Near-Infrared Afterglow Semiconducting Nano-Polycomplexes for the Multiplex Differentiation of Cancer Exosomes

Recent advances in nanomaterial-based biosensors for the detection of exosomes

Exosomes are a type of extracellular vesicle actively secreted by almost all eukaryotic cells. They are ideal candidates for reliable next-generation biomarkers in the early diagnosis and therapeutic response evaluation of cancer. Thus, the quantification of exosomes is crucial in facilitating clinical research and application. Compared with traditional materials, nanomaterials have better optical, magnetic, electrical, and catalytic properties due to their small size, high specific surface area, and variable structure. The incorporation of nanomaterials into sensing systems is an attractive approach towards improving sensitivity and can provide improved sensor selectivity and stability. In this paper, we summarize the progress in nanomaterial-based exosome detection methods, including electrochemical biosensors, photoelectrochemical biosensors, colorimetric biosensors, fluorescence biosensors, chemiluminescence biosensors, electrochemiluminescence biosensors, surface plasmon resonance biosensors, and surface-enhanced Raman spectroscopy biosensors. Moreover, future research directions and challenges in exosome detection methods are discussed. We hope that this article will offer an overview of nanomaterial-based exosome detection techniques and open new avenues in disease research.Graphical abstract.

Recent Progress on the Isolation and Detection Methods of Exosomes

Exosomes are known as one of extracellular vesicles, which are found in various body fluids and released by cells. As transport carrier, exosomes participate actively in intercellular communication and reflect their characteristics uniquely to the origin cells. Due to their unique biological physical properties and physiological functions, exosomes are considered to be one of best biomarkers of cancer diagnosis. At the same time, exosomes are potential therapeutic targets and drug delivery carriers. Therefore, the characteristics, functions and analytical methods of exosomes have increasingly attracted wide attention among scientists. In this review, the recent research progress on the basic characteristics and functional applications of exosomes are summarized. Furthermore and importantly, this review focuses on the recent advance in the purification and test methods of exosomes in recent years. Finally, issues pertaining to exosome detection are presented. Based on newly discovered characteristic of exosomes, the opportunities and challenges for future research of the purification and quantitative detection methods are outlined.

Ultra-stable tellurium-doped carbon quantum dots for cell protection and near-infrared photodynamic application

It is important to regulate the concentration of reactive oxygen species (ROS) in cells since they play important roles in metabolism. Thus, developing nanoreagents to control the ROS is critical. Herein, tellurium-doped carbon quantum dots (Te-CDs) were developed by a simple and efficient hydrothermal method, which can scavenge H₂O₂ to protect cells under ambient condition, but generate ·OH under 808 nm irradiation as photodynamic application. This contribution presented a kind of novel CDs with dual-functions, which can potentially regulate ROS under different conditions.

Exosome-Mimetic Supramolecular Vesicles with Reversible and Controllable Fusion and Fission*

The fusion and fission behaviors of exosomes are essential for the cell-to-cell communication. Developing exosome-mimetic vesicles with such behaviors is of vital importance, but still remains a big challenge. Presented herein is an artificial supramolecular vesicle that exhibits redox-modulated reversible fusion-fission functions. These vesicles tend to fuse together and form large-sized vesicles upon oxidation, undergo a fission process and then return to small-sized vesicles through reduction. Noteworthy, the aggregation-induced emission (AIE) characteristics of the supramolecular building blocks enable the molecular configuration during vesicular transformation to be monitored by fluorescence technology. Moreover, the presented vesicles are excellent nanocarrier candidates to transfer siRNA into cancer cells.

Nanozyme-assisted sensitive profiling of exosomal proteins for rapid cancer diagnosis

The proteins expressed on exosomes have emerged as promising liquid-biopsy biomarkers for cancer diagnosis. However, molecular profiling of exosomal proteins remains technically challenging. Herein, we report a nanozyme-assisted immunosorbent assay (NAISA) that enables sensitive and rapid multiplex profiling of exosomal proteins. This NAISA system is based on the installation of peroxidase-like nanozymes onto the phospholipid membranes of exosomes, thus avoiding the need for post-labelling detection antibodies. The exosomal proteins are determined by a sensitive nanozyme-catalyzed colorimetric assay less than 3 h, without the need for multi-step incubation and washing operations. Using NAISA to profile exosomal proteins from different cell lines and clinical samples, we reveal that tumor-associated exosomal proteins can serve as promising biomarkers for accurate cancer diagnosis in a cooperative detection pattern. Methods: Exosomes were engineered with DSPE-PEG-SH through hydrophobic interaction, and then were assembled with gold nanoparticles (2 nm) to produce Exo@Au nanozyme. The proteins on Exo@Au could be selectively captured by their specific antibodies seeded into a 96-well plate. The immobilized Exo@Au shows peroxidase-like activity to perform colorimetric assays by reaction with 3,3',5,5'-tetramethylbenzidine (TMB) and H₂O₂. The protein levels of exosomes were recorded on a microplate reader. Results: The NAISA platform is capable of profiling multiple exosomal proteins from both cancer cell lines and clinical samples. The expression levels of exosomal proteins, such as CD63, CEA, GPC-3, PD-L1 and HER2, were used to classify different cancer cell lines. Moreover, the protein profiles have been applied to differentiate healthy donors, hepatitis B patients, and hepatic cell carcinoma (HCC) patients with high accuracy. Conclusion: The NAISA nanozyme was allowed to rapidly profile multiple exosomal proteins and could have great promise for early HCC diagnosis and identification of other cancer types.

Grafted semiconducting polymer amphiphiles for multimodal optical imaging and combination phototherapy

Semiconducting polymer nanoparticles (SPNs) have gained growing attention in biomedical applications. However, the preparation of SPNs is usually limited to nanoprecipitation in the presence of amphiphilic copolymers, which encounters the issue of dissociation. As an alternative to SPNs, grafted semiconducting polymer amphiphiles (SPAs) composed of a semiconducting polymer (SP) backbone and hydrophilic side chains show increased physiological stability and improved optical properties. This review summarizes recent advances in SPAs for cancer imaging and combination phototherapy. The applications of SPAs in optical imaging including fluorescence, photoacoustic, multimodal and activatable imaging are first described, followed by the discussion of applications in imaging-guided phototherapy and combination therapy, light-triggered drug delivery and gene regulation. At last, the conclusion and future prospects in this field are discussed.

A portable point-of-care testing system to diagnose lung cancer through the detection of exosomal miRNA in urine and saliva

A lung cancer diagnostic kit (LCDK) with the advantages of low cost, easy operation and high sensitivity for the rapid diagnosis of lung cancer was developed. The proposed LCDK is able to noninvasively discriminate lung cancer using clinical salivary and urine samples in a short period of time.

Hydrophobic Plasmonic Nanoacorn Array for a Label-Free and Uniform SERS-Based Biomolecular Assay

A surface-enhanced Raman scattering (SERS) aptasensor based on a hydrophobic assembled nanoacorn (HANA) was developed with improved reproducibility and reduced nonspecific binding effect. In the fabrication process, a hexagonal-packed gold film over nanosphere (AuFON) arrays was first obtained and used as a hydrophobic plasmonic substrate. Then, a uniform sub-3 nm molecular spacer array (containing Raman reporters) was prepared by patterning nanometric hydrophilic ultrathin patches onto the hydrophobic AuFON, in which the hydrophilic thin layer is composed of polymers and aptamers. During the sensing process, the HANA aptasensor smartly impedes the adsorption of SERS probes as Au@Ag nanocubes (Au@Ag NCs) in the absence of targets. In the presence of targets, the displacement of aptamers occurs due to the specific interaction between the targets and the aptamers, and the Au@Ag NCs can be assembled onto the hydrophilic patches on AuFON through electrostatic interactions with polymers. Thus, SERS signals of reporter molecules inside the spacer can be dramatically enhanced due to the formation of a nanoparticle-on-mirror (NPoM) array. In such a SERS aptasensor, the well-ordered distribution of SERS probes ensures excellent repeatability, while the precise subnanometer junctions guarantee high sensitivity. More importantly, since the hydrophobic surface can greatly reduce nonspecific adsorption, the tedious process of nonspecific blocking that is employed in traditional biosensors is no longer needed. Using such a SERS HANA platform, human epidermal growth factor receptor 2 (HER2) and three exosomal proteins were analyzed with high sensitivity and good reproducibility (RSD < 7%) in whole-blood samples.

Urine biopsy technologies: Cancer and beyond

Since the discovery of circulating tumor cells in 1869, technological advances in the study of biomarkers from liquid biopsy have made it possible to diagnose disease in a less invasive way. Although blood-based liquid biopsy has been used extensively for the detection of solid tumors and immune diseases, the potential of urine-based liquid biopsy has not been fully explored. Advancements in technologies for the harvesting and analysis of biomarkers are providing new opportunities for the characterization of other disease types. Liquid biopsy markers such as exfoliated bladder cancer cells, cell-free DNA (cfDNA), and exosomes have the potential to change the nature of disease management and care, as they allow a cost-effective and convenient mode of patient monitoring throughout treatment. In this review, we addressed the advancement of research in the field of disease detection for the key liquid biopsy markers such as cancer cells, cfDNA, and exosomes, with an emphasis on urine-based liquid biopsy. First, we highlighted key technologies that were widely available and used extensively for clinical urine sample analysis. Next, we presented recent technological developments in cell and genetic research, with implications for the detection of other types of diseases, besides cancer. We then concluded with some discussions on these areas, emphasizing the role of microfluidics and artificial intelligence in advancing point-of-care applications. We believe that the benefits of urine biopsy provide diagnostic development potential, which will pave opportunities for new ways to guide treatment selections and facilitate precision disease therapies.

Optical, electrochemical and electrical (nano)biosensors for detection of exosomes: A comprehensive overview

Exosomes are small extracellular vesicles involved in many physiological activities of cells in the human body. Exosomes from cancer cells have great potential to be applied in clinical diagnosis, early cancer detection and target identification for molecular therapy. While this field is gaining increasing interests from both academia and industry, barriers such as supersensitive detection techniques and highly-efficient isolation methods remain. In the clinical settings, there is an urgent need for rapid analysis, reliable detection and point-of-care testing (POCT). With these challenges to be addressed, this article aims to review recent developments and technical breakthroughs including optical, electrochemical and electrical biosensors for exosomes detection in the field of cancer and other diseases and demonstrate how nanobiosensors could enhance the performance of conventional sensors. Working strategies, limit of detections, advantages and shortcomings of the studies are summarized. New trends, challenges and future perspectives of exosome-driven POCT in liquid biopsy have been discussed.

Recent advances of aptasensors for exosomes detection

Exosomes are nanoscale phospholipid bilayer membrane-enclosed vesicles released from cells with diameters of 30-150 nm. Their contents reflect significant information regarding the cancer microenvironment from their parent cells, which attracts increasing attention as potential biomarkers for noninvasive early diagnosis. Among their detection methods, aptasensor has been becoming an attractive star with its properties of affordability, easy to use, fast response, high sensitivity, remarkable specificity, and multiplexing capability. This review mainly summarizes the recent advances of single-stranded DNA (ssDNA) aptamer-based sensors for cancer and tumor-derived exosomes detection. Firstly, we present a brief overview of aptamers and exosomes. Then, we introduce the exosomal proteins used as potential biomarkers of various cancers, and their specific ssDNA aptamers used in aptasensors. We emphasize eight major types of aptasensors: fluorescent, electrochemical, colorimetric, luminescence, lateral flow strips, surface-enhanced Raman scattering, surface plasmon resonance, and giant magnetoresistance sensors, based on fabrication methods, bio-recognition mechanism, as well as detection evaluation. The future directions and challenges are finally proposed for aptamers and their more applications in exosomes research.

Exosomal biomarkers for cancer diagnosis and patient monitoring

Introduction: In recent years, extensive research has been conducted on using exosomes as biomarkers for cancer detection. Exosomes are 40-150 nm-sized extracellular vesicles released by all cell types, including tumor cells. Exosomes are stable in body fluids due to their lipid bilayer member and often contain DNA, RNA, and proteins. These exosomes can be harvested from blood, plasma, serum, urine, or saliva and analyzed for tumor-relevant mutations. Thus, exosomes provide an alternative to current methods of tumor detection.Areas covered: This review discusses the use of exosomal diagnostics in various tumor types as well as their examination in various clinical trials. The authors also discuss the limitations of exosome-based diagnostics in the clinical setting and provide examples of several studies in which the development and usage of microfluidic chips and nano-sensing devices have been utilized to address these obstacles.Expert commentary: In recent years, exosomes and their contents have exhibited potential as novel tumor detection markers despite the labor involved in their harvest and isolation. Despite this, much work is being done to optimize exosome capture and analysis. Thus, their roles as biomarkers in the clinical setting appear promising.

Extracellular vesicle tetraspanin-8 level predicts distant metastasis in non-small cell lung cancer after concurrent chemoradiation

Non-small cell lung cancer (NSCLC) is the most commonly diagnosed cancer and the leading cause of cancer death worldwide. More than half of patients with NSCLC die after developing distant metastases, so rapid, minimally invasive prognostic biomarkers are needed to reduce mortality. We used proteomics to identify proteins differentially expressed on extracellular vesicles (EVs) of nonmetastatic 393P and metastatic 344SQ NSCLC cell lines and found that tetraspanin-8 (Tspan8) was selectively enriched on 344SQ EVs. NSCLC cell lines treated with EVs overexpressing Tspan8 also exhibited increased Matrigel invasion. Elevated Tspan8 expression on serum EVs of individuals with stage III premetastatic NSCLC tumors was also associated with reduced distant metastasis-free survival, suggesting that Tspan8 levels on serum EVs may predict future metastasis. This result suggests that a minimally invasive blood test to analyze EV expression of Tspan8 may be of potential value to guide therapeutic decisions for patients with NSCLC and merits further study.

A nature-inspired colorimetric and fluorescent dual-modal biosensor for exosomes detection

As non-invasive biomarkers, exosomes are of great significance to diseases diagnosis. However, sensitive and accurate detection of exosomes still remains technical challenges. Herein, inspired by nature's "one-to-many" concept, we design a biosensor mimicking the cactus with numerous thorns to detect exosomes. The biosensor is composed of CD63 antibodies, resembling the roots of cactus, to capture exosomes, and the exosomes resemble the stems. Cholesterol-labeled DNA (DNA anchor) binding to streptavidin modified horseradish peroxidase (HRP) can insert into exosomes membrane, which seems the thorns. The readout signal is produced through HRP-catalyzed hydrogen peroxide (H₂O₂) mediated oxidation of 1,4-phenylenediamine (PPD) to form 2,5-diamino-NN'-bis-(p-aminophenyl)-1,4-benzoquinone di-imine (PPDox). The PPDox can quench fluorescence of fluorescein through inner filter effect (IFE), which provides fluorescent signal for exosomes detection. Based on this principle, the obtained exosomes solution is qualitatively and quantitatively analyzed by our biosensor, with the comparison to current standard methods by nanoparticle tracking analysis (NTA) and commercial enzyme-linked immunosorbent assay (ELISA) kit. The linear range is from 1.0 × 10⁴ to 5.0 × 10⁵ particles μL^-1 with the limit of detection 3.40 × 10³ particles μL^-1 and 3.12 × 10³ particles μL^-1 for colorimetric and fluorescent assays, respectively. Meanwhile, our biosensor exhibits good selectivity, and can eliminate the interference from proteins. This dual-modal biosensor shows favorable performance towards analytical application in clinic samples, pushing one step further towards practical clinical use.

Synthetic Applications of Oxidative Aromatic Coupling-From Biphenols to Nanographenes

Oxidative aromatic coupling occupies a fundamental place in the modern chemistry of aromatic compounds. It is a method of choice for the assembly of large and bewildering architectures. Considerable effort was also devoted to applications of the Scholl reaction for the synthesis of chiral biphenols and natural products. The ability to form biaryl linkages without any prefunctionalization provides an efficient pathway to many complex structures. Although the chemistry of this process is only now becoming fully understood, this reaction continues to both fascinate and challenge researchers. This is especially true for heterocoupling, that is, oxidative aromatic coupling with the chemoselective formation of a C-C bond between two different arenes. Analysis of the progress achieved in this field since 2013 reveals that many groups have contributed by pushing the boundary of structural possibilities, expanding into surface-assisted (cyclo)dehydrogenation, and developing new reagents.

H2S-activatable near-infrared afterglow luminescent probes for sensitive molecular imaging in vivo

Afterglow luminescent probes with high signal-to-background ratio show promise for in vivo imaging; however, such probes that can be selectively delivered into target sites and switch on afterglow luminescence remain limited. We optimize an organic electrochromic material and integrate it into near-infrared (NIR) photosensitizer (silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) and (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]) containing nanoparticles, developing an H2S-activatable NIR afterglow probe (F12+-ANP). F12+-ANP displays a fast reaction rate (1563 ± 141 M-1 s-1) and large afterglow turn-on ratio (~122-fold) toward H2S, enabling high-sensitivity and -specificity measurement of H2S concentration in bloods from healthy persons, hepatic or colorectal cancer patients. We further construct a hepatic-tumor-targeting and H2S-activatable afterglow probe (F12+-ANP-Gal) for noninvasive, real-time imaging of tiny subcutaneous HepG2 tumors (<3 mm in diameter) and orthotopic liver tumors in mice. Strikingly, F12+-ANP-Gal accurately delineates tumor margins in excised hepatic cancer specimens, which may facilitate intraoperative guidance of hepatic cancer surgery.

Biosensing extracellular vesicles: contribution of biomolecules in affinity-based methods for detection and isolation

Extracellular Vesicles (EVs) are lipid vesicles secreted by cells that allow intercellular communication. They are decorated with surface proteins, which are membrane proteins that can be targeted by biochemical techniques to isolate EVs from background particles. EVs have recently attracted attention for their potential applications as biomarkers for numerous diseases. This review focuses on the contribution of biomolecules used as ligands in affinity-based biosensors for the detection and isolation of EVs. Capturing biological objects like EVs with antibodies is well described in the literature through different biosensing techniques. However, since handling proteins can be challenging due to stability issues, sensors using non-denaturable biomolecules are emerging. DNA aptamers, short DNA fragments that mimic antibody action, are currently being developed and considered as the future of antibody-like ligands. These molecules offer undeniable advantages: unparalleled ease of production, very high stability in air, similar affinity constants to antibodies, and compatibility with many organic solvents. The use of peptides specific to EVs is also an exciting biochemical solution to target EV membrane proteins and complement other probes. These different ligands have been used in several types of biosensors: electrochemical, optical, microfluidic using both generic probes (targeting widely expressed membrane proteins such as the tetraspanins) and specific probes (targeting disease biomarkers such as proteins overexpressed in cancer).

Chemoenzymatic Labeling of Extracellular Vesicles for Visualizing Their Cellular Internalization in Real Time

Extracellular vesicles (EVs) are intercellular communicators that are heavily implicated in diverse pathological processes. However, it is poorly understood how EVs interact with recipient cells due to the lack of appropriate tracking techniques. Here, we report a robust chemoenzymatic labeling technique for visualizing the internalization process of EVs into target cells in real time. This method uses phospholipase D (PLD) to catalyze the in situ exchange of choline by alkyne in the native EV phosphatidylcholine. Subsequent alkyne-azide click chemistry allows conjugation of Cy5 dyes for visualizing EVs internalization by confocal fluorescence microscopy. The fluorescent labeling of EVs was accomplished in an efficient and biocompatible way, without affecting both the morphology and biological activity of EVs. We applied this chemoenzymatic labeling strategy to monitor the cellular uptake of cancer cell-derived EVs in real time and to further reveal multiple internalization mechanisms. This robust, biocompatible labeling strategy provides an essential tool for EV-related studies ranging from chemical biology to drug delivery.

An aggregation-induced emission dye-powered afterglow luminogen for tumor imaging

Semiconducting polymer (SP)-based afterglow luminogens are showing increasing potential for in vivo imaging because of their long-life luminescence and the associated benefits (e.g., zero-autofluorescence background and high signal-to-noise ratio). However, such organic afterglow luminescence agents are still rare and their application is usually limited by their relatively low afterglow intensity and short afterglow duration. Herein, we report an aggregation-induced emission (AIE) dye-powered SP afterglow luminogen by leveraging on the unique characteristics of an AIE dye to circumvent the concentration-quenching effect, enhance afterglow intensity and prolong afterglow duration. The underlying working mechanism is investigated by a series of experiments and it is found that the AIE dye provides sufficient 1O2 to excite SPs and form massive amounts of high-energy intermediates, and then the SP intermediates emit photons that can activate the AIE dye to generate 1O2 and simultaneously trigger the energy transfer process between the SPs and AIE dye, resulting in a deep-red emission. It is this closed-loop of "photon-1O2-SP intermediates-photon" that provides the afterglow emission even after the cessation of the excitation light. The as-prepared luminogen shows good performance in in vivo tumour imaging. This study demonstrates the advantages of AIE-facilitated afterglow luminescence and discloses its mechanism, and hopefully it could inspire the development of other innovative designs for cancer theranostics.

Cancer-Derived Exosomes: Their Role in Cancer Biology and Biomarker Development

Exosomes are a subset of tiny extracellular vesicles manufactured by all cells and are present in all body fluids. They are produced actively in tumor cells, which are released and utilized to facilitate tumor growth. Their characteristics enable them to assist major cancer hallmarks, leveraged by cancer cells in fostering cancer growth and spread while implementing ways to escape elimination from the host environment. This review updates on the latest progress on the roles of cancer-derived exosomes, of 30-100 nm in size, in deregulating paracrine trafficking in the tumor microenvironment and circulation. Thus, exosomes are being exploited in diagnostic biomarker development, with its potential in clinical applications as therapeutic targets utilized in exosome-based nanoparticle drug delivery strategies for cancer therapy. Ongoing studies were retrieved from PubMed^® and Scopus database and ClinicalTrials.gov registry for review, highlighting how cancer cells from entirely different cell lines rely on genetic information carried by their exosomes for homotypic and heterotypic intercellular communications in the microenvironment to favor proliferation and invasion, while establishing a pre-metastatic niche in welcoming cancer cells' arrival. We will elaborate on the trafficking of tumor-derived exosomes in fostering cancer proliferation, invasion, and metastasis in hematopoietic (leukemia and myeloma), epithelial (breast cancer), and mesenchymal (soft tissue sarcoma and osteosarcoma) cancers. Cancer-derived exosomal trafficking is observed in several types of liquid or solid tumors, confirming their role as cancer hallmark enabler. Their enriched genetic signals arising from their characteristic DNA, RNA, microRNA, and lncRNA, along with specific gene expression profiles, protein, or lipid composition carried by the exosomal cargo shed into blood, saliva, urine, ascites, and cervicovaginal lavage, are being studied as a diagnostic, prognostic, or predictive cancer biomarker. We reveal the latest research efforts in exploiting the use of nanoparticles to improve the overall cancer diagnostic capability in the clinic.

A three-dimensional multipedal DNA walker for the ultrasensitive detection of tumor exosomes

Herein, we developed a three-dimensional (3D) multipedal DNA walker based on aptamer-binding for ultrasensitive exosome sensing.

Stereospecific Synthesis and Photophysical Properties of Propeller-Shaped C90 H48 PAH

Herein, we have synthesized an enantiomerically pure propeller-shaped PAH, C90 H48 , possessing three [7]helicene and three [5]helicene subunits. This compound can be obtained in gram quantities in a straightforward manner. The photophysical and chiroptical properties were investigated using UV/Vis absorption and emission, optical rotation and circular dichroism spectroscopy, supported by DFT calculations. The nonlinear optical properties were investigated by two-photon absorption measurements using linearly and circularly polarized light. The extremely twisted structure and packing of the homochiral compound were investigated by single-crystal X-ray diffraction analysis.

Responsive Exosome Nano-bioconjugates for Synergistic Cancer Therapy

Exosomes hold great potential in therapeutic development. However, native exosomes usually induce insufficient effects in vivo and simply act as drug delivery vehicles. Herein, we synthesize responsive exosome nano-bioconjugates for cancer therapy. Azide-modified exosomes derived from M1 macrophages are conjugated with dibenzocyclooctyne-modified antibodies of CD47 and SIRPα (aCD47 and aSIRPα) through pH-sensitive linkers. After systemic administration, the nano-bioconjugates can actively target tumors through the specific recognition between aCD47 and CD47 on the tumor cell surface. In the acidic tumor microenvironment, the benzoic-imine bonds of the nano-bioconjugates are cleaved to release aSIRPα and aCD47 that can, respectively, block SIRPα on macrophages and CD47, leading to abolished "don't eat me" signaling and improved phagocytosis of macrophages. Meanwhile, the native M1 exosomes effectively reprogram the macrophages from pro-tumoral M2 to anti-tumoral M1.

Water-Soluble Conjugated Organic Molecules as Optical and Electrochemical Materials for Interdisciplinary Biological Applications

Apart from the wide applications in the field of electronic and optoelectronic devices, conjugated molecules have been established as useful functional materials for biological applications. By introducing hydrophilic side chains to conjugated backbones, water-soluble conjugated polymers or oligomers (CPs or COs) inherit the attractive optical and electronic properties from conjugated molecules, while their water solubility ensures interaction with biological substrates such as biomacromolecules, microorganisms, and living cells for further biological applications. Benefiting from high brightness, large extinction coefficients, excellent photostability, low cytotoxicity, stability in bodily fluids, and versatile structural modifications, water-soluble conjugated polymers and oligomers have offered powerful alternatives in a variety of biological applications including biological and chemical sensors, fluorescence imaging, disease diagnostics, and therapy. This Account will focus on our recent advances in design, synthesis, and interdisciplinary biological applications of a series of new water-soluble CP and CO materials, starting with a brief introduction to water-soluble CPs and COs and various methods and strategies developed for the preparation of advanced water-soluble CPs and COs. Since their properties can be tuned by rational design and synthesis at the level of the conjugated repeat unit and versatile pendant groups, CPs and COs provide a diverse toolbox for satisfying interdisciplinary biological applications. The application of water-soluble CPs and COs in the past five years can be broadly categorized into four areas. Specifically, integrating the unique optoelectronic properties of water-soluble CPs and COs with self-assembly and supramolecular strategies, efficacy regulation of antibiotic and anticancer drugs has been achieved, meanwhile drug resistance could be overcome and drug resistant "superbacteria" can be inhibited. For applications regulating cellular functions and biological processes, we introduce CPs and COs with the ability to regulate intracellular oxidative stress, cell-cell communication, cellular proliferation, cell membrane permeability, and quorum sensing of bacteria cells. By covalent linkage of reactive groups upon CPs and COs, these molecules are endowed with abilities like disassembly of amyloid polypeptides, biased distribution in cells, selective imaging of organelles, and distinguished interactions with biomolecules. For photothermal therapy (PTT) applications, photothermal-responsive conjugated polymer materials have been utilized for remote control of gene expression in living cells and in vivo photothermal therapy of cancer. Beyond these applications, we have achieved new interdisciplinary applications of water-soluble CP and CO materials for biological optoelectronic devices including photosynthesis, photocatalysis, and bioenergy. Specific features or properties of water-soluble CPs and COs are leveraged to bring opportunities for each of these applications. These studies open a new frontier for development of new functional conjugated molecule materials and provide better understanding of their interactions with biological systems as well as structure/property relationships. Current limitations confronted by CPs and COs are raised, and developmental direction for the future is proposed.

Self-Illuminating Agents for Deep-Tissue Optical Imaging

Optical imaging plays an indispensable role in biology and medicine attributing to its noninvasiveness, high spatiotemporal resolution, and high sensitivity. However, as a conventional optical imaging modality, fluorescence imaging confronts issues of shallow imaging depth due to the need for real-time light excitation which produces tissue autofluorescence. By contrast, self-luminescence imaging eliminates the concurrent light excitation, permitting deeper imaging depth and higher signal-to-background ratio (SBR), which has attracted growing attention. Herein, this review summarizes the progress on the development of near-infrared (NIR) emitting self-luminescence agents in deep-tissue optical imaging with highlighting the design principles including molecular- and nano-engineering approaches. Finally, it discusses current challenges and guidelines to develop more effective self-illuminating agents for biomedical diagnosis and treatment.

Structure-switching aptamer triggering hybridization displacement reaction for label-free detection of exosomes

Exosomes play important roles in intercellular communications, tumor migration and invasion. However, the specific detection of cancer exosomes remains as a big challenge due to its low concentration in biofluids. Therefore, the sensitive and selective detection of cancer cells-derived exosomes has attracted growing attention owing to their potential in diagnostic and prognostic applications. Activatable strategies have received great attention for the detection of low abundant analytes due to their high sensitivity. Herein, based on molecular recognition between DNA aptamer and exosome surface biomarker (protein tyrosine kinase-7), a novel activatable and label-free strategy was designed for highly sensitive and specific sensing of exosomes. In this work, the target exosomes trigger strand replacement reaction to form G-quadruplex, which result in an obvious fluorescence enhancement of N-methylmesoporphyrin IX due to the bonding between G-quadruplex and N-methylmesoporphyrin IX. Under the optimum experimental conditions, the linear range for exosomes was measured to be 5.0 × 10⁵-5.0 × 10⁷ particles/μL and the detection limit (LOD) was calculated to be 3.4 × 10⁵ particles/μL (3σ). This assay possesses high specificity to distinguish exosomes derived from different cell lines, and has successfully been validated in patient and healthy plasma samples. Furthermore, the probe can effectively detect the exosomes in 30% fetal bovine serum, indicating that the biological matrix has a negligible effect on this method. This developed label-free, convenient and highly sensitive biosensor will offer a great opportunity for exosomes quantification in biological study and clinical application.

An Acidic-Microenvironment-Driven DNA Nanomachine Enables Specific ATP Imaging in the Extracellular Milieu of Tumor

Extracellular ATP is an emerging target for cancer treatment because it is a key messenger for shaping the tumor microenvironment (TME) and regulating tumor progression. However, it remains a great challenge to design biochemical probes for targeted imaging of extracellular ATP in the TME. A TME-driven DNA nanomachine (Apt-LIP) that permits spatially controlled imaging of ATP in the extracellular milieu of tumors with ultrahigh signal-to-background ratio is reported. It operates in response to the mild acidity in the TME with the pH (low) insertion peptide (pHLIP) module, thus allowing the specific anchoring of the structure-switching signaling aptamer unit to the membrane of tumor cells for "off-on" fluorescence imaging of the extracellular ATP. Apt-LIP allows for acidity driven visualization of different extracellular concentrations of exogenous ATP, as well as the monitoring of endogenous ATP release from cells. Furthermore, it is demonstrated that Apt-LIP represents a promising platform for the specific imaging of the extracellular ATP in both primary and metastatic tumors. Ultimately, since diverse aptamers are obtained through in vitro selection, this design strategy can be further applied for precise detection of various extracellular targets in the TME.

An Organic Afterglow Protheranostic Nanoassembly

Cancer theranostics holds potential promise for precision medicine; however, most existing theranostic nanoagents are simply developed by doping both therapeutic agents and imaging agent into one particle entity, and thus have an "always-on" pharmaceutical effect and imaging signals regardless of their in vivo location. Herein, the development of an organic afterglow protheranostic nanoassembly (APtN) that specifically activates both the pharmaceutical effect and diagnostic signals in response to a tumor-associated chemical mediator (hydrogen peroxide, H₂ O₂ ) is reported. APtN comprises an amphiphilic macromolecule and a near-infrared (NIR) dye acting as the H₂ O₂ -responsive afterglow prodrug and the afterglow initiator, respectively. Such a molecular architecture allows APtN to passively target tumors in living mice, specifically release the anticancer drug in the tumor, and spontaneously generate the uncaged afterglow substrate. Upon NIR light preirradiation, the afterglow initiator generates singlet oxygen to react and subsequently transform the uncaged afterglow substrate into an active self-luminescent form. Thus, the intensity of generated afterglow luminescence is correlated with the drug release status, permitting real-time in vivo monitoring of prodrug activation. This study proposes a background-free design strategy toward activatable cancer theranostics.