Near-IR Photochemistry for Biology: Exploiting the Optical Window of Tissue

A versatile two-light mode triggered system for highly localized sequential release of reactive oxygen species and conjugated drugs from mesoporous organosilica particles

The increasing prevalence of antimicrobial resistance and adverse effects of systemic treatments calls for urgent reevaluation of current methods that rely on excessive, uncontrolled drug administration. In recent years triggerable systems have emerged as promising alternatives, enabling time-controlled and localized drug release, which are only activated if necessary. Light is an obvious candidate as an external trigger, since it allows for localized activation, is non-invasive and its wavelength and intensity can be tailored to fit the demands of the drug release system. Such localized and triggered systems minimize off-target effects and undesired exposure, making it a promising tool for combating health threats such as antimicrobial resistance. However, the limited tissue penetration of visible light significantly limits the applicability of this concept in vivo. Here, we introduce an innovative triggerable drug release system, based on mono-, bi-, and tri-functionalized mesoporous organosilica particles (MOPs). The limited tissue penetration is addressed by an advanced trigger system featuring two-photon absorption. Two-photon absorption enables utilization of near-infrared (NIR) light as a trigger, which is known to exhibit an enhanced penetration depth. The particles are designed to release reactive oxygen species (ROS) upon NIR irradiation and undergo Förster resonance energy transfer (FRET) to a ROS producing dye. Moreover, by oxidative cleavage, an additional therapeutic agent is released in a cascade reaction, enhancing the system's effectiveness. The ROS release is microscopically demonstrated in situ and, for the first time, release of a fluorescent compound (therapeutic agent) in a cascade reaction is observed in real-time, providing valuable insights into the behavior and performance of our particles. This novel sequential dual-release platform for light-triggered therapeutic delivery has great potential for advanced therapeutic applications in both superficial and deep tissue treatments.

Advances in Photonic Materials and Integrated Devices for Smart and Digital Healthcare: Bridging the Gap Between Materials and Systems

Recent advances in developing photonic technologies using various materials offer enhanced biosensing, therapeutic intervention, and non-invasive imaging in healthcare. Here, this article summarizes significant technological advancements in materials, photonic devices, and bio-interfaced systems, which demonstrate successful applications for impacting human healthcare via improved therapies, advanced diagnostics, and on-skin health monitoring. The details of required materials, necessary properties, and device configurations are described for next-generation healthcare systems, followed by an explanation of the working principles of light-based therapeutics and diagnostics. Next, this paper shares the recent examples of integrated photonic systems focusing on translation and immediate applications for clinical studies. In addition, the limitations of existing materials and devices and future directions for smart photonic systems are discussed. Collectively, this review article summarizes the recent focus and trends of technological advancements in developing new nanomaterials, light delivery methods, system designs, mechanical structures, material functionalization, and integrated photonic systems to advance human healthcare and digital healthcare.

Stimuli-Responsive Substrates to Control the Immunomodulatory Potential of Stromal Cells

Mesenchymal stromal cells (MSCs) have broad immunomodulatory properties that range from regulation, proliferation, differentiation, and immune cell activation to secreting bioactive molecules that inhibit inflammation and regulate immune response. These properties provide MSCs with high therapeutic potency that has been shown to be relevant to tissue engineering and regenerative medicine. Hence, researchers have explored diverse strategies to control the immunomodulatory potential of stromal cells using polymeric substrates or scaffolds. These substrates alter the immunomodulatory response of MSCs, especially through biophysical cues such as matrix mechanical properties. To leverage these cell-matrix interactions as a strategy for priming MSCs, emerging studies have explored the use of stimuli-responsive substrates to enhance the therapeutic value of stromal cells. This review highlights how stimuli-responsive materials, including chemo-responsive, microenvironment-responsive, magneto-responsive, mechano-responsive, and photo-responsive substrates, have specifically been used to promote the immunomodulatory potential of stromal cells by controlling their secretory activity.

Stimuli-Responsive Covalent Organic Frameworks for Cancer Therapy

Chemotherapy as a common anticancer therapeutic modality is often challenged by various obstacles such as poor stability, low solubility, and severe side effects of chemotherapeutic agents as well as multidrug resistance of cancerous cells. Nanoparticles in the role of carriers for chemotherapeutic drugs and platforms for combining different therapeutic approaches have effectively participated in overcoming such drawbacks. In particular, nanoparticles able to induce their therapeutic effect in response to specific stimuli like tumor microenvironment characteristics (e.g., hypoxia, acidic pH, high levels of glutathione, and overexpressed hydrogen peroxide) or extrinsic stimulus of laser light bring about more precise and selective treatments. Among them, nanostructures of covalent organic frameworks (COFs) have drawn great interest in biomedical fields during recent years. Possessing large surface area, high porosity, structural stability, and customizable architecture, these biocompatible porous crystalline polymers properly translate to promising platforms for drug delivery and induction of combination therapies. With the focus on stimuli-responsive characteristics of nanoscale COFs, this study aims to propose an overview of their potentiality in cancer treatment on the basis of chemotherapy alone or in combination with sonodynamic, chemodynamic, photodynamic, and photothermal therapies.

Visible-Light-Activated Carbon Monoxide Release from Porphyrin-Flavonol Hybrids

We report on porphyrin-flavonol hybrids consisting of a porphyrin antenna and four covalently bound 3-hydroxyflavone (flavonol) groups, which act as highly efficient photoactivatable carbon monoxide (CO)-releasing molecules (photoCORMs). These bichromophoric systems enable activation of the UV-absorbing flavonol chromophore by visible light up to 650 nm and offer precise spatial and temporal control of CO administration. The physicochemical properties of the porphyrin antenna system can also be tuned by inserting a metal cation. Our computational study revealed that the process occurs via endergonic triplet-triplet energy transfer from porphyrin to flavonol and may become feasible thanks to flavonol energy stabilization upon intramolecular proton transfer. This mechanism was also indirectly supported by steady-state and transient absorption spectroscopy techniques. Additionally, the porphyrin-flavonol hybrids were found to be biologically benign. With four flavonol CO donors attached to a single porphyrin chromophore, high CO release yields, excellent uncaging cross sections, low toxicity, and CO therapeutic properties, these photoCORMs offer exceptional potential for their further development and future biological and medical applications.

Multiplexing potential of NIR resonant and non-resonant Raman reporters for bio-imaging applications

Multiplexed imaging, which allows for the interrogation of multiple molecular features simultaneously, is vital for addressing numerous challenges across biomedicine. Optically unique surface-enhanced Raman scattering (SERS) nanoparticles (NPs) have the potential to serve as a vehicle to achieve highly multiplexed imaging in a single acquisition, which is non-destructive, quantitative, and simple to execute. When using laser excitation at 785 nm, which allows for a lower background from biological tissues, near infrared (NIR) dyes can be used as Raman reporters to provide high Raman signal intensity due to the resonance effect. This class of imaging agents are known as surface-enhanced resonance Raman scattering (SERRS) NPs. Investigators have predominantly utilized two classes of Raman reporters in their nanoparticle constructs for use in biomedical applications: NIR-resonant and non-resonant Raman reporters. Herein, we investigate the multiplexing potential of five non-resonant SERS: BPE, 44DP, PTT, PODT, and BMMBP, and five NIR resonant SERRS NP flavors with heptamethine cyanine dyes: DTTC, IR-770, IR-780, IR-792, and IR-797, which have been extensively used for biomedical imaging applications. Although SERRS NPs display high Raman intensities, due to their resonance properties, we observed that non-resonant SERS NP concentrations can be quantitated by the intensity of their unique emissions with higher accuracy. Spectral unmixing of five-plex mixtures revealed that the studied non-resonant SERS NPs maintain their detection limits more robustly as compared to the NIR resonant SERRS NP flavors when introducing more components into a mixture.

Photoacoustic and absorption spectroscopy imaging analysis of human blood

Photoacoustic and absorption spectroscopy imaging are safe and non-invasive molecular quantification techniques, which do not utilize ionizing radiation and allow for repeated probing of samples without them being contaminated or damaged. Here we assessed the potential of these techniques for measuring biochemical parameters. We investigated the statistical association between 31 time and frequency domain features derived from photoacoustic and absorption spectroscopy signals and 19 biochemical blood parameters. We found that photoacoustic and absorption spectroscopy imaging features are significantly correlated with 14 and 17 individual biochemical parameters, respectively. Moreover, some of the biochemical blood parameters can be accurately predicted based on photoacoustic and absorption spectroscopy imaging features by polynomial regression. In particular, the levels of uric acid and albumin can be accurately explained by a combination of photoacoustic and absorption spectroscopy imaging features (adjusted R-squared > 0.75), while creatinine levels can be accurately explained by the features of the photoacoustic system (adjusted R-squared > 0.80). We identified a number of imaging features that inform on the biochemical blood parameters and can be potentially useful in clinical diagnosis. We also demonstrated that linear and non-linear combinations of photoacoustic and absorption spectroscopy imaging features can accurately predict some of the biochemical blood parameters. These results demonstrate that photoacoustic and absorption spectroscopy imaging systems show promise for future applications in clinical practice.

Ligand-Directed Photocatalysts and Far-Red Light Enable Catalytic Bioorthogonal Uncaging inside Live Cells

Described are ligand-directed catalysts for live-cell, photocatalytic activation of bioorthogonal chemistry. Catalytic groups are localized via a tethered ligand either to DNA or to tubulin, and red light (660 nm) photocatalysis is used to initiate a cascade of DHTz oxidation, intramolecular Diels-Alder reaction, and elimination to release phenolic compounds. Silarhodamine (SiR) dyes, more conventionally used as biological fluorophores, serve as photocatalysts that have high cytocompatibility and produce minimal singlet oxygen. Commercially available conjugates of Hoechst dye (SiR-H) and docetaxel (SiR-T) are used to localize SiR to the nucleus and microtubules, respectively. Computation was used to assist the design of a new class of redox-activated photocage to release either phenol or n-CA4, a microtubule-destabilizing agent. In model studies, uncaging is complete within 5 min using only 2 μM SiR and 40 μM photocage. In situ spectroscopic studies support a mechanism involving rapid intramolecular Diels-Alder reaction and a rate-determining elimination step. In cellular studies, this uncaging process is successful at low concentrations of both the photocage (25 nM) and the SiR-H dye (500 nM). Uncaging n-CA4 causes microtubule depolymerization and an accompanying reduction in cell area. Control studies demonstrate that SiR-H catalyzes uncaging inside the cell, and not in the extracellular environment. With SiR-T, the same dye serves as a photocatalyst and the fluorescent reporter for microtubule depolymerization, and with confocal microscopy, it was possible to visualize microtubule depolymerization in real time as the result of photocatalytic uncaging in live cells.

A Switchable Near-Infrared-Absorbing Dye Based on Redox-Bistable Benzitetraazaporphyrin

Activatable near-infrared (NIR) dyes responsive to external stimuli are used in medical and other applications. Here, we describe the design and synthesis of bench-stable 18π- and 20π-electron benzitetraazaporphyrins (BzTAPs) possessing redox-switchable NIR properties. X-Ray, NMR, and UV/Visible-NIR analyses revealed that 20π-electron BzTAP 1 exhibits NIR absorption and antiaromaticity with a paratropic ring-current, while 18π-electron BzTAP 2 shows weakly aromatic character with NIR inertness. Notably, the NIR-silent BzTAP 2 was readily converted to the NIR-active BzTAP 1 in the presence of mild reducing agents such as amine. The intense NIR absorption band of BzTAP 1 is in sharp contrast to the very weak absorption bands of previously reported antiaromatic porphyrinoids. Molecular orbital analysis revealed that symmetry-lowering perturbation of the 20π-electron porphyrinoid skeleton enables the HOMO-LUMO transition of 1 to be electric-dipole-allowed. BzTAPs are expected to be useful for constructing activatable NIR probes working in reductive environments.

Amber Light Control of Peptide Secondary Structure by a Perfluoroaromatic Azobenzene Photoswitch

The incorporation of photoswitches into the molecular structure of peptides and proteins enables their dynamic photocontrol in complex biological systems. Here, a perfluorinated azobenzene derivative triggered by amber light was site-specifically conjugated to cysteines in a helical peptide by perfluoroarylation chemistry. In response to the photoisomerization (trans→cis) of the conjugated azobenzene with amber light, the secondary structure of the peptide was modulated from a disorganized into an amphiphilic helical structure.

Imaging Technologies for Cerebral Pharmacokinetic Studies: Progress and Perspectives

Pharmacokinetic assessment of drug disposition processes in vivo is critical in predicting pharmacodynamics and toxicology to reduce the risk of inappropriate drug development. The blood–brain barrier (BBB), a special physiological structure in brain tissue, hinders the entry of targeted drugs into the central nervous system (CNS), making the drug concentrations in target tissue correlate poorly with the blood drug concentrations. Additionally, once non-CNS drugs act directly on the fragile and important brain tissue, they may produce extra-therapeutic effects that may impair CNS function. Thus, an intracerebral pharmacokinetic study was developed to reflect the disposition and course of action of drugs following intracerebral absorption. Through an increasing understanding of the fine structure in the brain and the rapid development of analytical techniques, cerebral pharmacokinetic techniques have developed into non-invasive imaging techniques. Through non-invasive imaging techniques, molecules can be tracked and visualized in the entire BBB, visualizing how they enter the BBB, allowing quantitative tools to be combined with the imaging system to derive reliable pharmacokinetic profiles. The advent of imaging-based pharmacokinetic techniques in the brain has made the field of intracerebral pharmacokinetics more complete and reliable, paving the way for elucidating the dynamics of drug action in the brain and predicting its course. The paper reviews the development and application of imaging technologies for cerebral pharmacokinetic study, represented by optical imaging, radiographic autoradiography, radionuclide imaging and mass spectrometry imaging, and objectively evaluates the advantages and limitations of these methods for predicting the pharmacodynamic and toxic effects of drugs in brain tissues.

Stimuli-Responsive Gold Nanocages for Cancer Diagnosis and Treatment

With advances in nanotechnology, various new drug delivery systems (DDSs) have emerged and played a key role in the diagnosis and treatment of cancers. Over the last two decades, gold nanocages (AuNCs) have been attracting considerable attention because of their outstanding properties. This review summarizes current advancements in endogenous, exogenous, and dual/multi-stimuli responsive AuNCs in drug delivery. This review focuses on the properties, clinical translation potential, and limitations of stimuli-responsive AuNCs for cancer diagnosis and treatment.

Rhodopsins: An Excitingly Versatile Protein Species for Research, Development and Creative Engineering

The first member and eponym of the rhodopsin family was identified in the 1930s as the visual pigment of the rod photoreceptor cell in the animal retina. It was found to be a membrane protein, owing its photosensitivity to the presence of a covalently bound chromophoric group. This group, derived from vitamin A, was appropriately dubbed retinal. In the 1970s a microbial counterpart of this species was discovered in an archaeon, being a membrane protein also harbouring retinal as a chromophore, and named bacteriorhodopsin. Since their discovery a photogenic panorama unfolded, where up to date new members and subspecies with a variety of light-driven functionality have been added to this family. The animal branch, meanwhile categorized as type-2 rhodopsins, turned out to form a large subclass in the superfamily of G protein-coupled receptors and are essential to multiple elements of light-dependent animal sensory physiology. The microbial branch, the type-1 rhodopsins, largely function as light-driven ion pumps or channels, but also contain sensory-active and enzyme-sustaining subspecies. In this review we will follow the development of this exciting membrane protein panorama in a representative number of highlights and will present a prospect of their extraordinary future potential.

Assessment of Photoreleasable Linkers and Light-Capturing Antennas on a Photoresponsive Cobalamin Scaffold

Cobalamin has shown promise as a light-sensitive drug delivery platform owing to its ease of modification and the high quantum yields for drug photorelease. However, studies to date on the general photochemistry of alkyl cobalamins have primarily focused on methyl and adenosyl-substituted derivatives, the natural cofactors present in various enzymatic species. We describe the synthesis and photolytic behavior of cobalamin conjugates comprised of different combinations of fluorophores and β-axial ligands. In general, cobalamin conjugates containing β-axial alkyl substituents undergo efficient photolysis under aqueous conditions, with quantum yields up to >40%. However, substituents that are large and hydrophobic, or unable to readily support the presumed radical intermediate, suffer less efficient photolysis (<15%) than smaller, water-soluble, analogs. By contrast, quantum yields improve by 2-fold in DMF for cobalamins containing large hydrophobic β-axial substituents. This suggests that drug release from carriers comprised of membranous compartments, such as liposomes, may be significantly more efficient than the corresponding photorelease in an aqueous environment. Finally, we explored the impact of fluorophores on the photolysis of alkyl cobalamins under tissue-mimetic conditions. Cobalamins substituted with efficient photon-capturing fluorophores display up to 4-fold enhancements in photolysis relative to unsubstituted derivatives. In summary, we have shown that the photosensitivity of alkyl cobalamin conjugates can be tuned by altering the Co-appended alkyl moiety, modulating the polarity of the environment (solvent), and installing photon-capturing fluorophores onto the cobalamin framework.

A disulfide-based linker for thiol-norbornene conjugation: formation and cleavage of hydrogels by the use of light

Photolabile groups are the key components of photo-responsive polymers, dynamically tunable materials with multiple applications in materials and life sciences. They usually consist of a chromophore and a labile bond and are inherently light sensitive. An exception are disulfides, simple reversible linkages, which become photocleavable upon addition of a photoinitiator. Despite their practical features, disulfides are rarely utilized due to their impractical formation. Here, we report a disulfide-based linker series bearing norbornene terminals for facile crosslinking of thiol-functionalized macromers via light-triggered thiol-ene conjugation (TEC). Besides finding a highly reactive lead compound, we also identify an unexpected TEC-retardation, strongly dependent on the molecular linker structure and affecting hydrogel stability. Finally, we present a useful method for localized disulfide cleavage by two-photon irradiation permitting micropatterning of disulfide-crosslinked networks.

Conditionally Activatable Photoredox Catalysis in Living Systems

The transformational effect of photoredox catalytic chemistries has inspired new opportunities, enabling us to interrogate nature in ways that are not possible otherwise and to unveil new biotechnologies in therapy and diagnosis. However, the deployment of artificial photoredox catalysis in living systems remains challenging, mired by the off-target risk and safety concerns of photocatalyst toxicity. Here, we present an appealing approach, namely conditionally activatable photoredox catalysis (ConAPC), and as a proof of concept design the first ConAPC architecture (Se-NO2) based upon classic self-immolative chemistry, in which the inherent photocatalytic properties can be temporarily caged while the species becomes active only at the tumor sites via sensing to specific biomarkers. Such a masking strategy allows a spatial-temporal control of photoresponsivity in vitro and in vivo. In particular, for ConAPC design, a new biologically benign metal-free photocatalyst (Se-NH2), which is able to initiate NIR photoredox catalysis to manipulate the cellular electron pool in an O2-independent mechanism of action, is identified. With this unique strategy, potent tumor-specific targeting photocatalytic eradication (TGI: 95%) is obtained in a mouse model. Impressively, favorable features such as high-resolution tumor recognition (SBR: 33.6) and excellent biocompatibility and safety are also achieved. This work therefore offers a new possibility for chemists to leverage artificial photocatalytic reactions toward the development of facile and intelligent photocatalytic theranostics.

Contributions of photochemistry to bio-based antibacterial polymer materials

Surgical site infections constitute a major health concern that may be addressed by conferring antibacterial properties to surgical tools and medical devices via functional coatings. Bio-sourced polymers are particularly well-suited to prepare such coatings as they are usually safe and can exhibit intrinsic antibacterial properties or serve as hosts for bactericidal agents. The goal of this Review is to highlight the unique contribution of photochemistry as a green and mild methodology for the development of such bio-based antibacterial materials. Photo-generation and photo-activation of bactericidal materials are illustrated. Recent efforts and current challenges to optimize the sustainability of the process, improve the safety of the materials and extend these strategies to 3D biomaterials are also emphasized.

Molecular platforms based on biocompatible photoreactions for photomodulation of biological targets

Photoirradiation provides a convenient and biocompatible approach for spatiotemporal modulation of biological systems with photoresponsive components. The construction of molecular platforms with a photoresponse to be integrated into biomolecules for photomodulation has been of great research interest in optochemical biology. In this review, we summarize typical molecular platforms that are integratable with biomolecules for photomodulation purposes. We categorize these molecular platforms according to their excitation light source, namely ultraviolet (UV), visible (Vis) or near-infrared (NIR) light. The protype chemistry of these molecular platforms is introduced along with an overview of their most recent applications for spatiotemporal regulation of biomolecular function in living cells or mice models. Challenges and the outlook are also presented. We hope this review paper will contribute to further progress in the development of molecular platforms and their biomedical use.

Multifunctional CuO/Cu2O Truncated Nanocubes as Trimodal Image-Guided Near-Infrared-III Photothermal Agents to Combat Multi-Drug-Resistant Lung Carcinoma

Despite the development of various therapeutic modalities to tackle cancer, multidrug resistance (MDR) and incomplete destruction of deep tissue-buried tumors remain as long-standing challenges responsible for tumor recurrence and low survival rates. In addition to the MDR and deep tissue photoactivation problems, most primary tumors metastasize to the lungs and lymph nodes to form secondary tumors. Therefore, it leaves a great challenge to develop theranostic approaches to combat both MDR and deep tissue photoactivation problems. Herein, we develop a versatile plasmonic CuO/Cu₂O truncated nanocube-based theranostic nanomedicine to act as a triple modal near-infrared fluorescence (NIRF) imaging agent in the biological window II (1000-1500 nm)/photoacoustic imaging (PAI)/T₁-weighted magnetic resonance (MR) imaging agents, sensitize the formation of singlet oxygen (¹O₂) to exert nanomaterial-mediated photodynamic therapeutic (NIR-II NmPDT), and absorb long NIR light (i.e., 1550 nm) in the biological window III (1500-1700 nm) to exert nanomaterial-mediated photothermal therapeutic (NIR-III NmPTT) effects for the effective destruction of multi-drug-resistant lung tumors. We found that H69AR lung cancer cells do not create drug resistance toward plasmonic CuO/Cu₂O TNCs-based nanomedicines.

Enabling In Vivo Photocatalytic Activation of Rapid Bioorthogonal Chemistry by Repurposing Silicon-Rhodamine Fluorophores as Cytocompatible Far-Red Photocatalysts

Chromophores that absorb in the tissue-penetrant far-red/near-infrared window have long served as photocatalysts to generate singlet oxygen for photodynamic therapy. However, the cytotoxicity and side reactions associated with singlet oxygen sensitization have posed a problem for using long-wavelength photocatalysis to initiate other types of chemical reactions in biological environments. Herein, silicon-Rhodamine compounds (SiRs) are described as photocatalysts for inducing rapid bioorthogonal chemistry using 660 nm light through the oxidation of a dihydrotetrazine to a tetrazine in the presence of trans-cyclooctene dienophiles. SiRs have been commonly used as fluorophores for bioimaging but have not been applied to catalyze chemical reactions. A series of SiR derivatives were evaluated, and the Janelia Fluor-SiR dyes were found to be especially effective in catalyzing photooxidation (typically 3%). A dihydrotetrazine/tetrazine pair is described that displays high stability in both oxidation states. A protein that was site-selectively modified by trans-cyclooctene was quantitatively conjugated upon exposure to 660 nm light and a dihydrotetrazine. By contrast, a previously described methylene blue catalyst was found to rapidly degrade the protein. SiR-red light photocatalysis was used to cross-link hyaluronic acid derivatives functionalized by dihydrotetrazine and trans-cyclooctenes, enabling 3D culture of human prostate cancer cells. Photoinducible hydrogel formation could also be carried out in live mice through subcutaneous injection of a Cy7-labeled hydrogel precursor solution, followed by brief irradiation to produce a stable hydrogel. This cytocompatible method for using red light photocatalysis to activate bioorthogonal chemistry is anticipated to find broad applications where spatiotemporal control is needed in biological environments.

Light-Controllable PROTACs for Temporospatial Control of Protein Degradation

PROteolysis-TArgeting Chimeras (PROTACs) is an emerging and promising approach to target intracellular proteins for ubiquitination-mediated degradation, including those so-called undruggable protein targets, such as transcriptional factors and scaffold proteins. To date, plenty of PROTACs have been developed to degrade various disease-relevant proteins, such as estrogen receptor (ER), androgen receptor (AR), RTK, and CDKs. However, the on-target off-tissue and off-target effect is one of the major limitation that prevents the usage of PROTACs in clinic. To this end, we and several other groups have recently developed light-controllable PROTACs, as the representative for the third generation controllable PROTACs, by using either photo-caging or photo-switch approaches. In this review, we summarize the emerging light-controllable PROTACs and the prospective for other potential ways to achieve temporospatial control of PROTACs.

Photoacid Generators Activated through Sequential Two-Photon Excitation: 1-Sulfonatoxy-2-alkoxyanthraquinone Derivatives

Two sulfonate ester derivatives of anthraquinone, 1-tosyloxy-2-methoxy-9,10-anthraquinone (1a) and 1-trifluoromethylsulfonoxy-2-methoxy-9,10-anthraquinone (1b), were prepared and their ability to produce strong acids upon photoexcitation was examined. It is shown that these compounds generate acid with a yield that increases with light intensity when the applied photon dose is held constant. Additional experiments show that the rate of acid generation increases fourfold when visible light (532 nm) laser pulses are combined with ultraviolet (355 nm) compared with ultraviolet alone. Continuous wave diode laser photolysis also affects acid generation with a rate that depends quadratically on the light intensity. Density functional theory calculations, laser flash photolysis, and chemical trapping experiments support a mechanism, whereby an initially formed triplet state (T₁) is excited to a higher triplet state which in turn undergoes homolysis of the RS(O₂)-OAr bond. Secondary reactions of the initially formed sulfonyl radicals produce strong acids. It is demonstrated that high-intensity photolysis of either 1a or 1b can initiate cationic polymerization of ethyl vinyl ether.

Selecting Surface-Enhanced Raman Spectroscopy Flavors for Multiplexed Imaging Applications: Beyond the Experiment

Multiplexing capabilities and sensitivity of surface-enhanced Raman spectroscopy (SERS) nanoparticles (NPs) are strongly dependent on the selected Raman reporter. These Raman-active molecules are responsible for giving each batch of SERS NPs its unique spectral fingerprint. Herein, we studied four types of SERS NPs, namely, AuNPs labeled with trans-1,2-bis(4-pyridyl)ethylene (BPE), 4,4'-bis(mercaptomethyl)biphenyl (BMMBP), 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol (PODT), and 5-(4-pyridyl)-1H-1,2,4-triazole-3-thiol (PTT), and demonstrated that the best level of theory could be chosen based on inner products of DFT-calculated and experimental Raman spectra. We also calculated the theoretical spectra of these Raman reporters bound to Au₂₀ clusters to interrogate how SERS enhancement would affect their spectral fingerprint. Importantly, we found a correlation between B3LYP-D3 calculated and experimental enhancement factors, which opens up an avenue toward predicting which Raman reporters could offer improved sensitivity. We observed 0.5 and 3 fM limits of detection for BMMBP- and PTT-labeled 60 nm AuNPs, respectively.

PROTACs, molecular glues and bifunctionals from bench to bedside: Unlocking the clinical potential of catalytic drugs

The vast majority of currently marketed drugs rely on small molecules with an 'occupancy-driven' mechanism of action (MOA). Therefore, the efficacy of these therapeutics depends on a high degree of target engagement, which often requires high dosages and enhanced drug exposure at the target site, thus increasing the risk of off-target toxicities (Churcher, 2018 [1]). Although small molecule drugs have been successfully used as treatments for decades, tackling a variety of disease-relevant targets with a defined binding site, many relevant therapeutic targets remain challenging to drug due, for example, to lack of well-defined binding pockets or large protein-protein interaction (PPI) interfaces which resist interference (Dang et al., 2017 [2]). In the quest for alternative therapeutic approaches to address different pathologies and achieve enhanced efficacy with reduced side effects, ligand-induced targeted protein degradation (TPD) has gained the attention of many research groups both in academia and in industry in the last two decades. This therapeutic modality represents a novel paradigm compared to conventional small-molecule inhibitors. To pursue this strategy, heterobifunctional small molecule degraders, termed PROteolysis TArgeting Chimeras (PROTACs) have been devised to artificially redirect a protein of interest (POI) to the cellular protein homeostasis machinery for proteasomal degradation (Chamberlain et al., 2019 [3]). In this chapter, the development of PROTACs will first be discussed providing a historical perspective in parallel to the experimental progress made to understand this novel therapeutic modality. Furthermore, common strategies for PROTAC design, including assays and troubleshooting tips will be provided for the reader, before presenting a compendium of all PROTAC targets reported in the literature to date. Due to the recent advancement of these molecules into clinical trials, consideration of pharmacokinetics and pharmacodynamic properties will be introduced, together with the biotech landscape that has developed from the success of PROTACs. Finally, an overview of subsequent strategies for targeted protein degradation will be presented, concluding with further scientific quests triggered by the invention of PROTACs.

Surface-Enhanced Raman Scattering and Surface-Enhanced Infrared Absorption by Plasmon Polaritons in Three-Dimensional Nanoparticle Supercrystals

Surface-enhanced vibrational spectroscopy strongly increases the cross section of Raman scattering and infrared absorption, overcoming the limited sensitivity and resolution of these two powerful analytic tools. While surface-enhanced setups with maximum enhancement have been studied widely in recent years, substrates with reproducible, uniform enhancement have received less attention although they are required in many applications. Here, we show that plasmonic supercrystals are an excellent platform for enhanced spectroscopy because they possess a high density of hotspots in the electric field. We describe the near field inside the supercrystal within the framework of plasmon polaritons that form due to strong light-matter interaction. From the polariton resonances we predict resonances in the far-field enhancement for Raman scattering and infrared absorption. We verify our predictions by measuring the vibrations of polystyrene molecules embedded in supercrystals of gold nanoparticles. The intensity of surface-enhanced Raman scattering is uniform within 10% across the crystal with a peak integrated enhancement of up to 300 and a peak hotspot enhancement of 10⁵. The supercrystal polaritons induce pairs of incoming and outgoing resonances in the enhanced cross section as we demonstrate experimentally by measuring surface-enhanced Raman scattering with multiple laser wavelengths across the polariton resonance. The infrared absorption of polystyrene is likewise enhanced inside the supercrystals with a maximum enhancement of 400%. We show with a coupled oscillator model that the increase originates from the combined effects of hotspot formation and the excitation of standing polariton waves. Our work clearly relates the structural and optical properties of plasmonic supercrystals and shows that such crystals are excellent hosts and substrates for the uniform and predictable enhancement of vibrational spectra.

Red-Light Driven Photocatalytic Oxime Ligation for Bioorthogonal Hydrogel Design

Light-mediated polymer cross-linking is frequently employed for the preparation of hydrogels for biomedical applications. However, most photopolymerization processes require activation by UV light or short wavelength visible light, which are highly absorbed by skin and tissue, limiting their uses in transdermal initiation. Herein, we introduce red light-enabled oxime ligation by the in situ photogeneration of aldehydes, which rapidly react with hydroxylamines. We demonstrate efficient polymer cross-linking behind a dermal tissue model by red light initiation. Optimization of the photopolymerization conditions allows for 3D encapsulation of human foreskin fibroblasts with good cell viability postencapsulation.

Stimuli-Responsive Biomaterials: Scaffolds for Stem Cell Control

Stem cell fate is closely intertwined with microenvironmental and endogenous cues within the body. Recapitulating this dynamic environment ex vivo can be achieved through engineered biomaterials which can respond to exogenous stimulation (including light, electrical stimulation, ultrasound, and magnetic fields) to deliver temporal and spatial cues to stem cells. These stimuli-responsive biomaterials can be integrated into scaffolds to investigate stem cell response in vitro and in vivo, and offer many pathways of cellular manipulation: biochemical cues, scaffold property changes, drug release, mechanical stress, and electrical signaling. The aim of this review is to assess and discuss the current state of exogenous stimuli-responsive biomaterials, and their application in multipotent stem cell control. Future perspectives in utilizing these biomaterials for personalized tissue engineering and directing organoid models are also discussed.

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photoactivatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review.

Sensing refractive index gradients along dielectric nanopillar metasurfaces

Metasurfaces exhibit unique optical properties that depend on the ratio of their refractive index and that of their surroundings. As such, they are effective for sensing global changes in refractive index based on the shifts of resonances in their reflectivity spectra. However, when used as a biosensor, the metasurface can be exposed to a spatial distribution of biomolecules that brings about gradients in refractive index along the plane of the metasurface. Such gradients produce complex global reflectivity spectrum but with distinct optical enhancements in localized areas along the metasurface. Here, we propose a unique sensing paradigm that images and maps out the optical enhancements that are correlated with the spatial distribution of the refractive index. Moreover, we designed a metasurface whose resonances can be tuned to detect a range of refractive indices. Our metasurface consists of silicon nanopillars with a cylindrical nanotrench at their centers and a metal plane at the base. To assess its feasibility, we performed numerical simulations to show that the design effectively produces the desired reflectivity spectrum with resonances in the near-infrared. Using an incident light tuned to one of its resonances, our simulations further show that the field enhancements are correlated with the spatial mapping of the gradients of refractive indices along the metasurface.

Two-Photon-Triggered NO Release via a Ruthenium-Nitrosyl Complex with a Star-Shaped Architecture

We report herein a molecular engineering strategy based on the design of a multipolar ruthenium-nitrosyl (Ru-NO) complex with a three-branched architecture. The three Ru-NO units are introduced at the periphery of a highly π-delocalized truxene core bearing three terpyridine ligands. The two-photon absorption capabilities of the complex were investigated by the Z-scan technique. The strong electronic coupling among the individual arms gives rise to a very strong two-photon absorption response (δ_800 nm ∼ 1600 GM), which corresponds to a 16-fold enhancement of the capability of a single-arm reference, thereby promoting an efficient light-driven NO release process in aqueous media.

Nano adamantane-conjugated BODIPY for lipase affinity and light driven antibacterial

The increasing number of resistant bacterial strains has raised efforts in developing alternative treatment strategies. Lipase is highly expressed in most bacteria and lipase targeting dyes will be non-sacrificed materials for a sustainable method against microorganism. The combination of chemotherapy and antimicrobial photodynamic inactivation (aPDI) method will be an effective method due to enhanced antibacterial activity. Here we reported the spectroscopic features of five boron dipyrrolylmethene (BODIPY) derivatives with different functional groups for lipase affinity and antibacterial activity. Lipase affinity tests and antibacterial assays were conducted by spectroscopic methods. Adamantane-conjugated BODIPY (BDP-2) was found to be the active compound against E. coli. Next, BDP-2 was brominated, and then assembled with PEG resulting biocompatible BDP2-Br₂@mPEG nanoparticles. The MTT assay indicated that BDP2-Br₂@mPEG was less toxicity on BGC-823 cancer cells without irradiation. The BDP2-Br₂@mPEG can inhibit the proliferation of E. coli and damage the membrane of bacterial cell under green LED light irradiation. The results proved BDP2-Br₂@mPEG can be a very promising green LED light driven antibacterial material.

In vivo near-infrared fluorescent optical imaging for CNS drug discovery

INTRODUCTION

In vivo imaging technologies have become integral and essential component of drug discovery, development, and clinical assessment for central nervous system (CNS) diseases. Near-infrared (NIR) fluorescence imaging in the range of 650-950 nm is widely used for pre-clinical in vivo imaging studies. The recent expansion of NIR imaging into the shortwave infrared (SWIR, 1000-1700 nm) window enabled improvements in tissue penetration and resolution required for anatomical, dynamic, and molecular neuroimaging with high potential for clinical translation.

AREAS COVERED

This review focuses on the latest progress in near-infrared (NIR)-fluorescent optical imaging modalities with an emphasis on the SWIR window. Advantages and challenges in developing novel organic and inorganic SWIR emitters, with special attention to their toxicology and pharmacology, are discussed. Examples of their application in preclinical imaging of brain function and pathology provide a platform to assess the potential for their clinical translation.

EXPERT OPINION

Propelled through concomitant technological advancements in imaging instrumentation, algorithms and new SWIR emitters, SWIR imaging has addressed key barriers to optical imaging modalities used in pre-clinical studies addressing the CNS. Development of biocompatible SWIR emitters and adoption of SWIR into multi-modal imaging modalities promise to rapidly advance optical imaging into translational studies and clinical applications.

A New Threat to Dopamine Neurons: The Downside of Artificial Light

Growing awareness of adverse impacts of artificial light on human health has led to recognize light pollution as a significant global environmental issue. Despite, a large number of studies in rodent and monkey models of Parkinson's disease have reported that near infrared light has neuroprotective effects on dopaminergic neurons, recent findings have shown that prolonged exposure of rodents and birds to fluorescent artificial light results in an increase of neuromelanin granules in substantia nigra and loss of dopaminergic neurons. The observed detrimental effect seems to be dependent on a direct effect of light on the substantia nigra rather than a secondary effect of the alterations of circadian rhythms. Moreover, inferences from animal models to human studies have shown a positive correlation between the prevalence of Parkinson's disease and light pollution. The present article discusses experimental evidence supporting a potentially deleterious impact of light on dopaminergic neurons and highlights the mechanisms whereby light might damage neuronal tissue. Moreover, it analyses epidemiological evidence that suggests light pollution to be an environmental risk factor for Parkinson's disease.

Long-wavelength photoremovable protecting groups: On the way to in vivo application

Photoremovable protective groups (PPGs) and related "caged" compounds have been recognized as a powerful tool in an arsenal of life science methods. The present review is focused on recent advances in design of "caged" compounds which function in red or near-infrared region. The naive comparison of photon energy with that of organic bond leads to the illusion that long-wavelength activation is possible only for weak chemical bonds like N-N. However, there are different means to overcome this threshold and shift the uncaging functionality into red or near-infrared regions for general organic bonds. We overview these strategies, including the novel photochemical and photophysical mechanisms used in newly developed PPGs, singlet-oxygen-mediated photolysis, and two-photon absorption. Recent advances in science places the infrared-sensitive PPGs to the same usability level as traditional ones, facilitating in vivo application of caged compounds.

A Cyanine Photooxidation/β-Elimination Sequence Enables Near-infrared Uncaging of Aryl Amine Payloads

Uncaging strategies that use near-infrared wavelengths can enable the highly targeted delivery of biomolecules in complex settings. Many methods, including an approach we developed using cyanine photooxidation, are limited to phenol-containing payloads. Given the critical role of amines in diverse biological processes, we sought to use cyanine photooxidation to initiate the release of aryl amines. Heptamethine cyanines substituted with an aryl amine at the C4' position undergo only inefficient release, likely due electronic factors. We then pursued the hypothesis that the carbonyl products derived from cyanine photooxidation could undergo efficient β-elimination. After examining both symmetrical and unsymmetrical scaffolds, we identify a merocyanine substituted with indolenine and coumarin heterocycles that undergoes efficient photooxidation and aniline uncaging. In total, these studies provide a new scheme-cyanine photooxidation followed by β-elimination-through which to design photocages with efficient uncaging properties.

Trioxotriangulene with carbazole: a donor–acceptor molecule showing strong near-infrared absorption exceeding 1000 nm

A donor–acceptor type trioxotriangulene neutral radical derivative having three carbazolyl groups as electron-donors was newly synthesized, and exhibited a strong near-infrared photo absorption over 1000 nm.