Youngmo Jung

Chemiresistive Electronic Nose toward Detection of Biomarkers in Exhaled Breath

Detection of gas-phase chemicals finds a wide variety of applications, including food and beverages, fragrances, environmental monitoring, chemical and biochemical processing, medical diagnostics, and transportation. One approach for these tasks is to use arrays of highly sensitive and selective sensors as an electronic nose. Here, we present a high performance chemiresistive electronic nose (CEN) based on an array of metal oxide thin films, metal-catalyzed thin films, and nanostructured thin films. The gas sensing properties of the CEN show enhanced sensitive detection of H2S, NH3, and NO in an 80% relative humidity (RH) atmosphere similar to the composition of exhaled breath. The detection limits of the sensor elements we fabricated are in the following ranges: 534 ppt to 2.87 ppb for H2S, 4.45 to 42.29 ppb for NH3, and 206 ppt to 2.06 ppb for NO. The enhanced sensitivity is attributed to the spillover effect by Au nanoparticles and the high porosity of villi-like nanostructures, providing a large surface-to-volume ratio. The remarkable selectivity based on the collection of sensor responses manifests itself in the principal component analysis (PCA). The excellent sensing performance indicates that the CEN can detect the biomarkers of H2S, NH3, and NO in exhaled breath and even distinguish them clearly in the PCA. Our results show high potential of the CEN as an inexpensive and noninvasive diagnostic tool for halitosis, kidney disorder, and asthma.

Nonlinear characteristics in radio frequency nanoelectromechanical resonators

The nonlinear oscillations of nanoelectromechanical resonators have previously been studied both experimentally and analytically. Nanoresonators have achieved superior sensitivity and high quality factors in many applications. However, the linear operating range of nanoresonators is significantly limited because of the small dimensions and thus the linear regime of nanoresonators may be required to expand performance in various conditions. In order to increase the linear operating range, we proposed that proper adjustments of simultaneous application of drive and electrothermal power can be used to optimize the resonance performance, providing a wider linear range as well as to tune the resonance frequency. For a nanoresonator operated by simultaneous drive and electrothermal power, experimental data are theoretically supported using nonlinear damping and spring terms. In the transition between linearity and nonlinearity by proper combinations of ac drive and dc electrothermal power, the experimental data can be better fitted, by theoretical study, with newly derived nonlinear damping terms. We believe that better understanding of these effects with different ac/dc combinations on radio frequency oscillation is crucial for utilizing nanoresonators for various applications such as sensors, oscillators and filters.

Determination of the molecular assembly of actin and actin-binding proteins using photoluminescence

Actin, the most abundant protein in cells, polymerizes into filaments that play key roles in many cellular dynamics. To understand cell dynamics and functions, it is essential to examine the cytoskeleton structure organized by actin and actin-binding proteins. Here, we pave the way for determining the molecular assembly of the actin cytoskeleton using direct photonic in situ analysis, providing the photoluminescence characteristics of actin as a function of filament length and bundling, without labeling. In experiments for monomeric and filamentous actin reconstituted in vitro, structural forms of actin are identified from the peak positions and intensities of photoluminescence. Actin monomers exhibited small intensity emission peaks at 334 nm, whereas filamentous and bundled actin showed a shifted peak at 323 nm with higher intensity. The peak shift was found to be proportional to the length of the actin filament. With probing structural change of actin in various cells in vivo, our study provides an efficient and precise analytical in situ tool to examine the cytoskeleton structure. It will be beneficial for elucidating the mechanism of various cellular functions such as cell migration, differentiation, cytokinesis and adhesion. Furthermore, our technique can be applied to detect the alterations in the cell cytoskeleton that can occur during many pathological processes.

Selective vapor detection of an integrated chemical sensor array

Graphene is a promising material for vapor sensor applications because of its potential to be functionalized for specific chemical gases. In this work, we present a graphene gas sensor that uses single-stranded DNA (ssDNA) molecules as its sensing agent. We investigate the characteristics of graphene field effect transistors (FETs) coated with different ssDNAs. The sensitivity and recovery rate for a specific gas are modified according to the differences in the DNA molecules’ Guanine (G) and Cytosine (C) content. ssDNA-functionalized devices show a higher recovery rate compared to bare graphene devices. Pattern analysis of a 2-by-2 sensor array composed of graphene devices functionalized with different-sequence ssDNA enables identification of NH3, NO2, CO, SO2 using Principle Component Analysis (PCA).

Differentiation of vapor mixture with chemical sensor arrays

Arrays of partially selective chemical sensors have been the focus of extensive research over the past decades because of their potential for widespread application in ambient air monitoring, health and safety, and biomedical diagnostics. Especially, vapor sensor arrays based on functionalized nanomaterials have shown great promise with their high sensitivity by dimensionality and outstanding electronic properties. Here, we introduce experiments where individual vapors and mixtures of them are examined by different chemical sensor arrays. The collected data from those sensor arrays are further analyzed by a principal component analysis (PCA) and targeted vapors are recognized based on prepared database.

Vapor Detection of ssDNA Decorated Graphene Transistor

Abstract We report a way to improve the ability of graphene to operate as a gas sensor by applying single stranded deoxyribonucleic acid(DNA). The sensitivity and recovery of the DNA-graphene sensor depending on the different DNA sequences are analyzed. The dif-ferent sensor responses to reactive chemical vapors are demonstrated in the time domain. Because of the chemical gating effect of thedeposited DNA, the resulting devices show complete and rapid recovery to baseline unlike the bare graphene at room temperature. Theapplication of the pattern recognition technique can increase the potential of DNA-graphene sensors as a chemical vapor classifier.Keywords: Gas sensors, Graphene, DNA, NO 2 , NH 3 , Sensitivity, Recovery 1. 서론 그래핀은 뛰어난 전기역학적 물질특성 및 균일한 표면 특성으로 인해 많은 학문적 관심을 받은 물질이다. 2차원 탄소 원자격자의 반복 구조체로 이루어진 그래핀은 고유의 에너지 밴드구조로 인하여 탄소 원자 부근에서 전자가 에너지 손실 없이 이동하는 것이 가능하며, 전하 이동도(mobility)가 높아 미세한 전기적 신호 검출에 유리하다[1]. 또한 그래핀을 대면적으로 성장시키고 이를 원하는 지지체(substrate)상에 전사하기 위한 다양한 연구가 진행되어, 균일한 표면 특성을 가지는 그래핀을 얻는것이 가능해졌다[2].이러한 특성으로 인하여 그래핀을 센서로서 적용하기 위한 많은 연구가 진행되었다. 많은 연구 분야 중에서, 현재 주목 받고있는 분야 중 하나가 그래핀을 이용한 가스 검출 연구 분야이다. 선행 연구에서, 팽창 흑연(HOPG)의 기계적 박리법(mechanicalexfoliation) 을 이용한 그래핀 가스 센싱에 대한 연구 결과가 발표되었으며[3], 이후 화학증기 증착법(chemical vapor deposition)을 이용한 그래핀 및 산화 그래핀(graphene oxide)을 이용한 가스 센서에 대한 연구 결과가 발표되었다[4,5].최근에는 기존의 그래핀만을 이용한 센서 연구에서, 그래핀과다양한 바이오 물질의 적용을 통해 그래핀의 전기적 역학적 특성이 개량된 센서에 대한 연구가 진행되고 있다[6]. 상기 언급한 대로, 그래핀은 2차원에서 균일한 표면 특성을 지니고 있으며, 표면에 존재하는 sp2 오비탈 구조체와 결합하여 바이오 물질을 고정화할 수 있다. 또한 그래핀 표면에 작용기(functionalgroup)를 활성화하여 이를 통해 선택적 결합을 유도하는 것도가능하다[7]. 이를 통하여 순수 그래핀이 가지는 전기역학적 특성을 보완 및 진보시킨 센서 제작이 가능하다.본 논문에서는 Single stranded Deoxyribonucleic acid(ssDNA)을 그래핀 표면에 결합시킨 그래핀/DNA 센서 거동에대한 연구 결과를 제시한다. Chemical vapor deposition(CVD)에 의해 성장된 그래핀을 이용하여 2×2 배열을 지니는 그래핀센서를 제작하였으며, 이를 통하여 NO

Graphene Oxide based Metal ion Hybrid Supercapacitor

In this paper we are presenting a architecture of Co ion decorated graphene oxide as an electrode for supercapacitor application. Graphene oxide, which is exfoliated by oxidant from graphite, is the material for solving the problem of mass production and coating on the surface of working electrode. The ions are coated by using layer by layer(LBL) method on graphene oxide foam. The metal ion decorated graphene oxide shows enhanced capacitance performance when tested as supercapacitor electrode, showing the specific capacitance of .

Characteristic of Graphene Oxide based Device Assembled by Dielectrophoresis

Graphene oxide, which is exfoliated by oxidant from graphite, is the material for solving the problem of mass production and positioning. We made graphene oxide based devices by dielectrophoresis, studied and controlled factors which can affect the characteristic of graphene oxide channel. Graphene oxide channel assembled by dielectrophoresis can be constructed differently by various frequency options. We confirmed the change of gate characteristics and I-V characteristics in the range from 80K to 300K temperature.