Metal Modulation: An Easy-to-Implement Tactic for Tuning Lanthanide Phototheranostics

More is different: progressive β-thiolation induced-porphyrin aggregation switches singlet oxygen photosensitization

Incorporating sulfur atoms into photosensitizers (PSs) has been well-established to populate triplet states and increase singlet oxygen (1O2) production when exposed to light. In this work, we found that progressive thiolation of porphyrin β-periphery does promote intersystem crossing (ISC) between triplets and singlets, as seen in the excited state dynamics in dichloromethane or PS nanoparticles in water. However, in the latter case, more sulfur substitution deactivates 1O2 photosensitization, in contrast to the expected trend observed in dichloromethane. This observation was further supported by photocytotoxicity studies, where 1O2 photosensitization was switched off in living cells and multicellular spheroids despite being switched on in in vivo mice models. To understand the inconsistency, we performed molecular dynamics simulation and time-dependent density functional theory calculations to investigate possible aggregation and related excited states. We found that the extent of thiolation could regulate molecular packing inside nanoparticles, which gradually lowers the energy levels of triplet states even lower than that of 1O2 and, in turn, alters their energy dissipation pathways. Therefore, this study provides new insights into the design of metal-free PSs and sheds light on the excited state dynamics in aqueous media beyond the molecular level.

Lanthanide-dye hybrid luminophores for advanced NIR-II bioimaging

In vivo luminescence imaging in the second near-infrared window (NIR-II, 1000-2000 nm) is a potent technique for observing deep-tissue life activities, leveraging reduced light scattering, minimized autofluorescence, and moderate absorption attenuation to substantially enhance image contrast. Pushing the frontiers of NIR-II luminescence imaging forward, moving from static to dynamic event visualization, monochromatic to multicolor images, and fundamental research to clinical applications, necessitates the development of novel luminophores featuring bright emission, extendable wavelength, and optimal biocompatibility. Recently, lanthanide-dye hybrid luminophores (LDHLs) are gaining increasing attention for their wavelength extensibility, molecular size, narrowband emission, mega stokes shift, long lifetime, and high photostability. In this review, we will summarize the recent advances of NIR-II LDHLs and their applications in imaging and analysis of living mammals, and discuss future challenges in designing new LDHLs for deep-tissue imaging.

Tumor Microenvironment-Activatable Phototheranostic: Leveraging Nitric Oxide and Weak Acidity as Dual Biomarkers for Ratiometric Fluorescence, Photoacoustic Imaging, and Photothermal Therapy

Tumor microenvironment-responsive phototheranostic agents are highly sought after for their ability to improve diagnostic accuracy and treatment specificity. Here, we introduce a novel single-molecule probe, POZ-NO, which is activated by nitric oxide (NO) and weak acidity, enabling dual-mode imaging and photothermal therapy (PTT) of tumors. In acidic environments with elevated NO levels, POZ-NO exhibits a distinctive ratiometric fluorescence signal shift from the red to near-infrared, accompanied by a 700 nm photoacoustic signal. Additionally, POZ-NO demonstrated potent photothermal effects upon NO and acidity activation, achieving an impressive conversion efficiency of 74.3% under 735 nm laser irradiation. In vivo studies confirm POZ-NO's ability to accurately image tumors through ratiometric fluorescence and photoacoustic modes while selectively treating tumors with PTT.

Two-Photon Photodegradation of E3 Ubiquitin Ligase Cereblon by a Ru(II) Complex: Inducing Ferroptosis in Cisplatin-Resistant Tumor Cells

Using photodynamic therapy (PDT) to trigger nonconventional cell death pathways has provided a new scheme for highly efficient and non-side effects to drug-resistant cancer therapies. Nonetheless, the unclear targets of available photosensitizers leave the manner of PDT-induced tumor cell death relatively unpredictable. Herein, we developed a novel Ru(II)-based photosensitizer, Ru-Poma. Possessing the E3 ubiquitin ligase CRBN-targeting moiety and high singlet oxygen yield of 0.96, Ru-Poma was demonstrated to specifically photodegrade endogenous CRBN, increase lipid peroxide, downregulate GPX4 and GAPDH expression, and consequently induce ferroptosis in cisplatin-resistant cancerous cells. Furthermore, with the deep penetration of two-photon excitation, Ru-Poma achieved drug-resistant circumvention in a 3D tumor cell model. Thus, we describe the first sample of the CRBN-targeting Ru(II) complex active in PDT.

Recent Progress of Supramolecular Chemotherapy Based on Host-Guest Interactions

Chemotherapy is widely recognized as an effective approach for treating cancer due to its ability to eliminate cancer cells using chemotherapeutic drugs. However, traditional chemotherapy suffers from various drawbacks, including limited solubility and stability of drugs, severe side effects, low bioavailability, drug resistance, and challenges in tracking treatment efficacy. These limitations greatly hinder its widespread clinical application. In contrast, supramolecular chemotherapy, which relies on host-guest interactions, presents a promising alternative by offering highly efficient and minimally toxic anticancer drug delivery. In this review, an overview of recent advancements in supramolecular chemotherapy based on host-guest interactions is provided. The significant role it plays in guiding cancer therapy is emphasized. Drawing on a wealth of cutting-edge research, herein, a timely and valuable resource for individuals interested in the field of supramolecular chemotherapy or cancer therapy, is presented. Furthermore, this review contributes to the progression of the field of supramolecular chemotherapy toward clinical application.

Carbazole Based Smaragdyrins: Synthesis, Aromaticity Switching, and Formation of a Spiro-Dimer

Carbazole-incorporated smaragdyrin BF2-complex 3 was synthesized by SNAr reaction of 3,5-dibromo-8-mesityl-BODIPY 1 with 3,6-di(tert-butyl)-1,8-di(pyrrol-2-yl)carbazole 2 as a nucleophile. Demetalation of 3 with ZrCl4 gave the corresponding smaragdyrin free base 4 in a good yield. Oxidations of 3 and 4 with MnO2 gave smaragdyrins 5 and 6, respectively, both followed by aromaticity switching, since the oxidized products showed a moderate paratropic ring current owing to their 20π-electronic circuits. Further, treatment of 4 with [RhCl(CO)2]2 in the presence of NaOAc gave RhI complex 7, and oxidation of 3 with RuCl3 in the presence of triethylamine led to the formation of a spiro dimer product, 8.

A smart cysteine-activated and heavy-atom-free nano-photosensitizer for photodynamic therapy to treat cancers

A smart and heavy-atom-free photoinactive nano-photosensitizer capable of being activated by cysteine at the tumor site to generate highly photoactive nano-photosensitizers that show strong NIR absorption and fluorescence with a good singlet oxygen quantum yield (16.8%) for photodynamic therapy is reported.

Luminescent lanthanide-based molecular materials: applications in photodynamic therapy

Luminescent lanthanide molecular compounds have recently attracted attention as potential photosensitizers (PSs) for photodynamic therapy (PDT) against malignant cancer tumours because of their predictable systemic toxicity, temporospatial specificity, and minimal invasiveness. A photosensitizer exhibits no toxicity by itself, but in the presence of light and oxygen molecules, it can generate reactive oxygen species (ROS) to cause damage to proteins, nucleic acids, lipids, membranes, and organelles, which can induce cell apoptosis. This review focuses on the latest developments in luminescent lanthanide-based molecular materials as photosensitizers and their applications in photodynamic therapy. These molecular materials include lanthanide coordination complexes, nanoscale lanthanide coordination polymers, and lanthanide-based nanoscale metal-organic frameworks. In the end, the future challenges in the development of robust luminescent lanthanide molecular materials-based photosensitisers are outlined and emphasized to inspire the design of a new generation of phototheranostic agents.

Developing a Hetero-Trinuclear Erbium(III)-Copper(II) Complex Based on Apoferritin: Targeted Photoacoustic Imaging and Multimodality Therapy of Tumor

For the integration of targeted diagnosis and treatment of tumor, we innovatively designed and synthesized a single-molecule hetero-multinuclear Er(III)-Cu(II) complex (ErCu2) and then constructed an ErCu2@apoferritin (AFt) nanoparticle (NP) delivery system. ErCu2 and ErCu2@AFt NPs not only provided an evident photoacoustic imaging (PAI) signal of the tumor but also effectively inhibited tumor growth by integrating photothermal therapy, chemotherapy, and immunotherapy. ErCu2@AFt NPs improved the targeting ability and decreased the systemic toxicity of ErCu2 in vivo. Furthermore, we confirmed that ErCu2 and ErCu2@AFt NPs inhibited tumor growth by inducing apoptosis and autophagy of tumor cells and activating the immune system. The study not only provides a novel strategy to develop therapeutic metal agents but also reveals their potential for targeted accurate diagnosis and multimodality therapy of cancer.

Metal Modulation: An Effortless Tactic for Refining Photoredox Catalysis in Living Cells

The remarkable impact of photoredox catalytic chemistries has sparked a wave of innovation, opening doors to novel biotechnologies in the realm of catalytic antitumor therapy. Yet, the quest for novel photoredox catalysts (PCs) suitable for living systems, or the enhancement of catalytic efficacy in existing biocompatible PC systems, persists as a formidable challenge. Within this context, we introduce a readily applicable metal modulation strategy that significantly augments photoredox catalysis within living cells, exemplified by a set of metalloporphyrin complexes termed M-TCPPs (M = Zn, Mn, Ni, Co, Cu). Among these complexes, Zn-TCPP emerges as an exceptional catalyst, displaying remarkable photocatalytic activity in the oxidation of nicotinamide adenine dinucleotide (NADH), nicotinamide adenine dinucleotide phosphate (NADPH), and specific amino acids. Notably, comprehensive investigations reveal that Zn-TCPP's superior catalytic prowess primarily arises from the establishment of an efficient oxidative cycle for PC, in contrast to previously reported PCs engaged in reductive cycles. Moreover, theoretical calculations illuminate that amplified intersystem crossing rates and geometry alterations in Zn-TCPP contribute to its heightened photocatalytic performance. In vitro studies demonstrated that Zn-TCPP exhibits therapeutic potential and is found to be effective for photocatalytic antitumor therapy in both glioblastoma G98T cells and 3D multicellular spheroids. This study underscores the transformative role of "metal modulation" in advancing high-performance PCs for catalytic antitumor therapy, marking a significant stride toward the realization of this innovative therapeutic approach.

Nickel(II) Phototheranostics: A Case Study in Photoactivated H2O2-Enhanced Immunotherapy

Phototheranostics have emerged as a promising subset of cancer theranostics owing to their potential to provide precise photoinduced diagnoses and therapeutic outcomes. However, the design of phototheranostics remains challenging due to the nature of tumors and their microenvironment, including limitations to the oxygen supply, high rates of recurrence and metastasis, and the immunosuppressive state of cancer cells. Here we report a dual-functional oxygen-independent phototheranostic agent, Ni-2, rationally designed to provide a near-infrared (NIR) photoactivated thermal- and hydroxyl radical (•OH)-enhanced photoimmunotherapeutic anticancer response. Under 880 nm laser irradiation, Ni-2 exhibited high photostability and excellent photoacoustic and photothermal effects with a photothermal conversion efficacy of 58.0%, as well as novel photoredox features that allowed the catalytic conversion of H2O2 to •OH upon photooxidation of Ni(II) to Ni(III). As a multifunctional photoagent, Ni-2 was found not only to inhibit tumor growth in a CT26 tumor-bearing mouse model but also to activate an immune response via a combination of photothermal- and H2O2-induced effects. When combined with an antiprogrammed death-ligand 1 (aPD-L1), Ni-2 treatment allowed for the suppression of distant tumor growth and cancer metastasis. Collectively, the present results provide support for the proposition that Ni-2 or its analogues could emerge as useful tools for photoimmunotherapy. They also highlight the potential of appropriately designed 3d transition metal complexes as "all- in-one" phototheranostics.

Stable Inner 2H Tautomer of N-Confused-like Porphyrin Embedded with a Carbazole Subunit: Synthesis, Metal Coordination, and Magnetic and Anion Sensing Studies

A new class of N-confused porphyrin 1 embedded with a carbazole subunit was prepared via [3 + 1] acid-catalyzed condensation of appropriate precursors. 1 underwent smooth metal complexation with Pd(II) and Cu(II) salts to provide the corresponding diamagnetic 1-Pd and paramagnetic 1-Cu, respectively. The single-crystal X-ray structure of 1-Pd is evident with a square-planar Pd-center through C-H activation of inverted pyrrole. Superconducting quantum interference device analysis combined with electron paramagnetic resonance (EPR) results provided insights into the paramagnetic nature of 1-Cu. Further, a ratiometric enhancement of near-IR fluorescence at 746 nm was found to be reversible upon adding CN- and F- ions. The solid-state structure of 1-Pd confirms that the anionic species is due to NH deprotonation.

Multiresponsive Self-Healing Lanthanide Fluorescent Hydrogel for Smart Textiles

Lanthanide organometallic complexes exhibit strong luminescence characteristics, owing to their antenna effects. The f-d energy level transition causes this phenomenon, which occurs when ligands and the external electrons of lanthanide metals coordinate. Based on this phenomenon, we used two lanthanide metals, europium (Eu) and terbium (Tb), in the present study as the metal center for iminodiacetic acid ligands. Further, we developed the resulting fluorescent organometallic complex as a smart material. The ligand-metal bond in the material functioned as a metal chelating agent and a cross-linking agent in a dynamically coordinated form, thereby prompting the material to self-heal. Temperature-sensitive poly-N-isopropylacrylamide was incorporated into the material as the polymer backbone. Afterward, we combined it with water-soluble poly(vinyl alcohol) and an additional ligand from poly(acrylic acid) to fabricate a high-performance hydrogel composite material. The shrinkage and expansion of the polymer form a grid between the materials. Because of the different coordination stabilities of Eu3+ and Tb3+, the corresponding material exhibits environmental responses toward excitation wavelength, temperature, and pH, thus generating different colors. When used in fabrics, the cross-linking mechanism of the material effectively looped the material between fabric fibers; furthermore, the temperature sensitivity of the polymer adjusted the size of pores between fabric fibers. At relatively higher temperatures (>32 °C), the polymer structure shrank, fiber pores expanded, and air permeability improved. Thus, this material appears to be promising for use in smart textiles.

Synthesis of Mesoporous and Hollow SiO2@ Eu(TTA)3phen with Enhanced Fluorescence Properties

Lanthanide ions are extensively utilized in optoelectronic materials, owing to their narrow emission bandwidth, prolonged lifetime, and elevated fluorescence quantum yield. Inorganic non-metallic materials commonly serve as host matrices for lanthanide complexes, posing noteworthy challenges regarding loading quantity and fluorescence performance stability post-loading. In this investigation, an enhanced Stöber method was employed to synthesize mesoporous hollow silica, and diverse forms of SiO₂@Eu(TTA)₃phen (S@Eu) were successfully prepared. Transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) outcomes revealed the effective binding of silica with Eu(TTA)₃phen through both physical adsorption and chemical bonding. This includes the formation of Si-O-C bonds between silica and the ligand, as well as Si-O-Eu bonds between silica and europium ions. Fluorescence tests demonstrated that the mesoporous SiO₂@Eu(TTA)₃phen(MS@Eu) composite exhibited the highest fluorescence intensity among the three structured silica composites, with a notable enhancement of 46.60% compared to the normal SiO₂@Eu(TTA)₃phen composite. The Brunauer-Emmett-Teller (BET) analysis indicated that the specific surface area plays a crucial role in influencing the fluorescence intensity of SiO₂@Eu(TTA)₃phen, whereby the prepared mesoporous hollow silica further elevated the fluorescence intensity by 61.49%. Moreover, SiO₂@Eu(TTA)₃phen demonstrated 11.11% greater cyclic stability, heightened thermal stability, and enhanced alkaline resistance relative to SiO₂@Eu(TTA)₃phen.

Photothermal-driven disassembly of naphthalocyanine nano-photosensitizers for photothermal and photodynamic therapy

The disassembly of nanomaterials is of particular interest for high-quality imaging and targeted therapies in the field of nanomedicine. In this study, we developed a novel strategy for fabricating self-assembled naphthalocyanine photosensitizers (SiNc@CEL) with intrinsically unique photochemical and photophysical properties. SiNc@CEL could be disassembled under the photothermal effect, and its photoactivity could be enhanced by 780 nm laser irradiation. Moreover, SiNc@CEL generates reactive oxygen species, including superoxide radicals (O₂^•-) and singlet oxygen (¹O₂), as well as good photothermal properties, facilitating the application of multifunctional phototherapy. In vitro evaluation indicated that SiNc@CEL possesses an excellent bactericidal effect under a combination of photodynamic (PDT) and photothermal therapy (PTT). The in vivo treatment of a full-layer skin defect model of Escherichia coli (E. coli) infection showed that SiNc@CEL had superior antibacterial and wound-healing abilities. These results provide the basis for a feasible strategy to enhance the phototherapeutic effect of photosensitizer (PS) systems.

NIR-II Perylene Monoimide-Based Photothermal Agent with Strengthened Donor-Acceptor Conjugation for Deep Orthotopic Glioblastoma Phototheranostics

Extensive efforts have been devoted to the design of organic photothermal agents (PTAs) that absorb in the second near-infrared (NIR-II) bio-window, which can provide deeper tissue penetration that is significant for phototheranostics of lethal brain tumors. Herein, the first example of NIR-II-absorbing small organic molecule (N1) derived from perylene monoamide (PMI) and its bio-application after nano-encapsulation of N1 to function as a nano-agent for phototheranostics of deep orthotopic glioblastoma (GBM) is reported. By adopting a dual modification strategy of introducing a donor-acceptor unit and extending π-conjugation, the obtained N1 can absorb in 1000-1400 nm region and exhibit high photothermal conversation due to the apparent intramolecular charge transfer (ICT). A choline analogue, 2-methacryloyloxyethyl phosphorylcholine, capable of interacting specifically with receptors on the surface of the blood-brain barrier (BBB), is used to fabricate the amphiphilic copolymer for the nano-encapsulation of N1. The obtained nanoparticles demonstrate efficient BBB-crossing due to the receptor-mediated transcytosis as well as the small nanoparticle size of approximately 26 nm. The prepared nanoparticles exhibit excellent photoacoustic imaging and significant growth inhibition of deep orthotopic GBM. The current study demonstrates the enormous potential of PMI-based NIR-II PTAs and provides an efficient phototheranostic paradigm for deep orthotopic GBM.

Luminescent Lanthanide Complexes for Effective Oxygen-Sensing and Singlet Oxygen Generation

Oxygen quantification using luminescence has attracted considerable attention in various fields, including environmental monitoring and clinical analysis. Among the reported luminophores, trivalent lanthanide complexes have displayed characteristic narrow emission bands with high brightness. This bright emission is based on photo-sensitized energy transfer via organic triplet states. The organic triplet states in lanthanide complexes effectively react with the triplet oxygen, enabling oxygen quantification by lanthanide luminescence. Some Tb^III and Eu^III complexes with slow deactivation processes have also formed the excited state equilibrium, thus resulting in the emission-lifetime based oxygen sensing property. The combination of Tb^III /Eu^III emission, Eu^III /Sm^III emission, Eu^III /ligand phosphorescence, and ligand fluorescence/ligand phosphorescence provide the ratiometric oxygen-sensing properties. Moreover, the reaction generates singlet oxygen species which exhibit numerous applications in the photo-medical field. The ligands with large π-conjugated aromatic systems, such as porphyrin, phthalocyanine, and polyaromatic compounds, induces highly efficient oxygen generation. The combination of effective luminescence with singlet-oxygen generation by the lanthanide complexes render them suitable for photo-driven theranostics. This review summarizes the research progress of lanthanide complexes with efficient oxygen-sensing and singlet-oxygen generation properties.

Copper-Nitrogen-Coordinated Carbon Dots: Transformable Phototheranostics from Precise PTT/PDT to Post-Treatment Imaging-Guided PDT for Residual Tumor Cells

Phototheranostics has attracted considerable attention in the fields of cancer diagnosis and treatment. However, the complete eradication of solid tumors using traditional phototheranostics is difficult because of the limited depth and range of laser irradiation. New phototheranostics enabling precise phototherapy and post-treatment imaging-guided programmed therapy for residual tumors is urgently required. Accordingly, this study developed a novel transformable phototheranostics by assembling hyaluronic acid (HA) with copper-nitrogen-coordinated carbon dots (CDs). In this transformable nanoplatform, named copper-nitrogen-CDs@HA, the HA component enables the specific targeting of cluster determinant (CD) 44-overexpressing tumor cells. In the tumor cells, redox glutathione converts Cu(II) (cupric ions) into Cu(I) (cuprous ions), which confers the novel transformable functionality to phototheranostics. Both in vitro and in vivo results reveal that the near-infrared-light-photoactivated Cu^II-N-CDs@HA could target CD44-overexpressing tumor cells for precise synergistic photothermal therapy and photodynamic therapy. This study is the first to observe that Cu^II-N-CDs@HA could escape from lysosomes and be transformed in situ into Cu^I-N-CDs@HA in tumor cells, with the d⁹ electronic configuration of Cu(II) changing to the d¹⁰ electronic configuration of Cu(I), which turns on their fluorescence and turns off their photothermal properties. This transformable phototheranostics could be used for post-treatment imaging-guided photodynamic therapy on residual tumor cells. Thus, the rationally designed copper-nitrogen-coordinated CDs offer a simple in situ transformation strategy for using multiple-stimulus-responsive precise phototheranostics in post-treatment monitoring of residual tumor cells and imaging-guided programmed therapy.

Lanthanide-based MOFs: synthesis approaches and applications in cancer diagnosis and therapy

Metal-organic frameworks (MOFs) have attracted considerable attention as emerging nanomaterials. Based on their tunable size, high porosity, and large specific surface area, MOFs have a wide range of applications in the fields of chemistry, energy, and biomedicine. However, the MOF materials obtained from lanthanides with a unique electronic configuration as inorganic building units have unique properties such as optics, magnetism, and radioactivity. In this study, various synthetic methods for preparing MOF materials using lanthanides as inorganic building units are described. Combined with the characteristics of lanthanides, their application prospects of lanthanide-based MOFs in tumor diagnosis and treatment are emphasized. The authors hope to provide methodological reference for the construction of MOF materials of rare-earth elements, and to provide ideas and inspiration for their practical applications in the field of biomedicine.

Copper-Bridged Tetrakis(4-ethynylphenyl)ethene Aggregates with Photo-Regulated 1 O2 and O2 .- Generation for Selective Photocatalytic Aerobic Oxidation

Active species regulation is a key scientific issue that essentially determines the selectivity and activity of a photocatalyst. Herein, Cu^I -bridged tetrakis(4-ethynylphenyl)ethene aggregates (T₄ EPE-Cu) with photo-regulated ¹ O₂ and O₂ ^.- generation were demonstrated for selective photocatalytic aerobic oxidation. In this system, transient photovoltage combined with the density functional theory calculations confirmed that Cu-alkynyl was the main oxygen activation site. The adsorbed O₂ tends to produce O₂ ^.- because of the potential well effect of Cu-alkynyl under high-energy light excitation. But under low-energy light, O₂ tends to produce ¹ O₂ via resonance energy transfer with Cu-alkynyl. For α-terpinene oxidation, the ratios of ¹ O₂ products to O₂ ^.- products can be controlled from 1.3 (380 nm) to 10.7 (600 nm). Furthermore, T₄ EPE-Cu exhibited ultrahigh photocatalytic performance for Glaser coupling and benzylamine oxidation, with a conversion and selectivity of over 99 %.

Lanthanide porphyrinoids as molecular theranostics

In recent years, lanthanide (Ln) porphyrinoids have received increasing attention as theranostics. Broadly speaking, the term 'theranostics' refers to agents designed to allow both disease diagnosis and therapeutic intervention. This Review summarises the history and the 'state-of-the-art' development of Ln porphyrinoids as theranostic agents. The emphasis is on the progress made within the past decade. Applications of Ln porphyrinoids in near-infrared (NIR, 650-1700 nm) fluorescence imaging (FL), magnetic resonance imaging (MRI), radiotherapy, and chemotherapy will be discussed. The use of Ln porphyrinoids as photo-activated agents ('phototheranostics') will also be highlighted in the context of three promising strategies for regulation of porphyrinic triplet energy dissipation pathways, namely: regioisomeric effects, metal regulation, and the use of expanded porphyrinoids. The goal of this Review is to showcase some of the ongoing efforts being made to optimise Ln porphyrinoids as theranostics and as phototheranostics, in order to provide a platform for understanding likely future developments in the area, including those associated with structure-based innovations, functional improvements, and emerging biological activation strategies.

Luminescent Metal Complexes for Bioassays in the Near-Infrared (NIR) Region

Near-infrared (NIR, 700-1700 nm) luminescent imaging is an emerging bioimaging technology with low photon scattering, minimal autofluorescence, deep tissue penetration, and high spatiotemporal resolution that has shown fascinating promise for NIR imaging-guided theranostics. In recent progress, NIR luminescent metal complexes have attracted substantially increased research attention owing to their intrinsic merits, including small size, anti-photobleaching, long lifetime, and metal-centered NIR emission. In the past decade, scientists have contributed to the advancement of NIR metal complexes involving efforts to improve photophysical properties, biocompatibility, specificity, pharmacokinetics, in vivo visualization, and attempts to exploit new ligand platforms. Herein, we summarize recent progress and provide future perspectives for NIR metal complexes, including d-block transition metals and f-block lanthanides (Ln) as NIR optical molecular probes for bioassays.

Nonaromatic Organonickel(II) Phototheranostics

Earth-abundant metal-based theranostics, agents that integrate diagnostic and therapeutic functions within the same molecule, may hold the key to the development of low-cost personalized medicines. Here, we report a set of O-linked nonaromatic benzitripyrrin (C^N^N^N) macrocyclic organonickel(II) complexes, Ni-1-4, containing strong σ-donating M-C bonds. Complexes Ni-1-4 are characterized by a square-planar coordination geometry as inferred from the structural studies of Ni-1. They integrate photothermal therapy, photothermal imaging, and photoacoustic imaging (PAI) within one system. This makes them attractive as potential phototheranostics. Relative to traditional Ni(II) porphyrins, such as F₂₀TPP (tetrapentafluorophenylporphyrin), the lowest energy absorption of Ni-1 is shifted into the near infrared region, presumably as a consequence of Ni-C bonding. Ultrafast transient absorption spectroscopy combined with theoretical calculations revealed that, upon photoexcitation, a higher population of ligand-centered and ³MLCT states is seen in Ni-1 relative to NiTPBP (TPBP = 6,11,16,21-tetraphenylbenziporphyrin). Encapsulating Ni-1 in 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE-PEG₂₀₀₀) afforded nanoparticles, Ni-1@DSPE, displaying red-shifted absorption features, as well as good photothermal conversion efficiency (∼45%) in aqueous media. Proof-of-principle experiments involving thrombus treatment were carried out both in vitro and in vivo. It was found that Ni-1@DSPE in combination with 785 nm photo-irradiation for 3 min (0.3 W/cm²) proved successful in removing blood clots from a mouse thrombus model as monitored by photoacoustic imaging (PAI). The present work highlights the promise of organonickel(II) complexes as potential theranostics and the benefits that can accrue from manipulating the excited-state features of early transition-metal complexes via, for example, interrupting π-conjugation pathways.

Dual-Labelling Strategies for Nuclear and Fluorescence Molecular Imaging: Current Status and Future Perspectives

Molecular imaging offers the possibility to investigate biological and biochemical processes non-invasively and to obtain information on both anatomy and dysfunctions. Based on the data obtained, a fundamental understanding of various disease processes can be derived and treatment strategies can be planned. In this context, methods that combine several modalities in one probe are increasingly being used. Due to the comparably high sensitivity and provided complementary information, the combination of nuclear and optical probes has taken on a special significance. In this review article, dual-labelled systems for bimodal nuclear and optical imaging based on both modular ligands and nanomaterials are discussed. Particular attention is paid to radiometal-labelled molecules for single-photon emission computed tomography (SPECT) and positron emission tomography (PET) and metal complexes combined with fluorescent dyes for optical imaging. The clinical potential of such probes, especially for fluorescence-guided surgery, is assessed.

Gadolinium(III) Porphyrinoid Phototheranostics

Molecular phototheranostics as the emerging field of modern precision medicine recently has attracts increasing research attentions owing to non-invasiveness, high precision, and controllable nature of light. In this work, we reported alluring gadolinium (Gd3+) porphyrinoids phototheranostic agents for magnetic resonance imaging (MRI) and photodynamic therapy (PDT). The synthesized Gd-1-4-Glu featured with meso-glycosylation and β-lactonization to endow good biocompatibility and improved photophysical properties. In particular, β-lactonization of glycosylated Gd3+ porphyrinoids substantially red-shifted its absorption band to near-infrared (NIR) region and boosted generation of reactive oxygen species including 1O2, and some radical species that engaged both type II and type I PDT pathways. In addition, the number and regioisomerism of β-oxazolone moieties was observed to play an essential role in improving longitude relaxivity (r1) of Gd-1-4-Glu up to 4.6 mM-1s-1 for the first time by affecting environmental water exchange. Taking Gd-4-Glu as a promising complex, we further achieved real-time T1-weighted MRI and PDT on HeLa tumour mice in vivo, revealing the appealing potential of Gd3+ porphyrinoids in phototheranostics.

Direct [4 + 2] Cycloaddition to Isoquinoline-Fused Porphyrins for Near-Infrared Photodynamic Anticancer Agents

The synthesis of efficient porphyrin-based photosensitizers with intense near-infrared (NIR) absorption is in high demand for photodynamic therapy (PDT) but remains a challenging task. Herein we show the construction of a type of isoquinoline-fused porphyrins 3 and 4 with an impressive NIR-absorbing capacity. In light of the extraordinary singlet oxygen generation capabilities of 3 upon NIR irradiation, the representative nanoparticles (3a-NPs) assembled show excellent tumoricidal behavior with good biocompatibility in the phototherapeutic window (650-850 nm).

Biomimetically constructing a hypoxia-activated programmable phototheranostics at the molecular level

A programmable strategy at the molecular level to modulate the ratio of a catalyst and photosensitizer to maximize the collaborative efficiency of anti-angiogenesis and PDT.

Polythiophene for Near Full pH Photo-antimicrobial

Microbial infections are currently one of the world’s major public health cares, the evolution of which has resulted in the development of multiple tolerances (not just the drug or antibiotic...

An Aqueous Room-Temperature Phosphorescent Probe for Gd3+

An aqueous room-temperature phosphorescent (RTP) probe for Gd3+ is reported, based on Gd3+-induced intersystem promoting and the oxygen-shielding property of the Gd3+/AMP/fluorescein coordination polymer nanoparticles (CPNs). Besides selective Gd3+ detection,...

Conformationally Restricted and Three-dimensionally Extended Carbazole-Incorporating Expanded Porphyrinoids

Condensation of 3,6-(1-phenyl-1-(2-pyrroyl)methyl)carbazole with pentafluoroaldehyde and subsequent oxidation with DDQ gave a carbazole-incorporating octaphyrin(1.1.1.0.1.1.1.0) analogue, 7, which was shown to exists as locked conformers 7a and 7b. Both conformers were...

A facile design of thio-perylenediimides with controllable fluorescent, photodynamic and photothermal effects towards cancer theranostics

A series of thionated perylenediimides with modulating phototheranostic modalities have been synthesized by a one-pot method for multiple anti-cancer applications. Compared to the initial and 4-tert-butyl phenol-substituted fluorescent perylenediimide, the obtained monothionated perylenediimide became photodynamic. With the increase of thionation degree, tetrathionated perylenediimide changed into an optimal photothermal agent.

Recent progress in metal-based molecular probes for optical bioimaging and biosensing

Biological imaging and biosensing from subcellular/cellular level to whole body have enabled non-invasive visualisation of molecular events during various biological and pathological processes, giving great contributions to the rapid and impressive advances in chemical biology, drug discovery, disease diagnosis and prognosis. Optical imaging features a series of merits, including convenience, high resolution, good sensitivity, low cost and the absence of ionizing radiation. Among different luminescent probes, metal-based molecules offer unique promise in optical bioimaging and biosensing in vitro and in vivo, arising from their small sizes, strong luminescence, large Stokes shifts, long lifetimes, high photostability and tunable toxicity. In this review, we aim to highlight the design of metal-based molecular probes from the standpoint of synthetic chemistry in the last 2 years for optical imaging, covering d-block transition metal and lanthanide complexes and multimodal imaging agents.

Porpholactam-cinnamaldehyde conjugates for promoting ROS generation in photodynamic therapy

Photodynamic therapy (PDT) is a non-invasive method for cancer treatment that relies on the generation of excess reactive oxygen species (ROS), upon excitation of photosensitizer (PS), to eradicate tumor cells. However, the overexpress of endogenous antioxidants in tumor cells will eliminate the ROS and restrict the therapeutic efficacy of PDT. Herein, a novel type of PS was developed by conjugating cinnamaldehyde (CA), a kind of oxidative stress amplified agent, with porpholactam through a hydrazone bond. The new PS retains the photophysical properties of porpholactam, which displays high singlet oxygen quantum yield for the PDT function. The results of in vitro experiments performed including ROS assay and the cytotoxicity in cancer cells suggest that the rational design of the novel porpholactam-CA derivatives result in enhanced ROS generation upon irradiation, providing a possible approach to achieve enhanced therapeutic effects in PDT.