A supramolecular, polymer-dot-based ensemble has been developed for the ratiometric detection of lectins and targeted delivery of glycoprobes. Self-assembly between a blue-emitting polymer dot and a red-emitting glycoprobe, results in an ensemble that shows red emission upon excitation of the polymer dot because of Förster resonance energy transfer. Resulting in ratiometric detection of lectins in buffer solution as well as targeted delivery of the glycoprobe to cells that highly express a sugar receptor. Unlike conventional systems where both the agent and vector are codelivered intracellularly, our ensemble developed here shows a receptor-controlled dissociation on the cell membrane.Keywords: cell imaging; glycoprobe; polymer dot; probe; ratiometric;

As a hybrid imaging technique, photoacoustic imaging (PAI) can provide multiscale morphological information of tissues, and the use of multi-spectral PAI (MSPAI) can recover the spatial distribution of chromophores of interest, such as hemoglobin within tissues. Herein, we developed a contrast agent that can very effectively combine multiscale PAI with MSPAI for a more comprehensive characterization of complex biological tissues. Specifically, we developed novel PIID-DTBT based semi-conducting polymer dots (Pdots) that show broad and strong optical absorption in the visible-light region (500–700 nm). The performances of gold nanoparticles (GNPs) and gold nanorods (GNRs), which have been verified as excellent photoacoustic contrast agents, were compared with that of the Pdots based on the multiscale PAI system. Both ex vivo and in vivo experiments demonstrated that the Pdots have better photoacoustic conversion efficiency at 532 nm than GNPs and showed similar photoacoustic performance with GNRs at 700 nm at the same mass concentration. Photostability and toxicity tests demonstrated that the Pdots are photostable and biocompatible. More importantly, an in vivo MSPAI experiment indicated that the Pdots have better photoacoustic performance than the blood and therefore the signals can be accurately extracted from the background of vascular-rich tissues. Our work demonstrates the great potential of Pdots as highly effective contrast agents for the precise localization of lesions relative to the blood vessels based on multiscale PAI and MSPAI.

Photodynamic therapy (PDT) is a promising treatment modality for clinical cancer therapy. However, the therapeutic effect of PDT is strongly dependent on the property of photosensitizer. Here, we developed photo-cross-linkable semiconductor polymer dots doped with photosensitizer Chlorin e6 (Ce6) to construct a nanoparticle platform for photodynamic therapy. Photoreactive oxetane groups were attached to the side chains of the semiconductor polymer. After photo-cross-linking reaction, the Ce6-doped Pdots formed an interpenetrated structure to prevent Ce6 leaching out from the Pdot matrix. Spectroscopic characterizations revealed an efficient energy transfer from the polymer to Ce6 molecules, resulting in amplified generation of singlet oxygen. We evaluated the cellular uptake, cytotoxicity, and photodynamic effect of the Pdots in gastric adenocarcinoma cells. In vitro photodynamic experiments indicated that the Ce6-doped Pdots (∼10 μg/mL) effectively killed the cancer cells under low dose of light irradiation (∼60 J/cm2). Furthermore, in vivo photodynamic experiments were carried out in tumor-bearing nude mice, which indicated that the Pdot photosensitizer apparently suppressed the growth of solid tumors. Our results demonstrate that the photo-cross-linkable Pdots doped with photosensitizer are promising for photodynamic cancer treatment.Keywords: energy transfer; photo-cross-linking; photodynamic therapy; photosensitizer; semiconducting polymer;

Control of stereochemistry plays a key role in medicinal chemistry, material and life science. As a prominent AIE luminogen, tetraphenylethene (TPE) derivatives have E/Z isomers which are challenging to separate even by HPLC. Herein, we designed oxetane-substituted TPE (TPE-2OXE) and separated pure isomers by simple column chromatography with high yields, as confirmed by mass spectrometry, IR and NMR spectroscopy. The isomerization of the two isomers can occur by photo- and thermo-activation. Importantly, (Z)-TPE-2OXE isomer solid shows bathochromic emission with a quantum yield 5 times higher than that of (E)-TPE-2OXE. The differences in emission wavelength and quantum yield are derived from distinct emission mechanisms of locally excited (LE) state emission of (E)-TPE-2OXE and charge transfer (CT) state emission of (Z)-TPE-2OXE. The two isomers are also good piezochromic luminescent materials, which have not only an obvious emission color shift but also significantly enhanced luminescence brightness by external force. In addition, (E)-TPE-2OXE solids show self-healing ability, which can crystallize spontaneously from ground amorphous state. The higher brightness of (E)-TPE-2OXE can be retained in solution, so fluorescent AIE nanodots are prepared from the two isomers. Cell-labeling experiments also show that (Z)-TPE-2OXE AIE dots have higher labeling brightness as compared to the (E)-TPE-2OXE isomer. The synthesis and distinct properties of E/Z isomers are beneficial to further development of new TPE derivatives for various applications.

Chiral fluorescent composite films of gold nanoclusters (AuNCs) and photonic cellulose nanocrystals (CNCs) demonstrate modulated fluorescence emission due to the stopband- and band edge-photoemission coupling effect between the photonic CNCs and fluorescent AuNCs, showing promising potentials as fluorescent nanosensors, optical switches and optical memory devices.

This paper described the energy-transfer amplified singlet oxygen generation in semiconductor polymer dots (Pdots) for in vitro and in vivo photodynamic therapy. Hydrophobic photosensitizer tetraphenylporphyrin was facilely doped in the nanoparticles consisting of densely packed semiconductor polymers. Optical characterizations indicated that the fluorescence of Pdots was completely quenched by the photosensitizer, yielding an energy transfer efficiency of nearly 100% and singlet-oxygen generation quantum yield of ∼50%. We evaluated the cellular uptake, dark toxicity, and photodynamic therapy of the Pdot photosensizer in human gastric adenocarcinoma cells. The in vitro studies indicated that cancer cells were efficiently destroyed at very low dose of the Pdots such as 1 μg/mL by using the light dose of 90 J/cm2, which is considerably less than that in clinical practice. The antitumor effect of the Pdots was further evaluated in vivo with human gastric adenocarcinoma xenografts in Balb/c nude mice, which show that the xenograft tumors were significantly inhibited and eradicated in some cases. Our results indicate the energy transfer amplified Pdot platforms have great therapeutic potential for treating malignant cancers.Keywords: energy transfer; nanoparticle; photodynamic therapy; photosensitizer; semiconducting polymer

•An oxygen scavenging system was designed to manipulate properties of polymer dots.•Single-particle brightness of polymer dots enhanced about 2 times by the system.•The system suppressed the fast-bleaching proportion of polymer dots efficiently.•The photostability of polymer dots were improved about 2–3 times by the system.Semiconductor polymer dots (Pdots) are emerging as an excellent fluorescent probe in biology and medicine. However, the photostability of Pdots can't meet the requirements of long term single-particle imaging and tracking applications. Here we describe the enhanced single-particle brightness and photostability of Pdots by using an efficient enzymatic oxygen scavenging system (OSS). Pdots with particle diameters of 21 nm and 43 nm (PFBT21 and PFBT43) were prepared by a nanoprecipitation method. Single-particle imaging and photobleaching were performed to investigate the effect of OSS on the per-particle brightness and photostability of Pdots. Our results indicate that the single-particle brightness of the PFBT21 Pdots in OSS was enhanced nearly two times as compare to the PFBT21 Pdots in water. The photobleaching percentages of PFBT21 and PFBT43 in OSS were determined to be 29% and 33%, respectively. These values are decreased by 2–3 times as compared to those of the same Pdots in water, indicating the significantly improved photostability of Pdots by OSS. This study provides a promising approach for enhancing photostability of Pdots in long term single-particle tracking.Single-particle fluorescence brightness of polymer dots exhibits a two-fold increase by an enzymatic oxygen scavenging system. The photostability of Pdots in the oxygen scavenging system was significantly improved as compared to those in water, providing a useful approach for enhancing single-particle brightness and photostability in long term imaging and tracking applications.

Small molecules participate extensively in various life processes. However, specific and sensitive detection of small molecules in a living system is highly challenging. Here, we describe in vivo real-time dynamic monitoring of small molecules by a luminescent polymer-dot oxygen transducer. The optical transducer combined with an oxygen-consuming enzyme can sensitively detect small-molecule substrates as the enzyme-catalyzed reaction depletes its internal oxygen reservoir in the presence of small molecules. We exemplify this detection strategy by using glucose-oxidase-functionalized polymer dots, yielding high selectivity, large dynamic range, and reversible glucose detection in cell and tissue environments. The transducer–enzyme assembly after subcutaneous implantation provides a strong luminescence signal that is transdermally detectable and continuously responsive to blood glucose fluctuations for up to 30 days. In view of a large library of oxygen-consuming enzymes, this strategy is promising for in vivo detection and quantitative determination of a variety of small molecules.Keywords: dynamic monitoring; fluorescent nanoparticle; in vivo imaging; semiconductor polymer dots; small molecule

The photosensitizers used in photodynamic therapy are mainly based on porphyrin derivatives. However, clinical applications encounter several limitations regarding photosensitizers such as their low absorption coefficients, poor water-solubility, and leaching from delivery carriers. Here, we describe covalent incorporation of porphyrin in conjugated polymer backbone for development of efficient polymer-dot photosensitizer. Spectroscopic characterizations revealed that the light-harvesting polymer dominantly transfer the excitation energy to the porphyrin unit, yielding efficient singlet oxygen generation for photodynamic therapy. The polymer dots (Pdots) also possess excellent stability that overcomes the photosensitizer leaching problem as encountered in other nanoparticle carriers. In vitro cytotoxicity and photodynamic efficacy of the Pdots were evaluated in MCF-7 cells by in vitro assay, indicating that the Pdots can efficiently damage cancer cells. In vivo photodynamic therapy by using the Pdots was further investigated with xenograft tumors in Balb/c nude mice, which show that the tumors were significantly inhibited or eradicated in certain cases. The high-yield singlet oxygen generation and excellent stability of porphyrin-incorporated Pdots are promising for photodynamic treatment of malignant tumors.

Semiconductor polymer dots (Pdots) were encapsulated into a SiO2 matrix to form fluorescent nanocomposites using a modified Stöber method. Significantly, the photostability and thermal stability of the nanocomposites were greatly improved as compared to those of pure Pdots. The luminescent nanocomposites combined with blue LEDs result in white-light emitting devices with a high color-rendering index.

Fingerprint imaging and recognition represent the most important approach in personal identification. Here we designed and synthesized oxetane-functionalized semiconductor polymer dots (Ox-Pdots) for covalent patterning and rapid visualization of latent fingerprints. The high fluorescence brightness, large Stokes shift, and excellent surface properties of the Ox-Pdots lead to fingerprint imaging with high sensitivity and resolution. Fingerprint ridge structures with the first, second, and third levels of details were clearly developed within minutes. The method was facile and robust for visualization of fingerprints on various surfaces including glass, metal, and plastics. Moreover, the oxetane groups in the Ox-Pdots undergo cross-linking reactions induced by a short-time UV irradiation, yielding 3-D intermolecular polymer network. The resulting fingerprint patterns exhibit unparalleled stability against rigorous treatment, as compared to those by traditional Pdots. Our results demonstrate that the Ox-Pdots hold great promise for latent fingerprint imaging and fluorescence anticounterfeiting applications.Keywords: anticounterfeiting; fingerprint; fluorescence; nanoparticle; patterning; semiconductor polymer;

We report on a europium-complex-grafted polymer for preparing stable nanoparticle probes with high luminescence brightness, narrow emission bandwidth, and long luminescence lifetimes. A Eu complex bearing an amino group was used to react with a functional copolymer poly(styrene-co-maleic anhydride) by the spontaneous amidation reaction, producing the polymer grafted with Eu complexes in the side chains. The Eu-complex-grafted polymer was further used to prepare Eu-complex-grafted polymer dots (Pdots) and Eu-complex-blended poly(9-vinylcarbazole) composite Pdots, which showed improved colloidal stability as compared to those directly doped with Eu-complex molecules. Both types of Pdots can be efficiently quenched by a nile blue dye, exhibiting much lower detection limit and higher quenching sensitivity as compared to free Eu-complex molecules. Steady-state spectroscopy and time-resolved decay dynamics suggest the quenching mechanism is via efficient fluorescence resonance energy transfer from the Eu complex inside a Pdot to surface dye molecules. The amplified quenching in Eu-complex Pdots, together with efficient cell uptake and specific cell surface labeling observed in mammalian cells, suggests their potential applications in time-resolved bioassays and cellular imaging.

We report a ratiometric fluorescent sensor based on semiconducting polymer dots chelated with terbium ions to detect bacterial spores in aqueous solution. Fluorescent polyfluorene (PFO) dots serve as a scaffold to coordinate with lanthanide ions that can be sensitized by calcium dipicolinate (CaDPA), an important biomarker of bacterial spores. The absorption band of PFO dots extends to deep UV region, allowing both the reference and the sensitizer can be excited with a single wavelength (∼275 nm). The fluorescence of PFO remains constant as a reference, while the Tb3+ ions exhibit enhanced luminescence upon binding with DPA. The sharp fluorescence peaks of β-phase PFO dots and the narrow-band emissions of Tb3+ ions enable ratiometric and sensitive CaDPA detection with a linear response over nanomolar concentration and a detection limit of ∼0.2 nM. The Pdots based sensor also show excellent selectivity to CaDPA over other aromatic ligands. Our results indicate that the Tb3+ chelated Pdots sensor is promising for sensitive and rapid detection of bacterial spores.

Semiconducting polymer dots (Pdots) represent a new class of fluorescent nanoparticles for biological applications. In this study, we investigated their size-dependent fluorescence and cellular labeling properties. We demonstrate that the polymer conformation in solution phase largely affects the polymer folding and packing during the nanoparticle preparation process, resulting in solution-phase control over the fluorescence properties of semiconducting polymer nanoparticles. The resulting Pdots exhibit apparent size dependent absorption and emission, a characteristic feature of different chain packing behaviors due to the preparation conditions. Single-particle fluorescence imaging was employed to perform a side-by-side comparison on the Pdot brightness, indicating a quadratic dependence of single-particle brightness on particle size. Upon introducing a positively charged dye Nile blue, all the three type of Pdots were quenched very efficiently (Ksv > 1 × 107 M–1) in an applied quenching process at low dye concentrations, but exhibit apparent difference in quenching efficiency with increasing dye concentration. Furthermore, Pdots of different sizes were used for cell uptake and cellular labeling involving biotin–streptavidin interactions. Fluorescence imaging together with flow cytometry studies clearly showed size dependent labeling brightness. Small-sized Pdots appear to be more effective for immunolabeling of cell surface, whereas medium-sized Pdots exhibit the highest uptake efficiency. This study provides a concrete guidance for selecting appropriate particle size for biological imaging and sensing applications.

Semiconductor polymer dots (Pdots) were encapsulated into a SiO2 matrix to form fluorescent nanocomposites using a modified Stöber method. Significantly, the photostability and thermal stability of the nanocomposites were greatly improved as compared to those of pure Pdots. The luminescent nanocomposites combined with blue LEDs result in white-light emitting devices with a high color-rendering index.

Chiral fluorescent composite films of gold nanoclusters (AuNCs) and photonic cellulose nanocrystals (CNCs) demonstrate modulated fluorescence emission due to the stopband- and band edge-photoemission coupling effect between the photonic CNCs and fluorescent AuNCs, showing promising potentials as fluorescent nanosensors, optical switches and optical memory devices.