MAJOR RESEARCH PROJECTS

I. On-chip self-calibration/self-diagnosis of biochemical microsensors

Unpredictable baseline drift and sensitivity degradation are the most significant problems of biosensors during continuous use. The capability of on-chip, on-demand, in situ (possibly in vivo) self-calibration/self-diagnosis of biosensors is therefore inevitable for continuous monitoring with minimal human intervention. With the integrated microelectrodes in microsensor chips, two kinds of microenvironment, called the oxygen-saturated or oxygen-depleted phases, can be created by water electrolysis. The accuracy and viability of dissolved gas sensors (e.g. oxygen, hydrogen) sensors and oxidase enzyme-based biosensors (e.g. glucose, lactate) can be checked periodically in this microenvironment based on the oxygen dependency of sensor signals. Various types of devices are being designed and characterized to explore this novel on-chip intelligent functionality toward autonomous biosensors.

Fig 1. Microsensors are integrated with on-chip, in situ self-calibration/self-diagnosis modules by actively creating the calibration microenvironment around the microsensors.

II. Process development of photopolymer bioanalytical devices

There are growing interests in using functional polymers in bioanalytical devices due to its high flexibility in designing complicated microstructures. Various photocrosslinkable polymers (e.g. photoresists, hydrogels) are promising candidates for this application. We are developing fabrication processes to utilize an epoxy-based SU-8 photoresist as the main structural material of microfluidic devices. A photografting method was developed to modify the SU-8 surface in order to manipulate the surface wettability and to attach functional layers. Both hydrophilic polymers (e.g. polyethylene glycol; PEG) and hydrophobic polymers (e.g. polydimethylsiloxane; PDMS) can be patterned photolithographically to serve as sensing elements within SU-8 devices. It is applicable to electrochemical (amperometry) devices, optical (luminescence) devices and dual-sensing modality of both.


Fig 2. Photoinitiators are irradiated and react with the SU-8 photopolymer surface, and then monomers are added to grow off covalently grafted hydrogel polymers.

III. Chemical quantification with ubiquitous optoelectronic devices

Easily accessible optoelectronic devices are utilized to determine chemicals quantitatively. A liquid crystal display (LCD) screen and a color camera (CCD or CMOS) are employed as a light source for fluorescence excitation and a photodetector for emission measurement, respectively. The LCD screen illuminates a light on a meso-scale test platform incorporating sensor films to emit the fluorescence responding to gaseous oxygen. The color camera is used to map the distribution of fluorescence emission from sensor films based on single-color intensity measurements. This combination of ubiquitous LCD and camera enables a capability of uniform illumination and distribution recording over a large area with variable wavelength ranges. Possible niche application areas include multiple-analyte and high-throughput analysis over a large area.


Fig 3. Familiar devices we use in our daily life such as color displays and color cameras can be used as analytical instruments.

IV. Microsensor array for plant root zone monitoring in space environment

Plant growth experiments in space require new nutrient delivery concepts in which water and nutrients are replenished on a continuous basis for long-term healthy growth of plants. The goal of this study is to develop a novel microsensor array to provide the adequate environment to the plant root zone for optimum control of plant cultivation systems in the space environment. The microsensor array is fabricated on a flexible polymer substrate. Measurements either in a porous tube plant cultivation system or in a particulate substrate growth media are made. The unique features of the sensors (small size, multiple sensors, and mechanical flexibility) have benefits for the study and optimization of plant cultivation systems in both terrestrial and microgravity environments.


Fig 4. A close view of the flexible microsensor array (KaptonīŖ¨ substrate) wrapping the porous tube nutrient delivery system (PTNDS) to monitor the root zone in microgravity environment.


V. Integrated microsensor/microfluidic platform for plant physiology study

The objective of this work is to develop sensor-embedded fluidics platform to study the plant root responses in different rhizosphere environment (plant roots and immediate root zone interactions).


CURRNT AND PAST SPONSORS

University of Missouri System / Research Board
NASA / The Office of Biological and Physical Research (OBPR)
NSF / Electrical, Communications and Cyber Systems (ECCS)
NIH / National Institute of Biomedical Imaging and Bioengineering (NIBIB)
DOD / US Army Medical Research and Materiel Command (USAMRMC)


SELECTED PUBLICATIONS

  1. Zhan Gao, David B. Henthorn, Chang-Soo Kim, Sensor application of poly(ethylene glycol) diacrylate hydrogels chemically anchored on polymer surface, IEEE Sensors Journal, 13, 1690-1698, 2013.
  2. Sanghan Park, Satya Achanta, Chang-Soo Kim, Intensity-based oxygen imaging with a display screen and a color camera, Sensors & Actuators B-Chemical, 164, 101-108, 2012.
  3. Zhefei Li, Frank Blum, Massimo Bertino, Chang-Soo Kim, Amplified response and enhanced selectivity of metal-PANI fiber composite sensors, Sensors & Actuators B-Chemical, 161, 390-395, 2012.
  4. Jongwon Park, Wonhak Hong, Chang-Soo Kim, Color intensity method for hydrogel optical sensor array, IEEE Sensors Journal, 10(12), 1855-1861, 2010.
  5. Raghu Ambekar, Jongwon Park, David B. Henthorn, Chang-Soo Kim, Photopatternable optical membranes for integrated optical oxygen sensors, IEEE Sensors Journal, 9(2), 169-175, 2009.
  6. Zhefei Li, Frank Blum, Massimo Bertino, Chang-Soo Kim, Sunil Pillalamarri, One-step fabrication of a polyaniline nanofiber vapor sensor, Sensors & Actuators B-Chemical, 134(1), 31-35, 2008.
  7. Zhan Gao, David B. Henthorn, Chang-Soo Kim, Enhanced wettability of SU-8 photoresist through a photografting procedure for bioanalytical device applications, Journal of Micromechanics and Microengineering, 18(4), article no. 045013, 2008.
  8. Sandeep Sathyan, Chang-Soo Kim, H. Troy Nagle, Christopher S. Brown, D. Marshall Porterfield, A flexible microsensor array for root zone monitoring of a porous tube plant growth system for microgravity, Habitation Journal, 11, 5-14, 2006.
  9. Jongwon Park, Chang-Soo Kim, Minsu Choi, Oxidase-coupled amperometric glucose and lactate sensors with integrated electrochemical actuation system, IEEE Transactions on Instrumentation and Measurement, 55(4), 1348-1355, 2006.
  10. Jongwon Park, Chang-Soo Kim, Youngjin Kim, A simple on-chip self-diagnosis/self-calibration method of oxygen microsensor using electrochemically generated bubbles, Sensors and Actuators B - Chemical (Elsevier), 108, 633-638, 2005.
  11. Chang-Soo Kim, Stefan Ufer, Christopher M. Seagle, Connie L. Engle, H. Troy Nagle, Timothy A. Johnson, Wayne E. Cascio, Use of micromachined probes for the recording of cardiac electrograms in isolated heart tissues, Biosensors and Bioelectronics (Elsevier), 19, 1109-1116, 2004.