In a paper titled “Flexible organic light-emitting diodes for antimicrobial photodynamic therapy” published in Nature’s Flexible Electronics journal, they report flexible top-emitting OLEDs with a tunable emission peak (through chemistry) from 669 to 737nm to match methylene blue as a photosensitizer. The OLEDs were attached to a flexible graphite heat sink to limit heat generation and extend device’s lifetime. Driven at a constant current density to deliver an initial irradiance of 7.75mW/cm 2, the OLEDs exhibited a stable emission with less than 1% of intensity decay over 13h of operation, far exceeding the requirements of microbial disinfection.
The authors report that in combination with methylene blue, the conformable OLED can kill more than 99% of bacteria. Today photodynamic therapy is a commonly used therapeutic method in dermatology for skin cancer and acne treatment, but the specialized light sources required for its implementation are either expensive, cumbersome or both, especially for large-area treatments.
On the contrary, thin OLEDs, with their excellent emission uniformity, would be well suited for ambulatory PDT. The researchers used flexible top-emitting OLEDs based on the p–i–n (p-doped, intrinsic, n-doped) structure. This structure allows for the design of top-emitting OLEDs whose emission spectrum can be tuned without changing the device conductivity. A tunable spectrum also widens the potential range of usable photosensitizers.
The 4cm 2 large-area flexible OLEDs designed for the experiment had an optical output density in excess of 9 mW/cm 2 at 25 mA/cm 2, with a high emission uniformity. They were effective on killing staphylococcus aureus even at a lower-dose rate, which makes them promising for more wearable healthcare devices.