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

Synthesis of amphoteric fluorescent copolymers: materials exhibiting multicolor photophysical properties

Six emissive amphoteric copolymers were prepared and characterized (¹H NMR, DSC, steady-state UV-vis, and emission spectroscopy) in the paper. A system of multi-color emitters, composed of P1 (green and yellow), P2 (green), P3 (red), P4 (blue), P5 (yellow) and P6 (green and yellow), were presented. P5 showed multicolor fluorescence that belonged to the color-specially emissive system at different excitation wavelengths, and P6 exhibited color-correlated emission by efficient energy transfer.

Fluorescent conjugated polymer nanovector for in vivo tracking and regulating the fate of stem cells for restoring infarcted myocardium

Stem cell therapy holds great promise for cardiac regeneration. However, the lack of ability to control stem cell fate after in vivo transplantation greatly restricts its therapeutic outcomes. MicroRNA delivery has emerged as a powerful tool to control stem cell fate for enhanced cardiac regeneration. However, the clinical translation of therapy based on gene-transfected stem cells remains challenging, due to the unknown in vivo behaviors of stem cells. Here, we developed a nano-platform (i.e., PFBT@miR-1-Tat NPs) that can achieve triggered release of microRNA-1 to promote cardiac differentiation of mesenchymal stem cells (MSCs), and long-term tracking of transplanted MSCs through bright and ultra-stable fluorescence of conjugated polymer poly(9,9-dioctylfluorene-alt-benzothiadiazole) (PFBT). We found that PFBT@miR-1-Tat NP-treated MSCs significantly restored the infarcted myocardium by promoting stem cell cardiac differentiation and integration with the in situ cardiac tissues. Meanwhile, MSCs without gene delivery improved the infarcted heart functions mainly through a paracrine effect and blood vessel formation. The developed conjugated polymer nanovector should be a powerful tool for manipulating as well as revealing the fate of therapeutic cells in vivo, which is critical for optimizing the therapeutic route of gene and cell combined therapy and therefore for accelerating clinical translation. STATEMENT OF SIGNIFICANCE: The lack of controllability in stem cell fate and the unclear in vivo cellular behaviors restrict the therapeutic outcomes of stem cell therapy. Herein, we engineered fluorescent conjugated polymer nanoparticles as gene delivery nanovectors with controlled release and high intracellular delivery capability to harness the fate of mesenchymal stem cells (MSCs) in vivo, meanwhile to reveal the cellular mechanism of gene-treated stem cell therapy. As compared with only MSC treatment that improves infarcted myocardium functions through paracrine effect, treatment with conjugated polymer nanovector-treated MSCs significantly restored infarcted myocardium through enhancing MSC cardiac differentiation and integration with the in-situ cardiac tissues. These findings demonstrate that the conjugated polymer nanovector would be a powerful tool in optimizing gene and cell combined therapy.

Lipid-core/polymer-shell hybrid nanoparticles: synthesis and characterization by fluorescence labeling and electrophoresis

Among the lipid nanoparticles, lipid polymer hybrid nanoparticles (HNPs) composed of an oily core and a polymeric shell display interesting features as efficient drug carriers due to the high loading capability of the oil phase and the stability and surface functionalization of the polymer shell. Herein, we formulated lipid-core/polymer-shell hybrid nanoparticles (HNPs) using a simple nanoprecipitation method involving Vitamin E Acetate (VEA) as the oily core and a tailor-made amphiphilic polymer as a wrapping shell. The fluorescence labeling of the oil, using a newly developed green fluorogenic BODIPY tracker, and of the polymer using a covalent attachment of a red emitting rhodamine was done to assess the formation, the composition and the stability of these new hybrid nanoparticles using dual color electrophoresis gel analysis. This technique, combined to conventional DLS and electronic microscopy analysis, allowed us to quickly determine that 20 wt% of the polymer was an optimal ratio for obtaining stable HNPs by nanoprecipiation. Finally, we showed that using different polymeric shells, various HNPs can be obtained and finely discriminated using a combined approach of electrophoresis and two-color labeling.

Dye-Loaded Quatsomes Exhibiting FRET as Nanoprobes for Bioimaging

Fluorescent organic nanoparticles (FONs) are emerging as an attractive alternative to the well-established fluorescent inorganic nanoparticles or small organic dyes. Their proper design allows one to obtain biocompatible probes with superior brightness and high photostability, although usually affected by low colloidal stability. Herein, we present a type of FONs with outstanding photophysical and physicochemical properties in-line with the stringent requirements for biomedical applications. These FONs are based on quatsome (QS) nanovesicles containing a pair of fluorescent carbocyanine molecules that give rise to Förster resonance energy transfer (FRET). Structural homogeneity, high brightness, photostability, and high FRET efficiency make these FONs a promising class of optical bioprobes. Loaded QSs have been used for in vitro bioimaging, demonstrating the nanovesicle membrane integrity after cell internalization, and the possibility to monitor the intracellular vesicle fate. Taken together, the proposed QSs loaded with a FRET pair constitute a promising platform for bioimaging and theranostics.

Ultrabright fluorescent nanoscale labels for the femtomolar detection of analytes with standard bioassays

The detection and quantification of low-abundance molecular biomarkers in biological samples is challenging. Here, we show that a plasmonic nanoscale construct serving as an ‘add-on’ label for a broad range of bioassays improves their signal-to-noise ratio and dynamic range without altering their workflow and read-out devices. The plasmonic construct consists of a bovine-serum-albumin scaffold with approximately 210 IRDye 800CW fluorophores (with fluorescence intensity approximately 6700-fold that of a single 800CW fluorophore), a polymer-coated gold nanorod acting as a plasmonic antenna, and biotin as a high-affinity biorecognition element. Its emission wavelength can be tuned over the visible and near-infrared spectral regions by modifying its size, shape and composition. It is compatible with multiplexed bead-based immunoassays (it improves the limit of detection by up to 4,750-fold in fluorescence-linked immunosorbent assays), immuno-microarrays, flow-cytometry and immunocytochemistry methods, and it shortens overall assay times and lowers sample volumes, as shown for the detection of a pro-inflammatory cytokine in mouse interstitial fluid and of urinary biomarkers in patient samples.

Devising Efficient Red-Shifting Strategies for Bioimaging: A Generalizable Donor-Acceptor Fluorophore Prototype

Long emission wavelengths, high fluorescence quantum yields (FQYs), and large Stokes shifts are highly desirable features for fluorescent probes in biological imaging. However, the current development of many fluorescent probes remains largely trial-and-error and lacks efficiency. Moreover, to achieve far-red/near-infrared emission, a significant extension in the π -conjugation is usually adopted but accompanied by other drawbacks such as fluorescence loss. In this review, we discuss an effective red-shifting strategy built upon the green fluorescent protein chromophore, which enables a synergistic tuning of both the electronic ground and excited states. This approach could shorten the path toward redder emission in comparison to the conventional intramolecular charge transfer (ICT) strategy. We envision that this spectroscopy and computation-aided strategy may advance the noncanonical fluorescent protein design and be generalized to various fluorophore scaffolds for redder emission while preserving other superior properties such as high FQYs.

A nano-photosensitizer based on covalent organic framework nanosheets with high loading and therapeutic efficacy

Photooxidation provides a promising strategy for photocatalysis, photodynamic therapy, and environmental protection. Unfortunately, most organic photosensitizers possess weak hydrophilicity and a π-π conjugated structure, leading to singlet oxygen self-quenching, poor loadability and therefore unsatisfactory photooxidation efficiency. Thus, dispersion of these photosensitizers within a two-dimensional porous covalent organic framework has become a feasible strategy to hinder their self-aggregation and augment their loading capacity. Here, we report a phthalocyanine-based photosensitizer loaded on covalent organic framework nanosheets. This nano-photosensitizer exhibits highly dispersed organic fluorescent phthalocyanines and a high loading capacity. The fabricated nanosheets restrict self-aggregation of photosensitizer molecules and enhance the photooxidation activity, which may offer a new paradigm for photooxidation and its multiple applications.

Multifunctional Janus Particles Composed of Azo Polymer and Pyrene-Containing Polymer

This study investigated Janus particles (JPs) composed of an azo polymer and a pyrene-containing polymer, focusing on preparation, formation mechanism, photoinduced deformation behavior, and fluorescent properties as well as tunable colors of the dispersions. A methacrylate-based copolymer containing pyrenyl groups (P(MMA-co-PyMA)) and two azo polymers, i.e., a methacrylate-based polymer (PCNAZO) and an epoxy-based polymer (CH-TZ-NT) both bearing push-pull-type azo chromophores, were synthesized for this purpose. Two types of Janus particles, P(MMA-co-PyMA)/PCNAZO JPs and P(MMA-co-PyMA)/CH-TZ-NT JPs, were fabricated through microphase separation of the components in the droplets dispersed in aqueous media, induced by the evaporation of the organic solvent. The process of JP formation was thoroughly investigated by exploiting the function of pyrene moieties as a molecular probe through measuring the fluorescence emission spectra at different times during the structure evolution. The photoluminescent (PL) intensity, excimer emission, and vibrational fine structure of the fluorescence spectra were observed to give information about phase separation and solidification occurred in the dispersed droplets. The observations were rationalized by analysis with ternary phase diagrams calculated on the basis of the Flory-Huggins theory. Upon irradiation with a linearly polarized laser beam at 488 nm, the azo polymer parts in the P(MMA-co-PyMA)/PCNAZO JPs were observed to be elongated along the electric vibration direction of the polarized light and transformed into particles with unique morphologies. The dispersions of JPs with different compositions of the two types of the polymers showed highly tunable color changes originating from both fluorescence of the pyrenyl fluorophores and light absorption of the azo chromophores.

Simple Method to Supply Organic Nanoparticles with Excitation-Wavelength-Dependent Photoluminescence

Organic fluorescent nanoparticles (FNPs) have become increasingly prevalent in a variety of applications but the creation of organic FNPs using a simple procedure and that possess diverse morphology, multicolor luminescence, and high brightness has been challenging. Herein, a facile strategy to prepare this class of organic FNPs is established by way of preformed organic nanoparticles themselves. It was found that as long as the nanoparticles contained aromatic/heterocyclic rings in their base unit and regardless of morphologies (e.g., small-molecule micelles, polymeric micelles, reverse micelles, solid microspheres, and vesicles), simple UV irradiation can result in the particles exhibiting excitation-wavelength-dependent photoluminescence with considerable quantum yields (∼8.3-16.7% for tested particles). Upon initial investigation of the mechanism, the photoluminescence behavior was attributed to a polycyclic aromatic hydrocarbon (PAH) process. Furthermore, the application of the synthesized organic FNPs in cancer cell imaging is demonstrated as just one of the many potential applications. The straightforward method to supply preformed organic nanoparticles with photoluminescence would be attractive for scientists in both academia and industry.

Cobalt Oxyhydroxide-prompted Synthesis of Fluorescent Polydopamine Nanoparticles for Glutathione Detection

Glutathione (GSH) plays an important role in cells, which is an essential endogenous antioxidant. Here, we have developed a new detection platform to analyze GSH levels. In our system, fluorescent polydopamine (PDA) nanoparticles, as signal indicators, were obtained by oxidation through cobalt oxyhydroxide (CoOOH) nanosheets. When CoOOH was present, CoOOH could quickly oxidize dopamine to fluorescent PDA nanoparticles. However, once GSH existed, CoOOH nanosheets were decomposed into Co²⁺, and oxidation between CoOOH and dopamine was prevented with weaker fluorescence occurring. Thus, we could realize detection of the GSH concentration according to the decreased fluorescence value of the fluorescent polydopamine. This method provides a fast, simple, high sensitivity and desirable selectivity platform for GSH monitoring.

Tumor Targeting Gene Vector for Visual Tracking of Bcl-2 siRNA Transfection and Anti-Tumor Therapy

Tumor targeting provided more effective gene therapy. Bcl-2 is an oncogene, and Bcl-2 small interfering RNA (Bcl-2 siRNA) can inhibit its expression. Here, a fluorescent and gene-loading capacity vector DPL, derived from diketopyrrolopyrrole (DPP), was developed for Bcl-2 siRNA-targeted delivery and tumor imaging in vitro and in vivo. The vector DPL showed a significant emission enhancement after interacting with siRNA, which was used to track the gene transfer process. Compared to commercial transfection reagent Lipo 2000, DPL obviously downregulated the Bcl-2 protein expression and exhibited excellent antitumor efficacy with less Bcl-2 siRNA. Importantly, DPL can target tumors to transport Bcl-2 siRNA to tumor sites in vivo based on the enhanced permeability and retention (EPR) effect for effective in vivo tumor therapy. This work inspired us to design and synthesize a multifunctional gene vector for tumor targeting and gene therapy.

Red aggregation-induced emission luminogen and Gd3+ codoped mesoporous silica nanoparticles as dual-mode probes for fluorescent and magnetic resonance imaging

Fluorescence imaging and magnetic resonance imaging have been research hotspots for adjuvant therapy and diagnosis. However, traditional fluorescent probes or contrast agents possess insurmountable weaknesses. In this work, we reported the preparation of dual-mode probes based on mesoporous silica nanomaterials (MSNs), which were doped with an aggregation-induced emission (AIE) dye and Gd³⁺ through a direct sol-gel method. In this system, the obtained materials emitted strong red fluorescence, in which the maximum emission wavelength was located at 669 nm, and could be applied as effective fluorescence probes for fluorescence microscopy imaging. Furthermore, the introduction of Gd³⁺ made the nanoparticles effective contrast agents when applied in contrast-enhanced magnetic resonance (MR) imaging because they could improve the contrast of MR imaging. The excellent biocompatibility of these nanoparticles, as demonstrated via a typical CCK-8 assay, and their performance in fluorescence cell imaging and MR imaging shows their potential for applications in biomedical imaging.

Nanoparticle brain delivery: a guide to verification methods

Many reports conclude nanoparticle (NP) brain entry based on bulk brain analysis. Bulk brain includes blood, cerebrospinal fluid and blood vessels within the brain contributing to the blood–brain and blood–cerebrospinal fluid barriers. Considering the brain as neurons, glia and their extracellular space (brain parenchyma), most studies did not show brain parenchymal NP entry. Blood–brain and blood–cerebrospinal fluid barriers anatomy and function are reviewed. Methods demonstrating brain parenchymal NP entry are presented. Results demonstrating bulk brain versus brain parenchymal entry are classified. Studies are reviewed, critiqued and classified to illustrate results demonstrating bulk brain versus parenchymal entry. Brain, blood and peripheral organ NP timecourses are compared and related to brain parenchymal entry evidence suggesting brain NP timecourse informs about brain parenchymal entry.

Natural Nanofiber Shuttles for Transporting Hydrophobic Cargo into Aqueous Solutions

Hydrophobic biomolecules realize their functions in vivo in aqueous environments, often through a delicate balance of amphiphilicity and chaperones. Introducing exogenous hydrophobic biomolecules into in vivo aqueous systems is a challenge in drug delivery and regenerative medicine, where labile linkers, carriers, and fusions or chimeric molecules are often designed to facilitate such aqueous interfaces. Here, we utilize naturally derived silk nanofiber shuttles with the capacity to transport hydrophobic cargos directly into aqueous solutions. These nanofibers disperse in organic solvents and in aqueous solutions because of their inherent amphiphilicity, with enriched hydrophobicity and strategically interspersed negatively charged groups. Hydrophobic molecules loaded on these shuttles in organic solvent-water systems separated from the solvent after centrifugation. These concentrated hydrophobic molecule-loaded nanofibers could then be dispersed into aqueous solution directly without modification. These shuttle systems were effective for different hydrophobic molecules such as drugs, vitamins, and dyes. Improved biological stability and functions of hydrophobic cargos after loading on these nanofibers suggest potential applications in drug delivery, cosmetology, medical diagnosis, and related health fields, with a relatively facile process.

Intraductal Drug Delivery to the Breast: Effect of Particle Size and Formulation on Breast Duct and Lymph Node Retention

Drug delivery by direct intraductal administration can achieve high local drug concentration in the breast and minimize systemic levels. However, the clinical application of this approach for breast cancer treatment is limited by the rapid clearance of the drug from the ducts. With the goal of developing strategies to prolong drug retention in the breast, this study was focused on understanding the influence of particle size and formulation on breast duct and lymph node retention. Fluorescent-labeled polystyrene (PS) particles ranging in size from 100 to 1000 nm were used to study the influence of particle size. Polylactic acid-co-glycolic acid (PLGA) was used to develop and test formulations for intraductal delivery. Cy 5.5, a near-IR dye, was encapsulated in PLGA microparticles, nanoparticles, and the in situ gel to study the biodistribution in rats using an in vivo imager. PS microparticles (1 μm) showed longer retention in the duct compared to 100 and 500 nm nanoparticles. The ductal retention half-life was 5-fold higher for PS microparticles compared to the nanoparticles. On the other hand, the free dye was cleared from the breast within 6 h. PLGA nanoparticles sustained the release of Cy 5.5 for >4 days. Microparticles and gel showed a much slower release than nanoparticles. PLGA in situ gel and microparticles were retained in the breast for up to 4 days, while the nanoparticles were retained in the breast for 2 days. PLGA nanoparticles and microparticles drained to the axillary lymph node and were retained for up to 24 and 48 h, respectively, while the in situ gel and the free dye did not show any detectable fluorescence in the lymph nodes. Taken together, the results demonstrate the feasibility of prolonged retention in the breast duct and lymph node by optimal formulation design. The findings can serve as a framework to design formulations for localized treatment of breast cancer.

Zwitterionic Stealth Dye-Loaded Polymer Nanoparticles for Intracellular Imaging

Intracellular applications of fluorescent nanoparticles (NPs) as probes and labels are currently limited by significant molecular crowding and the high level of complexity encountered inside living cells. The solution is to develop very small, bright, and noninteracting (stealth) NPs. Combining these properties requires implementing the stealth behavior through the thinnest possible hydrophilic shell. Here, we propose a one-step process for preparing ultrasmall and bright stealth NPs based on a zwitterionic (ZI) methacrylate-based copolymer. Dye-loaded polymer NPs are assembled through nanoprecipitation of the copolymer together with the salt of a rhodamine B derivative and a bulky hydrophobic counterion to achieve high particle brightness. We found that 10 mol % ZI groups in the polymer yield NPs of less than 15 nm that are stable in physiological salt conditions and practically resistant to protein adsorption, as suggested by fluorescence correlation spectroscopy. The combination of the very small size with the nonfouling nature of these particles enables spreading of ZI polymer NPs in the whole cytosol after their microinjection into living cells. In addition, single-particle tracking showed up to four times faster diffusion of ZI NPs in the cytosol compared to PEGylated NPs. The obtained dye-loaded ZI polymer NPs open the route to intracellular single-particle tracking and biosensing applications.

Amine decorated polystyrene nanobeads incorporating π-conjugated OPV chromophore for picric acid sensing in water

A solution as well as solid state based sensor has been developed for selective detection of picric acid (PA) in water. Oligo (p-phenylenevinylene) (OPV) incorporated polystyrene nanobeads (PS-OPV-NH₂) having an average size of 180 nm have been synthesized through miniemulsion polymerization. Amine (–NH₂) functionalization was performed on the nanobead surface to enhance the efficiency of the sensor among a library of other nitro-organics and library of cations and anions.

A fluorescent sensor has been developed for selective detection of picric acid (PA) in water. Amine (–NH₂) functionalization on the nanobead surface enhanced the efficiency of the sensor among a library of nitro-organics, cations and anions.

Aqueous solubilization of hydrophobic tetrapyrrole macrocycles by attachment to an amphiphilic single-chain nanoparticle (SCNP)

Snapping a heterotelechelic amphiphilic polymer onto a tetrapyrrole imparts aqueous solubility to the otherwise hydrophobic macrocycle as demonstrated for a chlorin, bacteriochlorin and phthalocyanine.

Novel fluorescein polymer-based nanoparticles: facile and controllable one-pot synthesis, assembly, and immobilization of biomolecules for application in a highly sensitive biosensor

A key aspect of biochip and biosensor preparation is optimization of the optical or electrochemical techniques that combine high sensitivity and specificity. Among them, optical techniques such as the use of fluorescent polymeric nanoparticles have resulted in dramatic progress in the field of diagnostics due to their range of advantages. We herein report a facile approach for the development of novel fluorescein polymeric nanoparticles (FPNPs) with immobilization of specific biomolecules for application in a highly sensitive optical biosensor. A series of three amphiphilic fluorescein polymers (poly(FMA-r-NAS-r-MA)), comprising hydrophobic fluorescein O-methacrylate (FMA), hydrophilic N-acryloxysuccinimide (NAS), and methacrylic acid (MA) monomers were synthesized through radical polymerization. In an aqueous environment, these fluorescein polymers self-assembled into spherical shaped nanoparticles with a well-defined particle size, narrow particle size distribution, and enhanced fluorescence properties. The bio-immobilization properties of the FPNPs were also tunable by control of the activated N-hydroxysuccinimide ester group in the polymer series. Furthermore, the fluorescence sensitivity of bovine serum albumin detection by the FPNPs indicates that the limit of detection and sensitivity were improved compared to conventional fluorescence dye-labelled proteins. These novel FPNPs therefore represent a suitable technology for disease diagnosis and biomarker detection to ultimately improve the sensitivity of existing analytical methodologies in a facile and cost-effective manner.

We report a facile approach for the development of novel fluorescein polymeric nanoparticles (FPNPs) with immobilization of specific biomolecules for application in a highly sensitive optical biosensor.

Preparation of fluorescent polystyrene nanoparticles mediated by a multi-functional amphiphilic iridium complex under visible light irradiation in aqueous solution

Amphiphilc iridium(iii) complex has been synthesized and served as both a photoinitiator and a surfactant for the preparation of nanoparticles with high fluorescence intensity and uniform morphology by visible light irradiation of styrene in aqueous.

Noninvasive Assessment of Exosome Pharmacokinetics In Vivo: A Review

Exosomes, intraluminal vesicles that contain informative DNA, RNA, proteins, and lipid membranes derived from the original donor cells, have recently been introduced to therapy and diagnosis. With their emergence as an alternative to cell therapy and having undergone clinical trials, proper analytical standards for evaluating their pharmacokinetics must now be established. Molecular imaging techniques such as fluorescence imaging, magnetic resonance imaging, and positron emission tomography (PET) are helpful to visualizing the absorption, distribution, metabolism, and excretion of exosomes. After exosomes labelled with a fluorescer or radioisotope are administered in vivo, they are differentially distributed according to the characteristics of each tissue or lesion, and real-time biodistribution of exosomes can be noninvasively monitored. Quantitative analysis of exosome concentration in biological fluid or tissue samples is also needed for the clinical application and industrialization of exosomes. In this review, we will discuss recent pharmacokinetic applications to exosomes, including labelling methods for in vivo imaging and analytical methods for quantifying exosomes, which will be helpful for evaluating pharmacokinetics of exosomes and improving exosome development and therapy.

Ultrabright fluorescent silica nanoparticles for in vivo targeting of xenografted human tumors and cancer cells in zebrafish

New ultrabright fluorescent silica nanoparticles capable of the fast targeting of epithelial tumors in vivo are presented. The as-synthesized folate-functionalized ultrabright particles of 30-40 nm are 230 times brighter than quantum dots (QD450) and 50% brighter than the polymer dots with similar spectra (excitation 365 nm and emission 486 nm). To decrease non-specific targeting, particles are coated with polyethylene glycol (PEG). We demonstrate the in vivo targeting of xenographic human cervical epithelial tumors (HeLa cells) using zebrafish as a model system. The particles target tumors (and probably even individual HeLa cells) as small as 10-20 microns within 20-30 minutes after blood injection. To demonstrate the advantages of ultrabrightness, we repeated the experiments with similar but 200× less bright particles. Compared to those, ultrabright particles showed ∼3× faster tumor detection and ∼2× higher relative fluorescent contrast of tumors/cancer cells.

Multimodal Cleavable Reporters for Quantifying Carboxy and Amino Groups on Organic and Inorganic Nanoparticles

Organic and inorganic nanoparticles (NPs) are increasingly used as drug carriers, fluorescent sensors, and multimodal labels in the life and material sciences. These applications require knowledge of the chemical nature, total number of surface groups, and the number of groups accessible for subsequent coupling of e.g., antifouling ligands, targeting bioligands, or sensor molecules. To establish the concept of catch-and-release assays, cleavable probes were rationally designed from a quantitatively cleavable disulfide moiety and the optically detectable reporter 2-thiopyridone (2-TP). For quantifying surface groups on nanomaterials, first, a set of monodisperse carboxy-and amino-functionalized, 100 nm-sized polymer and silica NPs with different surface group densities was synthesized. Subsequently, the accessible functional groups (FGs) were quantified via optical spectroscopy of the cleaved off reporter after its release in solution. Method validation was done with inductively coupled plasma optical emission spectroscopy (ICP-OES) utilizing the sulfur atom of the cleavable probe. This comparison underlined the reliability and versatility of our probes, which can be used for surface group quantification on all types of transparent, scattering, absorbing and/or fluorescent particles. The correlation between the total and accessible number of FGs quantified by conductometric titration, qNMR, and with our cleavable probes, together with the comparison to results of conjugation studies with differently sized biomolecules reveal the potential of catch-and-release reporters for surface analysis. Our findings also underline the importance of quantifying particularly the accessible amount of FGs for many applications of NPs in the life sciences.

Excitons in Carbonic Nanostructures

Unexpectedly bright photoluminescence emission can be observed in materials incorporating inorganic carbon when their size is reduced from macro–micro to nano. At present, there is no consensus in its understanding, and many suggested explanations are not consistent with the broad range of experimental data. In this Review, I discuss the possible role of collective excitations (excitons) generated by resonance electronic interactions among the chromophore elements within these nanoparticles. The Förster-type resonance energy transfer (FRET) mechanism of energy migration within nanoparticles operates when the composing fluorophores are the localized electronic systems interacting at a distance. Meanwhile, the resonance interactions among closely located fluorophores may lead to delocalization of the excited states over many molecules resulting in Frenkel excitons. The H-aggregate-type quantum coherence originating from strong coupling among the transition dipoles of adjacent chromophores in a co-facial stacking arrangement and exciton transport to emissive traps are the basis of the presented model. It can explain most of the hitherto known experimental observations and must stimulate the progress towards their versatile applications.

Biofunctionalized Polyelectrolyte Microcapsules Encoded with Fluorescent Semiconductor Nanocrystals for Highly Specific Targeting and Imaging of Cancer Cells

Fluorescent semiconductor nanocrystals or quantum dots (QDs) are characterized by unique optical properties, including a high photostability, wide absorption spectrum, and narrow, symmetric fluorescence spectrum. This makes them attractive fluorescent nanolabels for the optical encoding of microcarriers intended for targeted drug delivery, diagnosis, and imaging of transport processes on the body, cellular, and subcellular levels. Incorporation of QDs into carriers in the form of polyelectrolyte microcapsules through layer-by-layer adsorption of oppositely charged polyelectrolyte polymers yields microcapsules with a bright fluorescence signal and adaptable size, structure, and surface characteristics without using organic solvents. The easily modifiable surface of the microcapsules allows for its subsequent functionalization with capture molecules, such as antibodies, which ensures specific and selective interaction with cells, including tumor cells, with the use of the bioconjugation technique developed here. We obtained stable water-soluble nanolabels based on QDs whose surface was modified with polyethylene glycol (PEG) derivatives and determined their colloidal and optical characteristics. The obtained nanocrystals were used to encode polyelectrolyte microcapsules optically. The microcapsule surface was modified with humanized monoclonal antibodies (Abs) recognizing a cancer marker, epidermal growth factor receptor (EGFR). The possibility of effective, specific, and selective delivery of the microcapsules to tumor cells expressing EGFR has been demonstrated. The results show that the QD-encoded polyelectrolyte microcapsules functionalized with monoclonal Abs against EGFR can be used for targeted imaging and diagnosis.

BOPHYs versus BODIPYs: A comparison of their performance as effective multi-function organic dyes

The computationally-aided photophysical and lasing properties of a selected battery of BOPHYs are described and compared to those of related BODIPY counterparts. The present joined theoretical-experimental study helps to put into context the weaknesses and strengths of both dye families under different irradiation conditions. The chemical versatility of the BOPHY scaffold has been also comparatively explored to modulate key photonic properties towards the development of red-emitting dyes, chiroptical dyes and singlet oxygen photosensitizers. Thus, BOPHY BINOLation by fluorine substitution with enantiopure BINOLs endows the BOPHY chromophore with chiroptical activity, as supporting by the simulated circular dichroism, decreasing deeply its fluorescent response due to the promotion of fluorescence-quenching intramolecular charge transfer (ICT). Interestingly, the sole alkylation of the BOPHY core strongly modulates the promotion of ICT, allowing the generation of highly bright BINOL-based BOPHY dyes. Moreover, 3,3'-dibromoBINOLating BOPHYs can easily achieve singlet-oxygen photogeneration, owing to spin-orbit coupling mediated by heavy-atom effect feasible in view of the theoretically predicted disposition of the bromines surrounding the chromophore. From this background, we have established the master guidelines to design bright fluorophores and laser dyes, photosensitizers for singlet oxygen production and chiroptical dyes based on BOPHYs. The possibility to finely mix and balance such properties in a given molecular scaffold outstands BOPHYs as promising dyes competing with the well-settled BODIPY dyes.

Antiproliferative Ability and Fluorescence Tracking of α-Linolenic Acid-Loaded Microemulsion as Label-Free Delivery Carriers in MDA-MB-231 Cells

In this work, the effects of α-linolenic acid (ALA) loaded in oil-in-water (O/W) and water-in-oil-in-water (W/O/W) microemulsions on cell viability, lactic dehydrogenase (LDH) viability, and reactive oxygen species (ROS) levels were examined using Cell Counting Kit-8 (CCK-8), an LDH assay kit, and a fluorescence microscope, respectively. The CCK-8 assay demonstrated that ALA inhibited MDA-MB-231 human breast cancer cell proliferation in a dose-dependent manner. Further, the results of LDH activity and ROS levels revealed that ALA-induced cancer cell damage was closely related to oxidative stress. Under the irradiation of ultraviolet light, the microemulsion without any added fluorescent dye would emit bright blue fluorescence, and the fluorescent images of the cells treated with ALA-loaded O/W and W/O/W microemulsions at different incubation times were taken, which exhibited long-term photostability and biocompatibility. In addition, the fluorescence mechanism of the microemulsion was explained by immobilizing surfactant molecules with aggregation-induced emission (AIE) properties at the water-oil interface through the microemulsion with a self-assembled structure. These findings showed the potential application of O/W and W/O/W microemulsions as the label-free delivery carriers in long-term imaging of living cells and real-time release monitoring of nutrients.

Simple fluorene oxadiazole-based Ir(iii) complexes with AIPE properties: synthesis, explosive detection and electroluminescence studies

Two novel phosphorescent Ir(iii) complexes, Ir(fom)₂(pic) and Ir(fof)₂(pic), containing fluorene oxadiazole groups have been synthesized and characterized. The photophysical properties of the complexes have been investigated. Interestingly, both complexes exhibited aggregation-induced phosphorescent emission. The X-ray diffraction study showed that the AIPE properties resulted from weak π-π and C-HN hydrogen-bonding interactions in the aggregated state restricting the rotation of the phenyl groups in the cyclometalating ligands. Owing to the sensitive and selective luminescence quenching of the complexes using picric acid (PA), the complexes were used for PA detection in aqueous media. Additionally, electroluminescence devices have been fabricated using the complexes at 5%-30% doping concentrations. The devices based on Ir(fof)₂(pic) obtained the highest luminance 11 877 cd m^-2 and current efficiency 23.2 cd A^-1, which implied that the incorporation of fluorine could improve the electron affinity and ameliorate the capability of electron injection or transporting.

Hybrid Azo-fluorophore Organic Nanoparticles as Emissive Turn-on Probes for Cellular Endocytosis

The development of fluorescent organic nanoparticles, serving as bioimaging agents or drug cargos, represents a buoyant field of investigations. Nevertheless, their ulterior fate and structural integrity after cell uptake remain elusive. Toward this aim, we have elaborated original photoactive organic nanoparticles (d_TEM ∼ 35-50 nm wide) with an off-on signal upon cellular internalization. Such nanoparticles are based on the noncovalent association of red-emitting benzothiadiazole (BDZ) derivatives and azo dyes, acting as fluorescence quenchers. Upon varying the azo/BDZ ratio, we found that quantitative emission quenching could be obtained with only a 0.2:1 azo/BDZ ratio and originated from exergonic oxidative and reductive photoinduced electron transfer from the azo units (Δ_elG⁰ = -0.21 and -0.29 eV, respectively). Such results revisited the origin of emission quenching, often confusedly ascribed to Förster resonance energy transfer. A nonlinear and sharp drop of the emission intensity with the increase in the azo unit density n was observed and presents comparable evolution to a n^-1/3 mathematical law. Thorough biological examinations involving cancer cells prove a receptor-independent endocytosis pathway, leading to progressive cell lighting upon nanoparticle accumulation in the late endosomal/lysosomal compartments. Complete emission recovery of the initially quenched azo/BDZ nanosystems could be achieved by using mefloquine, which caused endosomal/lysosomal disruption, and release of their content in the cytoplasm. Such results demonstrate that the dotlike emission from endosomes actually stems from fully dissociated individual dyes and not integer nanoparticles. They conclude on the high spatial confinement promoted by organelles and finally question its severe impact on functional compounds or nanoparticles whose properties are strongly distance dependent.

Facile Incorporation of "Aggregation-Induced Emission"-Active Conjugated Polymer into Mesoporous Silica Hollow Nanospheres: Synthesis, Characterization, Photophysical Studies, and Application in Bioimaging

Typical aggregation-induced emission (AIE) luminogens tetraphenylethylene (TPE) and triphenylamine have been used to construct an AIE-active conjugated polymer, namely, poly(N,N-diphenyl-4-(4-(1,2,2-triphenylvinyl)styryl)aniline) (PTPA), which consist of D-π-A architecture by Wittig polymerization. We fabricated mesoporous silica hollow nanospheres (MSHNs) which were encapsulated with the AIE-active polymer for applications in cellular imaging. It exhibits a positive solvatochromism effect by increasing solvent polarity, supported by theoretical calculation using density functional theory. The structure of the monomers and polymer was confirmed by Fourier transform infrared, nuclear magnetic resonance, and high-resolution mass spectrometry techniques. Considering the advantage of high brightness in the fluorescence of PTPA, it was encapsulated into MSHNs by a noncovalent approach, and the surface was functionalized with an anti-EpCAM (antiepithelial cell adhesion molecule) aptamer through conjugation with γ-glycidoxypropyltrimethoxysilane for targeting cancer cells specifically. The aptamer-functionalized Apt-MSHNs exhibited excellent biocompatibility with the liver cancer-Huh-7 cells used for this study and was efficiently internalized by these cells. Because EpCAM are overexpressed in multiple carcinomas, including liver cancer, these aptamer-conjugated AIE MSHNs are therefore good candidates for targeted cellular imaging applications.

Effect of substitution on the excited state photophysical and spectral properties of boron difluoride curcumin complex dye and their derivatives: A time dependent-DFT study

The optical, charge transport and electronic properties of boron difluoride curcumin (BFC) complex have been explored using the DFT (Density Functional Theory) method and B3LYP functional with the combination of 6-31 + G(d,p) as a basis set. The influence of substitution with various electron releasing and withdrawing groups on the above properties is analyzed and discussed in this work. The results reveal that the BFC complex on additional electron releasing substitution experiences redshifts in the optical transitions, and this is correlated with the dipole moment, NBO charges, HOMO-LUMO energy gap. Further, the absorption (λ_abs) and emission (λ_ems) spectra of substituted and unsubstituted BFCs are calculated using Time-Dependent Density Functional Theory (TD-DFT). The results show that the electron releasing groups strongly influence the absorption and emission spectra of BFC. Electron releasing groups in BFC derivatives generate the wavelength shift (Bathochromic), but the electron-withdrawing groups in BFC don't affect the λ_abs and λ_ems when compare to its original (parent) compound. The output of the research work strongly recommends that the amino, phenyl and N, N'-dimethylamino derivatives are potential candidates to act as fluorescent materials due to enhance the emission behavior of BFC and also can be used as an electron/charge transport material for organic light-emitting diodes (OLEDs).

Ionic aggregation-induced emission dye with bulky counterions for preparation of bright near-infrared polymeric nanoparticles

Dyes exhibiting aggregation-induced emission (AIE) are attractive building blocks for the preparation of bright fluorescent nanomaterials. AIEgens are especially efficient in pure dye aggregates, whereas they are much less explored as dopants in NPs built of hydrophobic polymers. Here, we describe an approach that combines cationic AIEgens with bulky hydrophobic counterions (fluorinated tetraphenylborates) that enables preparation of small and bright AIEgen-loaded polymeric NPs. To this end, we synthesised a cationic tetraphenylethylene (TPE) derivative and studied its salts with counterions of different sizes and hydrophobicities. In organic solvent/water mixtures, all these salts exhibited typical AIE behaviour, whereas only salts with bulky hydrophobic counterions exhibited strongly red-shifted emission in the near-infrared (NIR) region. Encapsulation of these salts into poly(methyl methacrylate-co-methacrylic acid) (PMMA-MA) NPs revealed that bulky counterions ensure (i) formation of small (∼50 nm) AIEgen-loaded polymeric NPs; (ii) good fluorescence quantum yield (up to 30%); and (iii) NIR emission reaching 700 nm. By contrast, AIEgens with small inorganic anions (perchlorate and hexafluorophosphate) blended with PMMA-MA produced large aggregates with emission in the far-red region. Single-particle microscopy revealed that our 50 nm AIEgen-loaded PMMA-MA NPs were 6-fold brighter than the NIR emitting quantum dots (QD705). These NPs feature low cytotoxicity and compatibility with live cell imaging, in contrast to large aggregates of AIEgens with small inorganic counterions that failed to internalize into the cells. The present work shows that combination of cationic AIEgens with bulky counterions opens new routes for the preparation of bright polymer-based nanomaterials.

Recent Progress in Time-Resolved Biosensing and Bioimaging Based on Lanthanide-Doped Nanoparticles

Luminescent nanomaterials have attracted great attention in luminescence-based bioanalysis due to their abundant optical and tunable surface physicochemical properties. However, luminescent nanomaterials often suffer from serious autofluorescence and light scattering interference when applied to complex biological samples. Time-resolved luminescence methodology can efficiently eliminate autofluorescence and light scattering interference by collecting the luminescence signal of a long-lived probe after the background signals decays completely. Lanthanides have a unique [Xe]4f^N electronic configuration and ladder-like energy states, which endow lanthanide-doped nanoparticles with many desirable optical properties, such as long luminescence lifetimes, large Stokes/anti-Stokes shifts, and sharp emission bands. Due to their long luminescence lifetimes, lanthanide-doped nanoparticles are widely used for high-sensitive biosensing and high-contrast bioimaging via time-resolved luminescence methodology. In this review, recent progress in the development of lanthanide-doped nanoparticles and their application in time-resolved biosensing and bioimaging are summarized. At the end of this review, the current challenges and perspectives of lanthanide-doped nanoparticles for time-resolved bioapplications are discussed.

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.