Eun Zoo Lee

Cubic Mesoporous Graphitic Carbon(IV) Nitride: An All-in-One Chemosensor for Selective Optical Sensing of Metal Ions

Carbon nitride is an appealing class of material which can complement carbon in a variety of applications. At ambient conditions a graphitic carbon nitride (g-C3N4) is regarded to be the most stable allotrope. Kroke et al. proposed that gC3N4 consists of sheets of ordered tri-s-triazine moieties connected through planar tertiary amino groups stacked in a graphitic fashion. The bulk material synthesis of g-C3N4 was attempted by thermal condensation of nitrogen-rich precursors, even though most reactants do not proceed significantly past the polymeric form owing to incomplete condensation or polymerization in the bulk. A higher condensation degree was achieved by carrying out the condensation in molten salts. Graphitic carbon nitride has recently attracted great interests because of its semiconductor properties, which makes it suitable for photocatalytic applications. The electronic band structure and band gap of g-C3N4 depend on the degree of condensation of the material. It was also proposed that the band gap can be tuned to lower or higher values by protonation or synthesis of inclusion complex with metal cations such as Zn and Fe. g-C3N4 has been used as a photocatalyst for the production of hydrogen and oxygen from water. The introduction of porosity into g-C3N4 yields an increase in the accessible surface area of the material. It was also shown that the catalytic and photocatalytic activity of mpg-C3N4 (“mesoporous graphitic carbon nitride”) greatly improved over that of the bulk material. 10] Optical sensors are molecular receptors whose optical properties change upon binding to specific guests. Optical sensing systems have been intensively investigated for their capability of providing sensitivity and fast and easy detection, biocompatibility, and adaptability to a wide variety of assay conditions. One notable application of optical sensors is in the sensing of metal ions. Especially in industrial areas, large amounts of toxic and carcinogenic metals have been released into the environment, which has strongly raised interest in the biological and environmental monitoring of such compounds. Various optical sensors based on azo-coupled macrocycles, porphyrin, and phenanthroline derivatives have been described for the detection of a wide range of metal ions. The Lewis basic site on these molecular receptors provides strong coordination to metal ions while the net electron transfer from chromophore/fluorophore group in the receptor to the complexed metal ions leads to the qualitative and semiquantitative sensing of metal ions. Recent development in mesoporous materials has improved the performance of these sensors through immobilization of receptors, whereby the receptors are attached to a large and accessible surface area and well-defined pores, favorable for high adsorption capacity of chromogenic/fluorescent molecules and efficient transport of analytes and thus low detection limits of below tens of nanomolar concentrations. There is, however, still growing demand for more advanced optical sensing system with lower detection limit and faster kinetic response. Considering the properties of present chromogenic/fluorescent receptors, it seems that nanostructured g-C3N4 would be a promising alternative. As previously described, the electronic structure of g-C3N4 is adjustable by coupling events of protons or metals to the surface. The surface functionalities of g-C3N4, that is, NH2/ NH /=N , are well-characterized ligands exhibiting high adsorption capacity for metal ions through chelation or redox reaction. Finally, an additional supporting material is not necessary because it is possible to tailor its nanostructure by using any kind of silica hard template. In comparison with the systems in which the receptor is supported on a porous material, and thus constitute just a minor part, considering weight and volume fraction of the overall system, in mpgC3N4 the entire material would be composed of the functional, in this case sensing, material, which principally gives rise to very high sensitivity. Such a nanostructuring is also necessary for efficient transport of metal ions to the surface. Herein, we utilized g-C3N4 as an all-in-one chemosensor to detect trace amounts of metal ions in aqueous solutions. For this purpose 3D cubic (Ia 3d) mesoporous g-C3N4 (c-mpgC3N4) with high surface area was synthesized for the first time. The electronic properties as well as the surface functionalities of c-mpg-C3N4 should make it an efficient optical sensor. Structural characterization of c-mpg-C3N4 was carried out by smalland wide-angle X-ray scattering (SAXS and WAXS), transmission electron microscopy (TEM), N2 sorption, thermogravimetric analysis (TGA), Fourier transform infrared [*] E. Z. Lee, Dr. Y.-S. Jun, Prof. W. H. Hong Department of Chemical and Biomolecular Engineering, KAIST 335 Gwahak-ro, Yuseong-gu, Daejeon, 305-701 (Korea) Fax: (+82)42-350-3910 E-mail: st9750@kaist.ac.kr whhong@kaist.ac.kr Homepage: http://sep.kaist.ac.kr

A fluorescent sensor for selective detection of cyanide using mesoporous graphitic carbon(IV) nitride

A turn-on fluorescence sensor, Cu(2+)-c-mpg-C(3)N(4), was developed for detection of CN(-) in aqueous solution by simply mixing cubic mesoporous graphitic carbon nitride (c-mpg-C(3)N(4)) and aqueous solution of Cu(NO(3))(2). The highly sensitive detection of CN(-) with a detection limit of 80 nM is not only possible in aqueous solution but also in human blood serum.

Removal of bovine serum albumin using solid-phase extraction with in-situ polymerized stationary phase in a microfluidic device.

Serum albumin, one of the most abundant serum proteins, blocks the expression of other important biomarkers. The objective of this study is to remove serum albumin effectively by using solid-phase extraction (SPE) in microfluidic devices. Photo-polymerized adsorbent as a stationary phase of SPE was used to remove bovine serum albumin (BSA). The adsorption capacity was examined with the effect of pH and concentration in BSA solution, and adjustment of monomer concentration such as hydrophilic 2-acrylamido-2-methyl-1-propanesulfonic acid and acrylamide in the adsorbent. The effect of hydrophobic butyl methacylate on BSA adsorption was also studied. Selective removal in a bicomponent with BSA and bovine gamma-globulin was performed by adjusting the pH as required.

Development of a fully integrated microfluidic system for sensing infectious viral disease

An active micromixer system utilizing the magnetic force was developed and examined for its ability to facilitate the mixing of more than two fluid flows. The mixing performance of the active micromixer was evaluated in aqueous–aqueous systems including dyes for visual observation. A complete analytical microfluidic system was developed by integrating various functional modules into a single chip, thus allowing cell lysis, sample preparation, purification of intracellular molecules, and subsequent analysis. Upon loading the cell samples and lysis solution into the mixing chamber, the integrated microfluidic device allows efficient cell disruption by rotation of a micromagnetic disk and control of mixing time using the Teflon‐coated hydrophobic film as a microvalve. This inflow is followed by separating the cell debris and contaminated proteins from the cell lysate sample using the acrylamide (AAm)‐functionalized SPE. The inflow of partially purified cell lysate sample containing the gold binding polypeptide (GBP)‐fusion protein was bound onto the gold micropatterns by means of its metal binding affinity. The GBP‐fusion method allows immobilization of proteins in bioactive forms onto the gold surface without surface modification suitable for studying antigen–antibody interaction. It was used for the detection of severe acute respiratory syndrome (SARS), an infectious viral disease, as an example case.

Advanced cleanup process of the free-flow microfluidic device for protein analysis.

The treatment of samples preparation is generally recognized as a bottleneck for the rapid analysis of protein because of the off-chip performance in many cases. In this study, we used the charge characteristics of protein to develop a simple and rapid electro-microfluidic desalting system as an effective means of cleaning up protein sample. When we loaded a urea-rich protein sample and a buffer solution into a free-flow zone electrophoresis (FFZE) chamber, the microfluidic device was able to separate the charged protein sample and the non-charged urea. With a 90 V electric field in the FFZE chamber, the removal efficiency of the urea was about 88% and the recovery of the protein was 78%. In addition, the desalted protein sample used in this device showed significant improvement with respect to the MALDI-TOF-MS spectrum signal of a fusion protein, which was fused to the gold-binding polypeptide with enhanced green fluorescent protein, as a model protein. The inflow of the purified fusion protein sample can be successfully immobilized on the gold surface and analyzed by confocal fluorescence microscopy and surface plasmon resonance for biotechnological sensors.

Clean up protein for analysis from salt-rich sample using facilitated by copper ion in micro-device

In this study, we made the simple and rapid microfluidic desalting systems. They are 3-phase flow micro-dialysis using simple diffusion and 5-phase flow micro-dialysis based on the coupling of simple diffusion and affinity of urea for the effective removal of urea. The facilitative desalting system is particularly useful for removal of urea and analysis of protein by mass spectroscopy because urea is removed by the mass transfer with the difference of concentration, molecular size and the affinity of urea to copper (II) ion resulting the complex. We also evaluated the activity and MALDI-TOF-MS spectrum of red fluorescent protein (RFP) for protein analysis.

Sample Clean-up of Red Fluorescent Protein for Analysis Using Electric Field in Microfluidic Device

Microfluidic technology allows the design and operation of effective and simple devices for sample preparation and cleanup. Majority of current sample preparation methods is focused on the complex and combined steps such as solid phase extraction and membrane dialysis. In addition, it is generally recognized that sample treatment often is the bottleneck for the rapid analysis of protein due to performing off-chip in many cases. In this study, for an effective cleaning of protein from a urea-rich protein sample, electro-microfluidic desalting system was applied using the charge characteristics of protein.