Laser Direct Writing of Graphene Quantum Dots inside a Transparent Polymer

Flexible Optoelectronic Hybrid Microfiber Long-period Grating Multimodal Sensor

Flexible wearable biosensors have emerged as a promising tool for tracking dynamic glycemic profiles of human body in diabetes management. However, it remains a challenge to balance the shrunken device space and multiple redundant sensing arrays for further advancement in miniaturization of multimodal sensors. Herein, this work proposes an entirely new optoelectronic hybrid multimodal optical fiber sensor which is composed of laser patterning of polydimethylsiloxane (PDMS) to form laser-induced graphene (LIG) as the interdigital electrodes, and a long period grating (LPG) prepared from an optical microfiber encapsulated into the PDMS modulated by periodical structure of LIG electrodes. This operation can simultaneously integrate two heterogeneous sensing mechanisms, optical and electrical, into a single sensor in a compact manner. Combining the LIG electrode with conductive hydrogel, a flexible glucose biosensor based on electrical mechanism is constructed by loading glucose oxidase into the hydrogel. Meanwhile, the microfiber LPG can also be served as a spectroscopically available sensor for biomechanical monitoring. Optical and electrical sensors can work simultaneously but independently of each other, particularly in the scene of wound healing for rat model and movement for human exercise. This platform represents a pivotal step toward multifunctional sensors that enable measurements of biomechanical information and glucose.

Laser Upcycling of Hemoglobin Protein Biowaste into Engineered Graphene Aerogel Architectures for 3D Supercapacitors

Graphene aerogels (GAs) with engineered architectures are a promising material for applications ranging from filtration to energy storage/conversion. However, current preparation approaches involve the combination of multiple intrinsically-different methodologies to achieve graphene-synthesis and architecture-engineering, complicating the entire procedure. Here, a novel approach to prepare GAs with engineered architectures based on the laser-upcycling of protein biowaste, hemoglobin, is introduced. Laser scanning achieves graphene-synthesis concurrently with architecture-engineering through the localized graphitization of hemoglobin along the laser-scan path, enabling the direct preparation of engineered GAs. The laser-upcycled GAs are uniquely decorated with fibrous graphitic structures, which significantly improves the surface area. Such structural formation is attributable to the inherent iron content of hemoglobin which leads to the formation of iron-based nanoparticles that catalyze the formation of nano-structured graphene. By leveraging the high electrical conductivity and unique structural morphology, the laser-upcycled GAs are applied as electrodes of symmetrical 3D supercapacitors. The fabricated supercapacitors exhibited a high specific capacitance (≈54.9 F g-1) and excellent cycle stability (≈94% retention), attributable to the laser-engineered architecture facilitating ion diffusion even for thick electrodes. Not only does this study provide a novel approach to prepare GAs with engineered architectures but showcases the potential of laser-upcycling in preparing advanced functional materials for future devices.

Unlocking high photosensitivity direct laser writing and observing atomic clustering in glass

The direct laser writing (DLW) of photoluminescent metal clusters is inspiring intensive research in functional glasses. However, understanding the influence of the host structure on cluster formation and visualizing DLW-induced clusters at the atomic scale remains challenging. In this work, we develop a highly photosensitive fluorophosphate glass through fluorine incorporation. The addition of fluorine establishes a conducive environment for Ag+ ions before DLW and enhances the availability of reducing agents and diffusion pathways during DLW. These advantages facilitate the formation of Ag clusters under low-energy single-pulsed DLW. Increasing laser energy results in a combination of Ag clusters and glasses defect, forming a dot + ring photoluminescent pattern. Atom probe tomography (APT), a technique capable of mapping the elemental spatial distribution and identifying clustering, is employed to gain more information on laser-induced clusters. Comparison of APT results between samples without and with DLW reveals the formation of Ag clusters after laser writing. The design concept and characterization enrich the understanding of Ag cluster behavior in glasses. This knowledge opens the possibility of rational design of clusters confined in glasses and inspires their synthesis for various applications.

Laser-Based Selective Material Processing for Next-Generation Additive Manufacturing

The connection between laser-based material processing and additive manufacturing is quite deeply rooted. In fact, the spark that started the field of additive manufacturing is the idea that two intersecting laser beams can selectively solidify a vat of resin. Ever since, laser has been accompanying the field of additive manufacturing, with its repertoire expanded from processing only photopolymer resin to virtually any material, allowing liberating customizability. As a result, additive manufacturing is expected to take an even more prominent role in the global supply chain in years to come. Herein, an overview of laser-based selective material processing is presented from various aspects: the physics of laser-material interactions, the materials currently used in additive manufacturing processes, the system configurations that enable laser-based additive manufacturing, and various functional applications of next-generation additive manufacturing. Additionally, current challenges and prospects of laser-based additive manufacturing are discussed.

Carbon Dot Synthesis in CYTOP Optical Fiber Using IR Femtosecond Laser Direct Writing and Its Luminescence Properties

Luminescent carbon dots (CDs) were locally synthesized in the core of CYTOP fibers using IR femtosecond laser direct writing (FLDW), a one-step simple method serving as a post-treatment of the pristine fiber. This approach enables the creation of several types of modifications such as ellipsoid voids. The CDs and photoluminescence (PL) distribute at the periphery of the voids. The PL spectral properties were studied through the excitation/emission matrix in the visible range and excitation/emission spectra in the UV/visible range. Our findings reveal the presence of at least three distinct luminescent species, facilitating a broad excitation range extending from UV to green, and light emission spanning from blue to red. The average laser power and dose influence the quantity and ratio of these luminescent CD species. Additionally, we measured the spatially resolved lifetime of the luminescence during and after the irradiation. We found longer lifetimes at the periphery of the laser-induced modified regions and shorter ones closer to the center, with a dominant lifetime ~2 ns. Notably, unlike many other luminophores, these laser-induced CDs are insensitive to oxygen, enhancing their potential for display or data storage applications.

In Situ Laser-Induced 3D Porous Graphene within Transparent Polymers for Encapsulation-Free and Tunable Ultrabroadband Terahertz Absorption

Three-dimensional (3D) porous carbon materials have great potential for fabricating flexible tunable broadband absorbers owing to their high electrical conductivity, strong dielectric loss, and unique microstructure. Herein, we introduce an innovative method for synthesizing 3D porous graphene that incorporates advanced tuning and encapsulation processes to augment its functional efficacy. Through the modulation of both thermal and nonthermal interactions between a femtosecond (fs) laser and a polydimethylsiloxane (PDMS) film, we have synergistically fine-tuned the surface morphology and lattice properties of 3D porous graphene. This approach enabled us to create a flexible terahertz (THz) absorber with customizable characteristics, boasting an impressive absorbance range of 80%-99% in the 0.4-1.0 THz spectrum, alongside a peak reflection loss (RL) of up to 35.6 dB. Furthermore, we have successfully demonstrated the production of photoinduced 3D porous graphene within a PDMS film, which serves as both a carbon precursor and protective layer. This simplifies the conventional packaging process. These devices exhibit a RL of up to 41.6 dB and an absorption bandwidth of 2.5 THz (0.6-3.1 THz). Our study presents a production methodology for high-performance, flexible THz absorbers, offering a straightforward and innovative solution for the rapid development of sophisticated, flexible THz absorbing materials.

Fluorescent Nanocarbons: From Synthesis and Structure to Cancer Imaging and Therapy

Nanocarbons are emerging at the forefront of nanoscience, with diverse carbon nanoforms emerging over the past two decades. Early cancer diagnosis and therapy, driven by advanced chemistry techniques, play a pivotal role in mitigating mortality rates associated with cancer. Nanocarbons, with an attractive combination of well-defined architectures, biocompatibility, and nanoscale dimension, offer an incredibly versatile platform for cancer imaging and therapy. This paper aims to review the underlying principles regarding the controllable synthesis, fluorescence origins, cellular toxicity, and surface functionalization routes of several classes of nanocarbons: carbon nanodots, nanodiamonds, carbon nanoonions, and carbon nanohorns. This review also highlights recent breakthroughs regarding the green synthesis of different nanocarbons from renewable sources. It also presents a comprehensive and unified overview of the latest cancer-related applications of nanocarbons and how they can be designed to interface with biological systems and work as cancer diagnostics and therapeutic tools. The commercial status for large-scale manufacturing of nanocarbons is also presented. Finally, it proposes future research opportunities aimed at engendering modifiable and high-performance nanocarbons for emerging applications across medical industries. This work is envisioned as a cornerstone to guide interdisciplinary teams in crafting fluorescent nanocarbons with tailored attributes that can revolutionize cancer diagnostics and therapy.

Direct in Situ Fabrication of Multicolor Afterglow Carbon Dot Patterns with Transparent and Traceless Features via Laser Direct Writing

Multicolor afterglow patterns with transparent and traceless features are important for the exploration of new functionalities and applications. Herein, we report a direct in situ patterning technique for fabricating afterglow carbon dots (CDs) based on laser direct writing (LDW) for the first time. We explore a facile step-scanning method that reduces the heat-affected zone and avoids uneven heating, thus producing a fine-resolution afterglow CD pattern with a minimum line width of 80 μm. Unlike previous LDW-induced luminescence patterns, the patterned CD films are traceless and transparent, which is mainly attributed to a uniform heat distribution and gentle temperature rise process. Interestingly, by regulating the laser parameters and CD precursors, an increased carbonization and oxidation degree of CDs could be obtained, thus enabling time-dependent, tunable afterglow colors from blue to red. In addition, we demonstrate their potential applications in the in situ fabrication of flexible and stretchable optoelectronics.

Production and Patterning of Fluorescent Quantum Dots by Cryogenic Electron-Beam Writing

Graphene quantum dots (GQDs) have emerged as a promising type of functional material with distinguished properties. Although tremendous effort was devoted to the preparation of GQDs, their applications are still limited due to a lack of methods for processing GQDs from synthesis to patterning smoothly. Here, we demonstrate that aromatic molecules, e.g., anisole, can be directly converted into GQD-containing nanostructures by cryogenic electron-beam writing. Such an electron-beam irradiation product exhibits evenly red fluorescence emission under laser excitation at 473 nm, and its photoluminescence intensity can be easily tuned with the electron-beam exposure dose. Experimental characterizations on the chemical composition of the product reveal that anisole undergoes a carbonization and further graphitization process during e-beam irradiation. With conformal coating of anisole, our approach can create arbitrary fluorescent patterns on both planar and curved surfaces for concealing information or anticounterfeiting applications. This study provides a one-step method for production and patterning of GQDs, facilitating their applications in highly integrated and compact optoelectronic devices.

Solvent-Type Passivation Strategy Controls Solid-State Self-Quenching-Resistant Behavior in Sulfur Dots

Treatment of sulfur dots with polyethylene glycol (PEG) has been an efficient way to achieve a high luminescence quantum yield, and such a PEG-related quantum dot (QD)-synthesis strategy has been well documented. However, the polymeric insulating capping layer acting as the "thick shell" will significantly slow down the electron-transfer efficiency and severely hamper its practical application in an optoelectric field. Especially, the employment of synthetic polymers with long alkyl chains or large molecular weights may lead to structural complexity or even unexpected changes of physical characteristics for QDs. Therefore, in sulfur dot preparation, it is a breakthrough to use short-chain molecular species to replace PEG for better control and reproducibility. In this article, a solvent-type passivation (STP) strategy has been reported, and no PEG or any other capping agent is required. The main role of the solvent, ethanol, is to directly react with NaOH, and the generated sodium ethoxide passivates the surface defects. The afforded STP-enhanced emission sulfur dots (STPEE-SDs) possess not only the self-quenching-resistant feature in the solid state but also the extension of fluorescence band toward the wavelength as long as 645 nm. The realization of sulfur dot emission in the deep-red region with a decent yield (8.7%) has never been reported. Moreover, a super large Stokes shift (300 nm, λ_ex = 345 nm, λ_em = 645 nm) and a much longer decay lifetime (109 μs) have been found, and such values can facilitate to suppress the negative influence from background signals. Density functional theory demonstrates that the surface passivation via sodium ethoxide is dynamically favorable, and the spectroscopic insights into emission behavior could be derived from the passivation effect of the sulfur vacancy as well as the charge-transfer process dominated by the highly electronegative ethoxide layer.