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Flexible and stretchable electrodes have been extensively explored in recent decades, promoting remarkable advances in wearable electronics. However, for the foreseeable future it will be hard to achieve a level of conductivity of stretchable electrodes equivalent to that of metallic electrodes, which undermines the potential for practical applications, especially for fiber-shaped electrodes with long length/diameter. Herein, the basic physical concept of the small resistance of parallel circuits was applied to a triboelectric nanogenerator (TENG) fiber/textile to dilute the negative effects of the huge resistance of stretchable electrode fibers. As a demonstration of the concept, stretchable gel electrode-based fibers were woven into parallel multi-fiber TENG structures (parallel-teng), which significantly reduced electrode resistance compared to single long-fiber knitting TENG (GS-teng). The output current of parallel-teng showed an 11.8 fold enhancement compared to that of GS-teng owing to the decrease in the inner resistance by an order of magnitude. This work demonstrates an easy method to reduce the electrode resistance using parallel multi-fiber structures, which provide an approach for dealing with low conductivity electrodes in practical application. Furthermore, other wearable devices where there is the challenge of stretchable high resistance of electrode fibers, such as fiber batteries and piezoelectric fibers, could be inspired by this work because of the versatility of the physical concept.

Smart drug delivery system of core–shell-type polypeptide nanogel of poly(Z-l-lysine-co-l-cystine) (PLL-LC) has been synthesized, which showed high drug loading content (DLC 16.5%) of DOX and pHe–glutathione (GSH) stepwise responsive disassembly. Modifying the shell of the nanogel by 2,3-dimethylmaleic anhydride (DMA) makes it quickly respond to the weak acidic tumor microenvironment (pHe 6.8–6.5), inducing the surface charge reversal and promoting the nanogel efficient uptake by cancer cells. Next, the nanogel can release encapsulated DOX in cytoplasm in the presence of high level of GSH therein via reduction and disassembly of the nanogel, resulting in highly selective cytotoxicity. MTT studies reveal the good biocompatibility of the nanogel before charge reversal and an efficient toxicity to cell under pHe microenvironment. In vitro experiments confirm the smart stepwise degradability of the nanogel and efficient therapy ability to cancer cell, indicating the nanogel is a potential drug delivery system.

A new dual-state emission (DSE) dye comprised of tetraphenylethene (TPE), triphenylamine (TPA), and indoline groups has been synthesized, which showed efficient fluorescence in both solution and solid. The dye is comprised of three parts and these parts show different fluorescence properties which can be very useful in some applications since the dye can produce information-rich responses. For example, the dye is pH-sensitive in both solution and solid states, and it emits yellow fluorescence in normal pH and red/NIR fluorescence in acidic condition. Cytotoxicity of the dye is low at concentration of 3 μM which was confirmed by a methyl thiazolyl tetrazolium (MTT) experiment, and in vitro experiments revealed that the pH responsive performance can be used in bioimaging. It provides a novel pH-sensitive DSE dye ever reported, which has potential application in many fields.

Photobleaching and biotoxicity are the main bottlenecks for organic fluorescent dyes applied in real-time dynamic monitoring of living cells. Here, an unnatural amino acid, 4-nitro-3-phenyl-l-alanine (NPA), was used as a scaffold to covalently link a near-infrared fluorophore Cy5.5 and an amphiphilic polypeptide, poly[oligo(ethylene glycol) methyl ether methacrylate]- block-poly[2-amino-N4-(2-diisopropylamino-ethyl)-l-aspartic acid] (P(OEGMA)21-P(Asp)16-iPr), was then conjugated for increasing the photostability and improving the biocompatibility simultaneously. The protective agent of NPA can service as an effective triplet state quenching by intramolecular electron transfer between Cy5.5 and NPA. The less sensitivity of the electron-transfer process for molecular oxygen makes it an ideal photostabilized strategy for fluorophores applied in live-cell imaging. Bonding to copolymer is a common way for hydrophobic dyes to expand their application in biomedical imaging and increase their functionality, depending on the delivery system. The results indicate that Cy5.5-NPA-linked polypeptide copolymer exhibited an enhanced photostability and an excellent biocompatibility, which means this scaffolding strategy has a potential application in fluorescence-guided surgery, lived-cell imaging, and super-resolution microscopy.

The rapid advancement of flexible and stretchable electronics has attracted intensive attention in recent decades. However, challenges still remain in developing wearable and sustainable power sources with comparable portability and stretchability. Here, a novel type of stretchable fiber-shaped triboelectric nanogenerator (AXF-TENG) was fabricated by inserting a negative Poisson-ratio auxetic fiber into a positive Poisson-ratio hollow circular sleeve, forming a synergistic structured TENG composed of opposite Poisson's ratios. Owing to the advanced structural designs, the inner auxetic fiber would expand in all directions to more effectively contact with the shrunk outer steel wire sleeve under stretching. The peak-to-peak voltage and transfer charge of composite based AXF-TENG could reach up to 42 V and 12.5 nC, respectively. The fabricated AXF-TENG can be used as a self‐powered multifunctional sensor to detect human motions and be woven into an energy‐harvesting fabric to scavenge biomechanical energy. With open-circuit voltage of 46 V and maximum instantaneous power density of 52.36 mW/m2, the AXF-TENG fabric was capable of lighting up 20 light emitting diodes (LEDs), charging commercial capacitors, powering an electronic watch and a calculator. All of these merits of the proposed AXF-TENGs suggest their promising potentials for versatile applications in biomechanical energy harvesting and self-powered sensing.

A novel pH-sensitive carborane and cyanine dye conjugated polypeptide and its micelles has been designed and synthesized for potential near infrared fluorescence imaging-guided boron neutron capture therapy (BNCT). The amphiphilic polymer we synthesized with tertiary amine as functional group could self-assemble to micelle nanoparticles at neutral pH, and responsive to acidic solution for the disassembly of the micelles for drug release. The tertiary amine sensitive induced process was observed via dynamic light scattering (DLS) and transmission electron microscopy (TEM). The efficiency of cell killing ability is studied by MTT assays and fluorescence microscope measurement, indicating a new intelligent system for potential NIR imaging-guided therapy.

Bioimaging requires probes with turn-on properties at all time for tracing, especially at the near-infrared (NIR) region with an intelligent performance. Here, A Schiff base dye conjugated with both pyrene and a cyanine (cy7) NIR flourophores has been synthesized, which showed a novel "see-saw" fluorescent performance via the combination of aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ). The new dye is always turn-on by the "see-saw" balance of the visible and NIR fluorescence, and it turns-on at visible region when it is in aggregative state due to the AIE while it emits NIR fluorescence in single molecular state. The as-prepared dye has many potential applications, especially in the field of bio-imaging, which was confirmed by the in vitro cells experiments.

A new strategy for pH-responsive near infrared (NIR) cyanine dye, based on the concept of triggered disaggregation-induced emission (DIE), has been developed. Schiff base group was introduced to the molecular scaffold of Cy7, and promoted the aggregation of cyanine in pH7.4 buffer due to the strong π-π interaction. While in an acidic (pH 5.8) environment, the Schiff base group was hydrolyzed by acid and the nanoparticles were disaggregated. The vanishing of the intermolecular aggregation-caused quenching thus induced a fluorescence recovery of 96 folds. Moreover, abundant kinds of Schiff base provide more potential cyanine dyes for pH-responsive ultrahigh NIR fluorescence "Off/On" ratio, which could work as the intelligent bio-imaging probes in near future.

Wearable electronics had drawn great attentions in recent years because of their valuable applications in our daily lives. Among them, triboelectric nanogenerator (TENG) textile was a promising candidate to alleviate electricity supply problem of wearable electronics. However, currently used electrodes in TENG textile are hard to fulfill the requirements of stretchable electronics. Here, organogel conductor was proposed as electrode to construct triboelectric fiber (GS-fiber), owing to its merits of flexibility, stretchability and conductivity. The core/shell structure GS-fiber was prepared from gel’s photo-crosslinking in transparent silicone hollow fiber, in which hollow fiber was the mold for gel electrode and outer friction layer. The flexibility and solid form of organogel electrode avoided the cracking problem of metallic electrode and leakage problem of liquid electrode in TENG textile, which make GS-fiber a stretchable and tailorable fiber. Moreover, the facile preparation process endowed GS-fiber with large-scale production ability and 30-meter GS-fiber was prepared for demonstration. The GS-fiber was then knitted into TENG textile (GS-teng) for bio-mechanical energy harvesting. This work indicated that organogel electrode has great potential in triboelectric fiber, which was a remarkable progress towards TENG textiles’ industrial application.

With the rapid advancement in wearable electronics, energy harvesting devices based on triboelectric nanogenerators (TENGs) have been intensively investigated for providing sustainable power supply for them. However, the fabrication of wearable TENGs still remains great challenges, such as flexibility, breathability and washability. Here, a route to develop a new kind of woven-structured triboelectric nanogenerator (WS-TENG) with a facile, low-cost, and scalable electrospinning technique is reported. The WS-TENG is fabricated with commercial stainless-steel yarns wrapped by electrospun polyamide 66 nanofiber and poly(vinylidenefluoride-co-trifluoroethylene) nanofiber, respectively. Triggered by diversified friction materials under a working principle of freestanding mode, the open-circuit voltage, short-circuit current and maximum instantaneous power density from the WS-TENG can reach up to 166 V, 8.5 µA and 93 mW/m2, respectively. By virtue of high flexibility, desirable breathability, washability and excellent durability, the fabricated WS-TENG is demonstrated to be a reliable power textile to light up 58 light-emitting diodes (LED) connected serially, charge commercial capacitors and drive portable electronics. A smart glove with stitched WS-TENGs is made to detect finger motion in different circumstances. The work presents a new approach for self-powered textiles with potential applications in biomechanical energy harvesting, wearable electronics and human motion monitoring.

Composites' interface is the contact area between filler and matrix, which is a critical issue in composites' permittivity and thereby of great value to improve friction composites' performance in triboelectric nanogenerators (TENGs). However, composites' interfacial influence on triboelectric performance was not clear in past years even numerous composites were prepared, which limited materials' advance of triboelectric performance. Here, a systematic investigation about the composites' interfacial influence was performed on liquid doping polydimethylsiloxane (PDMS) composites, in which interfacial area and compatibility were found with great importance to composites' permittivity and triboelectric performance. Through high preparation stirring speed and appropriate surfactant additive, interfacial modification of enlarging interfacial area and compatible interface was facilely achieved. The as-prepared composites' permittivity and triboelectric performance were remarkably promoted as compared to composites without interfacial modification, achieving 8.1-fold in output voltage and 9.5-fold in output current of pristine PDMS. Further, the composites were applied to assemble TENG for energy harvesting and movement detection. This work revealed the interface properties’ influence on composites permittivity and further demonstrated the importance of interfacial modification for enhancement of triboelectric performance, illustrating that the interface issues should be taken into consideration in doping triboelectric composites for high output performance TENG.

Rapid advancements in stretchable and multifunctional next-generation electronics have raised great demand in development of transparent, stretchable and reliable power sources. Here, an organogel electrode, consisted of Poly(4-acryloylmorpholine) frame and low polarity propylene carbonate swelling solvent, was prepared for constructing a new kind of organogel ionic electrode based triboelectric nanogenerator (TENG), called Og-TENG, which not only possessed high transparence (95%) and stretchability (~387%), but also exhibited excellent electric reliability and mechanical robustness (foldable and twistable) under daily working temperature range (−20°C- 45 °C). The electric performance of Og-TENG is extraordinary, reaching a high instantaneous power density of 4.03 W/m2. The rational design of organogel electrode endowed the Og-TENG with excellent anti-freezing and solvent retention properties. Moreover, the good compatibility between organogel and triboelectric elastomer improved the interface adhesion and further made Og-TENG as a high reliable device under mechanical deformations as compared to high polarity gels based TENGs. The Og-TENG was demonstrated in harvesting bio-mechanical energies and detecting human gestures. This work provides a new strategy to prepare transparent and stretchable TENGs of high power density for reliable and robust energy harvesting in daily working temperature range, exhibiting promising potentials in development of stretchable and multifunctional next-generation electronics.

The modification or functionalization of triboelectric materials is of great importance for improving triboelectric nanogenerator's triboelectric performance. Traditionally, chemical introduction was the major method for functionalization of TENG materials which relied on certain reactive molecules and complex chemical process. The variety of functionalization was limited as majority functionalization molecules such as halogens are not chemical reactive. Here, high permittivity liquid was dispersed in polydimethylsiloxane (PDMS) matrix by emulsion mixing and regarded as functional molecules micro-carrier for functionalization of triboelectric materials. Due to the solubility of liquid, functionalized PDMS composite could be facilely fabricated by corresponding functional additive dissolved liquid, avoiding functional additive's necessity of chemical reactivity and indicating great extensibility in functionalized triboelectric materials. Fluoroethylene carbonate (FEC) additive for fluorine functionalization and benzyl chloride additive for chloride functionalization were studied for demonstration of this concept. The PDMS composite possessed high permittivity and functional property synchronously and resulted enhancement of 5.7-fold in output voltage, 5.4-fold in current and 44.8-fold in power density as compared with pristine PDMS, which was obtained by fluorine functionalized composite, PDMS-FHD45. This work demonstrated that functional additive liquid doping composite was a promising method for functionalization of triboelectric materials for great extensibility.

A new bromine substituted near infrared (NIR) cyanine Br2-IR808 has been synthesized, and the heavy atom effect makes it an efficient photosensitizer with NIR fluorescence properties, and it can be used as both a photosensitizer and a fluorescent dye synchronously. An intelligent reduction-sensitive polypeptide nanogel has also been synthesized, and it worked as the nano-carrier for the Br2-IR808 dye. The as-prepared NIR nanogel showed imaging guided PDT properties for in vitro studies, and the reduction-induced disassembly of the nanogel could promote the delivery of the hydrophobic cyanine dye inside the cell, and it also enhances the efficiency of the photosensitizer release, which makes the nanogel potential for application in NIR theranosis of cancer. In addition, only 2 μM photosensitizer Br2-IR808 is required for efficient PDT here while 30 μM IR808 is required solely as reported.

An efficient pH-responsive multifunctional polypeptide micelle for simultaneous imaging and in vitro photodynamic therapy (PDT) has been prepared. The goal here is to detect and treat cancer cells by near-infrared fluorescence (NIRF) imaging and PDT synchronously. A photosensitizer BODIPY-Br2 with efficient singlet oxygen generation was synthesized at first which owns both seductive abilities in fluorescence emission and reactive oxygen species (ROS) generation under light irradiation. Then, amphiphilic copolymer micelles pH-triggered disassembly were synthesized from N-carboxyanhydride (NCA) monomer via a ring-opening polymerization and click reaction for the loading of BODIPY-Br2 by hydrophobic interaction, and the driving force is the protonation of the diisopropylethylamine groups conjugated to the polypeptide side chains. In vitro tests performed on HepG2 cancer cells confirm that the cell suppression rate was improved by more than 40% in the presence of light in the presence of an extremely low energy density (12 J/cm(2)) with very low concentration of 5.4 μM photosensitizer. At the same time, the internalization of the nanoparticles by cells can also be traced by NIRF imaging, indicating that the NIR nanoparticles presented imaging guided photodynamic therapy properties. It provides the potential of using polypeptide as a biodegradable carrier for NIR image-guided photodynamic therapy.