Deciphering Limitations to Meet Highly Stable Bio‐Hybrid Light‐Emitting Diodes

Abstract

Color down-converting filters with fluorescent proteins (FPs) embedded in a polymer matrix have led to new bio-hybrid light-emitting diodes (Bio-HLEDs), featuring stabilities of 100 h and <1 min at low and high applied currents, respectively. Herein, the FP deactivation mechanism in Bio-HLEDs at high driving currents is deciphered. Primarily, the nonradiative energy relaxation of FPs upon excitation promotes the release of excess energy to the polymer matrix, reaching 60 °C and, in turn, a significant thermal emission quenching. This is circumvented by changing the device architecture, achieving stabilities of >300 h at high driving currents. Here, the photoinduced deactivation mechanism takes place, consisting of a slow and reversible partial dehydration followed by a quick and irreversible deactivation of the highly emissive ionic form. This is supported by steady-state/time-resolved emission, circular dichroism, and electrochemical impedance spectroscopic techniques. Overall, the limitations of Bio-HLEDs concerning matrix, buffers, device design, and FP stability are highlighted as key aspects to achieve efficient and stable devices.

Long-living and highly efficient bio-hybrid light-emitting diodes with zero-thermal-quenching biophosphors

“…8). Note, also that previous Bio-HLEDs based on elastomeric filters with eGFP featured efficiencies of 27 lm/W and L 50 of 2 min at the same driving conditions 31 . This highlights the prospect of the mutant regardless of the chosen polymer matrices.…”

“…These approaches rely, however, on chemical modifications of PMMA and chemical reactions with the biocompounds, risking the stability and optical features of the final materials. To circumvent these issues, we have shown that the hydrophilic TMPE polymer significantly stabilizes FPs in gel and elastomeric forms with a high content of water under storage and device operating conditions 15,27,30,31 . Now, we state that this approach can also be applied to stabilize FPs in very dry media, shielding the surrounding of the FP structure against the toxic polymer solution environment for long periods of time (Fig.…”

“…These concerns have fueled the renaissance of hybrid LEDs (HLEDs) [13][14][15] . In these devices, the IPs are replaced by organic phosphors (OPs) ranging from polymer matrices doped with artificial emitters [16][17][18] , over luminescent metal organic frameworks (MOFs) [19][20][21] , to biophosphors based on either DNA/protein matrices to host artificial emitters 15,[22][23][24][25][26] or fluorescent proteins (FPs) embedded in polymer/MOF matrices or alone 15,[27][28][29][30][31][32][33][34] . Like IPs, OPs must exhibit a narrow emission with high photoluminescence quantum yields (ϕ), high molar extinction coefficients (ε), outstanding photobleaching stabilities under operating conditions, and low heat generation and thermal quenching upon continuous excitation.…”

“…These limitations have brought biophosphors into focus, leading to Bio-HLEDs featuring performances close to those with Ir-based OPs 15,[27][28][29][30][31][32][33][34] . Here, FP-phosphors stand out, since (i) the photoluminescence features of FPs fulfills all of the above requirements 27 , (ii) the protein backbone is an effective shield against ambient oxygen 40,41 , and (iii) FPs production can be carried out in a cheap and sustainable way using bacteria (please notice that lighting and laser applications do not require high purification levels).…”

“…The most critical aspect in the development of proteinphosphors is how to stabilize FPs out of aqueous solutions and physiological environments, preserving their bio-functionality over long periods of time. Although the idea of using FPs in lighting was proposed in 2000 42 , to date only three approaches have successfully realized FP-based Bio-HLEDs, namely (i) dry films prepared in a glass reservoir with a high concentration of FPs 32 , (ii) FPs encapsulated into MOFs 33 , and (iii) FP-polymer elastomeric coatings-i.e., a mixture of star-like hydrophilic polymer trimethylolpropane ethoxylate (TMPE) to stabilize the FPs and a linear polyethylene oxide polymer acting as a jellification agent [27][28][29][30][31][32][33][34] . The latter has provided the best performing devices with stabilities of <300 h 28,30 and <5 min 31 at low-and high-applied currents, respectively.…”