Kirigami-Structured, Low-Impedance, and Skin-Conformal Electronics for Long-Term Biopotential Monitoring and Human-Machine Interfaces.

Epidermal dry electrodes with high skin-compliant stretchability, low bioelectric interfacial impedance, and long-term reliability are crucial for biopotential signal recording and human-machine interaction. However, incorporating these essential characteristics into dry electrodes remains a challenge. Here, a skin-conformal dry electrode is developed by encapsulating kirigami-structured poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/polyvinyl alcohol (PVA)/silver nanowires (Ag NWs) film with ultrathin polyurethane (PU) tape. This Kirigami-structured PEDOT:PSS/PVA/Ag NWs/PU epidermal electrode exhibits a low sheet resistance (≈3.9 Ω sq-1 ), large skin-compliant stretchability (>100%), low interfacial impedance (≈27.41 kΩ at 100 Hz and ≈59.76 kΩ at 10 Hz), and sufficient mechanoelectrical stability. This enhanced performance is attributed to the synergistic effects of ionic/electronic current from PEDOT:PSS/Ag NWs dual conductive network, Kirigami structure, and unique encapsulation. Compared with the existing dry electrodes or standard gel electrodes, the as-prepared electrodes possess lower interfacial impedance and noise in various conditions (e.g., sweat, wet, and movement), indicating superior water/motion-interference resistance. Moreover, they can acquire high-quality biopotential signals even after water rinsing and ultrasonic cleaning. These outstanding advantages enable the Kirigami-structured PEDOT:PSS/PVA/Ag NWs/PU electrodes to effectively monitor human motions in real-time and record epidermal biopotential signals, such as electrocardiogram, electromyogram, and electrooculogram under various conditions, and control external electronics, thereby facilitating human-machine interactions.

A two-photon iridium(III) complex probe for sensitive detection of SO2 derivatives in living cell mitochondria.

The derivatives of sulfur dioxide (HSO3-) formed in the biological environment play a vital role in the circulation system. Excessive SO2 derivatives will cause serious damage to the living system. Herein, a two-photon phosphorescent probe based on Ir(III) complex (named as Ir-CN) was designed and synthesized. Ir-CN is extremely selective and sensitive to SO2 derivatives with significant phosphorescent enhancement and increased phosphorescent lifetime. The detection limit of Ir-CN for SO2 derivatives reaches 0.17 µM. More importantly, Ir-CN preferentially accumulates in mitochondria, so bisulfite derivatives can be detected at subcellular level, which enriching the application of metal complex probe in biological detection. In addition, both single-photon and two-photon images can clearly show that Ir-CN is targeted to mitochondria. Benefits from its good biocompatibility, Ir-CN may be used as a reliable tool to detect SO2 derivatives in mitochondrion of living cells.

Bioinspired fluorescent molecules realize super bright blue luminescence under sunlight.

In recent years, non-aromatic fluorescent materials have attracted widespread attention, but achieving a high quantum yield (QY) in their dilute solutions still remains a challenge. In this work, inspired by the Clustering-triggered emission (CTE) phenomenon of non-aromatic amino acids and poly(amino acids), we successfully designed a bioinspired molecule with a dipeptide-like structure and active silanol groups. The as-prepared bioinspired molecule can be hydrolyzed by simple heating to obtain the hydrolysate h-PDs, which can emit strong blue fluorescence in dilute solution. And this was the first time to realize the emission behavior of non-aromatic fluorescent materials under sunlight. The QY of h-PDs in aqueous solution and solid state were as high as 98.2% and 96.3%, respectively, which were attributed to the condensation of active silanol groups at the end of the molecule, and the existence of hydrogen bonds and N â†’ Si coordination bonds that made small molecules cross-linked and aggregated into dense clusters. Finally, the application of h-PDs in the detection of intracellular and exogenous Hg2+ and Cys and luminescent films were also explored. Significantly, this work provides a design strategy for synthesizing high-fluorescence QY non-aromatic fluorescent materials, and verifies their potential application value in the fields of environment, biology and light-emitting devices.

Two Ratiometric Fluorescent Probes Based on the Hydroxyl Coumarin Chalcone Unit with Large Fluorescent Peak Shift for the Detection of Hydrazine in Living Cells.

Hydrazine is widely used in industrial and agricultural production, but excessive hydrazine possesses a serious threat to human health and environment. Here two new ratiometric fluorescence probes, DDP and DDC, with the hydroxyl coumarin chalcone unit as the sensing site are developed, which can achieve colorimetric and ratiometric recognition for hydrazine with good sensitivity, excellent selectivity, and anti-interference. The calculated fluorescence limits of detections are 0.26 µM (DDC) and 0.14 µM (DDP). The ratiometric fluorescence response to hydrazine is realized through the adjustment of donor and receptor units in coumarin conjugate structure terminals, accompanied by fluorescence peak shift about 200 nm (DDC, 188 nm; DDP, 229 nm). Stronger electropositivity in the carbon-carbon double bond is helpful to the first phase addition reaction between the probe and hydrazine. Higher phenol activity in the hydroxyl coumarin moiety will facilitate the following dihydro-pyrazole cyclization reaction. In addition, both of these probes realized the convenient detection of hydrazine vapor. The probes were also successfully applied to detect hydrazine in actual water samples, different soils, and living cells.

Amide salt pyrolysis fabrication of graphene nanosheets with multi-excitation single color emission.

A novel and simple approach of using amide salt pyrolysis to produce photoluminescent (multi-excitation and single color emission) graphene nanosheets (GNs) with a thickness of <1 nm and a diameter of about 100-200 nm is described herein. It has characteristics of high water solubility, low toxicity, easy manufacturing, etc., and has potential application prospects in analytical chemistry and biomedicine.

A julolidine-chalcone-based fluorescent probe for detection of Al3+ in real water sample and cell imaging.

A fluorescent probe 1 based on julolidine-chalcone derivative, which can specifically recognize aluminum ion with high selectivity and anti-interference, was developed. Probe 1 has good fluorescence stability and can detect Al3+ with turn-on fluorescence in a wide pH range of 4.0-9.0. The probe has good repeatability for the detection of Al3+ and fluorescence turn-on and off can be repeated with the alternate Al3+ and EDTA. The sensing mechanism is speculated that Al3+ will coordinate with hydroxyl oxygen and carbonyl oxygen on the probe through in situ 1H NMR and HRMS combing with Job's plot. The probe can also detect Al3+ in actual water samples and applied to monitor Al3+ in biological system.

Sensing for hydrazine of a pyrene chalcone derivative with acryloyl terminal group.

Hydrazine, as a toxic substance, seriously endangers human health and the environment. Based on the excellent luminescent properties and low biological toxicity of pyrene derivatives, combing with chalcone derivatives easily attacked by nucleophilic group, a pyrene derivative PCA decorated by acryloyl terminal group as fluorescent probe for hydrazine was developed. The compound shows fluorescent peak red shift and intensity enhancement with increasing solvent polarity from hexane (459 nm) to methanol (561 nm). Based on strong fluorescence emission in methanol, methanol-HEPES mixed solution was used as the solvent in the spectral recognition experiments. The probe exhibits fluorescent change from yellow fluorescence (576 nm) to blue fluorescence (393 nm) with 800-fold ratiometric fluorescence enhancement (I393nm/I576nm) after the reaction with hydrazine. The probe can recognize hydrazine in fast response rate with kinetic constant calculated being 2.7 × 10-3 s-1 and 15 min as response time. The probe also can monitor hydrazine in real water samples and various soils.

The bright fluorescence of non-aromatic molecules in aqueous solution originates from pH-induced CTE behavior.

Non-aromatic fluorescent materials with inherent visible light emission have received widespread attention. In this work, a biomimetic fluorescent molecule CA-AEP with a dipeptide structure is introduced. CA-AEP will emit bright biomimetic fluorescence in aqueous solutions by adjusting the pH, which has never been reported. This unique luminescent characteristic can be rationalized by the clustering-triggered emission (CTE) mechanism. In addition, CA-AEP can be used to monitor the maximum dynamic pH in the alkaline range of aqueous systems. Finally, the cytotoxicity assay to A549 cells showed that CA-AEP was non-toxic. Therefore, this work provides a new type of luminogen, which has potential application prospects in the field of environmental monitoring and cell biology.

Aurone Derivative Revealing the Metabolism of Lipid Droplets and Monitoring Oxidative Stress in Living Cells.

Lipid droplets (LDs) are closely connected to many physiological processes and abnormal LDs are related to many diseases. Herein, a family of two-photon fluorescence compounds based on the aurone skeleton were developed as efficient LDs imaging probes. They exhibit the obvious solvatochromism effect from blue to orange emission (∼140 nm shift) in various solvents. The robust probes possess low toxicity to living cells, high photobleaching resistance, and superior photostability and can light up LDs with high specificity. Furthermore, the probe DMMB (aurone skeleton with dimethylamino) was carefully applied in real-time monitoring of the morphological changes of LDs and the interactions between LDs and mitochondria under specific physiological conditions (e.g., starvation). We have observed for the first time the dynamic change between mitochondria and LDs when mitochondrial damage is caused by a large excess of H2O2 in a short period of time.

A strategy to construct fluorescent non-aromatic small-molecules: hydrogen bonds contributing to the unexpected fluorescence.

Propanedioyl dihydrazide (PDH), traditionally believed to be non-fluorescent, was first discovered to emit substantial fluorescence in both the solid state and solvents. Then, significantly, a novel strategy is provided: fluorescent non-aromatic small molecules with rigid molecular structures could be constructed by forming hydrogen bonds.

A highly sensitive turn-on fluorescent probe for real-time detecting hypochlorite and its application in living cells.

It is very necessary to develop real-time, highly sensitive and selective fluorescent probes for hypochlorite (ClO-) in living cells owing to hypochlorite's important role in pathological and physiological processes and its short life. Herein, a pyrene Schiff's base derivative was successfully developed for real-time (within seconds), highly sensitive detecting ClO- with a low detection limit (5.7 nM) and wide pH range (4.0-11.0) based on nucleophilic addition and subsequent hydrolysis mechanism. The probe has aggregation-induced emission properties and emits yellow fluorescence (544 nm) in PBS solution, while it exhibits blue fluorescence in other organic solvents (426 nm (THF) - 460 nm (MeOH)). The probe can be used to response ClO- in A549 cells with low cytotoxicity, a good cell membranes penetration and good biocompatibility. Cell uptake experiment indicates that probe getting into the cells is energy-dependent and is not attributed to endocytosis. Moreover, the probe is successfully used in real water sample to detect ClO- and it can be expected to be applied to ClO- participated biological and pathological functions in biological systems.

Bioinspired non-aromatic compounds emitters displaying aggregation independent emission and recoverable photo-bleaching.

Aggregation dependence is a universal feature for fluorophores, ranging from classical planar fluorescent dyes displaying aggregation-caused quenching (ACQ) and propeller-shaped AIEgens that exhibit aggregation-induced emission (AIE). In this work, we report compounds emitters (CA-PDA) that display aggregation-independent fluorescence owing to the formation of robust intramolecular, rather than intermolecular hydrogen bonding. We achieved CA-PDA by synthesis of an amide from citric acid (CA) and propane diamine (PDA). Quantum chemistry calculations suggest the CA-PDA compounds have closed structures facilitated by intramolecular hydrogen bonds, which forces the lone pair electrons on oxygen and nitrogen to within 2.9 Å. Then the strong electron clustering generates a pseudo conjugated effect and leads to blue emission. This emission exhibits recoverable photobleaching, as UV irradiation only temporally breaks the intramolecular hydrogen bonds, which may form again upon relaxation. CA-PDA can be used in cell imaging as well as in probes for Hg2+ and sulfur-containing amino acids. We expect that the strategy of a bioinspired intramolecular hydrogen bonds-facilitated compounds emitters will provide a new avenue toward advanced fluorescent materials.

A coumarin chalcone ratiometric fluorescent probe for hydrazine based on deprotection, addition and subsequent cyclization mechanism.

A ratiometric fluorescent probe for hydrazine based on a coumarin chalcone framework and a levulinic acid terminal group with a low detection limit (0.1 ppb, 0.003 µM), a large ratiometric fluorescence change (I465/I575, 1265-fold enhancement) and a wide pH work range (3.0-12.0) was developed. The mechanism analysis of the isolated hydrazine product characterized by NMR, HRMS and the crystal structure indicates that the levulinic acid group is firstly removed by deprotection and then the dihydropyrazole ring is formed due to the addition and subsequent cyclization reaction in the presence of hydrazine.

Structurally regular arrangement induced fluorescence enhancement and specific recognition for glutathione of a pyrene chalcone derivative.

Glutathione (GSH) is an important antioxygen and free radical scavenger in the organism. Level of GSH in vivo is associated with many diseases and specific recognition for GSH is very important. Here, a pyrene chalcone derivative 1 1-(2-hydroxyphenyl)-3-(1-pyrenyl)-2-propen-1-one as specific probe for GSH was developed. The probe can give rise to rapid blue fluorescence enhancement for GSH based on Michael addition reaction in pure PBS solution with high sensitivity, fast response rate and high specificity. The compound also can be applied for GSH detection in HeLa cell. Simultaneously, the compound exhibits blue fluorescence emission enhancement in methanol-water (1:1, v/v) solution with fluorescence quantum yield being 0.45 due to the competition of water molecules for hydrogen bonds between hydroxyl and carbonyl and the formation of structurally regular rodlike crystals, which allows regulating fluorescence emission by different solvent condition.

Fluorescence Emission of Polyethylenimine-Derived Polymer Dots and Its Application to Detect Copper and Hypochlorite Ions.

Polymer dots with nonconjugated groups that are facile to synthesize and environmentally friendly generally attract substantial interest. However, their fluorescence-emitting mechanisms are not clear. In this paper, nonconjugated polymer dots (N-PDs) are synthesized by amidation reaction between polyethylenimine (PEI) and citric acid (CA), then self-assemble into rice-like dots in aqueous phase with a high fluorescence quantum yield. Such nitrogen-containing nonconjugated compounds N-PDs are believed to be inherently fluorescent, and the reported reasons for fluorescence-emitting are discussed. Importantly, these N-PDs can be used as an excellent fluorescent probe to detect Cu2+ and ClO- in aqueous solutions. Cu2+ could combine with the PEI moiety of the N-PDs to form a copper amine complex and then quench the fluorescence by an internal filtration effect. ClO- could oxidize the hydroxyl groups on the surface of the N-PDs to form a positive charge, blocking electron transfer between the hydroxyl groups and the chromophore groups. Finally, the sensor was successfully applied to the detection of Cu2+ and ClO- in environmental water samples.

Coumarin-Based Small-Molecule Fluorescent Chemosensors.

Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

A simple turn-on ESIPT and PET-based fluorescent probe for detection of Al3+ in real-water sample.

Aluminum is known as the most ubiquitous metal in earth's crust but its excessive exposure will cause damage to environment and health of the organism. Here, a turn-on Schiff base fluorescence probe STH based on excited state intramolecular proton transfer and photoelectron transfer processes for Al3+ detection with fast response rate (within minutes), low detection limit (4.26×10-8M), high selectivity and reasonable pH application range (5.0-8.0) was developed. Fluorescence titration experiments show that probe STH has an excellent linear relationship (R2=0.9694) with Al3+ concentration and could be applied to quantitatively recognize Al3+ in real-water samples. Based on Job's plot and in situ mass spectra, two STH molecules will complex with Al3+ to form 2:1 complexation with oxygen atoms of hydroxyl and carbonyl groups and nitrogen atom of CN bond participating in coordination.

Synthesis of novel organic-inorganic hybrid fluorescent microspheres and their applications as Fe(III), Hg(II) and biothiols probes.

Organic-inorganic hybrid fluorescent microspheres (OI-FMs) without typical fluorophores were prepared. Fluorescence quantum yield of OI-FMs is up to 70.0% after being heated in an oven at 120 °C (named as OI-FMs-120). Interestingly, OI-FMs-120 shows different detection performances in different solvents. It can be used for qualitative and quantitative detection of Fe3 + with a detection limit of 37.8 nM in absolute ethanol. While in aqueous solution, it can be applied as an ON-OFF-ON fluorescent probe. Fluorescence of the probe is quenched by Hg2 + and later recovered by biothiols. The detection limit is as low as 34.9 nM for Hg2 +, 91.0 nM for Cys, 0.12 µM for Hcy and 0.13 µM for GSH in aqueous medium, respectively.

Cyanide and biothiols recognition properties of a coumarin chalcone compound as red fluorescent probe.

A novel coumarin chalcone derivative 1 was designed, synthesized and characterized by nuclear magnetic resonance spectra and high resolution mass spectrum. The photophysical and recognition properties of the compound as red fluorescent probe for cyanide and biothiols including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) have been discussed systematically. Red fluorescence probe 1 was able to achieve rapid and selective identification for cyanide anion and biothiols in aqueous solutions with red fluorescence quench. In addition, the recognition mechanism of 1 was demonstrated by in situ 1H NMR. The compound has two potential nucleophilic sensing sites including carbon-carbon double bond and 4-position of coumarin. The results indicate that cyanide anions can be bonded to these two sites to afford 2:1 bonding product. But biothiols only are bonded to carbon-carbon double bond by Michael addition reaction. The bonding of both cyanide and biothiols to the probe disrupts intramolecular charge transfer and leads to fluorescence quench.