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Direct light‐to‐work conversion enables remote actuation through a non‐contact manner, among which the photothermal Marangoni effect is significant for developing light‐driven robots because of the diversity of applicable photothermal materials and light sources, as well as the high energy conversion efficiency. However, the lack of nanotechnologies that enable flexible integration of advanced photothermal materials with actuators of complex configurations significantly restricts their practical applications. In this paper, laser‐induced graphene (LIG) tape is reported as stick‐on photothermal labels for developing light‐driven actuators based on the Marangoni effect. With the help of direct laser writing technology, graphene patterns with superior photothermal properties are prepared on the PI tape. The patterned LIG tape can be stuck on any desired objects and generates an asymmetric photothermal field under light irradiation, forming a photothermal Marangoni actuator. Additionally, the PI tape with LIG patterns can be folded into 3D origami actuators that permit photothermal Marangoni actuation including both translation and rotation. The graphene‐based photothermal Marangoni actuators feature biocompatibility, which is confirmed by MDA‐MB‐231 cells proliferation experiments. Owing to the excellent photothermal property of LIG patterns, the as‐produced photothermal actuators can be manipulated by a variety of light sources, holding great promise for developing light‐driven soft robots. [ABSTRACT FROM AUTHOR]

Abstract: Actuators that can convert environmental stimuli into mechanical work are widely used in intelligent systems, robots, and micromechanics. To produce robust and sensitive actuators of different scales, efforts are devoted to developing effective actuating schemes and functional materials for actuator design. Carbon‐based nanomaterials have emerged as preferred candidates for different actuating systems because of their low cost, ease of processing, mechanical strength, and excellent physical/chemical properties. Especially, due to their excellent photothermal activity, which includes both optical absorption and thermal conductivities, carbon‐based materials have shown great potential for use in photothermal actuators. Herein, the recent advances in photothermal actuators based on various carbon allotropes, including graphite, carbon nanotubes, amorphous carbon, graphene and its derivatives, are reviewed. Different photothermal actuating schemes, including photothermal effect–induced expansion, desorption, phase change, surface tension gradient creation, and actuation under magnetic levitation, are summarized, and the light‐to‐heat and heat‐to‐work conversion mechanisms are discussed. Carbon‐based photothermal actuators that feature high light‐to‐work conversion efficiency, mechanical robustness, and noncontact manipulation hold great promise for future autonomous systems. [ABSTRACT FROM AUTHOR]

The combination of surface-enhanced Raman spectroscopy (SERS) technology with microfluidics makes it possible to diagnose genetic disease through label-free on-chip DNA detection. However, open problems including the integration of SERS substrate with microfluidic devices, controllable trapping and releasing of target molecules are still challenging. Here we demonstrate a facile laser scribing method to fabricate silver nanoparticles (AgNPs) and graphene oxide (GO) based biochips as a reusable SERS sensor for DNA detection. Programmable laser scribing of the AgNPs@GO composite film enables direct patterning of sensitive SERS channels that consist of graphene supported AgNPs by exfoliating the composites into hierarchical porous structures. Integrating the SERS-active patterns with a microfluidic chip forms a biochip for allowing SERS detection of DNA. The noncovalent interactions between DNA and graphene mediated controllable trapping and releasing of DNA sequences, enabling efficient on-chip SERS detection and the regeneration of the biochip. The simple, green and cost-effective fabrication of the SERS-active biochips reveals great potential for biomolecular sensing and genetic engineering applications. [ABSTRACT FROM AUTHOR]

Graphene is a promising sensing material that has been widely used for high-performance sensors. However, the development of graphene-based sensing device is limited by complex manufacturing procedures. Here, we report a facile fabrication of humidity sensors by flash reduction of graphene oxides (GO) with the help of a photographic camera flash. The flash treatment triggers a drastic deoxygenation of oxygen functional groups (OCGs) from the GO sheets, which not only restores its conductivity partly but also induces the formation of a highly porous structure. The reduced GO sensor shows high sensitivity at the relative humidity atmosphere of 11%–95%, small hysteresis, rapid response, and enhanced durability. The sensitive mechanism was discussed through the investigation of complex impedance plots. This facile flash reduction strategy holds great promise for chemical-free production of graphene-based sensing devices. [ABSTRACT FROM PUBLISHER]

Reported here is the facile fabrication of all-reduced graphene oxide (RGO) field-effect-transistor (FET) on flexible substrates using a solo femtosecond laser direct writing (FsLDW) technology. By simply tuning the intensity of a femtosecond laser pulse, GO could be reduced in a controlled manner. Metallic and semiconducting RGO micro-patterns could be achieved by FsLDW under high and moderate laser power, respectively, which enables direct writing of source/drain and gate electrodes, as well as semiconducting channel of a FET on flexible substrates in ambient condition. In this way, a metal-free all-RGO FET was successfully fabricated by FsLDW without the use of any masks or chemical reagents. FsLDW of all-RGO devices shows unique advantages in both facile fabrication and flexible integration of graphene-based micro-devices, revealing great potential for the development of future electronics. [ABSTRACT FROM PUBLISHER]

We report herein the engineering of the surface/interface properties of graphene oxide (GO) films by controllable photoreduction treatment. In our recent works, typical photoreduction processes, including femtosecond laser direct writing (FsLDW), laser holographic lithography, and controllable UV irradiation, have been employed to make conductive reduced graphene oxide (RGO) microcircuits, hierarchical RGO micro-nanostructures with both superhydrophobicity and structural color, as well as moisture-responsive GO/RGO bilayer structures. Compared with other reduction protocols, for instance, chemical reduction and thermal annealing, the photoreduction strategy shows distinct advantages, such as mask-free patterning, chemical-free modification, controllable reduction degree, and environmentally friendly processing. These works indicate that the surface and interface engineering of GO through controllable photoreduction of GO holds great promise for the development of various graphene-based microdevices. [ABSTRACT FROM AUTHOR]

Inspired from butterfly wings that exhibit unique dewetting properties and brilliant structural color synchronously, we reported here the preparation of biomimetic few-layer graphene films through a template-directed chemical vapor deposition method using laser-structured Cu foil as substrates. Hierarchical micronanostructures, including microscale stripes derived from the laser scanning and nanoscale laser-induced periodic surface structures (LIPSS), formed on Cu foil after a simple femtosecond laser treatment. By tuning the laser power, the surface roughness of the resultant Cu foils can be well controlled. Using the laser structures Cu foil as templates, biomimetic few-layer graphene films with both iridescence and superhydrophobicity have been successfully prepared. The present work may open up a new way to design and prepare structured graphene film in a biomimetic manner, and we deem that the bioinspired few-layer graphene films may find broad applications in the near future. [ABSTRACT FROM AUTHOR]

Inspired by natural autonomous systems that demonstrate controllable shape, appearance, and actuation under external stimuli, a facile preparation of moisture responsive graphene-based smart actuators by unilateral UV irradiation of graphene oxide (GO) papers is reported. UV irradiation of GO is found to be an effective protocol to trigger the reduction of GO; however, due to the limited light transmittance and thermal relaxation, thick GO paper cannot be fully reduced. Consequently, by tuning the photoreduction gradient, anisotropic GO/reduced GO (RGO) bilayer structure can be easily prepared toward actuation application. To get better control over the responsive properties, GO/RGO bilayer paper with a certain curvature and RGO patterns are successfully prepared for actuator design. As representative examples, smart humidity-driven graphene actuators that mimic the cilia of respiratory tract and tendril climber plant are successfully developed for controllable objects transport. [ABSTRACT FROM AUTHOR]

Reported here is a bioinspired fabrication of superhydrophobic graphene surfaces by means of two-beam laser interference (TBLI) treatment of graphene oxide (GO) films. Microscale grating-like structures with tunable periods and additional nanoscale roughness are readily created on graphene films due to laser induced ablation effect. Synchronously, abundant hydrophilic oxygen-containing groups (OCGs) on GO sheets can be drastically removed after TBLI treatment, which lower its surface energy significantly. The synergistic effect of micro-nanostructuring and the OCGs removal endows the resultant graphene films with unique superhydrophobicity. Additionally, dual TBLI treatment with 90° rotation is implemented to fabricate superhydrophobic graphene films with two-dimensional grating-like structures that can effectively avoid the anisotropic hydrophobicity originated from the grooved structures. Moreover, the superhydrophobic graphene films become conductive due to the laser reduction effect. Unique optical characteristics including transmission diffraction and brilliant structural color are also observed due to the presence of periodic microstructures. As a mask-free, chemical-free, and cost-effective method, the TBLI processing of GO may open up a new way to biomimetic graphene surfaces, and thus hold great promise for the development of novel graphene-based microdevices. [ABSTRACT FROM AUTHOR]

We report here a facile preparation of graphene quantum dots (GQDs) by chemical exfoliation of multiwall carbon nanotubes (MWCNTs) using a modified hummers' method. The resultant GQD samples possess strong electronic property, revealing great potential for photocatalyst design. As an efficient promoter, GQDs/P25 nanocomposites have been successfully prepared by simple wet impregnation and subsequent thermal annealing at 200 °C. In the tests of photocatalytic degradation of organic dyes under visible-light irradiation, the GQDs promoted P25 samples which shows much higher photocatalytic activity compared to the pure P25, indicating the crucial roles of GQDs. [ABSTRACT FROM AUTHOR]

Abstract: First-principles calculation identifies elementary processes in the thermal reduction of graphene oxide (GO) and reveals the effects of alkaline-earth metals (AEMs) in recovering the graphene. These metals are highly effective in removing residual oxygen groups resistive to thermal reduction, as well as healing the defects formed during the reduction, such as the carbonyl groups. In the AEM-assisted reduction, the AEMs serve as an electron reservoir of high chemical potential that forces electron transfer to the GO, whereas pristine carbon regions on the GO serve as a “bridge” to facilitate the electron transfer directly to oxidized carbon. This enables fast kinetics for the breaking of both C–O and CComplete reduction is observed in our simulation at T ≤600K within 32ps for a 28%-oxygen-coverage GO model. [Copyright &y& Elsevier]

Abstract: Two-beam-laser interference was used for the simultaneous reduction, patterning and nanostructuring of graphene oxide on flexible polyethylene terephthalate substrates for the production of a high performance humidity sensing device. Hierarchical graphene nanostructures were formed after laser interference treatment of graphene oxide, which holds great promise for gaseous molecular adsorption, and thereby significantly increases their sensing performance. By tuning the laser power, the content of oxygen functional groups, could be changed within a certain range, which contributes not only controllable conductivity but also tunable response/recovery time of the humidity sensor due to the interaction between water molecules and oxygen functional groups on the graphene oxide sheets. The laser interference processing of graphene oxide films is a mask-free, surfactant-free and large-area approach to the production of hierarchical graphene micro-nanostructures, and thus shows great potential for fabrication of future graphene-based microdevices. [Copyright &y& Elsevier]