Yoomin Ahn

Bio: Yoomin Ahn is an academic researcher from Hanyang University. The author has contributed to research in topics: Abrasive & Polishing. The author has an hindex of 20, co-authored 72 publications receiving 1385 citations. Previous affiliations of Yoomin Ahn include Chungbuk National University & Purdue University.

Measurement of the mechanical properties of electroplated gold thin films using micromachined beam structures

Abstract: We have measured the Young’s modulus, residual stress, and stress gradient of electroplated gold thin films using surface micromachined beam structures. Cantilever and bridge beam structures of different lengths were fabricated using UV-LIGA surface micromachining and dry-release methods. The Young’s modulus and residual stress of the fabricated beams were determined from the resonance frequencies of electrostatically excited beams, and the stress gradient was evaluated from the self-deformation of released cantilevers. The observed Young’s modulus was smaller than the bulk Young’s modulus, and showed small changes depending on the deposition current density. The average residual stress was found to be tensile in nature, and the observed residual stresses showed no differences, regardless of the current density. However, the stress gradient increased with increasing current density. The deformation of the cantilever beam after release was dependent on the plasma ashing time used. This result implies that additional thermal effects from the post-deposition process may have an influence on the final performance of fabricated micro electro mechanical systems (MEMS) devices.

On-Chip Immunoassay Using Surface-Enhanced Raman Scattering of Hollow Gold Nanospheres

Abstract: A surface-enhanced Raman scattering (SERS)-based gradient optofluidic sensor has been developed for a fast and sensitive immunoassay. In this work, a novel microfluidic sensor with functional internal structures has been designed and fabricated. This sensor is composed of three compartments consisting of the gradient channel that serially dilutes the target marker, the injection and mixing area of antibody-conjugated hollow gold nanospheres and magnetic beads, and the trapping area of sandwich immunocomplexes using multiple solenoids. Quantitative analysis of a specific target marker is performed by analyzing its characteristic SERS signals. This SERS-based gradient optofluidic sensor can replace the set of microwells or microtubes used in manual serial dilutions that have been traditionally used in enzyme-linked immunosorbent assay (ELISA)-type assays. The limit of detection for rabbit immunoglobin (IgG) is estimated to be 1−10 ng/mL. This novel SERS-based optofluidic immunoassay system is expected to be...

Voltage pulse frequency and duty ratio effects in an electrochemical discharge microdrilling process of Pyrex glass

Abstract: Electrochemical discharge machining (ECDM) is used to microdrill glass wafers. One of the drawbacks of ECDM is the heat-affected zone (HAZ) left on the microdrilled hole surface. To reduce the HAZ, a series of rectangular voltage pulses, were applied in this study instead of the rectified or full-wave DC voltages. The effect of the frequency and duty ratio of the voltage pulse on the ECDM of Pyrex glass was experimentally investigated. The experimental results show that the thermal damage of the microdrilled hole decreases as the frequency increases and as the duty ratio decreases. It was also found that the clearance increases as the tool diameter decreases. This experimental investigation provides a new method that exhibits several advantages over conventional ECDM.

The golden age: gold nanoparticles for biomedicine

Abstract: Gold nanoparticles have been used in biomedical applications since their first colloidal syntheses more than three centuries ago. However, over the past two decades, their beautiful colors and unique electronic properties have also attracted tremendous attention due to their historical applications in art and ancient medicine and current applications in enhanced optoelectronics and photovoltaics. In spite of their modest alchemical beginnings, gold nanoparticles exhibit physical properties that are truly different from both small molecules and bulk materials, as well as from other nanoscale particles. Their unique combination of properties is just beginning to be fully realized in range of medical diagnostic and therapeutic applications. This critical review will provide insights into the design, synthesis, functionalization, and applications of these artificial molecules in biomedicine and discuss their tailored interactions with biological systems to achieve improved patient health. Further, we provide a survey of the rapidly expanding body of literature on this topic and argue that gold nanotechnology-enabled biomedicine is not simply an act of ‘gilding the (nanomedicinal) lily’, but that a new ‘Golden Age’ of biomedical nanotechnology is truly upon us. Moving forward, the most challenging nanoscience ahead of us will be to find new chemical and physical methods of functionalizing gold nanoparticles with compounds that can promote efficient binding, clearance, and biocompatibility and to assess their safety to other biological systems and their long-term term effects on human health and reproduction (472 references).

Present and Future of Surface-Enhanced Raman Scattering

Abstract: The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.

Point of care diagnostics: Status and future

Abstract: Introduction A Why POC Diagnostics? B Time B Patient Responsibility and Compliance B Cost B Diagnostic Targets C Proteins C Metabolites and Other Small Molecules C Nucleic Acids C Human Cells D Microbes/Pathogens D Drugs and Food Safety D Current Context of POC Assays E POC Glucose Assays E Lateral Flow Assays E Limitations of “Traditional” POC Approaches F Enabling Technologies G Printing and Laminating G Microfluidic Technologies and Approaches: “Unit Operations” for POC Devices G Pumping and Valving H Mixing I Separation I Reagent Storage J Sample Preparation K Surface Chemistry and Device Substrates L Physical Adsorption L Bioaffinity Attachment L Covalent Attachment M Substrate Materials M Detection M Electrochemical Detection N Optical Detection N Magnetic Detection N Label-Free Methods O Enabling Multiplexed Assays O Recent Innovation O Lateral Flow Assay Technologies O Proteins P Antibodies P Protein Expression and Purification Q Nucleic Acids Q Aptamers R Infectious Diseases and Food/Water Safety R Blood Chemistry S Coagulation Markers S Whole Cells S Trends, Unmet Needs, Perspectives T Glucose T Global Health and the Developing World T Personalized Medicine and Home Testing U Technology Trends U Multiplexing V Author Information V Biographies V Acknowledgment W References W

Surface-enhanced Raman spectroscopy (SERS): progress and trends

Abstract: Surface-enhanced Raman spectroscopy (SERS) combines molecular fingerprint specificity with potential single-molecule sensitivity. Therefore, the SERS technique is an attractive tool for sensing molecules in trace amounts within the field of chemical and biochemical analytics. Since SERS is an ongoing topic, which can be illustrated by the increased annual number of publications within the last few years, this review reflects the progress and trends in SERS research in approximately the last three years. The main reason why the SERS technique has not been established as a routine analytic technique, despite its high specificity and sensitivity, is due to the low reproducibility of the SERS signal. Thus, this review is dominated by the discussion of the various concepts for generating powerful, reproducible, SERS-active surfaces. Furthermore, the limit of sensitivity in SERS is introduced in the context of single-molecule spectroscopy and the calculation of the 'real' enhancement factor. In order to shed more light onto the underlying molecular processes of SERS, the theoretical description of SERS spectra is also a growing research field and will be summarized here. In addition, the recording of SERS spectra is affected by a number of parameters, such as laser power, integration time, and analyte concentration. To benefit from synergies, SERS is combined with other methods, such as scanning probe microscopy and microfluidics, which illustrates the broad applications of this powerful technique.

Gold nanoparticle-enabled biological and chemical detection and analysis

Abstract: Gold nanoparticles (AuNPs) are some of the most extensively studied nanomaterials. Because of their unique optical, chemical, electrical, and catalytic properties, AuNPs have attracted enormous amount of interest for applications in biological and chemical detection and analysis. The purpose of this critical review is to provide the readers with an update on the recent developments in the field of AuNPs for sensing applications based on their optical properties. An overview of the optical properties of AuNPs is presented first, followed by a more detailed literature survey. As the last part of this review, we compare the advantages and disadvantages of each technique, briefly discuss their commercialization status, and some technical issues that remain to be solved in order to move the technique forward (151 references).