44 research outputs found
Interactive Effect of Hysteresis and Surface Chemistry on Gated Silicon Nanowire Gas Sensors
Gated silicon nanowire gas sensors have emerged as promising
devices
for chemical and biological sensing applications. Nevertheless, the
performance of these devices is usually accompanied by a âhysteresisâ
phenomenon that limits their performance under real-world conditions.
In this paper, we use a series of systematically changed trichlorosilane-based
organic monolayers to study the interactive effect of hysteresis and
surface chemistry on gated silicon nanowire gas sensors. The results
show that the density of the exposed or unpassivated SiâOH
groups (trap states) on the silicon nanowire surface play by far a
crucial effect on the hysteresis characteristics of the gated silicon
nanowire sensors, relative to the effect of hydrophobicity or molecular
density of the organic monolayer. Based on these findings, we provide
a tentative model-based understanding of (i) the relation between
the adsorbed organic molecules, the hysteresis, and the related fundamental
parameters of gated silicon nanowire characteristics and of (ii) the
relation between the hysteresis drift and possible screening effect
on gated silicon nanowire gas sensors upon exposure to different analytes
at real-world conditions. The findings reported in this paper could
be considered as a launching pad for extending the use of the gated
silicon nanowire gas sensors for discriminations between polar and
nonpolar analytes in complex, real-world gas mixtures
Sensors for Breath Testing: From Nanomaterials to Comprehensive Disease Detection
The analysis of volatile organic compounds in exhaled breath samples represents a new frontier in medical diagnostics because it is a noninvasive and potentially inexpensive way to detect illnesses. Clinical trials with spectrometry and spectroscopy techniques, the standard volatile-compound detection methods, have shown the potential for diagnosing illnesses including cancer, multiple sclerosis, Parkinsonâs disease, tuberculosis, diabetes, and more via breath tests. Unfortunately, this approach requires expensive equipment and high levels of expertise to operate the necessary instruments, and the tests must be done quickly and use preconcentration techniques, all of which impede its adoption.Sensing matrices based on nanomaterials are likely to become a clinical and laboratory diagnostic tool because they are significantly smaller, easier-to-use, and less expensive than spectrometry or spectroscopy. An ideal nanomaterial-based sensor for breath testing should be sensitive at very low concentrations of volatile organic compounds, even in the presence of environmental or physiological confounding factors. It should also respond rapidly and proportionately to small changes in concentration and provide a consistent output that is specific to a given volatile organic compound. When not in contact with the volatile organic compounds, the sensor should quickly return to its baseline state or be simple and inexpensive enough to be disposable.Several reviews have focused on the methodological, biochemical, and clinical aspects of breath analysis in attempts to bring breath testing closer to practice for comprehensive disease detection. This Account pays particular attention to the technological gaps and confounding factors that impede nanomaterial-sensor-based breath testing, in the hope of directing future research and development efforts towards the best possible approaches to overcome these obstacles. We discuss breath testing as a complex process involving numerous steps, each of which has several possible technological alternatives with advantages and drawbacks that might affect the performance of the nanomaterial-based sensors in a breath-testing system. With this in mind, we discuss how to choose nanomaterial-based sensors, considering the profile of the targeted breath markers and the possible limitations of the approach, and how to design the surrounding breath-testing setup. We also discuss how to tailor the dynamic range and selectivity of the applied sensors to detect the disease-related volatile organic compounds of interest. Finally, we describe approaches to overcome other obstacles by improving the sensing elements and the supporting techniques such as preconcentration and dehumidification
Effect of Functional Groups on the Sensing Properties of Silicon Nanowires toward Volatile Compounds
Molecular layers attached to a silicon
nanowire field effect transistor
(SiNW FET) can serve as antennas for signal transduction of volatile
organic compounds (VOCs). Nevertheless, the mutual relationship between
the molecular layers and VOCs is still a puzzle. In the present paper,
we explore the effect of the molecular layerâs end (functional)
groups on the sensing properties of VOCs. Toward this end, SiNW FETs
were modified with tailor-made molecular layers that have the same
backbone but differ in their end groups. Changes in the threshold
voltage (Î<i>V</i><sub>th</sub>) and changes in the
mobility (ÎÎŒ<sub>h</sub>) were then recorded upon exposure
to various VOCs. Model-based analysis indicates that the interaction
between molecular layers and VOCs can be classified to three main
scenarios: (a) dipoleâdipole interaction between the molecular
layer and the polar VOCs; (b) induced dipoleâdipole interaction
between the molecular layers and the nonpolar VOCs; and (c) molecular
layer tilt as a result of VOCs diffusion. Based on these scenarios,
it is likely that the electron-donating/withdrawing properties of
the functional groups control the dipole moment orientation of the
adsorbed VOCs and, as a result, determine the direction (or sign)
of the ÎV<sub>th</sub>. Additionally, it is likely the diffusion
of VOCs into the molecular layer, determined by the type of functional
groups, is the main reason for the ÎÎŒ<sub>h</sub> responses.
The reported findings are expected to provide an efficient way to
design chemical sensors that are based on SiNW FETs to nonpolar VOCs,
which do not exchange carriers with the molecular layers
Self-Healable Sensors Based Nanoparticles for Detecting Physiological Markers via Skin and Breath: Toward Disease Prevention via Wearable Devices
Flexible and wearable electronic
sensors are useful for the early diagnosis and monitoring of an individualâs
health state. Sampling of volatile organic compounds (VOCs) derived
from human breath/skin or monitoring abrupt changes in heart-beat/breath
rate should allow noninvasive monitoring of disease states at an early
stage. Nevertheless, for many reported wearable sensing devices, interaction
with the human body leads incidentally to unavoidable scratches and/or
mechanical cuts and bring about malfunction of these devices. We now
offer proof-of-concept of nanoparticle-based flexible sensor arrays
with fascinating self-healing abilities. By integrating a self-healable
polymer substrate with 5 kinds of functionalized gold nanoparticle
films, a sensor array gives a fast self-healing (<3 h) and attractive
healing efficiency in both the substrate and sensing films. The proposed
platform was used in sensing pressure variation and 11 kinds of VOCs.
The sensor array had satisfactory sensitivity, a low detection limit,
and promising discrimination features in monitoring both of VOCs and
pressure variation, even after full healing. These results presage
a new type of smart sensing device, with a desirable performance in
the possible detection and/or clinical application for a number of
different purposes
Field Effect Transistors Based on Polycyclic Aromatic Hydrocarbons for the Detection and Classification of Volatile Organic Compounds
We show that polycyclic aromatic
hydrocarbon (PAH) based field effect transistor (FET) arrays can serve
as excellent chemical sensors for the detection of volatile organic
compounds (VOCs) under confounding humidity conditions. Using these
sensors, w/o complementary pattern recognition methods, we study the
ability of PAH-FET(s) to: (i) discriminate between aromatic and non-aromatic
VOCs; (ii) distinguish polar and non-polar non-aromatic compounds;
and to (iii) identify specific VOCs within the subgroups (i.e., aromatic
compounds, polar non-aromatic compounds, non-polar non-aromatic compounds).
We further study the effect of water vapor on the sensor arrayâs
discriminative ability and derive patterns that are stable when exposed
to different constant values of background humidity. Patterns based
on different independent electronic features from an array of PAH-FETs
may bring us one step closer to creating a unique fingerprint for
individual VOCs in real-world applications in atmospheres with varying
levels of humidity
Utility of Resistance and Capacitance Response in Sensors Based on Monolayer-Capped Metal Nanoparticles
We investigate the utility of resistance and capacitance responses, as derived by impedance spectroscopy, in well-controlled and real-world applications of monolayer-capped metal nanoparticle (MCNP) sensors. Exposure of the MCNP films to well-controlled analytes showed stable sensing responses and low baseline drift of the pertinent capacitance signals, when compared with equivalent resistance signals. In contrast, exposure of the MCNP films to breath of chronic kidney disease patients under dialysis, as a representative example to real-world multicomponent mixtures, showed low baseline drift but relatively scattered signals when compared with the equivalent resistance response. We ascribe these discrepancies to the level and fluctuating concentration of water molecules in the real-world samples
In Situ and Real-Time Inspection of Nanoparticle Average Size in Flexible Printed Sensors
Nanoparticles play an integral part
for the production of contacts
and active sensing layers in the fast-developing printed electronic
technology on flexible devices. Unfortunately, all currently available
techniques for nanoparticle characterization are limited to ex situ
and/or off-line processing. Here, we describe a new approach composed
of two complementary parts for in situ and real-time estimation of
the nanoparticlesâ effective diameter on flexible substrates.
The first part of the approach is based on measurements of electrical
resistance of the device in response to strain, and correlation of
the response with the nanoparticlesâ diameter. The second part
takes place only when measuring the electrical resistance is unfeasible.
It is based on UVâvis absorption of the device and correlation
of the absorption peak with the nanoparticle diameter based on previous
calibration data from strain sensitivity. The new approach shows excellent
estimations of the nanoparticle diameter (2.5â20 nm) on the
substrate with the advantages of being online, in situ, and inexpensive.
In addition, the estimated nanoparticle diameter is in excellent agreement
with atomic force microscopy (AFM) measurements. These capabilities
are expected to improve the process of âquality controlâ
of the nanoscale-enabled flexible devices, which, until now, has been
considered to be one of the most annoying issues that inhibits the
commercialization of nanotechnology-based flexible products
Dynamic Nanoparticle-Based Flexible Sensors: Diagnosis of Ovarian Carcinoma from Exhaled Breath
Flexible sensors based on molecularly
modified gold nanoparticles
(GNPs) were integrated into a dynamic cross-reactive diagnostic sensing
array. Each bending state of the GNP-based flexible sensor gives unique
nanoparticle spatial organization, altering the interaction between
GNP ligands and volatile organic compounds (VOCs), which increases
the amount of data obtainable from each sensor. Individual dynamic
flexible sensor could selectively detect parts per billion (ppb) level
VOCs that are linked with ovarian cancers in exhaled breath and discriminate
them from environmental VOCs that exist in exhaled breath samples,
but do not relate to ovarian cancer <i>per se</i>. Strain-related
response successfully discriminated between exhaled breath collected
from control subjects and those with ovarian cancer, with data from
a single sensor being sufficient to obtain 82% accuracy, irrespective
of important confounding factors, such as tobacco consumption and
comorbidities. The approach raises the hope of achieving an extremely
simple, inexpensive, portable, and noninvasive diagnostic procedure
for cancer and other diseases
Designing Thin Film-Capped Metallic Nanoparticles Configurations for Sensing Applications
Thin
film-capped metallic nanoparticles (TFCMNPs) hold big promise
for rapid, low-cost, and portable tracing of gas analytes. We show
that sensing properties can be controlled by the configuration of
the TFCMNPs. To this end, two methods were developed: layer by layer
(LbL) and drop-by-drop, i.e., drop casting (DC). The TFCMNP prepared
via LbL method was homogeneous and gradually increased in thickness,
absorbance, and conductivity relative to TFCMNP prepared via DC method.
However, our results indicate that the sensing of TFCMNP devices prepared
via DC is significantly higher than that of equivalent LbL devices.
These discrepancies can be explained as follows: LbL forms a high
dense layer of TFCMNPs without vacancies, and a well-controlled deposition
of NPs. The distance between the adjacent NPs is controlled by the
capped ligands and the linker molecules making a rigid TFCMNP. Thus,
exposing LbL devices to analyte induces a marginal change in the NPâNP
distance. However, in DC devices, the analyte induces major change
in the NP distances and permittivity due to their lack of connection,
making the sensing much more pronounced. The DC and LbL methods used
thiol and amine ligands-capped metallic nanoparticles to demonstrate
the applicability of the methods to all types of ligands. Our results
are of practical importance for integrating TFCMNPs in chemiresistive
sensing platforms and for (bio) and chemical sensing applications
Facile Graphene Oxide Modification Method via Hydroxyl-yne Click Reaction for Ultrasensitive and Ultrawide Monitoring Pressure Sensors
Enhancing the durability and functionality of existing
materials
through sustainable pathways and appropriate structural design represents
a time- and cost-effective strategy for the development of advanced
wearable devices. Herein, a facile graphene oxide (GO) modification
method via the hydroxyl-yne click reaction is present for the first
time. By the click coupling between propiolate esters and hydroxyl
groups on GO under mild conditions, various functional molecules are
successfully grafted onto the GO. The modified GO is characterized
by FTIR, XRD, TGA, XPS, and contact angle, proving significantly improved
dispersibility in various solvents. Besides the high efficiency, high
selectivity, and mild reaction conditions, this method is highly practical
and accessible, avoiding the need for prefunctionalizations, metals,
or toxic reagents. Subsequently, a rGO-PDMS sponge-based piezoresistive
sensor developed by modified GO-P2 as the sensitive material exhibits
impressive performance: high sensitivity (335 kPaâ1, 0.8â150 kPa), wide linear range (>500 kPa), low detection
limit (0.8 kPa), and long-lasting durability (>5000 cycles). Various
practical applications have been demonstrated, including body joint
movement recognition and real-time monitoring of subtle movements.
These results prove the practicality of the methodology and make the
rGO-PDMS sponge-based pressure sensor a real candidate for a wide
array of wearable applications