How to make glass microfluidic device? mask design and photolithography

During my PhD at the University of Wyoming, I may have made ~400-500 microfluidic devices all from glass substrate. My PhD laboratory uses borosilicate based substrate/cover plate to make the chips for variety of applications such as immunoassay development, separation experiments, fuel cell units. Glass is one of the oldest materials in microfluidic field and has certain advantages (see below) over other materials that are being used in this field of research.

1. Inertness to many chemicals
2. Optical transparency
3. Low fluorescence
4. High resistance to mechanical stress
5. Well established surface modification procedures

Below are the steps taken for the fabrication of glass microfluidic device: starting from designing the channel network using CADopia software to bonding the glass plates. I will take you through each of these steps.

1. Mask design: We create a channel design using CAPopia drawing software. I had never used any drawing softwares before and found this one easy to use. Once the design is complete, we send it out to a printing company (Fineline Imaging, Colorado) to get the mask. 

Mask with channel design

2. Photolithographic procedure: Once the photo-mask arrives from the printing company, we perform basic photo-lithography procedure to transfer the channel pattern design onto the glass substrate.  We buy borosilicate glass substrate (Telic, CA, USA) which is 4” x 4” in dimension and 1.65 mm thick. One side of this glass substrate is coated with a layer of chromium and photoresist on top of each other. Both chromium and photoresist layers are about 100-200 nm in thickness. The photoresist coated on the substrate is polymer based positive photoresist which is sensitive to UV radiation. Therefore the box containing the substrate plates must be opened only in dark room.

In photolithography room turn on the UV light source before at least 15 min you plan to shine it to the substrate plate. We use a custom made box where one can place photo-mask on top of substrate plate. This assembly is then gently pressed by putting a glass plate on top of it. The whole thing is inside a box in which a shutter can be opened when ready to expose to UV radiation.

Typically we expose the substrate to the UV radiation for ~ 30-45sec. During this step the polymer of photoresist breaks down and is removed by soaking the substrate in a photo-developing solution (MF-319, Rohm and Haas) for ~ 5 min. The substrate is then washed with deionized (DI) water (DirectQ Water Purification System, Millipore) and dried by blowing N2 gas. After this washing step, one can clearly see the channel pattern on the glass substrate. 

click HERE for second part of this post

new trends in the application of paper based analytical devices

Recently, I went to ACS Fall 2013 National meeting in Indianapolis. I presented two talks. My first talk was about a new microfluidic based ELISA (enzyme linked immunosorbent assay) method for measuring very low concentrations of protein markers and it was in a session called "portable instrumentation for chemical analysis". My second talk was about a new kind of enzyme substrate for ELISA applications and was in a session called "capillary and microfluidic platforms for bioanalytical measurements". Both sessions were under analytical chemistry division. 

As I am more interested in paper based devices these days, I attended talks on low cost analytical devices primarily based on paper. Some talks by professors/students and more posters. I believe the research presented there will be seen more and more in future. Let me point out some of them.

1. paper based devices to monitor low quality pharmaceuticals and iodizing agents in salt.

PBAD used for testing pharmaceuticals. source: ACS

Professor Marya Lieberman and her group from the university of Notre Dame have developed paper based testing devices based on simple colorimetric chemistry. These devices are used to detect low quality pharmaceuticals, iodizing agents in salt etc. They have used these devices in really a low resource settings like in Kenya, Haiti, Iraq, India etc. The idea is that these devices can be sent out to every house/village to test whether the medicine (commonly used) contain what they are supposed to contain. In developing countries this is a very big problem. Prof Toni Barstis's group from Saint Mary's college is also working on paper based colorimetric devices that distinguishes between genuine and low quality anti-malaria ACT (artemisinin combination therapy) medications. The same group has also focused on identifying counterfeit drugs for river blindness.

2. paper based devices for detecting microorganism like bacteria, fungi etc.

One group in Canada are developing paper based culture devices for bacteria. Professor Carey's group from Taiwan are working on single step colorimetric sensing of human pathogenic bacteria in blood.  Their paper device has an array of several dyes (proprietary) that give a signal when reacted from different metabolic by-products of bacteria. This produces kind of finger print to identify bacteria. When successful, this technique could come to market for regular bacteria assays. click here to see their recent publication. Similar to the work by Dr. Carey's group, a group from the University of Illinois at Urbana-Champaign have worked on differentiation and identification of pathogenic fungi based on colorimetric sensor array that reacts with the volatile organic compounds produced from fungi.

Microfluidics for STD diagnostics in the developing world #SamualSia

Dr. Samuel Sia, Professor of Biomedical Engineering at Columbia University, talking on poin of care diagnostic devices for detecting disease markers during Cla2010 Conference on Global Health Diagnostics "GHDx Innovations Summit: Translating Ideas into Impact".