Heungjoo Shin

Scalable suspended carbon nanowire meshes as ultrasensitive electrochemical sensing platforms

This paper presents novel electrochemical sensing platforms consisting of a set of a suspended carbon nanowire mesh electrode of deliberately controlled shape (hexagonal or diamond) and a planar carbon electrode located just below the suspended electrode that achieved the electrochemical current signal amplification of 120 times in a micro-channel by redox cycling of redox species. The carbon sensing platform was fabricated using only series of photolithography and pyrolysis processes which are known as Carbon-MEMS processes enabling production of carbon nano-structures in designed manner without using expensive nanolithography tools. The functionality of the stacked carbon nanoelectrodes were studied using cyclic voltammetry.

Computational analysis for morphological evolution in pyrolysis for micro/nanofabrication

Pyrolysis is recently proposed as an efficient fabrication technique of micro/nanoscale carbon structures. In order to understand the morphological evolution in pyrolysis and design the final shape of carbon structure, this study proposes a comprehensive model that incorporates the essential mechanisms of pyrolysis based on the phase field framework. Computational analysis with the developed model provides information about the effect of interface energy and kinetic rate on the morphological evolution in pyrolysis.

Current Application of Micro/Nano-Interfaces to Stimulate and Analyze Cellular Responses

Microfabrication technologies have a high potential for novel approaches to access living cells at a cellular or even at a molecular level. In the course of reviewing and discussing the current application of microinterface systems including nanointerfaces to stimulate and analyze cellular responses with subcellular resolution, this article focuses on interfaces based on microfluidics, nanoparticles, and scanning electrochemical microscopy (SECM). Micro/nanointerface systems provide a novel, attractive means for cell study because they are capable of regulating and monitoring cellular signals simultaneously and repeatedly, leading us to an enhanced understanding and interpretation of cellular responses. Therefore, it is hoped that the integrated micro/nanointerfaces presented in this review will contribute to future developments of cell biology and facilitate advanced biomedical applications.

Surface Plasmon Polariton-based Coaxial Probe for Terahertz Near-field Microscopy

An enhanced sensitivity near-field terahertz microscope concept is presented based on surface plasmon polariton assisted tunneling through a sub-wavelength coaxial probe. A concentric metallo-dielectric coupling structure yields a field enhancement by two orders of magnitude.

Redox cycling-based electrochemical-enzymatic biosensor platform fabricated via electrodeposition of gold nanoparticles on carbon IDA nanoelectrodes

We developed a highly sensitive biosensor platform based on electrochemical-enzymatic redox cycling induced by selective enzyme immobilization on carbon interdigitated array (IDA) nanoelectrodes decorated with gold nanoparticles (AuNPs). The sensor platform fabricated using a simple, cost-effective, reproducible, and batch microfabrication process known as carbon-MEMS and electrodeposition. The 3D AuNP/carbon IDA facilitates the enhancement of surface reactivity, surface area, and reduces the inter-electrode gap; these enhance the redox-cycling-based electrochemical signal amplification. AuNP/carbon IDA is further applied to the amperometric detection of glucose and exhibited higher sensitivity and better LOD attributed its potential applicability to clinical applications.

Electrical conductivity enhancement of 1D glassy carbon nanostructure using rapid thermal annealing

Rapid thermal annealing (RTA) process enabling significant enhancement of electrical conductivity (up to 2.3 times greater than currently reported conductivity values) of 1D glassy carbon nanostructures fabricated using carbon-MEMS was developed. After the RTA process, the carbon/oxygen and G-/D-band ratios that are strongly correlated to the electrical conductivity were changed depending on the pyrolysis temperature. The architecture of a suspended carbon nanowire also plays strong role on RTA-based conductivity enhancement by up to 14 % compared to carbon nanowire built on the substrate. In addition, electrochemical reactivity can be enhanced via RTA enabling better redox current collection.

Circumferentially grown ZnO nanowire forest on a suspended carbon nanowire for a highly sensitive gas sensor

We present a suspended ZnO nanowire forest as a highly sensitive gas sensor. ZnO nanowires were grown selectively on a suspended single glassy carbon nanowire using hydrothermal method so that the detrimental effects from the substrate inclusive of contamination, stagnant layer and limited mass transfer could be alleviated. The novel geometry of the radially grown ZnO nanowires resembling burs of a chestnut is expected to enhance the gas sensing capability because of enhanced mass transfer.

Fabrication of a monolithic carbon mold for producing a mixed-scale PDMS channel network using a single molding process

We introduce a novel batch fabrication technique of a monolithic carbon mold for producing a mixed-scale polydimethylsiloxane (PDMS) channel network consisting of nanochannels and microchannels with micro-pillars. Nanofluidics has attracted much attention because of their distinguishing properties. However, the research on the nanofluidics is limited by complex nanofabrication techniques. In this paper, a mixed-scale monolithic carbon mold was simply fabricated using a batch carbon-MEMS process consisting of two successive UV-lithography processes and a single pyrolysis. Then, PDMS channel networks was completed by soft molding process. By modulating pyrolysis conditions, the surface energy of the pyrolyzed carbon mold could be optimized for efficient PDMS channel demolding.

Alignment-less microchannel integration onto a stacked carbon electrode set for highly sensitive electrochemical sensor applications

Herein, we present simple integration of the microchannel and stacked carbon electrode set enabling high electrochemical current signal amplification due to redox cycling effect. The stacked electrode set consists of a substrate-bound carbon electrode and a suspended carbon nanomesh electrode (width = ~300 nm, thickness = ~600 nm) with a narrow electrode gap (~4 μm) achieved using a polymerization-stop layer. A planar PDMS plate ceiling and the side walls of the carbon posts that support the carbon nanomesh enclose the electrode set and thus the sensor-integrated microchannel is completed by simple PDMS bonding process without any complex alignment process. The stacked electrode set embedded in the microchannel showed ~1,300 times amplified current signal in chronoamperometry.

Visible light response of tin oxide nanobelts

In the present work we report the effect of visible (VIS) light on the conductivity of SnO2 nanobelts. The existence of visible light effect is unusual, since bulk SnO2 is a wide band gap semiconductor. Two types of nanobelt alignment/trapping methods were used in fabricating devices for study of the visible light effect. Fluid flow alignment was used for making individual nanobelt devices, while AC dielectrophoresis was used to trap multiple nanobelts. DC current passing through the SnO2 nanobelt devices was monitored under VIS and UV light illumination. Visible photoluminescence was also observed in the nanobelt samples.