A Dual Luminescent Sensor Material for Simultaneous Imaging of Pressure and Temperature on Surfaces

A novel kind of composite material for simultaneous luminescent determination of air pressure and temperature is presented. The dual sensor consists of a fluorinated platinum porphyrin complex (PtTFPP) as an oxygen‐sensitive probe, and of the highly temperature‐sensitive europium complex Eu(tta)₃(dpbt) as temperature probe. Both are incorporated into different polymer microparticles to control response characteristics and to avoid interferences. Encapsulation of PtTFPP in poly(styrene‐co‐acrylonitrile) (PSAN) results in a broad dynamic range from 0.05 to 2.00 bar for pressure measurements. The europium complex was incorporated into poly(vinyl chloride) to reduce the cross sensitivity towards oxygen. This system represents a new class of luminescent sensor system, where the signals are separated via the different luminescence lifetimes of the indicators. It is possible to monitor the emission of the temperature‐sensitive probe by means of time‐resolved fluorescence imaging without interferences, because the luminescence lifetime of the temperature indicator is tenfold longer than that of the oxygen indicator. The temperature image can then be used to compensate cross sensitivity of the pressure indicator towards temperature. In combination with an appropriate time‐resolved measurement technique, this material enables simultaneous imaging of pressure (or oxygen partial pressure) and temperature distributions on surfaces. It is distinguished from other approaches of dual pressure and temperature sensitive paints because it avoids the need of signal separation by application of different cameras or by use of different optical filters or light sources.     

A Fluorophore‐Doped Polymer Nanomaterial for Referenced Imaging of pH and Temperature with Sub‐Micrometer Resolution

A new kind of pH and temperature sensitive material is reported. It is composed of dye‐doped polymer nanoparticles incorporated into a thin film of a polyurethane hydrogel. The new pH/temperature‐sensitive nanoparticles are obtained by post‐staining oxygen‐impermeable amino‐functionalized polyacrylonitrile nanoparticles with a long‐lifetime reference dye. Staining is followed by covalently linking fluorescein isothiocyanate onto the surface of the nanoparticle. The new sensor material has several distinct features: a) it enables imaging of pH via time domain dual‐lifetime referencing; b) effects of temperature on pH sensing may be compensated for; and c) temperature can simultaneously be visualized via rapid lifetime imaging. The new material enables referenced and temperature‐compensated pH imaging with superior spatial resolution due to the use of nanosized sensor nanoparticles.     

Exceptional Oxygen Sensing Properties of New Blue Light‐Excitable Highly Luminescent Europium(III) and Gadolinium(III) Complexes

New europium(III) and gadolinium(III) complexes bearing 8‐hydroxyphenalenone antenna combine efficient absorption in the blue part of the spectrum and strong emission in polymers at room temperature. The Eu(III) complexes show characteristic red luminescence whereas the Gd(III) dyes are strongly phosphorescent. The luminescence quantum yields are about 20% for the Eu(III) complexes and 50% for the Gd(III) dyes. In contrast to most state‐of‐the‐art Eu(III) complexes the new dyes are quenched very efficiently by molecular oxygen. The luminescence decay times of the Gd(III) complexes exceed 1 ms which ensures exceptional sensitivity even in polymers of moderate oxygen permeability. These sensors are particularly suitable for trace oxygen sensing and may be good substitutes for Pd(II) porphyrins. The photophysical and sensing properties can be tuned by varying the nature of the fourth ligand. The narrow‐band emission of the Eu(III) allows efficient elimination of the background light and autofluorescence and is also very attractive for use e.g., in multi‐analyte sensors. The highly photostable indicators incorporated in nanoparticles are promising for imaging applications. Due to the straightforward preparation and low cost of starting materials the new dyes represent a promising alternative to the state‐of‐the‐art oxygen indicators particularly for such applications as, e.g., food packaging.     

Triplet–Triplet Annihilation‐Based Anti‐Stokes Oxygen Sensing Materials with a Very Broad Dynamic Range

A novel concept for designing optical oxygen sensing materials is reported. Oxygen‐sensitive anti‐Stokes emission is generated via triplet–triplet annihilation‐based upconversion and serves as an analytical parameter. Porous glass beads are used to incorporate the “sensing chemistry” including a sensitizer and an annihilator dissolved in a high boiling solvent. The beads are dispersed in silicone rubber or Teflon AF to produce solid state optodes. Inexpensive low power light sources (LEDs) are used for the excitation. The upconverted emission shows unmatched sensitivity both for the luminescence decay time and for the luminescence intensity. The latter features unusual quadratic Stern‐Volmer plots. Much lower sensitivity of the residual NIR luminescence of the sensitizer allows determination of pO₂ in the broad dynamic range from trace oxygen quantities to ≈40 kPa. Interrogation of the sensors in frequency domain is demonstrated. Influence of the excitation light power on the calibration, temperature effects, dynamic response to altering pO₂, and photostability of the sensing materials are also investigated.     

Is Poly(vinylcarbazole) a Good Host for Blue Phosphorescent Dopants in PLEDs? Dimer Formation and Their Effects on the Triplet Energy Level of Poly(N‐vinylcarbazole) and Poly(N‐Ethyl‐2‐Vinylcarbazole)

The detailed measurement and analysis of the delayed emission from poly(vinylcarbazole) (PVK) and poly(N‐ethyl‐2‐vinyl‐carbazole) (P2VK) thin films is described. PVK has rapidly become a “polymer of choice” for hosting phosphorescent dopants in PLEDs, especially blue emitters. In this respect it is important to have a full understanding of the triplet properties of this host. It is concluded that in films, the electronic 0–0 peak energy of PVK phosphorescence is found at 2.88 eV (14 K). With an increase of temperature, >44 K, increasing emission from new long lived, lower energy species, previously ascribed to “trap states” in the literature, is observed. Increasing temperature enables thermally assisted triplet exciton hopping to these trap states. Critically it is shown that some of these triplet trap species are ground state triplet dimers in origin for both PVK (2.46 eV) and P2VK (2.1 eV), and not all of them are of excimer nature as previously thought. These species can quench the emission of blue heavy metal complexes doped in PVK and drastically effect performance over lifetime if the dimer formation increases over time and at elevated operating temperature. It is therefore concluded that PVK might not be such an ideal host material for blue phosphorescent emitters.     

Phosphorescent Polymeric Thermometers for In Vitro and In Vivo Temperature Sensing with Minimized Background Interference

Temperature plays a crucial role in many biological processes. Accurate temperature determination is important for diagnosis and treatment of diseases. Autofluorescence is an unavoidable interference in luminescent bioimaging. Hence, a large amount of research works has been devoted to reducing background autofluorescence and improving signal‐to‐noise ratio (SNR) in biodetection. Herein, a dual‐emissive phosphorescent polymeric thermometer has been developed by incorporating two long‐lived phosphorescent iridium(III) complexes into an acrylamide‐based thermosensitive polymer. Upon increasing temperature, this polymer undergoes coil‐globule transition, which leads to a decrease in polarity of the microenvironment surrounding the iridium(III) complexes and hence brings about emission enhancement of both complexes. Owing to their different sensitivity to surrounding environment, the emission intensity ratio of the two complexes is correlated to the temperature. Thus, the polymer has been used for temperature determination in vitro and in vivo via ratiometric luminescence imaging. More importantly, by using the long‐lived phosphorescence of the polymer, temperature mapping in zebrafish has been demonstrated successfully with minimized autofluorescence interference and improved SNR via time‐resolved luminescence imaging. To the best of our knowledge, this is the first example to use photoluminescent thermometer for in vivo temperature sensing.     

Switching Light Transmittance by Responsive Organometallic Poly(ionic liquid)s: Control by Cross Talk of Thermal and Redox Stimuli

A novel organometallic poly(ionic liquid) with both redox‐ and thermoresponsive properties is synthesized from a poly(ferrocenylsilane) (PFS) via a one‐step Strecker sulfite alkylation reaction by using tetraalkylphosphonium sulfite as an effective and versatile nucleophile. This dual‐responsive polymer is composed of a PFS backbone and quaternary phosphonium sulfonate side groups and exhibits a concentration‐dependent lower critical solution temperature (LCST)‐type phase transition in aqueous solution. Furthermore, the LCST‐type phase behavior of the polymer can be switched between the “off” state and “on” state by chemical or electrochemical oxidation and reduction on the ferrocene units in the polymer main chain. As a consequence, a classical LCST‐type phase transition, as well as an “isothermal” redox‐triggered phase transition can be induced by using thermal and electrochemical triggers without changing the composition of the system. On the basis of this dual responsiveness, a “smart window” device is fabricated. The optical characteristics of this device are completely unaltered after 100 thermal and/or redox cycles.     

Positively Thermo‐Sensitive Monodisperse Core–Shell Microspheres

In this paper, we report on a novel family of monodisperse thermo‐sensitive core–shell hydrogel microspheres that is featured with high monodispersity and positively thermo‐responsive volume phase transition characteristics with tunable swelling kinetics, i.e., the particle swelling is induced by an increase rather than a decrease in temperature. The microspheres were fabricated in a three‐step process. In the first step, monodisperse poly(acrylamide‐co‐styrene) seeds were prepared by emulsifier‐free emulsion polymerization. In the second step, poly(acrylamide) or poly[acrylamide‐co‐(butyl methacrylate)] shells were fabricated on the microsphere seeds by free radical polymerization. In the third step, the core–shell microspheres with poly‐ (acrylamide)/poly(acrylic acid) based interpenetrating polymer network (IPN) shells were finished by a method of sequential IPN synthesis. The proposed monodisperse core–shell microspheres provide a new mode of the phase transition behavior for thermo‐sensitive “smart” or “intelligent” monodisperse micro‐actuators that is highly attractive for targeting drug delivery systems, chemical separations, sensors, and so on.     

Multifunctional Up‐Converting Nanocomposites with Smart Polymer Brushes Gated Mesopores for Cell Imaging and Thermo/pH Dual‐Responsive Drug Controlled Release

Multifunctional nanocarriers based on the up‐conversion luminescent nanoparticles of NaYF₄:Yb³⁺/Er³⁺ core (UCNPs) and thermo/pH‐coupling sensitive polymer poly[(N‐isopropylacrylamide)‐co‐(methacrylic acid)] (P(NIPAm‐co‐MAA)) gated mesoporous silica shell are reported for cancer theranostics, including fluorescence imaging, and for controlled drug release for therapy. The as‐synthesized hybrid nanospheres UCNPs@mSiO₂‐P(NIPAm‐co‐MAA) show bright green up‐conversion fluorescence under 980 nm laser excitation and the thermo/pH‐sensitive polymer is active as a “valve” to moderate the diffusion of the embedded drugs in‐and‐out of the pore channels of the silica container. The anticancer drug doxorubicin hydrochloride (DOX) can be absorbed into UCNPs@mSiO₂‐P(NIPAm‐co‐MAA) nanospheres and the composite drug delivery system (DDS) shows a low level of leakage at low temperature/high pH values but significantly enhanced release at higher temperature/lower pH values, exhibiting an apparent thermo/pH controlled “on‐off” drug release pattern. The as‐prepared UCNPs@mSiO₂‐P(NIPAm‐co‐MAA) hybrid nanospheres can be used as bioimaging agents and biomonitors to track the extent of drug release. The reported multifunctional nanocarriers represent a novel and versatile class of platform for simultaneous imaging and stimuli‐responsive controlled drug delivery.     

Poly(ϵ‐caprolactone)‐Functionalized Carbon Nanotubes and Their Biodegradation Properties

Biodegradable poly(?‐caprolactone) (PCL) has been covalently grafted onto the surfaces of multiwalled carbon nanotubes (MWNTs) by the “grafting from” approach based on in‐situ ring‐opening polymerization of ?‐caprolactone. The grafted PCL content can be controlled easily by adjusting the feed ratio of monomer to MWNT‐supported macroinitiators (MWNT‐OH). The resulting products have been characterized with Fourier‐transform IR (FTIR), NMR, and Raman spectroscopies, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). After PCL was coated onto MWNT surfaces, core/shell structures with nanotubes as the “hard” core and the hairy polymer layer as the “soft” shell are formed, especially for MWNTs coated with a high density of polymer chains. Such a polymer shell promises good solubility/dispersibility of the MWNT–PCL nanohybrids in low‐boiling‐point organic solvents such as chloroform and tetrahydrofuran. Biodegradation experiments have shown that the PCL grafted onto MWNTs can be completely enzymatically degraded within 4 days in a phosphate buffer solution in the presence of pseudomonas (PS) lipase, and the carbon nanotubes retain their tubelike morphologies, as observed by SEM and TEM. The results present possible applications for these biocompatible PCL‐functionalized CNTs in bionanomaterials, biomedicine, and artificial bones.     

Surface‐Confined Atom Transfer Radical Polymerization from Sacrificial Mesoporous Silica Nanospheres for Preparing Mesoporous Polymer/Carbon Nanospheres with Faithful Shape Replication: Functional Mesoporous Materials

A facile approach for the preparation of mesoporous polymer nanospheres (MPN) and mesoporous carbon nanospheres (MCN) with complete shape retention based on surface‐confined atom transfer radical polymerization of various methacrylate monomers from in situ generated initiator‐modified hard silica nanospheres template is developed. This approach yields mesoporous silica‐polymer hybrid nanospheres (MSPN) with mesopores that are uniformly filled with covalently attached well‐defined poly(methacrylate)s. The silica frameworks are subsequently etched, resulting in MPN. Pyrolysis of MSPN and subsequent removal of silica template resulted in the production of MCN. They retain the size, shape, and mesoporous ordering of the silica template nanospheres. Gel permeation chromatography analysis of the silica free polymers reveals that they have controlled molecular weights and low polydispersities (PDIs). Kinetics studies reveal that the molecular weight of the grafted polymer increases linearly with time, maintaining low PDIs, indicating the living nature of the polymerization. The mesoporous polymer material is found to have low dielectric constant, which paves the way for their use as low‐dielectric constant materials in microelectronics. This approach allows fabrication of functional MPN using functional comonomers, which are successfully used for the synthesis of “clickable” mesoporous polymer nanospheres, removal of ionic contaminates through anion exchange, and glucose sensing.     

Colorimetric Logic Gates Based on Poly(2‐alkyl‐2‐oxazoline)‐Coated Gold Nanoparticles

A straightforward end‐capping strategy is applied to synthesize xanthate‐functional poly(2‐alkyl‐2‐oxazoline)s (PAOx) that enable gold nanoparticle functionalization by a direct “grafting to” approach with citrate‐stabilized gold nanoparticles (AuNPs). Owing to the presence of remaining citrate groups, the obtained PAOx@AuNPs exhibit dual stabilization by repulsive electrostatic and steric interactions giving access to water soluble molecular AND logic gates, wherein environmental temperature and ionic strength constitute the input signals, and the solution color the output signal. The temperature input value could be tuned by variation of the PAOx polymer composition, from 22 °C for poly(2‐ⁿpropyl‐2‐oxazoline)@AuNPs to 85 °C for poly(2‐ethyl‐2‐oxazoline)@AuNPs. Besides, advancing the fascinating field of molecular logic gates, the present research offers a facile strategy for the synthesis of PAOx@AuNPs of interest in fields spanning nanotechnology and biomedical sciences. In addition, the functionalization of PAOx with xanthate offers straightforward access to thiol‐functional PAOx of high interest in polymer science.     

Dopamine‐Modified Cationic Conjugated Polymer as a New Platform for pH Sensing and Autophagy Imaging

A dopamine‐modified conjugated polymer PFPDA is synthesized and characterized. At low pH, dopamine exists in its hydroquinone form and lacks the ability to quench fluorescence. At high pH, the proportion of the quinone form of dopamine increases due to its autooxidation, and efficient intramolecular electron transfer from the polymer main chain to quinone occurs, resulting in the quenching of the fluorescence of PFPDA. Thus, PFPDA exhibits a fluorescence “turn‐on” response at low pH. PFPDA possesses excellent photostability and exhibits no cytotoxicity, which makes it a good fluorescent material for pH sensing and cell imaging. A light‐induced hydroxyl anion emitter, MGCB, is also used to change the pH of the solution and thus regulate the fluorescence of PFPDA via remote control under light irradiation. Because the cytoplasm becomes acidic when cell autophagy occurs, PFPDA can also be used for autophagy imaging of HeLa cells with good selectivity.     

A Plastic Optical Fiber Sensor for the Dual Sensing of Temperature and Oxygen

This study presents a low-cost plastic optical fiber sensor for the dual sensing of temperature and oxygen. The sensor features commercially available epoxy glue coated on the side-polished fiber surface for temperature sensing and a fluorinated xerogel doped with platinum tetrakis pentrafluoropheny porphine coated on the fiber end for oxygen sensing. The temperature and oxygen indicators are both excited using an ultraviolet light-emitting diode light source with a wavelength of 380 nm. The luminescence emission spectra of the two indicators are well resolved and exhibit no crosstalk effects. Our studies show that the temperature response of the sensor is independent of the oxygen concentration. Overall, the results indicate that the dual sensor presented in this study provides an ideal solution for the noncontact, simultaneous sensing of temperature and oxygen in general biological and medical applications.     

New Conjugated Ladder Polymer Containing Carbazole Moieties

A new ladder polymer incorporating a polar carbazole group within the main chain, ladder‐type poly(para‐phenylene carbazole), LPPPC, was synthesized and characterized by luminescence techniques. Its properties are compared to that of the well‐known methyl‐substituted ladder‐type poly(para‐phenylene), MeLPPP. The results obtained evidence a very low energetic disorder in this new polymer, presumably due to its near‐perfect intrachain structure and low content of defects. It was found that although the density of states (DOS) distribution for neutral excitations is narrower than in MeLPPP, the manifold of charge‐transporting localized states is substantially more energetically disordered due to important dipolar disorder contributions.     

Mechanical Restoration of Damaged Polymer Films by “Repair‐and‐Go”

A microencapsulation and nanoparticle deposition technique, termed “repair‐and‐go,” is employed for inducing mechanical restoration of damaged polymer films. In “repair‐and‐go,” polymer‐stabilized emulsion droplets, containing surface‐functionalized SiO₂ nanoparticles, traverse a substrate and deposit their nanoparticle contents selectively into the damaged regions. Surface‐oxidized poly(dimethylsiloxane) is employed as the substrate, and dynamic mechanical analysis reveals the enhanced mechanical properties of the film following nanoparticle deposition. Healing efficiency is optimal when using thinner test substrates, repeated deposition cycles, and functional SiO₂ nanoparticles that afford access to postdeposition curing.     

Silver Stars: Silver–Polymer Composite Stars: Synthesis and Applications (Adv. Funct. Mater. 9/2011)

Colloidal “silver stars” were synthesized upon poly(lactic‐co‐glycolic) acid nanosphere templates via a facile two‐step silver reduction method. Myriad dendrimer‐like Ag star morphologies were synthesized by varying the amount of poly(vinyl alcohol) and trisodium citrate used during silver reduction. Scanning electron microscopy studies revealed that star‐shaped silver–polymer composites possessing nanoscopic, fractal morphologies with diameters ranging from 500 nm to 7 μm were produced. These composites have broad applications from antibacterial agents to catalysis; two such applications were tested here. Surface‐enhanced Raman spectroscopy (SERS) studies showed multiple hot spots of SERS activity within a single star. Electrochemical catalysis experiments demonstrated the feasibility of using the silver stars instead of platinum for the oxygen reduction reaction in alkaline fuel cells.     

Thermogelling,ABC Triblock Copolymer Platform for Resorbable Hydrogels with Tunable,Degradation‐Mediated Drug Release

Clinical application of injectable, thermoresponsive hydrogels is hindered by lack of degradability and controlled drug release. To overcome these challenges, a family of thermoresponsive, ABC triblock polymer‐based hydrogels has been engineered to degrade and release drug cargo through either oxidative or hydrolytic/enzymatic mechanisms dictated by the “A” block composition. Three ABC triblock copolymers are synthesized with varying “A” blocks, including oxidation‐sensitive poly(propylene sulfide), slow hydrolytically/enzymatically degradable poly(ε‐caprolactone), and fast hydrolytically/enzymatically degradable poly(d ,l ‐lactide‐co‐glycolide), forming the respective formulations PPS₁₃₅‐b‐PDMA₁₅₂‐b‐PNIPAAM₂₂₅ (PDN), PCL₈₅‐b‐PDMA₁₅₀‐b‐PNIPAAM₁₅₀ (CDN), and PLGA₆₀‐b‐PDMA₁₄₈‐b‐PNIPAAM₁₅₂ (LGDN). For all three polymers, hydrophilic poly(N,N‐dimethylacrylamide) and thermally responsive poly(N‐isopropylacrylamide) comprise the “B” and “C” blocks, respectively. These copolymers form micelles in aqueous solutions at ambient temperature that can be preloaded with small molecule drugs. These solutions quickly transition into hydrogels upon heating to 37 °C, forming a supra‐assembly of physically crosslinked, drug‐loaded micelles. PDN hydrogels are selectively degraded under oxidative conditions while CDN and LGDN hydrogels are inert to oxidation but show differential rates of hydrolytic/enzymatic decomposition. All three hydrogels are cytocompatible in vitro and in vivo, and drug‐loaded hydrogels demonstrate differential release kinetics in vivo corresponding with their specific degradation mechanism. These collective data highlight the potential cell and drug delivery use of this tunable class of ABC triblock polymer thermogels.     

A Biomimetic Actuator Based on an Ionic Networking Membrane of Poly(styrene‐alt‐maleimide)‐Incorporated Poly(vinylidene fluoride)

A novel electro‐active polymer actuator employing the ionic networking membrane of poly(styrene‐alt‐maleimide) (PSMI)‐incorporated poly(vinylidene fluoride) (PVDF) was developed to improve the electrical and mechanical performance of the artificial muscles. The main drawback of the previous ionic polymer‐metal composite actuator was the straightening‐back and relaxation under the constant voltage excitation. The present ionic networking membrane actuator overcomes the relaxation of the ionic polymer‐metal composite actuator under the constant voltage and also shows much larger tip displacement than that of the Nafion‐based actuator. Under the simple harmonic stimulus, the measured mechanical displacement was comparable to that of the Nafion‐based actuator. The excellent electromechanical response of the current polymer actuator is attributed to two factors: the inherent large ionic‐exchange capacity and the unique hydrophilic nano‐channels of the ionic networking membrane. The electro‐active polymer actuator of PSMI‐incorporated PVDF can be a promising smart material and may possibly diversify niche applications in biomimetic motion.     

Polymer Light‐Emitting Electrochemical Cells: The Formation and Effects of Doping‐Induced Micro Shorts

A planar surface cell structure has been utilized to investigate a polymer light‐emitting electrochemical cell (LEC), consisting of an active‐material mixture of poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV) and an ionic liquid, tetra‐n‐butylammonium trifluoromethanesulfonate, contacted by Au electrodes. It is shown that diffuse and needle‐shaped doping fronts originate from the electrodes (p‐type from the positive electrode and n‐type from the negative electrode) during the charging process at a temperature (T) of 393 K. After a turn‐on time, a significant portion of the doping fronts makes contact close to the negative electrode to form a light‐emitting p–i–n junction, but at some points p‐type doping protrudes all the way to the negative electrode to form what are effectively micro shorts. It is shown that the consequences of such doping‐induced micro shorts during a subsequent stabilized “frozen junction” operation at T = 200 K are drastic: the current‐rectification ratio (RR) is low and the quantum efficiency (QE) is far from optimum. Both RR and QE increase significantly during long‐term operation under frozen‐junction conditions, demonstrating that the lifetime of the doping‐induced micro shorts is limited even under such stabilized conditions. Still, it is clear that it is critical for the optimization and further development of LECs to find new types of active material and electrode combinations that allow for formation of a continuous p–i–n junction in the center of the interelectrode gap.