Semiconducting Polymer Dots Research Articles

Ratiometric Luminescent Detection of Bacterial Spores with Terbium Chelated Semiconducting Polymer Dots

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 Tb(3+) ions exhibit enhanced luminescence upon binding with DPA. The sharp fluorescence peaks of β-phase PFO dots and the narrow-band emissions of Tb(3+) 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 Tb(3+) chelated Pdots sensor is promising for sensitive and rapid detection of bacterial spores.

Semiconducting polymer dots doped with europium complexes showing ultranarrow emission and long luminescence lifetime for time-gated cellular imaging.

Bright dots: Semiconducting polymer dots (Pdots) doped with europium complexes possess line-like fluorescence emission, high quantum yield, and long fluorescence lifetime. The Pdots successfully labeled receptors on cells. The long fluorescence lifetime of the Pdots was used to distinguish them from other red fluorescence emitting nanoparticles, and improve the signal-to-noise ratio for time-gated cellular imaging. PVK=poly(9-vinylcarbazole).

Semiconducting Polymer Dots Doped with Europium Complexes Showing Ultranarrow Emission and Long Luminescence Lifetime for Time‐Gated Cellular Imaging

Semiconducting Polymer Dots Doped with Europium Complexes Showing Ultranarrow Emission and Long Luminescence Lifetime for Time‐Gated Cellular Imaging

ChemInform Abstract: Highly Fluorescent Semiconducting Polymer Dots for Biology and Medicine.

AbstractReview: 176 refs.

Ultrasensitive Detection of Proteins on Western Blots with Semiconducting Polymer Dots

Ultrasensitive fluorescence imaging of proteins on western blots using a bright, compact, and orange-emitting semiconducting polymer dot (CN-PPV) is demonstrated. A detection limit at the single-picogram level in dot blots is achieved; with conventional western blotting, 50 pg of transferrin and trypsin inhibitor after sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transfer onto a polyvinylidene fluoride membrane are detected. This method does not require any additional equipment or time compared with the conventional procedure with traditional fluorescent probes.

Lyophilization of semiconducting polymer dot bioconjugates.

Semiconducting polymer dot (Pdot) bioconjugates are a new class of ultrabright fluorescent probes. Here, we report a procedure for lyophilizing Pdot bioconjugates so that they successfully retain their optical properties, colloidal stability, and cell-targeting capability during storage. We found that, when Pdot bioconjugates were lyophilized in the presence of 10% sucrose, the rehydrated Pdot bioconjugates did not show any signs of aggregation and exhibited the same hydrodynamic diameters as before lyophilization. The brightness of the lyophilized Pdots was at least as good as before lyophilization, but in some cases, the quantum yield of lyophilized Pdots curiously showed an improvement. Finally, using flow cytometry, we demonstrated that lyophilized Pdot bioconjugates retained their biological targeting properties and were able to effectively label cells; in fact, cells labeled with lyophilized Pdot bioconjugates composed of PFBT, which were stored for 6 months at -80 °C, were ~22% brighter than those labeled with identical but unlyophilized Pdot bioconjugates. These results indicate lyophilization may be a preferred approach for storing and shipping Pdot bioconjugates, which is an important practical consideration for ensuring Pdots are widely adopted in biomedical research.

Highly Fluorescent Semiconducting Polymer Dots for Biology and Medicine

In recent years, semiconducting polymer nanoparticles have attracted considerable attention because of their outstanding characteristics as fluorescent probes. These nanoparticles, which primarily consist of π-conjugated polymers and are called polymer dots (Pdots) when they exhibit small particle size and high brightness, have demonstrated utility in a wide range of applications such as fluorescence imaging and biosensing. In this review, we summarize recent findings of the photophysical properties of Pdots which speak to the merits of these entities as fluorescent labels. This review also highlights the surface functionalization and biomolecular conjugation of Pdots, and their applications in cellular labeling, in vivo imaging, single-particle tracking, biosensing, and drug delivery. We discuss the relationship between the physical properties and performance, and evaluate the merits and limitations of the Pdot probes for certain imaging tasks and fluorescence assays. We also tackle the current challenges of Pdots and share our perspective on the future directions of the field.

Multicolor Fluorescent Semiconducting Polymer Dots with Narrow Emissions and High Brightness

Fluorescent semiconducting polymer dots (Pdots) have attracted great interest because of their superior characteristics as fluorescent probes, such as high fluorescence brightness, fast radiative rates, and excellent photostability. However, currently available Pdots generally exhibit broad emission spectra, which significantly limit their usefulness in many biological applications involving multiplex detections. Here, we describe the design and development of multicolor narrow emissive Pdots based on different boron dipyrromethene (BODIPY) units. BODIPY-containing semiconducting polymers emitting at multiple wavelengths were synthesized and used as precursors for preparing the Pdots, where intraparticle energy transfer led to highly bright, narrow emissions. The emission full width at half-maximum of the resulting Pdots varies from 40 to 55 nm, which is 1.5-2 times narrower than those of conventional semiconducting polymer dots. BODIPY 520 Pdots were about an order of magnitude brighter than commercial Qdot 525 under identical laser excitation conditions. Fluorescence imaging and flow cytometry experiments indicate that the narrow emissions from these bright Pdots are promising for multiplexed biological detections.

Photoactivated ratiometric copper(ii) ion sensing with semiconducting polymer dots

This paper describes a simple platform that employs spiropyran-functionalized semiconducting polymer dots as a fluorescent probe for photoactivated ratiometric and sensitive Cu(2+) detection, in which the sensing mechanism is based on photogenerated merocyanine that can selectively bind Cu(2+) to induce Förster resonance energy transfer.

High-intensity near-IR fluorescence in semiconducting polymer dots achieved by cascade FRET strategy.

Near-IR (NIR) emitting semiconducting polymer dots (Pdots) with ultrabright fluorescence have been prepared for specific cellular targeting. A series of π-conjugated polymers were synthesized to form water dispersible multicomponent Pdots by an ultrasonication-assisted co-precipitation method. By optimizing cascade energy transfer in Pdots, high-intensity NIR fluorescence (φ = 0.32) with tunable excitations, large absorption-emission separation (up to 330 nm), and narrow emission bands (FWHM = 44 nm) have been achieved. Single-particle fluorescence imaging show that the as-prepared NIR Pdots were more than three times brighter than the commercially available Qdot705 with comparable sizes under identical conditions of excitation and detection. Because of the covalent introduction of carboxylic acid groups into polymer side chains, the bioconjugation between NIR-emitting Pdots and streptavidins can be readily completed via these functional groups on the surface of Pdots. Furthermore, through flow cytometry and confocal fluorescence microscopy the NIR-emitting Pdot-streptavidin conjugates proved that they could effectively label EpCAM receptors on the surface of MCF-7 cells, via specific binding between streptavidin and biotin.

Ultrabright benzoselenadiazole-based semiconducting polymer dots for specific cellular imaging

Semiconducting polymer dots (Pdots) have recently emerged as a new class of extraordinarily bright fluorescent probes with promising applications in biological imaging and sensing. Herein we synthesized a novel series of highly emissive orange-fluorescent copolymers, poly[9,9-dioctylfluorenyl-2,7-diyl)-co-1,4-benzo-{2,1′-3}-selenadiazole)] (PFBS) and tuned the ratio of fluorene to benzoselenadiazole (BS) from 98 : 2 to 50 : 50 to investigate the influence of BS molar ratio on the emission properties of the resulting Pdots. An optimal quantum yield of 44% could be obtained for PFBS Pdots at a fluorene to BS ratio of 70 : 30. These PFBS Pdots also exhibited great photostability and superior single-particle brightness. We next conjugated biomolecules onto the surface of these PFBS Pdots and demonstrated their ability for specific cellular labeling without any noticeable nonspecific binding. We are now working on the synthesis of near-infrared Pdots based on this BS unit and anticipate this series of ultrabright Pdots will be very useful in a variety of in vitro and in vivo bioimaging applications.

Highly luminescent, fluorinated semiconducting polymer dots for cellular imaging and analysis

A highly fluorescent fluorinated semiconducting polymer dot (Pdot) with a quantum yield of up to 49% was developed. The fluorinated Pdot was eight times brighter in cell-labeling applications than its non-fluorinated counterpart, and was rod shaped rather than spherical.

Reversible Photoswitching of Spiropyran-Conjugated Semiconducting Polymer Dots

Semiconducting polymer dots (Pdots) recently have emerged as a new class of ultrabright fluorescent probes with promising applications in biological detection and imaging. We developed photoswitchable Pdots by conjugating photochromic spiropyran molecules onto poly[9,9-dioctylfluorenyl-2,7-diyl)-co-1,4-benzo-{2,1'-3}-thiadiazole)] (PFBT). The modulation of fluorescence was achieved by ultraviolet irradiation, which converted spiropyran into its visible-absorbing merocyanine form. The merocyanine efficiently quenched the fluorescence of PFBT via Förster resonance energy transfer (FRET). We then reversed the quenching by subsequent irradiation with visible light to get back the fluorescence of PFBT. This FRET-based photomodulation of Pdot fluorescence could be repeated multiple times. We next conjugated biomolecules onto the surface of these photoswitchable Pdots and demonstrated their specific cellular and subcellular labeling to different types of cells without any noticeable nonspecific binding. We anticipate these photoswitchable and biocompatible Pdots will be useful in developing bioimaging techniques in the future.

Covalent Cross‐Linking: Stable Functionalization of Small Semiconducting Polymer Dots via Covalent Cross‐Linking and Their Application for Specific Cellular Imaging (Adv. Mater. 26/2012)

Covalent Cross‐Linking: Stable Functionalization of Small Semiconducting Polymer Dots via Covalent Cross‐Linking and Their Application for Specific Cellular Imaging (Adv. Mater. 26/2012)

Stable Functionalization of Small Semiconducting Polymer Dots via Covalent Cross‐Linking and Their Application for Specific Cellular Imaging

A facile cross-linking strategy covalently links functional molecules to semiconducting polymer dots (Pdots) while simultaneously providing functional groups for biomolecular conjugation. In addition to greatly enhanced stability, the formed Pdots are small (<10 nm), which can be difficult to achieve with current methods but is highly desirable for most biological applications. These characteristics are significant for improving labeling efficiency and sensitivity in cellular assays that employ Pdots.

Importance of Having Low-Density Functional Groups for Generating High-Performance Semiconducting Polymer Dots

Semiconducting polymers with low-density side-chain carboxylic acid groups were synthesized to form stable, functionalized, and highly fluorescent polymer dots (Pdots). The influence of the molar fraction of hydrophilic side-chains on Pdot properties and performance was systematically investigated. Our results show that the density of side-chain carboxylic acid groups significantly affects Pdot stability, internal structure, fluorescence brightness, and nonspecific binding in cellular labeling. Fluorescence spectroscopy, single-particle imaging, and a dye-doping method were employed to investigate the fluorescence brightness and the internal structure of the Pdots. The results of these experiments indicate that semiconducting polymers with low density of side-chain functional groups can form stable, compact, and highly bright Pdots as compared to those with high density of hydrophilic side-chains. The functionalized polymer dots were conjugated to streptavidin (SA) by carbodiimide-catalyzed coupling and the Pdot-SA probes effectively and specifically labeled the cancer cell-surface marker Her2 in human breast cancer cells. The carboxylate-functionalized polymer could also be covalently modified with small functional molecules to generate Pdot probes for click chemistry-based bio-orthogonal labeling. This study presents a promising approach for further developing functional Pdot probes for biological applications.

Hybrid Semiconducting Polymer Dot–Quantum Dot with Narrow-Band Emission, Near-Infrared Fluorescence, and High Brightness

This communication describes a new class of semiconducting polymer nanoparticle-quantum dot hybrid with high brightness, narrow emission, near-IR fluorescence, and excellent cellular targeting capability. Using this approach, we circumvented the current difficulty with obtaining narrow-band-emitting and near-IR-fluorescing semiconducting polymer nanoparticles while combining the advantages of both semiconducting polymer nanoparticles and quantum dots. We further demonstrated the use of this new class of hybrid nanomaterial for effective and specific cellular and subcellular labeling without any noticeable nonspecific binding. This hybrid nanomaterial is anticipated to find use in a variety of in vitro and in vivo biological applications.

A versatile method for generating semiconducting polymer dot nanocomposites

This paper describes a method, based on co-precipitation, for generating small semiconducting polymer dot (Pdot) nanocomposites, which contain either gold or iron oxide nanoparticles within the Pdot matrix. We demonstrate the utility of Pdot-Au nanoparticles (Au-NP-Pdots) in dual-modality imaging in which co-localization of fluorescence from Pdot and scattering from Au was used to identify Au-NP-Pdot probes for downstream single-particle tracking and cellular imaging. We also demonstrate the potential of employing Pdot-FeO(x) nanoparticles (FeO(x)-NP-Pdots) for both sample preparation, where cells tagged with FeO(x)-NP-Pdots were isolated using an external magnet, and cellular imaging and detection, owing to the intense fluorescence from Pdots. The method we present here should be generalizable to the formation of other Pdot nanocomposites for creating the next generation of multi-functional Pdot probes.

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.

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.