Brightness Enhancement of Near-Infrared Semiconducting Polymer Dots for in Vivo Whole-Body Cell Tracking in Deep Organs

Biological Properties of Arginine-rich Peptides and their Application in Cargo Delivery to Cancer

Cell-penetrating peptides (CPPs) comprise short peptides of fewer than 30 amino acids, which are rich in arginine (Arg) or lysine (Lys). CPPs have attracted interest in the delivery of various cargos, such as drugs, nucleic acids, and other macromolecules over the last 30 years. Among all types of CPPs, arginine-rich CPPs exhibit higher transmembrane efficiency due to bidentate bonding between their guanidinium groups and negatively charged cellular components. Besides, endosome escape can be induced by arginine-rich CPPs to protect cargo from lysosome-dependent degradation. Here we summarize the function, design principles, and penetrating mechanisms of arginine-rich CPPs, and outline their biomedical applications in drug delivery and biosensing in tumors.

Ratiometric fluorescence imaging of lysosomal NO in living cells and mice brains with Alzheimer's disease

We report an integrated ratiometric lysosomal nitric oxide (NO) nanoprobe based on engineered semiconducting polymer dots (Pdots), LyNO-Pdots, which consist of a newly designed NO-responsive dye, a fluorescent conjugated polymer and two functional polymers. The developed probe LyNO-Pdots exhibit high specificity and stability, good photostability and favorable blood-brain barrier (BBB) penetration ability. The LyNO-Pdots are successfully applied to ratiometric imaging of lysosomal NO variations in brain-derived endothelial cells, brain tissues and mice brains with Alzheimer's disease (AD). The results demonstrate that the NO content in the brains of AD mice is considerably higher than that in normal mice.

Photophysics of fluorescent nanoparticles based on organic dyes - challenges and design principles

Fluorescent nanoparticles have become attractive for bioanalysis and imaging, due to their high brightness and photostability. Many different optical materials have been applied in fluorescent nanoparticles with a broad range of properties and characteristics. One appealing approach is the incorporation of molecular organic fluorophores in nanoparticles with the intention of transferring their known attractive solution-state properties directly to the nanoparticles. However, as molecular dyes are packed closely together in the nanoparticles their interactions most often result in fluorescence quenching and change in spectral properties making this approach challenging. In this perspective we will first discuss the origins of quenching and spectral shifts observed in dye based nanoparticles. On this background, we will then describe various designs of dye based NPs and how they address the challenges of dye-dye interactions and quenching. Our aim is to provide a general framework for understanding the supramolecular mechanisms that determine the photophysics of dye based nanoparticles. This framework of molecular photophysics and its relation to the internal structure of dye based nanoparticles can hopefully serve to assist rational design and optimization of new and improved dye based nanoparticles.

Semiconducting polymer dots for multifunctional integrated nanomedicine carriers

The expansion applications of semiconducting polymer dots (Pdots) among optical nanomaterial field have long posed a challenge for researchers, promoting their intelligent application in multifunctional nano-imaging systems and integrated nanomedicine carriers for diagnosis and treatment. Despite notable progress, several inadequacies still persist in the field of Pdots, including the development of simplified near-infrared (NIR) optical nanoprobes, elucidation of their inherent biological behavior, and integration of information processing and nanotechnology into biomedical applications. This review aims to comprehensively elucidate the current status of Pdots as a classical nanophotonic material by discussing its advantages and limitations in terms of biocompatibility, adaptability to microenvironments in vivo, etc. Multifunctional integration and surface chemistry play crucial roles in realizing the intelligent application of Pdots. Information visualization based on their optical and physicochemical properties is pivotal for achieving detection, sensing, and labeling probes. Therefore, we have refined the underlying mechanisms and constructed multiple comprehensive original mechanism summaries to establish a benchmark. Additionally, we have explored the cross-linking interactions between Pdots and nanomedicine, potential yet complete biological metabolic pathways, future research directions, and innovative solutions for integrating diagnosis and treatment strategies. This review presents the possible expectations and valuable insights for advancing Pdots, specifically from chemical, medical, and photophysical practitioners' standpoints.

Self-assembly of three-dimensional liver organoids: virtual reconstruction via endocytosed polymer dots for refactoring the fine structure

In vitro culture of organoids holds considerable promise for the treatment of diseases or the provision of artificial organs. Traditional 2D differentiation from mesenchymal stem cells (MSCs) faces challenges in replicating the development of embryonic organs at the cellular level; conversely, the cultivation of 3D organoids exhibits potential for application. It is crucial for clinicians and technology researchers to acquire insights into organoid tissue differentiation, autonomous morphogenesis, as well as 3D assembly processes in vitro. In this investigation, novel 3D organoids capable of engendering complex liver-like tissues in vitro were cultured, and a class of high-luminance semiconductor polymer dots (Pdots) was employed to monitor the self-assembly process of 3D liver organoid tissues and cellular interaction and migration dynamics. Three-dimensional liver-bud (3D-LB) organoid tissues were derived through the interplay of induced MSCs, Wharton's Jelly, and human umbilical vein endothelial cells (HUVECs), and their structural characteristics were determined during the liver-bud organoid development; ultimately, the co-cultured organoid spatial cellular clusters resembling a truffle were successfully replicated. Utilizing R8-Pdots with remarkable resolution and biocompatibility, the structural elements of functional and vascularized organs derived from liver organoid tissues were adeptly reconstituted, and this investigation shall contribute to a further understanding of human hepato-developmental physiology and liver-disease modeling.

Conjugated Polymer Nanoparticles for Tumor Theranostics

Water-dispersible conjugated polymer nanoparticles (CPNs) have demonstrated great capabilities in biological applications, such as in vitro cell/subcellular imaging and biosensing, or in vivo tissue imaging and disease treatment. In this review, we summarized the recent advances of CPNs used for tumor imaging and treatment during the past five years. CPNs with different structures, which have been applied to in vivo solid tumor imaging (fluorescence, photoacoustic, and dual-modal) and treatment (phototherapy, drug carriers, and synergistic therapy), are discussed in detail. We also demonstrated the potential of CPNs as cancer theranostic nanoplatforms. Finally, we discussed current challenges and outlooks in this field.

Semiconducting Polymer Dots for Point-of-Care Biosensing and In Vivo Bioimaging: A Concise Review

In recent years, semiconducting polymer dots (Pdots) have attracted much attention due to their excellent photophysical properties and applicability, such as large absorption cross section, high brightness, tunable fluorescence emission, excellent photostability, good biocompatibility, facile modification and regulation. Therefore, Pdots have been widely used in various types of sensing and imaging in biological medicine. More importantly, the recent development of Pdots for point-of-care biosensing and in vivo imaging has emerged as a promising class of optical diagnostic technologies for clinical applications. In this review, we briefly outline strategies for the preparation and modification of Pdots and summarize the recent progress in the development of Pdots-based optical probes for analytical detection and biomedical imaging. Finally, challenges and future developments of Pdots for biomedical applications are given.

Peptide-based assembled nanostructures that can direct cellular responses

Natural originated materials have been well-studied over the past several decades owing to their higher biocompatibility compared to the traditional polymers. Peptides, consisting of amino acids, are among the most popular programable building blocks, which is becoming a growing interest in nanobiotechnology. Structures assembled using those biomimetic peptides allow the exploration of chemical sequences beyond those been routinely used in biology. In this Review, we discussed the most recent experimental discoveries on the peptide-based assembled nanostructures and their potential application at the cellular level such as drug delivery. In particular, we explored the fundamental principles of peptide self-assembly and the most recent development in improving their interactions with biological systems. We believe that as the fundamental knowledge of the peptide assemblies evolves, the more sophisticated and versatile nanostructures can be built, with promising biomedical applications.

Versatile scaffold applications based on MoS2 quantum dots for imaging mitochondrial pH in living cells

Sensitive and accurate detection and imaging of mitochondrial pH have become significant methods in biological and biomedical research to elucidate the biological functions of mitochondria. Herein, a mitochondria-targeted ratiometric fluorescent nanoprobe was developed to image mitochondrial pH in living cells. This nanoprobe was prepared by covalently linking a mitochondria-targeted ligand (triphenylphosphonium, TPP) and a pH recognition fluorescent indicator (rhodamine, RhB) onto the surface of MoS2 quantum dots (QDs). In this multifunctional fluorescent nanoprobe, MoS2 QDs serve not only as nanocarrier for the targeting ligand and pH fluorescent indicator, but also as a fluorescent reference for the ratiometric signal. Indeed, the fluorescence intensity of the MoS2 QDs is highly resistant to increasing proton concentrations, while that of RhB is sensitive to pH. Ratiometric detection of pH was carried out by comparing the pH-sensitive fluorescence of the RhB-based group with the pH-resistant fluorescence of MoS2 QDs. After uptake in living cells, the nanoprobe could stain mitochondria specifically, and allowed to image and monitor pH in mitochondria in a satisfactory manner.

Visualization of Acute Inflammation through a Macrophage-Camouflaged Afterglow Nanocomplex

Acute inflammation is a basic innate, immediate, and stereotyped immune response to injury, which is characterized by rapid recruitment of immune cells to the vasculature and extravasation into the damaged parenchyma. Visualization of acute inflammation plays an important role in monitoring the disease course and understanding pathogenesis, which lacks specific targeted and observing tools in vivo. Here, we report a Trojan horse strategy of a macrophage-camouflaged afterglow nanocomplex (UCANPs@RAW) to specifically visualize acute inflammation. Due to the advantages of optical antibackground interference elimination, as well as particular immune homing and long-term tracking capacity, UCANPs@RAW demonstrates an excellent acute inflammatory recognition ability. In an arthritis model, previously intravenously injected UCANPs@RAW could directionally migrate from the liver to the inflammation site as soon as 3 h after the model was induced, which could be continuously lighted for at least 36 h with the highest imaging signal-to-background ratio (SBR) as 382 at the time point of 9 h. Additionally, UCANPs@RAW is observed to penetrate the blood-brain barrier and image the deep brain inflamed region covered by the thick skull in an acute brain inflammation model with an SBR_max of 258, which is based on the strong recruiting ability of macrophages to immune response. In view of this smart nanocomplex, our strategy holds great potential for inflammatory detection and treatments.

A pH-Responsive Nanoplatform Based on Fluorescent Conjugated Polymer Dots for Imaging-Guided Multitherapeutics Delivery and Combination Cancer Therapy

For cancer treatment, nanocarriers were designed with cationic lipids and polymers to improve the cytosolic delivery efficiency of siRNA. Though the positively charged nanocarriers showed great potential for RNA therapy, it was inevitable to generate the potential cytotoxicity. We constructed a pH-responsive nanoplatform, which co-carried siRNA and anticancer drug (hydroxycamptothecine, HCPT), to integrate gene therapy and chemotherapy for combination cancer therapy. The fluorescent conjugated polymer nanoparticles (CPNPs) modified with cell-penetrating peptides were employed as cores to carry siRNA molecules (siRNA-CPNPs) and track the biodistribution of nanotherapeutics by virtue of fluorescence. Calcium phosphate (CaP) nanocoatings were deposited on the surface of siRNA-CPNPs, followed by loading with HCPT and aptamers targeting cancer cells to obtain a targeted and tumor acid-responsive biocompatible nanoplatform. After the uptake of cancer cells, the CaP nanocoatings were decomposed in the acidic endo/lysosomes to release HCPT, and the siRNA-CPNPs were exposed to facilitate the siRNA endo/lysosome escape and cytoplasm delivery. Results obtained from both in vitro and in vivo studies in tumor inhibition expressed that the combined therapy exhibited a better therapeutic efficacy than any monotherapy.

Measuring Cellular Uptake of Polymer Dots for Quantitative Imaging and Photodynamic Therapy

There is a great deal of interest in the development of nanoparticles for biomedicine. The question of how many nanoparticles are taken up by cells is important for biomedical applications. Here, we describe a fluorescence method for the quantitative measurement of the cellular uptake of polymer dots (Pdots) and a further estimation of intracellular Pdots photosensitizer for fluorescence imaging and photodynamic therapy. The approach relies on the high brightness, excellent stability, minimal aggregation quenching, and metalloporphyrin doping properties of the Pdots. We correlated the single-cell fluorescence brightness obtained from fluorescence spectrometry, confocal microscopy, and flow cytometry with the number of endocytosed Pdots, which was validated by inductively coupled plasma mass spectrometry. Our results indicated that, on average, ∼1.3 million Pdots were taken up by single cells that were incubated for 4 h with arginine 8-Pdots (40 μg/mL, ∼20 nm diameter). The absolute number of endocytosed Pdots of individual cells could be estimated from confocal microscopy by comparing the single-cell brightness with the average intensity. Furthermore, we investigated the cell viability as a result of an intracellular Pdots photosensitizer, from which the half maximal inhibitory concentration was determined to be ∼7.2 × 10⁵ Pdots per cell under the light dose of 60 J/cm². This study provides an effective method for quantifying endocytosed Pdots, which can be extended to investigate the cellular uptake of various conjugated polymer carriers in biomedicine.

Photoluminescent Nanomaterials for Medical Biotechnology

Creation of various photoluminescent nanomaterials has significantly expanded the arsenal of approaches used in modern biomedicine. Their unique photophysical properties can significantly improve the sensitivity and specificity of diagnostic methods, increase therapy effectiveness, and make a theranostic approach to treatment possible through the application of nanoparticle conjugates with functional macromolecules. The most widely used nanomaterials to date are semiconductor quantum dots; gold nanoclusters; carbon dots; nanodiamonds; semiconductor porous silicon; and up-conversion nanoparticles. This paper considers the promising groups of photoluminescent nanomaterials that can be used in medical biotechnology: in particular, for devising agents for optical diagnostic methods, sensorics, and various types of therapy.

Cell-Penetrating Peptides in Diagnosis and Treatment of Human Diseases: From Preclinical Research to Clinical Application

Cell-penetrating peptides (CPPs) are short peptides (fewer than 30 amino acids) that have been predominantly used in basic and preclinical research during the last 30 years. Since they are not only capable of translocating themselves into cells but also facilitate drug or CPP/cargo complexes to translocate across the plasma membrane, they have potential applications in the disease diagnosis and therapy, including cancer, inflammation, central nervous system disorders, otologic and ocular disorders, and diabetes. However, no CPPs or CPP/cargo complexes have been approved by the US Food and Drug Administration (FDA). Many issues should be addressed before translating CPPs into clinics. In this review, we summarize recent developments and innovations in preclinical studies and clinical trials based on using CPP for improved delivery, which have revealed that CPPs or CPP-based delivery systems present outstanding diagnostic therapeutic delivery potential.

Cell-penetrating peptide: a means of breaking through the physiological barriers of different tissues and organs

The selective infiltration of cell membranes and tissue barriers often blocks the entry of most active molecules. This natural defense mechanism prevents the invasion of exogenous substances and limits the therapeutic value of most available molecules. Therefore, it is particularly important to find appropriate ways of membrane translocation and therapeutic agent delivery to its target site. Cell penetrating peptides (CPPs) are a group of short peptides harnessed in this condition, possessing a significant capacity for membrane transduction and could be exploited to transfer various biologically active cargoes into the cells. Since their discovery, CPPs have been employed for delivery of a wide variety of therapeutic molecules to treat various disorders including cranial nerve involvement, ocular inflammation, myocardial ischemia, dermatosis and cancer. The promising results of CPPs-derived therapeutics in various tumor models demonstrated a potential and worthwhile scope of CPPs in chemotherapy. This review describes the detailed description of CPPs and CPPs-assisted molecular delivery against various tissues and organs disorders. An emphasis is focused on summarizing the novel insights and achievements of CPPs in surmounting the natural membrane barriers during the last 5 years.

High resolution tracking of macrophage cells in deep organs and lymphatics using fluorescent polymer dots

In vivo cell tracking can provide information on cell migration and accumulation in the organs. Here, both folate and amino modified polymer dots were synthesized and screened for in vitro and in vivo tracking of macrophage Ana-1 cells. Flow cytometry analysis demonstrated that prepared polymer dots showed cellular uptake of approximately 98% within a short incubation time of 2 h, and these polymer dots maintained a cell labeling rate over 97% after 2 d. Moreover, a CCK-8 assay suggested that these polymer dots increased Ana-1 cell viabilities up to 110% at concentrations from 5 to 50 μg mL-1. Furthermore, the in vivo real time imaging of labelled Ana-1 cells in the alveolus of lung and lymph nodes were clearly detected by probe-based confocal laser endomicroscopy (pCLE). This study demonstrates a unique approach using polymer dots for real-time high resolution tracking of macrophage cells in deep organs and the lymphatic system.

Noninvasive Tracking and Regenerative Capabilities of Transplanted Human Umbilical Cord-Derived Mesenchymal Stem Cells Labeled with I-III-IV Semiconducting Nanocrystals in Liver-Injured Living Mice

Acute liver injury is a critical syndrome ascribed to prevalent death of hepatocytes and imperatively requires liver transplantation. Such a methodology is certainly hampered due to the deficit of healthy donors. In this regard, stem cell-based regenerative therapies are attractive in repairing injured tissues and organs for medical applications. However, it is crucial to understand the migration, engraftment, and regeneration capabilities of transplanted stem cells in the living animal models. For the first time, we demonstrate rapid labeling of umbilical cord-derived mesenchymal stem cells (MSCs) with near-infrared (NIR)-fluorescent CuInS₂-ZnS nanocrystals (CIZS-NCs) to develop innovative nanobioconjugates (MSCs-CIZS-NBCs) that exhibit 98% labeling efficiency. Before nanobioconjugate synthesis, the pristine CIZS-NCs were prepared via a two-step, hot-injection, rapid and low-cost domestic-microwave-refluxing (MW-R) method within 6 min. The as-synthesized CIZS-NCs display high photoluminescence quantum yield (∼88%) and long-lived lifetime (23.4 μs). In contrast to unlabeled MSCs, the MSCs-CIZS nanobioconjugates show excellent biocompatibility without affecting the stemness, as confirmed by cell viability, immunophenotyping (CD44⁺, CD105⁺, CD90⁺), multi-lineage-specific gene expressions, and differentiation into adipocytes, osteocytes, and chondrocytes. The in vivo fluorescence tracking analyses revealed that the MSCs-CIZS-NBCs after tail-vein injection were initially trapped in the lungs and gradually engrafted in the injured liver within 2 h. The regeneration potential of MSCs-CIZS-NBCs was confirmed via renewal of the portal tract composed of portal veins, bile ducts, and hepatic arteries around the hepatocytes. Consequently, no apparent inflammations, necrosis, or apoptosis was observed in the acetaminophen (APAP)-induced liver-injured BALB/c mice model over 3 days after transplantation, as corroborated using laser-scanning confocal microscopy and histopathological and hematological analyses. Hence, our innovative NIR-fluorescent MSCs-CIZS-NBCs offer an off-the-self technology for noninvasive tracking of transplanted MSCs in an acute-liver-injured animal model for future image-guided cell-therapies.