LED光刻技术快速制造微流控芯片

Microfluidic chips are generally fabricated by a soft lithography method employing  commercial lithography equipment. These heavy machines require a critical room environment  and high lamp power, and the cost remains too high for most normal laboratories. Here we  present a novel microfluidics fabrication method utilizing a portable ultraviolet (UV) LED  as an alternative UV source for photolithography. With this approach, we can repeat several  common microchannels as do these conventional commercial exposure machines, and both  the verticality of the channel sidewall and lithography resolution are proved to be acceptable.  Further microfluidics applications such as mixing, blood typing and microdroplet generation  are implemented to validate the practicability of the chips. This simple but innovative method  decreases the cost and requirement of chip fabrication dramatically and may be more popular  with ordinary laboratories.

Microfluidics is widely believed to be one of the keys to nextgeneration technology for biochemical analyses, including  high-throughput protein or cell biochemical assays in laboratories or diagnostics of body fluid in clinical applications, which would reduce costs tremendously both in time  consumption and amounts of chemicals due to the reduction  in volume from milliliters to nanoliters or even picoliters for  chemical reactions. To date, most microfluidic devices are  fabricated through soft lithography derived from the fabrication of integrated circuit boards based on lithography. Thanks  to Whiteside’s work, the flexible poly(dimethylsiloxane)  (PDMS) was found to be a simple, low cost alternative to  classical mold materials. Though people have also been devoting themselves to developing other convenient and  lower-cost methods for fabrication of microchips such as  waxing dipping , glass-based chips  and paper-based  chips , soft lithography, especially the replica molding  method, is still the most popular method for rapid prototyping  of microfluidic chips.

Soft lithography is a diverse set of techniques using elastomeric materials for rapid prototyping, and replica molding  is one of the most common methods. In essence, replica  molding refers to a procedure employed to fabricate PDMS  chips against relief structures made of photoresist on a silicon  wafer. There are many advantages for using PDMS for replica  molding, such as low cost, fast process, non-defect replication from SU-8 master, easy sealing and bonding to other substrates, suitability for biological and cellular applications and  so on. The detailed progress is shown in figure 1, and we  note that the fabrication of the SU-8 patterned master involves  traditional photolithography, which requires the most expensive equipment of all the steps due to the expensive machine  maintenance and high environment requirement.

Fig1

Soft lithography is a diverse set of techniques using elastomeric materials for rapid prototyping, and replica molding  is one of the most common methods. In essence, replica  molding refers to a procedure employed to fabricate PDMS  chips against relief structures made of photoresist on a silicon  wafer. There are many advantages for using PDMS for replica  molding, such as low cost, fast process, non-defect replication from SU-8 master, easy sealing and bonding to other substrates, suitability for biological and cellular applications and  so on. The detailed progress is shown in figure 1, and we  note that the fabrication of the SU-8 patterned master involves  traditional photolithography, which requires the most expensive equipment of all the steps due to the expensive machine  maintenance and high environment requirement.

The photomasks with the desired patterns are designed in  CorelDRAW software and then printed on high-transparency  photographic sheets. Before exposure, the mask is placed  directly on the photoresist and the lamp is vertically fixed on  the support. According to the scale, we can adjust the height  between the support and platform to control the separation  distance between the light source and the substrate. When the  distance is set to be 1cm, Si wafers with a layer (40µm) of SU-8- 2050 photoresist are exposed through the mask for 3min to form  a channel with the widths of 10–400µm and height of 40µm.  Repeating the well reported patterns made by technical exposure  machines, this portable LED UV light source really reduces both  the complexity in the operation procedure and the requirement  of conditions for fabricating microfluidics chips in laboratories.