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.

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.

Intracellular infection-responsive macrophage-targeted nanoparticles for synergistic antibiotic immunotherapy of bacterial infection

Intracellular bacteria are considered to play a key role in the failure of bacterial infection therapy and increase of antibiotic resistance. Nanotechnology-based drug delivery carriers have been receiving increasing attention for improving the intracellular antibacterial activity of antibiotics, but are accompanied by disadvantages such as complex preparation procedures, lack of active targeting, and monotherapy, necessitating further design improvements. Herein, nanoparticles targeting bacteria-infected macrophages are fabricated to eliminate intracellular bacterial infections via antibiotic release and upregulation of intracellular reactive oxygen species (ROS) levels and proinflammatory responses. These nanoparticles were formed through the reaction of the amino group on selenocystamine dihydrochloride and the aldehyde group on oxidized dextran (ox-Dex), which encapsulates vancomycin (Van) through hydrophobic interactions. These nanoparticles could undergo targeted uptake by macrophages via endocytosis and respond to the bacteria-infected intracellular microenvironment (ROS and glutathione (GSH)) for controlled release of antibiotics. Furthermore, these nanoparticles could consume intracellular GSH and promote a significant increase in the level of ROS in macrophages, subsequently up-regulating the proinflammatory response to reinforce antibacterial activity. These nanoparticles can accelerate bacteria-infected wound healing. In this work, nanoparticles were fabricated for bacteria-infected macrophage-targeted and microenvironment-responsive antibiotic delivery, cellular ROS generation, and proinflammatory up-regulation activity to eliminate intracellular bacteria, which opens up a new possibility for multifunctional drug delivery against intracellular infection.

Nitrogen-phosphorous co-doped carbonized chitosan nanoparticles for chemotherapy and ROS-mediated immunotherapy of intracellular Staphylococcus aureus infection

Staphylococcus aureus (S. aureus) residing in host macrophages is hard to clear because intracellular S. aureus has evolved mechanisms to hijack and subvert the immune response to favor intracellular infection. To overcome this challenge, nitrogen-phosphorous co-doped carbonized chitosan nanoparticles (NPCNs), which possess the polymer/carbon hybrid structures, were fabricated to clear intracellular S. aureus infection through chemotherapy and immunotherapy. Multi-heteroatom NPCNs were fabricated through the hydrothermal method, where chitosan and imidazole were used as the C and N sources and phosphoric acid as the P source. NPCNs can not only be used as a fluorescent probe for bacteria imaging but also kill extracellular and intracellular bacteria with low cytotoxicity. NPCNs could generate ROS and polarize macrophages into classically activated (M1) phenotypes to increase antibacterial immunity. Furthermore, NPCNs could accelerate intracellular S. aureus-infected wound healing in vivo. We envision that these carbonized chitosan nanoparticles may provide a new platform for clearing intracellular bacterial infection through chemotherapy and ROS-mediated immunotherapy.

A novel aggregation-induced emission fluorescent probe with large Stokes shift for sensitive detection of pH changes in live cells

The detection of intracellular pH is crucial for elucidating the pathological process of cancers, as well as for medical diagnostic applications. Here, we developed an aggregation-induced emission active pH-responsive fluorescent probe (TPE-DCP) for sensitively detecting cell pH changes. The probe shows obvious pH-sensing properties at ~615 nm, with a pKa value of 6.82 and a good linear pH response ranging from 8.5 to 4.5. TPE-DCP holds advantages such as excellent anti-interference performance, good photostability, and low cytotoxicity, and has been successfully used to image intracellular pH changes in cells.

A fluorescent pH probe for evaluating the freshness of chicken breast meat

A fluorescent probe, Nap-MOR, based on the naphthalimide fluorophore, was designed and developed for pH measurement in aqueous solutions. Nap-MOR had a close linear relationship between fluorescence intensity and pH, in the range 4.5-8, which covers the full range of pH found in normal fresh, defective and spoiled meat. pH measurement with Nap-MOR was free from interference by a wide range of ions and biochemicals found in meat and the results were not significantly different in comparison with a pH meter. Therefore, Nap-MOR is a robust and convenient way to evaluate the freshness of chicken breast meat by measuring its pH.

pH-Responsive Fluorescent Polymer-Drug System for Real-Time Detection and In Situ Eradication of Bacterial Biofilms

Bacterial biofilms encased in extracellular polymeric substances to create protected microenvironments are typically challenging to disperse by common antibiotics and cannot be in situ visualized under current modalities. Herein, a pH-responsive branched polymer [poly(MBA-AEPZ)-AEPZ-NA] capable of overcoming antibiotic resistance and real-time visualizing biofilms for fluorescence imaging-guided infection control is reported. The positively charged polymer can effectively penetrate bacterial biofilms, neutralize the anionic character, and then disrupt the structural integrity, thus significantly promoting the transport of antibiotics into biofilms. The polymer shows a weak fluorescence emission intensity under physiological conditions (pH 7.4) but emits intense green-light emission within the localized biofilm microenvironment (pH 5.5) to real-time visualize bacterial biofilms. A therapeutic system made of the polymer and a model antibiotic can significantly reduce the dosages of the drug, thereby minimizing biofilm-induced drug resistance. Notably, a green fluorescent polymer responding to localized pH conditions is demonstrated in living zebrafish. This work confirmed that combinations of the pH-responsive branched polymer and antibiotics could be administered to overcome drug resistance and realize fluorescence imaging-guided treatment of bacterial biofilm infections.

Dual-Targeting into the Mitochondria of Cancer Cells for Ratiometric Investigation of the Dynamic Fluctuation of Sulfur Dioxide and Formaldehyde with Two-Photon Integrated Semiconducting Polymer Dots

Mitochondrial sulfur dioxide (SO₂) and formaldehyde (FA) in cancer cells serve as important signal molecules in mediating multiple physiological and pathological activities. Accurate monitoring of the dynamic fluctuation of SO₂ and FA in the mitochondria of cancer cells is important for insight into their relationships and functions in cancer, understanding cancer mechanism, and the role of mitochondrial homeostasis in cancer invasion and metastasis. Herein, a novel integrated two-photon semiconducting polymer dot (BF@Pdots) with dual-targeting (cancer cells and mitochondrial) and dual-emission in green and red regions, which is rationally designed through a four-step engineering strategy by using two newly synthesized functionalized polymers PFNA and FD-PSMA as precursors, has been developed for accurate tracking of the dynamic variation of SO₂ and FA in the mitochondria of cancer cells. The sensing mechanism is on the basis of the fluorescence resonance energy transfer (FRET) process in BF@Pdots tuned by the reversible Michael addition reaction between the sensing-groups and SO₂ (or FA). The integrated BF@Pdots nanoprobes display excellent performances in the accurate detection of the dynamic fluctuation of SO₂ and FA such as precise positioning in the mitochondria of cancer cells, self-calibrating ratiometric, two-photon emission with long wavelength excitation, and fast reversible response. The BF@Pdots nanoprobes are also applied to the ratiometric detection of the dynamic fluctuation of exogenous and endogenous SO₂ and FA in the mitochondria of cancer cells for the first time with satisfactory results. Taken together, this work will provide an attractive way to develop versatile integrated Pdots-based fluorescent probes through flexible molecular engineering for applications in accurate imaging of biomolecules in living systems.

Conjugated Polymers-based Luminescent Probes for Ratiometric Detection of Biomolecules

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

19F-Grafted Fluorescent Carbonized Polymer Dots for Dual-Mode Imaging

Dual-modal imaging systems could provide complementary information by taking advantage of each imaging modality. Herein, a fluorescence and ¹⁹F magnetic resonance imaging nanoprobe was developed through preparation of ¹⁹F-grafted fluorescent carbonized polymer dots (FCPDs). Both fluorescence and ¹⁹F nuclear magnetic resonance intensities of these FCPDs can be modulated by controlling the carbonization processes. The strong yellow fluorescence renders these FCPDs capable of cell fluorescence imaging. The in vitro and in vivo assessments demonstrated that the as-prepared FCPDs were suitable for ¹⁹F magnetic resonance imaging (¹⁹F MRI), which would provide great potential for biological imaging and early diagnosis applications. Moreover, this fabrication strategy offers a new protocol for ¹⁹F MRI nanoprobe design.

Dual-Emission Carbonized Polymer Dots for Ratiometric pH Sensing, pH-Dependent Generation of Singlet Oxygen, and Imaging-Guided Dynamics Monitoring of Photodynamic Therapy

The pH environment in cancer cells has been demonstrated to display vital influences on the therapeutic effect of photodynamic therapy (PDT). It is very interesting to develop pH-responsive probes for simultaneous pH sensing and dynamics monitoring of the effects of PDT, and therefore assessing the correlation between them. In this study, a multifunctional fluorescence probe, dual-emission carbonized polymer dot (CPD) in blue and red regions, which uses ethylene imine polymer (PEI) and 4,4',4″,4‴-(porphine-5, 10, 15, 20-tetrayl) tetrakis (benzoic acid) (TCPP) as precursors through a one-step hydrothermal amide reaction, has been designed for ratiometric pH sensing, generating pH-dependent ¹O₂ for PDT of cancer cells, and investigating the dynamics effects of PDT through pH-guided imaging. The prepared CPDs were successfully used for ratiometric pH response, pH-dependent generation of ¹O₂, and dynamics monitoring PDT in HeLa cells. This study may provide an alternative strategy to prepare CPD-based theranostic integrated nanoprobes for PDT through the rational design of precursors.

General Strategy to Achieve Color-Tunable Ratiometric Two-Photon Integrated Single Semiconducting Polymer Dot for Imaging Hypochlorous Acid

It is highly desired and challenging to construct integrated (all-in-one) single semiconducting-polymer-derived dot (Pdot) without any postmodification but with desired performances for bioapplications. In this work, eight hypochlorous acid (HClO)-sensitive integrated polymers and corresponding polymer-derived Pdots are designed through molecular engineering to comparatively study their analytical performances for detecting and imaging HClO. The optimized polymers-derived Pdots are obtained through regulating donor-acceptor structure, the content of HClO-sensitive units, and the position of HClO-sensitive units in the polymer backbone. The designed Pdots display distinguished characteristics including multicolours with blue, yellow, and red three primary fluorescence colors, determination mode from single-channel to dual-channel (ratiometric) quantification, ultrafast response, low detection limit, and high selectivity for ClO^- sensing based on specific oxidation of ClO^--sensitive unit 10-methylphenothiazine (PT) accompanied by altering the intramolecular charge transfer (ICT) and fluorescence resonance energy transfer (FRET) processes in Pdots. The prepared integrated Pdots are also applied for two-photon ClO^- imaging in HeLa cells and one- and two-photon ClO^- imaging produced in acute inflammation in mice with satisfactory results. We believe that the present study not only provides excellent integrated fluorescent nanoprobes for ClO^- monitoring in living systems but also extends a general strategy for designing integrated semiconducting polymers and Pdots with desired performances for biological applications.

Simultaneous inhibition of planktonic and biofilm bacteria by self-adapting semiconducting polymer dots

Biofilm infections present an enormous challenge in today's healthcare settings. Currently, pH-switchable antibacterial agents are being developed to eradicate biofilms. However, most pH-switchable antibacterial agents are less lethal to planktonic bacteria under neutral conditions, and cannot prevent the dispersed bacteria from seeding acute infection again. Herein, this work reports the applications of semiconducting polymer dots (Pdots) with a double adhesion mechanism in imaging and inhibiting bacteria inside (weak acidic conditions) and outside (neutral conditions) biofilms. Clew-like Pdots were prepared by covalently linking phenylboronic acid (PBA) and pH-responsive naphthalimide (NA) ramification in semiconducting polymers. Under neutral conditions, the Pdots combined with bacteria through the formation of boronate esters between PBA and diols. Under weakly acidic conditions, the partial borate bond fractured, and the Pdots adhered onto the bacterial surface through the positively charged NA in Pdots. Furthermore, the Pdots display negligible toxicity to mammalian cells and tissues. More importantly, the Pdots can selectively damage the bacterial membrane and inhibit bacteria in vivo. This work highlights the feasibility of using semiconducting Pdots to image and inhibit bacteria inside and outside biofilms, which represents a highly effective strategy to cope with biofilm infections.

Engineering fluorescent semiconducting polymer nanoparticles for biological applications and beyond

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