Elucidating the Supramolecular Interaction of Positively Supercharged Fluorescent Protein with Anionic Phthalocyanines.

Developing bioinspired materials to convert sunlight into electricity efficiently is paramount for sustainable energy production. Fluorescent proteins are promising candidates as photoactive materials due to their high fluorescence quantum yield and absorption extinction coefficients in aqueous media. However, developing artificial bioinspired photosynthetic systems requires a detailed understanding of molecular interactions and energy transfer mechanisms in the required operating conditions. Here, the supramolecular self-assembly and photophysical properties of fluorescent proteins complexed with organic dyes are investigated in aqueous media. Supercharged mGreenLantern protein, mutated to have a charge of +22, is complexed together with anionic zinc phthalocyanines having 4 or 16 carboxylate groups. The structural characterization reveals a strong electrostatic interaction between the moieties, accompanied by partial conformational distortion of the protein structure, yet without compromising the mGreenLantern chromophore integrity as suggested by the lack of emission features related to the neutral form of the chromophore. The self-assembled biohybrid shows a total quenching of protein fluorescence, in favor of an energy transfer process from the protein to the phthalocyanine, as demonstrated by fluorescence lifetime and ultrafast transient absorption measurements. These results provide insight into the rich photophysics of fluorescent protein-dye complexes, anticipating their applicability as water-based photoactive materials.

Supercharged Fluorescent Protein-Apoferritin Cocrystals for Lighting Applications.

The application of fluorescent proteins (FPs) in optoelectronics is hindered by the need for effective protocols to stabilize them under device preparation and operational conditions. Factors such as high temperatures, irradiation, and organic solvent exposure contribute to the denaturation of FPs, resulting in a low device performance. Herein, we focus on addressing the photoinduced heat generation associated with FP motion and rapid heat transfer. This leads to device temperatures of approximately 65 °C, causing FP-denaturation and a subsequent loss of device functionality. We present a FP stabilization strategy involving the integration of electrostatically self-assembled FP-apoferritin cocrystals within a silicone-based color down-converting filter. Three key achievements characterize this approach: (i) an engineering strategy to design positively supercharged FPs (+22) without compromising photoluminescence and thermal stability compared to their native form, (ii) a carefully developed crystallization protocol resulting in highly emissive cocrystals that retain the essential photoluminescence features of the FPs, and (iii) a strong reduction of the device's working temperature to 40 °C, leading to a 40-fold increase in Bio-HLEDs stability compared to reference devices.

Genetically Encoded Oligomerization for Protein-Based Lighting Devices.

Implementing proteins in optoelectronics represents a fresh idea toward a sustainable new class of materials with bio-functions that can replace environmentally unfriendly and/or toxic components without losing device performance. However, their native activity (fluorescence, catalysis, and so on) is easily lost under device fabrication/operation as non-native environments (organic solvents, organic/inorganic interfaces, and so on) and severe stress (temperature, irradiation, and so on) are involved. Herein, a gift bow genetically-encoded macro-oligomerization strategy is showcased to promote protein-protein solid interaction enabling i) high versatility with arbitrary proteins, ii) straightforward electrostatic driven control of the macro-oligomer size by ionic strength, and iii) stabilities over months in pure organic solvents and stress scenarios, allowing to integrate them into classical water-free polymer-based materials/components for optoelectronics. Indeed, rainbow-/white-emitting protein-based light-emitting diodes are fabricated, attesting a first-class performance compared to those with their respective native proteins: significantly enhanced device stabilities from a few minutes up to 100 h keeping device efficiency at high power driving conditions. Thus, the oligomerization concept is a solid bridge between biological systems and materials/components to meet expectations in bio-optoelectronics, in general, and lighting schemes, in particular.

Core-Shell Structured Fluorescent Protein Nanoparticles: New Paradigm Toward Zero-Thermal-Quenching in High-Power Biohybrid Light-Emitting Diodes.

Stable and efficient high-power biohybrid light-emitting diodes (Bio-HLEDs) using fluorescent proteins (FPs) in photon downconverting filters have not been achieved yet, reaching best efficiencies of 130 lm W-1 stable for >5 h. This is related to the rise of the device temperature (70-80 °C) caused by FP-motion and quick heat-transmission in water-based filters, they lead to a strong thermal emission quenching followed by the quick chromophore deactivation via photoinduced H-transfer. To tackle both issues at once, this work shows an elegant concept of a new FP-based nanoparticle, in which the FP core is shielded by a SiO2 -shell (FP@SiO2 ) with no loss of the photoluminescence figures-of-merit over years in foreign environments: dry powder at 25 °C (ambient) or constant 50 °C, as well as suspensions in organic solvents. This enables the preparation of water-free photon downconverting coatings with FP@SiO2 , realizing on-chip high-power Bio-HLEDs with 100 lm W-1 stable for >120 h. Both thermal emission quenching and H-transfer deactivation are suppressed, since the device temperature holds <40 °C and remote high-power Bio-HLEDs exhibit final stabilities of 130 days compared to reference devices with water-based FP@SiO2 (83 days) and FP-polymer coatings (>100 h). Hence, FP@SiO2 is a new paradigm toward water-free zero-thermal-quenching biophosphors for first-class high-power Bio-HLEDs.