Radislav A. Potyrailo

Selective Gas Sensing with a Single Pristine Graphene Transistor

We show that vapors of different chemicals produce distinguishably different effects on the low-frequency noise spectra of graphene. It was found in a systematic study that some gases change the electrical resistance of graphene devices without changing their low-frequency noise spectra while other gases modify the noise spectra by inducing Lorentzian components with distinctive features. The characteristic frequency f(c) of the Lorentzian noise bulges in graphene devices is different for different chemicals and varies from f(c) = 10-20 Hz to f(c) = 1300-1600 Hz for tetrahydrofuran and chloroform vapors, respectively. The obtained results indicate that the low-frequency noise in combination with other sensing parameters can allow one to achieve the selective gas sensing with a single pristine graphene transistor. Our method of gas sensing with graphene does not require graphene surface functionalization or fabrication of an array of the devices with each tuned to a certain chemical.

Combinatorial and high-throughput screening of materials libraries: Review of state of the art

Rational materials design based on prior knowledge is attractive because it promises to avoid time-consuming synthesis and testing of numerous materials candidates. However with the increase of complexity of materials, the scientific ability for the rational materials design becomes progressively limited. As a result of this complexity, combinatorial and high-throughput (CHT) experimentation in materials science has been recognized as a new scientific approach to generate new knowledge. This review demonstrates the broad applicability of CHT experimentation technologies in discovery and optimization of new materials. We discuss general principles of CHT materials screening, followed by the detailed discussion of high-throughput materials characterization approaches, advances in data analysis/mining, and new materials developments facilitated by CHT experimentation. We critically analyze results of materials development in the areas most impacted by the CHT approaches, such as catalysis, electronic and functional materials, polymer-based industrial coatings, sensing materials, and biomaterials.

Materials and transducers toward selective wireless gas sensing.

Wireless sensors are devices in which sensing electronic transducers are spatially and galvanically separated from their associated readout/display components. The main benefits of wireless sensors, as compared to traditional tethered sensors, include the non-obtrusive nature of their installations, higher nodal densities, and lower installation costs without the need for extensive wiring.1–3 These attractive features of wireless sensors facilitate their development toward measurements of a wide range of physical, chemical, and biological parameters of interest. Examples of available wireless sensors include devices for sensing of pH, pressure, and temperature in medical, pharmaceutical, animal health, livestock condition, automotive, and other applications.4–7 Some implementations of wireless gas sensors can be already found in monitoring of analyte gases (e.g. carbon dioxide, water vapor, oxygen, combustibles) in relatively interference-free industrial and indoor environments.8,9 However, unobtrusive wireless gas sensors are urgently needed for many more diverse applications ranging from wearable sensors at the workplace, urban environment, and battlefield, to monitoring of containers with toxic industrial chemicals while in transit, to medical monitoring of hospitalized and in-house patients, to detection of food freshness in individual packages, and to distributed networked sensors over large areas (also known as wireless sensor networks, WSNs). Unfortunately, in these and numerous other practical applications, the available wireless gas sensors fall short of meeting emerging measurement needs in complex environments. In particular, existing wireless gas sensors cannot perform highly selective gas detection in the presence of high levels of interferences and cannot quantitate several components in gas mixtures. 1.1. Diversity Of Monitoring Needs Of Volatiles The monitoring of numerous gases of environmental, industrial, and homeland security concern is needed over the broad range of their regulated exposure concentrations. Figure 1 illustrates the relationships between several regulated exposure levels spanning several orders of magnitude of gas concentrations. Typical examples of concentrations of regulated exposure are presented in Table 110–14 for three groups of toxic volatiles such as volatile organic compounds (VOCs), toxic industrial chemicals (TICs), and chemical warfare agents (CWAs). These examples demonstrate the need for gas sensing capabilities with broad measurement dynamic ranges to cover 2 – 4 orders of magnitude in gas concentrations. Figure 1 Examples of regulated vapor-exposure limits established by different organizations: GPL: General Population Limit, established by USACHPPM – U.S. Army Center for Health Promotion and Preventative Medicine; PEL: Permissible Exposure Limit, established ... Table 1 Examples of regulated concentration levels (in ppm by volume) from three representative classes of toxic gases: VOCs, TICs, and CWAs.10–14 Additional needs for detection of volatiles originate from medical diagnostics, food safety, process monitoring, and other areas.15–17 In those applications, the types and levels of detected volatiles can provide the needed information for further control actions.

Combinatorial and High-Throughput Development of Sensing Materials: The First 10 Years

Chemical and biological sensors have found their niche among modern analytical instruments when real-time determination of the concentration of specific sample constituents is required. Development of sensors with new capabilities is driven by the ever-expanding monitoring needs of a wide variety of species in gases and liquids. On the basis of a variety of definitions of sensors, 1-3 here we will accept that a chemical or biological sensor is an analytical device that utilizes a chemically or biologically responsive sensing layer to recognize a change in a single or multiple chemical or biological parameters of a measured environment and to convert this information into an analytically useful signal. In a sensor device, a sensing material is applied onto a suitable physical transducer to convert a change in a property of a sensing material into a suitable physical signal. The obtained signal from a single transducer or an array of transducers is further processed to provide useful information about the identity and concentration of species in the sample. The energy transduction principles that have been employed for chemical and biological sensing involve radiant, electrical, mechanical, and thermal types of energy. 4,5 Specific sensing concepts are further implemented with each energy transduction. Sensors based on radiant energy of transduction can employ intensity, wavelength, polarization, phase, or time resolution detection. Sensors based on electrical energy of transduction can employ conductometric, potentiometric, or amperometric detection. Sensors based on mechanical energy of transduction can employ gravimetric or viscoelastic detection. Sensors based on thermal energy of transduction can employ calorimetric or pyroelectric detection. Hyphenated techniques in sensing are of significant importance and combine several transduction techniques in one sensor. 6,7 In addition to a sensing material layer and a transducer, a modern sensor system often incorporates other important components such as sample introduction and data processing components. In contrast to sensing based on intrinsic analyte properties (e.g., spectroscopic, dielectric, thermal), indirect sensing utilizes a responsive sensing material. 2,5,8-13 This approach dramatically expands the range of detected species, improves sensor performance (e.g., analyte detection limits), and is more straightforwardly adaptable for miniaturization. 6,14-33

Battery-free radio frequency identification (RFID) sensors for food quality and safety

Market demands for new sensors for food quality and safety stimulate the development of new sensing technologies that can provide an unobtrusive sensor form, battery-free operation, and minimal sensor cost. Intelligent labeling of food products to indicate and report their freshness and other conditions is one important possible application of such new sensors. This study applied passive (battery-free) radio frequency identification (RFID) sensors for the highly sensitive and selective detection of food freshness and bacterial growth. In these sensors, the electric field generated in the RFID sensor antenna extends from the plane of the RFID sensor and is affected by the ambient environment, providing the opportunity for sensing. This environment may be in the form of a food sample within the electric field of the sensing region or a sensing film deposited onto the sensor antenna. Examples of applications include monitoring of milk freshness, fish freshness, and bacterial growth in a solution. Unlike other food freshness monitoring approaches that require a thin film battery for operation of an RFID sensor and fabrication of custom-made sensors, the passive RFID sensing approach developed here combines the advantages of both battery-free and cost-effective sensor design and offers response selectivity that is impossible to achieve with other individual sensors.

Role of high-throughput characterization tools in combinatorial materials science

The process of combinatorial materials development couples parallel production of large arrays of compositionally varying samples together with measurements of their properties. The diverse spectrum of functionalities in materials represents a significant challenge in high-throughput characterization, often involving development of novel measurement instrumentation. Among the publications in the field, the number of publications related to measurement techniques and instrumentation in combinatorial materials science was the second largest category (34%) after materials synthesis (37%). This statistic underscores the critical role characterization tools play in combinatorial materials science.

Development of radio-frequency identification sensors based on organic electronic sensing materials for selective detection of toxic vapors

Selective vapor sensors are demonstrated that involve the combination of (1) organic electronic sensing materials with diverse response mechanisms to different vapors and (2) passive 13.56 MHz radio-frequency identification (RFID) sensors with multivariable signal transduction. Intrinsically conducting polymers such as poly(3,4-ethylenedioxythiophene) and polyaniline (PANI) were applied onto resonant antennas of RFID sensors. These sensing materials are attractive to facilitate the critical evaluation of our sensing concept because they exhibit only partial vapor selectivity and have well understood diverse vapor response mechanisms. The impedance spectra Z(f) of the RFID antennas were inductively acquired followed by spectral processing of their real Zre(f) and imaginary Zim(f) parts using principal components analysis. The typical measured 1σ noise levels in frequency and impedance magnitude measurements were 60 Hz and 0.025 Ω, respectively. These low noise levels and the high sensitivity of the resona...

Towards outperforming conventional sensor arrays with fabricated individual photonic vapour sensors inspired by Morpho butterflies

Combining vapour sensors into arrays is an accepted compromise to mitigate poor selectivity of conventional sensors. Here we show individual nanofabricated sensors that not only selectively detect separate vapours in pristine conditions but also quantify these vapours in mixtures, and when blended with a variable moisture background. Our sensor design is inspired by the iridescent nanostructure and gradient surface chemistry of Morpho butterflies and involves physical and chemical design criteria. The physical design involves optical interference and diffraction on the fabricated periodic nanostructures and uses optical loss in the nanostructure to enhance the spectral diversity of reflectance. The chemical design uses spatially controlled nanostructure functionalization. Thus, while quantitation of analytes in the presence of variable backgrounds is challenging for most sensor arrays, we achieve this goal using individual multivariable sensors. These colorimetric sensors can be tuned for numerous vapour sensing scenarios in confined areas or as individual nodes for distributed monitoring.

Discovery of the surface polarity gradient on iridescent Morpho butterfly scales reveals a mechanism of their selective vapor response.

Significance Morpho butterflies are a brilliant spectacle of nature’s capability for photonic engineering. Their conspicuous appearance arises from the interference and diffraction of light within tree-like nanostructures on their scales. Scientific lessons learned from these butterflies have already inspired designs of new displays, fabrics, and cosmetics. This study reports a vertical surface polarity gradient in these tree-like structures. This biological pattern design may be applied to numerous technological applications ranging from security tags to self-cleaning surfaces, gas separators, protective clothing, and sensors. Here it has allowed us to unveil a general mechanism of selective vapor response in photonic Morpho nanostructures and to demonstrate attractive opportunities for chemically graded sensing units for high-performance sensing. For almost a century, the iridescence of tropical Morpho butterfly scales has been known to originate from 3D vertical ridge structures of stacked periodic layers of cuticle separated by air gaps. Here we describe a biological pattern of surface functionality that we have found in these photonic structures. This pattern is a gradient of surface polarity of the ridge structures that runs from their polar tops to their less-polar bottoms. This finding shows a biological pattern design that could stimulate numerous technological applications ranging from photonic security tags to self-cleaning surfaces, gas separators, protective clothing, sensors, and many others. As an important first step, this biomaterial property and our knowledge of its basis has allowed us to unveil a general mechanism of selective vapor response observed in the photonic Morpho nanostructures. This mechanism of selective vapor response brings a multivariable perspective for sensing, where selectivity is achieved within a single chemically graded nanostructured sensing unit, rather than from an array of separate sensors.

Position-independent chemical quantitation with passive 13.56-MHz radio frequency identification (RFID) sensors.

Recently, we have demonstrated an attractive approach to adapt conventional radio frequency identification (RFID) tags for multianalyte chemical sensing. These RFID sensors could be very attractive as ubiquitous distributed remote sensor networks. However, critical to the wide acceptance of the demonstrated RFID sensors is the analyte-quantitation ability of these sensors in presence of possible repositioning errors between the RFID sensor and its pickup coil. In this study, we evaluate the capability for such position-independent analyte quantification using multivariate analysis tools. By measuring simultaneously several parameters of the complex impedance from such an RFID sensor and applying multivariate statistical analysis methods, we were able to compensate for the repositioning effects such as baseline signal offset and magnitude of sensor response to an analyte.