Ongoing Research Projects

innovation

Prof. MinJun Kim @ Drexel Innovations

 

 

 

 

Today, scientists and engineers can manipulate matter at the atomic and nanometer scales which will lead to extraordinary technologies in a diversity of fields spanning biology to robotics. There exist a wide range of nano/microfabrication techniques which directly access to the relevant length scale from nanometer to micrometer. Especially, miniaturization to the nanometer scale opens up the possibility to probe biology on the length scale where fundamental biological processes take place, such as epigenetic and genetic control of single cells. Our ongoing research program can be broadly categorized into three core subject areas: transport phenomena, bioinspired systems design and fabrication, and single molecule biophysics. Although each core program consists of a distinct project, we would like to emphasize their synergistic nature - advances in one core are expected to drive the development of the others. The unifying component of all the cores is "nanoscale engineering."

 

It is always happy to work with motivated studernts in research. If you are interested in joining our lab it is recommended that you kindly email Professor MinJun Kim to talk about your qualification and research interest as early as possible.

 

Research Thrust #1: Microbiorobotics for Manipulation and Sensing

Bacteria are an ideal system to use for a variety of microbiorobotic systems. They are easily "manufactured", self-contained and easy to fuel. Flagellated bacteria are integrated with engineered systems to construct microbiorobots (MBRs). MBRs are microfabricated SU-8 epoxy structures with typical feature sizes ranging from 5 - 100 microns coated with a monolayer of the swarming Serratia marcescens, where the adherent bacteial cells naturally coordinate to propel the microstructures in fluidic environments. We explore some design aspects, such as the effects of bacterial density, distribution and orientation on the surface of the MBRs, as well as various modalities to control the bacteria. A number of different stimuli, including ultraviolet light, electric field, chemotactic gradient, and thermal stimuli are used as control inputs to manipulate the MBRs, while measurement feedback is provided by a computer vision based system. The design of feedback control strategies is based on the abstract model, while explicitly taking into account the accuracy of the abstraction. For some control modalities, such as phototactic control using the ultraviolet light, the switching nature of the control makes it necessary to design the controller using the framework of hybrid control theory.

Actuation and control are some of the main challenges in micro-scale robotics (length scale of 1 micron to 1 mm). We have been working on the use of micro-scale inorganic and cellular actuators for object manipulation. Specifically, we are fusing inorganic actuators onto live microbial cells so as to use them as micro-scale robots, essentially creating what we call "micro-cyborgs". Our approach in fusing inorganic actuators and biological actuators constitutes a novel direction in microbiorobotics. Currently, researchers have explored separate use of bio-inspired engineered structures (such as artificial flagella) and live cells (such as bacterial swimmers) as micro-scale actuators. In this research, we seek to combine the merits of both types of actuators, e.g. repeatability and specificity of inorganic actuators and low cost of biological actuators. The biological part of our micro-cyborg is an artificially magnetotactic Tetrahymena pyriformis. Joint use of multiple micro-cyborgs can result in manipulation of larger objects. The range of operation of micro-cyborgs make them potentially useful in biomedical applications (e.g. cell manipulation) and micro-assembly.

 

 

Research Thrust #2: Synthetic Nanopore Fabrication and Single Molecule Analysis

The translocation of analytes through nanometer-sized pores in solid-state or biological membranes has attracted significant attention over the last decade, in both academia and industry. The key idea is to monitor the ionic (blockade) current across a nanopore, and to associate any transient modulation of this to the translocation of a molecular species through the pore. The resulting "signiature" in the blockade current may then be used for probing the biomolecule itself. The aim of our nanopore research is to define a new nanoanalytical technology which will enable the efficient detection of conformational changes with microsecond resolution in order to answer a fundamental question about structure and conformations of proteins and DNA molecules. It is achieved by electrophoretically translocating biomolecules through a solitary nanopore drilled in 50 nm thick silicon nitride membrane and analyzing current signatures obtained corresponding to the biomolecules. This has enabled us to study binding-unbinding and folding-unfolding kinetics of single protein molecules. In addition, we have developed DNA sensing platform based on graphene nanopores drilled in single or multi-layer graphene structures which provide exquisite control of the electric field drop within the pore. Nanopore edges are modified with Graphite Polyhydral Crystals (GPC) and the modified GPC nanopores can be used to sense small DNA molecules (down to 25 nucleotide long) which is a significant improvement in the sensing ability of solid-state nanopores. Lastly, we are developing smart solid-state nanopore and nanopore array with superior chemical and mechanical robustness and pore size variability as ultra-fast high throughput nanopore sensors for detecting and sequencing DNA/RNA by parallel optical readout.

 

 

Research Thrust #3: Biologically Inspired Metamaterials for Nano/Optoelectronics

Proteins are macromolecules that are part of the cellular machinery. Of particular interest to our research group is the ability to use these molecules either in their naive or genetically modified form to engineer micro- and nanosystems. Many protein, such as flagellin, have the ability to form higher ordered structures by self-assembly, such as bacterial flagella. In this research, we have been studying the unique properties of bacterial flagellar nanotubes and to exploit them for use in nanoscale sensing devices. Our research is to understand the fundamental scientific principles that govern the polymorphic transformation of bacterial flagellar nanotubes both in loaded and unloaded conditions due to chemical, thermal, and electrical stimulation, as well as to demonstrate the enabling technologies necessary to develop mineralization and metalization of flagellar nanotubes for nanoelectronic sensing devices. In addition, our effort is made to obtain the scientific knowledge necessary for using gold nanorods (GNRs) to eradicate surface-bound infectious pathogens through photon-to-thermal energy conversion. The most distinctive advantage of this photothermal disinfection method is that it will not cause any cross resistance with antibiotic or build up antimicrobial resistance in the environment. Through near infrared evanescent wave irradiation, disinfection of a large surface area can be achieved conveniently and energy-efficiently. Specifically targeted applications of this technology include reducing bloodstream infections in hospitalized patients during their continuous use of medical catheters and creating safe, self-sterilizing touchscreen computers for use in public areas.

 

 

Research Thrust #4: Swimming and Flying at Low Reynold Number

Low Reynolds Number Swimming: Many microorganisms swim through complex biomaterials, including sperm travelling through mucous in the femail reproductive tract and bacteria penetrating mucus layers in the respiratory and digestive tracts during infection and disease. Because the scale of microstructural features in such media can be similar to the size of microbes, microbial transport through these biomaterials is a complicated multiscale problem. At the microscale, mechanical deformation, long- and short-range hydrodynamic forces, and contact forces can all potentially influence microbial swimming. Macroscale transport through biomaterials depends on swimming speed and adhesion lifetimes mediated by all these microscale interactions. To address the challenges in microscale swimming, low Reynolds number microswimmers have been fabricated and successfully controlled. Three dimensional Helmholtz coils are used for precise control of microswimmers. By setting our goal on biomedical applications such as targeted and localized drug delivery, we maintain paramount investigations in the field of microswimming in complex media.

Flapping Wing Flight: By thoroughtly studying the aerodynamics of beetle flight, it is possible to bleach the limitations in developing micro/nano aerial vehicles, specifically the difficulties to fabricate an assortment of machinery parts and and developing miniaturized power sources. Our research is focused on characterizing the flapping wing kinematics and aerodynamics of beetles. Key interest lies in the beetles' ability for non-jumping take-off and hovering flight. The final goal of this research is to develop beetle cyborgs with the extraordinary flight characteristics of the beetles.

 

 

Past Research Projects

- Fabrication of Single-digit Nanometer Solid-state Pore for Single Molecule Analysis

- Bacterial Flows: Mixing and Pumping in Microfluidic Systems Using Flagellated Bacteria

- Microfluidic Flow Control Using Electroosmosis

 

For questions about research, click here. last updated May 1, 2013

 

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