A fluorescent thermometer operating in aggregation-induced emission mechanism: probing thermal transitions of PNIPAM in water

Tetraphenylethene (TPE) modified polyhedral oligomeric silsesquioxanes (POSS): unadulterated monomer emission, aggregation-induced emission and nanostructural self-assembly modulated by the flexible spacer between POSS and TPE

Mono-TPE modified POSS molecules exhibit monomer and AIE emission under different conditions.

Thermo-responsive poly(2-isopropyl-2-oxazoline) and tetraphenylethene hybrids for stimuli-responsive photoluminescence control

Poly(2-isopropyl-2-oxazoline) (POx), a typical thermo-responsive polymer, was conjugated with a tetraphenylethene derivative, having aggregation induced emission behavior, towards the thermal control of their fluorescence emission.

Patchable, flexible heat-sensing hybrid ionic gate nanochannel modified with a wax-composite

Heat-driven ionic gate nanochannels have been recently demonstrated, which exploit temperature-responsive polymer brushes based on wettability. These heat-sensing artificial nanochannels operate in a broad temperature-response boundary and fixed liquid cell environment, thereby experiencing limited system operation in the flat and solid state. Here we have developed a patchable and flexible heat-sensing artificial ionic gate nanochannel, which can operate in the range of the human body temperature. A wax-elastic copolymer, coated onto a commercial nanopore membrane by a controlled-vacuum filtration method, was used for the construction of temperature-responsive nanopores. The robust and flexible nanochannel heat sensor, which is combined with an agarose gel electrolyte, can sustain reversible thermo-responsive ionic gating based on the volumetric work of the wax-composite layers in a selective temperature range. The ionic current is also effectively distinguished in the patchable bandage-type nanochannel for human heat-sensing.

Fluorescent Molecular Rotor-in-Paraffin Waxes for Thermometry and Biometric Identification

Novel thermoresponsive sensor systems consisting of a molecular rotor (MR) and paraffin wax (PW) were developed for various thermometric and biometric identification applications. Polydiphenylacetylenes (PDPAs) coupled with long alkyl chains were used as MRs, and PWs of hydrocarbons having 16-20 carbons were utilized as phase-change materials. The PDPAs were successfully dissolved in the molten PWs and did not act as an impurity that prevents phase transition of the PWs. These PDPA-in-PW hybrids had almost the same enthalpies and phase-transition temperatures as the corresponding pure PWs. The hybrids exhibited highly reversible fluorescence (FL) changes at the critical temperatures during phase transition of the PWs. These hybrids were impregnated into common filter paper in the molten state by absorption or were encapsulated into urea resin to enhance their mechanical integrity and cyclic stability during repeated use. The wax papers could be utilized in highly advanced applications including FL image writing/erasing, an array-type thermo-indicator, and fingerprint/palmprint identification. The present findings should facilitate the development of novel fluorescent sensor systems for biometric identification and are potentially applicable for biological and biomedical thermometry.

Electrospun fibrous mats with conjugated tetraphenylethylene and mannose for sensitive turn-on fluorescent sensing of Escherichia coli

A rapid and sensitive detection of microbes in water and biological fluids is a key requirement in water and food safety, environmental monitoring, and clinical diagnosis and treatment. In the current study, electrospun polystyrene-co-maleic anhydride (PSMA) fibers with conjugated mannose and tetraphenylethylene (TPE) were developed for Escherichia coli (E. coli) detection, taking advantage of the high grafting capabilities of ultrafine fibers and the highly porous structure of the fibrous mat to entrap bacterial cells. The specific binding between mannose grafts on PSMA fibers and FimH proteins from the fimbriae of E. coli led to an efficient "turn-on" profile of TPE due to the aggregation-induced emission (AIE) effect. Poly(ethylene glycol) diamine was used as hydrophilic tethers to increase the conformational mobility of mannose grafts, indicating a more sensitive change in the fluorescence intensity against bacteria concentrations, a lower fluorescence background of fibers without bacteria incubation, and a sufficient space for bacteria binding, compared with the use of hexamethylenediamine or poly(ethylene imine) as spacers for mannose grafting. The addition of bovine serum albumin, glucose, or both of them into bacteria suspensions showed no significant changes in the fluorescence intensity of fibrous mats, indicating the anti-interference capability against these proteins and saccharides. An equation was drafted of the fluorescence intensities of fibrous mats against E. coli concentrations ranging from 10(2) to 10(5) CFU/mL. The test strip format was established on mannose-conjugated PSMA fibers after exposure to E. coli of different concentrations, providing a potential tool with a visual sensitivity of bacteria concentrations as low as 10(2) CFU/mL in a matter of minutes. This strategy may offer a capacity to be expanded to exploit electrospun fibrous mats and other carbohydrate-cell interactions for bioanalysis and biosensing of pathogenic bacteria.

Temperature-sensitive fluorescent organic nanoparticles with aggregation-induced emission for long-term cellular tracing

Temperature-sensitive organic nanoparticles with AIE effect were assembled in water from tetraphenylethene-based poly(N-isopropylacrylamide) (TPE-PNIPAM), which was synthesized by ATRP using TPE derivative as initiator. The size and fluorescence of TPE-PNIPAM nanoparticles can be tuned by varying the temperature. These nanoparticles can be internalized readily by HeLa cells and can be used as long-term tracer in live cells to be retained for as long as seven passages.

Synthesis of amphiphilic fluorescent PEGylated AIE nanoparticles via RAFT polymerization and their cell imaging applications

This work reports the fabrication of amphiphilic TPEV–PEG fluorescent copolymers via RAFT polymerization of polymerizable AIE and PEGMA with promising applications for bioimaging.

Tuning the fluorescence of aggregates for end-functionalized polymers through varying polymer chains with different polarities

Two pyrazoline initiators and their four end-functionalized polymers have been prepared and their tunable emission behaviors have been investigated.

Luminescent polymers and blends with hydrogen bond interactions

Intermolecular hydrogen bonds are effective forces in hampering molecular rotation and in enhancing emission of luminogenic polymers and blends with aggregation-induced emission property.

Thermo-responsive white-light emission based on tetraphenylethylene- and rhodamine B-containing boronate nanoparticles

White-light emissive boronate nanoparticles have been prepared, which exhibit reversible and thermo-responsive emission in the investigated temperature range (5–65 °C) with a temperature sensitivity of 1.1% K⁻¹ in water.

Polyaromatic nanocapsules displaying aggregation-induced enhanced emissions in water

V-shaped polyaromatic amphiphiles with phenanthrene or naphthalene rings spontaneously and quantitatively formed micelle-like nanocapsules in water at room temperature. In contrast to usual polyaromatic aggregates with weak fluorescent properties, the new capsules providing spherical polyaromatic shells with diameters of ∼2 nm show strong fluorescent emissions due to an aggregation-induced enhanced emission (AIEE) effect and moreover encapsulate a fluorescent coumarin dye to generate highly emissive host-guest composites.

Aggregation-Induced Emission Rotors: Rational Design and Tunable Stimuli Response

A novel molecular design strategy is provided to rationally tune the stimuli response of luminescent materials with aggregation-induced emission (AIE) characteristics. A series of new AIE-active molecules (AIE rotors) are prepared by covalently linking different numbers of tetraphenylethene moieties together. Upon gradually increasing the number of rotatable phenyl rings, the sensitivity of the response of the AIE rotors to viscosity and temperature is significantly enhanced. Although the molecular size is further enlarged, the performance is only slightly improved due to slightly increased effective rotors, but with largely increased rotational barriers. Such molecular engineering and experimental results offer more in-depth insight into the AIE mechanism, namely, restriction of intramolecular rotations. Notably, through this rational design, the AIE rotor with the largest molecular size turns out to be the most viscosensitive luminogen with a viscosity factor of up to 0.98.

Interfacing a tetraphenylethene derivative and a smart hydrogel for temperature-dependent photoluminescence with sensitive thermoresponse

We report, for the first time, the design and synthesis of thermoresponsive (TR) photoluminescent (PL) hydrogel nanoparticles, with a core consisting of poly[styrene-co-(N-isopropylacrylamide)] (PS-co-PNIPAM) and a PNIPAM-co-PAA shell. PAA represents polyacrylic acid which interacts with our emitting molecule 1,2-bis[4-(2-triethylammonioethoxy)phenyl]-1,2-diphenylethene dibromide (d-TPE). The electrostatic interaction between each water-soluble d-TPE molecule and two AA repeat units activates these d-TPE molecules to exhibit strong PL. Our d-TPE doped PS-co-PNIPAM/PNIPAM-co-PAA particles in water display remarkable TR PL: the emission intensity decreased in the course of heating from 2 to 80 °C and recovered during cooling from 80 to 2 °C. Such linear, reversible, and sensitive TR PL is achieved by the use of both PAA and PNIPAM as the shell polymeric chain and by careful optimization of the d-TPE to AA feed molar ratio. Thus, the emission of the d-TPE molecule is affected sensitively by temperature. In addition to such an exceptionally temperature-dependent PL, the presence of CrO4(2-) resulted in the decrease of the emission intensity, which was also temperature-dependent. The present study provides a unified conceptual methodology to engineer functional water-dispersible hydrogel nanoparticles that are stimuli-responsive with the potential to advance various PL-based applications.

Macro-/micro-environment-sensitive chemosensing and biological imaging

We have summarized the research progress on fluorescent sensors responsive to environmental factors, including local viscosity, polarity, temperature, hypoxia and pH.

Aggregation-induced emission block copolymers based on ring-opening metathesis polymerization

AIE amphiphilic block copolymers were developed from ROMP for the first time. By self-assembly in selective solvents, water soluble fluorescent nano-objects were prepared with varied structures including micelles and vesicles.

AIE macromolecules: syntheses, structures and functionalities

A comprehensive review of macromolecules with aggregation-induced emission attributes is presented, covering the frontiers of syntheses, structures, functionalities and applications.

Reaction-based and single fluorescent emitter decorated ratiometric nanoprobe to detect hydrogen peroxide

A novel reaction-based cross-linked polymeric nanoprobe with a self-calibrating ratiometric fluorescence readout to selectively detect H2O2 is reported. The polymeric nanoprobe is fabricated by using hydrophobic H2O2-reactive boronic ester groups, crosslinker units, and environmentally sensitive 3-hydroxyflavone fluorophores through a miniemulsion polymerization. On treatment with H2O2, the boronic esters in the polymer are cleaved to form hydrophilic alcohols and subsequently lead to a hydrophobic-hydrophilic transition. Covalently linked 3-hydroxyflavones manifest the change in polarity as a ratiometric transition from green to blue, accompanied by a 500-fold increase in volume. Furthermore, this nanoprobe has been used for ratiometric sensing of glucose by monitoring the H2O2 generated during the oxidation of glucose by glucose oxidase, and thus successfully distinguished between normal and pathological levels of glucose.

Complexation of fluorescent tetraphenylthiophene-derived ammonium chloride to poly(N-isopropylacrylamide) with sulfonate terminal: aggregation-induced emission, critical micelle concentration, and lower critical solution temperature

Amphiphilic polymers with hydrophilic poly(N-isopropylacylamide) (PNIPAM) shell connecting hydrophobic tetraphenylthiophene (TP) core, which has the novel aggregation-induced emission (AIE) property, by ionic bonds were prepared to explore the AIE-operative emission responses toward critical micelle concentration (CMC) and lower critical solution temperature (LCST). To exercise the idea, ammonium-functionalized TP2NH(3)(+) and sulfonate-terminated PNIPAM were separately prepared and mixed in different molar ratios to yield three amphiphilic TP-PNIPAMn complexes for the evaluations of CMC and LCST by fluorescence responses. The nonemissive dilute aqueous solutions of TP-PNIPAMn became fluorescent when increasing concentrations above CMC. Heating micelles solution to temperatures above LCSTs causes further enhancement on the emission intensity. The fluorescence responses are explained by the extent of aggregation in the micelles and in the globules formed at room temperature and at high temperatures, respectively.

Thermometry at the nanoscale

Non-invasive precise thermometers working at the nanoscale with high spatial resolution, where the conventional methods are ineffective, have emerged over the last couple of years as a very active field of research. This has been strongly stimulated by the numerous challenging requests arising from nanotechnology and biomedicine. This critical review offers a general overview of recent examples of luminescent and non-luminescent thermometers working at nanometric scale. Luminescent thermometers encompass organic dyes, QDs and Ln(3+)ions as thermal probes, as well as more complex thermometric systems formed by polymer and organic-inorganic hybrid matrices encapsulating these emitting centres. Non-luminescent thermometers comprise of scanning thermal microscopy, nanolithography thermometry, carbon nanotube thermometry and biomaterials thermometry. Emphasis has been put on ratiometric examples reporting spatial resolution lower than 1 micron, as, for instance, intracellular thermometers based on organic dyes, thermoresponsive polymers, mesoporous silica NPs, QDs, and Ln(3+)-based up-converting NPs and β-diketonate complexes. Finally, we discuss the challenges and opportunities in the development for highly sensitive ratiometric thermometers operating at the physiological temperature range with submicron spatial resolution.

Polymeric assemblies and nanoparticles with stimuli-responsive fluorescence emission characteristics

Fluorescent polymeric assemblies and nanoparticles (NPs) of nanoscale dimensions have become a focus of intensive investigations during the past few decades due to combined advantages such as improved biocompatibility, water dispersibility, stimuli-responsiveness, facile integration into optical detection devices, and the ability of further functionalization. In addition, the chemical composition and morphology of polymeric assemblies and NPs can be modulated via synthetic approaches, leading to the precise spatial organization of multiple fluorophores. Thus, polymeric assemblies and NPs have been utilized to optimize the photoluminescent properties of covalently or physically attached fluorophores and facilely modulate the fluorescence resonance energy transfer (FRET) processes when the polymeric matrix is endowed with stimuli-responsiveness. These fascinating fluorescent polymeric assemblies and NPs offer unique and versatile platforms for the construction of novel detection, imaging, biolabeling, and optoelectronic systems. This feature article focuses on the recent developments of polymeric assemblies and NPs-based stimuli-tunable fluorescent systems and highlights their future practical applications with selected literature reports.

Near-infrared fluorescent nanocapsules with reversible response to thermal/pH modulation for optical imaging

Polymeric near-infrared (NIR) fluorescent nanocapsules were developed, of which the fluorescence exhibited reversible response to local thermal/pH modulation. Our strategy was to use polymeric micelles made of temperature-sensitive Pluronic F-127 to encapsulate an amphiphilic NIR fluorescent dye-indocyanine green (ICG)-within the core and then cross-link the micelle corona by pH-sensitive poly(ethylenimine) (PEI). The size swelling/shrinking property of the micelles induced by temperature decrease/increase was used as a switch to control the fluorescence yield of the nanocapsules. It was found that the fluorescence yield significantly increased with the increase in temperature. The PEI cross-link made the fluorescence yield also sensitive to local pH change and enhanced intracellular delivery of the nanocapsules as well. Preliminary results suggest the NIR fluorescent probes could be potentially used as a contrast agent sensitive to local environment for translational optical imaging/sensing.

Aqueous polymeric sensors based on temperature-induced polymer phase transitions and solvatochromic dyes

This feature article provides, for the first time, an overview of the research that guided the way from fundamental studies of the thermo-responsive phase separation of aqueous polymer solutions to polymeric sensor systems. The incorporation of solvatochromic dyes into thermoresponsive polymers as well as the concepts of polymeric sensors are presented and discussed in detail.