Shape- and Dimension-Controlled Single-Crystalline Silicon and SiGe Nanotubes: Toward Nanofluidic FET Devices

We report here on the formation of robust and entirely hollow single-crystalline silicon nanotubes, from various tubular to conical structures, with uniform and well-controlled inner diameter, ranging from as small as 1.5 up to 500 nm, and controllable wall thickness. Second, and most important, these nanotubes can be doped in situ with different concentrations of boron and phosphine to give p/n-type semiconductor nanotubes. SixGe1−x-alloy nanotubes can also be prepared. This synthetic approach enables independent and precise control of diameter, wall thickness, shape, taper angle, crystallinity, and chemical/electrical characteristics of the nanotubular structures obtained. Notably, diameter and wall thickness of nearly any size can be obtained. This unique advantage allows the achievement of novel and perfectly controlled high-quality electronic materials and the tailoring of the tube properties to better fit many biological, chemical, and electrical applications. Electrical devices based on this new family of electrically active nanotubular building-block structures are also described with a view toward the future realization of nanofluidic FET devices

Wall-Selective Chemical Alteration of Silicon Nanotube Molecular Carriers

Recently, there has been significant interest in the synthesis and potential applications of semiconductor nanotubes (NTs). In this context, many efforts have been invested in developing new routes to control and engineer their surface chemistry. We report herein on a simple route to differentially and selectively functionalize the inner and outer surfaces of silicon nanotubes (SiNTs) with organic molecular layers containing different functional groups and hydrophobicity/hydrophilicity chemical nature, via covalent binding, to give nanotubular structures with dual chemical properties. Significantly, our unique synthetic approach can be further extended to directly form hollow crystalline nanotubular structures with their inner/outer surfaces independently and selectively altered chemically. Additionally, SiNTs inner and/or outer walls can be selectively decorated with metal nanoparticles. Both inner and outer walls can be individually and separately modified with the same metal nanoparticles, with different metal NPs in the inside and outside walls or with a combination of metal NPs decoration and molecular layers, if so required. Furthermore, the dually modified nanotubes were then exploited as phase extraction nanocarriers to demonstrate their potential in future chemical and biological separation, extraction, and filtering applications

From Crystalline Germanium–Silicon Axial Heterostructures to Silicon Nanowire–Nanotubes

One-dimensional (1D) nanostructures have attracted considerable attention as a result of their exceptional properties and potential applications. Among them, 1D axial heterostructures with well-defined and controlled heterojunctions between different nanomaterials or between different 1D nanostructures (i.e., nanowire–nanotube heterojunctions) have recently become of particular interest as potential building blocks in future high-performance nano-optoelectronic and nanoelectronic devices. Here, we report on the preparation and characterization of crystalline silicon nanowire–nanotube (SiNW-NT) heterostructures with controlled geometry, kinked and unkinked, and composition using germanium–silicon nanowire heterostructures with abrupt heterojunctions (∼2 nm wide) as a template via the VLS-CVD mechanism

Electronic Transduction of DNA Sensing Processes on Surfaces: Amplification of DNA Detection and Analysis of Single-Base Mismatches by Tagged Liposomes

Tagged, negatively charged, liposomes are used to amplify DNA sensing processes. The analyses of the target DNA are transduced electrochemically by using Faradaic impedance spectroscopy, or by microgravimetric measurements with Au-quartz crystals. By one method, a probe oligonucleotide (1) is assembled on Au-electrodes or Au-quartz crystals. The formation of the double-stranded assembly with the analyte DNA (2) is amplified by the association of the 3-oligonucleotide-functionalized liposomes to the sensing interface. The target DNA is analyzed by this method with a sensitivity limit that corresponds to 1 × 10-12 M. A second method to amplify the sensing of the analyte involves the interaction of the 1-functionalized electrode or Au-quartz crystal with the target DNA sample (2) that is pretreated with the biotinylated oligonucleotide (4). The formation of the three-component double-stranded assembly between 1/2/4 is amplified by the association of avidin and biotin-labeled liposomes to the sensing interfaces. By the secondary association of avidin and biotin-tagged liposomes, a dendritic-type amplification of the analysis of the DNA is accomplished. The analyte DNA (2) is sensed by this method with a sensitivity limit corresponding to 1 × 10-13 M. The biotin-tagged liposomes are also used to probe and amplify single-base mismatches in an analyte DNA. The 6-oligonucleotide-functionalized Au-electrode or Au-quartz crystal was used to differentiate the single-base mismatch (G) in the mutant (5) from the normal A-containing gene (5a). Polymerase-induced coupling of the biotinylated-C-base to the double-stranded assembly generated between 6 and 5 followed by the association of avidin and biotin-tagged liposomes is used to probe the single base mismatch. The functionalized liposomes provide a particulate building unit for the dendritic amplification of DNA sensing

Redox-Reactive Field-Effect Transistor Nanodevices for the Direct Monitoring of Small Metabolites in Biofluids toward Implantable Nanosensors Arrays

Chemically modified field-effect transistor (FET) nanodevices were shown to be a selective and extremely sensitive detection platform. In FET-based sensors, signal amplification and transduction is based on electrostatic gating of the nanometric semiconductor channel by analyte–receptor interactions, which measurably affect the transconductance of the device. However, chemically modified FETs must overcome several fundamental limitations before they can be effectively deployed as real-time sensors for bioevents occurring on their surface in complex biofluids. Here, we demonstrate the development of amperoFET devices for the real-time continuous monitoring of small molecular metabolites in biofluids. The surface of the nanowires is covalently modified with a redox reversible moiety, which is easily oxidized in the presence of H2O2. The reversible redox transformation of the surface-confined molecules is carried out by a hot electron injection mechanism, conducted simply by the modulation of the source–drain current through the nanoFET sensing device. By this approach, electrons may be injected by the nanowire element into the surface-confined redox moiety and thus maintain a whole-electrically actuated redox system in which the oxidation state is completely controlled by the current applied to the amperoFET system. The modulation of the source–drain current allows the control of the reduced versus oxidized redox moieties population on the nanowire surface, and this, in turn, is applied as the main sensing mechanism. At a given constant source–drain and gate voltage, the chemical perturbation exerted by the presence of chemical oxidants in the tested biofluid will lead to a measurable conductance change. Alteration in the concentration of the specific metabolite will chemically regulate the extent of perturbation applied to the redox system, which can be utilized for the quantification of the molecular metabolite of interest. These ‘equilibrium’-type sensors are fully electrically operated and can be further used in implantable sensing applications

Synthesis of Hybrid Multicomponent Disklike Nanoparticles

This manuscript describes the synthesis of a new generation of multicomponent disklike nanoparticles. In this work, we present for the first time, through the template-based sequential electrochemical deposition of metal/semiconductor/polymer segments, an innovative and effective method for preparing a wide range of metallic, semiconductor, and polymeric hybrid multicomponent disklike nanoparticles covering a wide and controlled dimension range from a few nanometers to hundreds of nanometers. Moreover, we can readily tailor the desired final size, aspect ratio, and composition of the disklike nanoparticles by varying the precursor material used and the electrochemical deposition approach. Furthermore, this simple route leads to a highly reproducible and high-throughput synthetic platform of new multicomponent and multifunctional nanoscale building blocks

Antigen-Dissociation from Antibody-Modified Nanotransistor Sensor Arrays as a Direct Biomarker Detection Method in Unprocessed Biosamples

The detection of biomolecules is critical for a wide spectrum of applications in life sciences and medical diagnosis. Nonetheless, biosamples are highly complex solutions, which contain an enormous variety of biomolecules, cells, and chemical species. Consequently, the intrinsic chemical complexity of biosamples results in a significant analytical background noise and poses an immense challenge to any analytical measurement, especially when applied without prior efficient separation and purification steps. Here, we demonstrate the application of antigen-dissociation regime, from antibody-modified Si-nanowire sensors, as a simple and effective direct sensing mechanism of biomarkers of interest in complex biosamples, such as serum and untreated blood, which does not require ex situ time-consuming biosample manipulation steps, such as centrifugation, filtering, preconcentration, and desalting, thus overcoming the detrimental Debye screening limitation of nanowire-based biosensors. We found that two key parameters control the capability to perform quantitative biomarkers analysis in biosamples: (i) the affinity strength (<i>k</i>_off rate) of the antibody–antigen recognition pair, which dictates the time length of the high-affinity slow dissociation subregime, and (ii) the “flow rate” applied during the solution exchange dissociation step, which controls the time width of the low-affinity fast-dissociation subregime. Undoubtedly, this is the simplest and most convenient approach for the SiNW FET-based detection of antigens in complex untreated biosamples. The lack of ex situ biosample manipulation time-consuming processes enhances the portability of the sensing platform and reduces to minimum the required volume of tested sample, as it allows the direct detection of untreated biosamples (5–10 μL blood or serum), while readily reducing the detection cycle duration to less than 5 min, factors of great importance in near-future point-of-care medical applications. We believe this is the first ever reported demonstration on the real-time, direct label-free sensing of biomarkers from untreated blood samples, using SiNW-based FET devices, while not compromising the ultrasensitive sensing capabilities inherent to these devices

Amplified DNA Sensing and Immunosensing by the Rotation of Functional Magnetic Particles

Amplified chemiluminescent detection of DNA−complementary DNA or of antigen−antibody interactions is accomplished in the presence of rotating functionalized magnetic particles

Nanodicing Single Crystalline Silicon Nanowire Arrays

Here, we demonstrate a novel method for the production of single-crystal Si nanowire arrays based on the top-down carving of Si-nanowall structures from a donor substrate, and their subsequent controlled and selective harvesting into a sacrificial solid material block. Nanosectioning of the nanostructures-embedding block by ultramicrotome leads to the formation of size, shape, and orientation-controlled high quality nanowire arrays. Additionally, we introduce a novel approach that enables transferring the nanowire arrays to any acceptor substrate, while preserving their orientation, and placing them on defined locations. Furthermore, crystallographic analysis and electrical measurements were performed, proving that the quality of the sectioned nanowires, which derive from their original crystalline donor substrate, are remarkably preserved

Direct and Selective Electrochemical Vapor Trace Detection of Organic Peroxide Explosives via Surface Decoration

The ability to detect traces of highly energetic explosive materials sensitively, selectively, accurately, and rapidly could be of enormous benefit to civilian national security, military applications, and environmental monitoring. Unfortunately, the detection of explosives still poses a largely unmet arduous analytical problem, making their detection an issue of burning immediacy and a massive current challenge in terms of research and development. Although numerous explosive detection approaches have been developed, these methods are usually time-consuming, require bulky equipment, tedious sample preparation, a trained operator, cannot be miniaturized, and lack the ability to perform automated real-time high-throughput analysis, strongly handicapping their mass deployment. Here, we present the first demonstration of the “direct” electrochemical approach for the sensitive, selective, and rapid vapor trace detection of TATP and HMTD, under ambient conditions, unaffected by the presence of oxygen and hydrogen peroxide species, down to concentrations lower than 10 ppb. The method is based on the use of Ag-nanoparticles-decorated carbon microfibers air-collecting electrodes (μCF), which allow for the selective direct detection of the organic peroxide explosives, through opening multiple redox routes, not existent in the undecorated carbon electrodes. Finally, we demonstrate the direct and rapid detection of TATP and HMTD explosive species from real-world air samples