Si nanostructures with various shapes, sizes and morphologies are fabricated by a simple, low-cost and versatile metal‐assisted chemical etching (MACE) technique using Ag nanoparticles as a catalyst, deposited on Si surface. The influence of etching time, temperature and intrinsic properties of the silicon substrate (e.g., orientation, crystallinity) on the basic process are studied. Fast preparation of porous silicon (PSi) was achieved on Si 〈100〉 at room temperature after only 30 s of exposure to etching solution. Meanwhile increased etching time led to increase the pore diameter and a well-aligned SiNWs was obtained after 10 min. However, the exposure of Si 〈100〉 to the etching solution at 60 °C for only 2 min produced a homogenous and dense SiNWs layer. Additionally, the orientation of Si wafer was found to play a key role during the MACE process. Particularly, the MACE has no effect on Si 〈111〉 before 30 min whereas a zigzage PSi was formed. PSi nanostructures with straight and zigzag structures were successfully fabricated for the first time in addition to well-aligned, uniform and vertical Si nanowires (SiNWs) with smooth and polygonal shapes. The as-prepared Si nanostructures are characterized by various techniques including field emission-scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), UV–vis. and photoluminescence spectroscopy (PL). The optical properties of as-prepared Si nanostructures are enhanced and the reasons for this improvement and its correlation with the morphology difference are presented and discussed.

Mass Transfer Limitations of Porous Silicon-Based Biosensors for Protein Detection.

Porous silicon (PSi) thin films have been widely studied for biosensing applications, enabling label-free optical detection of numerous targets. The large surface area of these biosensors has been commonly recognized as one of the main advantages of the PSi nanostructure. However, in practice, without application of signal amplification strategies, PSi-based biosensors suffer from limited sensitivity, compared to planar counterparts. Using a theoretical model, which describes the complex mass transport phenomena and reaction kinetics in these porous nanomaterials, we reveal that the interrelated effect of bulk and hindered diffusion is the main limiting factor of PSi-based biosensors. Thus, without significantly accelerating the mass transport to and within the nanostructure, the target capture performance of these biosensors would be comparable, regardless of the nature of the capture probe–target pair. We use our model to investigate the effect of various structural and biosensor characteristics on the capture performance of such biosensors and suggest rules of thumb for their optimization.

Graphene-encapsulated blackberry-like porous silicon nanospheres prepared by modest magnesiothermic reduction for high-performance lithium-ion battery anode

Porous silicon (Si) nanostructures have aroused much interest as lithium-ion battery anodes because of the large space to accommodate the volume change in lithiation and delithiation and shorter ion transfer distance. However, fabrication of porous structures tends to be difficult to control and complex, so, the final electrochemical performance can be compromised. Herein, a modest magnesiothermic reduction (MMR) reaction is demonstrated to produce blackberry-like porous Si nanospheres (PSSs) controllably using magnesium silicide (Mg2Si) as Mg source and SiO2 nanospheres as the reactant. This improved MR method provides good control of the kinetics and heat release compared to the traditional MR (TMR) method using Mg powder as the reactant. The PSSs obtained by MMR reaction has higher structural integrity than that fabricated by TMR. After encapsulation with reduced graphene oxide, the Si/C composite exhibits superior cycling stability and rates such as a high reversible capacity of 1034 mAh·g−1 at 0.5C (4200 mAh·g−1 at 1.0C) after 1000 cycles, capacity retention of 79.5%, and high rate capacity of 497 mAh·g−1 at 2.0C. This strategy offers a new route to fabricate high-performance porous Si anodes and can be extended to other materials such as germanium.

Cavity resonance tunability of porous silicon microcavities by Ar+ ion irradiation

Present work reports the effect of low-energy Ar+ ion beam irradiation on the optical properties and surface morphology of porous silicon (PSi) based optical microcavities. These microcavities were realized by an active λ/2 spacer layer sandwiched between two Distributed Bragg Reflectors fabricated by galvanostatic electrochemical etching. Low-energy 10 keV Ar+ ions at various fluences were used for this irradiation study for these microcavities and characterized. The peak in the reflectance spectra of resonant cavity shows a red-shift after ion irradiation. These experimental observations are in good agreement with transfer matrix simulations. The Raman studies show that the crystalline Si is modified in nanostructured PSi and subsequently, the structural features of Si-Si and Si-O bonds. The simulated depth profiles suggest that the penetration of Ar+ ion is limited to top two PSi layers and the reduction of effective refractive index of these two layers. These experimental findings, analytical simulations, and cavity modelling provide the evidence of resonent cavity peak tunability, optical field intensity modulation, and photon confinement within the microcavity. This approach could be useful to tune the optical properties of PSi and an effective method for producing widely tunable optical structures in Si-based photonic architectures.

Application of Cu/porous silicon nanocomposite screen printed sensor for the determination of formaldehyde

The copper–porous silicon (Cu/PS) nanostructure was synthesized by loading copper nanoparticles (CuNPs) on the etched PS through electroless deposition and characterized by various techniques. The electrocatalytic activity of the Cu/PS nanostructure modified screen printed carbon electrode (SPCE) was investigated for the electro oxidation of formaldehyde in alkaline media using cyclic voltammetry (CV). The modified electrode exhibits unique electrocatalytic activity for the oxidation of formaldehyde through an Electrochemical-Chemical (EC') pathway with 700 mV anodic shift toward negative potentials. Based on these results, a novel screen printed sensor for the determination of formaldehyde was developed. Due to oxidation of formaldehyde at very negative potentials, the hydrodynamic amperometric response of constructed nanosensor is very selective and linear from 0.4 mM to 4 mM of formaldehyde. The detection limit of amperometric method is 0.0124 µM. The catalytic response of proposed CuNPs/PS/SPCE for the oxidation of formaldehyde is very fast (less than 3 s), reproducible and stable. It was successfully applied as a new working electrode in amperometric determination of formaldehyde in water samples. This electrode can be used as a miniaturized sensor for the detection of formaldehyde at low concentrations.

Fabrication of Zinc Oxide and Nanostructured Porous Silicon Composite Micropatterns on Silicon

The luminescent properties of zinc oxide (ZnO) and nanostructured porous silicon (PSi) make these materials very appealing for photoemission applications. The current study reports on the fabrication of a composite of ZnO and nanostructured porous silicon micropatterns (ZnO + PSi micropatterns) onto heavily-doped silicon surfaces. The proposed composite micropattern is devoted to the future development of light-emitting diodes. The fabrication of the ZnO + PSi micropatterns was carried out in a two–step process. (1) A regular hexagonal micropattern of a photoresist/ZnO stack was fabricated by UV lithography on crystalline silicon substrates. (2) Before being lifted off the photoresist, nanostructured PSi micropatterns were fabricated by electrochemically etching the exposed areas of the silicon substrate. Subsequently, wet etching of the photoresist was carried out for the final development of the composite ZnO and PSi micropatterns. Further, thin films of ZnO and nanostructured PSi layers were characterized. In particular, their photoluminescent properties were analyzed, as well as their morphology and composition. The experimental PL results show that the ZnO layers have emission broadbands centered at (2.63 eV, blue), while the PSi layers show a band centered at (1.71 eV, red). Further, the emission peaks from the PSi layers can be tuned by changing their fabrication conditions. It was observed that the properties of the ZnO thin films are not influenced by either the surface morphology of PSi or by its PL emissions. Therefore, the PL properties of the composite ZnO + PSi micropatterns are equivalent to those featuring the addition of PSi layers and ZnO thin films. Accordingly, broadband optical emissions are expected to arise from a combination between the ZnO layer (blue band) and PSi (red band). Furthermore, the electrical losses associated with the PSi areas can be greatly reduced since ZnO is in contact with the Si surface. As a result, the proposed composite micropatterns might be attractive for many solid-state lighting applications, such as light-emitting diodes.

Electrical Characterization of MIS Schottky Barrier Diodes Based on Nanostructured Porous Silicon and Silver Nanoparticles with Applications in Solar Cells

The accurate determination of the electrical properties of photovoltaic devices is of utmost importance to predict and optimize their overall optoelectronic performance. For example, the minority carrier lifetime and the carrier diffusion length have a strong relationship with the carrier recombination rate. Additionally, parasitic resistances have an important effect on the fill factor of a solar cell. Within this context, the alternating current (AC) and direct current (DC) electrical characteristics of Si-based metal–insulator–semiconductor (MIS) Schottky barrier diodes with the basic structure Al/Si/TiO2/NiCr were studied, aiming at using them as photovoltaic devices. The basic diode structure was modified by adding nanostructured porous silicon (nanoPS) layers and by infiltrating silver nanoparticles (AgNPs) into the nanoPS layers, leading to Al/Si+nanoPS/TiO2/NiCr and Al/Si+nanoPS+AgNPs/TiO2/NiCr structures, respectively. The AC electrical properties were studied using a combination of electrochemical impedance spectroscopy and Mott–Schottky analysis, while the DC electrical properties were determined from current–voltage measurements. From the experimental results, an AC equivalent circuit model was proposed for the three different MIS Schottky barrier diodes under study. Additionally, the most significant electrical parameters were calculated. The results show a remarkable improvement in the performance of the MIS Schottky barrier diodes upon the addition of hybrid nanoPS layers with embedded Ag nanoparticles, opening the way to their use as photovoltaic devices.

Simulation of anti-reflecting dielectric films by the interference matrix method

In this work, the reflection coefficients of multilayer and gradient dielectric films are simulated. The basis of the conducted researches is the theoretical analysis of reflection coefficients for single and double layer films, which use the criterion of zero reflection coefficients for electromagnetic wave with a given wavelength. The specified length is selected based on the maximum spectral density data of the solar radiation. Numerical calculations were performed on the basis of the interference matrix method. Using this method, the reflection coefficients were calculated for the spectral range of electromagnetic radiation, in which photoelectric conversion of solar cells made of silicon occurs. The dependences of the reflection coefficients on the angle of incidence of the sun's rays are also calculated. Numerical methods were used to determine the average values of the reflection coefficients, taking into account the spectral density of solar radiation. Optimal values of the thicknesses of single and double layer films were found as well as gradient films with the linear law of change of the refractive index of the film material. The optimum values found were compared with the characteristics of the dielectric coatings used in solar power. Both traditional technologies based on CdTe and Cu(In,Ga)Se2 crystals and relatively new technologies based on the use of nanostructured films and porous silicon films have been considered. For these materials, the characteristics of the films are calculated, which provide values of reflection coefficients that are close to optimal values.

Simulation of field effect in porous silicon nanostructures

The peculiarities of field effect in porous silicon with a cylindrical pore shape have been theoretically studied. It has been established that the Debye screening length decreases with increasing surface curvature. The spatial distribution of the potential was obtained by computer simulation of the nonlinear Poisson’s equation. The coordinate dependences of the electrostatic potential were analyzed for various values of surface charge density. It has been shown that the redistribution of charge carriers caused by the field effect can lead to the inversion of the conductivity type of the porous semiconductor. The inversion depth depends on the surface charge density and pore radius. The features of the influence of surface charge on the change in conductivity of the porous silicon have been studied.

Aptamers vs. antibodies as capture probes in optical porous silicon biosensors.

Over the past decade aptamers have emerged as a promising class of bioreceptors for biosensing applications with significant advantages over conventional antibodies. However, experimental studies comparing aptasensors and immunosensors, under equivalent conditions, are limited and the results are inconclusive, in terms of benefits and limitations of each bioreceptor type. In the present work, the performance of aptamer and antibody bioreceptors for the detection of a his-tagged protein, used as a model target, is compared. The bioreceptors are immobilized onto a nanostructured porous silicon (PSi) thin film, used as the optical transducer, and the target protein is detected in a real-time and label-free format by reflective interferometric Fourier transform spectroscopy. For the antibodies, random-oriented immobilization onto the PSi nanostructure results in a poor biosensing performance. Contrary, Fc-oriented immobilization of the antibodies shows a similar biosensing performance to that exhibited by the aptamer-based biosensor, in terms of binding rate, dynamic detection range, limit of detection and selectivity. The aptasensor outperforms in terms of its reusability and storability, while the immunosensor could not be regenerated for subsequent experiments.

Bone Morphogenic Protein 2-Loaded Porous Silicon Carriers for Osteoinductive Implants.

Bone morphogenetic proteins (BMPs) are probably the most important growth factors in bone formation and healing. However, the utilization of BMPs in clinical applications is mainly limited due to the protein poor solubility at physiological pH, rapid clearance and relatively short biological half-life. Herein, we develop degradable porous silicon (PSi)-based carriers for sustained delivery of BMP-2. Two different loading approaches are examined, physical adsorption and covalent conjugation, and their effect on the protein loading and release rate is thoroughly studied. The entrapment of the protein within the PSi nanostructures preserved its bioactivity for inducing osteogenic differentiation of rabbit bone marrow mesenchymal stems cells (BM-MSCs). BM-MSCs cultured with the BMP-2 loaded PSi carriers exhibit a relatively high alkaline phosphatase (ALP) activity. We also demonstrate that exposure of MSCs to empty PSi (no protein) carriers generates some extent of differentiation due to the ability of the carrier’s degradation products to induce osteoblast differentiation. Finally, we demonstrate the integration of these promising BMP-2 carriers within a 3D-printed patient-specific implant, constructed of poly(caprolactone) (PCL), as a potential bone graft for critical size bone defects.

Porous Materials: Neuroprotective Effect of Nerve Growth Factor Loaded in Porous Silicon Nanostructures in an Alzheimer's Disease Model and Potential Delivery to the Brain (Small 45/2019)

Porous Materials: Neuroprotective Effect of Nerve Growth Factor Loaded in Porous Silicon Nanostructures in an Alzheimer's Disease Model and Potential Delivery to the Brain (Small 45/2019)

Neuroprotective Effect of Nerve Growth Factor Loaded in Porous Silicon Nanostructures in an Alzheimer's Disease Model and Potential Delivery to the Brain

Nerve growth factor (NGF) plays a vital role in reducing the loss of cholinergic neurons in Alzheimer's disease (AD). However, its delivery to the brain remains a challenge. Herein, NGF is loaded into degradable oxidized porous silicon (PSiO2 ) carriers, which are designed to carry and continuously release the protein over a 1 month period. The released NGF exhibits a substantial neuroprotective effect in differentiated rat pheochromocytoma PC12 cells against amyloid-beta (Aβ)-induced cytotoxicity, which is associated with Alzheimer's disease. Next, two potential localized administration routes of the porous carriers into murine brain are investigated: implantation of PSiO2 chips above the dura mater, and biolistic bombardment of PSiO2 microparticles through an opening in the skull using a pneumatic gene gun. The PSiO2 -implanted mice are monitored for a period of 8 weeks and no inflammation or adverse effects are observed. Subsequently, a successful biolistic delivery of these highly porous microparticles into a live-mouse brain is demonstrated for the first time. The bombarded microparticles are observed to penetrate the brain and reach a depth of 150 µm. These results pave the way for using degradable PSiO2 carriers as potential localized delivery systems for NGF to the brain.

One Spot—Two Sensors: Porous Silicon Interferometers in Combination With Gold Nanostructures Showing Localized Surface Plasmon Resonance

Sensors composed of a porous silicon monolayer covered with a film of nanostructured gold layer, which provide two optical signal transduction methods, are fabricated and thoroughly characterized concerning their sensing performance. For this purpose, silicon substrates were electrochemically etched in order to obtain porous silicon monolayers, which were subsequently immersed in gold salt solution facilitating the formation of a porous gold nanoparticle layer on top of the porous silicon. The deposition process was monitored by reflectance spectroscopy, and the appearance of a dip in the interference pattern of the porous silicon layer was observed. This dip can be assigned to the absorption of light by the deposited gold nanostructures leading to localized surface plasmon resonance. The bulk sensitivity of these sensors was determined by recording reflectance spectra in media having different refractive indices and compared to sensors exclusively based on porous silicon or gold nanostructures. A thorough analysis of resulting shifts of the different optical signals in the reflectance spectra on the wavelength scale indicated that the optical response of the porous silicon sensor is not influenced by the presence of a gold nanostructure on top. Moreover, the adsorption of thiol-terminated polystyrene to the sensor surface was solely detected by changes in the position of the dip in the reflectance spectrum, which is assigned to localized surface plasmon resonance in the gold nanostructures. The interference pattern resulting from the porous silicon layer is not shifted to longer wavelengths by the adsorption indicating the independence of the optical response of the two nanostructures, namely porous silicon and nanostructured gold layer, to refractive index changes and pointing to the successful realization of two sensors in one spot.

Photoluminescence polarization and refractive index anisotropy of porous silicon nanocrystals arrays

In this work, the simple way to form oriented arrays of silicon nanocrystals in a dielectric matrix was suggested. Porous silicon nanostructures obtained on the substrates with the [100] and [111] crystallographic orientations were separated from the silicon substrate using epoxy resin. Systems of the porous silicon nanoparticles were characterized by scanning electron microscopy, atomic-force microscopy, ellipsometry and luminescent spectroscopy. It is shown, that the use of epoxy resin suggests the preservation of the silicon nanostructures orientation after separation from the substrate. Based on the Bruggeman effective medium approximation, volume fractions of components of obtained nanosystems were determined for spherical and cylindrical shape of the porous silicon nanoparticles. The influence of the nanostructures orientation on optical and photoluminescent properties of the obtained nanosystems was studied. It is found that the photoluminescent polarization in silicon nanosystems is consistent with the anisotropy of their complex refractive index. Both phenomena originate from the morphological anisotropy of porous silicon nanocrystals.

The Influence of Anodization Time With The Electrochemical Cell Design on The Fabrication Process of Porous Silicon Nanostructures

The influence of anodization time with the electrochemical cell design on the fabrication process of porous silicon (PS) nanostructures based on two electrochemical anodization cells (designed single tank cell and double tank cell) with two anodization times (10 and 30 minutes) was studied. Atomic force Microscopy (AFM) characterization had revealed three types of pores, mesopores, mesopore fill of mesopores, and macropore fill of mesopores were obtained from designed single tank cell with (10 and 30 minutes) of anodization time, whilst for double tank cell has not revealed precise information about the size and type of pores. Pores formation have been further approved by current-voltage (I-V) measurement and photoluminescence emission by ultraviolet-lamp (254-366) nm for both electrochemical cells.

Plant-Derived Tandem Drug/Mesoporous Silicon Microcarrier Structures for Anti-Inflammatory Therapy.

The properties of nanostructured plant-derived porous silicon (pSi) microparticles as potential candidates to increase the bioavailability of plant extracts possessing anti-inflammatory activity are described in this work. pSi drug carriers were fabricated using an eco-friendly route from the silicon accumulator plant bamboo (tabasheer) powder by magnesiothermic reduction of plant-derived silica and loaded with ethanolic extracts of Equisetum arvense, another silicon accumulator plant rich in polyphenolic compounds. The anti-inflammatory properties of the active therapeutics present in this extract were measured by sensitive luciferase reporter assays; this active extract was subsequently loaded and released from the pSi matrix, with a clear inhibition of the activity of the inflammatory signaling protein NF-κB over a period of hours in a sustained manner. Our results showed that after loading the extracts of E. arvense into pSi microparticles derived from tabasheer, enhanced anti-inflammatory activity was observed owing to enhanced solubility of the extract.

(Invited) Electrochemical Preparation of Micro and Nano Structures and Systems in Silicon for (Bio)Sensing and Nano(Medicine) Applications

When dealing with biosensing and nanomedicine applications the length scale of targets may vary over more than 5 orders of magnitude moving from the molecular level (0.1-1 nm) up to the cell level (1-10 μm). A number of micro and nanostructuring technologies have been developed over the years to enable the preparation of both structures and systems with length scales suitable to match specific biological targets. In this talk, electrochemical preparation of nano and micro structures and systems in silicon with length scales spanning over 5 order of magnitudes, able to target different applications both in (nano)medicine (e.g. sinusoid-like liver on a chip, nanopillars for cell transfection, 3D microincubators for tumor cell screening) and (bio)sensing (e.g. microneedles for transdermal biosensing, optical biosensors for point-of-care clinical diagnostics, chemitransitor sensors for environmental monitoring), is presented and discussed. 1. S.Mariani, V. Robbiano, L. M. Strambini, A. Debrassi, G. Egri, L. Dähne, G. Barillaro, Layer-by-layer biofunctionalization of nanostructured porous silicon for high-sensitivity and high-selectivity label-free affinity biosensing, Nature Communications, 9, 5256, 1-13 (2018) 2. B. Delalat, C. Cozzi, S. R. Ghaemi, G. Polito, F. E. Kriel, T. D. Michl, F. J. Harding, C. Priest, G. Barillaro, N. H. Voelcker, Microengineered Bioartificial Liver Chip for Drug Toxicity Screening, Advanced Functional Materials 1801825 (2018).3. Robbiano, G. M. Paterno, A. A. La Mattina, S. G. Motti, G. Lanzani, F. Scotognella, G. Barillaro, Room-Temperature Low-Threshold Lasing From Monolithically Integrated Nanostructured Porous Silicon Hybrid Microcavities, ACS Nano12, 4536−4544 (2018). 4. J. Harding, S. Surdo, B. Delalat, C. Cozzi, R. Elnathan, S. Gronthos, N. H. Voelcker, G. Barillaro, Ordered Silicon Pillar Arrays Prepared by Electrochemical Micromachining: Substrates for High-Efficiency Cell Transfection, ACS Applied Materials and Interfaces, 8 (43), 29197-29202 (2016). 5. Mariani, L. M. Strambini, G. Barillaro, Femtomole Detection Of Proteins Using A Label-Free Nanostructured Porous Silicon Interferometer For Perspective Ultra-Sensitive Biosensing, ACS Analytical Chemistry, 88 (17), 8502-8509 (2016). 6. Mariani, L. Pino, L. M. Strambini, L. Tedeschi, G. Barillaro, 10000-Fold Improvement in Protein Detection Using Nanostructured Porous Silicon Interferometric Aptasensors, ACS Sensors, 1, 1471-1479(2016). 7. M. Sainato, L.M. Strambini, S. Rella, E. Mazzotta, G. Barillaro, Sub-Parts Per Million NO2 Chemi-Transistor Sensors Based on Composite Porous Silicon/Gold Nanostructures Prepared by Metal-Assisted Etching, ACS Applied Materials and Interfaces 7, 7136 (2015). 8. M. Strambini, A. Longo, S. Scarano, T. Prescimone, I. Palchetti, M. Minunni, D. Giannessi, G. Barillaro, Self-Powered Microneedle-Based Biosensors for Pain-Free High-Accuracy Measurement of Glycaemia in Interstitial Fluid, Biosensors and Bioelectronics,66, 162 (2015).

Formation of Platinum Nanocrystals on Silicon Nanotubes and In Vitro Anti-Cancer Activity of the Composites

The semiconductor Silicon (Si) remains a significant material in the electronic device and photovoltaic industries [1]. Especially, nanostructured forms of Si with a porous morphology (pSi) exhibit interesting properties which can be controlled via modulating pore structure and surface chemistry [1]. Recently, synthesis of a unique one-dimensional form of Si, namely nanotubes, with tunable structure (shell thickness, length, inner diameter and porous morphology) has been demonstrated, thereby suggesting newly emerging applications [2]. For instance, recent works have indicated Si nanotubes (SiNTs) can efficiently serve as a reaction vessel for formation of organometal perovskite nanostructures and a template for superparamagnetic iron oxide (Fe3O4) loading [3], [4]. In an observation of dissolution of SiNTs with a porous morphology (pSiNTs), the material readily resorbed in buffered media at physiological conditions in a similar manner to bioactive nanostructured porous silicon, thereby implying potential therapeutic applications of this material [2]. In chemotherapy, platinum-based cancer drugs, such as cisplatin and carboplatin, are widely used as effective drugs against various types of cancer [5]. Interestingly, while elemental platinum nanoparticles (Pt NPs) have been well investigated in diverse catalytic processes, in recent years, Pt NPs have also been discovered as a potent anti-cancer agent in nanomedicine, implying the use of the nanodrug to counteract chemoresistance in some cancer cell lines [6], [7]. Recent reports have also indicated that enhanced cytotoxicity against selected cancer cell lines is ascribed to ultra-small Pt NPs, especially those with size less than 3 nm [7]. In this report, pSiNTs were investigated as a template for the formation of Pt NPs, and in vitro cytotoxicity of the composites was evaluated against HeLa cancer cells. Regarding fabrication, pSiNTs with short lengths (~500 nm) and thin walls (~10 nm) were synthesized via a ZnO nanowire sacrificial template method (Fig. 1A). Based on a combination of characterization techniques [High resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray analysis (TEM-EDX)], it is suggested that pSiNTs surface functionalized with 3-aminopropyltriethoxysilane can facilitate formation of Pt nanocrystals (Pt NCs) with size ranging from 1-3 nm utilizing a K2PtCl4 precursor. By varying reaction conditions (concentration of Pt salt and incubation time), the amount of Pt NCs deposited on SiNTs can be sensitively tuned from 20 to 55 wt% (Fig. 1 B, C; Table 1). In terms of cytotoxicity evaluation of the composites against HeLa cells, cellular viability was assessed using CellTiter-Glo assays, which quantified the amount of ATP in metabolically active cells. Our findings suggest that Pt NCs-SiNTs composites were toxic to HeLa cells, and less than 50% cells were still viable after 3 days of treatment with the composites at doses of 35 μg/ml and 50 μg/ml (Fig. 2). Results from caspase 3/7 assays also showed that caspase 3/7 level in cells treated with Pt NCs-SiNTs approximately ranged from 1.5 to 2-fold increase compared to cells without treatment, thereby suggesting apoptosis as the likely mechanism. In vitro cellular uptake studies analyzed by confocal microscopy also confirmed accumulation of the composites within the cytoplasm of the cells after the treatment, consistent with a “Trojan horse” mechanism in which high concentrations of Pt NCs are internalized within cells assisted by pSiNTs and subsequently released via dissolution of the nanotube matrix. The studies presented herein describe a novel strategy to form and immobilize highly compact clusters of Pt NCs by using pSiNTs as a template. In terms of bio-relevant applications, in vitro studies provide new insights into the anti-cancer properties of the newly discovered composites in inducing apoptosis in HeLa cells, thereby providing significant potential uses of Pt NCs-SiNTs in cancer treatment. Further investigations into gene expression profile(s) may be necessary in order to clarify the impact of the composites on cell survival in terms of molecular mechanisms. References H. Santos, Porous Silicon for Biomedical Applications, Ed. Cambridge: Woodhead Publishing, (2014).X. Huang, R. Gonzalez-Rodriguez, R. Rich, Z. Gryczynski and J. L. Coffer, Chem. Commun., 49, 5760 (2013).R. Gonzalez-Rodriguez, N. Arad-Vosk, N. Rozenfeld, A. Sa'ar and J.L. Coffer, Small, 12(33), (2016).P. Granitzer, K. Rumpf, R. Gonzalez, J. Coffer, M. Reissner, Nanoscale Res. Lett., 9, 413 (2014).T. C. Johnstone, K. Suntharalingam and S. J. Lippard, Chem. Rev., 116 (5), 3436–3486, (2016).X. Li, G. Li, W. Zhang, L. Wang and X. Zhang, Catal. Sci. Technol., 4, 3290-3297 (2014).H. Xia, F. Li, X. Hu, W. Park, S. Wang, Y. Jang, Y. Du, S. Baik, S. Cho, T. Kang, D. Kim, D. Ling, K. M. Hui and T. Hyeon, ACS Cent. Sci., 2, 802−811 (2016). Figure 1

Porous Silicon Nanostructures as Effective Faradaic Electrochemical Sensing Platforms

AbstractThe electrochemical performance of porous silicon (pSi) stabilized via thermal decomposition of acetylene gas is investigated for the first time. In this study, pSi undergoes two thermal treatments at either 525 or 800 °C, which result in hydrogen‐terminated thermally hydrocarbonized pSi (THCpSi) and hydroxyl‐terminated thermally carbonized pSi (TCpSi), respectively, the latter upon dipping in hydrofluoric acid to activate the surface termination. Electrochemical characterization, using cyclic voltammetry, chronocoulometry, and electrochemical impedance spectroscopy in the presence of several redox pairs, [Fe(CN)6]3/4−, [Ru(NH3)6]2/3+, and hydroquinone/quinone, is used to demonstrate the versatility and high stability to degradation of carbon‐stabilized pSi nanostructures and their excellent electrochemical performance. Added to the large surface area, adjustable pore morphology and tailorable surface chemistry of THCpSi and TCpSi, these nanostructures demonstrate fast electron‐transfer kinetics, providing key advantages over conventional carbon electrodes. The versatile surface chemistry of THCpSi and TCpSi offer various possibilities to introduce multiple functional groups depending on the nature of the bioreceptor to be immobilized. For proof of principle, the use of a THCpSi‐based immunosensor to detect MS2 bacteriophage is demonstrated by means of electrochemical impedance spectroscopy, showing a detection limit of 4.9 pfu mL−1. Carbon‐stabilized pSi structures represent a new class of nanostructured electrodes for biosensing applications.