Ratiometric temperature sensing with semiconducting polymer dots

This communication describes ultrabright single-nanoparticle ratiometric temperature sensors based on semiconducting polymer dots (Pdots). We attached the temperature sensitive dye-Rhodamine B (RhB), whose emission intensity decreases with increasing temperature-within the matrix of Pdots. The as-prepared Pdot-RhB nanoparticle showed excellent temperature sensitivity and high brightness because it took advantage of the light harvesting and amplified energy transfer capability of Pdots. More importantly, the Pdot-RhB nanoparticle showed ratiometric temperature sensing under a single wavelength excitation and has a linear temperature sensing range that matches well with the physiologically relevant temperatures. We employed Pdot-RhB for measuring intracellular temperatures in a live-cell imaging mode. The exceptional brightness of Pdot-RhB allows this nanoscale temperature sensor to be used also as a fluorescent probe for cellular imaging.     

Generation of functionalized and robust semiconducting polymer dots with polyelectrolytes

We describe a facile method to functionalize semiconducting polymer dots (Pdots) with polyelectrolytes. The polyelectrolyte coating dramatically improves the colloidal stability of the Pdots in solutions which are either of high ionic strength or contain bivalent metal ions: this feature allows Pdots to be used under physiologically relevant environments without losing their functionality. We conjugated the polyelectrolyte-coated Pdots with streptavidin to demonstrate their application in specific cell labeling.     

TADF-based NIR-II semiconducting polymer dots for in vivo 3D bone imaging

Intraoperative fluorescence imaging in the second near-infrared (NIR-II) region heralds a new era in image-guided surgery since the success in the first-in-human liver-tumor surgery guided by NIR-II fluorescence. Limited by the conventional small organic NIR dyes such as FDA-approved indocyanine green with suboptimal NIR-II fluorescence and non-targeting ability, the resulting shallow penetration depth and high false positive diagnostic values have been challenging. Described here is the design of NIR-II emissive semiconducting polymer dots (Pdots) incorporated with thermally activated delayed fluorescence (TADF) moieties to exhibit emission maxima of 1064–1100 nm and fluorescence quantum yields of 0.40–1.58% in aqueous solutions. To further understand how the TADF units affect the molecular packing and the resulting optical properties of Pdots, in-depth and thorough density-functional theory calculations were carried out to better understand the underlying mechanisms. We then applied these Pdots for in vivo 3D bone imaging in mice. This work provides a direction for future designs of NIR-II Pdots and holds promising applications for bone-related diseases.

A series of NIR-II fluorescent TADF-incorporated polymer dots were successfully synthesized. The function of the TADF moiety was fully studied and the bio-applications of these polymer dots including bone imaging were also demonstrated.     

Facile synthesis of ultrabright luminogens with specific lipid droplets targeting feature for in vivo two-photon fluorescence retina imaging

The application of fluorescent probes for in vivo retinal imaging is of great importance, which could provide direct and crucial imaging evidence for a better understanding of common eye diseases. Herein, a group of bright organic luminogens with typical electron-donating (D) and electron-accepting (A) structures (abbreviated as LDs-BDM, LDs-BTM, and LDs-BHM) was synthesized through a simple single-step reaction. They were found to be efficient solid-state emitters with high fluorescence quantum yields of above 70% (e.g., 83.7% for LDs-BTM). Their light-emission properties could be tuned by the modulation of π-conjugation effect with methoxy groups at different substituent positions. Their resulting fluorescent nanoparticles (NPs) were demonstrated as specific lipid droplets (LDs) targeting probes with high brightness, good biocompatibility, and satisfactory photostability. LDs-BTM NPs with a large two-photon absorption cross section (σ₂ = 249 GM) were further utilized as ultrabright two-photon fluorescence (2PF) nanoprobes for in vivo retina imaging of live zebrafish by NIR excitation at an ultralow concentration (0.5 µmol/L). Integrated histological structures at the tissue level and corresponding fine details at the cellular level of the embryonic retina of live zebrafish were clearly demonstrated. This is the first report of using ultrabright LDs-targeting nanoprobes to accurately measure fine details in the retina with 2PF microscopic technique. These good results are anticipated to open up a new avenue in the development of efficient 2PF emitters for non-invasive bioimaging of living animals.     

Thermo-sensitive imprinted polymer coating CdTe quantum dots for target protein specific recognition

A thermo-sensitive imprinted polymer coating CdTe quantum dots was developed to prepare fluorescent thermo-sensitive protein-affinity materials, which exhibited high specific recognition ability towards target proteins.     

Copper(II) and iron(II) ion sensing with semiconducting polymer dots

This communication describes a simple platform that employs carboxyl functionalized semiconducting polymer dots as a fluorescent probe for sensitive ratiometric Cu(2+) and Fe(2+) detection, in which the sensing mechanism is based on aggregation-induced fluorescence quenching.     

Optimization of functionalized polymer layers for specific targeting of mobile receptors on cell surfaces

The reversible binding between a planar polymer layer functionalized by ligands and a planar cell surface containing different densities of mobile receptors has been studied by Monte Carlo simulations. Using the acceptance-ratio method, the distance-dependent profiles for the average number of ligands bound to receptors, the total free energy for the polymer layer-cell surface interaction and the interaction force were obtained. Four main design parameters for the polymer layer were considered: the degree of functionalization, chain degree of polymerization, polymer grafting density and the binding energy for the ligand-receptor interaction. We found that an increase in the degree of functionalization or in the absolute energy of ligand-receptor binding results in a larger number of ligands bound to the receptors, lower free energy, and stronger attractive force. Polymer layers composed of shorter chains were found to exhibit a deeper and narrower free energy profile and a larger attractive force, while longer tethers can interact with the cell surface at a larger and broader range of separation distances, in agreement with experimental observations. Our simulation results show that the increase in polymer grafting density from the mushroom to brush regime enhances the ligand availability and results in a stronger attractive force, increases the maximum binding distance, but exhibits a shallower free energy minimum due to the smaller tolerance to compression for polymer layers with high grafting density. We used two measures of the polymer layer binding affinity to the cell surface: the free energy minimum, related to the equilibrium binding constant and the fraction of bound ligands. We found that the polymer layers with a smaller chain length and grafting density, larger degree of functionalization, and larger absolute binding energy exhibit both a larger equilibrium binding constant to the cell surface and a larger average number of bound ligands, except for high binding energies when the maximum level of binding is reached independently of polymer length and grafting density. We showed that high binding specificity can be achieved by the polymer layers with intermediate ligand-receptor binding energies or an intermediate number of ligands, as a larger binding energy or number of ligands ensures a high binding affinity but lacks specificity while a smaller binding energy or number of ligands provides inadequate affinity. We found that the results for polymer layers with different properties follow a similar pattern when both high binding affinity to cells with high receptor density and high binding specificity are considered. As a result, the optimal design of the polymer layers can be achieved by using several different strategies, which are discussed.     

Bioconjugation of protein-repellent zwitterionic polymer brushes grafted from silicon nitride

A new method for attaching antibodies to protein-repellent zwitterionic polymer brushes aimed at recognizing microorganisms while preventing the nonspecific adsorption of proteins is presented. The poly(sulfobetaine methacrylate) (SBMA) brushes were grafted from α-bromo isobutyryl initiator-functionalized silicon nitride (Si(x)N(4), x ≥ 3) surfaces via controlled atom-transfer radical polymerization (ATRP). A trifunctional tris(2-aminoethyl)amine linker was reacted with the terminal alkylbromide of polySBMA chains. N-Hydroxysuccinimide (NHS) functionalization was achieved by reacting the resultant amine-terminated polySBMA brush with bifunctional suberic acid bis(N-hydroxysuccinimide ester). Anti-Salmonella antibodies were subsequently immobilized onto polySBMA-grafted Si(x)N(4) surfaces through these NHS linkers. The protein-repellent properties of the polySBMA-grafted surface after antibody attachment were evaluated by exposing the surfaces to Alexa Fluor 488-labeled fibrinogen (FIB) solution (0.1 g·L(-1)) for 1 h at room temperature. Confocal laser scanning microscopy (CLSM) images revealed the minimal adsorption of FIB onto the antibody-coated polySBMA in comparison with that of antibody-coated epoxide monolayers and also bare Si(x)N(4) surfaces. Subsequently, the interaction of antibodies immobilized onto polySBMA with SYTO9-stained Salmonella solution without using blocking solution was examined by CLSM. The fluorescent images showed that antibody-coated polySBMA efficiently captured Salmonella with only low background noise as compared to antibody-coated monolayers lacking the polymer brush. Finally, the antibody-coated polySBMA surfaces were exposed to a mixture of Alexa Fluor 647-labeled FIB and Salmonella without the prior use of a blocking solution to evaluate the ability of the surfaces to capture bacteria while simultaneously repelling proteins. The fluorescent images showed the capture of Salmonella with no adsorption of FIB as compared to antibody-coated epoxide surfaces, demonstrating the potential of the zwitterionic layer in preventing the nonspecific adsorption of the proteins during the detection of bacteria in complex matrices.     

Diarylethene doped biocompatible polymer dots for fluorescence switching

The photochromic molecule diarylethene works as a "toggle switch" for biocompatible fluorescence polymer dots and enables fluorescence switching in biological samples.     

Grafted semiconducting polymer amphiphiles for multimodal optical imaging and combination phototherapy

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

This review summarizes the applications of grafted semiconducting polymer amphiphiles (SPAs) as multimodal optical nanoagents for cancer imaging and combination phototherapy.     

Magnetic targeting and cellular uptake of polymer microcapsules simultaneously functionalized with magnetic and luminescent nanocrystals

By using a flow channel system for modeling the bloodstream in the circulatory system and by locally creating a magnetic field gradient caused by a permanent magnet, we demonstrate specific trapping of polymer capsules simultaneously functionalized with two types of nanoparticles--magnetic and luminescent nanocrystals. In the regions where the capsules were trapped by the magnetic field, drastically increased uptake of capsules by cells has been observed. The uptake of capsules by cells could be conveniently monitored with a fluorescence microscope by the luminescence of CdTe nanocrystals that had been embedded into the shells of the capsules. Our experiments envisage the feasibility of magnetic targeting of polymer capsules loaded by pharmaceutical agents to pathogenic parts of a tissue.     

Cellular internalization and targeting of semiconductor quantum dots

Peptide-mediated internalization and organelle targeting of quantum dots.     

FRET-based polymer materials for detection of cellular microenvironments

Effective detection of cellular microenvironments and understanding of physiological activities in living cells remain a considerable challenge.In recent years,fluore scence(or Forster) resonance energy trans fe r(FRET) technology has emerged as a valuable method for real-time imaging of intracellular environment with high sensitivity,specificity and spatial resolution.Particularly,polymer-based imaging systems show enhanced stability,improved biodistribution,increased dye payloads,and amplified signal/noise ratio compared with small molecular sensors.This review summarizes the recent progress in FRET-based polymeric systems for probing the physiological environments in cells.     

PAA-derived gold nanorods for cellular targeting and photothermal therapy

A single-step LbL procedure to functionalize CTAB-capped GNRs via electrostatic self-assembly is reported. This approach allows for consistent biomolecule/GNR coupling using standard carboxyl-amine conjugation chemistry. The focus is on cancer-targeting biomolecule/GNR conjugates and selective photothermal destruction of cancer cells by GNR-mediated hyperthermia and NIR light. GNRs were conjugated to a single-chain antibody selective for colorectal carcinoma cells and used as probes to demonstrate photothermal therapy. Selective targeting and GNR uptake in antigen-expressing SW 1222 cells were observed using fluorescence microscopy. Selective photothermal therapy is demonstrated using SW 1222 cells, where >62% cell death was observed after cells are treated with targeted A33scFv-GNRs.     

Encapsulating of single quantum dots into polymer particles

Single semiconductor quantum dots were embedded into polymer particles with diameters below 0.1 μm by an emulsion polymerization procedure or via a secondary dispersion approach. The photoluminescence properties of the nanocrystals are retained upon encapsulation, as demonstrated by fluorescence confocal microscopy.

In-situ encapsulation of quantum dots into polymer microspheres

We have incorporated fluorescent quantum dots (QDs) into polystyrene microspheres using functionalized oligomeric phosphine (OP) ligands. We find that a uniform distribution of quantum dots is loaded inside each polymer bead. Some local close-packing of quantum dots in the beads is attributed to the self-polymerization of the functionalized ligands. The presence of quantum dots disturbs the nucleation and growth processes during the formation of polymer microspheres and results in a wider size distribution of the quantum dot-embedded polystyrene beads than for the control without dots. The change in quantum efficiency of the quantum dots before (approximately 20%) and after (12%) loading into the beads substantiates the protection of oligomeric phosphine ligands yet indicates that the properties of these quantum dots are still affected during processing.     

Inkjet printing of well-defined polymer dots and arrays

Inkjet printing represents a highly promising polymer deposition method, which is used for, for example, the fabrication of multicolor polyLED displays and polymer-based electronics parts. The challenge is to print well-defined polymer structures from dilute solution. We have eliminated the formation of ring stains by printing nonvolatile acetophenone-based inks on a perfluorinated substrate using different polymers. (De)pinning of the contact line of the printed droplet, as related to the choice of solvent, is identified as the key factor that determines the shape of the deposit, whereas the choice of polymer is of minor importance. Adding 10 wt % or more of acetophenone to a volatile solvent (ethyl acetate)-based polymer solution changes the shape of the deposit from ring-like to dot-like, which may be due to the establishment of a solvent composition gradient. Arrays of closely spaced dots have also been printed. The size of the dots is considerably smaller than the nozzle diameter. This may prove a potential strategy for the inkjet printing of submicrometer structures.