PRISM :: Browsing by Author "Kim, Seonghwan"

Browsing by Author "Kim, Seonghwan"

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Open Access
3D printing in Clinical Diagnostics: A Versatile Tool to Develop Testing Devices for the Diagnosis of Infectious Diseases
(2023-01-05) Aburashed, Raied; Sanati Nezhad, Amir; Lewis, Ian; Kim, Seonghwan; Murari, Kartikeya
3D printing (3DP) has recently emerged as an advanced manufacturing technology in the pharmaceutical and biomedical industries. 3DP has virtually become a synonym for rapid prototyping. The ease of use and low cost of in-house 3D printing has also revolutionized product development, and many manufacturers of medical tools have adopted the technology to produce brand-new medical devices and surgical instruments. 3DP allows for a fast feedback loop which accelerates design development; designers and manufacturers can rely on the use of early 3D printed parts to support clinical trials or early commercialization while the final design is still being optimized. This relationship was crucial in support of enhanced health care and general emergency response, as shown during the COVID-19 pandemic. A few examples where 3DP technologies were used to validate product efficacy include 3DP nasal pharyngeal swabs, multiplexing of bi-level positive airway pressure (BiPAP) machines to support multiple patients, patient-specific dental moulding, and antigen testing kits for COVID-19. In this dissertation, I show the versatility of 3D printing within the infectious disease workflow. Firstly, I demonstrate the use of 3D printing in patient sample collection through the development of a novel 3D manufacturing and efficacy validation for nasal pharyngeal (NP) swabs. With the aim to develop a swab (a) 3D printed with complex tip structures for enhanced sample collection efficacy, eliminating the need to apply flocks at the tips (b) scalability with a network of 3D printing capacity in biomedical devices and biocompatible material applications, and (c) ability to rapidly iterate prototypes quickly and effectively without incurring costs of machining moulds for injection moulding. In the following chapter, I discuss the importance and use of rapid manufacturing techniques to develop diagnostic assay kits for various diseases; predominantly in the development of point-of-care (POC) devices through the combination of microfluidic and microelectromechanical systems (MEMS). 3DP techniques can be utilized to develop various fluidic systems to streamline laboratory testing methodologies. I explore the development of a centrifugal microfluidic platform and the manufacturability of various centrifugal fluidic systems within the limitation of 3DP. This work aims to provide the building blocks of the 3D printing of various centrifugal microfluidic modules and establishes a proof-of-concept AST platform for bloodstream infections by sensing and monitoring the growth and antibiotic susceptibility of E. coli. Finally, I show the utility of 3DP in clinical diagnostics through the rapid development of a custom 96-well plate platform; microbial containment device (MCD) and software package FUGU-MS – Filtering Utility for Grouping untargeted mass spectrometry data and open-source software tool to compliment the metabolic data acquired via the MCD. The 3D printed MCD that allows water-soluble metabolites to diffuse from a microbial culture well into a bacteria-free well through a semi-permeable membrane, which allows for streamline sample processing for clinical diagnostics of bloodstream infections. The MCD validated through the analysis of the metabolic flux to identify different strains of bacteria, including Escherichia coli, Klebsiella pneumonia, Enterococcus faecalis and Staphylococcus aureus following a 4-hour incubation period of various bloodstream and urinary tract pathogens and direct sampling onto a Q Exactive HF Hybrid Quadrupole-Orbitrap Mass Spectrometer.
Open Access
Acoustic subsurface-atomic force microscopy: Three-dimensional imaging at the nanoscale
(2021-01) Sharahi, Hossein J.; Janmaleki, Mohsen; Tetard, Laurene; Kim, Seonghwan; Sadeghian, Hamed; Verbiest, Gerard J.
The development of acoustic subsurface atomic force microscopy, which promises three-dimensional imaging with single-digit nanometer resolution by introduction of ultrasound actuations to a conventional atomic force microscope, has come a long way since its inception in the early 1990s. Recent advances provide a quantitative understanding of the different experimentally observed contrast mechanisms, which paves the way for future applications. In this perspective, we first review the different subsurface atomic force microscope modalities: ultrasonic force microscopy, atomic force acoustic microscopy, heterodyne force microscopy, mode-synthesizing atomic force microscopy, and near-field picosecond ultrasonic microscopy. Then, we highlight and resolve a debate existing in the literature on the importance of the chosen ultrasound excitation frequencies with respect to the resonance frequencies of the cantilever and the observed contrast mechanisms. Finally, we discuss remaining open problems in the field and motivate the importance of new actuators, near-field picosecond ultrasonics, and integration with other techniques to achieve multi-functional non-destructive three dimensional imaging at the nanoscale.
Open Access
An experimental and theoretical study on suppression and employment of the coffee-ring phenomenon in electrochemical sensing applications
(2022-06-27) Zargartalebi, Hossein; Sanati Nezhad, Amir; Hejazi, Hossein; Kim, Seonghwan
Coffee-ring effect presents in many natural phenomena, and the ubiquitous nature of this physical impact makes it difficult to circumvent. Depending on the application, coffee-ring can be a detrimental or beneficial effect. This research is aimed at scrutinizing a multidisciplinary study on the underlying physics behind this effect for controlling or taking advantage of it. To be more specific, understanding the reasons causing this phenomenon, I theoretically and experimentally investigate the non-invasive ways to suppress ring-like particles’ deposition, applicable for ultrasensitive platforms, such as electrochemical sensors. On the other hand, I use the coffee-ring effect to increase the sensitivity of nano-biosensors, expedite detection, and enhance the diagnosis and prognosis of diseases.In the first part of this thesis, a non-intrusive meniscus-free and coffee-ring-free method, inspired by nature, is developed to form uniform particle films. When a saline lake evaporates, a uniform layer of salt deposits on the lake-bed due to a meniscus-free air-water interface. The deposition nature of the salt layer is emulated on a small scale by placing a particle-laden sessile droplet on an accurately designed shadow mold over a substrate, eliminating the radial particle migration. This method demonstrated forming of highly ordered monolayers and fabrication of self-organized multilayer constructs, customized patterns, nanoscale continuously variablesize filters, and highly reproducible functionalized electrodes for nano-biosensing. A theoretical model is also developed to simulate the effects of geometrical and physicochemical parameters involved in particle deposition. Enabling the repeatable generation of highly uniform layers makes this method a versatile approach for applications spanning from genotyping to molecular diagnosis.In the next part of the thesis, I incorporate the coffee-ring approach with the molecular pendulum (MP) electrochemical sensing method to develop a reagentless SARS-CoV-2 sensor with improved response time and sensitivity. To achieve this, the natural capillary flow, offered by the coffee ring effect, provides enhanced sensitivity without external manipulation, developing the first coffee ring-enabled reagentless sensor. Sensors are fabricated from preexisting screen-printed electrodes through laser removal of the electrode interior, resulting in uniform ring-shaped electrodes; electrode ring thickness and gold nanoneedles are carefully optimized to ensure maximum sensitivity. By incorporating the coffee ring effect with MPbased sensing, we achieve significantly enhanced sensitivity towards detecting both antigens and body of the target viruses, demonstrated with clinical SARS-CoV-2 samples. In addition to experimental results, a comprehensive theoretical study is conducted to verify and support the robustness of this coffee-ring preconcentration approach.Finally, in the last step of my thesis, I use a microfluidic-based electrochemical sensing approach to not only eliminate the coffee-ring effect by avoiding evaporation during fluid manipulation but also assist scalability and robustness of functionalizing sensors. In the absence of reliable methods for large-scale production of reproducible and repeatable nanomaterial morphologies on the electrodes, they are fabricated individually in batch production. This has become a significant challenge in the practical implementation of electrochemical nano-biosensors. To address this challenge, an automated microfluidic-based platform (NanoChip) is designed for the semi-scale production of reproducible complex nanomaterial structures with a defined order of nanocomposites and biomaterials to fabricate ultrasensitive nano-biosensors. In this regard, using an automated liquid handling system, the desired reagent is delivered to electrodes integrated temporarily into the chip for amending their surfaces by depositing different nanomaterials. The NanoChip platform is utilized to form a multilayer nanocomposite structure on the electrode surface. These reproducible nanobiosensors are then applied to detect breast cancer cells in the blood. The Performance of nanobiosensors produced by NanoChip demonstrates similar dynamic range and selectivity along with enhanced sensitivity and reproducibility compared to the sensors created utilizing the batch process. These factors make the designed NanoChip platform a versatile and reliable tool for fabricating ultrasensitive nano-sensors to monitor different markers in clinical, medical, and environmental applications.
Open Access
Atomic Scale Characterization of Graphitic Surfaces
(2016) Chan, Nicholas; Egberts, Philip; Barclay, Paul; Kim, Seonghwan; Cheng, Frank
Characterization of materials at smaller scales is important for device miniaturization and understanding fundamental mechanics of materials at atomistic levels. In this thesis, characterization of graphitic surfaces was performed using various atomic force microscopy techniques. Tip convolution effects across graphite step edges were studied using amplitude-modulated atomic force microscopy and compared with molecular dynamics (MD) simulations for varying tip sizes. Larger step widths were observed for both experiments and simulations when compared with a geometric model of the system and was attributed to material deformation. Secondly, friction studies were performed on single layer graphitic surfaces grown on Pt(111) to observe the influence of structural changes at the graphene/Pt(111) interface on lubrication. Variation in measured lateral forces and average friction forces were observed for different graphene domains due to graphene/Pt(111) lattice mismatching. These results were compared to simulations performed within the framework of the Prandtl-Tomlinson (PT) model and through Molecular Statics.
Open Access
Cantilever Tip Radius Estimation through Contact Resonance Atomic Force Microscopy
(2023-09-04) Mathias, Thomas; Egberts, Philip; Kim, Seonghwan; Badv, Maryam
The mechanical characteristics of materials, particularly those of composite materials, can be mapped spatially and quantified using Contact Resonance Atomic Force Microscopy (CR-AFM). This technique operates by measuring the changes in resonance frequency as an AFM cantilever tip comes into contact with a sample surface. Such frequency shifts are primarily related to contact stiffness, although it can also influence other factors such as viscoelasticity. While several theories aim to connect the modal shape and resonant frequency of the AFM cantilever with contact stiffness, no direct application of these models has been developed to directly transform the resonant frequency into a physical mechanical property measurement. Instead, the majority of experimental studies utilising CR-AFM calibrate the frequency conversion factor relating to contact stiffness using a known reference sample, bypassing the direct use of these cantilever models. This thesis brings into focus two novel aspects aimed at enhancing and refining the CR-AFM technique: using thermal resonance to monitor the oscillation modes of an AFM cantilever during an experiment and establishing a connection between cantilever dynamics theory and the calibration of CR-AFM data that eliminates the requirement for normalisation to a known sample. In the first segment of this thesis, cantilever thermal displacement time series data is transformed into frequency space utilising the short-time Fourier transform(STFT) and continuous wavelet transform (CWT). It will be demonstrated that only the STFT calculations are capable of delivering the time-frequency resolution necessary to track AFM modal vibrations, at least currently. The application of the STFT allows for real-time tracking of the contact resonance frequency and Quality factor throughout a force spectroscopy experiment. The ensuing analysis reveals the fluctuations in contact resonance frequency over the course of this experiment. However, utilising cantilever analytical models to interpret this data using known contact mechanics models resulted in nonphysical estimates. Further studies are underway to reconcile the often problematic assumptions made in contact mechanics for AFM measurements with dynamic, STFT measurements. The experimental findings underscore the reasons why normalisation or calibration of CR-AFM results to samples with known stiffness has been prevalent until now. Despite progress, the comprehensive understanding of the contact mechanics and vibration theory necessary to analyse the dynamics of AFM cantilevers in such experiments remains an open challenge.
Open Access
Characterization of Viscoelastic Materials Using Atomic Force Microscopy
(2017) Hoorzad, Hamid; Kim, Seonghwan; Du, Ke; Egberts, Philip; Amrein, Matthias
Atomic Force Microscopy (AFM) is a versatile method for nanoscale measurement of the properties of materials. While many methods have been developed to utilize AFM for nanoscale characterization of stiffness, damping characterization has remained less explored. In this research, we present a method for measuring stiffness and damping using Contact Resonance Atomic Force Microscopy (CR-AFM) and Modal Finite Element Analysis (FEA). To do so we compare resonance peaks and quality factors obtained from FEA and CR-AFM and we adjust the parameters until there are in good agreement. We use this method to measure the stiffness and damping of several polymers.
Open Access
Chemical Characterization and Source Apportionment of Ambient PM2.5 over Key Emission Regions in China
(2016) Zhou, Jiabin; Du, Ke; Johansen, Craig; Kim, Seonghwan; Song, Hua
A year-round campaign was completed for comprehensive characterization of PM2.5 over four key emission regions in China. The annual average PM2.5 mass concentrations ranged from 60.5 to 148.9 μg m-3. Nine water-soluble ions collectively contributed 33–41% of PM2.5 mass, with three dominant ionic species being SO42-, NO3-, NH4+, and carbonaceous particulate matter contributed 16-23% of the PM2.5 mass. The characteristic chemical species combined with back trajectory analysis indicated that Wuqing site was heavily influenced by air masses originating from Mongolia and North China Plain regions, whereas Deyang site suffered from both local emissions of Sichuan Basin and biomass burning via long-range transport from South Asia. A molecular marker-chemical mass balance (MM-CMB) receptor model revealed that the major primary contributors to PM2.5 OC were vehicle emission, coal combustion, biomass burning, meat cooking and natural gas combustion, which collectively accounted for 84±24% of measured OC. The major contributors to PM2.5 mass were secondary sulfate (26-30%), vehicle emission (12-26%), secondary nitrate (12-23%), coal combustion (6-12%), secondary ammonium (7-9%), biomass burning (4-12%), meat cooking (2-5%), natural gas combustion (1-2%), and other OM (2-13%) on annual average at these sites. This study found the source apportionment has distinct regional and seasonal characteristics. This knowledge is essential for government to make region specific control strategies for fine particles pollution in China.
Open Access
Contrast Mechanisms on Nanoscale Subsurface Imaging in Ultrasonic AFM: Scattering of Ultrasonic Wave and Contact Stiffness of Tip-Sample
(Royal Society of Chemistry, 2017-01-13) Sharahi, Hossein J; Shekhawat, Gajendra; Dravid, Vinayak; Park, Simon; Egberts, Philip; Kim, Seonghwan
Ultrasonic atomic force microscopy (AFM) and its associated derivatives are nondestructive techniques that can elucidate subsurface nanoscale structures and properties. Despite the usefulness of these techniques, the physical contrast mechanisms responsible for the reported subsurface features observed in ultrasonic AFM are not well defined. In this study, we present a comprehensive model combining ultrasonic wave scattering and tip–sample contact stiffness to better reproduce the experimentally measured phase variations over subsurface features in two model systems. These model systems represent the two extreme sample types typically imaged by ultrasonic AFM, one being a hard material and the other a soft polymeric material. The theoretical analysis presented and associated comparisons with experimental results suggest that the image contrast depends on the combination of two contrast mechanisms: the perturbation of the scattered ultrasonic waves and the local variation of the contact stiffness at the tip–sample contact. The results of this study open up a new door for the depth estimation of buried nanoscale features into hard (engineering structures) and soft (polymers and biological structures) materials, and eventually lead to non-invasive, high-resolution 3D nano-tomography by ultrasonic AFM.
Open Access
Development of a High-pressure Rotational Rheometer for Investigation of Effects of Dissolved CO2
(2018-01-08) Lee, Keonje; Park, Simon; Kim, Seonghwan; Wong, Joanna; Natale, Giovanniantonio
Rheological information is often used to determine viscoelastic fluid properties, and to model and predict fluid behavior under influence of external stress or deformation. Many industrial processes involve the dissolution of gas under high pressure, so it is important to evaluate the rheological properties of viscoelastic materials under high pressure. In this research, a high pressure rotational rheometer was developed to measure the rheological parameters of viscoelastic fluids and investigate the influence of the dissolution of gases on rheology. The rheometer utilized a piezoelectric torque transducer, which enabled transient and dynamic rheological measurements under high pressure. First, the rheometer was designed, fabricated, and calibrated using a calibration fluid. Second, the capability of the rheometer was verified using polydimethylsiloxane (PDMS), which is a typical viscoelastic fluid. Viscosity and viscoelastic properties, such as storage/loss modulus, and complex viscosity, were evaluated. Thirdly, the effects of the dissolved CO2 on the rheological properties of PDMS were investigated. The effects of temperature and dissolved CO2 were investigated individually at the temperature of 25, 50, 80°C and CO2 saturation pressures of 1, 2, 3 MPa. Then, the combined effect was correlated using a generalized Arrhenius model. The proposed model expressed viscosity as a function of temperature and pressure without the need for thermodynamic and volumetric information of the fluid. The achievement of this research provides an alternative method to measure rheological properties of viscoelastic materials under high pressure and enables the prediction of the viscosity of a fluid with dissolved gas through modelling.
Open Access
Development of an Improved Repeater-free Acoustic Telemetry System Through Experimental Investigation and Modelling
(2021-11-23) Pagtalunan, Jediael R.; Park, Simon; Kim, Seonghwan; Xue, Deyi; Wang, Xin
Measurement while drilling (MWD) enables real-time measurement of downhole conditions for directional drilling, but most commercial MWD telemetry techniques such as mud pulse or electromagnetic methods suffer from limited transmission speeds. Acoustic telemetry has the potential for significantly faster transmission speeds, albeit with limited range due to drill string attenuation and noise. A common solution to this is to use acoustic repeaters, which incur high costs and require complex implementation. Instead of using repeaters, we utilized two carrier frequencies at the modes to transmit redundant data in combination with a lock-in amplifier (LIA) to extract the signals from the carriers. The extracted signals were then fused at the receiver to increase signal fidelity. An experimental setup was developed to transmit acoustic signals through a simulated drill string. The signals were first attenuated by the rubber section of the simulated drill string. The results show that the proposed system was able to achieve error-free transmission of packets at 64 bps up to 1.95 km without the use of a repeater which is an order of magnitude faster than current commercial MWD methods.Moreover, the acoustic telemetry system requires the identification of the carrier frequencies near the natural frequencies of drill string with specified boundary conditions. This work proposes a finite element (FE) model based on the Timoshenko beam theory that predicts the dynamics of an actual drill-string over a wide frequency range. The frequency response of the model is compared to models in literature with similar components. Then, three configurations that follow a specified trajectory are defined with increasing lengths and curvature to represent the drill string assembly as it approaches the target reservoir. The frequency responses of the of the three configurations are determined and a carrier frequency was selected at the center of the third passband. Like the lab-scale experiments, packets of bits are first generated as telemetry data and then convolutionally encoded to reduce errors at the receiver. The signal is modulated using differential binary phase shift keying (DBPSK) and upconverted to the carrier frequency which is used as the force input to the model. Finally, the receiver at the surface demodulates and decodes the received acceleration to recover the transmitted bits using a digitally implemented LIA. The transmitted and received bits are again compared to calculate the bit-error rate (BER) for each signal-to-noise ratio (SNR) condition and used as the measure of performance. To simulate transmission, the time impulse responses are first recorded for the three different drill string configurations. These are then used to develop a finite impulse response filter (FIR) for simulation of the acoustic transmissions. The results show that the passband locations stay at the same frequencies and that transmission speed is limited by the passband widths.
Open Access
Development of Non-contact Laser Ultrasonic System for Nondestructive Evaluation
(2018-04-26) Mirsadeghi, Seyed Mehdi; Hugo, Ronald J.; Park, Simon S.; Kim, Seonghwan; Sun, Qiao; Murari, Kartikeya
The development of cracks and corrosion in pipelines could pose a potential hazard to the community and the pipeline industry. Particularly for buried or insulated pipelines, corrosion and other types of defects may remain invisible unless the pipe is physically excavated or the insulation layers are removed. In this regard, advanced guided wave techniques are rapidly growing due to the advantages that they offer over traditional direct assessment inspection methods. To overcome the challenges associated with the use of conventional ultrasonic techniques, a non-contact laser-based non-destructive evaluation system is proposed in this research work. Compared to conventional ultrasonic transducers, a laser-based technique remains functional at elevated temperatures and can result in high-resolution damage visualization. Using the laser Doppler vibrometer as the ultrasonic detection subsystem, and the pulsed Nd:YAG laser for the ultrasonic generation, a complete non-contact ultrasonic system was implemented. The pulsed laser heats the surface of the specimen, and as a result, thermal and ultrasonic waves are generated in the structure. A reliable numerical model was created using the finite element analysis. The numerical results were validated with experiments in the time and frequency domains. The application of a Nd:YAG laser for ultrasonic wave generation was limited due to a lack of repeatability in the signals and low signal-to-noise ratio and potential damages to the surface. Instead, a piezoelectric transducer in combination with the laser Doppler vibrometer was used to enhance defect identification in aluminum plates. The results show that the proposed method can successfully identify the location and the approximate shape of hidden defects.
Open Access
Development of Novel Nanocomposite Photoelectrodes for Photoelectrochemical Cathodic Protection
(2020-01-08) Yang, Yao; Cheng, Yufeng Frank; Egberts, Philip; Kim, Seonghwan; Shi, Yujun; Jar, Pean Yue Ben
Novel photoelectrodes are developed for photoelectrochemical cathodic protection (CP) of steels. In a photoelectrochemical CP system, the photoelectrode acts as an anode and absorbs photons to inject electrons from valence band into the conduction band, producing photogenerated holes in the photoelectrode. Then these photogenerated holes are eliminated by hole scavengers and the photoelectrons are utilized to cathodically polarize a steel, making it the cathode. In such a system, the photoelectrode remains intact and converts solar light into electricity for cathodic protection. Compared with conventional CP systems, the photoelectrochemical CP system is more suitable for long-time application in remote areas. To achieve photoelectrochemical CP, photoelectrodes need to work under some conditions. The conduction band potential should be more negative than the corrosion potential of a steel to be protected. High light intensity, efficient hole scavengers and high surface area of the photoelectrode benefit its performance. The electrochemical activity of protected metals and the corrosivity of aqueous environments can affect the performance of this novel CP system. SrTiO3 and ZnO nanorod photoelectrodes are developed for photoelectrochemical CP under ultraviolet (UV) illumination. Compared with SrTiO3 photoelectrode, ZnO nanorod photoelectrode has much higher photoelectrochemical activity due to the high active surface area of ZnO nanorods. Moreover, the methodology of electrodeposition proved to be a more facile and efficient technique for fabrication of a high-performance photoelectrode. Co3O4@ZnO core-shell nanocomposite photoelectrodes are developed to enable photoelectrochemical CP under visible light. The optical absorption edge of the fabricated photoelectrode shifts to the visible light range due to the narrow band gap of Co3O4. Combined with high surface area of ZnO nanorods, the Co3O4@ZnO nanocomposite photoelectrodes achieve high-performance photoelectrochemical CP under visible light. Nano-scaled compounds, i.e., CeO2 and WO3, with energy storage ability are incorporated into the photoelectrodes to develop photoelectrodes for continuous CP with/without illumination. The fabricated CeO2-SrTiO3 and WO3-TiO2-BiVO4 photoelectrodes enable photoelectrochemical CP and energy storage under UV and visible light illumination, respectively. Photocorrosion may occur on passivated carbon steel due to the existence of iron oxides film on the steel surface. The passive film shows a behavior of an n-type semiconductor, and affects the corrosion behavior of the carbon steel under visible light illumination.
Open Access
Electromagnetic Interference Shielding Effectiveness of Hybrid Polymer Nanocomposites
(2019-06-18) Mende Anjaneyalu, Abilash; Sundararaj, Uttandaraman; Kim, Seonghwan; Lu, Qingye
In recent years, electronics have become pervasive in our society. This has resulted in an increase in electromagnetic (EM) pollution, which has significant impact on many sectors. In order to attenuate the radiation from the EM pollution, extensive investigations are performed with different materials for attenuating this radiation. For EM wave attenuation, conductive polymer nanocomposites (CPN) is a promising candidate due to low cost, lightweight, easy processability, high flexibility and tailoring properties and nanocomposites also attenuates microwaves by absorption mechanism. Using single nanofiller, CPN has shown higher shielding effectiveness with higher fraction of nanofillers and thicker sample size. Dual nanofillers in CPN also help attain good EMI shielding properties, but with lower fraction of nanofillers and thinner sample compared to single nanofillers. This is attributed to the synergetic effect of both the fillers to attenuate the incoming EM waves. In this dissertation, the primary objective is to investigate the effect of secondary fillers in the hybrid polymer nanocomposites on the electrical properties, i.e., electrical conductivity, dielectric and EMI shielding properties. Due to the low mass density, high aspect ratio and lower electrical percolation threshold in the polymer matrix, multiwall carbon nanotubes (MWCNT) were used as primary conductive nanofiller in most of the studies. Various secondary conductive, magnetic and dielectric nanofillers were employed to study the effect of secondary nanofiller properties on EMI shielding performance of polymer-based nanocomposites. Different mixing techniques, such as melt mixing and solution mixing technique were also investigated. The results show that, the addition of secondary nanofillers improves the dispersion quality of the primary nanofillers in both mixing techniques. Additionally, based on geometry and aspect ratio of the secondary nanofillers, the shielding properties of nanocomposites were improved through the synergistic effect associated with hybrid fillers. Using the dual filler approach, CPN showed higher EMI shielding effectiveness (SE) with low filler content and lower thickness, which makes it a potential candidate for numerous commercial applications as microwave absorber.
Open Access
Enhanced nanoplasmonic heating in standoff sensing of explosive residues with infrared reflection-absorption spectroscopy
(2020-03-10) Simin, Nicholas; Park, Yangkyu; Lee, Dongkyu; Thundat, Thomas; Kim, Seonghwan
Various standoff sensing techniques employing optical spectroscopy have been developed to address challenges in safely identifying trace amounts of explosives at a distance. A flexible anodic aluminum oxide (AAO) microcantilever and a high-power quantum cascade laser utilized as the infrared (IR) source are used for standoff IR reflection-absorption spectroscopy to detect explosive residues on a metal surface. Standoff sensing of trinitrotoluene (TNT) is demonstrated by exploiting the high thermomechanical sensitivity of a bimetallic AAO microcantilever. Moreover, sputtering gold onto the fabricated AAO nanowells generates a strong scattering and absorption of IR light in the wavelength range of 5.18 μm to 5.85 μm resulting in enhanced nanoplasmonic heating. Utilizing the IR absorption enhancement in this wavelength range, the plasmonic AAO cantilever could detect TNT molecules 7 times better than the bimetallic AAO cantilever.
Open Access
Fabrication and investigation of nano-channeled anodized aluminum oxide (AAO) microcantilever gas/vapour sensors with enhanced sensitivity and modified selectivity
(2021-04-30) Taghvaie, Ehsan; Kim, Seonghwan; Du, Ke; Dalton, Colin
Microcantilevers as one of the most fundamental forms of MEMS devices have found extensive applications in various fields including sensors during the last decade. Simple mechanism, high throughput fabrication, direct and fast conversion of chemical/ biological stimulus to mechanical response in orders of a few nanometers, and high-precision are among the most significant merits of microcantilevers as sensors. As for the material used for designing microcantilever-based sensors, Anodic Aluminum Oxide (AAO) shows promise for its nano-porous nature which leads to increased surface area. This research explores the possibility of increasing the sensitivity of AAO-based microcantilever sensors by transforming the nano-welled porous surface into nano-channels. Effect of channel dimensions on the mechanical characteristics are studied. Despite all the qualities microcantilever offers as a sensor platform, it lacks the inherent selectivity. So, while measuring a certain gas, it may adsorb miscellaneous molecules such as moisture leading to false positive results. In this research, we have attempted to tailor the selectivity of the sensor preventing water molecules by rendering the cantilever surface’s hydrophobic. Furthermore, while most of the previous studies dealt with merely the resonant frequency and quality factor of the microcantilever sensor in a single flow or gas condition, it has been tried to go further and investigate the cantilever’s response in both forms of resonant frequency and quality factor exposed to different flow conditions and find the correlation between the physical and chemical modification made to the cantilevers on their dynamic responses.
Open Access
Fabrication of Hybrid Atomic Force Microscopy Probe for Enhancing Sensitivity of AFM-Infrared Nanoscale Spectroscopy
(2019-08-30) Ebrahimi, Mohamad; Kim, Seonghwan; Lee, Jihyun; Lu, Qingye
Atomic force microscopy infrared-spectroscopy (AFM-IR) has emerged as a novel method that combines nanoscale resolution of AFM with IR-spectroscopy. In this technique heat generated by IR absorption within the sample will induce thermal expansion, which is detected by AFM probe, in contact with the sample, to discover the chemical composition of the sample based on IR absorption spectrum. One of the issues in applying this technique is that the heat generated in sample will also diffuse to the probe, due to thermal conduction which results in reducing the sensitivity of the probe. One of the alternative solutions to overcome this problem is to replace the AFM probe, which is commonly made by silicon, with a photopolymeric AFM probe. Since thermal conductivity of photopolymers are orders of magnitude lower than silicon, this alternative seems to be promising. To address this issue, I am developing a MEMS fabrication method enabling us to make a hybrid AFM probe (silicon cantilever with photopolymeric tip). Fabrication process starts with fixating a conventional AFM probe over a Petri dish with some photopolymeric resin which covers underneath of the cantilever. Secondly, I silanize the surface of the cantilever and then I replicate the tip of the cantilever using soft lithography with PDMS (Polydimethylsiloxane) to make a mold for tip fabrication. Finally, I cure a photopolymer inside the PDMS tip mold in contact with a silicon cantilever. I have utilized the hybrid probe in AFM imaging and AFM-IR spectroscopy over standard samples. Hybrid probes showed comparable results with standard silicon probes for AFM imaging. On the other hand, hybrid probes - in comparison with silicon probes - showed about 1.6 times increasement in signal to noise ratio in AFM-IR spectroscopy. Based on the measured results the sensitivity of AFM-IR technique has been improved utilizing hybrid probes.
Open Access
Facile and rapid synthesis of functionalized Zr-BTC for the optical detection of the blistering agent simulant 2-chloroethyl ethyl sulfide (CEES)
(Royal Society of Chemistry, 2021-02) Abuzalat, Osama; Homayoonnia, Setareh; Wong, Danny; Tantawy, Hesham R.; Kim, Seonghwan
2-chloroethyl ethyl sulfide (CEES) is a simulant for the chemical warfare agent, bis(2-chloroethyl) sulfide, also known as mustard gas. Here, we demonstrate a facile and rapid method to synthesize a functionalized metal-organic framework (MOF) material for the detection of CEES in trace level. While Zr-BTC is synthesized, in-situ encapsulation of fluorescent material (Fluorescein) into Zr-BTC voids is performed with a simple solvothermal reaction. The produced F@Zr-BTC is used as a fluorescent probe for CEES detections. The synthesized material shows fluorescence quenching under illumination at excitation wavelength of 470 nm when the F@Zr-BTC is exposed to CEES. This sensing material shows the highest fluorescence quenching at an emission wavelength of 534 nm with CEES concentration as low as 50 ppb. Therefore, the demonstrated sensing method with F@Zr-BTC offers a fast and convenient protocol for selective and sensitive detection of CEES in practical applications.
Open Access
Facile and rapid synthesis of functionalized Zr-BTC for the optical detection of the blistering agent simulant 2-chloroethyl ethyl sulfide (CEES)
(Royal Society of Chemistry, 2021-02) Kim, Seonghwan; Abuzalat, Osama; Homayoonnia, Setareh; Wong, Danny; Tantawy, Hesham R
2-chloroethyl ethyl sulfide (CEES) is a simulant for the chemical warfare agent, bis(2-chloroethyl) sulfide, also known as mustard gas. Here, we demonstrate a facile and rapid method to synthesize a functionalized metal-organic framework (MOF) material for the detection of CEES in trace level. While Zr-BTC is synthesized, in-situ encapsulation of fluorescent material (Fluorescein) into Zr-BTC voids is performed with a simple solvothermal reaction. The produced F@Zr-BTC is used as a fluorescent probe for CEES detections. The synthesized material shows fluorescence quenching under illumination at excitation wavelength of 470 nm when the F@Zr-BTC is exposed to CEES. This sensing material shows the highest fluorescence quenching at an emission wavelength of 534 nm with CEES concentration as low as 50 ppb. Therefore, the demonstrated sensing method with F@Zr-BTC offers a fast and convenient protocol for selective and sensitive detection of CEES in practical applications.
Open Access
High-Performance, Room Temperature Hydrogen Sensing With a Cu-BTC/Polyaniline Nanocomposite Film on a Quartz Crystal Microbalance
(2019-01) Abuzalat, Osama; Wong, Danny; Park, Simon S.; Kim, Seonghwan
In this paper, we demonstrate a high-performance hydrogen sensor under ambient conditions by growing a Cu-BTC/polyaniline (PANI) nanocomposite film on a quartz crystal microbalance (QCM) using intense pulsed light. The QCM was first sputter coated with a 200-nm-thin layer of copper. The copper layer was then oxidized by sodium hydroxide and ammonium persulfate. A solution containing the organic ligand (BTC) and PANI was then dropped and dried on the copper hydroxide surface of a QCM with intense pulsed light which resulted in Cu-BTC/PANI nanocomposite film on a QCM. The gas sensing performance of the Cu-BTC film and Cu-BTC/PANI composite film was compared under ambient conditions. It was found selectivity and sensitivity of the Cu-BTC/PANI nanocomposite film to hydrogen were significantly improved. In addition, a fast response time (from 2 to 5 s), operation at room temperature even in the presence of high relative humidity (up to 60%), good repeatability were achieved with the Cu-BTC/PANI nanocomposite film-grown QCM sensor.
Open Access
Highly selective and sensitive fluorescent zeolitic imidazole frameworks sensor for nitroaromatic explosive detection
(Royal Society of Chemistry, 2020-06) Kim, Seonghwan
Nitroaromatic explosives, such as 2-4-6 trinitrotoluene (TNT) are dangerous materials that pose safety and environmental risks. Even though many sensors have been reported for the detection of nitroaromatic explosives, a facile, rapid, cost effective sensor is still sought-after in the field. Here we demonstrate a facile and rapid method to synthesize a fluorescent metal-organic framework for the highly selective and sensitive detection of nitroaromatic explosives. Zeolitic imidazole framework-8 (ZIF-8) is synthesized and enhanced with fluorescent 8-hydroxyquinoline zinc (ZnQ). The synthesized material shows visible colour changes upon exposure to TNT from ivory to light red. In addition, fluorescence quenching is noted under UV illumination when the ZnQ@ZIF-8 is exposed to TNT. The ZnQ@ZIF-8-coated paper sensors show the highest fluorescence quenching at an emission wavelength of 455 nm with TNT concentration as low as 1 ppm. Therefore, the proposed strategy not only offers a fast and convenient protocol for selective detection of TNT but also offers great potential in practical applications, especially for airport/railway security inspection and prevention of terrorist attacks.