Hoyoung Yun

Simultaneous counting of two subsets of leukocytes using fluorescent silica nanoparticles in a sheathless microchip flow cytometer

A portable flow cytometer has been recognized as an important tool for many clinical applications such as HIV/AIDS screening in developing countries and regions with limited medical facilities and resources. Conventional flow cytometers typically require multiple detectors for simultaneous identification of multiple subsets of immune cell. To minimize the number of detectors toward portable flow cytometry or to analyze multi-parametric cellular information with minimum number of detectors in conventional flow cytometers, we propose a versatile multiplexed cell-counting method using functional silica nanoparticles (SiNPs). FITC-doped SiNPs, which are 100 times brighter than the FITC molecules itself, were used as new intensity-based fluorescent dye complexes to simultaneously measure two subsets of leukocytes using a single detector. CD45(+)CD4(+) cells tagged with these FITC-doped SiNPs were 50 times brighter than CD45(+)CD4(-) cells tagged only with FITC. To make the overall system compact, a disposable microchip flow cytometer that does not require sheath flow was developed. Combining these dye-doped SiNPs based detection schemes and the sheathless microchip flow cytometer scheme, we successfully identified and counted two subsets of leukocytes simultaneously (R(2) = 0.876). These approaches can be the building blocks for a truly portable and disposable flow cytometer for various clinical cytometry applications.

Nanointerstice‐Driven Microflow

To generate flow in microchannels, various actuation schemes such as electrokinetic, pressure-driven, and capillary-driven flow have been suggested. Capillary-driven flow is widely used in plastic disposable diagnostic platforms due to its simplicity and because it requires no external power. However, plastics such as poly(methyl methacrylate) (PMMA), generally used in microfluidics, are hydrophobic, which inhibits capillary force generation and requires surface enhancement that deteriorates with age. It is shown that the microchannels made of PMMA lose their acquired hydrophilicity by oxygen plasma treatment in long-term storage and tend to generate slow capillary flow exhibiting large variability. To promote consistency and drive flow in the microchannel, nanointerstices (NI) are introduced at the side wall of the microchannel, which results in capillary flow that is less dependent on surface characteristics. The results show that NI flow generation can be a useful alternative technique to create long-term predictable flow in commercialized products with microchannels.

Active sealing for soft polymer microchips: method and practical applications

This paper presents a new sealing method for soft polymer (elastomer) microchips. A robust and reversible sealing method, which allows various materials to be bonded and sealed tightly with each other even in aqueous solutions, is developed. A poly (dimethylsiloxane) microchip system, which can actively generate bonding and sealing forces by itself, is invented. By inducing negative pressure into additional closed areas, an instant sucking disc is made. This disc is used to tighten up the conformal contact of soft polymers. Other functionalities of active sealing such as making reusable microchips, patterning cells and performing cellular assays in a single dish have also been examined and will be discussed hereunder. This technique gives a robust and universal solution for microchip sealing issues by sealing soft polymers with diverse materials under various conditions. Active sealing will simplify numerous assays in lab-on-a-chip industry and will open a new era for cellular microchip assays.

Tunable Microchip Design for Solvent-Based Bonding of Poly(methyl methacrylate) Substrates by Capillary Force Inequality

Among various bonding methods for polymeric microfluidic chips, solvent-based bonding techniques present a relatively high bonding strength and a simple bonding process. However, there are still several considerations for bonding success: the bonding time to achieve a high throughput and a low temperature, and the clogging issue from the solvent overflowing into microfluidic channels. In this work, a novel design method and fabrication of microfluidic chips with solvent-based bonding without microchannel clogging are demonstrated. These microfluidic chips could be bonded in just 10 s at room temperature without additional steps or materials. By using the capillary force inequality caused by height differences between the inside and outside of the microchannel, we could control the solvent movement for bonding two chips. In conclusion, the tunable microchips obtained by the proposed solvent bonding technology might make mass production possible.