Bong Seop Kwak

Quantitative analysis of sialic acid on erythrocyte membranes using a photothermal biosensor

The quantitative analysis of sialic acid (SA) at an erythrocyte membrane is becoming an important clinical parameter in diagnosing cancer and diabetes. In spite of such clinical importance, there are only a few, very expensive, time consuming and complicated quantifying methods established. To solve this problem, we demonstrate a novel and direct measurement technique for SA exposed to the cell membrane using a photothermal biosensing system in which the hemoglobin molecules in the erythrocyte absorb a specific wavelength of photons (532 nm) and convert it to a temperature change. For measuring the quantity of SA, we first modified the sensor surface of a micro-scaled thermometer using phenylboronic acid (PBA) containing a self-assembled monolayer (SAM) to capture the SA-expressing erythrocytes. Second, the sensor surface was thoroughly washed, and when more SA was expressed, tighter association of erythrocytes to the biosensor was expected. Thirdly, blood sample changes in temperature, heated by the 532 nm wavelength laser, were measured by the bottom layers micron sized platinum thermometer. The temperature changes from the erythrocytes captured on the sensor surface could be estimated by the amount of SA expressed on the erythrocyte membrane. This novel SA analysis system can solve the problems raised by conventional methods such as multiple enzyme reactions and a time consuming process. We expect that this system will help provide a new tool in the quantitative analysis of SA expression level for the diagnosis of diabetes and cancers.

Signal amplification in a microfluidic paper-based analytical device (µ-PAD) by confinement of the fluidic flow

This is a one-step POC biosensor that guarantees rapid assay times, low-cost analysis, simple handling, stability, and is easy to mass product. However, it has several drawbacks such as limited sample volume and relatively low sensitivity. To overcome these disadvantages, we have designed and fabricated the µ-PAD to confine fluid flow by creating a hydrophobic channel in the paper to improve the sensitivity. The channel pattern was drawn by a computer-aided design program and directly printed by a commercially available wax printer which generates the hydrophobic channel pattern. While maintaining a constant sample, absorption, and conjugation pad, the width of the detection pad was reduced from 5 mm to 2 mm at intervals of 1 mm. The intensity of bands from the single- and double-orifice patterns increased identically compared with the device with no orifice. The relative intensity of the signal bands increased from 141 to 158. Also, numerical simulation was performed to validate the experimental result by using lattice Boltzmann method. We observed that the sensitivity was enhanced at a specific detection pad width (3 mm). Therefore, our simple structural change of the channel led to improve the colorimetric intensity. Cortisol, which is a known stress biomarker, was used to validation the device, an enhanced signal was obtained indicating that our device can be used for the detection psychological stress in humans.

An integrated photo-thermal sensing system for rapid and direct diagnosis of anemia.

This article presents a thermal biosensor to diagnose the anemia without chemical treatments using temperature increase of red blood cells (RBC) when hemoglobin molecules absorb specific wavelength of photons and convert them to thermal energy. For measuring temperature change of red blood cell, the micro-scaled platinum resistance temperature detector (Pt RTD) was developed. For maintenance of constant ambient temperature, we designed and fabricated a thermostat system. The thermostat system consists of a K-type thermocouple and two electric heaters that serve to increase the system temperature, which is monitored by the thermocouple. Both heaters and the thermocouple were connected to a proportional-integral-derivative (PID) controller and enabled to maintain the temperature constant (<±0.1°C). For specific heating of red blood cell, 8.0 W/cm(2) diode pumped solid state (DPSS) continuous wave (CW) laser module was used with 532 nm wavelength. Using this system, we successfully measured the temperature variations (from 66.33±2.72°C to 74.16±2.06°C) of whole blood samples from 10 anemic patients and subsequently determined the concentration of hemoglobin (from 7.2 g/dL to 9.8 g/dL). The method proposed in this paper requires significantly less amount of whole blood sample (6 μl) compared with the conventional methods (175 μl) and allows instantaneous diagnosis (3 s) of anemia.

Direct photo-thermal diagnosis of anemia using platinum resistance temperature detector

This article presents a thermal biosensor to diagnose anemia without chemical treatments using temperature increases of red blood cells when hemoglobin molecules absorb photons of specific wavelengths and convert them to thermal energy. For measuring the temperature changes, a micro-scaled platinum resistance temperature detector was developed. We also designed and fabricated a thermostat system to maintain a constant ambient temperature (<±0.1°C). An 8.0W/cm2 diode pumped solid state (DPSS) continuous wave (CW) laser module with a wavelength of 532 nm was used to heat the red blood cells. Using this system, we successfully measured temperature variations of whole blood samples from 10 anemic patients and subsequently determined the concentration of hemoglobin. The method proposed in this paper requires significantly smaller quantities of whole blood (6µl), as compared with conventional methods (175µl), and allows instantaneous diagnosis (6 seconds) of anemia.

Micro cell analysis device using cellular photothermal effect and thermal sensor

This article presents a new micro-device for analysis of a laser-induced cellular photothermal effect using a microfabricated platinum resistance temperature detector (platinum RTD). The thermometer was fabricated with platinum thin layer using a microelectromechanical system (MEMS) technique and the microchannel was made of polydimethylsiloxane (PDMS) using a standard soft-lithography. Platinum RTD has 2µm of the electrode width with the serpentine shaped platinum element and the electric resistance at 0°C is 247.88Ω. To measure erythrocyte-specific heat variations, 1 to 300mW power tunable diode pumped solid state (DPSS) laser module was used with 532nm wavelength. Temperature variations of blood cells after laser-irradiation were measured using the platinum RTD. For manipulating the cells, a microfluidic channel and hydrodynamic focusing were used.