Biomedical subjects

Swee Chuan Tjin

Publications and source records attributed to Swee Chuan Tjin.

5 recordsLinked to original sources

PubMed2006

Adjustable refractive index modulation for a waveguide with SU-8 photoresist by dual-UV exposure lithography.

We present a new fabrication technique based on a two-step UV exposure lithographic process to marginally modulate the refractive index in commercial SU-8 photoresist. This technique achieves refractive index modulation as different regions undergo different thermal densification prior to UV-induced polymerization. A small refractive index contrast of 0.0008 or lower can be achieved, and this is especially useful for fabricating waveguides with a low level of propagation modes. This technique may be extended to other UV-curable epoxy photoresists and can easily be applied in the fabrication of optical elements such as optical interconnects and integrated optical sensors without the development process.

Journal Article↗

PubMed2006

Compact fluorescence detection using in-fiber microchannels-its potential for lab-on-a-chip applications.

This paper reports a compact and practical fluorescence sensor using an in-fiber microchannel. A blue LED, a multimode PMMA or silica fiber and a mini-PMT were used as an excitation source, a light guide and a fluorescence detector, respectively. Microfluidic channels of 100 microm width and 210 microm depth were fabricated in the optical fibers using a direct-write CO(2) laser system. The experimental results show that the sensor has high sensitivity, able to detect 0.005 microg L(-1) of fluorescein in the PBS solution, and the results are reproducible. The results also show that the silica fiber sensor has better sensitivity than that of the PMMA fiber sensor. This could be due to the fouling effect of the frosty layer formed at the microchannel made within the PMMA fiber. It is believed that this fiber sensor has the potential to be integrated into microfluidic chips for lab-on-a-chip applications.

Fluorescein↗

PubMed2006

Photothermally enabled lithography for refractive-index modulation in SU-8 photoresist.

We present a new lithographic technique based on a hybrid photothermal process to modulate the refractive index in commercial SU-8 photoresist. Owing to a difference in cross-linking, the refractive index of unexposed SU-8 cross-linked by thermally induced polymerization is 0.0072 higher than that of SU-8 cross-linked by UV exposure and postbaking. Making use of this property, we fabricated two thick, flat-topped index-modulated diffractive optical elements (DOEs) that contain different phase distributions and measured their wavefront reconstruction. The good experimental reconstructions of the index DOEs demonstrate the potential to extend the refractive-index modulation technique for the fabrication of three-dimensional optical elements without needing a development step.

Journal Article↗

PubMed2005

Cross-talk problem on a fluorescence multi-channel microfluidic chip system.

Development of a compact fluorescence-based detection system for use in a micro-analytical system, such as a point-of-care diagnostic system, often requires a multi-channel microfluidic chip system. Since the materials used for microfluidic chips usually are transparent in the visible region and have a refractive indices higher than that of air or the surrounding environment, the fluorescence emission and scattered excitation light can propagate through the chip. We observed that such propagation can cause cross-talk between adjacent channels, and may become the major source of noise in the system and/or photo bleach the fluorescent samples in the adjacent channels, particularly for the small distances between the channels found in microfluidic chips, usually in order of several micro m. We monitored this cross-talk using fluorescein as a fluorescent sample and Mylar sheeting as a microfluidic chip material. We then discuss how this cross-talk can be avoided using a simple, inexpensive and effective method.

Artifacts↗

PubMed2004

Two-stage hybrid optimization of fiber Bragg gratings for design of linear phase filters.

We present a new hybrid optimization method for the synthesis of fiber Bragg gratings (FBGs) with complex characteristics. The hybrid optimization method is a two-tier search that employs a global optimization algorithm [i.e., the tabu search (TS) algorithm] and a local optimization method (i.e., the quasi-Netwon method). First the TS global optimization algorithm is used to find a "promising" FBG structure that has a spectral response as close as possible to the targeted spectral response. Then the quasi-Newton local optimization method is applied to further optimize the FBG structure obtained from the TS algorithm to arrive at a targeted spectral response. A dynamic mechanism for weighting of different requirements of the spectral response is employed to enhance the optimization efficiency. To demonstrate the effectiveness of the method, the synthesis of three linear-phase optical filters based on FBGs with different grating lengths is described.

Journal Article↗