Ender Yildirim

Investigation on replication of microfluidic channels by hot embossing

ABSTRACT In this study, effects of embossing temperature, time, and force on production of a microfluidic device were investigated. Polymethyl methacrylate (PMMA) substrates were hot embossed by using a micromilled aluminum mold. The process parameters were altered to observe the variation of replication rate in width and depth as well as symmetry of the replicated microfluidic channels. Analysis of variance (ANOVA) on the experimental results indicated that embossing temperature was the most important process parameter, whereas embossing time and force have less impact. One distinguishing aspect of this study is that, the channels were observed to be skewed to either side of the channel depending on the location of the protrusions on the mold. The mechanism of the skewness was investigated by finite element analysis and discussed in detail. Results showed that the skewness depends on the flow characteristics of the material and could be reduced by increasing the embossing temperature. The best replication rates were obtained at parameter settings of 115°C, 10 kN, and 8 min for the molds with minimum 56 µm wide features of 120 µm depth. We also showed that the fabricated channels could be successfully sealed by solvent-assisted thermo-compressive bonding at 85°C under 5.5 kN force.

Fluorescent on-chip imager by using a tunable absorption filter

In this work, we present a fluorescent on-chip imaging system utilizing a custom-made dye-doped-resin type filter. The filter used in the system was characterized to determine its transmission properties. Unique steep cut-off property of the filter allows to align emission wavelength of the fluorophores to provide better signal-to-noise ratio (SNR). We precisely showed that fluorescent micro-objects can be detected by using the proposed system. The system is believed to be useful especially in medical assessment where precise detection of bio-materials is necessary. Fluorescent imaging systems offer highly sensitive and specific identification and detection of various bio-molecules and cells [1]. However, due to scattering and absorbing nature of the medium (e.g. blood, serum, tissue etc.) emitted signals attenuate at detector level. These limitations demand for development of a new generation of fluorescent filters with sharp cut-off wavelengths. To improve the imaging efficiency, different methods were proposed such as interference and/or absorption based filters [2, 3]. However, such methods are often expensive due to fabrication complexity. We have recently proposed a novel filter with tunable and sharp cut-off wavelength [4]. The filter was fabricated by spin coating a thin layer of dye (Orasol Yellow) and photopolymer (NOA 60) mixture on glass substrate. By modifying the process parameters, it is possible to tune transmission rate of the filter in the range of ∼400–700 nm, which may be extended to infrared region as well. This filter was used as a part of the fluorescent on-chip imaging platform to view fluorescent polystyrene beads of 4 μm diameter suspended in a microfluidic channel. The microfluidic channel was implemented by sandwiching a scribed layer of double-adhesive tape in the form of the channel between two layers of cover glass (Fig. 1a).