나노다공성 인듐 주석 산화물 전극에서의 구조 효과 연구 및 바이폴라 전극 센서로의 응용

학위논문(박사)--서울대학교 대학원 :자연과학대학 화학부,2020. 2. 정택동.Along with the fast development of technology and the advent of environmental issues, the need for efficient and cost-effective electrocatalysts used in energy devices and sensors have increased greatly. Numerous researches have focused on improving the efficiency of electrocatalysts while reducing the contents of noble metals. In this context, fabricating nanostructured catalysts in order to enhance its catalytic activity has long been crucial in electrocatalyst development. In particular, nanoporous electrodes are widely utilized as competent catalysts due to its enlarged surface area and catalytic active surface characteristics. The catalytic contribution from an additional catalytic factor arising from the nanoporous morphology (nanoconfinement effects) has been suggested and investigated by several groups, most of which have utilized noble metal based nanoporous electrodes. In this thesis, nanoconfinement effects were investigated by employing low catalytic material with systematically varied nanoporous layer thickness. Furthermore, the effect of structure modification towards sensor sensitivity were demonstrated. In the first part of the thesis, the acceleration of electron transfer kinetics at the nanoporous indium tin oxide (ITO) electrodes were investigated. In this study, the catalytic activity of nanoporous electrodes was explored regarding the effects of confined morphology of the electrode towards heterogeneous electron transfer reactions. In order to observe the geometric contribution towards the electrocatalytic activity, ITO was chosen as the electrode material due to its low catalytic activity. Systematically varying the nanoporous ITO layer thickness allowed the exclusion of surface-originated catalytic effects of the nanoporous electrodes such as defect densities. Experimental results showed that the single electron transfer of Fe2+/3+ that involve no proton transfer is more facilitated with thickening ITO nanoporous layers, which have higher proportion of nanoconfined geometry. In the second part of the thesis, a novel indium-tin oxide (ITO) bipolar electrode (BPE) based sensor by the implementation of nanoporous ITO, is introduced. The nanoporous ITO layer implemented BPE showed markedly enhanced ECL signals compared to the planar ITO based BPE, enabling the detection of H2O2 even under a mild operating voltage. The ECL calibration curves towards H2O2 detection using BPEs of various nanoporous layer thicknesses exhibited lowered LODs and improved sensitivities with thickening nanoporous layers. We speculate that the nanopore morphologies may have spatially confined the analytes, thus leading to amplified ECL signals.효율적인 에너지 전환 장치 혹은 저장 장치, 그리고 센서 등에 대한 수요가 높아짐에 따라, 이들의 성능을 결정짓는 전기화학 촉매에 대한 연구가 활발히 진행되고 있다. 이러한 촉매 연구들은 촉매 효율을 최대한으로 끌어올리면서 동시에 귀금속 재료를 줄이는 방향으로 이루어지고 있다. 이러한 맥락에서 촉매들을 나노구조체로 제작하는 전략 또한 전극 표면적을 늘리거나 표면 자체의 촉매성을 높이려는 의도로 자주 쓰인다. 그 중에서도 나노다공성 구조의 전극들은 부피 대비 표면적 증가 및 표면 활성화 측면에서 주목받는 촉매 물질이다. 하지만 나노다공성 전극의 표면 성질로부터 파생되는 촉매 효과 외에도, 나노동공 구조 내부 반응종의 갇힘 효과에 의한 추가적인 촉매 효과가 있을 것이라는 주장이 제기된 바가 있다. 이러한 '나노 갇힘 효과' 연구들은 주로 귀금속 재료의 나노다공성 전극을 이용하여 연구가 진행되어 왔다. 본 연구에서는 낮은 촉매성을 가지는 인듐 주석 산화물 (indium tin oxide, ITO) 을 재료로 하여 나노다공성 층의 두께를 변화시켜가면서 나노 갇힘 효과를 관찰하였다. 또한 나노 갇힘 효과에 바탕한 구조 개조의 촉매 개발 응용 가능성을 센서 성능으로 보여주었다. 챕터 1 에서는 나노다공성 인듐 주석 산화물 전극을 도입하여 하나의 전자 전달이 가속화됨을 관찰하였고, 나노다공성 전극에서의 촉매 메커니즘을 구조 효과 측면에서 살펴보았다. 이를 위해, 촉매 효과가 느리다고 알려진 인듐 주석 산화물을 전극 재료로 택하였으며, 나노다공성 층 두께에 따른 전자전달 반응 빠르기를 관찰함으로써 전극 표면 성질로부터 파생되는 촉매 효과를 상쇄시킬 수 있었다. 이로부터 Fe2+/3+ 전자 전달 빠르기가 두꺼운 나노다공성 층에서 점차 증가하는 것을 보았으며, 이는 나노다공성 구조로부터 기인한 것으로 분석하였다. 챕터 2에서는 나노다공성 인듐 주석 산화물을 바이폴러 전극 (bipolar electrode, BPE) 센서에 도입함으로써 과산화수소에 대한 분석 능력이 향상됨을 관찰하였다. 과산화수소 농도에 따른 적정 곡선을 통해 BPE 센서에 나노다공성 구조를 도입할 경우, 그렇지 않은 평탄한 전극에 비해 감도가 매우 크게 향상하였으며, 약한 작동 전압에서도 효율적인 측정을 할 수 있었다.1. General Introduction 1 1.1 Background and overview 3 1.1.1 Conventional approaches in developing electrocatalysts 3 1.1.2 Chemistry in confined space 5 1.1.3 Molecular dynamics in confined space 6 1.1.4 Electron transfer models and rate formalism based on microscopic theories 8 1.2 Effect of confined space in electrochemistry 14 1.2.1 Electrochemical confinement effects 14 1.2.2 Nanoconfinement effects in nanoporous electrodes 17 1.2.3 Challenges in investigations of nanoconfinement effects 18 2. Investigation of Nanoconfinement effects at Nanoporous Indium Tin Oxide Electrodes 21 2.1 Introduction 23 2.2 Experimental 26 2.2.1 Reagents 26 2.2.2 Fabrication and Characterization of nanoporous Indium Tin Oxide electrodes with various thicknesses 26 2.2.3 Electrochemical Methods 28 2.3 Results and Discussion 29 2.3.1 Characterization of nanoporous Indium Tin Oxide electrodes 29 2.3.2 Measurements of Fe2+/3+ electrokinetics at nanoporous ITO electrodes 32 2.3.3 The surface area normalized rate constants of Fe2+/3+ at nanoporous ITO electrodes 39 2.3.4 Nanoconfinement effects as a function of temperature 43 2.4 Conclusion 48 3. Nanoporous ITO implemented Bipolar Electrode Sensor for enhanced Electrochemiluminescence 51 3.1 Introduction 53 3.2 Experimental 55 3.2.1 Chemicals and Materials 55 3.2.2 Instruments 56 3.2.3 Fabrication of Nanoporous Indium Tin Oxide BPEs 57 3.2.4 Optical Analysis 59 3.2.5 Electrochemical Methods 59 3.3 Results and Discussion 60 3.3.1 Design of the BPE microchip and the sensing system 60 3.3.2 Characterization of nanoporous Indium Tin Oxide layer 62 3.3.3 Optical analysis of H2O2 detection 67 3.3.4 Nanoconfinement effects of nanoporous structures towards H2O2 detection 72 3.4 Conclusion 75 4. Conclusions and Perspective 77 References 83 Abstract (in Korean) 95Docto

Wireless and conventional electrochemiluminescence for analytical applications

Electrochemiluminescence (ECL) or alternatively electrogenerated chemiluminescence is a light-emitting process brought about by electron-transfer reactions. ECL can occur via two pathways namely, ion annihilation and coreactant pathway. Coreactant ECL generation predominates over annihilation pathway due to the ease of ECL generation in aqueous solution. The discovery of ECL emission in aqueous media has led to major applications in analytical chemistry, especially in the field of biosensing, that is, immunoassays and DNA-probe assays. Thus, the scope of this work was to develop a simple, sensitive ECL immunosensor for cardiac injury and to study and present newly fabricated platforms for analytical applications by using conventional and bipolar ECL as detection mechanism. Herein, two types of electrodes were investigated, that is, thin film electrodes made up of carbon micro-particles and three-dimensional (3D) printed electrodes made up of titanium alloy (Ti-6AI-4V) powder. The generation of ECL at these electrodes was based on two approaches, that is, ECL generated by conventional electrochemistry and ECL generation based on bipolar or wireless electrochemistry. Firstly, the conductivity of the thin film electrodes as well as their ability to generate ECL was investigated. The obtained results revealed that the films exhibited very low conductivity (65% (by volume) carbon particles using [Ru(bpy)3]2+ as the luminophore and tripropylamine as the coreactant, at an electric field of 14 V cm−1. A simple additive 3D printing technique based on selective laser melting (SLM) technology was used to fabricate 1 cm2 footprint 3D-printed titanium electrodes. The 3D-printed structures were characterised topographically and electrochemically by scanning electron microscopy and cyclic voltammetry, respectively. An electrochemical surface modification method was used to functionalise the surface of the 3D titanium electrodes with a thin gold layer which significantly enhanced the dynamics of heterogeneous electron transfer. Despite the slow rate of heterogeneous electron transfer at the bare 3D titanium electrodes, significant ECL was generated and the intensity increased with increasing scan rate. The obtained results suggest that it’s possible to fabricate customisable electrodes with control over the morphology, size, and performance, thus opens up exciting new possibilities for specific functions and studies like chemical sensing and biology, respectively. Secondly, the thesis focused on the synthesis, characterisation and application of an interesting ECL luminophore, ruthenium (II) (bis-2,2-bipyridyl)-2(4-carboxylphenyl) imidazo[4,5-f][1,10]phenanthroline [Ru(bpy)2(picCOOH)]2+. The luminophore was found to exhibit impressive electrochemical and photophysical properties, and for this reason, was covalently coupled to a secondary antibody via NHS/EDC for employment as ECL emitters in the fabrication of a sandwich-type immunosensor for the detection of cardiac troponin I, an important biomarker for cardiac injury. The ECL immunosensor was fabricated by the assembly of a new custom-made primary antibody with a carboxylic acid-terminated alkanethiol modified gold electrode. The primary antibody modified gold electrode was first treated with 1% bovine serum albumin and thereafter it was reacted with various concentrations of human cardiac troponin-I, followed by the introduction of the secondary antibody dye-conjugate. In the presence of the tripropylamine coreactant, an increase in ECL signal was observed. The ECL intensity versus the concentration of cardiac troponin I was linear in the range from 0.001 pg mL-1 to 0.50 pg mL-1 with an extremely low detection limit of 0.03 pg mL-1 (SD, n=3). Furthermore, this immunoassay was extended to a bipolar electrochemical system so that wireless detection of cTnI could be realised. Comparison studies were also carried out to study the difference in ECL intensity between conventional and bipolar ECL approach

Smartphone as a Portable Detector, Analytical Device, or Instrument Interface

The Encyclopedia Britannia defines a smartphone as a mobile telephone with a display screen, at the same time serves as a pocket watch, calendar, addresses book and calculator and uses its own operating system (OS). A smartphone is considered as a mobile telephone integrated to a handheld computer. As the market matured, solid-state computer memory and integrated circuits became less expensive over the following decade, smartphone became more computer-like, and more more-advanced services, and became ubiquitous with the introduction of mobile phone networks. The communication takes place for sending and receiving photographs, music, video clips, e-mails and more. The growing capabilities of handheld devices and transmission protocols have enabled a growing number of applications. The integration of camera, access Wi-Fi, payments, augmented reality or the global position system (GPS) are features that have been used for science because the users of smartphone have risen all over the world. This chapter deals with the importance of one of the most common communication channels, the smartphone and how it impregnates in the science. The technological characteristics of this device make it a useful tool in social sciences, medicine, chemistry, detections of contaminants, pesticides, drugs or others, like so detection of signals or image

Numerical Modeling of Novel Co-Reactant Electrogenerated Chemiluminescence Systems for Analytical Applications

This thesis focuses on the numerical modeling of co-reactant electrogenerated chemiluminescence (ECL) systems that have been recently proposed for analytical applications. Co-reactant ECL is light emission triggered by an electrochemical reaction of a luminophore with a co-reactant. Many researchers are trying to expand its application in the analytical field with carrying out various experiments. However, recent reports on the co-reactant ECL have revealed several phenomena that are not yet fully understood from theoretical viewpoint. Better understanding of the reaction mechanism for ECL generation is necessary for further improvement of the co-reactant ECL. In this context, three kinds of recently-proposed co-reactant ECL systems were numerically modeled in this study to analyze the reaction mechanism. The numerical modeling in this study mainly deals with dynamic ECL behavior while the potential of a working electrode changes with time. The modeling of this kind of dynamic ECL behavior provides us more information than that of static ECL behavior because very precise analysis can be carried out by the consideration of dynamic changes in the modeling parameters. In conclusion, the numerical modeling in this study contributed to the better understanding of the reaction mechanism for ECL generation, which can support further improvement of co-reactant ECL systems. Analysis for the reaction mechanism from theoretical viewpoint should be adequately considered in future experimental studies

Exploring the Kinetic and Thermodynamic Relationship of Charge Transfer Reactions Used in Localized Electrodeposition and Patterning in a Scanning Bipolar Cell

Bipolar electrochemistry involves spatial separation of charge balanced reduction and oxidation reactions on an electrically floating electrode, a result of intricate coupling of the work piece with the ohmic drop in the electrochemical cell and to the thermodynamics and kinetics of the respective bipolar reactions. When paired with a rastering microjet electrode, in a scanning bipolar cell (SBC), local electrodeposition and patterning of metals beneath the microjet can be realized without direct electrical connections to the workpiece. Here, we expand on prior research detailing electrolyte design guidelines for electrodeposition and patterning with the SBC, focusing on the relationship between kinetics and thermodynamics of the respective bipolar reactions. The kinetic reversibility or irreversibility of the desired deposition reaction influences the range of possible effective bipolar counter reactions. For kinetically irreversible deposition systems (i.e., nickel), a wider thermodynamic window is available for selection of the counter reaction. For kinetically reversible systems (i.e., copper or silver) that can be easily etched, tight thermodynamic windows with a small downhill driving force for spontaneous reduction are required to prevent metal patterns from electrochemical dissolution. Furthermore, additives used for the bipolar counter reaction can influence not only the kinetics of deposition, but also the morphology and microstructure of the deposit. Cyclic voltammetry measurements help elucidate secondary parasitic reduction reactions occurring during bipolar nickel deposition and describe the thermodynamic relationship of both irreversible and reversible bipolar couples. Finally, finite element method simulations explore the influence of bipolar electrode area on current efficiency and connect experimental observations of pattern etching to thermodynamic and kinetic relationships

Nanoscale Electrodes for Bionanosensing

Cancer is globally the second most common cause of death. Cancer burden rises to about 10 million deaths and more than 18 million new cases in 2018. Cancers are often diagnosed at a later stage preventing curative treatment. This underscores the need for an early stage diagnosis of cancer. Consequently, screening methods that can test patients’ samples taken by less invasive methods capable of early stage diagnosis are highly sought for. Based on this motivation, here we developed lab-on-a-chip diagnostic systems that can be used for early detection of cancer. Three different types of nanoscale electrodes were fabricated: (i) nanogap electrodes (ii) nano interdigitated electrodes and (iii) nanodisc electrodes and the possibility of using them for sensing and signal transduction were investigated. Chapter 2 describes the fabrication of nanogap device using conventional optical lithography and DNA detection across it using the electrical method. Chapter 3 details the fabrication of nano interdigitated electrodes (nIDEs) and their electrochemical validation. Chapter 4 describes the biosensing application of nIDEs using nanoparticle sandwich assay for the detection of DNA molecules. Chapter 5 describes the capturing of tdEVs on nIDEs, and its quantification using a sandwich immunosorbent assay on nIDEs. Chapter 6 proposes a new type of nanoscale electrodes which are termed as nanodisc electrodes. Chapter 7 explores the possibility of developing the nanodisc technology to a business idea. In short, the whole thesis tries to explore the different possibilities in developing a sensor that can be useful for cancer diagnosis

Ruthenium

Ruthenium is a precious metal not widely known to non-scientists. It is a target of much research, however. It is used in computer hard drives, the tips of fountain pens, and as a catalyst to purify car exhaust, among other uses. This book presents information and research on the properties and applications of ruthenium, including potential uses in phytochemical functions and anticancer activity

Novel Electrochemical Biosensors for Clinical Assays

Biosensors, i.e., devices where biological molecules or bio(mimetic)structures are intimately coupled to a chemo/physical transducer for converting a biorecognition event into a measurable signal, have recently gained a wide (if not huge) academic and practical interest for the multitude of their applications in analysis, especially in the field of bioanalysis, medical diagnostics, and clinical assays. Indeed, thanks to their very simple use (permitting sometimes their application at home), the minimal sample pretreatment requirement, the higher selectivity, and sensitivity, biosensors are an essential tool in the detection and monitoring of a wide range of medical conditions from glycemia to Alzheimer’s disease as well as in the monitoring of drug responses. Soon, we expect that their importance and use in clinical diagnostics will expand rapidly so as to be of critical importance to public health in the coming years. This Special Issue would like to focus on recent research and development in the field of biosensors as analytical tools for clinical assays and medical diagnostics