Polymer-encapsulated organic nanoparticles for fluorescence and photoacoustic imaging

Dual color pH probes made from silica and polystyrene nanoparticles and their performance in cell studies

Ratiometric green-red fluorescent nanosensors for fluorometrically monitoring pH in the acidic range were designed from 80 nm-sized polystyrene (PS) and silica (SiO₂) nanoparticles (NPs), red emissive reference dyes, and a green emissive naphthalimide pH probe, analytically and spectroscopically characterized, and compared regarding their sensing performance in aqueous dispersion and in cellular uptake studies. Preparation of these optical probes, which are excitable by 405 nm laser or LED light sources, involved the encapsulation of the pH-inert red-fluorescent dye Nile Red (NR) in the core of self-made carboxylated PSNPs by a simple swelling procedure and the fabrication of rhodamine B (RhB)-stained SiO₂-NPs from a silane derivative of pH-insensitive RhB. Subsequently, the custom-made naphthalimide pH probe, that utilizes a protonation-controlled photoinduced electron transfer process, was covalently attached to the carboxylic acid groups at the surface of both types of NPs. Fluorescence microscopy studies with the molecular and nanoscale optical probes and A549 lung cancer cells confirmed the cellular uptake of all probes and their penetration into acidic cell compartments, i.e., the lysosomes, indicated by the switching ON of the green naphthalimide fluorescence. This underlines their suitability for intracellular pH sensing, with the SiO₂-based nanosensor revealing the best performance regarding uptake speed and stability.

Microdroplet-Facilitated Assembly of Thermally Activated Delayed Fluorescence-Encoded Microparticles with Non-interfering Color Signals

Encoded microparticles (EMPs) have shown demonstrative value for multiplexed high-throughput bioassays such as drug discovery and diagnostics. Herein, we propose for the first time the incorporation of thermally activated delayed fluorescence (TADF) dyes with low-cost, heavy metal-free, and long-lived luminescence properties into polymer matrices via a microfluidic droplet-facilitated assembly technique. Benefiting from the uniform droplet template sizes and polymer-encapsulated structures, the resulting composite EMPs are highly monodispersed, efficiently shield TADF dyes from singlet oxygen, well preserve TADF emission, and greatly increase the delayed fluorescence lifetime. Furthermore, by combining with phase separation of polymer blends in the drying droplets, TADF dyes with distinct luminescent colors can be spatially separated within each EMP. It eliminates optical signal interference and generates multiple fluorescence colors in a compact system. Additionally, in vitro studies reveal that the resulting EMPs show good biocompatibility and allow cells to adhere and grow on the surface, thereby making them promising optically EMPs for biolabeling.

Albumin-Consolidated AIEgens for Boosting Glioma and Cerebrovascular NIR-II Fluorescence Imaging

The application of an exogenous polymer matrix to construct aggregation-induced emission (AIE) nanoprobes promotes the utility of AIE luminogens (AIEgens) in diagnosing brain diseases. However, the limited fluorescence (FL) and low active-targeting abilities of AIE-based nanoprobes impede their imaging application. Here, we employed endogenous albumin as an effective matrix to encapsulate AIEgens to enhance FL quantum yield (QY) and active-targeting ability. The albumin-consolidated strategy effectively inhibited the intramolecular vibration of AIEgens and enhanced endocytosis mediated by the gp60 receptor. The QYs of three kinds of albumin-based AIE nanoprobes with FL emissions ranging from the visible (400-650 nm) to the second near-infrared (NIR-II, 1000-1700 nm) region was at least 10% higher, and the tumor-targeting efficiency was ∼25% higher, compared with those of nanoprobes constructed by the exogenous polymer. Albumin-based AIE nanoprobes have achieved active-targeting NIR-II imaging of brain tumors and cerebrovascular imaging with a high signal-to-background ratio (SBR, ∼90) and high resolution (∼70 μm) in mouse models. Therefore, the albumin-based AIE nanoprobes will enable FL imaging-guided surgery of brain tumors and cerebral ischemia, which will improve surgical efficacy to prevent recurrence and side effects.

Rational Design of Asymmetric Polymethines to Attain NIR(II) Bioimaging at >1100 nm

Organic molecules having emission in the NIR(II) region are emergent and receiving enormous attention. Unfortunately, attaining accountable organic emission intensity around the NIR(II) region is hampered by the dominant internal conversion operated by the energy gap law, where the emission energy gap and the associated internal reorganization energy λ_int play key roles. Up to the current stage, the majority of the reported organic NIR(II) emitters belong to those polymethines terminated by two symmetric chromophores. Such a design has proved to have a small λ_int that greatly suppresses the internal conversion. However, the imposition of symmetric chromophores is stringent, limiting further development of organic NIR(II) dyes in diversity and versatility. Here, we propose a new concept where as far as the emissive state of the any asymmetric polymethines contains more or less equally transition density between two terminated chromophores, λ_int can be as small as that of the symmetric polymethines. To prove the concept, we synthesize a series of new polymethines terminated by xanthen-9-yl-benzoic acid and 2,4-diphenylthiopyrylium derivatives, yielding AJBF1112 and AEBF1119 that reveal emission peak wavelength at 1112 and 1119 nm, respectively. The quantum yield is higher than all synthesized symmetric polymethines of 2,4-diphenylthiopyrylium derivatives (SC1162, 1182, 1185, and 1230) in this study. λ_int were calculated to be as small as 6.2 and 7.3 kcal/mol for AJBF1112 and AEBF1119, respectively, proving the concept. AEBF1119 was further prepared as a polymer dot to demonstrate its in vitro specific cellular imaging and in vivo tumor/bone targeting in the NIR(II) region.

Recent Advances of Anticancer Studies Based on Nano-Fluorescent Metal-Organic Frameworks

Nano-fluorescent metal-organic frameworks (NF-MOFs), a kind of newly emerged nano-scaled platform, can provide visual, rapid, and highly sensitive optical imaging of cancer lesions both in vitro and in vivo. Meanwhile, the excellent porosity, structural tunability, and chemical modifiability also enable NF-MOFs to achieve simultaneous loading of targeted molecules and therapeutic agents. These NF-MOFs not only possess excellent targeted imaging ability, but also can guide the carried cargos to perform precise therapy, drawing considerable attention in current framework of anticancer drug design. In this review, we outline the fluorescence types and response mechanisms of NF-MOFs, and highlight their applications in cancer diagnosis and therapy in recent years. Based on this panorama, we also discuss current issues and future trends of NF-MOFs in biomedical fields, attempting to clarify the potential value of fluorescence imaging guided anticancer investigations.

Fluorescent Multifunctional Organic Nanoparticles for Drug Delivery and Bioimaging: A Tutorial Review

Fluorescent organic nanoparticles (FONs) are a large family of nanostructures constituted by organic components that emit light in different spectral regions upon excitation, due to the presence of organic fluorophores. FONs are of great interest for numerous biological and medical applications, due to their high tunability in terms of composition, morphology, surface functionalization, and optical properties. Multifunctional FONs combine several functionalities in a single nanostructure (emission of light, carriers for drug-delivery, functionalization with targeting ligands, etc.), opening the possibility of using the same nanoparticle for diagnosis and therapy. The preparation, characterization, and application of these multifunctional FONs require a multidisciplinary approach. In this review, we present FONs following a tutorial approach, with the aim of providing a general overview of the different aspects of the design, preparation, and characterization of FONs. The review encompasses the most common FONs developed to date, the description of the most important features of fluorophores that determine the optical properties of FONs, an overview of the preparation methods and of the optical characterization techniques, and the description of the theoretical approaches that are currently adopted for modeling FONs. The last part of the review is devoted to a non-exhaustive selection of some recent biomedical applications of FONs.

Biocompatible Magnetic Conjugated Polymer Nanoparticles for Optical and Lifetime Imaging Applications in the First Biological Window

Conjugated polymers are organic semiconductors that can be used for fluorescence microscopy of living specimens. Here, we report the encapsulation of the bright-red-emitting conjugated polymer, poly[{9,9-dihexyl-2,7-bis(1-cyanovinylene)fluorenylene}-alt-co-{2,5-bis(N,N'-diphenylamino)-1,4-phenylene}] (CN-FO-DPD), and superparamagnetic iron oxide nanoparticles (SPIONs) within poly(styrene-co-maleic anhydride) (PSMA) micelles. The resulting particles exhibited an emission peak at 657 nm, a fluorescence quantum yield of 21%, an average diameter of 65 nm, and a ζ potential of -30 mV. They are taken up by cells, and we describe their use in fluorescence microscopy of living Hela cells and zebrafish embryos and their associated cytotoxicity in HEK, HeLa, and HCE cells.

NIR-II AIEgens with Photodynamic Effect for Advanced Theranostics

Phototheranostics that concurrently integrates accurate diagnosis (e.g., fluorescence and photoacoustic (PA) imaging) and in situ therapy (e.g., photodynamic therapy (PDT) and photothermal therapy (PTT)) into one platform represents an attractive approach for accelerating personalized and precision medicine. The second near-infrared window (NIR-II, 1000-1700 nm) has attracted considerable attention from both the scientific community and clinical doctors for improved penetration depth and excellent spatial resolution. NIR-II agents with a PDT property as well as other functions are recently emerging as a powerful tool for boosting the phototheranostic outcome. In this minireview, we summarize the recent advances of photodynamic NIR-II aggregation-induced emission luminogens (AIEgens) for biomedical applications. The molecular design strategies for tuning the electronic bandgaps and photophysical energy transformation processes are discussed. We also highlight the biomedical applications, such as image-guided therapy of both subcutaneous and orthotopic tumors, and multifunctional theranostics in combination with other treatment methods, including chemotherapy and immunotherapy; and the precise treatment of both tumor and bacterial infection. This review aims to provide guidance for PDT agents with long-wavelength emissions to improve the imaging precision and treatment efficacy. We hope it will provide a comprehensive understanding about the chemical structure-photophysical property-biomedical application relationship of NIR-II luminogens.

Dye-sensitized lanthanide containing nanoparticles for luminescence based applications

Due to their exceptional luminescent properties, lanthanide (Ln) complexes represent a unique palette of probes in the spectroscopic toolkit. Their extremely weak brightness due to forbidden Ln electronic transitions can be overcome by indirect dye-sensitization from the antenna effect brought by organic ligands. Despite the improvement brought by the antenna effect, (bio)analytical applications with discrete Ln complexes as luminescent markers still suffers from low sensitivity as they are limited by the complex brightness. Thus, there is a need to develop nano-objects that cumulate the spectroscopic properties of multiple Ln ions. This review firstly gives a brief introduction of the spectral properties of lanthanides both in complexes and in nanoparticles (NPs). Then, the research progress of the design of Ln-doped inorganic NPs with capping antennas, Ln-complex encapsulated NPs and Ln-complex surface functionalized NPs is presented along with a summary of the various photosensitizing ligands and of the spectroscopic properties (excited-state lifetime, brightness, quantum yield). The review also emphasizes the problems and limitations encountered over the years and the solutions provided to address them. Finally, a comparison of the advantages and drawbacks of the three types of NP is provided as well as a conclusion about the remaining challenges both in the design of brighter NPs and in the luminescence based applications.

The sound of drug delivery: Optoacoustic imaging in pharmacology

Optoacoustic (photoacoustic) imaging offers unique opportunities for visualizing biological function in vivo by achieving high-resolution images of optical contrast much deeper than any other optical technique. The method detects ultrasound waves that are generated inside tissue by thermo-elastic expansion, i.e., the conversion of light absorption by tissue structures to ultrasound when the tissue is illuminated by the light of varying intensity. Listening instead of looking to light offers the major advantage of image formation with a resolution that obeys ultrasonic diffraction and not photon diffusion laws. While the technique has been widely used to explore contrast from endogenous photo-absorbing molecules, such as hemoglobin or melanin, the use of exogenous agents can extend applications to a larger range of biological and possible clinical applications, such as image-guided surgery, disease monitoring, and the evaluation of drug delivery, biodistribution, and kinetics. This review summarizes recent developments in optoacoustic agents, and highlights new functions visualized and potent pharmacology applications enabled with the use of external contrast agents.

Sweet, Sugar-Coated Hierarchical Platinum Nanostructures for Easy Support, Heterogenization and Separation

Metal nanoparticles are increasingly gaining interest in the field of heterogeneous catalysis. Here, we present a novel strategy for synthesizing sugar-coated platinum nanostructures (SC-Pt-NS) from the carbohydrates sucrose and D(-)-fructose. In the synthesis from a mixture of H2PtCl6·6H2O, the carbohydrate in an ionic liquid (IL) yielded primary particles of a homogeneous average size of ~10 nm, which were aggregated to hierarchical Pt nanostructures of ~40–65 nm and surrounded or supported by the carbohydrate. These sugar-coated platinum nanostructures present a facile way to support and heterogenize nanoparticles, avoid leaching and enable easier separation and handling. The catalytic activity of the SC-Pt-NS was shown in the hydrosilylation test reaction of phenylacetylene with triethylsilane, where very high turnover frequency (TOF) values of up to 87,200 h−1 could be achieved, while the platinum metal leaching into the product was very low.

Design and assembly of AIE-active fluorescent organic nanoparticles for anti-counterfeiting fluorescent hydrogels and inks

Two kinds of AIE-active fluorescent organic nanoparticles were designed and constructed as anti-counterfeiting photoresponsive materials. One is fluorescent organic nanoparticles (TPELs) based on a self-assembly strategy, which were self-assembled from novel amphiphilic tetraphenylethylene (TPE) molecules decorated with a lactose moiety and different photoresponsive tags. The other is polymeric fluorescent organic nanoparticles (F-TPEs) derived from the nanoprecipitation strategy, which utilized pluronic copolymer F127 to encapsulate hydrophobic TPEs without lactosyl modifications. Upon UV light irradiation, these AIE-active materials exhibit different photooxidation behaviors in an aqueous solution to give cyan, orange and green fluorescence emissions, and they were successfully used as an anti-counterfeiting fluorescent hydrogel and ink.

In Situ Visualization of Dynamic Cellular Effects of Phospholipid Nanoparticles via High-Speed Scanning Ion Conductance Microscopy

Phospholipid nanoparticles have been actively employed for numerous biomedical applications. A key factor in ensuring effective and safe applications of these nanomaterials is the regulation of their interactions with target cells, which is significantly dependent on an in-depth understanding of the nanoparticle-cell interactions. To date, most studies investigating these nano-bio interactions have been performed under static conditions and may lack crucial real-time information. It is, however, noteworthy that the nanoparticle-cell interactions are highly dynamic. Consequently, to gain a deeper insight into the cellular effects of phospholipid nanoparticles, real-time observation of cellular dynamics after nanoparticle introduction is necessary. Herein, a proof-of-concept in situ visualization of the dynamic cellular effects of sub-100 nm phospholipid nanoparticles using high-speed scanning ion conductance microscopy (HS-SICM) is reported. It is revealed that upon introduction into the cellular environment, within a short timescale of hundreds of seconds, phospholipid nanoparticles can selectively modulate the edge motility and surface roughness of healthy fibroblast and cancerous epithelial cells. Furthermore, the dynamic deformation profiles of these cells can be selectively altered in the presence of phospholipid nanoparticles. This work is anticipated to further shed light on the real-time nanoparticle-cell interactions for improved formulation of phospholipid nanoparticles for numerous bioapplications.

Semiconducting polymer dots as fluorescent probes for in vitro biosensing

Semiconducting polymer dots (Pdots) have emerged as novel fluorescent probes with excellent characteristics, such as ultrahigh molar extinction coefficient, easy tunable absorption and emission bands, high brightness, and excellent photostability. Combined with good biocompatibility properties, much effort has been devoted to Pdots for in vivo biological imaging and therapy applications, such as deep-tissue fluorescent imaging, photodynamic therapy, photothermal therapy, and nanocarriers of genes or chemical drugs. Many reviews have been presented in these fields. On the other hand, a large number of studies employing Pdots for in vitro biosensing applications have been reported during the past few years, and there are barely any relevant reports to summarize the progress in this area. Hence, it is necessary to review these studies to promote the comprehensive application of Pdots. Herein, we introduce the properties and functionalization of Pdots, and systematically summarize the progress in the in vitro applications of Pdots, including the detection of DNAs, microRNAs, proteins, enzymatic activity, and some biological small molecules and ions. Finally, we share our perspectives on the future direction of this field.

Aggregation-induced emission (AIE)-Based nanocomposites for intracellular biological process monitoring and photodynamic therapy

As a non-invasive visualization technique, photoluminescence imaging (PLI) has found its huge value in many biological applications associated with intracellular process monitoring and early and accurate diagnosis of diseases. PLI can also be combined with therapeutics to build imaging-guided theragnostic platforms for achieving early and precise treatment of diseases. Photodynamic therapy (PDT) as a quintessential phototheranostics technology has gained great benefits from the combination with PLI. Recently, aggregation-induced emission (AIE)-active materials have emerged as one of the most promising bioimaging and phototheranostic agents. Most of AIEgens, however, need to be chemically engineered to form versatile nanocomposites with improved their photophysical property, photochemical activity, biocompatibility, etc. In this review, we focus on three categories of AIE-active nanocomposites and highlight their application progresses in the intracellular biological process monitoring and PLI-guided PDT. We hope this review can guide further development of AIE-active nanocomposites and promote their practical applications for monitoring intracellular biological processes and imaging-guided PDT.

Recent Progress Toward Imaging Application of Multifunction Sonosensitizers in Sonodynamic Therapy

Sonodynamic therapy (SDT) is a rapidly developing non-surgical therapy that initiates sensitizers’ catalytic reaction using ultrasound, showing great potential for cancer treatment due to its high safety and non-invasive nature. In addition, recent research has found that using different diagnostic and therapeutic methods in tandem can lead to better anticancer outcomes. Therefore, as essential components of SDT, sonosensitizers have been extensively explored to optimize their functions and integrate multiple medical fields. The review is based on five years of articles evaluating the combined use of SDT and imaging in treating cancer. By developing multifunctional sonosensitive particles that combine imaging and sonodynamic therapy, we have integrated diagnosis into the treatment of precision medicine applications, improving SDT cell uptake and antitumor efficacy utilizing different tumour models. This paper describes the imaging principle and the results of cellular and animal imaging of the multifunctional sonosensitizers. Efforts are made in this paper to provide data and design references for future SDT combined imaging research and clinical application development and to provide offer suggestions.

A universal strategy for the fabrication of single-photon and multiphoton NIR nanoparticles by loading organic dyes into water-soluble polymer nanosponges

The development of optical organic nanoparticles (NPs) is desirable and widely studied. However, most organic dyes are water-insoluble such that the derivatization and modification of these dyes are difficult. Herein, we demonstrated a simple platform for the fabrication of organic NPs designed with emissive properties by loading ten different organic dyes (molar masses of 479.1–1081.7 g/mol) into water-soluble polymer nanosponges composed of poly(styrene-alt-maleic acid) (PSMA). The result showed a substantial improvement over the loading of commercial dyes (3.7–50% loading) while preventing their spontaneous aggregation in aqueous solutions. This packaging strategy includes our newly synthesized organic dyes (> 85% loading) designed for OPVs (242), DSSCs (YI-1, YI-3, YI-8), and OLEDs (ADF-1–3, and DTDPTID) applications. These low-cytotoxicity organic NPs exhibited tunable fluorescence from visible to near-infrared (NIR) emission for cellular imaging and biological tracking in vivo. Moreover, PSMA NPs loaded with designed NIR-dyes were fabricated, and photodynamic therapy with these dye-loaded PSMA NPs for the photolysis of cancer cells was achieved when coupled with 808 nm laser excitation. Indeed, our work demonstrates a facile approach for increasing the biocompatibility and stability of organic dyes by loading them into water-soluble polymer-based carriers, providing a new perspective of organic optoelectronic materials in biomedical theranostic applications.

Size Optimization of Organic Nanoparticles with Aggregation-Induced Emission Characteristics for Improved ROS Generation and Photodynamic Cancer Cell Ablation

Aggregation-induced emission (AIE) fluorogens provide new opportunities to promote efficient reactive oxygen species (ROS) production in aggregates, which represent the promising candidates to construct theranostic nanoparticles for photodynamic therapy (PDT), but the size effect has been rarely explored. Herein, a universal method to fabricate organic nanoparticles with controllable sizes is reported and it demonstrates that ≈45 nm is the optimal size of AIE nanoparticles for PDT. Different from conventional Ce6 nanoparticles which show largely reduced fluorescence and ROS generation with increasing nanoparticle size, AIE nanoparticles show gradually enhanced brightness and ROS generation upon increasing the sizes from 6 to ≈45 nm. Further increasing sizes could continue to intensify the nanoparticle's brightness at the expense of ROS production, with the optimal size for ROS generation being achieved at ≈45 nm. Both 2D monolayer cell and 3D multicellular spheroid experiments confirm that 45 nm AIE nanoparticles have the highest cellular uptake, the deepest penetration depth, and the best photodynamic killing effect. Such a study not only manifests the advantages of AIE photosensitizers, but also delivers the optimal size ranging for efficient PDT, which shall provide an attractive paradigm to guide the development of phototheranostic nanoparticles besides molecular design to further promote PDT applications.

Integrated DNA triangular prism nanomachines for two-stage dynamic recognizing and bio-imaging from surface to the inside of living cells

The identification and detection of biomarkers in cancer cells play an essential role in the early detection of diseases, especially the detection of dual-biomarker. However, one of the most important limiting factors is how to realize the identification and labeling of biomarkers dynamically from the plasma membrane to the cytoplasm in living cells. In this study, integrated DNA triangular prism nanomachines (IDTPNs), a two-stage identification and dynamic bio-imaging strategy, recognize biomarkers from the plasma membrane to the cytoplasm have been designed. DNA triangular prism (DTP) was selected to act as a delivery platform with the aptamer Sgc8c and P53 modified on the side as the recognition molecules. Through the specific recognition of aptamers and the superior internalization of DTP, the IDTPNs realize the dynamic responses to PTK7 and p53 from the membrane to the cytoplasm in living cells. It is proved that the IDTPNs can be used for dynamic dual-biomarker recognition and bio-image from the surface to the inside of tumor cells automatically. Therefore, the strategy we developed provides a reliable platform for tumor diagnosis and biomarker research.

Improving Photodynamic Therapy Anticancer Activity of a Mitochondria-Targeted Coumarin Photosensitizer Using a Polyurethane-Polyurea Hybrid Nanocarrier

Integration of photosensitizers (PSs) within nanoscale delivery systems offers great potential for overcoming some of the “Achiles’ heels” of photodynamic therapy (PDT). Herein, we have encapsulated a mitochondria-targeted coumarin PS into amphoteric polyurethane–polyurea hybrid nanocapsules (NCs) with the aim of developing novel nanoPDT agents. The synthesis of coumarin-loaded NCs involved the nanoemulsification of a suitable prepolymer in the presence of a PS without needing external surfactants, and the resulting small nanoparticles showed improved photostability compared with the free compound. Nanoencapsulation reduced dark cytotoxicity of the coumarin PS and significantly improved in vitro photoactivity with red light toward cancer cells, which resulted in higher phototherapeutic indexes compared to free PS. Importantly, this nanoformulation impaired tumoral growth of clinically relevant three-dimensional multicellular tumor spheroids. Mitochondrial photodamage along with reactive oxygen species (ROS) photogeneration was found to trigger autophagy and apoptotic cell death of cancer cells.

A Facile Composite Strategy to Prepare a Biodegradable Polymer Based Radiopaque Raw Material for "Visualizable" Biomedical Implants

Enabling a biodegradable polymer radiopaque under X-ray is much desired for many medical devices. Physical blending of a present biodegradable polymer and a commercialized medical contrast agent is convenient yet lacks comprehensive fundamental research. Herein, we prepared a biodegradable polymer-based radiopaque raw material by blending poly(l-lactic acid) (PLLA or simply PLA) and iohexol (IHX), where PLA constituted the continuous phase and IHX particles served as the dispersed phase. The strong X-ray adsorption of IHX enabled the composite radiopaque; the hydrolysis of the polyester and the water solubility of the contrast agent enabled the composite biodegradable in an aqueous medium. The idea was confirmed by in vitro characterizations of the resultant composite, in vivo subcutaneous implantation in rats up to 6 months, and the clear visualization of a part of a biodegradable occluder in a Bama piglet under X-ray. We also found that the crystallization of PLA was significantly enhanced in the presence of the solid particles, which should be taken into consideration in the design of an appropriate biomaterial composite because crystallization degree influences the biodegradation rate and mechanical property of a material to a large extent. We further tried to introduce a small amount of poly(vinylpyrrolidone) into the blend of PLA and IHX. Compared to the bicomponent composite, the tricomponent one exhibited decreased modulus and increased elongation at break and tensile strength. This paves more ways for researchers to select appropriate raw materials according to the regenerated tissue and the application site.

Minimally invasive nanomedicine: nanotechnology in photo-/ultrasound-/radiation-/magnetism-mediated therapy and imaging

Traditional treatments such as chemotherapy and surgery usually cause severe side effects and excruciating pain. The emergence of nanomedicines and minimally invasive therapies (MITs) has brought hope to patients with malignant diseases. Especially, minimally invasive nanomedicines (MINs), which combine the advantages of nanomedicines and MITs, can effectively target pathological cells/tissues/organs to improve the bioavailability of drugs, minimize side effects and achieve painless treatment with a small incision or no incision, thereby acquiring good therapeutic effects. In this review, we provide a comprehensive review of the research status and challenges of MINs, which generally refers to the medical applications of nanotechnology in photo-/ultrasound-/radiation-/magnetism-mediated therapy and imaging. Additionally, we also discuss their combined application in various fields including cancers, cardiovascular diseases, tissue engineering, neuro-functional diseases, and infectious diseases. The prospects, and potential bench-to-bedside translation of MINs are also presented in this review. We expect that this review can inspire the broad interest for a wide range of readers working in the fields of interdisciplinary subjects including (but not limited to) chemistry, nanomedicine, bioengineering, nanotechnology, materials science, pharmacology, and biomedicine.

Quantifying the shape effect of plasmonic gold nanoparticles on photoacoustic conversion efficiency

Gold nanoparticles with strong localized plasmonic effects have found wide applications in photoacoustic imaging, which are ascribed to their unique microscopic mechanism of converting photons to ultrasound. In this report, we quantitatively model the time-resolved temperature field, thermal expansion, and pressure distribution based on the finite element analysis method, and two-dimensional gold nanoparticles spanning from the triangle, square, pentagon, and hexagon to the circle have been systematically studied. Results show that the shape of gold nanoparticles has a nontrivial effect on photoacoustic conversion efficiency, and the square-shaped gold structure exhibits the best performance. Our findings could shed light on the shape design of high-performance photoacoustic agents in the future.

Polymeric agents for activatable fluorescence, self-luminescence and photoacoustic imaging

Numerous polymeric agents have been widely applied in biology and medicine by virtue of the facile chemical modification, feasible nano-engineering approaches and fine-tuned pharmacokinetics. To endow polymeric imaging agents with ability to monitor and measure subtle molecular or cellular alterations at diseased sites, activatable polymeric probes that can elicit signal changes in response to biomolecular interactions or the analytes of interest have to be developed. Herein, this review aims to provide a systemic interpretation and summarization of the design methodology and imaging utility of recently emerged activatable polymeric probes. An introduction of activatable probes allowing for precise imaging and classification of polymeric imaging agents is reported first. Then, we give a detailed discussion of the contemporary design approaches toward activatable polymeric probes in diverse imaging modes for the detection of various stimuli and their imaging applications. Finally, current challenges and future advances are discussed and highlighted.

Interfaces Based on Laser-Structured Arrays of Carbon Nanotubes with Albumin for Electrical Stimulation of Heart Cell Growth

Successful formation of electronic interfaces between living cells and electronic components requires both good cell viability and performance level. This paper presents a technology for the formation of nanostructured arrays of multi-walled carbon nanotubes (MWCNT) in biopolymer (albumin) layer for higher biocompatibility. The layer of liquid albumin dispersion was sprayed on synthesized MWCNT arrays by deposition system. These nanostructures were engineered using the nanosecond pulsed laser radiation mapping in the near-IR spectral range (λ = 1064 nm). It was determined that the energy density of 0.015 J/cm² provided a sufficient structuring of MWCNT. The structuring effect occurred during the formation of C–C bonds simultaneously with the formation of a cellular structure of nanotubes in the albumin matrix. It led to a decrease in the nanotube defectiveness, which was observed during the Raman spectroscopy. In addition, laser structuring led to a more than twofold increase in the electrical conductivity of MWCNT arrays with albumin (215.8 ± 10 S/m). Successful electric stimulation of cells on the interfaces with the system based on a culture plate was performed, resulting in the enhanced cell proliferation. Overall, the MWCNT laser-structured arrays with biopolymers might be a promising material for extended biomedical applications.

Pulsed Laser Excited Photoacoustic Effect for Disease Diagnosis and Therapy

Pulsed laser can excite light absorber to generate photoacoustic (PA) effect, that is, when the absorber is irradiated with pulsed laser, the absorbed light energy is converted into local heat to cause rapid thermoelastic expansion and generate acoustic wave. The generated PA signal has been widely employed for the diagnosis of many diseases with superb contrast, high penetrability and sensitivity. In addition, with the increase of pulsed laser energy, the resulting PA shockwave and cavitation can promote efficient drug release at lesion sites to potentiate the resulting therapeutic efficacy. Furthermore, the PA shockwave/cavitation can mechanically inhibit disease and produce reactive species. In this Concept article, the principle and research status of pulsed laser excited disease theranostics are briefly summarized, extra suggestions are proposed to inspire extensive PA probes and photodynamic materials as well as novel methodologies.

Synthesis of fluorescent organic nano-dots and their application as efficient color conversion layers

Efficient conversion of light from short wavelengths to longer wavelengths using color conversion layers (CCLs) underpins the successful operation of numerous contemporary display and lighting technologies. Inorganic quantum dots, based on CdSe or InP, for example, have received much attention in this context, however, suffer from instability and toxic cadmium or phosphine chemistry. Organic nanoparticles (NPs), though less often studied, are capable of very competitive performance, including outstanding stability and water-processability. Surfactants, which are critical in stabilizing many types of nano-structures, have not yet been used extensively in organic NPs. Here we show the utility of surfactants in the synthesis and processing of organic NPs by thoroughly characterizing the effect of ionic and non-ionic surfactants on the properties of fluorescent organic NPs. Using this information, we identify surfactant processing conditions that result in nearly 100 % conversion of organic fluorophores into sub-micrometer particles, or nano-dots, with outstanding performance as CCLs. Such water dispersions are environmentally benign and efficiently convert light. They can be used for a range of fluorophores covering a full spectral gamut, with excellent color purity, including full-width at half-maximum (FWHM) values as low as 21 nm. Compared to inorganic (InP) reference CCLs, the organic nano-dot based CCLs show superior color conversion efficiency and substantially improved long-term stability.

Supramolecular self-assembly mediated aggregation-induced emission of fluorene-derived cyanostilbenes: multifunctional probes for live cell-imaging

The first discovery of aggregation-induced emission (AIE), whereby luminogen aggregation plays a positive role in enhancing the light-emission efficiency, has piqued the interest of many researchers as it opens up a new avenue for the exploration of practically beneficial luminescent materials. Diverse AIE-active luminogens (or AIEgens) with tunable emission colours and very high quantum yields (up to unity) in the solid state have been extensively utilised in a broad range of fields including optoelectronics, energy and bioscience. In this article, we describe novel fluorene-based fluorogens that exhibit bright emission in the solid-state, mechanical stimuli-responsive optical properties and aggregation-induced emissive ability, and were able to modulate their donor and acceptor properties. The target compounds were synthesized by a Knoevenagel condensation followed by Suzuki cross-coupling reaction, which tends to result in good yields. The target cyanostilbenes (4a-4d) show different reversibly switched states with high contrast through morphology modulation and demonstrate solvatochromic, vapochromic, and AIE properties. These results strongly suggest that compound 4d has better properties than the other derivatives (4a-c) due to the presence of extended donor-acceptor ability. Moreover, density-functional theory (DFT) calculations strongly support the UV-Vis and fluorescence spectral studies. The formation of nano-flakes and cuboid-shaped nanocrystals was further confirmed by FE-SEM and AFM studies. The synthesized compound 4d displayed very bright emission in the solid state and in the aggregate state as compared with the other derivatives (4a-4c). These results might be due to the presence of high-color contrast, which is an advantage for elucidation and overcomes the challenges exhibited in live-cell imaging applications. Moreover, an MTT assay on live A549 cells incubated with the target compound (4d) showed very low cytotoxicity even at high concentrations.

Threonine-Based Stimuli-Responsive Nanoparticles with Aggregation-Induced Emission-Type Fixed Cores for Detection of Amines in Aqueous Solutions

Stimuli-responsive polymeric nanoparticles (NPs) exhibit reversible changes in the dispersion or aggregation state in response to external stimuli. In this context, we designed and synthesized core-shell NPs with threonine-containing weak polyelectrolyte shells and fluorescent cross-linked cores, which are applicable for the detection of pH changes and amine compounds in aqueous solution. Stable and uniform NP(dTh) and NP(Fl), consisting of fluorescent symmetric diphenyl dithiophene (dTh) and diphenyl fluorene (Fl) cross-linked cores, were prepared by site-selective Suzuki coupling reactions in self-assembled block copolymer. NP(Fl) with the Fl unit in the core showed a high fluorescence intensity in different solvents, which is regarded as an aggregation-induced emission-type NP showing strong emission in aggregated states in the cross-linked core. Unimodal NPs were observed in water at different pH values, and the diameter of NP(Fl) changed from 122 (pH = 2) to 220 nm (pH = 11). Furthermore, pH-dependent changes of the fluorescence peak positions and intensities were detected, which may be due to the core aggregation derived from the deprotonation of the threonine-based shell fragment. Specific interactions between the threonine-based shell of NP(Fl) and amine compounds (triethylamine and p-phenylenediamine) resulted in fluorescence quenching, suggesting the feasibility of fluorescent amine detection.

Aggregation-Induced Emission Boosting the Study of Polymer Science

The past one hundred years witness the great development of polymer science. The advancement of polymer science is closely related with the developing of characterization techniques and methods, from viscometry in molecular weight determination to advanced techniques including differential scanning calorimetry, nuclear magnetic resonance and scanning electron microscopy. However, these techniques are normally constrained to tedious sample preparation, high cost, harsh experimental condition, or ex-situ characterization. Fluorescence technology has the merits of high sensitivity and direct visualization. Contrary to conventional aggregation-causing quenching fluorophores, those dyes with aggregation-induced emission characteristic show high emission efficiency in aggregate states. Based on the restriction of intramolecular motions for AIE properties, the AIE materials are very sensitive to the surrounding microenvironments owing to the twisted propeller-like structures and therefore reveal great potentials in polymer's study. The AIE concept has been successfully used in polymer's study and provides us a deeper understanding on polymer structure and properties. In this review, the applications of AIEgens in polymer science for visualizing polymerization, glass transition, dissolution, crystallization, gelation, self-assembly, phase separation, cracking and self-healing were exemplified and summarized. Lastly, the challenges and perspectives in the study of polymer science using AIEgens are addressed. This article is protected by copyright. All rights reserved.

Reasonable design of NIR AIEgens for fluorescence imaging and effective photothermal/photodynamic cancer therapy

The development of a multifunctional single molecule phototherapeutic agent with excellent fluorescence imaging, photothermal therapy and photodynamic therapy at the same time is still a challenging task, which mainly arises from the low absorbance of the molecule, and the complexity of energy dissipation and molecular design. Herein, four donor-acceptor (D-A) compounds were synthesized by linking triphenylamine (TPA), thiophene/thieno[3,2-b]thiophene and different cyano acceptor structures. In this design, we propose a molecular design strategy to redshift absorption and increase the molar extinction coefficient (ε) by enhancing electron-withdrawing acceptors and enlarging the π-conjugation plane unit. Due to the twisted structure of TPA, these compounds exhibit aggregation-induced emission (AIE) characteristics. Notably, these AIEgens have long emission wavelengths, excellent photostability, biocompatibility, photothermal stability and singlet oxygen (¹O₂) generation performance. Among them, the photothermal conversion efficiency of a compound (named TCF-SS-TPA NPs) can reach 84.5%. Cellular internalization and therapy showed that TCF-SS-TPA NPs have good biocompatibility, excellent cell bioimaging and cancer phototherapy capabilities in vitro. This study will stimulate the molecular design of multifunctional phototherapeutics to realize effective synergistic cancer therapy.

Chemical Design of Activatable Photoacoustic Probes for Precise Biomedical Applications

Photoacoustic (PA) imaging technology, a three-dimensional hybrid imaging modality that integrates the advantage of optical and acoustic imaging, has great application prospects in molecular imaging due to its high imaging depth and resolution. To endow PA imaging with the ability for real-time molecular visualization and precise biomedical diagnosis, numerous activatable molecular PA probes which can specifically alter their PA intensities upon reacting with the targets or biological events of interest have been developed. This review highlights the recent developments of activatable PA probes for precise biomedical applications including molecular detection of the biotargets and imaging of the biological events. First, the generation mechanism of PA signals will be given, followed by a brief introduction to contrast agents used for PA probe design. Then we will particularly summarize the general design principles for the alteration of PA signals and activatable strategies for developing precise PA probes. Furthermore, we will give a detailed discussion of activatable PA probes in molecular detection and biomedical imaging applications in living systems. At last, the current challenges and outlooks of future PA probes will be discussed. We hope that this review will stimulate new ideas to explore the potentials of activatable PA probes for precise biomedical applications in the future.

Monitoring Clinical-Pathological Grading of Hepatocellular Carcinoma Using MicroRNA-Guided Semiconducting Polymer Dots

MicroRNAs (miRNAs) are a class of small, noncoding RNAs involved in nearly all genetic central dogma processes and human biological behavior, which also play a significant role in the pathological activity of tumors, such as gene transcription, protein translation, and exosome secretion. Therefore, through the navigation of certain specific miRNAs, we can trace the specific physiological processes or image some specific tissues. Designing and accurately positioning microRNA (miRNA)-sensitive fluorescent nanoprobes with benign specificity and recognition in cells or tissues are a challenging research field. To solve the difficulties, we introduce four semiconducting polymer dots (Pdots) as nanoprobes linked by specific miRNA antisense sequences for monitoring the pathological grading by the variation in miRNA expression. Based on the base pairing principle, these miRNA-sensitive Pdots could bind to specific miRNAs within the cancerous cells. As impacted by the background of different pathology gradings, the proportions of the four hepatocellular carcinoma (HCC)-specific miRNAs within the cancerous cell are different, and the pathological grading of the patient tissues can be determined by comparing the palette combinations. The short single-stranded RNA-functionalized Pdots, which have excellent microRNA sensitivity, are observed in an experimental cell model and a series of tissue specimens from HCC patients for the first time. Using the Förster (or fluorescence) resonance energy transfer (FRET) model of Pdots and Cy3dt tag to simulate in vivo miRNA detection, the superior sensitivity and specificity of these nanoprobes are verified. The interference of subjective factors in traditional single/bis-dye emission intensity detection is abandoned, and multiple label staining is used to enhance sensitivity further and reduce the false-positive rate. The feasibility exhibited by this novel staining method is verified in normal hepatocellular HCC cell lines and 16 frozen ultrathin tissue sections, which are employed to quantify pathological grading-related color presentation systems for clinical doctors and pathologists' use. The intelligently designed miRNA-guided Pdots will emerge as an ideal platform with promising biological imaging.

Biosensors to Monitor Cell Activity in 3D Hydrogel-Based Tissue Models

Three-dimensional (3D) culture models have gained relevant interest in tissue engineering and drug discovery owing to their suitability to reproduce in vitro some key aspects of human tissues and to provide predictive information for in vivo tests. In this context, the use of hydrogels as artificial extracellular matrices is of paramount relevance, since they allow closer recapitulation of (patho)physiological features of human tissues. However, most of the analyses aimed at characterizing these models are based on time-consuming and endpoint assays, which can provide only static and limited data on cellular behavior. On the other hand, biosensing systems could be adopted to measure on-line cellular activity, as currently performed in bi-dimensional, i.e., monolayer, cell culture systems; however, their translation and integration within 3D hydrogel-based systems is not straight forward, due to the geometry and materials properties of these advanced cell culturing approaches. Therefore, researchers have adopted different strategies, through the development of biochemical, electrochemical and optical sensors, but challenges still remain in employing these devices. In this review, after examining recent advances in adapting existing biosensors from traditional cell monolayers to polymeric 3D cells cultures, we will focus on novel designs and outcomes of a range of biosensors specifically developed to provide real-time analysis of hydrogel-based cultures.

Gadolinium and Polythiophene Functionalized Polyurea Polymer Dots as Fluoro-Magnetic Nanoprobes

A rapid and one-pot synthesis of poly 3-thiopheneacetic acid (PTAA) functionalized polyurea polymer dots (Pdots) using polyethyleneimine and isophorone diisocyanate is reported. The one-pot mini-emulsion polymerization technique yielded Pdots with an average diameter of ~20 nm. The size, shape, and concentration of the surface functional groups could be controlled by altering the synthesis parameters such as ultrasonication time, concentration of the surfactant, and crosslinking agent, and the types of isocyanates utilized for the synthesis. Colloidal properties of Pdots were characterized using dynamic light scattering and zeta potential measurements. The spherical geometry of Pdots was confirmed by scanning electron microscopy. The Pdots were post-functionalized by 1,4,7,10 tetraazacyclododecane-1,4,7,10-tetraacetic acid for chelating gadolinium nanoparticles (Gd³⁺) that provide magnetic properties to the Pdots. Thus, the synthesized Pdots possess fluorescent and magnetic properties, imparted by PTAA and Gd³⁺, respectively. Fluorescence spectroscopy and microscopy revealed that the synthesized dual-functional Gd³⁺-Pdots exhibited detectable fluorescent signals even at lower concentrations. Magnetic levitation experiments indicated that the Gd³⁺-Pdots could be easily manipulated via an external magnetic field. These findings illustrate that the dua- functional Gd³⁺-Pdots could be potentially utilized as fluorescent reporters that can be magnetically manipulated for bioimaging applications.

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.

Understanding the solid state luminescence and piezochromic properties in polymorphs of an anthracene derivative

Luminescent molecular crystals have gained significant research interest for optoelectronic applications. However, fully understanding their structural and electronic relationships in the condensed phase and under external stimuli remains a significant challenge. Here, piezochromism in the molecular crystal 9,10-bis((E)-2-(pyridin-4-yl)vinyl)anthracene (BP4VA) is studied using a combination of density functional theory (DFT) and time-dependent TD-DFT. We investigate the effects that molecular packing and geometry have on the electronic and phonon structure and the excited state properties in this archetypal system. We find that the luminescence properties are red-shifted with the transition from a herringbone to a sheet packing arrangement. An almost continuous red-shift in the band gap is found with the application of an external pressure through the enhancement of π-π and CH-π interactions, and is a mechanism in fine tuning an emissive response. The analysis of the phonon structure of the molecular crystal suggests restriction of motion in the herringbone packing arrangement, with motion restricted at higher pressure. This is supported by the Huang-Rhys factors which show a decrease in the reorganisation energy with the application of pressure. Ultimately, a balance between the decrease in reorganisation energies and the increase in exciton coupling will determine whether nonradiative decay is enhanced or decreased with the increase in pressure in these systems.

Exogenous Contrast Agents in Photoacoustic Imaging: An In Vivo Review for Tumor Imaging

The field of cancer theranostics has grown rapidly in the past decade and innovative ‘biosmart’ theranostic materials are being synthesized and studied to combat the fast growth of cancer metastases. While current state-of-the-art oncology imaging techniques have decreased mortality rates, patients still face a diminished quality of life due to treatment. Therefore, improved diagnostics are needed to define in vivo tumor growths on a molecular level to achieve image-guided therapies and tailored dosage needs. This review summarizes in vivo studies that utilize contrast agents within the field of photoacoustic imaging—a relatively new imaging modality—for tumor detection, with a special focus on imaging and transducer parameters. This paper also details the different types of contrast agents used in this novel diagnostic field, i.e., organic-based, metal/inorganic-based, and dye-based contrast agents. We conclude this review by discussing the challenges and future direction of photoacoustic imaging.