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Selective isolation of individual target cells from a heterogeneous population is technically challenging; however, the ability to retrieve single cells can have high significance in various aspects of biological research. Here, we present a new photoelectrochemical surface based on a transparent electrode that is compatible with high-resolution fluorescence microscopy for isolating individual rare cells from complex biological samples. This is underpinned by two important factors: (i) careful design of the electrode by patterning discrete Au disks of micron dimension on amorphous silicon-indium tin oxide films and (ii) orthogonal surface chemistry, which modifies the patterned electrode with self-assembly layers of different functionalities, to selectively capture target cells on the Au disks and resist cell binding to the amorphous silicon surface. The co-stimulation of the surface using light from a microscope and an electric potential triggers the reductive desorption of the alkanethiol monolayer from the Au disks to release the single cells of interest from the illuminated regions only. Using circulating tumor cells as a model, we demonstrate the capture of cancer cells on an antibody-coated surface and selective release of single cancer cells with low expression of epithelial cell adhesion molecules.

Light can be used to spatially resolve electrochemical measurements on a semiconductor electrode. This phenomenon has been explored to detect DNA hybridization with light-addressable potentiometric sensors and, more recently, with light-addressable amperometric sensors based on organic-monolayer-protected Si(100). Here, a contribution to the field is presented by comparing sensing performances when bovine serum albumin (BSA) and hexaethylene glycol (OEG 6 ) are employed as antifouling layers that resist nonspecific adsorption to the DNA-modified interface on Si(100) devices. What is observed is that both sensors based on BSA or OEG 6 initially allow electrochemical distinction among complementary, noncomplementary, and mismatched DNA targets. However, only surfaces based on OEG 6 can sustain electroactivity over time. Our results suggest that this relates to accelerated SiO x formation occasioned by BSA proteins adsorbing on monolayer-protected Si(100) surfaces. Therefore, DNA biosensors were analytically explored on low-doped Si(100) electrodes modified on the molecular level with OEG 6 as an antifouling layer. First, light-activated electrochemical responses were recorded over a range of complementary DNA target concentrations. A linear semilog relation was obtained from 1.0 × 10 -11 to 1.0 × 10 -6 mol L -1 with a correlation coefficient of 0.942. Then, measurements with three independent surfaces indicated a relative standard deviation of 4.5%. Finally, selectivity tests were successfully performed in complex samples consisting of a cocktail mixture of four different DNA sequences. Together, these results indicate that reliable and stable light-activated amperometric DNA sensors can be achieved on Si(100) by employing OEG 6 as an antifouling layer.

Fluorescence lifetime imaging microscopy is successfully demonstrated in both one- and two-photon cases with surface modified, nanocrystalline silicon quantum dots in the context of bioimaging. The technique is further demonstrated in combination with Förster resonance energy transfer studies where the color of the nanoparticles is tuned by using organic dye acceptors directly conjugated onto the nanoparticle surface., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Herein is presented a microsensor technology as a diagnostic tool for detecting specific matrix metalloproteinases (MMPs) at very low concentrations. MMP-2 and MMP-9 are detected using label free porous silicon (PSi) photonic crystals that have been made selective for a given MMP by filling the nanopores with synthetic polymeric substrates containing a peptide sequence for that MMP. Proteolytic cleavage of the peptide sequence results in a shift in wavelength of the main peak in the reflectivity spectrum of the PSi device, which is dependent on the amount of MMP present. The ability to detect picogram amounts of MMP-2 and MMP-9 released by primary retinal pigment epithelial (RPE) cells and iris pigment epithelial (IPE) cells stimulated with lipopolysaccharide (LPS) is demonstrated. It was found that both cell types secrete higher amounts of MMP-2 than MMP-9 in their stimulated state, with RPE cells producing higher amounts of MMPs than IPE cells. The microsensor performance was compared to conventional protease detection systems, including gelatin zymography and enzyme linked immunosorbent assay (ELISA). It was found that the PSi microsensors were more sensitive than gelatin zymography; PSi microsensors detected the presence of both MMP-2 and MMP-9 while zymography could only detect MMP-2. The MMP-2 and MMP-9 quantification correlated well with the ELISA. This new method of detecting protease activity shows superior performance to conventional protease assays and has the potential for translation to high-throughput multiplexed analysis.

Two different interfaces prepared via UV-hydrosilylation of undecylenic acid and 1,8-nonadiyne on silicon(111) have been explored to develop a robust electrochemical DNA sensor. Electrodes modified with undecylenic acid were found to stably immobilise DNA but could not resist the growth of insulating oxides, whereas 1,8-nonadiyne modified electrodes satisfy both requirements.

Herein, the ability of porous silicon (PSi) particles for selectively binding to specific cells is investigated. PSi microparticles with a high reflectance band in the reflectivity profile are fabricated, and subsequently passivated and modified with antibodies via the Cu(I)-catalyzed alkyne-azide cycloaddition reaction and succimidyl activation. To demonstrate the ability of the antibody-modified PSi particles to selectively bind to one cell type over others, HeLa cells were transfected with surface epitopes fused to fluorescent proteins. The antibody-functionalized PSi particles showed good selectivity for the corresponding surface protein on HeLa cells, with no significant cross-reactivity. The results are important for the application of PSi particles in cell sensing and drug delivery.

In this study, we describe a solution procedure for the preparation and surface modification of photostable colloidal silicon quantum dots (SiQDs) for imaging of cancer cells. Photoluminescent SiQDs were synthesized by reduction of halogenated silane precursors using a microemulsion process. It was shown that 1,8-nonadiyne molecules could be grafted onto the surface of hydrogen-terminated SiQDs via ultraviolet (UV)-promoted hydrosilylation, demonstrated by Fourier transform infrared spectroscopy (FTIR) measurements. In addition, various azide molecules were coupled onto nonadiyne-functionalized particles, rendering particles dispersible in selected polar and nonpolar solvents. The photoluminescence of functionalized SiQDs was stable against photobleaching and did not vary appreciably within biologically applicable pH and temperature ranges. To demonstrate compatibility with biological systems, water-soluble SiQDs were used for fluorescent imaging of HeLa cells. In addition, the SiQDs were shown to be non-cytotoxic at concentrations up to 240 μg/mL. The results presented herein provide good evidence for the versatility of functionalized SiQDs for fluorescent bioimaging application.

We report on an exceedingly mild chemical functionalization of hydrogen-terminated Si(100) with unactivated and unprotected bifunctional α,ω-dialkynes. Monolayer formation occurs rapidly in the dark, and at room temperature, from dilute solutions of an aromatic-conjugated acetylene. The method addresses the poor reactivity of p-type substrates under mild conditions. We suggest the importance of several factors, including an optimal orientation for electron transfer between the adsorbate and the Si surface, conjugation of the acetylenic function with a π-system, as well as the choice of a solvent system that favors electron transfer and screens Coulombic interactions between surface holes and electrons. The passivated Si(100) electrode is amenable to further functionalization and shown to be a viable model system for redox studies at non-oxide semiconductor electrodes in aqueous solutions.

Concerns over possible toxicities of conventional metal-containing quantum dots have inspired growing research interests in colloidal silicon nanocrystals (SiNCs), or silicon quantum dots (SiQDs). This is related to their potential applications in a number of fields such as solar cells, optoelectronic devices and fluorescent bio-labelling agents. The past decade has seen significant progress in the understanding of fundamental physics and surface properties of silicon nanocrystals. Such understanding is based on the advances in the preparation and characterization of surface passivated colloidal silicon nanocrystals. In this critical review, we summarize recent advances in the methods of preparing high quality silicon nanocrystals and strategies for forming self-assembled monolayers (SAMs), with a focus on their bio-applications. We highlight some of the major challenges that remain, as well as lessons learnt when working with silicon nanocrystals (239 references).

Porous silicon (PSi) is an ideal platform for label-free biosensing, and the development of porous silicon patterning will open a pathway to the development of highly parallel PSi biochips for detecting multiple analytes. The optical response of PSi photonic crystal is determined by the changes in the effective bulk refractive index resulting from reactions/events occurring within the internal pore space. Therefore, introducing precise chemical functionalities in the pores of PSi is essential to ensure device selectivity. Here we describe the fabrication of PSi patterns that possess discrete chemical functionalities that are restricted to precise locations. The key difference to previous patterning protocols for PSi is that the entire porous material is first modified with a self-assembled monolayer of a α,ω-diyne adsorbate prior to patterning using a microfabricated titanium mask. The distal alkyne moieties in the monolayer are then amenable to further selective modification by the archetypal "click" reaction, the copper catalyzed alkyne-azide cycloaddition (CuAAC), using the titanium mask as a resist. This type of patterning is suitable for further immobilization of biological recognition elements, and presents a new platform for highly parallel PSi biosensor for multiple detections.

Poly(ethylene glycol) (PEG) is one of the most extensively studied antifouling coatings due to its ability to reduce protein adsorption and improve biocompatibility. Although the use of PEG for antifouling coatings is well established, the stability and density of PEG layers are often inadequate to provide optimum antifouling properties. To improve on these shortcomings, we employed the stepwise construction of PEG layers onto a silicon surface. Acetylene-terminated alkyl monolayers were attached to nonoxidized crystalline silicon surfaces via a one-step hydrosilylation procedure with 1,8-nonadiyne. The acetylene-terminated surfaces were functionalized via a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction of the surface-bound alkynes with an azide to produce an amine terminated layer. The amine terminated layer was then further conjugated with PEG to produce an antifouling surface. The antifouling surface properties were investigated by testing adsorption of human serum albumin (HSA) and lysozyme (Lys) onto PEG layers from phosphate buffer solutions. Detailed characterization of protein fouling was carried out with X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with principal component analysis (PCA). The results revealed no fouling of albumin onto PEG coatings whereas the smaller protein lysozyme adsorbed to a very low extent.

In this paper we explore a multi-step synthetic strategy toward fabrication of monolayer-modified Si(100) electrodes that can be electrochemically switched. The synthetic scheme is modular and benefits from an established intramolecular lactonization scheme of benzoquinone analogs. A redox-tagged pendant group can be released from the surface such as to allow for in situ monitoring of the switch process. We show that this model system can be used to elucidate chemical and structural events for a surface dynamic system that is rapidly gaining popularity. The influence of polarization times, overpotentials and semiconductor doping type on the kinetic of the switch event is also investigated. In both basic and acidic aqueous electrolytes the release of suitable redox-active markers is found to require unexpectedly large cathodic overpotentials. The release event is accompanied by minor oxidation of the electrode surface and the switched constructs can be regenerated by chemical means with no appreciable deterioration of surface quality.

Herein, mesoporous silicon (PSi) is configured as a single sensing device that has dual readouts; as a photonic crystal sensor in a Rugate filter configuration, and as a high surface area porous electrode. The as-prepared PSi is chemically modified to provide it with stability in aqueous media and to allow for the subsequent coupling of chemical species, such as via Cu(I)-catalyzed cycloaddition reactions between 1-alkynes and azides ("click" reactions). The utility of the bimodal capabilities of the PSi sensor for monitoring surface coupling procedures is demonstrated by the covalent coupling of a ferrocene derivative, as well as by demonstrating ligand-exchange reactions (LER) at the PSi surface. Both types of reactions were monitored through optical reflectivity measurements, as well as electrochemically via the oxidation/reduction of the surface tethered redox species.

A solution method for preparing surface functionalized colloidal silicon quantum dots (SiQDs) is presented. SiQDs prepared by this method are reasonably monodispersed and can be further functionalized via thiol-ene click reactions to introduce specific functionalities (i.e. -NH(2), -COOH, -SO(3)(-), alkane, alkene).

The ability to impart discrete surface chemistry to the inside and outside of mesoporous silicon is of great importance for a range of biomedical applications, from selective (bio)sensing to tissue-specific drug delivery. Here we present a generic strategy toward achieving depth-resolved functionalization of the external and internal porous surfaces by a simple change in the wavelength of the light being used to promote surface chemical reactions. UV-assisted hydrosilylation, limited by the penetration depth of UV light, is used to decorate the outside of the mesoporous structure with carboxylic acid molecules, and white light illumination triggers the attachment of dialkyne molecules to the inner porous matrix.

In this paper we demonstrate the possibility of modifying porous silicon (PSi) particles with surface chemistry and recognition molecules (antibodies) such that these devices could potentially be used for single-cell identification or sensing. This is achieved by modifying PSi Rugate filters via hydrosilylation with surface chemistry that serves firstly, to protect the silicon surfaces from oxidation; secondly, renders the surfaces resistant to nonspecific adsorption of proteins and cells and thirdly, allows further functionality to be added such as the coupling of antibodies. The surface chemistry remained unchanged after sonication of the PSi to form PSi microparticles. The ability to monitor the spectroscopic properties of microparticles, and shifts in the optical signature due to changes in the refractive index of the material within the pore space, is demonstrated. The particles are shown to remain stable in physiological buffers and human blood for longer than one week. Finally, the modification of the PSi particles with functional antibodies is achieved.

In this article we present an optical biosensor for label-free detection of trace levels of protease activity. The scheme is based on surface functionalized porous silicon optical structures which supports optical Bloch surface modes. The optical structure provides a resonant optical mode for high sensitivity detection and open access of the sensing layer to the target enzyme. Protease detection is based on the digestion of gelatin, covalently attached inside the pore space, resulting in a spectral blue-shift of the optical mode. Monitoring of spatially separated resonant optical modes is used to eliminate optical response from nonspecific adsorption.

This paper demonstrates the direct electron transfer between the heme moiety of horse hearth cytochrome c and a pyridinyl group on self-assembled-monolayer-modified Si(100) electrodes. Self-assembled monolayers (SAMs) containing the putative receptor ligand were prepared by a step-wise procedure using "click" reactions of acetylene-terminated alkyl monolayers and isonicotinic acid azide derivatives. Unoxidized Si(100) electrodes, possessing either isonicotinate or isonicotinamide receptor ligands, were characterized using X-ray photoelectron spectroscopy, contact-angle goniometry, cyclic voltammetry, and electrochemical impedance spectroscopy. The ability of isonicotinic acid terminated layers to coordinatively bind the redox center of cytochrome c was found to be restricted to pyridinyl assemblies with a para-ester linkage present. The protocol detailed here offers an experimentally simple modular approach to producing chemically well-defined SAMs on silicon surfaces for direct electrochemistry of a well-studied model redox protein.

Herein, we report on the production of nanoelectrode arrays by attaching colloidal gold on silicon-bound mixed self-assembled monolayers of TFA-protected alkenylthiol (C(11)-S-TFA) and undecylenic acid (acid). Effective modification of the surface, tethering of the nanoparticles, and the direct influence of the deprotected alkenylthiol (C(11)-SH) /acid ratio on the number of adherent particles were demonstrated using X-ray photoelectron spectroscopy, electrochemistry, and atomic force microscopy. Cyclic voltammetry showed that the enhancement of electron transfer to the silicon surface by the presence of nanoparticles is influenced by the number of tethered nanoparticles.

Here we report on the functionalization of alkyne-terminated alkyl monolayers on highly doped Si(100) using "click" reactions to immobilize ferrocene derivatives. The reaction of hydrogen-terminated silicon surfaces with a diyne species was shown to afford very robust functional surfaces where the oxidation of the underlying substrate was negligible. Detailed characterization using X-ray photoelectron spectroscopy, X-ray reflectometry, and cyclic voltammetry demonstrated that the surface acetylenes had reacted in moderate yield to give surfaces exposing ferrocene moieties. Upon extensive exposure of the redox-active architecture to oxidative environments during preparative and characterization steps, no evidence of SiOx contaminants was shown for derivatized SAMs prepared from single-component 1,8-nonadiyne, fully acetylenylated, monolayers. An analysis of the redox behavior of the prepared Si(100) electrodes based on relevant parameters such as peak splitting and position and shape of the reduction/oxidation waves depicted a well-behaved redox architecture whose spectroscopic and electrochemical properties were not significantly altered even after prolonged cycling in aqueous media between -100 and 800 mV versus Ag|AgCl. The reported strategy represents an experimentally simple approach for the preparation of silicon-based electrodes where, in addition to close-to-ideal redox behavior, remarkable electrode stability can be achieved. Both the presence of a distal alkyne moiety and temperatures of formation above 100 degrees C were required to achieve this surface stabilization.

The ease of fabricating high quality photonic crystals from porous silicon and its biocompatibility have inspired the conception of various biosensing schemes using this material. However, the instability of porous silicon has significantly slowed progress in this area. Here we discuss the potential of different porous silicon photonic crystals for biosensing in the context of its surface chemistry and nanostructure, both of which need to be optimized to obtain sensitive and stable devices. Of particular promise are recent approaches that use porous silicon as sensors for enzymatic activity, for cell capture and concentration devices.

Porous silicon has shown potential for various applications in biology and medicine, which require that the material (1) remain stable for the length of the intended application and (2) resist non-specific adsorption of proteins. Here we explore the efficacy of short oligo(ethylene glycol) moieties incorporated into organic layers via two separate strategies in achieving these aims. In the first strategy the porous silicon structure was modified in a single step via hydrosilylation of alpha-oligo(ethylene glycol)-omega-alkenes containing three or six ethylene glycol units. The second strategy employs two steps: (1) hydrosilylation of succinimidyl-10-undecenoate and (2) coupling of an amino hexa(ethylene glycol) species. The porous silicon photonic crystals modified by the two-step strategy displayed greater stability relative to the single step procedure when exposed to conditions of physiological temperature and pH. Both strategies produced layers that resist non-specific adsorption of proteins as determined with fluorescently labelled bovine serum albumin. The antifouling behaviour and greater stability to physiological conditions provided by this chemistry enhances the suitability of porous silicon for biomaterials applications.

Cholera toxin levels are optically detected by affinity capture within hybrid lipid bilayer membranes formed in the nanostructures of porous silicon photonic crystals.

Self-assembled monolayers formed by thermal hydrosilylation of a trifluoroacetyl-protected alkenylthiol on Si-H surfaces, followed by removal of the protecting groups, yield essentially oxide-free monolayers suitable for the formation of Si-C11H22-S-Hg and Si-C11H22-S-Au junctions in which the alkyl chains are chemically bound to the silicon surface (via Si-C bonds) and the metal electrode (via Hg-S or Au-S bonds). Two barriers to charge transport are present in the system: at low bias the current is temperature activated and hence limited by thermionic emission over the Schottky barrier in the silicon, whereas as at high bias transport is limited by tunneling through the organic monolayer. The thiol-terminated monolayer on oxide-free silicon provides a well-characterized system allowing a careful study of the importance of the interfacial bond to the metal electrode for current transport through saturated molecules.

Hydrosilylation of alkenes with epoxide-terminated tri(ethylene oxide) moieties on Si-H surfaces yields homogeneous monolayers for the efficient coupling of biomolecules. The wetting properties of the epoxide-functionalized surface allow for the spotting of solutions of biomolecules, making the surface amenable to microarraying. Immobilization of thiolated DNA was achieved in a single step to fabricate biorecognition interfaces showing the hybridization of complementary DNA at low concentrations and negligible binding of noncomplementary DNA.

Surface modification with oligo(ethylene oxide) functionalized monolayers terminated with reactive headgroups constitutes a powerful strategy to provide specific coupling of biomolecules with simultaneous protection from nonspecific adsorption on surfaces for the preparation of biorecognition interfaces. To date, oligo(ethylene oxide) functionalized monolayer-forming molecules which can be activated for attachment of biomolecules but which can selectively form monolayers onto hydrogen terminated silicon have yet to be developed. Here, self-assembled monolayers (SAMs) containing tetra(ethylene oxide) moieties protected with tert-butyl dimethylsilyl groups were formed by thermal hydrosilylation of alkenes with single-crystal Si(111)-H. The protection group was used to avoid side reactions with the hydride terminated silicon surface. Monolayer formation was carried out using solutions of the alkene in the high-boiling-point solvent 1,3,5-triethylbenzene. The protecting group was removed under very mild acidic conditions to yield a free hydroxyl functionality, a convenient surface moiety for coupling of biological entities via carbamate bond formation. The chemical composition and structure of the monolayers before and after deprotection were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray reflectometry. To demonstrate the utility of this surface for covalent modification, two reagents were compared and contrasted for their ability to activate the surface hydroxyl groups for coupling of free amines, carbonyl diimidazole (CDI), and disuccinimidyl carbonate (DSC). Analysis of XP spectra before and after activation by CDI or DSC, and after subsequent reaction with glycine, provided quantitative information on the extent of activation and overall coupling efficiencies. CDI activated surfaces gave poor coupling yields under various conditions, whereas DSC mediated activation followed by aminolysis at neutral pH was found to be an efficient method for the immobilization of amines on tetra(ethylene oxide) modified surfaces.

We report on the observation of significant optical bistability in the transmission and reflection properties of mesoporous silicon microcavities when illuminated with a 150 ns pulsed laser at 532 nm. The observed optical hysteresis is shown to be transient in nature and the properties are strongly dependent on the porosity of the cavity layer. The onset and damage threshold intensity are also shown to be porosity dependent. Our modeling suggests that the observed effects are due to changes in the nonlinear refractive index where the transient lifetime increases with increasing porosity. We investigate the role of surface states on influencing the bistable process by passivating the internal porous surface with hydrosilylation chemistry. [ABSTRACT FROM AUTHOR]

The reaction of hydrogen‐terminated Si(100) with 1,8‐nonadiyne was previously shown to afford robust surfaces where oxidation of the substrate is not evident. Here, the experimental conditions required for reacting hydrogen‐terminated Si(100) with α,ω‐diynes of different lengths is explored via thermal hydrosilylation of 1,6‐heptadiyne, 1,8‐nonadiyne, 1,10‐undecadiyne and 1,15‐hexadecadiyne. X‐ray photoelectron spectroscopy indicated monolayers were successfully formed with oxide levels below the XPS detection limit for molecules with lengths varying from 7 to 11 carbons. It was observed that the apparent rate of electron transfer (ket) was affected not only by the SAM thickness, but also by hopping between ferrocene moieties where the presence of tiny oxidative defects act as electron transfer hotspots. Electron transfer on monolayer protected silicon: SAM thickness plays a major influence on electron transfer kinetics. However, on silicon, the process is also affected by the presence of SiOx hotspots and by the surface coverage of tethered redox species. The consequence is SAMs with a higher‐coverage of redox species on 9 or 11 carbons length displaying faster ket than SAMs with a lower‐coverage of redox species on 7 carbons length. [ABSTRACT FROM AUTHOR]

Etching rate is a major concern for the effective mass production of high-aspect-ratio microstructures, especially in p-type silicon. In this work, controlled electrochemical growth of high-aspect-ratio (from 15 to 110) macropores in p-type silicon at ultrafast etching rate (from 16 to 30 µm min−1) has been studied. Based on current-burst-model, pore formation was systematically investigated from the nucleation phase to stable pore growth. Good macropores with depth up to 180 µm and aspect ratio beyond 110 was achieved in just 11 min. This sets a new record on state-of-the-art p-type silicon microfabrication and can promote the development of microdevices. High-aspect-ratio macropores at ultrahigh etching rate were achieved in p-type silicon, which sets a novel record among p-type silicon microfabrication and can promote the effective mass production of microdevices. [ABSTRACT FROM AUTHOR]

Organic functionalization of non-oxidized silicon surfaces, while allowing for robust chemical passivation of the inorganic substrate, is intended and expected to broaden the chemical, physical and electronic properties of the currently most relevant technological material. Numerous protocols are now available for the preparation of Si-C, Si-O and Si-N bound layers. In particular, the covalent attachment of 1-alkenes and 1-alkynes onto hydride-terminated Si(100) and Si(111) has seen a wealth of research activity starting from the pioneering work of Linford and Chidsey (Alkyl monolayers covalently bonded to silicon surfaces, J. Am. Chem. Soc., 1993, 115(26), 12631-12632). This critical review aims to bring together the available wet-chemical routes toward the formation of silicon-organic monolayers under ambient conditions. Particular emphasis is placed on discussing the reasons behind the need for novel chemical approaches that are straightforward, modular and of wide scope so as to allow the application of silicon electrodes in aqueous electrolytes. A general introduction to biomolecular recognition events at functionalized silicon surfaces is also presented (281 references). [ABSTRACT FROM AUTHOR]

Harnessing triboelectricity is a promising form of energy harvesting technology. Unlike conventional triboelectric nanogenerators, which convert friction between insulators into alternating current, a sliding metal‒semiconductor contact converts small movements into direct current (d.c.), which can power electronic circuitry without the need of electrical rectification. The zero-bias d.c. output of a dynamic metal‒semiconductor contact is assumed to increase linearly with its area, posing restrictions on the miniaturization of this new type of power sources. By implementing silicon surfaces that are electrically heterogeneous, it is found that d.c. outputs are not steady-state, but instead peak when the metal contact slides across concave boundaries between highly and poorly rectifying silicon crystal facets. Sharp lateral changes in electrical rectification, coupled to a concave surface curvature, are more important to maximize current densities than applied normal force or surface friction. These findings help alleviating device-wear issues, as well as removing physical constraints to the miniaturization of sliding-diode nanogenerators. Image 1 • Direct-current produced by a sliding Schottky diode peaks at boundaries between highly and poorly rectifying crystal planes • Removing device wear: current outputs from out-of-equilibrium diodes do not necessarily scale with friction • Pressure effects on the flow of minority carrier are a path to maximize tribocurrents in sliding-diode nanogenerators [ABSTRACT FROM AUTHOR]

In this paper we report on the light emitting properties of mesoporous silicon vertical-cavity optical resonators with II-VI colloidal quantum dots selectively deposited in the cavity layer. Optical resonator structures exhibit reflectivity stop bands of several hundred nanometres and resonant modes with line-widths less than 3.5 nm. The observed modification of spectral and spatial emission properties of the quantum dots and tenfold enhancement at the resonance wavelength is consistent with cavity enhanced spontaneous emission. Using this hybrid fabrication approach we show that narrow band light emitting structures may be fabricated over a broad spectral region in the visible and near-infrared. [ABSTRACT FROM AUTHOR]

Here, a printing technology is reported that enables the functionalization of photoconducting materials with an arbitrary user‐defined pattern of nanocrystals. Two sets of information can be encoded into the same unit area; control over the polyhedral shape of individual nanocrystals and high lateral resolution (micrometer scale) for large 2D patterns (millimeter scale) of Cu2O that were grown over unstructured amorphous silicon. The key to this new technology is a parallel modulation of both the electrode kinetics at the silicon/electrolyte interface and the light‐assisted control of adsorption of halide ions on the growing Cu2O particles. This is achieved using local pixelation of a visible light stimulus by adapting to the field of photoelectrochemistry spatial light modulation more often used in super resolution microscopy. Any user‐defined pattern (i.e., any arbitrary bitmap image file or a sequence of images) is converted within seconds into an array of nanoparticles. The process does not rely on the use of physical masks or chemical templating and it is parallel, meaning, for example, that it is possible to guide the exclusive growth of cubic nanoparticles in an area defined at will by the operator, while the neighboring section(s) are being covered exclusively by octahedrons. Cryptic nanoinks. Development of a photoelectrochemical printing technology with applications in the assembly of nanoparticle‐based electrical circuitry or anticounterfeiting labels. This technology is based on a parallel modulation of both the electrode kinetics at the silicon/electrolyte interface as well as the light‐assisted control of adsorption of halide ions on growing metal oxide particles. [ABSTRACT FROM AUTHOR]

Light-activated electrochemistry is a powerful concept, where faradaic electrochemistry at a monolayer protected monolithic silicon electrode can be ‘turned on’ at any location with micron scale resolution simply by illuminating that region with light. The three requirements for light-activated electrochemistry are that i) the silicon must be protected from oxidation with a self-assembled monolayer (SAM), ii) the semiconducting electrode must be biased into depletion at the redox potential of the species of interest and iii) the redox couple must be covalently attached to the electrode. Herein it is shown that light-activated electrochemistry can be performed with solution species if they adsorb to the surface of the SAM. It is shown that redox species such as ferrocene and ruthenium hexamine adsorb onto the 1,8-nonadiyne modified silicon surface and undergo electron transfer upon illumination while potassium ferrocyanide does not. It is proposed this adsorption causes an increase in electronic coupling between the redox species and the silicon electrode such that appreciable electron transfer through the monolayer was achieved. Furthermore, it is demonstrated that light-activated electrochemistry can be used to rapidly switch between macroelectrode- and microelectrode-type voltammetry at the same interface by simple means of modulating the light intensity. This work expands our understanding of light-activated electrochemistry and its application for interrogating discrete regions on an electrode in a highly parallel way. [ABSTRACT FROM AUTHOR]

The immobilization of gold nanoparticles (AuNPs) on functionalized electrodes has been shown to be an effective way for switching on the electrochemistry at an otherwise passivated surface. Herein, the attachment of AuNPs onto the industrially available p + - Si(100) electrodes was studied by means of cyclic voltammetry and X-ray photoelectron spectroscopy. The hydrosilylation of p + -Si(100) with 1,8-nonadiyne followed by the “click” of azido propylamine onto the alkyne end formed a self-assembled monolayer (SAM), which protected the p + -Si(100) against oxidation and prevented the electron transfer from dissolved Ru(NH 3 ) 6 3 + . Upon the attachment of AuNPs, however, electron transfer was initially restored. The performance of the p + –Si–SAM–AuNP electrode was found to decay with repeated voltammetric cycling due to the formation of SiO x underneath the SAM. These results suggest that p + –Si–SAM–AuNP electrodes can be used in electrochemical devices for single use applications but are not suitable for long-term use. [ABSTRACT FROM AUTHOR]

Abstract: Herein reported is the synthesis of functionalised oligoethylene glycol molecules, with an azido group at one end and an ionisable group at the other end, and their attachment onto alkyne-terminated silicon(100) surfaces using ‘click’ chemistry. The modified surfaces were characterised using X-ray photoelectron spectroscopy (XPS) and water contact angle goniometry. The antifouling behaviour of these surfaces was assessed and it was shown that while surfaces presenting both charged and ethylene glycol moieties are antifouling, the antifouling effectiveness is influenced by the surface charge as modulated via the pH of the solution. [Copyright &y& Elsevier]

Abstract: High-density, surface-mounted ferrocene has been prepared using covalent immobilisation of an alcohol substituted ferrocene derivative to a pre-assembled single-walled carbon nanotubes directly anchored to silicon(100) surface (SWCNTs-Si). The formation of these ferrocene-modified electrodes (Fc-SWCNTs-Si) has been followed using X-ray photoelectron spectroscopy and atomic force microscopy. Electrochemical results show the surface concentration of ferrocenemethanol molecules is 9.26×10−8 molcm−2, which is about 500–1000 times greater than the experimentally measured coverage of ferrocene directly attached to flat Si(100) surfaces. The reversible one-electron wave of the ferrocene/ferrocenium couple was observed at 490mV versus Ag+/Ag and the apparent rate constant of electron transfer, k app, was 21s−1. These results suggest these ferrocene-modified electrodes are excellent candidates for molecular memory devices. [Copyright &y& Elsevier]