UV Flash

Some substances can be chemically 'caged', injected into a cell, and released by a flash of light. This has been done with calcium ions which e.g. can be caged with NP-EGTA. Brief exposure to UV-light breaks the cage apart and releases the calcium, triggering physiological processes inside the cell. To deliver sufficient energy for the uncaging UV-lasers (very expensive) or high powered Xenon flashes (lots of electromagnetic side effects) are typically used. Recent development in LED technology now also allows using LEDs. How to build such a LED UV flash was nicely described by Bernardinelli et al. (Cell Calcium, Vol. 37, pages 565-572, 2005). The flash shown here is largely based on this design.

The flash consitsts of a constant current supply, a single UV-LED mounted on a heat sink, and an adapter to couple a UV glass fiber (Fig. 1). A circuit diagram for a constant current supply can be found in the Bernardielli et. al. paper.

Figure 1: The flash consists of a constant current source, a UV-LED mounted on a heat sink, and a coupled quartz glass fiber.

The only currently available UV LED powerful enough for this project is the Nichia i-LED NCCU033. It can be obtained directly from Nichia USA (phone 248-349-9800) after signing a waiver form. As it is SMD device, it was soldered onto a small PCB which was then mounted to a (probably a little oversized) heat sink. Directly on top of the LED sits a sapphire ball lens (Edmund Scientific, sapphire has good UV transmission) which is held in place by a modified light fiber adapter (from a fiber optic illuminator). The ball lens projects the light into a quartz glass fiber suitable for UV transmission (Dolan-Jenner BIUV636).

Figure 2: The LED is mounted on a small PCB in contact with the heat sink. A sapphire ball lens is held by an optical fiber adapter on top of the LED.

The optical fiber is placed under or next to the preparation with the caged compounds. Using the BNC input on the constant current source, the time the LED is on can be controlled. While we didn't measure the UV-light output of the flash - it is very, very bright and certainly suitable to uncage or photo-inactivate substances. Protect your eyes from unexpected reflections (e.g. bouncing off the microscope lens...) as your eye lid reflex will not work with UV light.

2^nd Generation

After Nichia updated the performance of their UV-LED NCSU033A - the power is now specified with 190 mW - it was time for a new generation of UV illumination. Instead of the previously described constant current source, the new design simply uses a voltage regulator and (high power) resistor to provide the LED with current. The LED is glued to a brass post using heat conducting silver epoxy (Fig. 3) which in turn is soldered to a brass square which holds the other components and serves as a heat sink. The assembly is designed to be mounted in a micro manipulator and positioned directly over the speciment (Fig. 4). Eliminating the optical components further increased the amount of UV illumination available for photo release.

Figure 3: With the 2^nd generation UV illumination, the LED is mounted on a post so it can be positioned directly over the speciment.

Figure 4: The new design eliminates the optical components to maximize the amount of usable UV light, however, it needs to be very compact to fit into the experimental setup.
The voltage regulator and resistor are protected by a cover as they can get pretty hot.

to www.ludwar.net/science


	UV Flash Some substances can be chemically 'caged', injected into a cell, and released by a flash of light. This has been done with calcium ions which e.g. can be caged with NP-EGTA. Brief exposure to UV-light breaks the cage apart and releases the calcium, triggering physiological processes inside the cell. To deliver sufficient energy for the uncaging UV-lasers (very expensive) or high powered Xenon flashes (lots of electromagnetic side effects) are typically used. Recent development in LED technology now also allows using LEDs. How to build such a LED UV flash was nicely described by Bernardinelli et al. (Cell Calcium, Vol. 37, pages 565-572, 2005). The flash shown here is largely based on this design. The flash consitsts of a constant current supply, a single UV-LED mounted on a heat sink, and an adapter to couple a UV glass fiber (Fig. 1). A circuit diagram for a constant current supply can be found in the Bernardielli et. al. paper. Figure 1: The flash consists of a constant current source, a UV-LED mounted on a heat sink, and a coupled quartz glass fiber. The only currently available UV LED powerful enough for this project is the Nichia i-LED NCCU033. It can be obtained directly from Nichia USA (phone 248-349-9800) after signing a waiver form. As it is SMD device, it was soldered onto a small PCB which was then mounted to a (probably a little oversized) heat sink. Directly on top of the LED sits a sapphire ball lens (Edmund Scientific, sapphire has good UV transmission) which is held in place by a modified light fiber adapter (from a fiber optic illuminator). The ball lens projects the light into a quartz glass fiber suitable for UV transmission (Dolan-Jenner BIUV636). Figure 2: The LED is mounted on a small PCB in contact with the heat sink. A sapphire ball lens is held by an optical fiber adapter on top of the LED. The optical fiber is placed under or next to the preparation with the caged compounds. Using the BNC input on the constant current source, the time the LED is on can be controlled. While we didn't measure the UV-light output of the flash - it is very, very bright and certainly suitable to uncage or photo-inactivate substances. Protect your eyes from unexpected reflections (e.g. bouncing off the microscope lens...) as your eye lid reflex will not work with UV light. 2^nd Generation After Nichia updated the performance of their UV-LED NCSU033A - the power is now specified with 190 mW - it was time for a new generation of UV illumination. Instead of the previously described constant current source, the new design simply uses a voltage regulator and (high power) resistor to provide the LED with current. The LED is glued to a brass post using heat conducting silver epoxy (Fig. 3) which in turn is soldered to a brass square which holds the other components and serves as a heat sink. The assembly is designed to be mounted in a micro manipulator and positioned directly over the speciment (Fig. 4). Eliminating the optical components further increased the amount of UV illumination available for photo release. Figure 3: With the 2^nd generation UV illumination, the LED is mounted on a post so it can be positioned directly over the speciment. Figure 4: The new design eliminates the optical components to maximize the amount of usable UV light, however, it needs to be very compact to fit into the experimental setup. The voltage regulator and resistor are protected by a cover as they can get pretty hot. to www.ludwar.net/science