Oxygen Sensing Difluoroboron β-Diketonate Polylactide Materials with Tunable Dynamic Ranges for Wound Imaging

Abstract

Difluoroboron β–diketonate poly(lactic acid) materials exhibit both fluorescence (F) and oxygen sensitive room-temperature phosphorescence (RTP). Introduction of halide heavy atoms (Br and I) is an effective strategy to control the oxygen sensitivity in these materials. A series of naphthyl-phenyl (nbm) dye derivatives with hydrogen, bromide and iodide substituents were prepared for comparison. As nanoparticles, the hydrogen derivative was hypersensitive to oxygen (0–0.3%), while the bromide analogue was suited for hypoxia detection (0–3% O2). The iodo derivative, BF2nbm(I)PLA, showed excellent F to RTP peak separation and an 0–100% oxygen sensitivity range unprecedented for metal-free RTP emitting materials. Due to the dual emission and unconventionally long RTP lifetimes of these O2 sensing materials, a portable, cost-effective camera was used to quantify oxygen levels via lifetime and red/green/blue (RGB) ratiometry. The hypersensitive H dye was well matched to lifetime detection, simultaneous lifetime and ratiometric imaging was possible for the bromide analogue, whereas the iodide material, with intense RTP emission and a shorter lifetime, was suited for RGB ratiometry. To demonstrate the prospects of this camera/material design combination for bioimaging, iodide boron dye-PLA nanoparticles were applied to a murine wound model to detect oxygen levels. Surprisingly, wound oxygen imaging was achieved without covering (i.e. without isolating from ambient conditions, air). Additionally, would healing was monitored via wound size reduction and associated oxygen recovery, from hypoxic to normoxic. These single-component materials provide a simple tunable platform for biological oxygen sensing that can be deployed to spatially resolve oxygen in a variety of environments.

Enhanced Room‐Temperature Phosphorescence through Intermolecular Halogen/Hydrogen Bonding

“…In the general process, an organic molecule is excited from the ground state (S 0 ) to the excited singlet state (S n , n ≥1), which is allowed because of the same spin value (step 1). On the contrary, the S 1 →T 1 ISC process (step 2) is often spin‐forbidden for metal‐free organic molecules and is mostly promoted by mixing the singlet–triplet states of different molecular orbital configurations (El‐Sayed rule; for example, aromatic carbonyls), by decreasing the singlet–triplet splitting energy (Δ E ST ) through intramolecular charge‐transfer (ICT) interactions, and by introducing the heavy‐atom effect . Then the phosphorescence process occurs if the T 1 state undergoes radiative decay to the ground state (step 3) .…”

Phosphorescence Tuning through Heavy Atom Placement in Unsymmetrical Difluoroboron β‐Diketonate Materials

“…These are important considerations for tailoring the sensitivity and designing fluorophores for lifetime imaging, such as fluorescence lifetime imaging microscopy (FLIM) and phosphorescence lifetime imaging microscopy (PLIM) . For lifetime‐based imaging, sensors like BF 2 nbmPLA, a compound with similar properties to compounds 1 and 3 in this study with long phosphorescence lifetimes, can be dynamically quenched by oxygen more quickly, and exhibit a linear response to O 2 within a small range (0.0–0.3 % O 2 ) The large Stern–Volmer constant makes the sensors sensitive to minor changes in O 2 concentration. This type of sensor may be suitable for measurements in environments depleted of oxygen, such as tumors .…”

“…This type of sensor may be suitable for measurements in environments depleted of oxygen, such as tumors . Shorter phosphorescence lifetime sensors such as BF 2 nbm(Br)PLA, analogous to compound 2 , with a broader linear sensing range (0–3 %) are capable of monitoring O 2 in environments more rich in oxygen, such as wounds and tissues …”

Modulation of the cis‐ and trans‐Conformations in Bis‐o‐carborane Substituted Benzodithiophenes and Emission Enhancement Effect on Luminescent Efficiency by Solidification

“…Even though intense luminescence can be observed in the solution state, optical properties were often spoiled through ACQ by intermolecular interactions in the solid state. [5][6][7] It has been reported that some of the o-carborane [8][9][10][11][12][13] derivatives presented AIE [14][15][16][17][18][19][20][21] and can be applied as a solid-state luminescent material. [1][2][3] Intense solid-state luminescent properties originating from AIE were found and applied for developing the conjugated materials, including polymers.…”