Fluorescent/phosphorescent dual-emissive conjugated polymer dots for hypoxia bioimaging

Metal ion-manipulated afterglow on rhodamine 6G derivative-doped room-temperature phosphorescent PVA films

The long-lived room-temperature phosphorescence (RTP) originating from thiophene boronate polyvinyl alcohol (PVA) has enabled the creation of metal-ion-responsive RTP films doped with spirolactam ring-containing rhodamine 6G (1). In this study, RTP-active PVA films, namely, TDB@PVA and ATB@PVA, were prepared through boronate esterification of thiophene-2,5-diboronic acid (TDB) and 5-acetylthiophene-2-boronic acid (ATB) with the diol units of PVA. The delayed emission properties were evaluated, revealing an emission band at 477 nm with a turquoise afterglow for TDB@PVA and at 510 nm with a green afterglow for ATB@PVA after UV light irradiation ceased. The photophysical properties were assessed using TD-DFT and DFT calculations at the B3LYP/cc-pVDZ level. N-(rhodamine-6G)lactam dye with a salicylimine unit (1) was doped into the RTP-based PVA films, producing a multicolored afterglow upon the addition of metal ions. This phenomenon is explained by a triplet-to-singlet Förster-type resonance energy transfer process from the cross-linked thiophene boronate in PVA to the metal-ion-activated colored form of 1. This photophysical feature finds applicability in encryption techniques. Notably, the reversible metal-ligand coordination of 1 in the PVA system enabled a write/erase information process.

Investigation of tumour environments through advancements in microtechnology and nanotechnology

Cancer has a significant negative social and economic impact on both developed and developing countries. As a result, understanding the onset and progression of cancer is critical for developing therapies that can improve the well-being and health of individuals with cancer. With time, study has revealed, the tumor microenvironment has great influence on this process. Micro and nanoscale engineering techniques can be used to study the tumor microenvironment. Nanoscale and Microscale engineering use Novel technologies and designs with small dimensions to recreate the TME. Knowing how cancer cells interact with one another can help researchers develop therapeutic approaches that anticipate and counteract cancer cells' techniques for evading detection and fighting anti-cancer treatments, such as microfabrication techniques, microfluidic devices, nanosensors, and nanodevices used to study or recreate the tumor microenvironment. Nevertheless, a complicated action just like the growth and in cancer advancement, and their intensive association along the environment around it that has to be studied in more detail.

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.

NIR-II Fluorescence Imaging for In Vivo Quantitative Analysis

In vivo real-time qualitative and quantitative analysis is essential for the diagnosis and treatment of diseases such as tumors. Near-infrared-II (NIR-II, 1000-1700 nm) bioimaging is an emerging visualization modality based on fluorescent materials. The advantages of NIR-II region fluorescent materials in terms of reduced photon scattering and low tissue autofluorescence enable NIR-II bioimaging with high resolution and increasing depth of tissue penetration, and thus have great potential for in vivo qualitative and quantitative analysis. In this review, we first summarize recent advances in NIR-II imaging, including fluorescent probe selection, quantitative analysis strategies, and imaging. Then, we describe in detail representative applications to illustrate how NIR-II fluorescence imaging has become an important tool for in vivo quantitative analysis. Finally, we describe the future possibilities and challenges of NIR-II fluorescence imaging.

Synthesis and Electron Transporting Properties of Diblock Copolymers Consisting of Polyfluorene and Polystyrene

Poly(9,9-di-n-octylfluorene) (PFO) is a promising material for polymer light-emitting diodes (PLEDs) due to its advantageous properties. To enhance its electron transporting capabilities, diblock polymers were synthesized by attaching polystyrene (PSt) chains of varying lengths to one end of the PFO molecule. In a comparative study with PFO homopolymer, the diblock polymers maintained similar thermal properties, absorption spectra, and photoluminescent stability, while exhibiting slightly deeper lowest unoccupied molecular orbital (LUMO) levels and higher crystallinity. Notably, diblock polymers with shorter polystyrene blocks demonstrated higher electron mobility than the PFO homopolymer and diblock polymers with excessively long polystyrene blocks. These findings suggest that the optimal chain length of the polystyrene block is crucial for maximizing electron mobility, thus offering valuable insights for designing high-performance PLED materials.

Organosilica Nanosensors for Monitoring Spatiotemporal Changes in Oxygen Levels in Bacterial Cultures

Oxygen plays a central role in aerobic metabolism, and while many approaches have been developed to measure oxygen concentration in biological environments over time, monitoring spatiotemporal changes in dissolved oxygen levels remains challenging. To address this, we developed a ratiometric core-shell organosilica nanosensor for continuous, real-time optical monitoring of oxygen levels in biological environments. The nanosensors demonstrate good steady state characteristics (KpSV = 0.40 L/mg, R2 = 0.95) and respond reversibly to changes in oxygen concentration in buffered solutions and report similar oxygen level changes in response to bacterial cell growth (Escherichia coli) in comparison to a commercial bulk optode-based sensing film. We further demonstrated that the oxygen nanosensors could be distributed within a growing culture of E. coli and used to record oxygen levels over time and in different locations within a static culture, opening the possibility of spatiotemporal monitoring in complex biological systems.

Design, Synthesis, and Characterization of Organometallic BODIPY-Ru(II) Dyads: Redox and Photophysical Properties with Singlet Oxygen Generation Capability†

A series of Ru(II)-acetylide complexes (Ru1, Ru2, and Ru1m) with alkynyl-functionalized borondipyrromethene (BODIPY) conjugates were designed by varying the position of the linker that connects the BODIPY unit to the Ru(II) metal center through acetylide linkage at either the 2-(Ru1) and 2,6-(Ru2) or the meso-phenyl (Ru1m) position of the BODIPY scaffold. The Ru(II) organometallic complexes were characterized by various spectroscopic methods, including nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, CHN, and high-resolution mass spectrometry (HRMS) analyses. The Ru(II)-BODIPY conjugates exhibit fascinating electrochemical and photophysical properties. All BODIPY-Ru(II) complexes exhibit strong absorption (εmax = 29,000-72,000 M-1 cm-1) in the visible region (λmax = 502-709 nm). Fluorescence is almost quenched for Ru1 and Ru2, whereas Ru1m shows the residual fluorescence of the corresponding BODIPY core at 517 nm. The application of the BODIPY-Ru(II) dyads as nonporphyrin-based triplet photosensitizers was explored by a method involving the singlet oxygen (1O2)-mediated photo-oxidation of diphenylisobenzofuran. Effective π-conjugation between the BODIPY chromophore and Ru(II) center in the case of Ru1 and Ru2 was found to be necessary to improve intersystem crossing (ISC) and hence the 1O2-sensitizing ability. In addition, electrochemical studies indicate electronic interplay between the metal center and the redox-active BODIPY in the BODIPY-Ru(II) dyads.

Molecular Engineering Design of Enhanced Donor-Acceptor Therapeutic Reagent for Efficient Image-Guided Photodynamic Therapy

The greatest barrier to the further development and clinical application of tumor image-guided photodynamic therapy (PDT), is the inconsistency between the fluorescence intensity and singlet oxygen generation yield of the photosensitizer under light excitation. Herein, a novel donor-acceptor (D-A) system is designed from the point of molecular selection by wrapping a classical porphyrin molecule (5,10,15,20-tetraphenylphorphyrin, H2 TPP) as an acceptor into conjugated polymer (Poly[N,N'-bis(4-butylpheny)-N,N'-bis(phenyl)benzidine], ADS254BE) as a donor through fluorescence resonance energy transfer (FRET) mechanism, which exhibits bright red emission centered at 650 nm (quantum yield, 0.12), relatively large Stoke shift of 276 nm, enhanced singlet oxygen generation rate of 0.73, and excellent photostability. The investigations on distribution and killing effect of nanomaterials in cancer cells reveal that ADS254BE/H2 TPP NPs can accumulate in the cytoplasm for imaging while simultaneously producing a large amount of singlet oxygen to remarkably kill cancer cells, which can be used for real-time image-guided PDT. In the xenograft tumor model, real-time imaging and long-term tracing in tumor tissue with ADS254BE/H2 TPP NPs disclose that the growth of lung cancer in mice can be effectively inhibited during in situ imaging. From the standpoint of molecular engineering design, this work provides a feasible strategy for novel D-A systems to improve the development of image-guided PDT.

Dual-Emissive Monoruthenium Complexes of N(CH3)-Bridged Ligand: Synthesis, Characterization, and Substituent Effect

Three monoruthenium complexes 1(PF6)2-3(PF6)2 bearing an N(CH3)-bridged ligand have been synthesized and characterized. These complexes have a general formula of [Ru(bpy)2(L)](PF6)2, where L is a 2,5-di(N-methyl-N'-(pyrid-2-yl)amino)pyrazine (dapz) derivative with various substituents, and bpy is 2,2'-bipyridine. The photophysical and electrochemical properties of these compounds have been examined. The solid-state structure of complex 3(PF6)2 is studied by single-crystal X-ray analysis. These complexes show two well-separated emission bands centered at 451 and 646 nm (Δλmax = 195 nm) for 1(PF6)2, 465 and 627 nm (Δλmax = 162 nm) for 2(PF6)2, and 455 and 608 nm (Δλmax = 153 nm) for 3(PF6)2 in dilute acetonitrile solution, respectively. The emission maxima of the higher-energy emission bands of these complexes are similar, while the lower-energy emission bands are dependent on the electronic nature of substituents. These complexes display two consecutive redox couples owing to the stepwise oxidation of the N(CH3)-bridged ligand and ruthenium component. Moreover, these experimental observations are analyzed by computational investigation.

Micro-engineering and nano-engineering approaches to investigate tumour ecosystems

The interactions among tumour cells, the tumour microenvironment (TME) and non-tumour tissues are of interest to many cancer researchers. Micro-engineering approaches and nanotechnologies are under extensive exploration for modelling these interactions and measuring them in situ and in vivo to investigate therapeutic vulnerabilities in cancer and extend a systemic view of tumour ecosystems. Here we highlight the greatest opportunities for improving the understanding of tumour ecosystems using microfluidic devices, bioprinting or organ-on-a-chip approaches. We also discuss the potential of nanosensors that can transmit information from within the TME or elsewhere in the body to address scientific and clinical questions about changes in chemical gradients, enzymatic activities, metabolic and immune profiles of the TME and circulating analytes. This Review aims to connect the cancer biology and engineering communities, presenting biomedical technologies that may expand the methodologies of the former, while inspiring the latter to develop approaches for interrogating cancer ecosystems.

Self-assembled super-small AIEgen nanoprobe for highly sensitive and selective detection of protamine and trypsin

Amphiphilic aggregation-induced emission (AIE) molecules show superior potential for fabricating novel ultrasmall nanoprobes. Here, an anionic dipyridyl tetraphenylethene (TPE) derivative is rationally designed and a super-small self-assembled AIEgen nanoprobe (TPE-2Py-SO₃NaNPs, ca. 2.48 nm) is thus conveniently constructed for the supersensitive detection of protamine and trypsin. In HEPES/DMSO solution (8 : 2, v/v, pH = 7.4), negatively charged TPE-2Py-SO₃NaNPs exhibited an AIE effect in the presence of positively charged protamine, presenting a fluorescence enhancement at 498 nm together with a large Stokes shift of 150 nm and a low detection limit of 8.0 ng mL^-1. In addition, the in situ formed TPE-2Py-SO₃Na/protamine nanocomposite can be dissociated by trypsin due to the highly selective degradation of protamine via enzymatic hydrolysis, achieving a detection limit for trypsin as low as 5.0 ng mL^-1.

Near-infrared metal agents assisting precision medicine: from strategic design to bioimaging and therapeutic applications

Metal agents have made incredible strides in preclinical research and clinical applications in recent years, but their short emission/absorption wavelengths continue to be a barrier to their distribution, therapeutic action, visual tracking, and efficacy evaluation. Nowadays, the near-infrared window (NIR, 650-1700 nm) provides a more accurate imaging and treatment option. Thus, there has been ongoing research focusing on developing multifunctional NIR metal agents for imaging and therapy that have deeper tissue penetration. The design, characteristics, bioimaging, and therapy of NIR metal agents are covered in this overview of papers and reports published to date. To start with, we focus on describing the structure, design strategies, and photophysical properties of metal agents from the NIR-I (650-1000 nm) to NIR-II (1000-1700 nm) region, in order of molecular metal complexes (MMCs), metal-organic complexes (MOCs), and metal-organic frameworks (MOFs). Next, the biomedical applications brought by these superior photophysical and chemical properties for more accurate imaging and therapy are discussed. Finally, we explore the challenges and prospects of each type of NIR metal agent for future biomedical research and clinical translation.

BODIPY-based near-infrared semiconducting polymer dot for selective yellow laser-excited cell imaging

Semiconducting polymer dots (Pdots) with both narrow-band absorption and emission are desirable for multiplexed bioassay applications, but such Pdots with absorption peaks beyond 400 nm are difficult to achieve. Here we describe a donor-energy transfer unit-acceptor (D-ETU-A) design strategy to produce a BODIPY-based Pdot that exhibits simultaneously narrow absorption and emission bands. A green BODIPY (GBDP) unit was employed as the main building block of the polymer backbone, conferring a strong, narrow-band absorption around 551 nm. An NIR720 acceptor provides narrow-band NIR emission. The small Stokes shift of the GBDP donor allows introduction of a benzofurazan-based ETU, resulting in a ternary Pdot with a fluorescence quantum yield of 23.2%, the most efficient yellow-laser excitable Pdot. Due to the strong absorbance band centered at 551 nm and weak absorbance at 405 nm and 488 nm, the Pdot showed high single-particle brightness when excited by a 561 nm (yellow) laser, and selective yellow laser excitation when used to label MCF cells, with much greater brightness when excited at 561 nm than at 405 nm or 488 nm.

Aqua-friendly organometallic Ir-Pt complexes: pH-responsive AIPE-guided imaging of bacterial cells

In this work, the aggregation-induced photoluminescence emission (AIPE) of three water-soluble heterobimetallic Ir-Pt complexes was reported with insight into their photophysical and electrochemical properties and imaging of bacterial cells. An alkyne appended Schiff's base L, bridges bis-cyclometalated iridium(III) and platinum(II) terpyridine centre. The Schiff's base (N-N fragment) serves as the ancillary ligand to the iridium(III) centre, while the alkynyl end is coordinated to platinum(II). The pH and ionic strength influence the aggregation kinetics of the alkynylplatinum(II) fragment, leading to metal-metal and π-π interactions with the emergence of a triplet metal-metal-to-ligand charge transfer (³MMLCT) emission. The excellent reversibility and photostability of aggregation-induced emission (AIE) of these aqua-friendly complexes were tested for their ability to sense and selectively image E. coli cells at various pH values.

Afterglow/Fluorescence Dual-Emissive Ratiometric Oxygen Probe for Tumor Hypoxia Imaging

Hypoxia is a common feature of many diseases such as solid tumors. The measurement and imaging of oxygen (O₂) are extremely important for disease diagnosis and therapy evaluation. In this work, the afterglow/fluorescence dual-emissive ratiometric O₂ probe based on a photochemical reaction-based afterglow system is reported. The afterglow is highly sensitive to O₂ because the O₂ content is directly related to the ¹O₂ yield and eventually affects the afterglow intensity. The O₂-insensitive fluorescence of an emitter can serve as an internal reference. As the O₂ concentration changes from 0.08 to 18.5 mg L^-1, the ratio value shows a remarkable 53-fold increase. Compared with the intensity of a single peak, the ratiometric signal can eliminate the interference of the probe concentration to achieve higher accuracy. This afterglow/fluorescence dual-emissive ratiometric O₂ probe is successfully applied to hypoxia imaging in tumor-bearing mice, which may further promote the development of O₂ sensing in the biomedical field.

Persistent and Efficient Multimodal Imaging for Tyrosinase Based on Two-Photon Excited Fluorescent and Room-Temperature Phosphorescent Probes

Tyrosinase is crucial to regulate the metabolism of phenol derivatives, playing an important role in the biosynthesis of melanin pigments, whereas an abnormal level of tyrosinase would lead to severe diseases. It is rather necessary to develop a sensitive and selective imaging tool to assess the level of tyrosinase in vivo. We thoroughly researched the luminous mechanism of the existing TPTYR probe and provided design strategies to improve its two-photon excited fluorescence properties. The designed probes benza2-TPTYR and product benza2-TPTYR-coumarin have large two-photon absorption cross sections at the NIR spectral region (41 GM/706 nm, 71 GM/852 nm), while benza2-TPTYR-coumarin possesses easily distinguishable spectrum in the visible region and a high fluorescence efficiency (Φ_F = 0.27). What is more, novel two-photon excited multimodal imaging based on the pure organic small molecule benza1-TPTYR-coumarin (61 GM/936 nm) is proposed first, simultaneously possessing strong instantaneous fluorescent (563.79 nm) and persistent room-temperature phosphorescent emissions (767.68 nm, 0.54 ms).

Near Infrared Emitting Semiconductor Polymer Dots for Bioimaging and Sensing

Semiconducting polymer dots (Pdots) are rapidly becoming one of the most studied nanoparticles in fluorescence bioimaging and sensing. Their small size, high brightness, and resistance to photobleaching make them one of the most attractive fluorophores for fluorescence imaging and sensing applications. This paper highlights our recent advances in fluorescence bioimaging and sensing with nanoscale luminescent Pdots, specifically the use of organic dyes as dopant molecules to modify the optical properties of Pdots to enable deep red and near infrared fluorescence bioimaging applications and to impart sensitivity of dye doped Pdots towards selected analytes. Building on our earlier work, we report the formation of secondary antibody-conjugated Pdots and provide Cryo-TEM evidence for their formation. We demonstrate the selective targeting of the antibody-conjugated Pdots to FLAG-tagged FLS2 membrane receptors in genetically engineered plant leaf cells. We also report the formation of a new class of luminescent Pdots with emission wavelengths of around 1000 nm. Finally, we demonstrate the formation and utility of oxygen sensing Pdots in aqueous media.

Cyclometalated iridium-coumarin ratiometric oxygen sensors: improved signal resolution and tunable dynamic ranges

In this work we introduce a new series of ratiometric oxygen sensors based on phosphorescent cyclometalated iridium centers partnered with organic coumarin fluorophores. Three different cyclometalating ligands and two different pyridyl-containing coumarin types were used to prepare six target complexes with tunable excited-state energies. Three of the complexes display dual emission, with fluorescence arising from the coumarin ligand, and phosphorescence from either the cyclometalated iridium center or the coumarin. These dual-emitting complexes function as ratiometric oxygen sensors, with the phosphorescence quenched under O2 while fluorescence is unaffected. The use of blue-fluorescent coumarins results in good signal resolution between fluorescence and phosphorescence. Moreover, the sensitivity and dynamic range, measured with Stern-Volmer analysis, can be tuned two orders of magnitude by virtue of our ability to synthetically control the triplet excited-state ordering. The complex with cyclometalated iridium 3MLCT phosphorescence operates under hyperoxic conditions, whereas the two complexes with coumarin-centered phosphorescence are sensitive to very low levels of O2 and function as hypoxic sensors.

Dual-lifetime luminescent probe for time-resolved ratiometric oxygen sensing and imaging

Fluorescent/phosphorescent dual-emissive polymers or hybrids consisting of both fluorophore and phosphor have been used as self-calibrating probes and imaging reagents for cellular molecular oxygen. Oxygen selectively quenches the phosphorescence and the fluorescence serves as an internal reference. The phosphorescence/fluorescence ratio is used as a quantitative indicator of oxygen content. In wavelength-ratiometric probes, the fluorophore and phosphor are designed to emit at different wavelengths. It is easy to achieve spectral separation, but the phosphorescence/fluorescence ratio fluctuates due to the difference in the absorption and scattering of light at different wavelengths by biological samples. Herein we reported a lifetime-ratiometric luminescent polymeric probe where the fluorophore and phosphor emitted at the same wavelength. Spectral separation was achieved based on the difference in their excited-state lifetimes via time-resolved luminescence analysis and imaging. The probe exhibited a phosphorescence lifetime of about 931 ns with a phosphorescence/fluorescence ratio of 4.49 in deaerated aqueous buffer. The lifetime was shortened to 251 ns and the ratio decreased to 1.08 in oxygen saturated solution because of phosphorescence quenching. The utilization of the probe for quantitative oxygen sensing and mapping in living HeLa cells was demonstrated using calibration curves obtained from fixed cells.

Conjugated polymer nanoparticles and their nanohybrids as smart photoluminescent and photoresponsive material for biosensing, imaging, and theranostics

The emergence of conjugated polymers (CPs) has provided a pathway to attain smart multifunctional conjugated polymer nanoparticles (CPNs) with enhanced properties and diverse applications. CPNs based on π-extended CPs exhibit high fluorescence brightness, low cytotoxicity, excellent photostability, reactive oxygen species (ROS) generation ability, high photothermal conversion efficiency (PCE), etc. which endorse them as an excellent theranostic tool. Furthermore, the unique light-harvesting and energy transfer properties of CPNs enables their transformation into smart functional nanohybrids with augmented performance. Owing to such numerous features, simple preparation method and an easy separation process, the CPNs and their hybrids have been constantly rising as a frontrunner in the domain of medicine and much work has been done in the respective research area. This review summarizes the recent progress that has been made in the field of CPNs for biological and biomedical applications with special emphasis on biosensing, imaging, and theranostics. Following an introduction into the field, a first large section provides overview of the conventional as well as recently established synthetic methods for various types of CPNs. Then, the CPNs-based fluorometric assays for biomolecules based on different detection strategies have been described. Later on, examples of CPNs-based probes for imaging, both in vitro and in vivo using cancer cells and animal models have been explored. The next section highlighted the vital theranostic applications of CPNs and corresponding nanohybrids, mainly via imaging-guided photodynamic therapy (PDT), photothermal therapy (PTT) and drug delivery. The last section summarizes the current challenges and gives an outlook on the potential future trends on CPNs as advanced healthcare material.

Recent Advances in the Development and Applications of Conjugated Polymer dots

Conjugated polymer dots or semiconducting polymer nanoparticles (Pdots) are nanoparticles prepared based on organic polymers. Pdots have the advantages of lower cost, simple preparation process, good biocompatibility, excellent stability, easy...

Conjugated Polymers-based Luminescent Probes for Ratiometric Detection of Biomolecules

Accurate monitoring of the biomolecular changes in biological and physiological environments is of great significance for pathogenesis, development, diagnosis and treatment of diseases. Compared with traditional luminescent probes on the...

Advanced NIR ratiometric probes for intravital biomedical imaging

Near-infrared (NIR) fluorescence imaging technology (NIR-I region, 650-950 nm and NIR-II region, 1000-1700 nm), with deeper tissue penetration and less disturbance from auto-fluorescence than that in visible region (400-650 nm), is playing a more and more extensive role in the field of biomedical imaging. With the development of precise medicine, intelligent NIR fluorescent probes have been meticulously designed to provide more sensitive, specific and accurate feedback on detection. Especially, recently developed ratiometric fluorescent probes have been devoted to quantify physiological and pathological parameters with a combination of responsive fluorescence changes and self-calibration. Herein, we systemically introduced the construction strategies of NIR ratiometric fluorescent probes and their applications in biological imagingin vivo, such as molecular detection, pH and temperature measurement, drug delivery monitoring and treatment evaluation. We further summarized possible optimization on the design of ratiometric probes for quantitative analysis with NIR fluorescence, and prospected the broader optical applications of ratiometric probes in life science and clinical translation.

Phosphorescent NIR emitters for biomedicine: applications, advances and challenges

Application of NIR (near-infrared) emitting transition metal complexes in biomedicine is a rapidly developing area of research. Emission of this class of compounds in the "optical transparency windows" of biological tissues and the intrinsic sensitivity of their phosphorescence to oxygen resulted in the preparation of several commercial oxygen sensors capable of deep (up to whole-body) and quantitative mapping of oxygen gradients suitable for in vivo experimental studies. In addition to this achievement, the last decade has also witnessed the increased growth of successful alternative applications of NIR phosphors that include (i) site-specific in vitro and in vivo visualization of sophisticated biological models ranging from 3D cell cultures to intact animals; (ii) sensing of various biologically relevant analytes, such as pH, reactive oxygen and nitrogen species, RedOx agents, etc.; (iii) and several therapeutic applications such as photodynamic (PDT), photothermal (PTT), and photoactivated cancer (PACT) therapies as well as their combinations with other therapeutic and imaging modalities to yield new variants of combined therapies and theranostics. Nevertheless, emerging applications of these compounds in experimental biomedicine and their implementation as therapeutic agents practically applicable in PDT, PTT, and PACT face challenges related to a critically important improvement of their photophysical and physico-chemical characteristics. This review outlines the current state of the art and achievements of the last decade and stresses the most promising trends, major development prospects, and challenges in the design of NIR phosphors suitable for biomedical applications.

High-Speed and Continuous-Wave Programmable Luminescent Tags Based on Exclusive Room Temperature Phosphorescence (RTP)

Most materials recently developed for room temperature phosphorescence (RTP) lack in practical relevance due to their inconvenient crystalline morphology. Using amorphous material systems instead, programmable luminescent tags (PLTs) based on organic biluminescent emitter molecules with easy processing and smooth sample shapes are presented recently. Here, the effective quenching of the emitter's RTP by molecular oxygen (O₂ ) and the consumption of the excited singlet O₂ through a chemical reaction represent the central features. With customized activation schemes, high-resolution content can be written and later erased multiple times into such films, providing a versatile yet simple photonic platform for information storage. However, two important limitations remain: The immutable fluorescence of the emitters outshines the phosphorescent patterns by roughly one order of magnitude, allowing readout of the PLTs only after the excitation source is turned off. The programming of these systems is a rather slow process, where lowest reported activation times are still >8 s. Here, a material-focused approach to PLTs with fast activation times of 120 ± 20 ms and high-contrast under continuous-wave illumination is demonstrated, leading to accelerated programming on industry relevant time scales and a simplified readout process both by eye and low cost cameras.

Current Strategies for Tumor Photodynamic Therapy Combined With Immunotherapy

Photodynamic therapy (PDT) is a low invasive antitumor therapy with fewer side effects. On the other hand, immunotherapy also has significant clinical applications in the treatment of cancer. Both therapies, on their own, have some limitations and are incapable of meeting the demands of the current cancer treatment. The efficacy of PDT and immunotherapy against tumor metastasis and tumor recurrence may be improved by combination strategies. In this review, we discussed the possibility that PDT could be used to activate immune responses by inducing immunogenic cell death or generating cancer vaccines. Furthermore, we explored the latest advances in PDT antitumor therapy in combination with some immunotherapy such as immune adjuvants, inhibitors of immune suppression, and immune checkpoint blockade.

Ru(ii)/BODIPY core co-encapsulated ratiometric nanotools for intracellular O2 sensing in live cancer cells

Oxygen is a crucial reagent in many biochemical processes within living cells and its concentration can be an effective marker in disease, particularly in cancer where tissue hypoxia has been shown to indicate tumour growth. Probes that can reflect the oxygen concentration and distribution using ratiometric signals can be applied to a range of conventional methods without the need for specialised equipment and are particularly useful. The preparation and in cellulo study of luminescent ratiometric core–shell nanoparticles are presented. Here, a new lipophilic and oxygen-responsive Ru(ii) tris-heteroleptic polypyridyl complex is co-encapsulated with a reference BODIPY dye into the core of poly-l-lysine-coated polystyrene particles. The co-core encapsulation ensures oxygen response but reduces the impact of the environment on both probes. Single wavelength excitation of the particles, suspended in aqueous buffer, at 480 nm, triggers well-resolved dual emission from both dyes with peak maxima at 515 nm and 618 nm. A robust ratiometric oxygen response is observed from water, with a linear dynamic range of 3.6–262 μM which matches well with typical biological ranges. The uptake of RuBDP NPs was found to be cell-line dependent, but in cancerous cell lines, the particles were strongly permeable with late endosomal and partial lysosomal co-staining observed within 3 to 4 hours, eventually leading to extensive staining of the cytoplasm. The co-localisation of the ruthenium and BODIPY emission confirms that the particles remain intact in cellulo with no indication of dye leaching. The ratiometric O₂ sensing response of the particles in cellulo was demonstrated using a plate-based assay and by confocal xyλ scanning of cells exposed to hypoxic conditions.

Uptake and quantitative ratiometric oxygen sensing response of core–shell nanoparticles containing ruthenium probe and BODIPY reference is demonstrated using a plate reader-based assay and by confocal xyλ scanning of live cancer cells under hypoxic conditions.

Review: Nanomaterials for Reactive Oxygen Species Detection and Monitoring in Biological Environments

Reactive oxygen species (ROS) and dissolved oxygen play key roles across many biological processes, and fluorescent stains and dyes are the primary tools used to quantify these species in vitro. However, spatio-temporal monitoring of ROS and dissolved oxygen in biological systems are challenging due to issues including poor photostability, lack of reversibility, and rapid off-site diffusion. In particular, ROS monitoring is hindered by the short lifetime of ROS molecules and their low abundance. The combination of nanomaterials and fluorescent detection has led to new opportunities for development of imaging probes, sensors, and theranostic products, because the scaffolds lead to improved optical properties, tuneable interactions with cells and media, and ratiometric sensing robust to environmental drift. In this review, we aim to critically assess and highlight recent development in nanosensors and nanomaterials used for the detection of oxygen and ROS in biological systems, and their future potential use as diagnosis tools.

Ultrafine fluorene-pyridine oligoelectrolyte nanoparticles for supersensitive fluorescence sensing of heparin and protamine

A new fluorene-pyridine oligoelectrolyte (OFP) is rationally proposed and readily synthesized via a simple one-pot Sonogashira approach. Hence, an unexpectedly small cationic oligomer nanosensor (i.e. OFPNPs, ∼ 1.2 nm in diameter) was conveniently fabricated owing to the enhanced flexibility endowed by the meta-substituted pyridyl unit. Inspiringly, this facile nanoplatform with low cytotoxicity favors the ultrasensitive fluorescence assay for heparin and protamine with a detection limit (LOD, S/N = 3) as low as 1.2 ng mL^-1 and 0.5 ng mL^-1, respectively, involving heparin-induced aggregation of OFPNPs through electrostatic interaction or competitive rebinding of protamine to heparin.

Relaxation characteristics for efficient fluorescence lifetime detection of gain media in the fiber laser

By using different active materials as gain media, we demonstrate a system aimed to measure the fluorescence lifetime of gain media in the fiber laser by utilizing the correlation between the laser's relaxation oscillation characteristics and the fluorescence lifetime of the active materials. As the advantages of extremely compact configuration, non-destructive and real time of the system, the fluorescence lifetime of gain media composed of materials of erbium-ytterbium-doped or erbium-doped have been measured, whose results are 20.2 µs and 1.62 ms, respectively. The proposed method provides a new, to the best of our knowledge, idea for real-time monitoring of fluorescence lifetime in the fiber laser.

Photoresponsive metallopolymer nanoparticles for cancer theranostics

Over the past decades, transition metal complexes have been successfully used in anticancer phototherapies. They have shown promising properties in many different areas including photo-induced ligand exchange or release, rich excited state behavior, and versatile biochemical properties. When encorporated into polymeric frameworks and become part of nanostructures, photoresponsive metallopolymer nanoparticles (MPNs) show enhanced water solubility, extended blood circulation and increased tumor-specific accumulation, which greatly improves the tumor therapeutic effects compared to low-molecule-weight metal complexes. In this review, we aim to present the recent development of photoresponsive MPNs as therapeutic nanomedicines. This review will summarize four major areas separately, namely platinum-containing polymers, zinc-containing polymers, iridium-containing polymers and ruthenium-containing polymers. Representative MPNs of each type are discussed in terms of their design strategies, fabrication methods, and working mechanisms. Current challenges and future perspectives in this field are also highlighted.

The development of phosphorescent probes for in vitro and in vivo bioimaging

Phosphorescence is a process that slowly releases the photoexcitation energy after the removal of the excitation source. Although transition metal complexes and purely organic room-temperature phosphorescence (RTP) materials show excellent phosphorescence property, their applications in in vitro and in vivo bioimaging are limited due to their poor solubility in water. To overcome this issue, phosphorescent materials are modified with amphiphilic or hydrophilic polymers to endow them with biocompatibility. This review focuses on recent advances in the development of phosphorescent probes for in vitro and in vivo bioimaging. The photophysical mechanism and the design principles of transition metal complexes and purely organic RTP materials for the stabilization of the triplet excited state for enhanced phosphorescence are first discussed. Then, the applications in in vitro and in vivo bioimaging using transition metal complexes including iridium(iii) complexes, platinum(ii) complexes, rhodium(i) complexes, and purely organic RTP materials are summarized. Finally, the current challenges and perspectives for these emerging materials in bioimaging are discussed.

A near infrared ratiometric platform based π-extended porphyrin metal-organic framework for O2 imaging and cancer therapy

Photodynamic therapy (PDT) is widely researched in tumor treatment, but its therapeutic effect is affected by oxygen (O₂) concentration of tumor site. Here, we developed a Pd-coordinated π-conjugated extended porphyrin doped porphyrin metal-organic-framework (named as PTP). PTP can achieve near infrared (NIR) O₂ concentration ratiometric imaging, solving the problems of short detection wavelengths and influence of self-concentrations. With the NIR excitation wavelength and the ability of higher singlet oxygen (¹O₂) generation, PTP can induce PDT more effectively. The efficient PDT also mediates cancer immunogenic cell death (ICD), which combines with the immune checkpoint inhibitor αPD-1 to achieve obviously cancer suppression and anti-metastasis effect. This theranostic NIR ratiometric nanoprobe can be used as a pre-evaluation on the outcome of PDT and high-efficient cancer combined treatment system, which will find great potential in tumor diagnosis and treatment.

Recent Developments in Semiconducting Polymer Dots for Analytical Detection and NIR-II Fluorescence Imaging

In recent years, semiconducting polymer dots (Pdots) have attracted enormous attention in applications from fundamental analytical detection to advanced deep-tissue bioimaging due to their ultrahigh fluorescence brightness with excellent photostability and minimal cytotoxicity. Pdots have therefore been widely adopted for a variety types of molecular sensing for analytical detection. More importantly, the recent development of Pdots for use in the optical window between 1000 and 1700 nm, popularly known as the "second near-infrared window" (NIR-II), has emerged as a class of optical transparent imaging technology in the living body. The advantages of the NIR-II region over the traditional NIR-I (700-900 nm) window in fluorescence imaging originate from the reduced autofluorescence, minimal absorption and scattering of light, and improved penetration depths to yield high spatiotemporal images for biological tissues. Herein, we discuss and summarize the recent developments of Pdots employed for analytical detection and NIR-II fluorescence imaging. Starting with their preparation, the recent developments for targeting various analytes are then highlighted. After that, the importance of and latest progress in NIR-II fluorescence imaging using Pdots are reported. Finally, perspectives and challenges associated with the emergence of Pdots in different fields are given.

Engineering fluorescent semiconducting polymer nanoparticles for biological applications and beyond

We summarize the recent advances in engineering approaches to obtain functionalized semiconducting polymer nanoparticles (SPNs) for biological applications. The challenges and outlook of fabricating functionalized SPNs are also provided.

Nano versus Molecular: Optical Imaging Approaches to Detect and Monitor Tumor Hypoxia

Hypoxia is a ubiquitous feature of solid tumors, which plays a key role in tumor angiogenesis and resistance development. Conventional hypoxia detection methods lack continuous functional detection and are generally less suitable for dynamic hypoxia measurement. Optical sensors hereby provide a unique opportunity to noninvasively image hypoxia with high spatiotemporal resolution and enable real-time detection. Therefore, these approaches can provide a valuable tool for personalized treatment planning against this hallmark of aggressive cancers. Many small optical molecular probes can enable analyte triggered response and their photophysical properties can also be fine-tuned through structural modification. On the other hand, optical nanoprobes can acquire unique intrinsic optical properties through nanoconfinement as well as enable simultaneous multimodal imaging and drug delivery. Furthermore, nanoprobes provide biological advantages such as improving bioavailability and systemic delivery of the sensor to enhance bioavailability. This review provides a comprehensive overview of the physical, chemical, and biological analytes for cancer hypoxia detection and focuses on discussing the latest nano- and molecular developments in various optical imaging approaches (fluorescence, phosphorescence, and photoacoustic) in vivo. Finally, this review concludes with a perspective toward the potentials of these optical imaging approaches in hypoxia detection and the challenges with molecular and nanotechnology design strategies.

Photoluminescent and Chromic Nanomaterials for Anticounterfeiting Technologies: Recent Advances and Future Challenges

Counterfeiting and inverse engineering of security and confidential documents, such as banknotes, passports, national cards, certificates, and valuable products, has significantly been increased, which is a major challenge for governments, companies, and customers. From recent global reports published in 2017, the counterfeiting market was evaluated to be $107.26 billion in 2016 and forecasted to reach $206.57 billion by 2021 at a compound annual growth rate of 14.0%. Development of anticounterfeiting and authentication technologies with multilevel securities is a powerful solution to overcome this challenge. Stimuli-chromic (photochromic, hydrochromic, and thermochromic) and photoluminescent (fluorescent and phosphorescent) compounds are the most significant and applicable materials for development of complex anticounterfeiting inks with a high-security level and fast authentication. Highly efficient anticounterfeiting and authentication technologies have been developed to reach high security and efficiency. Applicable materials for anticounterfeiting applications are generally based on photochromic and photoluminescent compounds, for which hydrochromic and thermochromic materials have extensively been used in recent decades. A wide range of materials, such as organic and inorganic metal complexes, polymer nanoparticles, quantum dots, polymer dots, carbon dots, upconverting nanoparticles, and supramolecular structures, could display all of these phenomena depending on their physical and chemical characteristics. The polymeric anticounterfeiting inks have recently received significant attention because of their high stability for printing on confidential documents. In addition, the printing technologies including hand-writing, stamping, inkjet printing, screen printing, and anticounterfeiting labels are discussed for introduction of the most efficient methods for application of different anticounterfeiting inks. This review would help scientists to design and develop the most applicable encryption, authentication, and anticounterfeiting technologies with high security, fast detection, and potential applications in security marking and information encryption on various substrates.

Dual-Emissive Platinum(II) Metallacage with a Sensitive Oxygen Response for Imaging of Hypoxia and Imaging-Guided Chemotherapy

Imaging of hypoxia in vivo helps with accurate cancer diagnosis and evaluation of therapeutic outcomes. A Pt^II metallacage with oxygen-responsive red phosphorescence and steady fluorescence for in vivo hypoxia imaging and chemotherapy is reported. The therapeutic agent and diagnostic probe were integrated into the metallacage through heteroligation-directed self-assembly. Nanoformulation by encapsulating the metallacage into nanoparticles greatly enhanced its stability the in physiological environment, rendering biomedical applications feasible. Apart from enhanced red phosphorescence upon hypoxia, the ratio between red and blue emissions, which only varies with intracellular oxygen level, provides a more precise standard for hypoxia imaging and detection. Moreover, in vivo explorations demonstrate the promising potential applications of the metallacage-loaded nanoparticles as theranostic agents for tumor hypoxia imaging and chemotherapy.