Fluorescent Polymer Nanoparticles Based on Dyes: Seeking Brighter Tools for Bioimaging

Facile Hydrophobication of Glutathione-Protected Gold Nanoclusters and Encapsulation into Poly(lactide-co-glycolide) Nanocarriers

We report a simple surface functionalization of glutathione-capped gold nanoclusters by hydrophobic ion pairing with alkylamine followed by a complete phase transfer to various organic solvents with maintained colloidal stability and photoluminescence properties. The described surface hydrophobication enables efficient encapsulation of gold nanoclusters into PLGA nanocarriers allowing their visualization inside cultured cells using confocal fluorescent microscopy. The simplicity and efficiency of the described protocols should extend the biomedical applications of these metallic nanoclusters as a fluorescent platform to label hydrophobic polymeric nanocarriers beyond conventional organic dyes.

Synthesis of fluorescent polycarbonates with highly twisted N,N-bis(dialkylamino)anthracene AIE luminogens in the main chain

A synthetic route to embed aggregation-induced-emission-(AIE)-active luminophores in polycarbonates (PCs) in various ratios is reported. The AIE-active monomer is based on the structure of 9,10-bis(piperidyl)anthracene. The obtained PCs display good film-forming properties, similar to those observed in poly(bisphenol A carbonate) (Ba-PC). The fluorescence quantum yield (Φ) of the PC with 5 mol% AIE-active monomer was 0.04 in solution and 0.53 in solid state. Moreover, this PC is also miscible with commercially available Ba-PC at any blending ratio. A combined analysis by scanning electron microscopy and differential scanning calorimetry did not indicate any clear phase separation. These results thus suggest that even engineering plastics like polycarbonates can be functionalized with AIE luminogens without adverse effects on their physical properties.

Recent advances in the use of fluorescent nanoparticles for bioimaging

Rapid and recent progress in fluorescence microscopic techniques has allowed for routine discovery and viewing of biological structures and processes in unprecedented spatiotemporal resolution. In these imaging techniques, fluorescent nanoparticles (NPs) play important roles in the improvement of reporting systems. A short overview of recently developed fluorescent NPs used for advanced in vivo imaging will be discussed in this mini-review. The discussion begins with the contribution of fluorescence imaging in exploring the fate of NPs in biological systems. NP applications for in vivo imaging, including cell labeling, multimodal imaging and theranostic agents, are then discussed. Finally, despite all of the advancements in bioimaging, some unsolved challenges will be briefly discussed concerning future research directions.

Controlling Size and Fluorescence of Dye-Loaded Polymer Nanoparticles through Polymer Design

Nanoprecipitation is a straightforward yet powerful technique to synthesize polymer nanoparticles loaded with various biologically active compounds or contrast agents. Particle formation in this approach is kinetically controlled, and various assembly parameters have been used to control the size distribution and properties of the formed nanoparticles. Here, the influence of the nature of the polymer on the formation of nanoparticles in nanoprecipitation is studied systematically by varying its hydrophobicity and charge over a broad range. For this, methacrylate copolymers with different types and fractions of hydrophobic, hydrophilic, and charged side groups are synthesized. Nanoprecipitation of these polymers shows that particle size increases with increasing global hydrophobicity of the polymers. At the same time, both hydrophilic and charged groups reduce particle size. In this way, we achieve control over particle size from ∼10 to 200 nm. Furthermore, the effect of the polymer nature on the photophysical properties of nanoparticles loaded with a fluorescent dye, a rhodamine B derivative with a bulky hydrophobic counterion (fluorinated tetraphenylborate), is studied. It is found that the hydrophobic/hydrophilic balance of the polymer modulates to a large extent the spectral properties and fluorescence quantum yield of the dye encapsulated at high concentration, which reflects changes in the dye aggregation within the polymer matrix. Thus, we show how polymer chemistry can tune kinetically controlled formation of nanoparticles and encapsulation of the load. The concepts introduced here should be valuable tools for the design of nanoparticles for imaging and drug-delivery applications.

Ultrabright fluorescent microsphere and its novel application for improving the sensitivity of immunochromatographic assay

Fluorescent microsphere (FM) is widely used as probe in immunochromatographic assay (ICA). However, the performance of conventional FM is limited because of the aggregation-caused quenching effect. Herein, we compared a kind of conventional FM (DMFFM, loading DMF) with novel aggregation-induced emission FM (AIEFM, loading TCBPE). The fluorescence intensity of DMFFM initially increased and then decreased as the concentrations of the loading DMF increased. The fluorescence intensity of AIEFM increased as the concentrations of the loading TCBPE increased and retained a high value. AIEFM was compared with two commercial FMs purchased from Ocean (OFM) and Merk (MFM). The maximum fluorescence intensity and relative quantum yield of AIEFM was approximately 5 and 4.5 times higher than those of two commercial FMs. We used the novel AIEFM as a probe to improve the sensitivity of ICA. When Escherichia coli O157:H7 was detected as the target, the limit of detection of ICA based on AIEFM, OFM and MFM were 3.98 × 10³ CFU/mL, 4.48 × 10⁴ and 2.78 × 10⁴ CFU/mL, respectively. The ICA of AIEFM had 11 and 7 times improvement in sensitivity compared with that of OFM and MFM. Our results could be used as a basis for novel probes in practical ICA applications.

Surface Modifications for Photon-Upconversion-Based Energy-Transfer Nanoprobes

An emerging class of inorganic optical reporters are near-infrared (NIR) excitable lanthanide-based upconversion nanoparticles (UCNPs) with multicolor emission and long luminescence lifetimes in the range of several hundred microseconds. For the design of chemical sensors and optical probes that reveal analyte-specific changes in their spectroscopic properties, these nanomaterials must be combined with sensitive indicator dyes that change their absorption and/or fluorescence properties selectively upon interaction with their target analyte, utilizing either resonance energy transfer (RET) processes or reabsorption-related inner filter effects. The rational development of UCNP-based nanoprobes for chemical sensing and imaging in a biological environment requires reliable methods for the surface functionalization of UCNPs, the analysis and quantification of surface groups, a high colloidal stability of UCNPs in aqueous media as well as the chemically stable attachment of the indicator molecules, and suitable instrumentation for the spectroscopic characterization of the energy-transfer systems and the derived nanosensors. These topics are highlighted in the following feature article, and examples of functionalized core-shell nanoprobes for the sensing of different biologically relevant analytes in aqueous environments will be presented. Special emphasis is placed on the intracellular sensing of pH.

Optimizing the Fluorescence Properties of Nanoemulsions for Single Particle Tracking in Live Cells

Nanoemulsions (NEs) are biocompatible lipid nanoparticles composed of an oily core stabilized by a surfactant shell. It is acknowledged that the surface decoration with poly(ethylene glycol), through the use of nonionic surfactants, confers high stealth in biological medium with reduced nonspecific interactions. Tracking individual NE by fluorescence microscopy techniques would lead to a better understanding of their behavior in cells and thus require the development of bright single particles with enhanced photostability. However, the understanding of the relationship between the physicochemical properties and chemical composition of the NEs, on the one hand, and its fluorescence properties of encapsulated dyes, on the other hand, remains limited. Herein, we synthesized three new dioxaborine barbituryl styryl (DBS) dyes that displayed high molar extinction coefficients (up to 120 000 M^-1 cm^-1) with relatively low quantum yields in solvents and impressive fluorescence enhancement when dissolved in viscous oils (up to 0.98). The reported screening of nine different oils allowed disclosing a range of efficient "oil/dye" couples and understanding the main parameters that lead to the brightest NEs. We determine vitamin E acetate/DBS-C₈ as the representative most efficient couple, combining high dye loading capabilities and low aggregation-induced quenching, leading to <50 nm ultrabright NEs (with brightness as high as 30 × 10⁶ M^-1 cm^-1) with negligible dye leakage in biological media. Beyond a comprehensive optical and physicochemical characterization of fluorescent NEs, cellular two-photon excitation imaging was performed with polymer-coated cell penetrating NEs. Thanks to their impressive brightness and photostability, NEs displaying different charge surfaces were microinjected in HeLa cells and were individually tracked in the cytosol to study their relative velocity.

Self-Assembled Biocompatible Fluorescent Nanoparticles for Bioimaging

Fluorescence is a powerful tool for mapping biological events in real-time with high spatial resolution. Ultra-bright probes are needed in order to achieve high sensitivity: these probes are typically obtained by gathering a huge number of fluorophores in a single nanoparticle (NP). Unfortunately this assembly produces quenching of the fluorescence because of short-range intermolecular interactions. Here we demonstrate that rational structural modification of a well-known molecular fluorophore N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) (NBD) produces fluorophores that self-assemble in nanoparticles in the biocompatible environment without any dramatic decrease of the fluorescence quantum yield. Most importantly, the resulting NP show, in an aqueous environment, a brightness which is more than six orders of magnitude higher than the molecular component in the organic solvent. Moreover, the NP are prepared by nanoprecipitation and they are stabilized only via non-covalent interaction, they are surprisingly stable and can be observed as individual bright spots freely diffusing in solution at a concentration as low as 1 nM. The suitability of the NP as biocompatible fluorescent probes was demonstrated in the case of HeLa cells by fluorescence confocal microscopy and MTS assays.

Towards more accurate bioimaging of drug nanocarriers: turning aggregation-caused quenching into a useful tool

One of the current challenges in the monitoring of drug nanocarriers lies in the difficulties in discriminating the carrier-bound signals from the bulk signals of probes. Environment-responsive probes that enable signal switching are making steps towards a solution to this problem. Aggregation-caused quenching (ACQ), a phenomenon generally regarded as unfavorable in bioimaging, has turned out to be a promising characteristic for achieving environment-responsiveness and eliminating free-probe interference. So-called ACQ probes emit fluorescence when dispersed molecularly within the carrier matrix but quench immediately and absolutely once they are released into the ambient aqueous environment upon the degradation of the nanocarriers. Therefore, the fluorescence observed represents integral nanocarriers. Based on this rationale, the in vivo fates of various nanocarriers have been explored using live imaging equipment, with very interesting findings revealing the role of the particles. The current applications are however restricted to nanocarriers with highly hydrophobic matrices (lipid or polyester nanoparticles) or with a hydrophobic core-hydrophilic shell structure (micelles). The ACQ-based bioimaging strategy is emerging as a promising tool to achieve more accurate bioimaging of drug nanocarriers. This review article provides an overview of the ACQ phenomenon and the rationale for and examples of applications, as well as the limitations of the ACQ-based strategy, with a focus on improving the accuracy of bioimaging of nanoparticles.

Ultrafast and Noninvasive Long-Term Bioimaging with Highly Stable Red Aggregation-Induced Emission Nanoparticles

Strongly red luminescent and water-soluble probes are very important for studying biological events and processes. Fluorescent nanoparticles (NPs) built from the aggregation-induced emission luminogen (AIEgen) and amphipathic polymeric matrixes have been considered as promising candidates for bioimaging. However, AIE NPs with long-wavelength absorption suitable for in vivo application are still scarce. In this work, three AIE-active red-emissive BODIPY derivatives with long-wavelength absorption were rationally designed and synthesized. Then three NPs based on these AIEgens exhibit bright red photoluminescence with high fluorescence quantum yield in aqueous media. These NPs uniformly dispersed in water and showed excellent stability and good biocompatibility. They can be readily internalized by HeLa cells, and the staining process is performed by simply shaking the culture with cells for just a few seconds at room temperature, which indicates an ultrafast and easy-to-operate staining protocol. More importantly, long-term tracing in living cells and mouse over 15 days is successfully achieved. The strong fluorescence signals, ultrafast staining procedure, and long-term tracing abilities indicate that these AIE NPs hold great potential for monitoring biological processes.

In Situ Monitoring of Fluorescent Polymer Brushes by Angle-Scanning Based Surface Plasmon Coupled Emission

Fluorescent polymers have attracted interest in many fields such as sensing, diagnostics, imaging, and organic electronic devices. Real-time techniques to monitor and understand the polymerization process are important for obtaining controllable fluorescence polymers. We present a new technique to in situ monitor the growth process of fluorescent polymer brushes by using angle-scanning based surface plasmon coupled emission (AS-SPCE) approach during electrochemically mediated atom-transfer radical polymerization. The polymer thickness was determined by modeling the location of SPCE emission angle(s) with theoretical calculation. The advantages of unique angle distribution patterns, thickness dependence and effective background rejection of AS-SPCE guarantee the success in the real-time investigation for controllable fabrication of fluorescent polymers.

Multicolor Raman Beads for Multiplexed Tumor Cell and Tissue Imaging and in Vivo Tumor Spectral Detection

Developing new nanomaterials with strong and distinctive Raman vibrations in the biological Raman-silent region (1800-2800 cm^-1) were highly desirable for Raman hyperspectral detection and imaging in living cells and animals. Herein, polymeric nanoparticles with monomers containing alkyne, cyanide, azide, and carbon-deuterate were prepared as Raman-active nanomaterials (Raman beads) for bioimaging applications. Intense Raman signals were obtained due to the high density of alkyne, cyanide, azide, and carbon-deuterate in single nanoparticles, in absence of metal (such as Au or Ag) as Raman enhancers. We have developed a library of Raman beads for frequency multiplexing through the end-capping substitutions of monomers and demonstrated five-color SRS imaging of mixed nanoparticles with distinct Raman frequencies. In addition, with further surface functionalization of targeting moieties (such as nucleic acid aptamers and targeting peptides), targetable Raman beads were successfully used as probes for tumor targeting and Raman spectroscopic detection, including multicolor SRS imaging in living tumor cells and tissues with high specificity. Further in vivo studies indicated that Raman beads anchored with targeting moieties were successfully employed to target tumors in living mice after tail intravenous injection, and Raman spectral detection of tumor in live mice was achieved only through spontaneous Raman signal at the biological Raman-silent region without any signal enhancement due to a high density of Raman reporters in Raman beads. With further copolymerization of these monomers, Raman beads with supermultiplex barcoding could be readily achieved.

Interchromophoric Interactions Determine the Maximum Brightness Density in DNA Origami Structures

An ideal point light source is as small and as bright as possible. For fluorescent point light sources, homogeneity of the light sources is important as well as that the fluorescent units inside the light source maintain their photophysical properties, which is compromised by dye aggregation. Here we propose DNA origami as a rigid scaffold to arrange dye molecules in a dense pixel array with high control of stoichiometry and dye-dye interactions. In order to find the highest labeling density in a DNA origami structure without influencing dye photophysics, we alter the distance of two ATTO647N dyes in single base pair steps and probe the dye-dye interactions on the single-molecule level. For small distances strong quenching in terms of intensity and fluorescence lifetime is observed. With increasing distance, we observe reduced quenching and molecular dynamics. However, energy transfer processes in the weak coupling regime still have a significant impact and can lead to quenching by singlet-dark-state-annihilation. Our study fills a gap of studying the interactions of dyes relevant for superresolution microscopy with dense labeling and for single-molecule biophysics. Incorporating these findings in a 3D DNA origami object will pave the way to bright and homogeneous DNA origami nanobeads.

Bioimaging Tools Based on Polyelectrolyte Microcapsules Encoded with Fluorescent Semiconductor Nanoparticles: Design and Characterization of the Fluorescent Properties

Fluorescent imaging is a widely used technique for detecting and monitoring the distribution, interaction, and transformation processes at molecular, cellular, and tissue level in modern diagnostic and other biomedical applications. Unique photophysical properties of fluorescent semiconductor nanocrystals "quantum dots" (QDs) make them advanced fluorophores for fluorescent labeling of biomolecules or optical encoding of microparticles to be used as bioimaging and theranostic agents in targeted delivery, visualization, diagnostics, and imaging. This paper reports on the results of development of an improved approach to the optical encoding of polyelectrolyte microcapsules with stable, covered with the multifunctional polyethyleneglycol derivatives water-soluble QDs, as well as characterization of the optical properties, morphological and structural properties of the encoded microcapsules. The embedding of QDs into the polymer microcapsule membrane through layer-by-layer deposition on a preliminarily formed polymeric polyelectrolyte shell makes it possible to obtain bright fluorescent particles with an adapted charge and size distribution that are distinctly discernible by flow cytometry as individual homogeneous populations. The fluorescent microcapsules developed can be used in further designing bioimaging and theranostic agents sensitive to various external stimuli along with photoexcitation.

Core-modified of fluoranthene with "propeller" structure for highly sensitive detection of nitroaromatic compounds

Two fluoranthene derivatives with "propeller" structure, named as 7,8,9,10-tetraphenylfluoranthene (TPFA) and 3-phenoxy-7,8,9,10-tetraphenyl fluoranthene (PO-TPFA), were designed and synthesized by introducing outer phenyl and phenoxy substituents to fluoranthene. Given the steric hindrance of this unique structure, both organic dyes exhibited similar fluorescence spectra and strong fluorescence emission from the solution to the film state. The introduction of a phenoxy group showed obvious influence to the molecular optical properties of fluoranthene. Density functional theory calculations were further conducted to verify this finding. Both dyes were used as fluorescent probes and exhibited and sensitive fluorescence response to nitroaromatic explosives and highly selectivity to picric acid. Furthermore, PO-TPFA exhibited better detection performance to nitroaromatic explosives than TPFA. This work can serve as a guide for molecular fluorescence design because these dyes possess excellent fluorescence in solution and film states and can be used for the sensitive fluorescence detection of nitroaromatic explosives.

Core–shell polymeric nanoparticles comprising BODIPY and fluorescein as ultra-bright ratiometric fluorescent pH sensors

Ultra-bright pH-sensitive fluorescent nanoparticles, including BODIPY in their core and fluorescein in their shell, are synthesized. They contain more than 2500 fluorophores and exhibit a linear fluorescence response between pH 5.5 and 7.5.

Inverted energy gap law for the nonradiative decay in fluorescent floppy molecules: larger fluorescence quantum yields for smaller energy gaps

The non-radiative decay of substituted dicyano-distyrylbenzenes in solution increase with the Franck–Condon energy, being opposite to the conventional energy gap law.

Organic Fluorescent Dye-based Nanomaterials: Advances in the Rational Design for Imaging and Sensing Applications

Self-assembled fluorescent nanomaterials based on small-molecule organic dyes are gaining increasing popularity in imaging and sensing applications over the past decade. This is primarily due to their ability to combine spectral properties tunability and biocompatibility of small molecule organic fluorophores with brightness, chemical and colloidal stability of inorganic materials. Such a unique combination of features comes with rich versatility of dye-based nanomaterials: from aggregates of small molecules to sophisticated core-shell nanoarchitectures involving hyperbranched polymers. Along with the ongoing discovery of new materials and better ways of their synthesis, it is very important to continue systematic studies of fundamental factors that regulate the key properties of fluorescent nanomaterials: their size, polydispersity, colloidal stability, chemical stability, absorption and emission maxima, biocompatibility, and interactions with biological interfaces. In this review, we focus on the systematic description of various types of organic fluorescent nanomaterials, approaches to their synthesis, and ways to optimize and control their characteristics. The discussion is built on examples from reports on recent advances in the design and applications of such materials. Conclusions made from this analysis allow a perspective on future development of fluorescent nanomaterials design for biomedical and related applications.

A two-photon fluorophore labeled multi-functional drug carrier for targeting cancer therapy, inflammation restraint and AIE active bioimaging

Functional drug carriers with simultaneous effective delivery of therapeutic agents to target sites and great imaging ability have attracted great attention in nanomedicine research.

Dual detection of bioaccumulated Hg2+ based on luminescent bacteria and aggregation-induced emission

We develop a dual detection strategy for bioaccumulated Hg²⁺ based on turn-off of the bioluminescence of P. phosphoreum bacteria by disrupting the quorum sensing system and turn-on of the photoluminescence of an aggregation-induced emission (AIE) probe by forming aggregates with Hg²⁺ inside the bacteria.

BODIPY-loaded polymer nanoparticles: chemical structure of cargo defines leakage from nanocarrier in living cells

Hydrophobicity of a fluorescent cargo loaded into PLGA nanoparticles is crucial for minimizing its leakage in biological media.

Cell-penetrating peptide modified AIE polymeric nanoparticles by miniemulsion polymerization and application for cell fluorescence imaging

AIE polymeric nanoparticles surface-modified with HIV Tat peptides for cell fluorescence imaging are efficiently prepared through miniemulsion polymerization, carbodiimide reaction, and thiol-maleimide click reaction in sequence.

Protein-modified conjugated polymer nanoparticles with strong near-infrared absorption: a novel nanoplatform to design multifunctional nanoprobes for dual-modal photoacoustic and fluorescence imaging

Engineering conjugated polymer nanoparticles (CPNs) with an easily-modified surface is essential to construct multifunctional nanoprobes as contrast agents for dual-modal photoacoustic (PA) and fluorescence imaging, which can take advantages of the complementary information from a single modality. In this study, an abundant protein with plenty of functional groups was introduced for the first time to produce easily-modified CPNs, leading to a robust nanoplatform to engineer PA-based multifunctional nanoprobes due to their strong optical absorption in the near-infrared region. Meanwhile, the bovine serum albumin (BSA)-modified CPNs were further engineered by introducing gold clusters in situ, which can serve as fluorescent nanoprobes for dual-modal molecular imaging. In particular, the developed nanoplatform exhibited superior stability and excellent biocompatibility, making it an ideal candidate for various cancer-theranostics applications. More importantly, our imaging results demonstrated that the BSA-modified CPNs were excellent candidates to design PA-based contrast agents for multimodal imaging using the function of the protein. In addition, other functional blocks can also be added to the nanoplatform based on its easily-modified surface, making it a general method for the construction of multifunctional nanoprobes for disease theranostics.

Dual-Mode, Anisotropy-Encoded, Ratiometric Fluorescent Nanosensors: Towards Multiplexed Detection

A nanosensor with dual-mode fluorescence response to pH and an encoded identification signal, was developed by exploiting excitation energy transfer and tailored control of molecular organization in core-shell nanoparticles. Multiple signals were acquired in a simple single-excitation dual-emission channels set-up.

Glycan targeted polymeric antibiotic prodrugs for alveolar macrophage infections

Alveolar macrophages resident in the lung are prominent phagocytic effector cells of the pulmonary innate immune response, and paradoxically, are attractive harbors for pathogens. Consequently, facultative intracellular bacteria, such as Francisella tularensis, can cause severe systemic disease and sepsis, with high morbidity and mortality associated with pulmonary infection. Current clinical treatment, which involves exhaustive oral or intravenous antibiotic therapy, has limitations such as systemic toxicity and off-target effects. Pulmonary administration represents a promising alternative to systemic dosing for delivering antibiotics directly to the lung. Here, we present synthesized mannosylated ciprofloxacin polymeric prodrugs for efficient pulmonary delivery, targeting, and subsequent internalization by alveolar macrophages. We demonstrate significant improvement in efficacy against intracellular infections in an otherwise uniformly lethal airborne Francisella murine model (F. novicida). When administered to the lungs of mice in a prophylactic regimen, the mannosylated ciprofloxacin polymeric prodrugs led to 50% survival. In a treatment regimen that was concurrent with infection, the survival of mice increased to 87.5%. Free ciprofloxacin antibiotic was ineffective in both cases. This significant difference in antibacterial efficacy demonstrates the impact of this delivery platform based on improved physiochemical, pharmacokinetic, and pharmacodynamic properties of ciprofloxacin administered via our glycan polymeric prodrug. This modular platform provides a route for overcoming the limitations of free drug and increasing efficacy in treatment of intracellular infection.

Recent Advances in Tracking the Transplanted Stem Cells Using Near-Infrared Fluorescent Nanoprobes: Turning from the First to the Second Near-Infrared Window

Stem cell-based regenerative medicine has attracted tremendous attention for its great potential to treat numerous incurable diseases. Tracking and understanding the fate and regenerative capabilities of transplanted stem cells is vital for improving the safety and therapeutic efficacy of stem cell-based therapy, therefore accelerating the clinical application of stem cells. Fluorescent nanoparticles (NPs) have been widely used for in vivo tracking of the transplanted stem cells. Among these fluorescent NPs, near-infrared (NIR) NPs have greatly improved the sensitivity, tissue penetration depth, spatial and temporal resolutions of the fluorescence imaging-based stem cell tracking technologies due to the reduced absorption, scattering, and autofluorescence of NIR fluorescence in tissues. Here, this review summarizes the recent studies regarding the tracking of transplanted stem cells using NIR NPs and emphasizes the recent advances of fluorescence imaging in the second NIR window (NIR-II, 1000-1700 nm). Furthermore, the challenges and future prospects of the NIR NP-based technologies are also discussed.

Assembly of Plasmonic and Magnetic Nanoparticles with Fluorescent Silica Shell Layer for Tri-functional SERS-Magnetic-Fluorescence Probes and Its Bioapplications

In this study, we report on the fabrication of multilayered tri-functional magnetic-SERS-fluorescence nanoprobes (MF-SERS particles) containing clustered superparamagnetic Fe3O4 nanoparticles (NPs), silver NPs, and a fluorescent silica layer. The MF-SERS particles exhibited strong SERS signals from the silver NPs as well as both superparamagnetism and fluorescence. MF-SERS particles were uptaken by cells, allowing successful separation using an external magnetic field. SERS and fluorescence signals could be detected from the NP-containing cells, and CD44 antibody-conjugated MF-SERS particles selectively targeted MDA-MB-231 cells. Based on these properties, MF-SERS particles proved to be a useful nanoprobe for multiplex detection and separation of cancer cells.

Intrinsically Fluorescent, Stealth Polypyrazoline Nanoparticles with Large Stokes Shift for In Vivo Imaging

Recent advances in super-resolution microscopy and fluorescence bioimaging allow exploring previously inaccessible biological processes. To this end, there is a need for novel fluorescent probes with specific features in size, photophysical properties, colloidal and optical stabilities, as well as biocompatibility and ability to evade the reticuloendothelial system. Herein, novel fluorescent nanoparticles are introduced based on an inherently fluorescent polypyrazoline (PPy) core and a polyethylene glycol (PEG) shell, which address all aforementioned challenges. Synthesis of the PPy-PEG amphiphilic block copolymer by phototriggered step-growth polymerization is investigated by NMR spectroscopy, size-exclusion chromatography, and mass spectrometry. The corresponding nanoparticles are characterized for their luminescent properties and hydrodynamic size in various aqueous environments (e.g., cell culture media). PPy nanoparticles particularly exhibit a large Stokes shift (Δλ = 160 nm or Δν > 7000 cm^-1 ) with visible light excitation and strong colloidal stability. While clearance by macrophages and endothelial cells is minimal, PPy displays good biocompatibility. Finally, PPy nanoparticles prove to be long circulating when injected in zebrafish embryos, as observed by in vivo time-lapse fluorescence microscopy. In summary, PPy nanoparticles are highly promising to be further developed as fluorescent nanodelivery systems with low toxicity and exquisite retention in the blood stream.

Synthesis and Postpolymerization Modification of Fluorine-End-Labeled Poly(Pentafluorophenyl Methacrylate) Obtained via RAFT Polymerization

Chain-end-labeled polymers are interesting for a range of applications. In polymer nanomedicine, chain-end-labeled polymers are useful to study and help understand cellular internalization and intracellular trafficking processes. The recent advent of fluorescent label-free techniques, such as nanoscale secondary ion mass spectrometry (NanoSIMS), provides access to high-resolution intracellular mapping that can complement information obtained using fluorescent-labeled materials and confocal microscopy and flow cytometry. Using poly(N-(2-hydroxypropyl)methacrylamide) (PHPMA) as a prototypical polymer nanomedicine, this paper presents a synthetic strategy to polymers that contain trace element labels, such as fluorine, which can be used for NanoSIMS analysis. The strategy presented in this paper is based on reversible addition fragmentation chain transfer (RAFT) polymerization of pentafluorophenyl methacrylate (PFMA) mediated by two novel chain-transfer agents (CTAs), which contain either one (α) or two (α,ω) fluorine labels. In the first part of this study, via a number of polymerization experiments, the polymerization properties of the fluorinated RAFT CTAs were established. 19F NMR spectroscopy revealed that these fluorinated RAFT agents possess unique spectral signatures, which allow to directly monitor RAFT agent conversion and measure end-group fidelity. Comparison with 4-cyanopentanoic acid dithiobenzoate, which is a standard CTA for the RAFT polymerization of PFMA, revealed that the introduction of one or two fluorine labels does not significantly affect the polymerization properties of the CTA. In the last part of this paper, a proof-of-concept study is presented that demonstrates the feasibility of the fluorine-labeled poly(pentafluorophenyl methacrylate) polymers as platforms for the postpolymerization modification to generate PHPMA-based polymer nanomedicines.

Quantum Dots-Based Multifunctional Nano-Prodrug Fabricated by Ingenious Self-Assembly Strategies for Tumor Theranostic

The rapid developments of quantum dots (QDs)-based nanoagents for imaging tumor and tracking drug delivery have been proven to be reliable nanodiagnostic techniques. Although abundant types of QD nanoagents have been developed for fighting against cancer, it still is a challenge to control their quality and achieve prefect repetition due to the complicated synthetic steps. The precise intermolecular self-assembly (SA) may afford a facile and low-cost strategy for this challenge. Herein, a pH and H₂O₂ dual-sensitive Sb-cyclodextrin (CD)-doxorubicin (DOX) molecule was designed to construct a QD-based theranostic prodrug (named as Sb-CD-DOX-ZAISe/ZnS) via host-guest strategy (1st SA strategy), in which QDs water-transfer and drug-uploading were integrated well. That is, the nano-prodrug (NPD) inherited highly luminescent properties from "host" QDs for bioimaging, as well as environment sensitivities from "guest" Sb-CD-DOX for drug release. Experimental results indicate that the Sb-CD-DOX-ZAISe/ZnS exhibited effectively passive tumor-targeting and could provide clear imaging for malignant tumors in metaphase or advanced stages; meanwhile, after coating with folic acid (FA) through electric attraction (2nd SA strategy), the final Sb-CD-DOX-ZAISe/ZnS@FA NPD showed expected pH-controlled negative-to-positive charge reversal ability and a better curative effect compared with free DOX. Hence, fabricating nanocomposites by highly efficient self-assembly strategies is favorable toward inorganic nanoparticles-based prodrug delivery system for tumor-targeting theranostic.

DNA-Functionalized Dye-Loaded Polymeric Nanoparticles: Ultrabright FRET Platform for Amplified Detection of Nucleic Acids

Going beyond the limits of optical biosensing motivates exploration of signal amplification strategies that convert a single molecular recognition event into a response equivalent to hundreds of fluorescent dyes. In this respect, Førster Resonance Energy Transfer (FRET) with bright fluorescent nanoparticles (NPs) is an attractive direction, but it is limited by poor efficiency of NPs as FRET donors, because their size is typically much larger than the Førster radius (∼5 nm). Here, we established FRET-based nanoparticle probes that overcome this fundamental limitation by exploiting a phenomenon of giant light harvesting with thousands of strongly coupled dyes in a polymer matrix. These nanoprobes are based on 40 nm dye-loaded poly(methyl methacrylate- co-methacrylic acid) (PMMA-MA) NPs, so-called light-harvesting nanoantennas, which are functionalized at their surface with oligonucleotides. To achieve this functionalization, we developed an original methodology: PMMA-MA was modified with azide/carboxylate bifunctional group that enabled assembly of small polymeric NPs and their further Cu-free click coupling with oligonucleotides. The obtained functionalized nanoantenna behaves as giant energy donor, where hybridization of target nucleic acid (encoding survivin cancer marker) with ∼23 grafted oligonucleotides/Cy5-acceptors switches on/off FRET from ∼3200 rhodamine-donors of the nanoantenna, leading to 75-fold signal amplification. In solution and on surfaces at single-particle level, the nanoprobe provides sequence-specific two-color ratiometric response to nucleic acids with limit of detection reaching 0.25 pM. It displays unprecedented brightness for a FRET biosensor: it outperforms analogous FRET-based molecular probe by >2000-fold and QDot-605 by ∼100-fold. The developed concept of amplified sensing will increase orders of magnitude sensitivity of fluorescent probes for biomolecular targets.

Thermochemiluminescent semiconducting polymer dots as sensitive nanoprobes for reagentless immunoassay

Thermochemiluminescence (TCL) is a potentially simple and sensitive detection principle, as the light emission is simply elicited by thermally-triggered decomposition of a molecule to produce a singlet excited-state product. Here we report about TCL semiconductive polymer dots (TCL-Pdots) obtained by doping fluorescent cyano-polyphenylene vinylene (CN-PPV) Pdots with an acridine 1,2-dioxetane derivative. The TCL-Pdots showed remarkable stability over time and minimum leaching of the thermo-responsive species. Furthermore, detectability of TCL-Pdots was improved by taking advantage of both the high number of 1,2-dioxetanes entrapped in each nanoparticle (about 20 molecules per Pdot) and the 5-fold enhancement of TCL emission due to energy transfer from 1,2-dioxetane to the polymer matrix, which itself acted as an energy acceptor. Indeed, upon heating the TCL-Pdots to 110 °C, 1,2-dioxetane decomposes generating an acridanone product in its electronically excited state. The latter transfers its energy to the surrounding CN-PPV chains via the Förster mechanism (φFRET about 80%), resulting in intense yellow light emission (550 nm wavelength). We next conjugated streptavidin onto the surface of these TCL-Pdots and demonstrated their suitability for use in biological studies. In particular, we used TCL-Pdots as labels in a model non-competitive immunoassay for IgG detection, which showed a LOD of 13 nM IgG and a dynamic range extending up to 230 nM. By combining the biocompatibility, brightness and tunability of Pdot fluorescence emission with the thermally-triggered reagentless light generation from TCL 1,2-dioxetanes, a broad panel of ultrabright TCL nanosystems could be designed for a variety of bioscience applications, even in multiplexed formats.