Light-emitting diodes (LEDs) will rule the market in solid-state lighting in the coming years. However, the inorganic phosphor used as color down-converting filter in LEDs is based on rare-earth elements, which brings several drawbacks, such as i) disruption of the ecosystem due to mining and disposal, and ii) lack of efficient recycling protocols leading to a future shortage. [1] Consequently, bio-hybrid LEDs (Bio-HLEDs) are progressing to replace inorganic phosphors with biological materials for photon down-conversion.

Encouraged by the excellent refolding capability under temperature/pH/chemical stress and high compatibility with polysaccharides of phycobiliproteins found in both, extremophiles and living fossils, we present herein our recent advances in the field of Bio-HLEDs. On one hand, the small Ultra Red Fluorescent Protein (smURFP) in HPC was optimized, reaching devices that outperformed those with the archetypal b-barrel FP mCherry with stable record devices of 108 days.[2] On the other hand, we identified the most versatile ancestral-like phycobiliprotein (Allophycocyanin subunit α) in the hyperthermophilic organism Synechococcus sp.OH28. We obtained a new phycobiliprotein (SPritZ) that emits in the orange region of the visible spectrum by heterologously expressing this protein with phycoerythrobilin as the attached chromophore. Further improvement of SPritZ via rational mutagenesis led to the enhanced variant eSPritZ featuring a higher brightness and thermal stability. Finally, both designed FPs yielded stable Bio-HLEDs, while the implementation of eSPritZ led to a 2.5-fold improvement in stability compared to SPritZ. [3]

References
[1] E. Fresta, V. Fernández-Luna, P. B. Coto, R. D. Costa Adv. Funct. Mater., 2018, 28, 1707011.
[2] M. Hasler, M. Patrian, J. A. Banda‐Vázquez, S. Ferrara, A. C. Stiel, J. Fuenzalida‐Werner, R. D. Costa, Adv. Funct. Mater. 2024, 34, 2301820.
[3] M. Patrian, M. Hasler, J. A. Banda-Vázquez, E. Borisova, J. P. Fuenzalida Werner, R. D. Costa, ACS Mater. Lett. 2025, 3041.