Oxygen-Sensing Probes and Bandage for Optical Detection of Inflammation

Shining New Light on Biological Systems: Luminescent Transition Metal Complexes for Bioimaging and Biosensing Applications

Luminescence imaging is a powerful and versatile technique for investigating cell physiology and pathology in living systems, making significant contributions to life science research and clinical diagnosis. In recent years, luminescent transition metal complexes have gained significant attention for diagnostic and therapeutic applications due to their unique photophysical and photochemical properties. In this Review, we provide a comprehensive overview of the recent development of luminescent transition metal complexes for bioimaging and biosensing applications, with a focus on transition metal centers with a d6, d8, and d10 electronic configuration. We elucidate the structure-property relationships of luminescent transition metal complexes, exploring how their structural characteristics can be manipulated to control their biological behavior such as cellular uptake, localization, biocompatibility, pharmacokinetics, and biodistribution. Furthermore, we introduce the various design strategies that leverage the interesting photophysical properties of luminescent transition metal complexes for a wide variety of biological applications, including autofluorescence-free imaging, multimodal imaging, organelle imaging, biological sensing, microenvironment monitoring, bioorthogonal labeling, bacterial imaging, and cell viability assessment. Finally, we provide insights into the challenges and perspectives of luminescent transition metal complexes for bioimaging and biosensing applications, as well as their use in disease diagnosis and treatment evaluation.

Achieving Smart Photochromics Using Water-Processable, High-Contrast, Oxygen-Sensing, and Photoactuating Thiazolothiazole-Embedded Polymer Films

Water-soluble dipyridinium thiazolo[5,4-d]thiazole (TTz) compounds are incorporated into inexpensive poly(vinyl alcohol) (PVA)/borax films and exhibit fast (<1 s), high-contrast photochromism, photofluorochromism, and oxygen sensing. Under illumination, the films change from clear/yellow TTz2+ to purple TTz•+ and then blue TTz0. The contrast and speed of the photochromism are dependent on the polymer matrix redox properties and the concentration of TTz2+. The photoreduced films exhibit strong, near-infrared light (1000-1500 nm) absorbances in addition to visible color changes. Spectroscopic ellipsometry was used to establish the complex dielectric function for the TTz2+ and TTz0 states. Incorporating non-photochromic dyes yields yellow-to-green and pink-to-purple photochromism. Additionally, when illuminated, reversible photoactuation occurs, causing mechanical contraction in the TTz-embedded films. The blue film returns to its colorless state via exposure to O2, making the films able to sense oxygen and leak direction for smart packaging. These films show potential for use in self-tinting smart windows, eyeglasses, displays, erasable memory devices, fiber optic communication, and oxygen sensing.

Iridium-based Polymeric Multifunctional Imaging Tools for Biochemistry

Herein, we report the development of a macromolecular multifunctional imaging tool for biological investigations, which is comprised of an N-(2-hydroxypropyl)methacrylamide backbone, iridium-based luminescent probe, glutamate carboxypeptidase II (GCPII) targeting ligand, and biotin affinity tag. The iridium luminophore is a tris-cyclometalated complex based on [Ir(ppy)3] with one of its 2-phenylpyridine ligands functionalized to allow conjugation. Synthesized macromolecular probes differed in the structure of the polymer and content of the iridium complex. The applicability of the developed imaging tools has been tested in flow cytometry (FACS) based assay, laser confocal microscopy, and fluorescence lifetime imaging microscopy (FLIM). The FACS analysis has shown that the targeted iBodies containing the iridium luminophore exhibit selective labelling of GCPII expressing cells. This observation was also confirmed in the imaging experiments with laser confocal microscopy. The FLIM experiment has shown that the iBodies with the iridium label exhibit a lifetime greater than 100 ns, which distinguishes them from typically used systems labelled with organic fluorophores exhibiting short fluorescence lifetimes. The results of this investigation indicate that the system exhibits interesting properties, which supports the development of additional biological tools utilizing the key components (iridium complexes, iBody concept), primarily focusing on the longer lifetime of the iridium emitter.

In Vivo Imaging of Lipid Droplets and Oxygen Status in Hepatic Tissues of Nonalcoholic Fatty Liver Model Mice Using a Lipophilic Ir(III) Complex

Nonalcoholic fatty liver disease (NAFLD) is becoming common worldwide. In pathophysiological studies of NAFLD, an in vivo optical probe that enables visualization of lipid droplets (LDs) and imaging of oxygen status in hepatic tissues simultaneously would be very useful. Here, we present the phosphorescent Ir(III) complex BTP ((btp)₂Ir(acac) (btp = benzothienylpyridine, acac = acetylacetone)) as the first probe that meets this requirement. BTP was efficiently taken up into cultured 3T3-L1 adipocytes and selectively accumulated into LDs. Quantifying oxygen levels in LDs based on the phosphorescence lifetime of BTP allowed us to track changes in cellular oxygen tension after treatment with metabolic stimulants. Phosphorescence lifetime imaging microscopy combined with intravenously administered BTP in mice enabled specific visualization of LDs in hepatic lobules and simultaneous imaging of the oxygen gradient that decreased from the portal vein (PV) to the central vein (CV). NAFL model mice were created by feeding a high-fat diet (HFD) to mice for 3 or 7 days. The mice fed an HFD showed a marked increase in the amount and size of LDs in hepatocytes compared with those fed a normal diet, leading to abnormal microvascular structures. In addition, HFD-fed mice also exhibited reduced oxygen tension in areas other than the CV. Multicolor imaging with the LD-accumulated oxygen probe BTP and vasculature-staining FITC-lectin suggested that structural distortions of the sinusoidal microvasculature caused by enlarged LDs were associated with partial hypoxia in NAFL.

Oxygen-Sensitive Probe and Hydrogel for Optical Imaging and Photodynamic Antimicrobial Chemotherapy of Chronic Wounds

A small molecular probe (Ir-fliq) and a macromolecular optical probe (Ir-fliq-PVP) based on iridium complex are designed for hypoxia imaging and antibacterial chemotherapy in this work. The existence of both...