DIY Low-cost UV Flood Light for Adhesive-free Bonding of PMMA Microfluidic Chips

Microfluidic devices fabricated in thermoplastics are increasingly being used due to rigidity, transparency, reduced gas permeability, biocompatibility, and easier translation to mass production methods such as injection moulding. Bonding methods for thermoplastics usually involve increasing temperature above the polymer’s Tg (glass transition temperature) or using solvents that can lead to channel deformation or leaching of unwanted substances from the substrate. UV assisted bonding processes produce clean results, no need for solvents and no deformation of microstructures [1]. However, commercial UV irradiation equipment is quite expensive (>2000 USD). By following this tutorial, you can build a DIY low-cost alternative that performs similarly to professional equipment and yields reproducible and permanent bonding of PMMA microfluidic chips for less than 100 USD.

Supplies:

- 250 W mercury vapor lamp (such as Osram HQL or Philips HPL)

- 250 W ballast for mercury vapor lamps

- Flood light housing with a matching socket for the lamp

- Wires (0.5 mm2 minimum section)

- Small hammer

- Steel metal nail

- Needle-nose pliers

- Thick fabric bag and thick plastic bag

- Oil-free compressed air or inert gas

- Personal protective equipment: gloves, dust mask, and security glasses

Step 1: Step 1

Wear the mentioned personal protective equipment at all times during this process

Step 2: Step 2

With care, put the mercury vapor lamp inside the plastic bag and subsequently inside the fabric bag to avoid glass debris and fluorescent powder to spread

Step 3: Step 3

Outdoors (or in a well-ventilated area), use the hammer and the nail to break up the lamp’s exterior glass taking extra care not to destroy the interior bulb. WARNING: fluorescent (white) the powder can be toxic so avoid breathing or touching it

Step 4: Step 4

Take the lamp (always holding from the thread) from the bag and remove any remaining glass (up to the lamp’s metal thread) with the help of the pliers. WARNING: the glass debris might be very sharp

Step 5: Step 5

Clean the lamp with compressed air and store properly. Avoid touching the bulb with bare hands. Dispose the glass debris following local regulations.

Step 6: Step 6

Wire up the lamp socket to the ballast and to the power cord. WARNING: Keep in mind that wiring electrical circuits carries substantial risk. If the wiring is not correct, you can be shocked or electrocuted or the device can cause a fire. If you are unsure of what you are doing you should let someone more skilled in electrical wiring do the job

Step 7: Step 7

Screw the lamp (mercury bulb) to the lamp socket in the housing. WARNING: dangerous UV radiation and ozone are generated by the bulb when the outer cover is removed. Always wear appropriate eye and skin protection and use the system in a ventilated environment

Step 8: Figure 1

Figure 1. a) Detail of the exposed quartz mercury bulb, the black rubber is just there for visualization purposes. b) Photograph of the housing, lamp, and lamp socket. c) Photograph of the flood lamp and the ballast. d) Photograph of the UV lamp ON

Step 9: What Else Do I Need to Know?

The aim of this tutorial is to show how to build a low-cost UV flood light for performing photodegradation of PMMA samples for bonding. Bonding parameters should be optimized accordingly to the lamp, housing, distance from the UV source, type of PMMA, etc. For more information refer to the literature [1].

Microfluidic chips as the one shown in Figure 2 can be obtained by using this bonding lamp.

Step 10: Figure 2

Figure 2. Multilayer PMMA microfluidic chip bonded with the presented UV lamp

Step 11: References

1- Truckenmüller, R., Henzi, P., Herrmann, D. et al. Microsystem Technologies (2004) 10: 372

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    3 Discussions

    1
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    Alex in NZ

    4 days ago

    This is an interesting way to get some quite concentrated UVC onto a surface, but I'm a bit concerned about the risk of damage to the Hg envelope when you break the outer glass cover as well as the risks of older (and more toxic) phosphors which might be on the shards of broken glass. A new UVC (285um) generator (LED or H23 discharge) can be got from somewhere like AliExpress for ten or fifteen USD which might be the basis for a safer solution?

    2 replies
    0
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    aconde85Alex in NZ

    Reply 2 days ago

    Hi Alex. As you said, the risk of damaging the quartz tube containing the mercury can only be mitigated by being really careful when breaking the cover glass. The wavelength that produces the photodegradation necessary to bond the PMMA layers is 254 mm. Moreover, the intensity necessary to do this must be quite high (>100 mW/cm2). To the best of my knowledge, LEDs cannot achieve this energy levels on this wavelength yet. I'm not aware of H23 discharge lamps. Could you provide a link with a description? Best

    0
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    Alex in NZaconde85

    Reply 2 days ago

    I do beg your pardon:- finger trouble. I should have typed _G_23 (the connector style, not some weird GaGe discharge). These ones (just a quick google) seem to be at the 254nm peak and go to quite high power for not much money.
    I take your point about the power output of UVC LEDs, but they can be ganged together pretty easily. These ones quote 3.5mW/cm^2 per junction, two per chip, four chips per carrier would mean that you would only need three to approach your 100mW.