16 research outputs found
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
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><sub>off</sub> 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
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
Controlled Formation of Radial Core–Shell Si/Metal Silicide Crystalline Heterostructures
The
highly controlled formation of “radial” silicon/NiSi
core−shell nanowire heterostructures has been demonstrated
for the first time. Here, we investigated the “radial”
diffusion of nickel atoms into crystalline nanoscale silicon pillar
11 cores, followed by nickel silicide phase formation and the creation
of a well-defined shell structure. The described approach is based
on a two-step thermal process, which involves metal diffusion at low
temperatures in the range of 200–400 °C, followed by a
thermal curing step at a higher temperature of 400 °C. In-depth
crystallographic analysis was performed by nanosectioning the resulting
silicide–shelled silicon nanopillar heterostructures, giving
us the ability to study in detail the newly formed silicide shells.
Remarkably, it was observed that the resulting silicide shell thickness
has a self-limiting behavior, and can be tightly controlled by the
modulation of the initial diffusion-step temperature. In addition,
electrical measurements of the core–shell structures revealed
that the resulting shells can serve as an embedded conductive layer
in future optoelectronic applications. This research provides a broad
insight into the Ni silicide “radial” diffusion process
at the nanoscale regime, and offers a simple approach to form thickness-controlled
metal silicide shells in the range of 5–100 nm around semiconductor
nanowire core structures, regardless the diameter of the nanowire
cores. These high quality Si/NiSi core–shell nanowire structures
will be applied in the near future as building blocks for the creation
of utrathin highly conductive optically transparent top electrodes,
over vertical nanopillars-based solar cell devices, which may subsequently
lead to significant performance improvements of these devices in terms
of charge collection and reduced recombination
Controlled Formation of Radial Core–Shell Si/Metal Silicide Crystalline Heterostructures
The
highly controlled formation of “radial” silicon/NiSi
core−shell nanowire heterostructures has been demonstrated
for the first time. Here, we investigated the “radial”
diffusion of nickel atoms into crystalline nanoscale silicon pillar
11 cores, followed by nickel silicide phase formation and the creation
of a well-defined shell structure. The described approach is based
on a two-step thermal process, which involves metal diffusion at low
temperatures in the range of 200–400 °C, followed by a
thermal curing step at a higher temperature of 400 °C. In-depth
crystallographic analysis was performed by nanosectioning the resulting
silicide–shelled silicon nanopillar heterostructures, giving
us the ability to study in detail the newly formed silicide shells.
Remarkably, it was observed that the resulting silicide shell thickness
has a self-limiting behavior, and can be tightly controlled by the
modulation of the initial diffusion-step temperature. In addition,
electrical measurements of the core–shell structures revealed
that the resulting shells can serve as an embedded conductive layer
in future optoelectronic applications. This research provides a broad
insight into the Ni silicide “radial” diffusion process
at the nanoscale regime, and offers a simple approach to form thickness-controlled
metal silicide shells in the range of 5–100 nm around semiconductor
nanowire core structures, regardless the diameter of the nanowire
cores. These high quality Si/NiSi core–shell nanowire structures
will be applied in the near future as building blocks for the creation
of utrathin highly conductive optically transparent top electrodes,
over vertical nanopillars-based solar cell devices, which may subsequently
lead to significant performance improvements of these devices in terms
of charge collection and reduced recombination
Probing the Interactions of Intrinsically Disordered Proteins Using Nanoparticle Tags
The structural plasticity of intrinsically
disordered proteins serves as a rich area for scientific inquiry.
Such proteins lack a fix three-dimensional structure but can interact
with multiple partners through numerous weak bonds. Nevertheless,
this intrinsic plasticity possesses a challenging hurdle in their
characterization. We underpin the intermolecular interactions between
intrinsically disordered neurofilaments in various hydrated conditions,
using grafted gold nanoparticle (NP) tags. Beyond its biological significance,
this approach can be applied to modify the surface interaction of
NPs for the creation of future tunable “smart” hybrid
biomaterials
Manipulating and Monitoring On-Surface Biological Reactions by Light-Triggered Local pH Alterations
Significant
research efforts have been dedicated to the integration
of biological species with electronic elements to yield smart bioelectronic
devices. The integration of DNA, proteins, and whole living cells
and tissues with electronic devices has been developed into numerous
intriguing applications. In particular, the quantitative detection
of biological species and monitoring of biological processes are both
critical to numerous areas of medical and life sciences. Nevertheless,
most current approaches merely focus on the “monitoring”
of chemical processes taking place on the sensing surfaces, and little
efforts have been invested in the conception of sensitive devices
that can simultaneously “control” and “monitor”
chemical and biological reactions by the application of on-surface
reversible stimuli. Here, we demonstrate the light-controlled fine
modulation of surface pH by the use of photoactive molecularly modified
nanomaterials. Through the use of nanowire-based FET devices, we showed
the capability of modulating the on-surface pH, by intensity-controlled
light stimulus. This allowed us simultaneously and locally to control
and monitor pH-sensitive biological reactions on the nanodevices surfaces,
such as the local activation and inhibition of proteolytic enzymatic
processes, as well as dissociation of antigen–antibody binding
interactions. The demonstrated capability of locally modulating the
on-surface effective pH, by a light stimuli, may be further applied
in the local control of on-surface DNA hybridization/dehybridization
processes, activation or inhibition of living cells processes, local
switching of cellular function, local photoactivation of neuronal
networks with single cell resolution and so forth
Supplement 1: Full rotational control of levitated silicon nanorods
Supplement 1 Originally published in Optica on 20 March 2017 (optica-4-3-356
Optically-Gated Self-Calibrating Nanosensors: Monitoring pH and Metabolic Activity of Living Cells
Quantitative
detection of biological and chemical species is critical to numerous
areas of medical and life sciences. In this context, information regarding
pH is of central importance in multiple areas, from chemical analysis,
through biomedical basic studies and medicine, to industry. Therefore,
a continuous interest exists in developing new, rapid, miniature,
biocompatible and highly sensitive pH sensors for minute fluid volumes.
Here, we present a new paradigm in the development of optoelectrical
sensing nanodevices with built-in self-calibrating capabilities. The
proposed electrical devices, modified with a photoactive switchable
molecular recognition layer, can be optically switched between two
chemically different states, each having different chemical binding
constants and as a consequence affecting the device surface potential
at different extents, thus allowing the ratiometric internal calibration
of the sensing event. At each point in time, the ratio of the electrical
signals measured in the ground and excited states, respectively, allows
for the absolute concentration measurement of the molecular species
under interest, without the need for electrical calibration of individual
devices. Furthermore, we applied these devices for the real-time monitoring
of cellular metabolic activity, extra- and intracellularly, as a potential
future tool for the performance of basic cell biology studies and
high-throughput personalized medicine-oriented research, involving
single cells and tissues. This new concept can be readily expanded
to the sensing of additional chemical and biological species by the
use of additional photoactive switchable receptors. Moreover, this
newly demonstrated coupling between surface-confined photoactive molecular
species and nanosensing devices could be utilized in the near future
in the development of devices of higher complexity for both the simultaneous
control and monitoring of chemical and biological processes with nanoscale
resolution control
Si Nanowires Forest-Based On-Chip Biomolecular Filtering, Separation and Preconcentration Devices: Nanowires Do it All
The development of efficient biomolecular separation
and purification
techniques is of critical importance in modern genomics, proteomics,
and biosensing areas, primarily due to the fact that most biosamples
are mixtures of high diversity and complexity. Most of existent techniques
lack the capability to rapidly and selectively separate and concentrate
specific target proteins from a complex biosample, and are difficult
to integrate with lab-on-a-chip sensing devices. Here, we demonstrate
the development of an on-chip all-SiNW filtering, selective separation,
desalting, and preconcentration platform for the direct analysis of
whole blood and other complex biosamples. The separation of required
protein analytes from raw biosamples is first performed using a antibody-modified
roughness-controlled SiNWs (silicon nanowires) forest of ultralarge
binding surface area, followed by the release of target proteins in
a controlled liquid media, and their subsequent detection by supersensitive
SiNW-based FETs arrays fabricated on the same chip platform. Importantly,
this is the first demonstration of an <i>all-NWs device</i> for the whole direct analysis of blood samples on a single chip,
able to selectively collect and separate specific low abundant proteins,
while easily removing unwanted blood components (proteins, cells)
and achieving desalting effects, without the requirement of time-consuming
centrifugation steps, the use of desalting or affinity columns. Futhermore,
we have demonstrated the use of our nanowire forest-based separation
device, integrated in a single platform with downstream SiNW-based
sensors arrays, for the real-time ultrasensitive detection of protein
biomarkers directly from blood samples. The whole ultrasensitive protein
label-free analysis process can be practically performed in less than
10 min