A Cell‐Targeted Non‐Cytotoxic Fluorescent Nanogel Thermometer Created with an Imidazolium‐Containing Cationic Radical Initiator

Temperature-Activated Near-Infrared-II Fluorescence and SERS Dynamic-Reversible Probes for Long-Term Assessment of Osteoarthritis In Vivo

The abnormal fluctuation of temperature in vivo usually reflects the progression of inflammatory diseases. Noninvasive, real-time, and accurate monitoring and imaging of temperature variation in vivo is advantageous for guiding the early diagnosis and treatment of disease, but it remains difficult to achieve. Herein, we developed a temperature-activated near-infrared-II fluorescence (NIR-II FL) and surface-enhanced Raman scattering (SERS) nanoprobe for long-term monitoring of temperature changes in rat arthritis and timely assessment of the status of osteoarthritis. The thermosensitive polymer bearing NIR-II FL dye was grafted onto the surface of nanoporous core-satellite gold nanostructures to form the nanoprobe, wherein the nanoprobe contains NIR-II FL and Raman reference signals that are independent of temperature change. The ratiometric FL1150/FL1550 and S1528/S2226 values of the nanoprobe exhibited a reversible conversion with temperature changes. The nanoprobe accurately distinguishes the temperature variations in the inflamed joint versus the normal joint in vivo by ratiometric FL and SERS imaging, allowing for an accurate diagnosis of inflammation. Meanwhile, it can continuously monitor fluctuations in temperature over an extended period during the onset and treatment of inflammation. The tested temperature change trend could be used as an indicator for early diagnosis of inflammation and real-time evaluation of therapeutic effects.

Ultrasensitive Ratiometric Fluorescent Nanothermometer with Reverse Signal Changes for Intracellular Temperature Mapping

Sensing temperature at the subcellular level is pivotal for gaining essential thermal insights into diverse biological processes. However, achieving sensitive and accurate sensing of the intracellular temperature remains a challenge. Herein, we develop a ratiometric organic fluorescent nanothermometer with reverse signal changes for the ultrasensitive mapping of intracellular temperature. The nanothermometer is fabricated from a binary mixture of saturated fatty acids with a noneutectic composition, a red-emissive aggregation-caused quenching luminogen, and a green-emissive aggregation-induced emission luminogen using a modified nanoprecipitation method. Different from the eutectic mixture with a single phase-transition point, the noneutectic mixture possesses two solid-liquid phase transitions, which not only allows for reversible regulation of the aggregation states of the encapsulated luminogens but also effectively broadens the temperature sensing range (25-48 °C) across the physiological temperature range. Remarkably, the nanothermometer exhibits reverse and sensitive signal changes, demonstrating maximum relative thermal sensitivities of up to 63.66% °C-1 in aqueous systems and 44.01% °C-1 in the intracellular environment, respectively. Taking advantage of these outstanding thermometric performances, the nanothermometer is further employed to intracellularly monitor minute temperature variations upon chemical stimulation. This study provides a powerful tool for the exploration of dynamic cellular thermal activities, holding great promise in unveiling intricate physiological processes.

Novel Single Emissive Component Tridurylboron-TPU Solid Polymer Ratiometric Fluorescence Thermometers

Temperature measurements with high spatial resolution and accuracy can provide crucial data for understanding the changing process of microregion. Non-contact ratiometric fluorescence thermometers have received widespread attention for their sensitivity and interference resistibility. However, polymer and organic dye thermometers with such ratiometric fluorescence are very rare, and their applicability and processability are limited. In this study, novel tridurylboron compounds PPB1, PPB2, and PPB3 are designed and synthesized. They exhibit significant temperature responsive ratiometric fluorescence when dispersed in thermoplastic polyurethane elastomers (TPU). With a self-referencing feature and protection of TPU solid polymer, such fluorescence thermometers possess strong interference resistibility. From -10° to 60 °C, the fluorescence peak of PPB1-TPU system redshifted by 41 nm, the fluorescence color changes from blue to green. For the fluorescence ratiometric temperature measurement procedure, the absolute sensitivity is 14.5% °C-1 (40 °C) and relative sensitivity is 6.3% °C-1 (35 °C), which is much higher than reported solid polymer fluorescence thermometers. The temperature-responsive ranges can be adjusted by altering the types of polymer substrate and the number of the substituents. Such tridurylboron-TPU polymer fluorescence thermometers can be applied in aqueous environment and processed into devices of various shapes and sizes, demonstrating great potential for application.

Contact-Killing Antibacterial Polystyrene Polymerized Using a Quaternized Cationic Initiator

Contact-killing antibacterial materials are attracting attention owing to their ability for sustained antibacterial activity. However, contact-killing antibacterial polystyrene (PS) has not been extensively studied because its chemically stable structure impedes chemical modification. In this study, we developed an antibacterial PS sheet with a contact-killing surface using PS synthesized from 2,2'-azobis-[2-(1,3-dimethyl-4,5-dihydro-1H-imidazol-3-ium-2-yl)]propane triflate (ADIP) as a radical initiator with cationic moieties. The PS sheet synthesized with ADIP (ADIP-PS) exhibited antibacterial activity in contrast to PS synthesized with other azo radical initiators. Surface ζ-potential measurements revealed that only ADIP-PS had a cationic surface, which contributed to its contact-killing antibacterial activity. The ADIP-PS sheets also exhibited antibacterial activity after washing. In contrast, PS sheets containing silver, a typical leachable antibacterial agent, lost all antibacterial activity after the same washing treatment. The antibacterial ADIP-PS sheet demonstrated strong broad-spectrum activity against both Gram-positive and Gram-negative bacteria, including drug-resistant bacteria. Cytotoxicity tests using L929 cells showed that the ADIP-PS sheets were noncytotoxic. This contact-killing antibacterial PS synthesized with ADIP thus demonstrated good prospects as an easily producible antimicrobial material.

Multimode adaptive logic gates based on temperature-responsive DNA strand displacement

Living organisms switch their intrinsic biological states to survive environmental turbulence, in which temperature changes are prevalent in nature. Most artificial temperature-responsive DNA nanosystems work as switch modules that transit between "ON-OFF" states, making it difficult to construct nanosystems with diverse functions. In this study, we present a general strategy to build multimode nanosystems based on a temperature-responsive DNA strand displacement reaction. The temperature-responsive DNA strand displacement was controlled by tuning the sequence of the substrate hairpin strands and the invading strands. The nanosystems were demonstrated as logic gates that performed a set of Boolean logical functions at specific temperatures. In addition, an adaptive logic gate was fabricated that could exhibit different logic functions when placed in different temperatures. Specifically, upon the same input strands, the logic gate worked as an XOR gate at 10 °C, an OR gate at 35 °C, an AND gate at 46 °C, and was reset at 55 °C. The design and fabrication of the multifunctional nanosystems would help construct advanced temperature-responsive systems that may be used for temperature-controlled multi-stage drug delivery and thermally-controlled multi-step assembly of nanostructures.

Warm Cells, Hot Mitochondria: Achievements and Problems of Ultralocal Thermometry

Temperature is a crucial regulator of the rate and direction of biochemical reactions and cell processes. The recent data indicating the presence of local thermal gradients associated with the sites of high-rate thermogenesis, on the one hand, demonstrate the possibility for the existence of "thermal signaling" in a cell and, on the other, are criticized on the basis of thermodynamic calculations and models. Here, we review the main thermometric techniques and sensors developed for the determination of temperature inside living cells and diverse intracellular compartments. A comparative analysis is conducted of the results obtained using these methods for the cytosol, nucleus, endo-/sarcoplasmic reticulum, and mitochondria, as well as their biological consistency. Special attention is given to the limitations, possible sources of errors and ambiguities of the sensor's responses. The issue of biological temperature limits in cells and organelles is considered. It is concluded that the elaboration of experimental protocols for ultralocal temperature measurements that take into account both the characteristics of biological systems, as well as the properties and limitations of each type of sensor is of critical importance for the generation of reliable results and further progress in this field.

Water-Soluble Cationic Eu3+-Metallopolymer with High Quantum Yield and Sensitivity for Intracellular Temperature Sensing

Lanthanide-based (Ln³⁺) luminescent materials are ideal candidates for use in fluorescence intracellular temperature sensing. However, it remains a great challenge to obtain a Ln³⁺-ratiometric fluorescence thermometer with high sensitivity and quantum yield in an aqueous environment. Herein, a cationic Eu³⁺-metallopolymer was synthesized via the coordination of Eu(TTA)₃·2H₂O with an AIE active amphipathic polymer backbone that contains APTMA ((3-acrylamidopropyl) trimethylammonium) and NIPAM (N-isopropylacrylamide) units, which can self-assemble into nanoparticles in water solution with APTMA and NIPAM as the hydrophilic shell. This polymer exhibited highly efficient dual-emissive white-light emission (Φ = 34.3%). Particularly, when the temperature rises, the NIPAM units will transform from hydrophilic to hydrophobic in the spherical core of the nanoparticle, while the VTPE units are moved from inside the nanoparticle to the shell, activating its nonradiative transition channel and thereby decreasing its energy transfer to Eu³⁺ centers, endowing the Eu³⁺-metallopolymer with an extremely high temperature sensing sensitivity within the physiological temperature range. Finally, the real-time monitoring of the intracellular temperature variation is further conducted.

A Ratiometric Organic Fluorescent Nanogel Thermometer for Highly Sensitive Temperature Sensing

Sensing temperature in biological systems is of great importance, as it is constructive to understanding various physiological and pathological processes. However, the realization of highly sensitive temperature sensing with organic fluorescent nanothermometers remains challenging. In this study, we report a ratiometric fluorescent nanogel thermometer and study its application in the determination of bactericidal temperature. The nanogel is composed of a polarity-sensitive aggregation-induced emission luminogen with dual emissions, a thermoresponsive polymer with a phase transition function, and an ionic surface with net positive charges. During temperature-induced phase transition, the nanogel exhibits a reversible and sensitive spectral change between a red-emissive state and a blue-emissive state by responding to the hydrophilic-to-hydrophobic change in the local environment. The correlation between the emission intensity ratio of the two states and the external temperature is delicately established, and the maximum relative thermal sensitivities of the optimal nanogel are determined to be 128.42 and 68.39% °C⁻¹ in water and a simulated physiological environment, respectively. The nanogel is further applied to indicate the bactericidal temperature in both visual and ratiometric ways, holding great promise in the rapid prediction of photothermal antibacterial effects and other temperature-related biological events.

Nanothermometer with Temperature Induced Reversible Emission for Evaluation of Intracellular Thermal Dynamics

Temperature dynamics reflect the physiological state of cells, and accurate measurement of intracellular temperature helps to understand the biological processes. Herein, we report a novel nanothermometer by conjugating a fluorescent probe 3-ethyl-2-[4-(1,2,2-triphenylvinyl)styryl]benzothiazol-3-ium iodide (TPEBT) with a thermoresponsive polymer poly(N-isopropylacrylamide-co-tetrabutylphosphonium styrenesulfonate) [P(NIPAM-co-TPSS)]. The derived nanoprobe TPEBT-P(NIPAM-co-TPSS) self-assembles into micelles with TPEBT as hydrophobic core and PNIPAM as hydrophilic shell. It exhibits aggregation-induced emission (AIE) at λ_ex/λ_em = 420/640 nm in aqueous medium with a quantum yield of Φ_F 11.9%. The rise in temperature transforms PNIPAM chains from linear to compact spheres to serve as the core of micelles, and meanwhile converts TPEBT from the state of aggregation to dispersion and redistributes in the micellar shell. Temperature-driven phase transition of P(NIPAM-co-TPSS) mediates the reversible aggregation and disaggregation of TPEBT and endows the nanothermometer with temperature-dependent AIE features and favorable sensitivity for temperature sensing in 32-40 °C. TPEBT-P(NIPAM-co-TPSS) is taken up by HeLa cells to distribute mainly in lysosomes. It enables quantitative visualization of in situ thermal dynamics in response to stimuli from carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone, oligomycin, genipin, and lipopolysaccharide. The real-time monitoring of photothermal-induced intracellular temperature variation is further conducted.

Carbonized Silk Nanofibers in Biodegradable, Flexible Temperature Sensors for Extracellular Environments

Temperature is one of the key parameters for activity of cells. The trade-off between sensitivity and biocompatibility of cell temperature measurement is a challenge for temperature sensor development. Herein, a highly sensitive, biocompatible, and degradable temperature sensor was proposed to detect the living cell extracellular environments. Biocompatible silk materials were applied as sensing and packing layers, which endow the device with biocompatibility, biodegradability, and flexibility. The silk-based temperature sensor presented a sensitivity of 1.75%/°C and a working range of 35-63 °C with the capability to measure the extracellular environments. At the bending state, this sensor worked at promising response of cells at different temperatures. The applications of this developed silk material-based temperature sensor include biological electronic devices for cell manipulation, cell culture, and cellular metabolism.

Anion-π Catalysis Enabled by the Mechanical Bond

We report a series of rotaxane‐based anion–π catalysts in which the mechanical bond between a bipyridine macrocycle and an axle containing an NDI unit is intrinsic to the activity observed, including a [3]rotaxane that catalyses an otherwise disfavoured Michael addition in >60 fold selectivity over a competing decarboxylation pathway that dominates under Brønsted base conditions. The results are rationalized by detailed experimental investigations, electrochemical and computational analysis.

Fluorescent Polymers Conspectus

The development of luminescent materials is critical to humankind. The Nobel Prizes awarded in 2008 and 2010 for research on the development of green fluorescent proteins and super-resolved fluorescence imaging are proof of this (2014). Fluorescent probes, smart polymer machines, fluorescent chemosensors, fluorescence molecular thermometers, fluorescent imaging, drug delivery carriers, and other applications make fluorescent polymers (FPs) exciting materials. Two major branches can be distinguished in the field: (1) macromolecules with fluorophores in their structure and (2) aggregation-induced emission (AIE) FPs. In the first, the polymer (which may be conjugated) contains a fluorophore, conferring photoluminescent properties to the final material, offering tunable structures, robust mechanical properties, and low detection limits in sensing applications when compared to small-molecule or inorganic luminescent materials. In the latter, AIE FPs use a novel mode of fluorescence dependent on the aggregation state. AIE FP intra- and intermolecular interactions confer synergistic effects, improving their properties and performance over small molecules aggregation-induced, emission-based fluorescent materials (AIEgens). Despite their outstanding advantages (over classic polymers) of high emission efficiency, signal amplification, good processability, and multiple functionalization, AIE polymers have received less attention. This review examines some of the most significant advances in the broad field of FPs over the last six years, concluding with a general outlook and discussion of future challenges to promote advancements in these promising materials that can serve as a springboard for future innovation in the field.

Stimuli-responsive fluorescent nanogel: a nonconventional donor for ratiometric temperature and pH sensing

A reactive stimuli responsive fluorescent polyaminoamide nanogel (NANO-PAMAM) is synthesized via an aza-Michael polyaddition reaction in water and subsequently transformed to a ratiometric nanosensor via post-polymerization modification of the reactive NANO-PAMAM.

Fluorescence Thermometer: Intermediation of the Fontal Temperature and Light

The rapid advance of thermal materials and fluorescence spectroscopy has extensively promoted micro-scale fluorescence thermometry development in recent years. Based on the advantages of fast response, high sensitivity, simple operation,...

Targeted Nanoscale 3D Thermal Imaging of Tumor Cell Surface with Functionalized Quantum Dots

Measuring the changes in tumor cell surface temperature can provide insights into cellular metabolism and pathological features, which is significant for targeted chemotherapy and hyperthermic therapy. However, conventional micro-nano scale methods are invasive and can only measure the temperature of cells across a single plane, which excludes specific organelles. In this study, fluorescence quantum dots (QDs) are functionalized with the membrane transport protein transferrin (Tf) as a thermo-sensor specific for tumor cell membrane. The covalent conjugation is optimized to maintain the relative fluorescence intensity of the Tf-QDs to >90%. In addition, the Tf-QDs undergo changes in the fluorescence spectra as a function of temperature, underscoring its thermo-sensor function. Double helix point spread function imaging optical path is designed to locate the probe at nanoscale, and 3D thermal imaging technology is proposed to measure the local temperature distribution and direction of heat flux on the tumor cell surface. This novel targeted nanoscale 3D thermometry method can be a highly promising tool for measuring the local and global temperature distribution across intracellular organelles.

A Sensitive and Reliable Organic Fluorescent Nanothermometer for Noninvasive Temperature Sensing

Sensing temperature at the subcellular level is of great importance for the understanding of miscellaneous biological processes. However, the development of sensitive and reliable organic fluorescent nanothermometers remains challenging. In this study, we report the fabrication of a novel organic fluorescent nanothermometer and study its application in temperature sensing. First of all, we synthesize a dual-responsive organic luminogen that can respond to the molecular state of aggregation and environmental polarity. Next, natural saturated fatty acids with sharp melting points as well as reversible and rapid phase transition are employed as the encapsulation matrix to correlate external heat information with the fluorescence properties of the luminogen. To apply the composite materials for biological application, we formulate them into colloidally dispersed nanoparticles by a technique that combines in situ surface polymerization and nanoprecipitation. As anticipated, the resultant zwitterionic nanothermometer exhibits sensitive, reversible, reliable, and multiparametric responses to temperature variation within a narrow range around the physiological temperature (i.e., 37 °C). Taking spectral position, fluorescence intensity, and fluorescence lifetime as the correlation parameters, the maximum relative thermal sensitivities are determined to be 2.15% °C^-1, 17.06% °C^-1, and 17.72% °C^-1, respectively, which are much higher than most fluorescent nanothermometers. Furthermore, we achieve the multimodal temperature sensing of bacterial biofilms using these three complementary fluorescence parameters. Besides, we also fabricate a cationic form of the nanothermometer to facilitate efficient cellular uptake, holding great promise for studying thermal behaviors in biological systems.

Lanthanide doped luminescence nanothermometers in the biological windows: strategies and applications

The development of lanthanide-doped non-contact luminescent nanothermometers with accuracy, efficiency and fast diagnostic tools attributed to their versatility, stability and narrow emission band profiles has spurred the replacement of conventional contact thermal probes. The application of lanthanide-doped materials as temperature nanosensors, excited by ultraviolet, visible or near infrared light, and the generation of emissions lying in the biological window regions, I-BW (650 nm-950 nm), II-BW (1000 nm-1350 nm), III-BW (1400 nm-2000 nm) and IV-BW (centered at 2200 nm), are notably growing due to the advantages they present, including reduced phototoxicity and photobleaching, better image contrast and deeper penetration depths into biological tissues. Here, the different mechanisms used in lanthanide ion-doped nanomaterials to sense temperature in these biological windows for biomedical and other applications are summarized, focusing on factors that affect their thermal sensitivity, and consequently their temperature resolution. Comparing the thermometric performance of these nanomaterials in each biological window, we identified the strategies that allow boosting of their sensing properties.

Stimuli-responsive polymer-based systems for diagnostic applications

Stimuli-responsive polymers exhibit properties that make them ideal candidates for biosensing and molecular diagnostics. Through rational design of polymer composition combined with new polymer functionalization and synthetic strategies, polymers with myriad responsivities, e.g., responses to temperature, pH, biomolecules, CO2, light, and electricity can be achieved. When these polymers are specifically designed to respond to biomarkers, stimuli-responsive devices/probes, capable of recognizing and transducing analyte signals, can be used to diagnose and treat disease. In this review, we highlight recent state-of-the-art examples of stimuli-responsive polymer-based systems for biosensing and bioimaging.

Mitochondria-Anchored Molecular Thermometer Quantitatively Monitoring Cellular Inflammations

Temperature in mitochondria can be a critical indicator of cell metabolism. Given the highly dynamic and inhomogeneous nature of mitochondria, it remains a big challenge to quantitatively monitor the local temperature changes during different cellular processes. To implement this task, we extend our strategy on mitochondria-anchored thermometers from "on-off" probe Mito-TEM to a ratiometric probe Mito-TEM 2.0 based on the Förster resonance energy transfer mechanism. Mito-TEM 2.0 exhibits not only a sensitive response to temperature through the ratiometric changes of dual emissions but also the specific immobilization in mitochondria via covalent bonds. Both characters support accurate and reliable detection of local temperature for a long time, even in malfunctioning mitochondria. By applying Mito-TEM 2.0 in fluorescence ratiometric imaging of cells and zebrafishes, we make a breakthrough in the quantitative visualization of mitochondrial temperature rises in different inflammation states.

Mapping intracellular thermal response of cancer cells to magnetic hyperthermia treatment

Temperature is a key parameter for optimal cellular function and growth. Temperature perturbation may directly lead to cell death. This can be used in cancer therapies to kill cells in tumors, a therapeutic approach called hyperthermia. To avoid overheating of tumors that may damage healthy tissues, a knowledge of the intracellular temperature reached during the hyperthermia treatment of cancer cells is relevant. Recently, several luminescent intracellular nanothermometers have been proposed; however an application to sense temperature during a hyperthermia treatment is lacking. Here we present a technique to measure intracellular temperature changes in in vitro cancer cell models. For this purpose, we study for the first time the temperature dependence of the green fluorescent protein (GFP)'s fluorescence lifetime parameter. We find the fluorescence lifetime of GFP can be used for nanothermosensing. We use GFP in a bound form to actin filaments as an intracellular thermal reporter. Furthermore, we assess intracellular temperature during in vitro magnetothermal therapy on live HeLa cells incubated with polyacrylic acid-coated iron oxide nanoparticles. Compared to other thermosensitive materials and formulations reported so far, the GFP nanothermosensor is easily expressed via transfection and various GFP variants are commercially available. We foresee that the nanothermometer developed might find widespread applications in cancer therapy research and development.

A Dual-Excitation Decoding Strategy Based on NIR Hybrid Nanocomposites for High-Accuracy Thermal Sensing

Optical thermal sensing holds great promise for disease theranostics. However, traditional ratiometric thermometry methods, in which intensity ratio of two nonoverlapping emissions is defined as the thermosensitive parameter, may have a limited accuracy in temperature read-out due to the deleterious interference from wavelength- and temperature-dependent photon attenuation in tissue. To overcome this limitation, a dual-excitation decoding strategy based on NIR hybrid nanocomposites comprising self-assembled quantum dots (QDs) and Nd3+ doped fluoride nanocrystals (NCs) is proposed for thermal sensing. Upon excitation at 808 nm, the intensity ratio of two emissions at identical wavelength (1057 nm) from QDs and NCs, respectively, is defined as the thermometric parameter R. By employing another 830 nm laser beam following the same optical path as 808 nm laser to exclusively excite QDs, the two overlapping emissions can be easily decoded. The acquired R proves to be inert to the detection depth in tissue, with a minimized temperature reading error of ≈2.3 °C at 35 °C (at a depth of ≈1.1 mm), while the traditional thermometry mode based on the nonoverlapping 1025 and 863 nm emissions may exhibit a large error of ≈43.0 °C. The insights provided by this work pave the way toward high-accuracy deep-tissue biosensing.

Robust liquid-core nanocapsules as biocompatible and precise ratiometric fluorescent thermometers for living cells

Intracellular thermometry with favorable biocompatibility and precision is essential for insight into temperature-related cellular events. Here, liquid-core nanocapsule ratiometric fluorescent thermometers (LCN-RFTs) were prepared by encapsulating thermosensitive organic fluorophores (N,N'-di(2-ethylhexyl)-3,4,9,10-perylene tetracarboxylic diimide, DEH-PDI) with hydrophobic solvent (2,2,4-trimethylpentane, TMP) into polystyrene/silica hybrid nanoshells. As the fluorescent thermosensitive unit of the LCN-RFT, the TMP solution of DEH-PDI was responsible for the fluorescence response to temperature. Benefitting from the hydrophilic nanoshells, the LCN-RFTs exhibited favorable anti-interference and biocompatibility. Furthermore, the LCN-RFTs showed an excellent precision of 0.02 °C-0.10 °C in a simulated physiological environment from 10.00 °C to 90.00 °C, and were employed to realize intracellular thermometry with an outstanding precision of 0.06 °C-0.14 °C. This work provides a feasible method of using hydrophobic organic fluorophores for intracellular thermometry by encapsulating them into nanocapsules.

TICT-Based Near-Infrared Ratiometric Organic Fluorescent Thermometer for Intracellular Temperature Sensing

Fluorescent thermometers with near-infrared (NIR) emission play an important role in visualizing the intracellular temperature with high resolution and investigating the cellular functions and biochemical activities. Herein, we designed and synthesized a donor-Π-acceptor luminogen, 2-([1,1'-biphenyl]-4-yl)-3-(4-((E)-4-(diphenylamino)styryl) phenyl) fumaronitrile (TBB) by Suzuki coupling reaction. TBB exhibited twisted intramolecular charge transfer-based NIR emission, aggregation-induced emission, and temperature-sensitive emission features. A ratiometric fluorescent thermometer was constructed by encapsulating thermosensitive NIR fluorophore TBB and Rhodamine 110 dye into an amphiphilic polymer matrix F127 to form TBB&R110@F127 nanoparticles (TRF NPs). TRF NPs showed a good temperature sensitivity of 2.37%·°C^-1, wide temperature response ranges from 25 to 65 °C, and excellent temperature-sensitive emission reversibility. Intracellular thermometry experiments indicated that TRF NPs could monitor the cellular temperature change from 25 to 53 °C for Hep-G2 cells under the photothermal therapy agent heating process, indicating the considerable potential applications of TRF NPs in the biological thermometry field.

Luminescent Anion Sensing by Transition-Metal Dipyridylbenzene Complexes Incorporated into Acyclic, Macrocyclic and Interlocked Hosts

A series of novel acyclic, macrocyclic and mechanically interlocked luminescent anion sensors have been prepared by incorporation of the isophthalamide motif into dipyridylbenzene to obtain cyclometallated complexes of platinum(II) and ruthenium(II). Both the acyclic and macrocyclic derivatives 7⋅Pt, 7⋅Ru⋅PF6 , 10⋅Pt and 10⋅Ru⋅PF6 are effective sensors for a range of halides and oxoanions. The near-infra red emitting ruthenium congeners exhibited an increased binding strength compared to platinum due to the cationic charge and thus additional electrostatic interactions. Intramolecular hydrogen-bonding between the dipyridylbenzene ligand and the amide carbonyls increases the preorganisation of both acyclic and macrocyclic metal derivatives resulting in no discernible macrocyclic effect. Interlocked analogues were also prepared, and preliminary luminescent chloride anion spectrometric titrations with 12⋅Ru⋅(PF6 )2 demonstrate a marked increase in halide binding affinity due to the complementary chloride binding pocket of the [2]rotaxane. 1 H NMR binding titrations indicate the interlocked dicationic receptor is capable of chloride recognition even in competitive 30 % aqueous mixtures.

Ratiometric dual fluorescence tridurylboron thermometers with tunable measurement ranges and colors

Noncontact ratiometric fluorescent thermometers have received great interests in recent years. Besides being a sensitive and easily observable detection signal, the ratiometric dual fluorescence are also highly accurate and resistable to interference. However, organic molecular thermometers with such fluorescence property are very rare, and their measurement ranges and colors are limited. In this work, a series of ratiometric dual fluorescent tridurylboron thermometers, with tunable measurement ranges and colors, are designed and synthesized. The measurement ranges of the thermometers are -20 °C-40 °C, -10 °C-50 °C and -25 °C-30 °C in solid polymeric systems, and -50 °C-100 °C and -30 °C-110 °C in liquid organic solvent. With decreasing temperature, the fluorescence colors of tridurylboron-MOE thermometers are from green yellow to yellow red, green to green yellow, blue to green. This study provides a novel strategy for developing tunable ratiometric dual fluoresence organic molecular thermometers.

The challenge of intracellular temperature

This short review begins with a brief introductory summary of luminescence nanothermometry. Current applications of luminescence nanothermometry are introduced in biological contexts. Then, theoretical bases of the “temperature” that luminescence nanothermometry determines are discussed. This argument is followed by the 10⁵ gap issue between simple calculation and the measurements reported in literatures. The gap issue is challenged by recent literatures reporting single-cell thermometry using non-luminescent probes, as well as a report that determines the thermal conductivity of a single lipid bilayer using luminescence nanothermometry. In the end, we argue if we can be optimistic about the solution of the 10⁵ gap issue.

A Personal Journey across Fluorescent Sensing and Logic Associated with Polymers of Various Kinds

Our experiences concerning fluorescent molecular sensing and logic devices and their intersections with polymer science are the foci of this brief review. Proton-, metal ion- and polarity-responsive cases of these devices are placed in polymeric micro- or nano-environments, some of which involve phase separation. This leads to mapping of chemical species on the nanoscale. These devices also take advantage of thermal properties of some polymers in water in order to reincarnate themselves as thermometers. When the phase separation leads to particles, the latter can be labelled with identification tags based on molecular logic. Such particles also give rise to reusable sensors, although molecular-scale resolution is sacrificed in the process. Polymeric nano-environments also help to organize rather complex molecular logic systems from their simple components. Overall, our little experiences suggest that researchers in sensing and logic would benefit if they assimilate polymer concepts.

Cationic Fluorescent Nanogel Thermometers based on Thermoresponsive Poly(N-isopropylacrylamide) and Environment-Sensitive Benzofurazan

Cationic nanogels of N-isopropylacrylamide (NIPAM), including NIPAM-based cationic fluorescent nanogel thermometers, were synthesized with a cationic radical initiator previously developed in our laboratory. These cationic nanogels were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), zeta potential measurements and fluorescence spectroscopy, as summarized in the temperature-dependent fluorescence response based on the structural change in polyNIPAM units in aqueous solutions. Cellular experiments using HeLa (human epithelial carcinoma) cells demonstrated that NIPAM-based cationic fluorescent nanogel thermometers can spontaneously enter the cells under mild conditions (at 25 °C for 20 min) and can show significant fluorescence enhancement without cytotoxicity with increasing culture medium temperature. The combination of the ability to enter cells and non-cytotoxicity is the most important advantage of cationic fluorescent nanogel thermometers compared with other types of fluorescent polymeric thermometers, i.e., anionic nanogel thermometers and cationic/anionic linear polymeric thermometers.

Using green emitting pH-responsive nanogels to report environmental changes within hydrogels: a nanoprobe for versatile sensing

Remotely reporting the local environment within hydrogels using inexpensive laboratory techniques has excellent potential to improve our understanding of the nanometer-scale changes that cause macroscopic swelling or deswelling. Whilst photoluminescence (PL) spectroscopy is a popular method for such studies this approach commonly requires bespoke and time-consuming synthesis to attach fluorophores which may leave toxic residues. A promising and more versatile alternative is to use a pre-formed nanogel probe that contains a donor/acceptor pair and then "dope" that into the gel during gel assembly. Here, we introduce green-emitting methacrylic acid-based nanogel probe particles and use them to report the local environment within four different gels as well as stem cells. As the swelling of the nanogel probe changes within the gels the non-radiative energy transfer efficiency is strongly altered. This efficiency change is sensitively reported using the PL ratiometric intensity from the donor and acceptor. We demonstrate that our new nanoprobes can reversibly report gel swelling changes due to five different environmental stimuli. The latter are divalent cations, gel degradation, pH changes, temperature changes and tensile strain. In the latter case, the nanoprobe rendered a nanocomposite gel mechanochromic. The results not only provide new structural insights for hierarchical natural and synthetic gels, but also demonstrate that our new green-fluorescing nanoprobes provide a viable alternative to custom fluorophore labelling for reporting the internal gel environment and its changes.

Polyelectrolyte-Mediated Nontoxic AgGa xIn1- xS2 QDs/Low-Density Lipoprotein Nanoprobe for Selective 3D Fluorescence Imaging of Cancer Stem Cells

Cancer stem cells, which are a population of cancer cells sharing common properties with normal stem cells, have strong self-renewal ability and multi-lineage differentiation potential to trigger tumor proliferation, metastases, and recurrence. From this, targeted therapy for cancer stem cells may be one of the most promising strategies for comprehensive treatment of tumors in the future. We design a facile approach to establish the colon cancer stem cells-selective fluorescent probe based on the low-density lipoprotein (LDL) and the novel AgGa _xIn_{(1- x)}S₂ quantum dots (AGIS QDs). The AGIS QDs with a high crystallinity are obtained for the first time via cation-exchange protocol of Ga³⁺ to In³⁺ starting from parent AgInS₂ QDs. Photoluminescence peak of AGIS QDs can be turned from 502 to 719 nm by regulating the reaction conditions, with the highest quantum yield up to 37%. Subsequently, AGIS QDs-conjugated LDL nanocomposites (NCs) are fabricated, in which a cationic polyelectrolyte was used as a coupling reagent to guarantee the electrostatic self-assembly. The structural integrity and physicochemical properties of the LDL-QDs NCs are found to be maintained in vitro, and the NCs exhibit remarkable biocompatibility. The LDL-QDs can be selectively delivered into cancer stem cells that overexpress LDL receptor, and three-dimensional imaging of cancer stem cells is realized. The results of this study not only demonstrate the versatility of nature-derived lipoprotein nanoparticles, but also confirm the feasibility of electrostatic conjugation using cationic polyelectrolyte, allowing reseachers to design nanoarchitectures for targeted diagnosis and treatment of cancer.

A ratiometric fluorescent thermometer based on amphiphilic alkynylpyrene derivatives

A new alkynylpyrene derivative shows thermoresponsive, ratiometric, and reversible fluorescence color switching from red to green in an ambient atmosphere.

An ultrasensitive ratiometric fluorescent thermometer based on frustrated static excimers in the physiological temperature range

We report here an ultrasensitive ratiometric fluorescent thermometer (RFT) based on the frustrated static excimers (FSEs) of DEH-PDI (N,N′-di(2-ethylhexyl)-3,4,9,10-perylenetetracarboxylic diimide) in the physiological temperature range.

A Facile Approach towards Fluorescent Nanogels with AIE-Active Spacers

A facile and efficient approach for design and synthesis of organic fluorescent nanogels has been developed by using a pre-synthesized polymeric precursor. This strategy is achieved by two key steps: (i) precise synthesis of core⁻shell star-shaped block copolymers with crosslinkable AIEgen-precursor (AIEgen: aggregation induced emission luminogen) as pending groups on the inner blocks; (ii) gelation of the inner blocks by coupling the AIEgen-precursor moieties to generate AIE-active spacers, and thus, fluorescent nanogel. By using this strategy, a series of star-shaped block copolymers with benzophenone groups pending on the inner blocks were synthesized by grafting from a hexafunctional initiator through atom transfer radical copolymerization (ATRP) of 4-benzoylphenyl methacrylate (BPMA) or 2-(4-benzoylphenoxy)ethyl methacrylate (BPOEMA) with methyl methacrylate (MMA) and tert-butyldimethylsilyl-protected 2-hydroxyethyl methacrylate (ProHEMA) followed by a sequential ATRP to grow PMMA or PProHEMA. The pendent benzophenone groups were coupled by McMurry reaction to generate tetraphenylethylene (TPE) groups which served as AIE-active spacers, affording a fluorescent nanogel. The nanogel showed strong emission not only at aggregated state but also in dilute solution due to the strongly restricted inter- and intramolecular movement of TPE moiety in the crosslinked polymeric network. The nanogel has been used as a fluorescent macromolecular additive to fabricate fluorescent film.