Covalent Organic Framework Embedded with Magnetic Nanoparticles for MRI and Chemo-Thermotherapy

Tailored Covalent Organic Framework Platform: From Multistimuli, Targeted Dual Drug Delivery by Architecturally Engineering to Enhance Photothermal Tumor Therapy

Engineering bulk covalent organic frameworks (COFs) to access specific morphological structures holds paramount significance in boosting their functions in cancer treatment; nevertheless, scant effort has been dedicated to exploring this realm. Herein, silica core-shell templates and multifunctional COF-based reticulated hollow nanospheres (HCOFs) are novelly designed as a versatile nanoplatform to investigate the simultaneous effect of dual-drug chemotherapy and photothermal ablation. Taking advantage of the distinct structural properties of the template, the resulting two-dimensional (2D) HCOF, featuring large internal voids and a peripheral interconnected mesoporous shell, presents intriguing benefits over its bulk counterparts for cancer treatment, including a well-defined morphology, an outstanding drug loading capability (99.6%) attributed to its ultrahigh surface area (2087 m2/g), great crystallinity, improved tumor accumulation, and an adjustable drug release profile. After being loaded with hydrophilic doxorubicin with a remarkable loading capacity, the obtained drug-loaded HCOFs were coated with gold nanoparticles (Au NPs) to confer them with three properties, including pore entrance blockage, active-targeting capability, and improved biocompatibility via secondary modification, besides high near infrared (NIR) absorption for efficient photothermal hyperthermia cancer suppression. The resultant structure was functionalized with mono-6-thio-β-cyclodextrin (β-CD) as a second pocket to load docetaxel as the hydrophobic anticancer agent (combination index = 0.33). The dual-drug-loaded HCOF displayed both pH- and near-infrared-responsive on-demand drug release. In vitro and in vivo evaluations unveiled the prominent synergistic performance of coloaded HCOF in cancer elimination upon NIR light irradiation. This work opens up a new avenue for exciting applications of structurally engineered HCOFs as hydrophobic/hydrophilic drug carriers as well as multimodal treatment agents.

Enhanced Removal of Ultratrace Levels of Gold from Wastewater Using Sulfur-Rich Covalent Organic Frameworks

In view of the increasing global demand and consumption of gold, there is a growing need and effort to extract gold from alternative sources besides conventional mining, e.g., from water. This drive is mainly due to the potential benefits for the economy and the environment as these sources contain large quantities of the precious metal that can be utilized. Wastewater is one of these valuable sources in which the gold concentration can be in the ppb range. However, the effective selective recovery and recycling of ultratrace amounts of this metal remain a challenge. In this article, we describe the development of a covalent imine-based organic framework with pores containing thioanisole functional groups (TTASDFPs) formed by the condensation of a triazine-based triamine and an aromatic dialdehyde. The sulfur-functionalized pores served as effective chelating agents to bind Au3+ ions, as evidenced by the uptake of more than 99% of the 9 ppm Au3+ solution within 2 min. This is relatively fast kinetics compared with other adsorbents reported for gold adsorption. TTASDFP also showed a high removal capacity of 245 mg·g-1 and a clear selectivity toward gold ions. More importantly, the material can capture gold at concentrations as low as 1 ppb.

Hypoxia-triggered degradable porphyrinic covalent organic framework for synergetic photodynamic and photothermal therapy of cancer

Nanomedicines receive great attention in cancer treatment. Nevertheless, nonbiodegradable and long-term retention still limit their clinical translation. Herein, we successfully synthesize a hypoxia-triggered degradable porphyrinic covalent organic framework (HPCOF) for antitumor therapy in vivo. HPCOF possesses wide absorption in near infrared region (NIR) which endows HPCOF excellent photothermal conversion efficiency and photoacoustic (PA) imaging ability. Moreover, HPCOF exhibits excellent photodynamic and photothermal effect under special-wavelength laser irradiation. For the first time, the in vitro and in vivo tests demonstrate that HPCOF shows effective therapeutic effect for the combination of PDT and PTT under the monitoring of PA imaging. Importantly, in tumor region, HPCOF could be triggered by hypoxia microenvironment and collapsed gradually, then cleared from the body after treatment. This work fabricates a novel COF for cancer treatment and testifies great potential of HPCOF in clinical application with reducing long-term toxicity.

Preparation of mesoporous silica/hydroxyapatite loaded quercetin nanoparticles and research on its antibacterial properties

In this study, amino-functionalized mesoporous silica/hydroxyapatite nanoparticles (MSNS/HAP) with the property of acid dissociation have been prepared as a traditional Chinese medicine monomer carriers to improve the drug loading rate and antibacterial properties of antimicrobial quercetin (QUE) in vitro. The experimental results confirm that the drug loading rate of MSNs/HAP is 28.94 %, which is about 3.6 times higher than that of aminated mesoporous sililca nanoparticles (MSNs). The drug release of QUE on MSNs/HAP is pH-sensitive in phosphate buffered saline (pH=4.0-7.4). The above fabricated traditional Chinese medicine monomer modified nanocomposites (QUE@MSNs/HAP) displays concentration-dependent inhibitory effect, which shows better antibacterial effect than free QUE. The minimum inhibitory concentration for two tested bacteria, Staphylococcus aureus (S.aureus) and Escherichia coli (E.coli), is 256 mg·L -1. In summary, QUE@MSNs/HAP have successfully prepared, which not only improves the bio-availability of QUE, but also has acid-sensitive drug release properties. Compared with free QUE, its antibacterial performance significantly enhances, which provides a theoretical basis for the application of Chinese medicine molecules in bacterial treatment.

Defect-Engineered Tin Disulfide Nanocarriers as "Precision-Guided Projectile" for Intensive Synergistic Therapy

Nanoformulations with endogenous/exogenous stimulus-responsive characteristics show great potential in tumor cell elimination with minimal adverse effects and high precision. Herein, an intelligent nanotheranostic platform (denoted as TPZ@Cu-SnS2-x /PLL) for tumor microenvironment (TME) and near-infrared light (NIR) activated tumor-specific therapy is constructed. Copper (Cu) doping and the resulting sulfur vacancies can not only improve the response range of visible light but also improve the separation efficiency of photogenerated carriers and increase the carrier density, resulting in the ideal photothermal and photodynamic performance. Density functional theory calculations revealed that the introduction of Cu and resulting sulfur vacancies can induce electron redistribution, achieving favorable photogenerated electrons. After entering cells through endocytosis, the TPZ@Cu-SnS2-x /PLL nanocomposites show the pH responsivity property for the release of the TPZ selectively within the acidic TME, and the released Cu2+ can first interact with local glutathione (GSH) to deplete GSH with the production of Cu+ . Subsequently, the Cu+ -mediated Fenton-like reaction can decompose local hydrogen peroxide into hydroxyl radicals, which can also be promoted by hyperthermia derived from the photothermal effect for tumor cell apoptosis. The integration of photoacoustic/computed tomography imaging-guided NIR phototherapy, TPZ-induced chemotherapy, and GSH-elimination/hyperthermia enhanced chemodynamic therapy results in synergistic therapeutic outcomes without obvious systemic toxicity in vivo.

Metal-Organic Framework as a New Type of Magnetothermally-Triggered On-Demand Release Carrier

The development of external stimuli-controlled payload systems has been sought after with increasing interest toward magnetothermally-triggered drug release (MTDR) carriers due to their non-invasive features. However, current MTDR carriers present several limitations, such as poor heating efficiency caused by the aggregation of iron oxide nanoparticles (IONPs) or the presence of antiferromagnetic phases which affect their efficiency. Herein, a novel MTDR carrier is developed using a controlled encapsulation method that fully fixes and confines IONPs of various sizes within the metal-organic frameworks (MOFs). This novel carrier preserves the MOF's morphology, porosity, and IONP segregation, while enhances heating efficiency through the oxidation of antiferromagnetic phases in IONPs during encapsulation. It also features a magnetothermally-responsive nanobrush that is stimulated by an alternating magnetic field to enable on-demand drug release. The novel carrier shows improved heating, which has potential applications as contrast agents and for combined chemo and magnetic hyperthermia therapy. It holds a great promise for magneto-thermally modulated drug dosing at tumor sites, making it an exciting avenue for cancer treatment.

Covalent Organic Frameworks: Opportunities for Rational Materials Design in Cancer Therapy

Nanomedicines are extensively used in cancer therapy. Covalent organic frameworks (COFs) are crystalline organic porous materials with several benefits for cancer therapy, including porosity, design flexibility, functionalizability, and biocompatibility. This review examines the use of COFs in cancer therapy from the perspective of reticular chemistry and function-oriented materials design. First, the modification sites and functionalization methods of COFs are discussed, followed by their potential as multifunctional nanoplatforms for tumor targeting, imaging, and therapy by integrating functional components. Finally, some challenges in the clinical translation of COFs are presented with the hope of promoting the development of COF-based anticancer nanomedicines and bringing COFs closer to clinical trials.

Recent bio-applications of covalent organic framework-based nanomaterials

Appearing as a new class of functional organic materials, covalent organic frameworks (COFs) have aroused a huge wave of interest in versatile fields ever since they were first proposed in 2005. Thanks to but not limited to their ultralight weights, high surface areas, ordered channels, variable functional groups and well-defined crystal structures, the applications of COF-based biomaterials in the fields of drug loading and delivery, photodynamic therapy, photothermal therapy, bioimaging, etc. are comprehensively summarized and introduced. The existing challenges and future prospects for this emerging but hot research direction are also discussed. It is hoped that this review will serve as a guidance for future research on COFs as multifunctional bioplatforms.

Nanoscale Covalent Organic Framework with Staggered Stacking of Phthalocyanines for Mitochondria-Targeted Photodynamic Therapy

Phthalocyanine photosensitizers (PSs) have shown promise in fluorescence imaging and photodynamic therapy (PDT) of malignant tumors, but their practical application is limited by the aggregation-induced quenching (AIQ) and inherent photobleaching of PSs. Herein, we report the synthesis of a two-dimensional nanoscale covalent organic framework (nCOF) with staggered (AB) stacking of zinc-phthalocyanines (ZnPc), ZnPc-PI, for fluorescence imaging and mitochondria-targeted PDT. ZnPc-PI isolates and confines ZnPc PSs in the rigid nCOF to reduce AIQ, improve photostability, enhance cellular uptake, and increase the level of reactive oxygen species (ROS) generation via mitochondrial targeting. ZnPc-PI shows efficient tumor accumulation, which allowed precise tumor imaging and nanoparticle tracking. With high cellular uptake and tumor accumulation, intrinsic mitochondrial targeting, and enhanced ROS generation, ZnPc-PI exhibits potent PDT efficacy with >95% tumor growth inhibition on two murine colon cancer models without causing side effects.

Injectable Hydrogels Including Magnetic Nanosheets for Multidisciplinary Treatment of Hepatocellular Carcinoma via Magnetic Hyperthermia

Relapse and unresectability have become the main obstacle for further improving hepatocellular carcinoma (HCC) treatment effect. Currently, single therapy for HCC in clinical practice is limited by postoperative recurrence, intraoperative blood loss and poor patient outcomes. Multidisciplinary therapy has been recognized as the key to improving the long-term survival rate for HCC. However, the clinical application of HCC synthetic therapy is restricted by single functional biomaterials. In this study, a magnetic nanocomposite hydrogel (CG-IM) with iron oxide nanoparticle-loaded mica nanosheets (Iron oxide nanoparticles@Mica, IM) is reported. This biocompatible magnetic hydrogel integrated high injectability, magnetocaloric property, mechanical robustness, wet adhesion, and hemostasis, leading to efficient HCC multidisciplinary therapies including postoperative tumor margin treatment and percutaneous locoregional ablation. After minimally invasive hepatectomy of HCC, the CG-IM hydrogel can facilely seal the bleeding hepatic margin, followed by magnetic hyperthermia ablation to effectively prevent recurrence. In addition, CG-IM hydrogel can inhibit unresectable HCC by magnetic hyperthermia through the percutaneous intervention under ultrasound guidance.

Hydrated alginate polysaccharide fabrics grafted with sliver nanocrystals for wearable thermal and health management

The creation of functional components with precise chemistries on carbohydrate polymers is of great significance for future wearable biomedicine and health management. Among various carbohydrate polymers, marine polysaccharide featured with antimicrobial, biodegradable and biocompatible properties is an ideal platform while the water-swelling nature makes it difficult to form stable interface. Here, well-dispersed silver nanoparticles have been in-situ assembled on hydrated alginate fabric (AF), involving chemical absorption of Ag ions and in-situ reduction of conductive Ag layer. Owing to the stable complex formed between Ag ions and carboxyl groups, the Ag-grafted AF exhibits superior Joule heating capability, including low operating voltage (1-3 V), high saturation temperature (63 °C), rapid response time (25 s) and outstanding durability against harsh conditions. Furthermore, the Ag-grafted AF demonstrates noticeable inhibition against E. coli and S. aureus as compared with the pristine AF. This work provides a rational strategy for the functionalization of hydrated polysaccharide and enables wearable thermotherapy devices for human health management.

pH-Responsive doxorubicin-loaded magnetosomes for magnetic resonance-guided focused ultrasound real-time monitoring and ablation of breast cancer

MR-guided focused ultrasound surgery (MRgFUS) is driving a new direction in non-invasive thermal ablation therapy with spatial specificity and real-time temperature monitoring. Although widely used in clinical practice, it remains challenging to completely ablate the tumor margin due to fear of damaging the surrounding tissues, thus leading to low efficacy and a series of complications. Herein, we have developed novel pH-responsive drug-loading magnetosomes (STPSD nanoplatform) for increasing the T2-contrast and improved the ablation efficiency with a clinical MRgFUS system. Specifically, this STPSD nanoplatform is functionalized by pH-responsive peptides (STP-TPE), encapsulating superparamagnetic iron oxide (SPIO) and doxorubicin (DOX), which can cause drug release and SPIO deposition at the tumor site triggered by acidity and MRgFUS. Under MRgFUS treatment, the increased vascular permeability caused by hyperthermia can improve the uptake of SPIO and DOX by tumor cells, so as to enhance ultrasound energy absorption and further enhance the efficacy of chemotherapy to completely ablate tumor margins. Moreover, we demonstrated that a series of MR sequences including T2-weighted imaging (T2WI), contrast-enhanced T1WI imaging (T1WI C+), maximum intensity projection (MIP), volume rendering (VR) and ADC mapping can be further utilized to monitor the MRgFUS ablation effect in rat models. Overall, this smart nanoplatform has the capacity to be a powerful tool to promote the therapeutic MRgFUS effect and minimize the side effects to surrounding tissues.

Platinum-Based Twin Drug Modulates Tumor-Infiltrating Immune Cells to Improve Immune Checkpoint Blockade Therapy

Chemoimmunotherapy is an area of active research and development with a growing body of evidence supporting its potential benefits for the treatment of cancer. However, chemotherapy components of chemoimmunotherapy have several limitations, including systemic toxicity and poor performance in reversing the immunosuppressive tumor microenvironment. Here, we designed a twin drug, MROP, complexed with all-trans retinoic acid and oxaliplatin, and showed that the twin drug significantly enhanced the synergetic therapeutic efficacy with anti-PD-1 in a colorectal cancer mouse model. We demonstrated by mechanistic analyses of tumor tissue that the combination of anti-PD-1 and MROP induced immunogenic cell death and regulated tumor-infiltrating immune cells, including the polarization of tumor-associated macrophages toward type 1, a reduction in myeloid-derived suppressor cells, and a significant increase in the proportion of T cells, particularly CD8+ T cells. This paper provides a promising strategy for cancer treatment and new insight into the mechanism of chemoimmunotherapy.

Biodegradable covalent organic frameworks achieving tumor micro-environment responsive drug release and antitumor treatment

The emergence of nanocarriers has greatly improved the therapeutic efficacy of chemotherapeutic drugs. As emerging nanocarriers, covalent organic frameworks (COFs) have been increasingly used in biomedicine in recent years. However, due to their inherent chemical stability, existing COF nanocarriers hardly undergo in vivo degradation, which brings potential safety hazards to further applications. In this work, we introduce the azo bond into COFs. When the nanocarrier enters the cell, ˙OH generated by the coordinated Fe response to the H2O2 in the cell will break the azo bond and cause the degradation of the framework structure, accelerating the release of internally loaded DOX to effectively realize tumor treatment. We verified the degradation ability of the materials by constructing model compounds, in vitro drug release, MTT assay and antitumor experiments. Compared with the control groups, the degradable COF accelerates the release of DOX and shows a stronger killing effect on 4T1 cells. Serum biochemical analysis and H&E sections of organs show good biocompatibility for both COFs and degradation products. This work provides a new idea for the design of biodegradable COFs in vivo, and greatly explores the potential application of COF materials in the biomedical field.

Delivery of Small-Molecule Drugs and Protein Drugs by Injectable Acid-Responsive Self-Assembled COF Hydrogels for Combinatorial Lung Cancer Treatment

Covalent organic frameworks (COFs) have revealed enormous application prospects for cancer therapeutics recently, but their assembly systems face considerable challenges, such as the codelivery of hydrophobic and hydrophilic protein drugs with different physicochemical properties for in vivo delivery and release, as well as endosomal/lysosomal escape of protein drugs. To address these issues, we leveraged the high specific surface area, lipotropism, and structural tunability of boronate ester-linked COFs (COF-1) for the construction of advanced drug delivery systems. We first encapsulated the small-molecule drug doxorubicin (DOX) into a lipophilic COF (COF-1@DOX) and immobilized the functional protein drug ribonuclease A (RNase A) on the surface of the COF (RNase A-COF-1@DOX). We then created a novel composite delivery system (RNase A-COF-1@DOX gel) by cross-linking an albumin-oxygenated hydrogel (gel) network into the pores of COFs, allowing targeted codelivery of protein and small-molecule drugs in vivo. Using in-living body and multichannel fluorescence imaging, we analyzed the in vivo codelivery of protein and small-molecule drugs in a Lewis lung carcinoma (LLC) model. Finally, we applied the RNase A-COF-1@DOX gel to treat lung cancer in mice. This study paves an avenue for constructing COF-based drug delivery systems for lung cancer treatment and holds the potential to be extended to other types of cancer for more effective and targeted therapeutic treatments.

Orally delivered 2D covalent organic frameworks releasing kynurenine generate anti-inflammatory T cell responses in collagen induced arthritis mouse model

Covalent organic framework (COF) crystalline biomaterials have great potential for drug delivery since they can load large amounts of small molecules (e.g. metabolites) and release them in a controlled manner, as compared to their amorphous counterparts. Herein, we screened different metabolites for their ability to modulate T cell responses in vitro and identified Kynurenine (KyH) as a key metabolite that not only decreases frequency of pro-inflammatory RORgt + T cells but also supports frequency of anti-inflammatory GATA3+ T cells. Moreover, we developed a methodology to generate imine-based TAPB-PDA COF at room temperature and loaded these COFs with KyH. KyH loaded COFs (COF-KyH) were able to then release KyH in a controlled manner for 5 days in vitro. Notably, COF-KyH when delivered orally in mice induced with collagen-induced rheumatoid arthritis (CIA) were able to increase frequency of anti-inflammatory GATA3+CD8+ T cells in the lymph nodes and decrease antibody titers in the serum as compared to the controls. Overall, these data demonstrate that COFs can be an excellent drug delivery vehicle for delivering immune modulating small molecule metabolites.

Magnetic Covalent Organic Framework Composites for Wastewater Remediation

Covalent organic frameworks (COFs) with high specific surface area, tailored structure, easy functionalization, and excellent chemical stability have been extensively exploited as fantastic materials in various fields. However, in most cases, COFs prepared in powder form suffer from the disadvantages of tedious operation, strong tendency to agglomerate, and poor recyclability, greatly limiting their practical application in environmental remediation. To tackle these issues, the fabrication of magnetic COFs (MCOFs) has attracted tremendous attention. In this review, several reliable strategies for the fabrication of MCOFs are summarized. In addition, the recent application of MCOFs as outstanding adsorbents for the removal of contaminants including toxic metal ions, dyes, pharmaceuticals and personal care products, and other organic pollutants is discussed. Moreover, in-depth discussions regarding the structural parameters affecting the practical potential of MCOFs are highlighted in detail. Finally, the current challenges and future prospects of MCOFs in this field are provided with the expectation to boost their practical application.

Microenvironment Restruction of Emerging 2D Materials and their Roles in Therapeutic and Diagnostic Nano-Bio-Platforms

Engineering advanced therapeutic and diagnostic nano-bio-platforms (NBPFs) have emerged as rapidly-developed pathways against a wide range of challenges in antitumor, antipathogen, tissue regeneration, bioimaging, and biosensing applications. Emerged 2D materials have attracted extensive scientific interest as fundamental building blocks or nanostructures among material scientists, chemists, biologists, and doctors due to their advantageous physicochemical and biological properties. This timely review provides a comprehensive summary of creating advanced NBPFs via emerging 2D materials (2D-NBPFs) with unique insights into the corresponding molecularly restructured microenvironments and biofunctionalities. First, it is focused on an up-to-date overview of the synthetic strategies for designing 2D-NBPFs with a cross-comparison of their advantages and disadvantages. After that, the recent key achievements are summarized in tuning the biofunctionalities of 2D-NBPFs via molecularly programmed microenvironments, including physiological stability, biocompatibility, bio-adhesiveness, specific binding to pathogens, broad-spectrum pathogen inhibitors, stimuli-responsive systems, and enzyme-mimetics. Moreover, the representative therapeutic and diagnostic applications of 2D-NBPFs are also discussed with detailed disclosure of their critical design principles and parameters. Finally, current challenges and future research directions are also discussed. Overall, this review will provide cutting-edge and multidisciplinary guidance for accelerating future developments and therapeutic/diagnostic applications of 2D-NBPFs.

Recent development of pH-responsive theranostic nanoplatforms for magnetic resonance imaging-guided cancer therapy

The acidic characteristic of the tumor site is one of the most well-known features and provides a series of opportunities for cancer-specific theranostic strategies. In this regard, pH-responsive theranostic nanoplatforms that integrate diagnostic and therapeutic capabilities are highly developed. The fluidity of the tumor microenvironment (TME), with its temporal and spatial heterogeneities, makes noninvasive molecular magnetic resonance imaging (MRI) technology very desirable for imaging TME constituents and developing MRI-guided theranostic nanoplatforms for tumor-specific treatments. Therefore, various MRI-based theranostic strategies which employ assorted therapeutic modes have been drawn up for more efficient cancer therapy through the raised local concentration of therapeutic agents in pathological tissues. In this review, we summarize the pH-responsive mechanisms of organic components (including polymers, biological molecules, and organosilicas) as well as inorganic components (including metal coordination compounds, metal oxides, and metal salts) of theranostic nanoplatforms. Furthermore, we review the designs and applications of pH-responsive theranostic nanoplatforms for the diagnosis and treatment of cancer. In addition, the challenges and prospects in developing theranostic nanoplatforms with pH-responsiveness for cancer diagnosis and therapy are discussed.

A Smart Benzothiazole-Based Conjugated Polymer Nanoplatform with Multistimuli Response for Enhanced Synergistic Chemo-Photothermal Cancer Therapy

The combination of chemotherapy and phototherapy has received tremendous attention in multimodal cancer therapy. However, satisfactory therapeutic outcomes of chemo-photothermal therapy (chemo-PTT) still remain challenging. Herein, a biocompatible smart nanoplatform based on benzothiazole-linked conjugated polymer nanoparticles (CPNs) is rationally designed, for effectively loading doxorubicin (DOX) and Mo-based polyoxometalate (POM) through both dynamic chemical bond and intermolecular interactions, with an expectation to obtain new anticancer drugs with multiple stimulated responses to the tumor microenvironment (TME) and external laser irradiation. Controlled drug release of DOX from the obtained nanoformulation (CPNs-DOX-PEG-cRGD-BSA@POM) triggered by both endogenous stimulations (GSH and low pH) and exogenous laser irradiation has been well demonstrated by pharmacodynamics investigations. More intriguingly, incorporating POM into the nanoplatform not only enables the nanomedicine to achieve mild hyperthermia but also makes it exhibit self-assembly behavior in acidic TME, producing enhanced tumor retention. Benefiting from the versatile functions, the prepared CPNs-DOX-PEG-cRGD-BSA@POM exhibited excellent tumor targeting and therapeutic effects in murine xenografted models, showing great potential in practical cancer therapy.

Pt nanozyme-bridged covalent organic framework-aptamer nanoplatform for tumor targeted self-strengthening photocatalytic therapy

Covalent organic frameworks (COFs) have emerged as a promising platform for nanomedicine, while developing multifunctional COF nanoplatforms remains challenging due to the lack of efficient strategies for COF modification. Herein, we propose a nanozyme bridging (NZB) strategy for COF functionalization. Platinum nanoparticles (Pt NPs) as catalase mimics were in situ grown on the surface of COF NPs without reducing their drug loading capacity (CP), and thiol-terminated aptamer was further densely decorated onto CP NPs via a stable Pt-S bond (CPA). Pt nanozyme engineering and aptamer functionalization rendered the nanoplatform with excellent photothermal conversion, tumor targeting, and catalase-like catalytic performances. Using clinical-approved photosensitizer indocyanine green (ICG) as a model drug, we fabricated a nanosystem (ICPA) for tumor-targeted self-strengthening therapy. ICPA can effectively accumulate into tumor tissue and relieve the hypoxia microenvironment by decomposing the overexpressed H₂O₂ and generating O₂. Under monowavelength NIR light irradiation, the catalase-like catalytic and singlet oxygen generation activities of ICPA can be significantly strengthened, leading to admirable photocatalytic treatment effects against malignant cells as well as tumor-bearing mice in a self-strengthening manner.

β-Cyclodextrin Stabilized Nanoceria for Hydrolytic Cleavage of Paraoxon in Aqueous and Cationic Micellar Media

Beta-cyclodextrin (β-CD) stabilized cerium oxide nanoparticles (β-CD@CeO₂ NPs) were synthesized through a hydrothermal route. The electronic properties, surface functional group, surface composition, size, and morphologies of the as-synthesized β-CD@CeO₂ NPs were characterized using UV-visible spectroscopy, FTIR analysis, high resolution X-ray photoelectron spectroscopy (HRXPS), high resolution transmission electron microscopy (HRTEM), and field emission scanning electron microscopy (FESEM). The pH-dependent variation of the ζ-potential of β-CD@CeO₂ NPs and the catalytic activity of the NPs for the hydrolysis of paraoxon were investigated. The observed pseudo-first-order rate constant (k_obs) for the hydrolysis of paraoxon is increased with increasing pH and the ζ-potential of β-CD@CeO₂ NPs. The kinetics and mechanism of hydrolysis of paraoxon in the aqueous and cationic micellar media have been discussed.

COF-based artificial probiotic for modulation of gut microbiota and immune microenvironment in inflammatory bowel disease

Conventional strategies for treating inflammatory bowel disease merely relieve inflammation and excessive immune response, but fail to solve the underlying causes of IBD, such as disrupted gut microbiota and intestinal barrier. Recently, natural probiotics have shown tremendous potential for the treatment of IBD. However, probiotics are not recommended for IBD patients, as they may cause bacteremia or sepsis. Herein, for the first time, we constructed artificial probiotics (Aprobiotics) based on artificial enzyme-dispersed covalent organic frameworks (COFs) as the "organelle" and a yeast shell as the membrane of the Aprobiotics to manage IBD. The COF-based artificial probiotics, with the function of natural probiotics, could markedly relieve IBD by modulating the gut microbiota, suppressing intestinal inflammation, protecting the intestinal epithelial cells, and regulating immunity. This nature-inspired approach may aid in the design of more artificial systems for the treatment of various incurable diseases, such as multidrug-resistant bacterial infection, cancer, and others.

Covalent Organic Frameworks as Emerging Nonlinear Optical Materials

The vastness of organic synthetic strategies and knowledge of reticular chemistry have made covalent organic frameworks (COFs) one of the most chemically and structurally diverse class of materials with potential applications ranging from gas storage, molecular separation, and catalysis to energy storage and magnetism. Recently, this class of porous materials has garnered increasing interest as potential nonlinear optical (NLO) materials. Traditionally, inorganic crystals, small-molecule organic chromophores, and oligomers have been studied for their NLO response. Nevertheless, COFs offer significant advantages over existing NLO materials in terms of higher mechanical strength, thermochemical stability, and extended conjugation. Herein, we discuss crucial aspects, terminology, and measurement techniques related to NLO, followed by a critical analysis of the design principles for COFs with NLO response. Furthermore, we touch on selected potential applications of these NLO materials. Finally, future prospects and challenges of COFs as NLO materials are discussed.

Multifunctional nanotheranostics for near infrared optical imaging-guided treatment of brain tumors

Malignant brain tumors, a heterogeneous group of primary and metastatic neoplasms in the central nervous system (CNS), are notorious for their highly invasive and devastating characteristics, dismal prognosis and low survival rate. Recently, near-infrared (NIR) optical imaging modalities including fluorescence imaging (FLI) and photoacoustic imaging (PAI) have displayed bright prospect in innovation of brain tumor diagnoses, due to their merits, like noninvasiveness, high spatiotemporal resolution, good sensitivity and large penetration depth. Importantly, these imaging techniques have been widely used to vividly guide diverse brain tumor therapies in a real-time manner with high accuracy and efficiency. Herein, we provide a systematic summary of the state-of-the-art NIR contrast agents (CAs) for brain tumors single-modal imaging (e.g., FLI and PAI), dual-modal imaging (e.g., FLI/PAI, FLI/magnetic resonance imaging (MRI) and PAI/MRI) and triple-modal imaging (e.g., MRI/FLI/PAI and MRI/PAI/computed tomography (CT) imaging). In addition, we update the most recent progress on the NIR optical imaging-guided therapies, like single-modal (e.g., photothermal therapy (PTT), chemotherapy, surgery, photodynamic therapy (PDT), gene therapy and gas therapy), dual-modal (e.g., PTT/chemotherapy, PTT/surgery, PTT/PDT, PDT/chemotherapy, PTT/chemodynamic therapy (CDT) and PTT/gene therapy) and triple-modal (e.g., PTT/PDT/chemotherapy, PTT/PDT/surgery, PTT/PDT/gene therapy and PTT/gene/chemotherapy). Finally, we discuss the opportunities and challenges of the CAs and nanotheranostics for future clinic translation.

Biological Applications of Silica-Based Nanoparticles

Silica nanoparticles have been widely explored in biomedical applications, mainly related to drug delivery and cancer treatment. These nanoparticles have excellent properties, high biocompatibility, chemical and thermal stability, and ease of functionalization. Moreover, silica is used to coat magnetic nanoparticles protecting against acid leaching and aggregation as well as increasing cytocompatibility. This review reports the recent advances of silica-based magnetic nanoparticles focusing on drug delivery, drug target systems, and their use in magnetohyperthermia and magnetic resonance imaging. Notwithstanding, the application in other biomedical fields is also reported and discussed. Finally, this work provides an overview of the challenges and perspectives related to the use of silica-based magnetic nanoparticles in the biomedical field.

Covalent Organic Framework Nanocarriers of Singlet Oxygen for Oxygen-Independent Concurrent Photothermal/Photodynamic Therapy to Ablate Hypoxic Tumors

Photodynamic therapy (PDT) of cancers is seriously restricted by tumor hypoxia. In addition to the intrinsic hypoxic microenvironment, continuous photoirradiation further aggravates intratumoral hypoxia, thereby reducing the PDT effect significantly. Oxygen-independent PDT is recognized as an efficient approach to overcome this issue. Herein, singlet oxygen (¹ O₂ )-stored covalent organic framework (COF) nanoparticles loading the near-infrared (NIR) dye cypate, which realize oxygen-independent ¹ O₂ production for concurrent photothermal therapy (PTT) and PDT under NIR irradiation, are presented. The cypate-loading COF nanoparticles are prepared by using the photosensitizers and ¹ O₂ -stored molecules via formation of Schiff base bonds, followed by coverage of poly(vinyl pyrrolidone). The COF nanoparticles significantly improve the photostability and photothermal conversion efficiency of cypate by protecting them from photodegradation under NIR irradiation. Upon 660 nm laser irradiation, ¹ O₂ is produced by the photosensitizer motifs and is successfully stored by the ¹ O₂ -stored moieties. After intravenous injection and tumor accumulation, the COF nanoparticles can generate heat quickly upon 808 nm irradiation which induces the efficient release of the stored ¹ O₂ to ablate tumors via O₂ -independent concurrent PTT/PDT. Accordingly, the COF nanocarriers of ¹ O₂ provide a paradigm to develop O₂ -independent concurrent PTT/PDT for precise cancer treatment upon NIR irradiation.

Porous organic polymers for drug delivery: hierarchical pore structures, variable morphologies, and biological properties

Porous organic polymers have received considerable attention in recent years because of their applicability as biomaterials. In particular, their hierarchical pore structures, variable morphologies, and tunable biological properties make them suitable as drug-delivery systems. In this review, the synthetic and post forming/control methods including templated methods, template-free methods, mechanical methods, electrospun methods, and 3D printing methods for controlling the hierarchical structures and morphologies of porous organic polymers are discussed, and the different methods affecting their specific surface areas, hierarchical structures, and unique morphologies are highlighted in detail. In addition, we discuss their applications in drug encapsulation and the development of stimuli (pH, heat, light, and dual-stimuli)-responsive materials, focusing on their use for targeted drug release and as therapeutic agents. Finally, we present an outlook concerning the research directions and applications of porous polymer-based drug delivery systems.

Confining Metal-Organic Framework in the Pore of Covalent Organic Framework: A Microscale Z-Scheme System for Boosting Photocatalytic Performance

The search for building hierarchical porous materials with accelerated photo-induced electrons and charge-carrier separation is important because they hold great promise for applications in various fields. Here, a facile strategy of confining metal-organic framework (MOF) in the 1D channel of the 2D covalent organic framework (COF) to construct a novel COF@MOF micro/nanopore network is proposed. Specifically, a nitrogen-riched COF (TTA-BPDA-COF) is chosen as the platform for in-situ growth of a Co-based MOF (ZIF-L-Co) to form a TTA-BPDA-COF@ZIF-L-Co hybrid material. The hierarchical porous structure endows TTA-BPDA-COF@ZIF-L-Co with superior adsorption capacity. In addition, the integration of TTA-BPDA-COF and ZIF-L-Co forms a Z-scheme photocatalytic system, which significantly improved the redox properties and accelerated the separation of photogenerated charges and holes, achieving great improvement in photocatalytic activity. This confinement engineering strategy provides a new idea to construct a versatile molecular-material photocatalytic platform.

Facile Preparation of a Thienoisoindigo-Based Nanoscale Covalent Organic Framework with Robust Photothermal Activity for Cancer Therapy

The covalent organic frameworks (COFs) so far are usually built with small aromatic subunits, which makes their absorption spectra mainly located in the high-energy part of the visible region. In this work, we have developed a COF with a low band gap by integrating electron-deficient thienoisoindigo and electron-rich triphenylamine. The intramolecular charge-transfer effect combining the extended length of the π-conjugated backbone of COF endow it with broad absorption even to the second near-infrared region. After optimizing the solvent, a uniform size and colloidal stable COF is obtained. Benefiting from the coplanar structure of the monomer, this COF achieves a considerable photothermal conversion efficiency (PCE) of 48.2%. With these advantages, it displays convincing cancer cell killing effect upon laser irradiation in vitro or in vivo. This work provides a simple and practical method to acquire promising a COF-based phototherapy reagent that is applied in biomedicine field.

Sensitive and precise visually guided drug delivery nanoplatform with dual activation of pH and light

Controlled-release drug carriers in cancer therapy are the most ideal way to reduce toxicity and improve drug efficacy. Since light stimulation is precise and operable, most multi-stimulation response carriers utilize phototherapy to enhance release efficiency. However, phototoxicity severely limits the application of phototherapy. Herein, we designed and synthesized a Cou-ONB lipid with sensitive fluorescence feedback and multi-stimulus response. COBL liposomes prepared from Cou-ONB lipids will passively aggregate at the tumor and guide phototherapy by fluorescence. More importantly, it can reflect the drug release effect in vivo through its own sensitive fluorescence changes, further enabling precise phototherapy and reducing phototoxicity. In this paper, the multi-stimulus superimposed response and precise fluorescence-guided performance of COBL liposomes were investigated at the molecular, liposome, cellular, and animal levels. Finally, tumor treatment experiments showed that the d-COBL-UV group had the best tumor suppression effect (5.3-fold). This paper highlights a real-time fluorescence-guided multi-stimulus superposition strategy and provides a design idea to precisely implement exogenous stimuli by displaying the degree of drug release, aiming to achieve less toxic and more efficient cancer therapy through timely and precise multi-stimulation. STATEMENT OF SIGNIFICANCE: Multi-stimulus responsive drug carriers have been extensively developed in the last decade. Visual guidance is an important tool to achieve precision medicine and precise control of drug release. However, the available visualization materials are more aimed at directing stimulation at the optimal moment. There is little discussion on when to stop exogenous stimulation and how to minimize the damage of stimulation to the patient. Here, we provide a Cou-ONB lipid that not only responds to multiple stimuli, but also provides sensitive feedback on its own dissociation with a fluorescent signal so that physicians can adjust exogenous stimuli in a timely manner. This paper provides insights to facilitate precision drug delivery systems, providing viable design ideas for precise, efficient, and less toxic cancer therapies.

Theranostic applications of stimulus-responsive systems based on Fe2O3

According to the interaction of nanoparticles with biological systems, enthusiasm for nanotechnology in biomedical applications has been developed in the past decades. Fe2O3 nanoparticles, as the most stable iron oxide, have special merits that make them useful widely for detecting diseases, therapy, drug delivery, and monitoring the therapeutic process. This review presents the fabrication methods of Fe2O3-based materials and their photocatalytic and magnetic properties. Then, we highlight the application of Fe2O3-based nanoparticles in diagnosis and imaging, different therapy methods, and finally, stimulus-responsive systems, such as pH-responsive, magnetic-responsive, redox-responsive, and enzyme-responsive, with an emphasis on cancer treatment. In addition, the potential of Fe2O3 to combine diagnosis and therapy within a single particle called theranostic agent will be discussed.

Characteristic Synthesis of a Covalent Organic Framework and Its Application in Multifunctional Tumor Therapy

For decades, covalent organic frameworks (COFs) have attracted wide biomedical interest due to their unique properties including ease of synthesis, porosity, and adjustable biocompatibility. Versatile COFs can easily encapsulate various therapeutic drugs due to their extremely high payload and porosity. COFs with abundant functional groups can be surface-modified to achieve active targeting and enhance biocompatibility. In this paper, the latest developments of COFs in the biomedical field are summarized. First, the classification and synthesis of COFs are discussed. Cancer diagnosis and treatment based on COFs are studied, and the advantages and limitations of each method are discussed. Second, the specific preparation methods to obtain specific therapeutic properties are summarized. Finally, based on the combination and modification of COFs with various components, this review system summarizes different combination therapies. In addition, the main challenges faced in COF research and prospects for applying COFs to cancer diagnosis and treatment are evaluated. This review provides enlightening insights into the interdisciplinary research on COFs and applications in biomedicine, which highlight the great expectations for their further clinical transformation.

Emerging porous organic polymers for biomedical applications

This review summarizes and discusses the recent progress in porous organic polymers for diverse biomedical applications such as drug delivery, biomacromolecule immobilization, phototherapy, biosensing, bioimaging, and antibacterial applications.

Post-synthetic modifications in porous organic polymers for biomedical and related applications

Porous organic polymers (POPs) are prepared by crosslinked polymerization of multidimensional rigid aromatic building blocks. Generally, POPs can be classified into crystalline covalent organic frameworks (COFs) and other poorly crystalline or amorphous porous polymers. Due to their remarkable intrinsic properties, such as high porosity, stability, tunability, and presence of numerous building blocks, several new POPs are being developed for application across various scientific fields. The essential sensitive functional groups needed for specific applications are not sustained under harsh POP preparation conditions. The recently developed post-synthetic modification (PSM) strategies for POPs have enabled their advanced applications that are otherwise restricted. Owing to the advanced PSM strategies POPs have experienced a blossoming resurgence with diverse functions, particularly in biomedical applications, such as bioimaging tools, drugs, enzymes, gene or protein delivery systems, phototherapy, and cancer therapy. This tutorial review focuses on the recently developed PSM strategies for POPs, especially for biomedical applications, and their future perspectives as promising bioapplicable materials.

Ionic Covalent Organic Frameworks for Energy Devices

Covalent organic frameworks (COFs) are a class of porous crystalline materials whose facile preparation, functionality, and modularity have led to their becoming powerful platforms for the development of molecular devices in many fields of (bio)engineering, such as energy storage, environmental remediation, drug delivery, and catalysis. In particular, ionic COFs (iCOFs) are highly useful for constructing energy devices, as their ionic functional groups can transport ions efficiently, and the nonlabile and highly ordered all-covalent pore structures of their backbones provide ideal pathways for long-term ionic transport under harsh electrochemical conditions. Here, current research progress on the use of iCOFs for energy devices, specifically lithium-based batteries and fuel cells, is reviewed in terms of iCOF backbone-design strategies, synthetic approaches, properties, engineering techniques, and applications. iCOFs are categorized as anionic COFs or cationic COFs, and how each of these types of iCOFs transport lithium ions, protons, or hydroxides is illustrated. Finally, the current challenges to and future opportunities for the utilization of iCOFs in energy devices are described. This review will therefore serve as a useful reference on state-of-the-art iCOF design and application strategies focusing on energy devices.

Nanoscale porous organic polymers for drug delivery and advanced cancer theranostics

Finding a personalized nano theranostics solution, a nanomedicine for cancer diagnosis and therapy, is among the top challenges of current medicinal science. Porous organic polymers (POPs) are permanent porous organic materials prepared by linking relatively rigid multidimensional organic building blocks. POP nanoparticles have a remarkable advantage for cancer theranostics owing to their specific physicochemical characteristics such as high surface area, convincing pore size engineering, stimuli-responsive degradability, negligible toxicity, open covalent post-synthesis modification possibilities etc. POPs have crystalline and non-crystalline characteristics; crystalline POPs are popularly known as covalent organic frameworks (COFs), and have shown potential application across research areas in science. The early research and development on theranostics applications of nanoscale POPs has shown tremendous future potential for clinical translation. This tutorial review highlights the recently developed promising applications of nPOPs in drug loading, targeted delivery, endogenous and exogenous stimuli-responsive release, cancer imaging and combination therapy, regardless of their crystalline and poorly crystalline properties. The review will provide a platform for the future development and clinical translation of nPOPs by solving fundamental challenges of cancer nanomedicines in drug loading efficiency, size-optimization, biocompatibility, dispersibility and cell uptake ability.

A Tri-Stimuli Responsive (Maghemite/PLGA)/Chitosan Nanostructure with Promising Applications in Lung Cancer

A (core/shell)/shell nanostructure (production performance ≈ 50%, mean diameter ≈ 330 nm) was built using maghemite, PLGA, and chitosan. An extensive characterization proved the complete inclusion of the maghemite nuclei into the PLGA matrix (by nanoprecipitation solvent evaporation) and the disposition of the chitosan shell onto the nanocomposite (by coacervation). Short-term stability and the adequate magnetism of the nanocomposites were demonstrated by size and electrokinetic determinations, and by defining the first magnetization curve and the responsiveness of the colloid to a permanent magnet, respectively. Safety of the nanoparticles was postulated when considering the results from blood compatibility studies, and toxicity assays against human colonic CCD-18 fibroblasts and colon carcinoma T-84 cells. Cisplatin incorporation to the PLGA matrix generated appropriate loading values (≈15%), and a dual pH- and heat (hyperthermia)-responsive drug release behaviour (≈4.7-fold faster release at pH 5.0 and 45 °C compared to pH 7.4 and 37 °C). The half maximal inhibitory concentration of the cisplatin-loaded nanoparticles against human lung adenocarcinoma A-549 cells was ≈1.6-fold less than that of the free chemotherapeutic. Such a biocompatible and tri-stimuli responsive (maghemite/PLGA)/chitosan nanostructure may found a promising use for the effective treatment of lung cancer.

Smart magnetic resonance imaging-based theranostics for cancer

Smart theranostics are dynamic platforms that integrate multiple functions, including at least imaging, therapy, and responsiveness, in a single agent. This review showcases a variety of responsive theranostic agents developed specifically for magnetic resonance imaging (MRI), due to the privileged position this non-invasive, non-ionising imaging modality continues to hold within the clinical imaging field. Different MRI smart theranostic designs have been devised in the search for more efficient cancer therapy, and improved diagnostic efficiency, through the increase of the local concentration of therapeutic effectors and MRI signal intensity in pathological tissues. This review explores novel small-molecule and nanosized MRI theranostic agents for cancer that exhibit responsiveness to endogenous (change in pH, redox environment, or enzymes) or exogenous (temperature, ultrasound, or light) stimuli. The challenges and obstacles in the design and in vivo application of responsive theranostics are also discussed to guide future research in this interdisciplinary field towards more controllable, efficient, and diagnostically relevant smart theranostics agents.

Recent advances in covalent organic frameworks for cancer diagnosis and therapy

In recent years, the number of patients diagnosed with cancer has been soaring. Therefore, the design, development, and implementation of new approaches for the diagnosis and therapy of different types of cancers have attracted an increasing amount of attention. To date, different methods have been used for cancer diagnosis and therapy with main drawbacks in terms of severe side effects, e.g., damage to healthy cells, development of drug resistance and tumor recurrence. Therefore, there is an urgent need for the introduction and application of innovative methods. Covalent organic frameworks (COFs) are versatile materials with excellent properties in terms of biocompatibility, porous and crystalline structure, and easy functionalization. The porous structure and organic monomers in COFs allow them to load different therapeutic drugs and/or functional species efficiently. These promising properties make COFs ideal candidates for medical application, especially in cancer diagnosis and therapy. To date, many studies have focused on the design and synthesis of novel COFs while their application as diagnostic and therapeutic materials remains less understood. In this review, different synthesis and functionalization approaches of COFs were summarized. In particular, cancer diagnosis and therapy based on COFs were investigated and the advantages and limitations of each method were discussed. Most importantly, the mechanism for cancer therapy of COFs and fundamental challenges and perspectives for the application of COFs in cancer theranostics were assessed.

Imparting multi-functionality to covalent organic framework nanoparticles by the dual-ligand assistant encapsulation strategy

The potential applications of covalent organic frameworks (COFs) can be further developed by encapsulating functional nanoparticles within the frameworks. However, the synthesis of monodispersed core@shell structured COF nanocomposites without agglomeration remains a significant challenge. Herein, we present a versatile dual-ligand assistant strategy for interfacial growth of COFs on the functional nanoparticles with abundant physicochemical properties. Regardless of the composition, geometry or surface properties of the core, the obtained core@shell structured nanocomposites with controllable shell-thickness are very uniform without agglomeration. The derived bowl-shape, yolk@shell, core@satellites@shell nanostructures can also be fabricated delicately. As a promising type of photosensitizer for photodynamic therapy (PDT), the porphyrin-based COFs were grown onto upconversion nanoparticles (UCNPs). With the assistance of the near-infrared (NIR) to visible optical property of UCNPs core and the intrinsic porosity of COF shell, the core@shell nanocomposites can be applied as a nanoplatform for NIR-activated PDT with deep tissue penetration and chemotherapeutic drug delivery.

Delivery nanoplatforms based on dynamic covalent chemistry

As a paramount factor to restrict the potential action of drugs and biologics, nanoplatforms based on dynamic covalent chemistry have been demonstrated as promising candidates to fulfill the full requirements during the whole delivery process by the virtue of their remarkable features such as adaptiveness, stimuli-responsiveness, specificity, reversibility and feasibility. This contribution summarizes the latest progress in dynamic covalent bond-based nanoplatforms with improved delivery efficiency and therapeutic performance. In addition, major challenges and perspectives in this field are also discussed. We expect that this feature article will provide a valuable and systematic reference for the further development of dynamic covalent bond-based nanoplatforms.

Engineering of magnetic nanoparticles as magnetic particle imaging tracers

Magnetic particle imaging (MPI) has recently emerged as a promising non-invasive imaging technique because of its signal linearly propotional to the tracer mass, ability to generate positive contrast, low tissue background, unlimited tissue penetration depth, and lack of ionizing radiation. The sensitivity and resolution of MPI are highly dependent on the properties of magnetic nanoparticles (MNPs), and extensive research efforts have been focused on the design and synthesis of tracers. This review examines parameters that dictate the performance of MNPs, including size, shape, composition, surface property, crystallinity, the surrounding environment, and aggregation state to provide guidance for engineering MPI tracers with better performance. Finally, we discuss applications of MPI imaging and its challenges and perspectives in clinical translation.

Nanoscale Covalent Organic Frameworks with Donor-Acceptor Structure for Enhanced Photothermal Ablation of Tumors

Covalent organic frameworks (COFs) have shown great potential in catalysis and the biomedical fields, but monodisperse COFs with tunable sizes are hard to obtain. Herein, we successfully developed a series of COFs based on electron donor-acceptor strategy in mild conditions. The synthetic COFs exhibit excellent colloidal stability with uniform spherical morphology. The sizes can be flexibly adjusted by the amount of catalyst, and the absorption spectra also vary with the sizes. By changing the electron-donating ability of the monomers, the corresponding COFs possess a wide range of absorption spectra, which can be even extended to the second near-infrared biowindow. The obtained COFs possess potent photothermal activity under laser irradiation, and could inhibit the growth of tumors effectively. This work provides a strategy for the synthesis of monodisperse COFs with variable absorption for their potential applications.