Jun Yong Lee

A fully microfabricated carbon nanotube three-electrode system on glass substrate for miniaturized electrochemical biosensors

We present an integration process to fabricate single-walled carbon nanotube (SWCNT) three-electrode systems on glass substrate for electrochemical biosensors. Key issues involve optimization of the SWCNT working electrode to achieve high sensitivity, developing an optimal Ag/AgCl reference electrode with good stability, and process development to integrate these electrodes. Multiple spray coatings of the SWCNT film on glass substrate enabled easier integration of the SWCNT film into an electrochemical three-electrode system. O2 plasma etching and subsequent activation of spray-coated SWCNT films were needed to pattern and functionalize the SWCNT working electrode films without serious damage to the SWCNTs, and to remove organic residues. The microfabricated three-electrode systems were characterized by microscopic and spectroscopic techniques, and the electrochemical properties were investigated using cyclic voltammetry and chrono-amperometry. The fully-integrated CNT three-electrode system showed an effective working electrode area about three times larger than its geometric surface area and an improved electrochemical activity for hydrogen peroxide decomposition. Finally, the effectiveness of miniaturized pf-SWCNT electrodes as biointerfaces was examined by applying them to immunosensors to detect Legionella(L) pneumophila, based on a direct sandwich enzyme-linked immunosorbent assay (ELISA) format with 3,3′,5,5′-tetramethylbenzidine dihydrochloride/hydrogen peroxide(TMB/H2O2) as the substrate/mediator system. The lower detection limit of the pf-SWCNT-based immunosensors to L. pneumophila is about 1500 times lower than that of the standard ELISA assay.

Plasma-activated carbon nanotube-based high sensitivity immunosensors for monitoring Legionella pneumophila by direct detection of maltose binding protein peptidoglycan-associated lipoprotein (MBP-PAL)

Transferred multi‐walled carbon nanotube (MWCNT)‐modified platinum thin‐film immunosensing electrode material was engineered on a glass substrate and fabricated a fully‐integrated electrochemical three‐electrode system for monitoring Legionella pneumophila. The transferred MWCNT film was treated with oxygen plasma to improve its electrochemical response and electrical conductivity. We voltammetrically characterized and optimized the electrochemical performance of the fabricated electrode for direct detection of Legionella pneumophila‐specific peptidoglycan‐associated lipoprotein (PAL) and maltose binding protein (MBP) peptidoglycan‐associated lipoprotein (MBP‐PAL) fusion. The latter, as an intermediate product to yield the former, has important roles in the growth and purification of PAL, which commercial enzyme‐linked immunosorbent assay (ELISA) kits require as a target substrate. Consequently, direct electrochemical detection of MBP‐PAL compared to PAL by square‐wave voltammetry showed a greater than 50% increase in sensitivity with a lower detection limit of 5 pg mL−1. We also investigated the affinity properties by determining kinetic parameters of the PAL and the MBP‐PAL in relation to polyclonal antibodies immobilized on transferred MWCNT substrates using Michaelis–Menten assumptions and a Hanes–Woolf plot. This new method presented herein could save the time and effort for the separation and purification of PAL form MBP‐PAL fusions that are required for performing ELISA‐based immunoassay. Biotechnol. Bioeng. 2012; 109:1471–1478.

Electrochemical Characterization of O2 Plasma Functionalized Multi-Walled Carbon Nanotube Electrode for Legionella pneumophila DNA Sensor

An electrochemical DNA sensor for Legionella pneumophila detection was constructed using O2 plasma functionalized multi-walled carbon nanotube (MWCNT) film as a working electrode (WE). The cyclic voltammetry (CV) results revealed that the electrocatalytic activity of plasma functionalized MWCNT (pf-MWCNT) significantly changed depending on O2 plasma treatment time due to some oxygen containing functional groups on the pf-MWCNT surface. Scanning electron microscope (SEM) images and X-ray photoelectron spectroscopy (XPS) spectra were also presented the changes of their surface morphologies and oxygen composition before and after plasma treatment. From a comparison study, it was found that the pf-MWCNT WEs had higher electrocatalytic activity and more capability of probe DNA immobilization: therefore, electrochemical signal changes by probe DNA immobilization and hybridization on pf-MWCNT WEs were larger than on Au WEs. The pf-MWCNT based DNA sensor was able to detect a concentration range of 10 pM–100 nM of target DNA to detect L. pneumophila.

Plasma-Enhanced Surface Modification of Sprayed Carbon Nanotube Electrodes for Lithographically Integrated Biosensing System

A sprayed carbon nanotube (CNT)-modified working electrode was successfully integrated into an electrochemical three-electrode system based on a glass substrate. The integrated biosensing system was fabricated through a series of photolithographic patterning and plasma etching processes. A CNT-dispersed solution was sprayed on the three-electrode system, and the CNT-modified surface was treated with O2 plasma to pattern, clean, and activate the CNT layer. The optimized plasma treatment conditions were verified in terms of plasma power and treatment time by scanning electron microscopy (SEM), cyclic voltammetry (CV), and X-ray photoelectron spectroscopy (XPS).

A fully microfabricated coplanar single-walled carbon nanotube three-electrode system for biosensors

A co-planar single walled carbon nanotube (SWCNT) electrode system with all electrodes (working, counter and reference) was fully microfabricated on a glass substrate. The process is based on: (a) a standard microfabrication process to define the conducting tracks and a nitride passivation, (b) a transfer printing of SWCNT film, and (c) a chlorination process of thin-film Ag to form AgCl reference electrode. This three electrode device exhibits clear electrochemistry both under voltammetric and amperometric conditions and is thus a candidate for all electrochemical biosensors. An amperometric glucose biosensor based on this electrode system has been prepared by immobilizing glucose oxidase (GOx) on well-defined SWCNT working electrodes. The glucose biosensor shows a linear relationship between current response and glucose concentrations from 0.5 to 10 mM/L; the sensitivity is 30 (uA/cm2)/(mol/L).