Mar 23 2017
Optical sensing can be incorporated onto lab-on-a-chip devices in a cost-effective and easier manner using a new fabrication process.
These devices incorporate laboratory functions onto a glass or plastic “chip” that is not more than a few square centimeters in size, permitting automated testing in the doctor’s office or several other types of biological and chemical analysis with portable instruments.
The silicone poly-dimethylsiloxane (PDMS) is currently considered to be the most common material used to make lab-on-a-chip devices because of its chemical, mechanical and optical properties, and the easy and cost-effective manner in which it can be structured at the microscale.
As these become increasingly complex and common, there is a requirement for expensive ways that will help integrate all-PDMS optical components such as direct light and waveguides within and onto the chip.
Our new method is compatible with the development of lab-on-chip platforms where integrated optical waveguides can be a great tool for light-based diagnostics or monitoring applications.
Mathieu Hautefeuille, Universidad National Autonomous University of Mexico
The researchers describe their cost-effective and simple method for developing PDMS waveguides that can be integrated in an effortless manner into a lab-on-a-chip device made of the same material in the journal Optical Materials Express, from The Optical Society (OSA).
This new approach has been used by the researchers to fabricate a PDMS beam splitter, which is capable of splitting laser output into two beams.
To the best of our knowledge, this is the first time that low-power laser etching has been used to microstructure polymers for optical waveguide fabrication. This study shows that a very inexpensive laser platform, based on a CD/DVD unit in our case, can compete with high-power lasers for such applications.
Mathieu Hautefeuille, Universidad National Autonomous University of Mexico
The researchers stated that their new fabrication approach is capable of being used for other applications, including those demanding precision microstructuring. They also highlight the possibility of using this approach to etch other polymer materials in addition to PDMS.
Low-power etching of a transparent material
The researchers started by producing a mold in order to make the PDMS waveguides. The strongly focused laser beam of a CD/DVD burner was used by the team to etch a clear sheet of acrylic.
The team coated the acrylic with highly absorbent nanocarbon as low-power laser sources like the ones in CD/DVD burners were not typically absorbed by transparent materials. This developed pinpoint areas of extreme heat that could be used to etch the material with micro-scale resolution.
Next, the researchers developed PDMS with two different indices of refraction by altering the material’s mixing and curing conditions in a cautious manner. The etched micromold was filled with PDMS of one refractive index, after which the material was cured and then placed in a PDMS layer with a different refractive index on top.
The PDMS was removed from the mold after another curing step, and flipped. Another layer of PDMS was added to produce a waveguide totally embedded into two slabs of PDMS.
The researchers verified the mixing and curing recipe used to control the optical properties of PDMS by measuring the refractive index of their fabricated PDMS layers for a number of times. They also demonstrated that the optical losses of waveguides created with this technique matched with those reported for more complex fabrication techniques.
In addition to being low-cost, our technique accomplishes rapid prototyping of waveguides that can make it possible to integrate light-based capabilities such as interferometric devices into lab-on-a-chip devices. It is also possible to fabricate long waveguides with our method, which can be a great advantage in lab-on-chip devices.
Mathieu Hautefeuille, Universidad National Autonomous University of Mexico
Making a PDMS beam splitter
An 8-millimeter long, Y-shaped beam splitter was fabricated by the researchers with the help of the new approach. The researchers showed that the beam splitter separated a laser beam into the two output arms and also demonstrated the possibility of switching the light between each arm by changing the angle and position of the optical fiber delivering the light.
Currently, the researchers focus on demonstrating that their method is capable of being used to fabricate more integrated complex optical devices such as an interferometer that can be used as an all-PDMS platform for sensing applications.
The team’s success with this new approach breathes new life into traditional technology while proving that high precision does not always need cutting-edge, expensive equipment.
Our study shows that short-pulsed lasers are not strictly necessary to etch transparent polymers and plastics with a micron-scale resolution. The use of a recycled CD/DVD unit further shows that you might be able to stretch the usage of equipment that could be starting to look out of date.
Mathieu Hautefeuille, Universidad National Autonomous University of Mexico
DGAPA-PAPIIT and CONACyT grants as well as the Red Temática de Biofotónica, CONACyT, supported this research.