Curvature effects on surface plasmon resonance for wearable devices

이현웅 Graduate School, Yonsei University 2023 국내박사

최근 수 십년간 플라스모닉스 응용 연구는 다양한 분야에서 활발하게 이루어져 왔다. 표면에서 강하게 집속되는 전기장을 이용하여 생체시료를 고감도로 검출, 화학 반응의 촉진, 그리고 기존에 달성할 수 없었던 새로운 광학적 특성을 구현해내는 등 다양한 학술 분야에서 중요한 역할을 하고 있다. 본 논문은 기존 평판 구조 기반의 플라스모닉스 연구에서 한 걸음 더 나아가 곡면을 갖는 플라스모닉 소자에 대해 표면 플라스몬 공명 특성을 연구하였고, 향후 플라스모닉 메타물질 등 곡면 플라스모닉 소자에 널리 활용될 수 있는 가능성을 제시하였다. 본 연구는 웨어러블 소자 개발에 대한 기술적 트렌드에 발맞추어 플라스모닉스가 웨어러블 소자에 활용될 수 있는 가능성을 보여준다. 제 1장에서는 플라스모닉 소자의 제작과 측정 등에 대한 기초적인 내용에 대해 기술하였다. 나노구조가 플라스모닉스에서 어떻게 활용되는지 살펴보았고 곡면 소자에서의 플라스모닉스 연구 동향에 대해 알아보았다. 이어 플라스모닉 소자에서 핵심적인 전자빔 리소그래피를 이용한 소자 제작에 대한 기술을 하였다. 기존 단일층 전자빔 레지스트 기반의 공정에서는 100 nm 이하의 소자제작 분해능을 달성하기 어려웠던 반면, 이중층 전자빔 레지스트 공정을 적용하여 약 70 nm 수준의 소자 제작 분해능이 달성 가능함을 보였다. 또한 곡면 구조를 제작하기 위해 기존 마이크로 렌즈 제작 등에 활용되던 열 재유동 (thermal reflow) 공정을 적용하여 플라스모닉 곡면 소자 제작하였다. 끝으로 플라스모닉 소자의 여러가지 광학적 측정 방법들에 대해 알아보고, 광시야 조명 (wide-field illumination) 광학계를 활용해 플라스모닉 소자의 특성을 측정하고 그 결과를 보였다. 제 2장에서는 곡면 플라스모닉 소자에 대해서도 평판 계산이 수행되던 기존 연구의 한계를 극복하기 위해 분할파 분석 (Segmented-wave analysis) 방법을 제안하였다. 분할파 분석법은 곡면을 분할하여 전체 곡면 소자의 특성을 근사하는 방법이다. 분할파 분석법을 이용하여 기존 광학 계산 방법으로 수행하기 어려웠던 대면적 비주기 곡면 구조를 매우 빠른 시간에 계산할 수 있음을 곡면 소자의 표면 플라스몬 공명 (Surface plasmon resonance, SPR) 계산을 통해 보였다. 또한 바이오 센서로서 성능을 평가하기 위한 센서 감도를 DNA 혼성화 모델을 이용해 계산하였다. 이후 분할파 분석법을 검증하기 위해 작은 곡면 구조에서 더 작은 단위로 곡면을 분할하였고, 유한요소법 (Finite element method, FEM)을 이용하여 분할파 분석법에 대한 검증을 수행하였다. 분할파 분석법과 유한요소법을 비교하여 분할파 분석법의 한계와 유효성에 대한 검토를 수행하였으며, 특히 수직 입사 조건 (perpendicular incidence)에서 분할파 분석법이 높은 곡률에서도 유효성을 가짐을 확인하였다. 제 3장에서는 실험적 검증을 위해 곡면 플라스모닉 소자를 직접 제작하여 SPR 특성을 측정하고, 분할파 분석법 및 유한요소법 결과와 비교하였다. 실험 결과를 통해 분할파 분석법이 실제 곡면 소자의 성능을 평가하는 데에 유의미한 결과를 제시할 수 있음을 확인하였고, 유한요소법과 상보적으로 곡면 플라스모닉 소자를 분석하는 데에 중요한 방법이 될 수 있음을 보였다. In recent decades, plasmonics and its application research have been actively conducted in various fields. It plays an important role in various research fields, such as detecting biological samples with high sensitivity using an electric field strongly confined on the surface, promoting chemical reactions, and generating unprecedented optical properties. In this paper, we went one step further from the conventional planar structure-based plasmonics research and studied the surface plasmon resonance (SPR) characteristics of curved plasmonic devices, which will be widely used in a wearable platform such as plasmonic metamaterials in the future. This study shows the possibility that plasmonics can be used in wearable devices in line with the technological trend for wearable device development. In Chapter 1, the fundamental concepts of the fabrication and measurement of curved plasmonic devices are described. How curved structures are utilized in plasmonics, and plasmonics research trends in curved surfaces are presented. Subsequently, the technology for device fabrication using electron beam lithography (EBL), which is a key element in plasmonic devices, is described. In addition, to fabricate the curved structure, a curved plasmonic device is fabricated by applying the thermal reflow process used in conventional microlens fabrication. Finally, a few types of optical measurement methods of the plasmonic device were explored, and the characteristics of the plasmonic device are measured using a wide-field illumination optical system and the results are shown. In Chapter 2, segmented-based method is proposed to overcome the limitations of previous studies in which planar-based calculation was performed for curved plasmonic devices. The segmented-wave analysis is a method of approximating the characteristics of an entire curved surface by dividing a curved surface. It is shown through SPR calculation of a curved device that the segmented-wave analysis can be used to calculate a large-area aperiodic curved structure in a very short time, which was difficult to perform with conventional optical calculation methods. In addition, the sensor sensitivity to evaluate the performance as a biosensor is calculated using a deoxyribonucleic acid (DNA) hybridization model. Furthermore, the curved surface was divided into shorter lengths to model a small, curved surface structure. Finally, segmented-wave analysis is validated using the finite element method (FEM). The evaluation of limitations and effectiveness of the segmented-wave analysis are performed by comparing it with the FEM. In Chapter 3, a curved plasmonic device is fabricated to characterize the experimental results of the SPR, and the results are compared with the calculation results. It was confirmed that the segmented-wave analysis can provide a highly efficient method to evaluate the performance of the curved plasmonic surface.

공진 특성 조절이 가능한 Otto 구조의 표면 플라즈몬 공명 센서에 대한 연구

이연수 전북대학교 일반대학원 2021 국내박사

Surface plasmon polaritons are collective oscillation of electrons in the surface of the metals such as gold, silver and aluminum and it is caused by the incident light. When the specific conditions such as angle of incidence, wavelength and refractive index of materials, are satisfied, the incident light can be absorbed as a surface plasmon polaritons and the reflectance is rapidly decreased. This phenomenon is called as surface plasmon resonance. Characteristics of the surface plasmon resonance is changed sensitively according to a dielectric constant and refractive index change of the materials near the metal surface. Thus, if target molecules contact on the metal surface, surface plasmon resonance effect is changed and we can use this system as a sensor. The surface plasmon resonance sensor has been widely used in the chemical biology and drug design with advantages of label free detection, room temperature detection, and real time monitoring. There are two types of coupling configuration for surface plasmon resonance system using thin metal film. In the kretschmann configuration, metal film is located on the glass surface. On the other hand, metal film of the Otto configuration is located with a distance of the few micrometers from the glass. Due to the robust structure and convenience of fabrication, most of the surface plasmon resonance sensors are based on the kretschmann configuration. However, Otto configuration has a potential for tunable resonance characteristics according to the air-gap distance. If the air-gap distance between the glass substrate and the metal thin film can be stably adjusted, it will be possible to use a surface plasmon resonance sensor with the structural flexibility of the Otto configuration. In this study, the Otto configuration based sensor was fabricated through silicon on quartz bonding process. An air-gap distance of the sensor was designed to be 2.2 um and whole size of the sensor is 30*30*1 mm^3. Characteristics of the sensor was measured using a laser module with wavelength of 975.1 nm and the results was compared with FEM simulation results. It was verified that the characteristics can be sensitively changed according to the refractive index of the metal film. Performance of the sensor for gas sensing application was verified with simulation results and the results was compared with those of the other researches. The sensitivity of the fabricated sensor is 55 degree/RIU where the refractive index of the sensing medium is varied from 1 to 1.008. To verify the potential of the fabricated sensor as a pressure sensor, resonance characteristics was measured with applied pressure level from 0.23 bar to 1.3 bar. The air-gap distance of the fabricated Otto configuration was varied according to the pressure and the resonance characteristics was also changed. From the measurement results, the sensor has a sensitivity and resolution of about 0.17 degree/bar and 0.029 bar, respectively, as a pressure sensing application. Results show that the fabricated Otto configuration based sensor can be used as a hazardous gas and pressure level of the industrial facility with high sensitivity. Otto configuration with stepped air-gap (1.86 um, 2.42 um, 3.01 um, 3.43 um) was fabricated and the resonance characteristics at each air-gap was measured with 980 nm laser source. Minimum reflectance is measured to be 0.688, 0.716, 0.766, 0.86 at each section and the measurement results was analyzed with FEM simulation results. To verify the variability of characteristics of the Otto configuration and its applicability, the air-gap between the prism and the metal film was adjusted by using a commercial piezoelectric actuator. When the wavelength of the incident light was 786 nm, the reflectance was measured as 0.25 where the displacement of the piezoactuator was about 10.5 um, and it was confirmed that the maximum surface plasmon resonance occurred. Likewise, when a light source having a wavelength of 977 nm is used, the minimum reflectance becomes 0.22 where the displacement of the piezoactuator is about 9.3 um. The results shows that the wavelength of incident light for the maximum surface plasmon resonance in the Otto configuration is proportional to the air-gap in the actual measurement results. With an aim of inducing the variability of characteristics of the Otto configuration, a serpentine spring based MEMS actuator was designed and the driving characteristics were theoretically analyzed through numerical calculation and FEM simulation methods. The MEMS actuator for adjusting the air-gap of the Otto configuration was designed based on low-resistivity silicon. A 200 nm-thick gold thin film is located on the upper surface of the driving part. The initial distance between the silicon driving part and the driving electrode on the surface of the glass substrate is designed to be 18 um, and the distance between the gold film and the glass substrate is adjusted to be about 1 um from the initial value of 6 um. A resonance frequency of the driving part was calculated to be about 1.34 kHz, and it was confirmed that the driving part of the designed MEMS actuator can maintain a stable state even if an external shock is applied. FEM simulation results show that driving part of the proposed sensor can be moved vertically as much as 5.1 um when a potential difference of 59.2 V is applied between the driving electrode on the glass substrate and the driving part. It is expected that the results of this study can be used as a background data for the development of Otto configuration based surface plasmon resonance sensors with variable resonance characteristics, which has not been reported so far.

Fabrication of plasmonics platform for the chemical and environmental sensors

이수승 서울대학교 대학원 2013 국내박사

In the various field of nanotechnology and nanoscience, such as biomedical and environmental science, the design and synthesis of certain nanostructure for a desired purpose is important. Metallic nanostructures have attracted significant attention in the research area of chemical and environmental sensor due to the superior physic-chemical properties and, especially, applicability to the utilization of surface plasmon resonance phenomena. This thesis mainly deals with the application of novel metallic nanostructures to the surface plasmon resonance phenomena for the realization of effective chemical and environmental sensor. And more detailed strategies and results related with these topics, as follows; Firstly, highly selective detection system for Cu2+ ions by exploiting specific interactions between the Cu-demetallated form (E,Zn-SOD1) of Cu/Zn-superoxide dismutase (SOD1) and Cu2+ ions using surface plasmon resonance spectroscopy (SPRS) was suggested. I demonstrated that Cu2+ ions have a high affinity for vacant metal-binding sites in the E,Zn-SOD1 protein, compared to other divalent metal ions. On the basis of these measurements, it can be concluded that small amounts of Cu2+ ions can be readily detected as the result of the selective binding between the E,Zn-SOD1 protein and Cu2+ ions. It appears that metalloproteins have considerable potential for use as a novel sensing actuator, as evidenced by the selective binding of E,Zn-SOD1 proteins with Cu2+ ion. This approach can be used in conjunction with other fully or partially demetallated metalloproteins, hence it could be potentially useful in the determination of specific metal ions in aqueous media or demetallated proteins in biological fluids. Additionally, the applicability of gold nanoparticles as a ratiometric sensor was suggested. From the theoretical study using discrete dipole approximation method, it is investigated that dimer structure of gold nanoparticles has unique optical properties compared to separated single gold nanoparticle. It can be appeared new plasmon band with longer wavelength due to the electron oscillations along the longitudinal interparticle axis, and this band can be distinguished clearly with the inherent plasmon band. The intensity ratio of inherent and additional plasmon band could be utilized as the value for the ratiometric sensor. Finally, simple method to fabricate highly branched gold nanostructures with abundant petal-shaped tips by direct growth on the substrate was suggested. A lot of experiments and theoretical calculations have shown highly enhancement of the electromagnetic field in complex gold nanostructures due to the abundant ‘hot spots’ in the individual nanostructures. Among them, multi-branched nanostructure has attracted much attention because of their stronger SERS enhancement factor than other gold nanostructures. In this work, I synthesized and characterized the multi-branched gold nanoparticles, which are applicable to the surface-enhanced Raman detection. It was directly grown on the substrate with simple seed-mediated method, and the optical properties as growth procedure was investigated for the better understanding on the growth process. The multi-branched gold nanoparticles show the very high enhancement factor, thus it can be promising materials for the effective SERS substrate.

The disease analysis using Surface Plasmon Resonance (SPR) label-free optical biosensors : The analysis of fibrinogen protein of plasma of Alzheimer's disease Patients using Surface Plasmon Resonance (SPR) label-free optical biosensors

김지수 가천대학교 일반대학원 2017 국내석사

I report quantitative detection of proteins, fibrinogens present in human blood plasma, using the label-free biosensor which used Surface Plasmon Resonance (SPR) with multimode optical fibers. The sensor head employed fiber optical SPR excited at a wavelength of 632.8nm at the interface between fiber core and bimetallic layer which replaced hard polymer cladding of the fiber along its 5cm length. I coupled He-Ne laser into the SPR fiber and monitored the sensor output power change as analyte materials were adsorbed on the sensor surface. A Nickel layer of about 1nm thickness was deposited on the bi-metal layer for immobilizing histidine-tagged peptide (HP) on top of which antibody, i.e., immunoglobulin G (IgG) could be immobilized for specific reaction with fibrinogen in blood plasma of Alzheimer’s disease patients. The SPR fiber sensors presented enabled quantitative detection of various concentrations of fibrinogen with the limit of detection (LOD) of about 20ng/mL which was well below the level required for disease diagnosis. Additionally, I demonstrated regeneration of the sensor head by removing HP layers with imidazole for its multiple times use. Results of the label-free optical sensor presented also exhibited correlation with those obtained by enzyme-linked immunosorbent assay (ELISA). The fiber optical SPR biosensor presented is expected to find a use in where human access is limited such as underground and extraterrestrial space due to advantages including the sensor head regeneration and its inherent compactness, and possibility of its integration into a device.

Multifunctional nanoframe architectures for advanced sensing applications : design, synthesis, and characterization

Al Hammad, Hajir Hilal Khaleel Sungkyunkwan University 2023 국내박사

Metal nanoparticles (NPs) exhibit unique properties, including localized surface plasmon resonance (LSPR), which is influenced by their size, shape, and composition. This distinction sets them apart from bulk materials. Various types of plasmonic NPs have been developed and characterized to tailor their properties for specific applications. Nanoframes, a group of NPs with large cavities accessible to light and chemicals, have gained significant attention. However, previous studies on single-rim-based NFs have faced limitations in near-field focusing capabilities due to their structural simplicity, necessitating the development of a conceptually new NF architect. This thesis contributes to the comprehensive understanding of multifunctional nanoframe architectures by combining the fields of plasmonics, nanomaterial synthesis, and surface chemistry. It showcases the potential of these nanoframes in various sensing modalities, demonstrating their capabilities in different sensing applications. In Chapter 2, a brief introduction is presented on a biosensing platform that utilizes a mixture of Au nanorods and magnetically responsive Pt@Ni nanorings. The platform utilizes a rotating magnetic field to induce dynamic assays, enabling the monitoring of surface biorecognition on Au nanorods through periodic changes in extinction. This approach provides an alternative to conventional biosensors based on peak shift of localized surface plasmon resonance. In chapter 3, I address the challenges in realizing complex three-dimensional (3D) nanoframe structures for effective optical-based sensing. A novel synthesis method for complex 3D nanoframes is presented, where two-dimensional (2D) dual-rim nanostructures are engraved on each facet of octahedral nanoframes. The synthesis proceeds through multiple executables on-demand steps, involving edge-selective Pt deposition, inner Au etching, and tunable geometric patterning. The resulting plasmonic dual-rim engraved nanoframes exhibit strong light entrapping capability verified by single-particle surface-enhanced Raman scattering (SERS), highlighting their potential as nanoprobes for biosensing applications through SERS-based immunoassay. In Chapter 4, focuses on the synthesis of Au truncated octahedral dual-rim nanoframes with two functional facets. The nanoframes feature eight hot nanogaps formed by hexagonal nanoframes and six flat squares that facilitate well-ordered arrays through self-assembly. The existence of intra-nanogaps enables strong electromagnetic near-field focusing, allowing single-particle surface-enhanced Raman spectroscopy. The construction of "all-hot-spot bulk SERS substrates" using these nanoframes demonstrates highly ordered and uniform superlattices with a significantly lower limit of detection for 2-naphthalenethiol, achieved through the synergistic effect of inter- and intraparticle coupling in the superlattice. In chapter 5, presents the design and synthesis of elongated pseudo-hollow nanoframes named "Au dodecahedral-walled nanoframes" for efficient detection of gaseous analytes. The nanoframes are composed of four rectangular plates enclosing the sides and two open-frame ends with ridges for near-field focusing. The hollow interior allows for the penetration of gaseous analytes, enabling their efficient detection in combination with Raman spectroscopy. The nanoframes exhibit high homogeneity in size and shape and demonstrate significantly enhanced SERS activity compared to other nanostructures. The application of these nanoframes in detecting chemical agent simulants in the gas phase showcases their 20 times higher sensitivity compared to their solid counterpart. Overall, this thesis contributes to the advancement of multifunctional nanoframe architectures in various sensing applications, offering novel strategies for design, synthesis, and characterization in diverse sensing modalities and nanomaterial engineering. Metal nanoparticles (NPs) exhibit unique properties, including localized surface plasmon resonance (LSPR), which is influenced by their size, shape, and composition. This distinction sets them apart from bulk materials. Various types of plasmonic NPs have been developed and characterized to tailor their properties for specific applications. Nanoframes, a group of NPs with large cavities accessible to light and chemicals, have gained significant attention. However, previous studies on single-rim-based NFs have faced limitations in near-field focusing capabilities due to their structural simplicity, necessitating the development of a conceptually new NF architect. This thesis contributes to the comprehensive understanding of multifunctional nanoframe architectures by combining the fields of plasmonics, nanomaterial synthesis, and surface chemistry. It showcases the potential of these nanoframes in various sensing modalities, demonstrating their capabilities in different sensing applications. In Chapter 2, a brief introduction is presented on a biosensing platform that utilizes a mixture of Au nanorods and magnetically responsive Pt@Ni nanorings. The platform utilizes a rotating magnetic field to induce dynamic assays, enabling the monitoring of surface biorecognition on Au nanorods through periodic changes in extinction. This approach provides an alternative to conventional biosensors based on peak shift of localized surface plasmon resonance. In chapter 3, I address the challenges in realizing complex three-dimensional (3D) nanoframe structures for effective optical-based sensing. A novel synthesis method for complex 3D nanoframes is presented, where two-dimensional (2D) dual-rim nanostructures are engraved on each facet of octahedral nanoframes. The synthesis proceeds through multiple executables on-demand steps, involving edge-selective Pt deposition, inner Au etching, and tunable geometric patterning. The resulting plasmonic dual-rim engraved nanoframes exhibit strong light entrapping capability verified by single-particle surface-enhanced Raman scattering (SERS), highlighting their potential as nanoprobes for biosensing applications through SERS-based immunoassay. In Chapter 4, focuses on the synthesis of Au truncated octahedral dual-rim nanoframes with two functional facets. The nanoframes feature eight hot nanogaps formed by hexagonal nanoframes and six flat squares that facilitate well-ordered arrays through self-assembly. The existence of intra-nanogaps enables strong electromagnetic near-field focusing, allowing single-particle surface-enhanced Raman spectroscopy. The construction of "all-hot-spot bulk SERS substrates" using these nanoframes demonstrates highly ordered and uniform superlattices with a significantly lower limit of detection for 2-naphthalenethiol, achieved through the synergistic effect of inter- and intraparticle coupling in the superlattice. In chapter 5, presents the design and synthesis of elongated pseudo-hollow nanoframes named "Au dodecahedral-walled nanoframes" for efficient detection of gaseous analytes. The nanoframes are composed of four rectangular plates enclosing the sides and two open-frame ends with ridges for near-field focusing. The hollow interior allows for the penetration of gaseous analytes, enabling their efficient detection in combination with Raman spectroscopy. The nanoframes exhibit high homogeneity in size and shape and demonstrate significantly enhanced SERS activity compared to other nanostructures. The application of these nanoframes in detecting chemical agent simulants in the gas phase showcases their 20 times higher sensitivity compared to their solid counterpart. Overall, this thesis contributes to the advancement of multifunctional nanoframe architectures in various sensing applications, offering novel strategies for design, synthesis, and characterization in diverse sensing modalities and nanomaterial engineering.

Development of Surface Plasmon Resonance Biochip Based on Recognition-Functional Monolayers

진홍하 부산대학교 대학원 2008 국내박사

인식에 의한 생체 분자간의 특이한 상호작용과 연관된 과정의 이해는 약학 및 의약공학에서 매우 중요할 뿐만 아니라 과학적이며 실용적인 가치를 보여주고 있다. 현재 생체 분자간 상호작용 연구에 사용되어지는 기술의 대부분은 대량의 용액내에서 특정 분자와 인식 기능성 분자 사이의 선택적인 상호작용에 의한 것이다. 우수한 인식기술을 개발하기 위해서는 생체 분자간 상호작용에 대한 조사 및 특정 생체 분자에 대한 높은 감도와 선택성을 가진 분자 인식체계의 구성이 매우 중요하다. 또한, 효율적인 신호증폭 체계와의 조합이 필수적으로 요구되어진다. 인식 기능성의 유리를 위한 정렬된 분자의 표면구조를 만들기 위하여 간단한 방법으로 알려져 있는 자기조립 단분자막(Self-Assembled Monolayer) 기술을 응용하고, 생체 분자간 상호작용에 의해 발생하는 물리적 신호를 효과적으로 증폭하기 위한 표면 플라즈몬 공명(Surface Plasmon Resonance)을 조합하여, 가장 예민하며 유용한 기술중의 하나인 SPR 바이오 칩을 형성할 수 있고, 이를 이용하여 실시간 측정 및 표지(Labeling) 과정 없이 바이오 물질간 특이적 상호작용 분석을 고감도로 직접 시행할 수 있다. 본 논문에서는 당, 아미노산, 단백질, 이온 등에 대한 인식 기능성 분자들을 자기조립 방식에 의해 단분자막을 형성하여 SPR 칩을 구성하였으며, 원자힘 현미경(AFM), 적외선 반사 흡수 분광기(FTIR-RAS), 주기성 전압전류계(CV) 등을 이용하여 표면화학적, 광학적 특성을 분석하였다. 구축한 SPR칩을 기반으로 하여, 특정 분자에 대하여 우수한 감도와 선택성을 가진 바이오분자 칩의 개발을 위한 기초적인 연구를 수행하였다. 이는 앞으로 더욱 고도화된 바이오 탐색체제의 개발을 위한 유용한 방법에 적용될 것으로 생각된다. Understanding the processes involved in the specific interactions of biomolecules with surfaces by the recognition adsorption has been showed significant scientific and practical values in pharmacy. Therefore, many of the techniques that are currently used for the investigation of biomolecular interactions, are based on the specific interaction between target molecules in the bulk solution and recognition molecules confined to various types of surfaces. To develop more precise biosensing interface for allowing investigating the interaction of biomolecules, it is important to construct a molecular recognition system with high sensitivity and selectivity for target biomolecules. In addition, the coupling of molecular recognition system with an efficient signal amplification method is required. In this study, ions, small biomolecules and proteins recognition-functional molecular monolayers were constructed. The self-assembled monolayers (SAMs) were applied to the organization of the functional molecules for biospecific recognition. The recognition monolayers were formed by self-assembly method and characterized by atomic force microscopy (AFM), Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS), and cyclic voltammetry (CV). The molecular recognition system generates a signal by specific molecular interaction between receptor and target molecules that was investigated by surface plasmon resonance (SPR). It was applied as a significantly useful method for the development of biosensing interface with high sensitivity and selectivity for target molecules based on SPR and SAM technique.

Gap-plasmon based fluorescence correlation spectroscopy

이홍기 Graduate School, Yonsei University 2020 국내박사

고전 광학에서 입사광은 회절 한계에 의하여 감소될 수 있는 크기에 제한을 받는다. 아베(Abbe) 회절 한계에 따르면 입사광의 크기는 주로 입사광의 파장과 사용된 광학 시스템의 개구 수(numerical aperture, NA)에 의해 결정된다. 이 회절 한계를 극복하기 위해서 다른 방법론이 광학 시스템에 적용되어야 하며 나노 스케일에서의 광 제어를 이루기 위해서 많은 종류의 연구가 수행되어왔다. 본 논문은 플라스모닉스 기술이 회절 한계를 극복한 나노 스케일 영역에서 광신호를 국소화 및 조정하여 높은 신호 대 잡음비(signal-to-noise ratio, SNR) 및 정밀도로 생물학적 정보를 획득할 수 있음을 보였다. 본 논문은 먼저 제 2 장에서 나노 스케일 물질의 플라스몬 특성을 조사하기 위해 박막의 광열 반응을 고려한 반복 계산 방법을 사용하여 금속 나노 구조의 전기장 분포와 열팽창을 분석하였다. 다양한 입사 조건에서 플라스몬 금속 박막의 전기장 향상 및 에너지 흡수의 측정이 가능한 탐침 기반의 측정법을 제시하였다. 또한, 비대칭 다층 계에서의 파동 분산 관계에 의해 설명될 수 있는 금 박막의 누설 방사(leakage radiation, LR)를 조사하였다. LR은 금속 박막의 표면 플라스몬 폴라리톤(surface plasmon polariton, SPP)의 전파를 시각화하며 이를 통하여 금속 표면의 굴절률 분포를 확인할 수 있다. 본 논문은 누설 방사 현미경(leakage radiation microscopy, LRM) 및 표면 플라스몬 공명 현미경(surface plasmon resonance microscopy, SPRM) 기술의 성능을 하드웨어 및 소프트웨어적으로 개선시킬 수 있는 방법에 대하여 논의하였다. 제 3 장은 다양한 크기 및 주기를 가지는 원형, 마름모꼴, 삼각형 모양의 나노 구조에 초단파 펄스가 가해졌을 때 인가되는 국소화된 표면 플라스몬(localized surface plasmon, LSP)에 대하여 살펴본다. 더 나아가, 플라스몬 구조에 인가되는 입사광의 특성을 조정함으로써 회절 한계로 제한된 영역 내에서 근접장 분포의 공간 제어가 가능하며, 고해상도 형광 이미징에 적용이 가능함을 보여주었다. 제 4 장에서는 18 nm 갭을 갖는 플라스몬 나노 구조체 어레이가 형광 상관 분석법 (fluorescence correlation spectroscopy, FCS)의 성능을 개선할 수 있음을 입증하였다. FCS는 형광 신호의 자기 상관 함수로부터 분자의 확산 및 결합 상호 작용과 같은 특성을 조사하는데 용이한 기술로, 특히 세포 내 및 세포막 상의 생체 분자의 운동 특성을 조사하는데 적용된다. FCS는 일반적으로 회절 한계에 의해 제한된 관찰 부피를 사용하여 수행되어 왔다. 예를 들어, 공초점 현미경을 사용한 실험 조건 하에서 FCS는 횡축으로 약 200 nm 및 종축으로 600 nm으로 제한된 관찰 부피를 갖는다. 본 논문에서는, 플라스몬을 사용하여 개선된 형광 상관 분광법(plasmonic-enhanced fluorescence correlation spectroscopy, pFCS)이 생체 분자의 운동 특성 연구에 어떻게 기여할 수 있는지 탐구하였다. p-FCS는 입사광을 나노 갭에 국소화시켜 회절 한계보다 작은 영역에서 생체분자를 관찰할 수 있도록 하였다. 나노 갭 내에 국소화된 전자기장은 근접장 주사 광학 현미경(near-field scanning optical microscopy, NSOM)을 사용하여 실험적으로 확인되었다. 이러한 나노 스케일 영역에서의 전자기장 국소화는 회절한계보다 작은 산란 단면을 가지며 LR의 세기를 증대한다. 본 논문에서는 소실파 내에서 동시에 표면 플라스몬 공명(surface plasmon resonance, SPR) 이미징을 수행할 수 있는 영상장치를 구축하여, 나노 입자를 높은 정밀도로 추적할 수 있게 하였다. 제 2 장과 3 장에서 논의한 바와 같이, 플라스몬 나노 구조체의 근접장 증폭은 형광 여기와 LR 강도 모두를 향상시킬 수 있음을 입증하였다. In classical optics, there is a theoretical limitation of the size to which a focused incident beam can be reduced. The size is mainly governed by the incident wavelength and a numerical aperture of an optical system. To break this diffraction limit, other methodologies should be employed to the optical system and many kinds of research have been performed to achieve a nanoscale light confinement. In this sense, plasmonics can be substantial to manipulate the optical signal within the nanoscale area and collect biological information from the sample with a high signal-to-noise ratio (SNR) and precision. To investigate the plasmonic properties of nanoscale materials, we first analyzed a field distribution and a thermal expansion of metallic nanostructures which were compared with an iterative calculation method considering the opto-thermal response of thin films in Chapter 2. The experimental results had a good agreement with calculation methods. The results have provided direct measurements of optical responses of plasmonic thin films by measuring field enhancements and absorption with various incident conditions. In addition, we have investigated the leakage radiation (LR) of gold thin films which can be explained by the dispersion relation in the asymmetric multi-layered system. We have discussed a good advantage of LR to visualize the surface plasmon polariton (SPP) propagation on gold thin films and how to improve the imaging performance. In Chapter 3, we have explored spatial field localization under ultrashort light pulses based on localized surface plasmon (LSP) by three-dimensional geometrical nanoapertures, which were circular, rhombic, and triangular with various combinations of size and period. Moreover, it was shown that plasmonic nanostructures enable spatial control of near-field distribution within the diffraction-limited area and also applicable to high-resolution fluorescence imaging. In Chapter 4, it was shown that the performance of fluorescence correlation spectroscopy (FCS) could be improved using plasmonic nanostructure arrays which have an 18-nm gap. FCS is a well-known technique that enables molecular detection to obtain biological information such as properties of diffusion and binding interaction by acquiring an autocorrelation of fluorescence fluctuation. FCS is typically conducted using a diffraction-limited volume in which target molecules diffuse. Under the typical experimental condition of confocal microscopy, diffraction-limited FCS has a volume of 200-nm lateral width and 600-nm axial length. We have explored how plasmon-enhanced FCS (p-FCS) was feasible and potential for biomolecular study using lysosomes in the human embryonic kidney (HEK) 293 cells. The p-FCS have provided arrays of sub-diffraction-limited light volume. The field localization within a nanodimer’s gap was confirmed experimentally using near-field scanning optical microscopy (NSOM). Those nanoscale localizations have much smaller scattering cross-section with higher SNR. We have established p-FCS imaging set-up which was able to perform surface plasmon resonance (SPR) imaging simultaneously in the evanescent field, allowing tracking nanoscale molecules with improved precision. As discussed in Chapters 2 and 3, it has been demonstrated that near-field amplification of plasmonic nanostructure had improved both fluorescence excitation and LR intensity. It should be emphasized that plasmonic nanostructures confining electromagnetic field into the nanoscale area have great potential in various biomedical engineering applications. In the dissertation, we have demonstrated near-field and far-field properties of plasmonic nanostructures and their applications for biological studies. The properties and performance of plasmonic nanostructures are expected to be investigated in more extensive areas of research as a critical component of nanotechnology and to find more applications for delivery of nanoscale biomolecular information.

Plasmonic-enhanced dye-sensitized solar cells with Ag and Au nanoparticles

宋多賢 서울大學校 大學院 2017 국내박사

Dye-sensitized solar cell (DSSC) is one of the efficient devices for generating electrons from solar light energy. Their advantages are low-cost processing, and various colors and transparent design for building integrated photovoltaics (BIPVs). Although DSSCs have numerous advantages, their power conversion efficiency (PCE) is lower than that of other solar cells. There are several ways to develop highly efficient DSSCs, such as improving light harvesting and electron transport. Applying plasmonic metal nanoparticles (NPs), exhibiting localized surface plasmon resonances (LSPRs), to the DSSCs seems to be very effective for highly efficient DSSCs. Because their strong plasmonic near-fields increase the photon scattering cross-section enormously, thereby increasing the overall dye absorption and efficiency improvement by many different route such as light trapping. Therefore, when plasmonic metal NPs are applied to the DSSCs, light harvesting or carrier collection can be improved. Many attempts have been made to apply plasmonic metal NPs to increase the efficiency in DSSCs. Among the various plasmonic metal NPs, Ag and Au NPs are the most widely used metallic materials for triggering plasmonic enhancement in solar cells, because of their remarkable optical properties. The maximum absorption wavelengths of spherical Ag and Au NPs are approximately 400 nm and 530 nm, respectively. The absorption bands of these NPs are well matched to those of N719 dye which is the most commonly used Ru-based dye molecules for DSSCs. Therefore, in this thesis, Ag and Au NPs were incorporated together in DSSCs to enhancing two absorption bands of N719 dye at the same time for highly efficient DSSCs. First, we fabricated Ag and Au NPs and used them to fabricate plasmonic DSSCs based on double-layered composite films. Compared to DSSCs without metal NPs, the PCE of the double-layered plasmonic DSSC enhanced from 8.42% to 10.03%, corresponding to 19% enhancement due to LSPR effect of Ag and Au NPs. The high efficiency of double-layered plasmonic DSSC might be due to a well optical spectra matching between the LSPRs of Ag and Au NPs and two strong absorption bands of N719 dye. For double-layered plasmonic DSSCs, the plasmonic metal NPs were dispersed into the TiO2 photoactive layer and play a role as light harvesting and charge separation sites. By LSPR effect of Ag and Au NPs, the electric field around the metal NPs enhances and the light absorption cross section of the dye and the number of generated photoelectrons increase which in turn increases the efficiency of DSSCs. Next, to fabricate highly efficient DSSCs, it is required to prevent the aggregation of metal NPs in the fabrication process of the composite film with TiO2 and metal NPs. Therefore, we fabricated plasmonic layer consisting of Ag and Au NPs and incorporated on the TiO2 photoactive layer of DSSCs. In this experiment, the plasmonic layer was fabricated by immobilizing plasmonic metal NPs on the surface of the TiO2 film coated with poly(4-vinylpyridine) (P4VP) to prevent the aggregation of metal NPs. The optimal conditions for metal NPs, such as immobilizing time and order, were examined. When both Au and Ag NPs were employed together at optimum conditions as the plasmonic layer, the PCE further improved from 8.39% to 10.17%, corresponding to 21.16% enhancement compared to DSSCs without metal NPs. The significant improvement of the PCE could be attributed to the LSPRs of plasmonic layer consisting of Au and Ag NPs. The plasmonic layer, which is located between the photoactive and scattering layers, functions as light scattering site and results in increase optical path length of the incident light, the light absorption and the electron transfer yields. Lastly, multi-shaped Ag NPs were prepared and applied to DSSCs to enhance their PCE by broad absorption in visible region. Prepared multi-shaped Ag NPs were composed of various shapes such as spherical, rod, and triangle structures, which exhibited broader absorption than that of the spherical Ag NPs. The absorption of the plasmonic layer based on multi-shaped Ag and Au NPs could cover the absorption range of N719 dye. To study the plasmonic effect of the multi-shaped Ag NPs, we have compared the effect of spherical Ag NPs and multi-shaped Ag NPs on the photovoltaic properties of DSSCs based on a layer-by-layer structure and a composite film structure with Ag and Au NPs. The maximum absorption wavelength (λmax) of the multi-shaped Ag NPs is 420 nm, including the shoulder with a full width at half maximum (FWHM) of 121 nm. This is a broad absorbance wavelength compared to spherical Ag NPs, whose λmax is 400 nm, without the shoulder of 61 nm FWHM. For DSSCs based on layer-by-layer structure with multi-shaped Ag and Au NPs, the PCE increased from 9.90% to 10.22%, a 3.2% enhancement, compared to DSSCs with spherical Ag and Au NPs. The PCE of the DSSCs based on layer-by-layer structure with multi-shaped Ag and Au NPs enhanced by 21.09%, compared to DSSCs without metal NPs. Similar to the layer-by-layer structure, the PCE of DSSCs based on the composite film structure with multi-shaped Ag and Au NPs increased from 9.99% to 10.34%, a 3.5% enhancement, compared to DSSCs with spherical Ag and Au NPs. The PCE of the DSSCs based on composite film structure with multi-shaped Ag and Au NPs enhanced by 20.51%, compared to DSSCs without metal NPs. It is concluded that the DSSCs with spherical Ag or multi-shaped Ag NPs was improved by the plasmonic effect, and the DSSCs with multi-shaped Ag NPs, which have broader absorption wavelengths range in the absorption of N719 dye at 393nm, exhibited better PCE than the DSSCs with spherical Ag NPs.

Synthesis and Optical Application of Plasmonic Noble Metal Nanostructures

김준기 서울대학교 대학원 2020 국내박사

독창적이고 기능적인 플라즈모닉 귀금속 나노입자의 합성과 광학적 특성에 대해 주로 연구하였다. 다양한 합성방식으로 코어쉘, 속이 빈 껍질, 나노스파이크 그리고 나노입자 어레이 구조를 합성해보았다. 분광광도계와 라만광도계, 전자현미경 등을 이용하여 제작된 나노구조물의 광학적, 구조적 특성을 연구해보았다. 귀금속 나노입자 합성방법과 플라즈모닉 공명현상을 Chapter 1에 간략히 소개하였다. Chapter 2에서는 금 클러스터가 흡착된 Ag@SiO2 코어쉘 나노입자의 금속-증강 형광 (Metal-enhanced fluorescence, MEF)에 대해 연구하였다. 금속나노입자는 입사 광에 의해서 표면의 자유전자들이 집단적인 진동하는 표면플라즈몬공명 (surface plasmon resonance, SPR)이라는 독특한 광학적 특성을 가진다. 이러한 현상을 통해 나노입자 표면에서는 입사되는 전자기장의 세기보다 수천~수만 배 더 큰 세기로 증폭될 수 있으며, 이러한 현상을 근접장증폭이라 불리고 있다. 이러한 광학적인 기능성을 가지는 금속나노입자에 실리카 껍질을 두르면, 금속입자 표면이 보호되거나 SPR 현상을 더욱 증강시킬 수 있다. 은 나노입자는 수용액상에서 은 이온의 화학적 환원을 통해 구 형태로 합성한 다음, 실리카 물질의 전구체를 이용한 Stober method를 통해 은 나노입자 표면에 실리카 껍질을 구현하였다. TEOS 양을 달리 함에 따라 실리카 쉘 두께를 변화시켜 각기 다른 Ag@SiO2 코어쉘 나노입자를 합성한 다음, 거리-의존적인 SPR 현상을 관찰하였습니다. 보통, 나노입자는 열역학적으로 가장 안정한 구(sphere) 형태로 합성된다. 열역학적의 한계를 넘어서 좀 더 고차원적이고 기능성을 가지는 나노입자 제작에 관한 연구가 국내외 연구진에서 활발하게 진행되고 있다. 나노쉘 (nanoshell) 형태의 입자란, 실리카 같은 유전물질이 중심에 존재하고, 그 표면을 금속물질로 껍질처럼 둘러싸인 구조를 말하는데, 나노쉘입자는 구 형태의 입자보다 SPR 현상을 더욱 강하게 발현시키고, 적외선 영역 쪽에서 광학적 활성을 보이는 고기능성 구조이다. Chapter 3에서는 이전에 보고되지 않았던 구조인, 속이 비어있고 그 안쪽에 표면에 거칠기가 있는 금 나노쉘 입자를 합성에 대해 설명하였다. 나노입자의 표면이 거칠다면, 나노미터 스케일에서 전자기장을 산란시킬 수 있으므로 SPR 효과를 더욱 증강시킬 수 있다. 속이 비어있고 안쪽의 표면이 거진 나노쉘 구조를 만들기 위해 메조포러스(mesoporous) 실리카 나노입자를 주형으로 이용했는데, 메조포러스 실리카는 입자 내에 CTAB 분자들의 자가조립에 의해서 만들어진 공동이 무수히 존재하는 실리카 입자를 말한다. 메조포러스 실리카 공동에 표면처리를 통해서 자그마한 금 나노입자를 부착시키고, 화학적 환원법을 통해 금 나노입자들을 성장시킨다. 성장되는 금 나노입자들은 입자가 커짐에 따라 실리카 공동구조를 부분적으로 채우게 되고, 추후 실리카를 HF로 에칭함으로서 속이 비어있고 안쪽에 거친 표면을 가지는 금 나노쉘 (hollow and bumpy gold nanoshell, HBA NS) 합성할 수 있었다. 어떠한 금속 나노구조물에 나노스케일의 거칠기나 나노팁 형태를 부여하면 더욱 향상된 플라즈모닉 성질을 보일 수 있다. 음의 유전율을 가지는 귀금속 나노구조물은 입사하는 전자기장을 국부적으로 구속하는 능력이 가지게 되고, 특히나 나노팁과 같이 구조체의 곡률이 심하게 변화하는 곳은 그 효과가 더욱 증폭됩니다. Chapter 4에서는 입자 안의 cavity가 확실히 존재하고 표면에 나노팁이 무수한 입자를 합성하고자 노력하였다. SH-로 표면개질된 실리카 나노입자를 합성한 다음, 아주 작은 크기의 은 나노입자를 실리카 표면에 합성한다. 이후, 점진적인 galvanic replacement 반응을 통해서 실리카 표면 위에 금 나노팁이 무수하게 존재하는 나노성게 입자(spiky Au nanourchins, SANUs) 를 합성한다. HAADF-STEM 측정방식을 통해서 SANUs 입자 중간에 실리카 입자가 확실히 보이며, galvanic replacement 반응으로 금 나노껍질이 환원된 모습이 관찰된다. 또한 EDX line-mapping과 원소분석을 통해서, SANUs 입자는 속이 비어있고 금 성분이 98 wt%로 관찰되는 데 반해, 은 성분은 0.2 wt% 아주 극미량으로 구성되어있음을 확인하였다. 최종적으로 합성된 SANUs 입자에 HF로 실리카 성분을 녹여서 속이 비어있고 나노팁이 무성한 금 나노성게 (hollow and spiky Au nanourchins, HSANUs)를 얻어보았다. FIB (focused-ion beam) 기법으로 그 단면을 조사하여 HSANUs 입자 안쪽에 확연한 cavity 형태를 확인하여, 중국의 연구진들에 의해 제안된 나노성게 입자의 cavity의 크기가 확연히 비교됨을 확인하였다. 레이저를 이용한 미세구조 가공기술은 레이저 빔의 고집속성 및 시공간적 정밀함으로 인해 반도체, 전자, 메카트로닉스 등의 첨단산업 분야에서 필수적인 기술로서, 신 공정 개발에 기여해왔습니다. 광열적 부작용이 적어서 마이크로-나노 급의 형상 가공이 가능한 극초단파 레이저(ultrafast laser)의 도입과 연구가 활발히 진행되고 있는데, chapter 5에서는 극초단파 레이저 광원을 사용하여 금속 나노구조를 손쉽게 제작한 연구를 설명하였다. 나노세컨드 레이저는 연속파 레이저에 비해 강한 파워를 가짐과 동시에 비교적 열적 영역 (heat-affected zone)이 넓어서 벌크물질에 극심한 형태변화를 유도할 수 있기 때문에 top-down 방식의 제작에 유리하다 판단하였습니다. 1.3 J/cm2의 파워와 50 μm/s의 속도로 레이저를 십자가 형태로 스캔한 (cross-line scanning) 실버 페이스트 필름에서, 균일한 나노입자배열이 십자가의 왼쪽, 오른쪽 가지에 관찰되었고 위, 아래의 가지에서는 이전에 관찰되었던 미세하고 무수한 은 입자들이 제작되었다. 가로방향의 스캔으로 통해 미세하고 무수한 은 나노입자를 제작한 다음, 세로방향으로 스캔 할 때, 불균일한 에너지 분포 형태의 Gaussian form을 가지는 레이저 빔에 의해서 dewetting threshold를 넘어가는 공간적 영역에서는 dewetting 현상이 일어나 나노입자배열이 제작되는 것을 발견하였다. 십자가 레이저 스캔 모드 양식의 확장으로서, 그물모양의 레이저 스캔을 시행하면 센티미터급의 대면적의 플라즈모닉 나노구조배열을 얻을 수 있었고 강한 전자기장 증강으로 표면증강라만산란기법 (Surface-enhanced Raman scattering)을 통해서 하여금 분석하고자 하는 물질의 농도가 nM 수준으로 내려가도 충분히 검출 가능한 기능성 기판 제작에 성공하였다. In this dissertation, synthesis and optical application of plasmonic noble metal nanostructures are mainly discussed. Various methods to fabricate core-shell, nanoshells, nanospike, and nanoparticle arrays structures have been investigated. The optical and morphological properties of as-prepared nanostructures have been also studied by using UV/vis spectroscopy, Raman spectroscopy, and electron microscopy. A brief overview on preparation methods and the plasmonic resonance of noble metal nanostructures are presented in Chapter 1. Chapter 2 presents the metal-enhanced fluorescence (MEF) of gold nanoclusters adsorbed onto Ag@SiO2 core-shell nanoparticle. The static and time-resolved MEF of Au25-adsorbed Ag@SiO2 core-shell nanoparticles (NPs) has been studied systematically with variation of shell thicknesses, core sizes, and excitation wavelengths. The emission of Au25-adsorbed Ag@SiO2 NPs is blue-shifted and highly enhanced compared with that of free Au25 clusters. The photoluminescence (PL) intensity of Au25-adsorbed Ag@SiO2 NPs is higher as much as 7.4 times than that of free Au25 clusters. The increase of the radiative decay rate constant with separation is identical to that of PL enhancement, suggesting that the MEF of Au25-adsorbed Ag@SiO2 NPs arises from the increase of the radiative decay rate constant induced by the near-field enhancement of plasmonic Ag NPs. Chapter 3 describes the fabrication of hollow and bumpy Au (HBA) NSs with rough surfaces using expanded silica mesopores as templates. Because some Au seeds were located at the inner surfaces of silica mesopores, produced Au NSs have inherent inward-grown nanobumps. During seven successive reduction steps, the LSPR peak of Au nanostructures shifted progressively toward a longer wavelength as the sizes of Au seeds increased gradually. Measuring the cross-sections of HBA NSs milled by a focused ion beam, we have found that hollow and bumpy nanostructures arose from the pore structures of mSiO2 NPs. HBA NSs confine Raman-probe molecules well owing to their hollow structures and have ragged surfaces due to their inward-bumpy morphologies, exhibiting highly efficient surface-enhanced Raman scattering activity. Chapter 4 presents the fabrication of genuinely hollow Au nanourchins (HANUs) using SiO2 NPs as hard templates. Ag-SiO2 NPs were fabricated via amine-assisted reduction. Then, Au nanourchins (ANUs) were synthesized by the galvanic replacement reaction of Ag-SiO2 NPs using L-3,4-dihydroxyphenylalanine (DOPA) as a reductant and a capping agent. The silica cores of ANUs were etched using HF(aq) to produce HANUs. Measuring cross sections, we have found that HANUs have well-defined hollow morphologies. Compared with nanourchins made via DOPA-mediated reduction, HANUs hardly contain residual silver because very tiny silver seeds were used as the initiation sites of galvanic replacement. HANUs have revealed large surface-enhanced Raman scattering enhancement and a significant photothermal effect under a weak illumination. Chapter 5 describes that highly dense plasmonic silver NP arrays have been fabricated by laser-induced dewetting of commercially available silver paste as a starting bulk material. The first laser-scan mode has produced unprecedented intermediate structures, so called laser-induced fine silver nanostructures (LIFSNs) while the second laser-scan mode has transformed LIFSNs into plasmonic silver NP arrays via the dewetting of the priorly formed nanostructures. The laser-induced fabrication of silver NP arrays has been found to be very sensitive to distance from secondly irradiated laser pulses, suggesting that the fine control of laser intensity is very important. As-prepared silver NP arrays have generated numerous hot spots to show highly strong surface-enhanced Raman scattering signals.

Synthetic strategies and optical properties of anisotropic plasmonic nanostructures

이정훈 서울대학교 대학원 2014 국내박사

Designing and synthesizing plasmonic nanostructures allow us to manipulate and mix the optical, magnetic and electrical characteristics of materials. Optical response of individual nanoparticles mainly dominated by localized surface plasmon resonance (LSPR) strongly depends on their size, shape, composition. This structure- and environment-dependent LSPR has been used to enhance optical signals such as Raman scattering or fluorescence in a wide range of fields from optics and spectroscopy to biomedical applications. Important reason that enhances such an optical signal is the extraordinarily amplified electromagnetic fields (EM fields) at the junction area positioned between a pair of nanoparticles or at internal crevice of the single nanoparticle. Among many structures, dimeric nanostructures with inter-particle spacing have been the most heavily studied because it is simple and they generate a very strong EM field in their junctions. In a homodimer system, redshift of longitudinal bonding plasmon modes is typically observed while decreasing inter-particle distance (hybridization of individual particle plasmons) but antibonding mode is dark. However, recent results show that diverse plasmon modes can be shown and excitable in the heterodimers with different size of nanoparticles or composition. This phenomenon is due to the symmetry breaking of plasmon modes and resulted in strong enhancement of various plasmon coupling. In both cases, it is particularly important to control ~1 nm gap because effective plasmon coupling can be generated in ~1 nm gap or less. Therefore, it is still highly challenging to precisely and reproducibly synthesize and assemble them into well-defined structures at nanometer scale for making them ideal for a range of fundamental studies and applications. In this thesis, we introduce DNA-based synthetic strategies to study optical properties and design plasmonic nanostructures with high structural controllability. These strategies allow us to manipulate the shape and assembly of nanostructures, such as dimer/trimmers with inter-particle spacing, single particles with intra-nanogap or different compositions. We investigate the relationships between plasmon response, signal amplification and structural changes of those plasmonic nanostructures such as inter-/intra-particle distance and particle size/composition. In the assembled system with inter-particle spacing, we performed single-molecule correlation studies on single-DNA-tethered Au-Ag core-shell dimeric nanostructures for surface-enhanced Raman scattering (SERS). We showed strategies to design the assembly of plasmonic nanoparticles and control the distance between particles for amplifying SERS signal. With DNA-modified AuNPs, We developed a new salt-tuned synthetic strategy for anisotropic growth of secondary nanoparticles on primary nanoparticles to form Au-Ag bimetallic heterodimers. We further focused in controlling the extent and sharpness of overlapped region on merged Au-Ag heterodimers and investigated the plasmon response dependent on structural changes and also size of nanoparticles. Understanding and utilizing the relationships between structural changes and plasmon coupling in nanostructures herein could greatly increase our knowledge in plasmonics, give insights in designing and synthesizing the plasmonic nanostructures. The chapter 1 provides an overview and perspective of recent advances in the use of DNA-tailored plasmonic nanostructures in biosensing applications. The plasmonic properties of metallic nanoparticles (NPs) such as Au and Ag NPs and the plasmonic coupling between them are of enormous interest for their strong and controllable optical signal enhancement and manipulation capabilities. The strong optical properties of these plasmonic structures are promising for various biosensing applications, but the widespread use of these structures is limited largely due to the absence of high-yield synthetic method for targeted nanoprobes with nanometer precision and the poor understanding of the plasmonics of these structures. DNA is a promising material that can be used as both specific biorecognition and versatile synthetic template in forming and controlling plasmonic nanostructures and their aggregations. In chapter 2, two different single-DNA-tethered Au-Ag core-shell nanodumbbell (GSND) designs with an engineerable nanogap were used in this study: the GSND-I with various inter-particle nanogaps from ∼4.8 nm to <1 nm or with no gap and the GSND-II with the fixed inter-particle gap size and varying particle size from a 23-30 nm pair to a 50-60 nm pair. With two probe design, we extensively study the relationships between single-molecule surface-enhanced Raman scattering (SMSERS) intensity, enhancement factor (EF) distribution over many particles, inter-particle distance, particle size/shape/composition and excitation laser wavelength using the single-particle AFM-correlated Raman measurement method and theoretical calculations. From the GSND-I, we learned that synthesizing a <1 nm gap is a key to obtain strong SMSERS signals with a narrow EF value distribution. Importantly, in the case of the GSND-I with <1 nm inter-particle gap, an EF value of as high as 5.9 × 1013 (average value = 1.8 × 1013) was obtained and the EF values of analyzed particles were narrowly distributed between 1.9 × 1012 and 5.9 × 1013. In the case of the GSND-II probes, a combination of >50 nm Au cores and 514.5 nm laser wavelength that matches well with Ag shell generated stronger SMSERS signals with a more narrow EF distribution than <50 nm Au cores with 514.5 nm laser or the GSND-II structures with 632.8 nm laser. Our results show the usefulness and flexibility of these GSND structures in studying and obtaining SMSERS structures with a narrow distribution of high EF values and that the GSNDs with<1nm are promising SERS probes with highly sensitive and quantitative detection capability when optimally designed. In chapter 3, we performed single-molecule correlation studies on DNA-tethered Au-Ag core-shell heterodimers to find out the relationship between SERS and LSPR. Using a multistep AFM tip-matching strategy that enables us to gain the optical spectra with the optimal signal-to-noise ratio as well as high reliability in correlation measurement between LSPR and SERS, the coupled longitudinal dipolar and high-order multipolar LSPs were detected within a dimeric structure, where a single Raman dye is located via a single-DNA hybridization between two differently sized Au-Ag core-shell particles. On the basis of the characterization of each LSP component, the distinct phase differences, attributed to different quantities of the excited quadrupolar LSPs, between the transverse and longitudinal regimes were observed for the first time. By assessing the relative ratio of dipolar and quadrupolar LSPs, we found that these LSPs of the dimer with ∼1 nm gap were simultaneously excited, and large longitudinal bonding dipolar LSP/longitudinal bonding quadrupolar LSP value is required to generate high SERS signal intensity. Interestingly, a minor population of the examined dimers exhibited strong SERS intensities along not only the dimer axis but also the direction that arises from the interaction between the coupled transverse dipolar and longitudinal bonding quadrupolar LSPs. Overall, our high-precision correlation measurement strategy with a plasmonic heterodimer with ∼1 nm gap allows for the observation of the characteristic spectral features with the optimal signal-to-noise ratio and the subpopulation of plasmonic dimers with a distinct SERS behavior, hidden by a majority of dimer population, and the method and results can be useful in understanding the whole distribution of SERS enhancement factor values and designing plasmonic nanoantenna structures. In chapter 4, we report a salt-tuned synthetic strategy using DNA-modified Au nanoparticles (DNA-AuNPs) to form Au-Ag head-body nanosnowman structures in >95% yield. We propose a mechanism for the formation of asymmetric Au-Ag nanosnowmen from DNA-AuNPs, salts, and Ag-precursor-loaded polymers. Importantly, we show that oriented assemblies of various nanostructures are readily obtained using nanosnowmen with asymmetrically modified DNA as building blocks. Synthesizing and assembling nanoscale building blocks to form anisotropic nanostructures with the desired composition and property are of paramount importance for the understanding and use of nanostructured materials. In chapter 5, we further developed the DNA-based synthetic strategies for asymmetric Au-Ag bimetallic heterodimers with structural controllability especially within overlapped region. These strategies allow us to manipulate the shape and composition of nanostructures within single particle level. We investigate the relationships between plasmon response and structural changes. We have shown that the extent of overlap and sharpness of anti-wedge region in merged conductive area along with symmetry breaking by different composition and size are responsible for various plasmon modes. Especially, the charge transfer plasmon and capacitive plasmon modes at low frequency showed most sensitive response on those changes. We have further shown that reproducible SERS signal can be generated from this structures that show linear dependence on particle concentration (5 fM). SERS enhancement factor was confirmed to 1.3 × 106 ~ 1.9 × 106. Besides, Tunable and wide range of LSPR from visible to near IR makes this structure attractive for many plasmon-based applications.