Chang-Keun Lim

Department
School of Engineering and Digital Sciences, Chemical and Materials Engineering
Title
Assistant Professor
Office
3e.557
Email
changkeun.lim@nu.edu.kz
Phone
+77172692668
Website
https://research.nu.edu.kz/en/persons/changkeun-lim

Education/Academic qualification

Materials Science and Engineering, Ph.D., Seoul National University

Chemistry, M.Sc., Seoul National University

 

Areas of Research

  1. Aggregation-induced emission luminophores for photonic and biomedical applications

Conventional π-conjugated molecules in the solid-state typically show concentration (aggregation) fluorescence quenching. Meanwhile, a unique photoluminescence property, aggregation-induced emission (AIE), of cyanostilbene derivatives that elegantly circumvent these problems. A large torsional or conformational changes in the cyanostilbene backbone play an important role in achieving favorable intermolecular interactions that lead to both high photoluminescence and excellent charge carrier mobility in self-assembled structures. I have investigated photonic and biomedical applications of these AIE materials. For a sensitization system, improving the optical output of photoactive materials by reinforcement of light absorbance, AIE luminophores (LP) can realize an ultimate absorption due to the immunity to concentration quenching. Through the sensitization with AIE LP, I achieved 2260-enhancement of quantum cutting, converting a UV photon to two near-infrared photons, in lanthanides doped nanophosphors and 4% increased efficiency of silicon solar cell. Due to the strong luminescence and electron-accepting property of cyanostilbene, I developed highly fluorescent excited-state charge-transfer complexes (exciplexes) formed at the interfacial region between a polymeric donor matrix (poly( N-vinylcarbazole)) and embedded nanostructured acceptors. For biomedical applications of AIE LPs, I have developed 1) highly fluorescent molecular/polymer nanoparticles for sentinel lymph node imaging in vivo and cellular imaging, 2) chemiluminescence sensitization system in nanoparticles for in vivo imaging, and 3) pH/DNA sensors.

 

  1. Solar energy materials

Considering the limited supply and (potential) pollution of fossil and nuclear energy, alternation of them to renewable and clean energy sources is not an option but a necessity. In this regard, I have been conducted studies on photovoltaic cells generating electricity by using an abundant, clean, accessible, and almost limitless solar light as an energy source. In this research area, I have been focusing my researches on the following two topics: i) interfacial engineering between thin film layers and/or crystalline grains in perovskite solar cell to prolong the lifetime of the cell devices with improved carrier transporting property, ii) photon-conversion to the photoactive wavelength of the semiconducting material in solar cell from the less or non-efficient region to overcome a limit in the maximum solar conversion efficiency (Shockley-Queisser limit) using energy converting lanthanide nanophosphors.     

 

  1. Photo-switchable material on nano-bio interface

The ability of peptides to bind to specific inorganic materials via multiple noncovalent interactions provides a basis for biomolecule-mediated control of the nucleation, growth, organization, and activation of hybrid inorganic/organic nanostructures. My research in this area is based on the interest in the self-assembly of the nano-bio inferfacial hybrid materials and addressing at a specific point in the assembly by light illumination. I have been studying on the linear/nonlinear optical properties of photo-switchable molecules on the nano-bio interface depending on their thermodynamic and photophysical interactions. In addition, I have studied on the tunability of catalytic behaviors of the hybrids upon photoswitching.  

 

  1. Biosensors response to reactive oxygen species (ROS)

I have developed optical molecular and nanoparticle sensors and ultrasonographic nanosensors to detect ROS in vivo and vitro. Chemiluminescent nanosensors were developed to image inflammatory diseases and blood glucose level in vivo with highly suppressed background signals due to the absence of excitation light source inducing autofluorescence. By colocalization of catalytic molecules with fluorogenic sensors in a nanoparticle, the nanosensor realized spatiotemporal imaging of a signal level of hydrogen peroxide in living cells by highly boosted sensing kinetics. Colorimetric sensor molecule generated resonance Raman signature at the biologically silent spectral window in response to ROS. Crosslinked peroxalate nanogels were inflated to micro-bubbles at the inflammatory region to give a robust ultrasonographic contrast enhancement. For the present, my research on this area is focusing on gas- and bio-sensors based on perovskite materials.

 

  1. Theranostic materials

I have developed nano- and molecular materials for optical, magnetic, and x-ray imaging. Also, for therapeutic function, I have developed nano-photosensitizers for photodynamic therapy and photo-induced heat-generating nanomaterials for photothermal therapy. Heavy atomic-construction of photosensitizers were applied to the effective diagnosis of cancer with optical/x-ray imaging and photodynamic therapy based on the improved intersystem crossing efficiency and electron density by the intraparticular heavy-atom effect. Chitosan/heparin-coated phthalocyanine-aggregated Pluronic nanoparticles were enabled robust photothermal treatment of cancer with high targeting efficiency. Gadolinium-coordinated nanogels were well accumulated in tumor sites in their prolonged blood circulation by the elastic nature of the gel phase and provided high MRI contrast for cancer imaging. Resonance Raman probes were developed for organelle-specific imaging in live cells upon less or non-invasive light illumination. My researches in this area will be extended to ROS responsive theranostics to see and treat inflammatory diseases simultaneously.