The rapid development of miniaturized electronic devices has increased the demand for compact on-chip energy storage. Microscale supercapacitors have great potential to complement or replace batteries and electrolytic capacitors in a... more
The rapid development of miniaturized electronic devices has increased the demand for compact on-chip energy storage. Microscale supercapacitors have great potential to complement or replace batteries and electrolytic capacitors in a variety of applications. However, conventional micro-fabrication techniques have proven to be cumbersome in building cost-effective micro-devices, thus limiting their widespread application. Here we demonstrate a scalable fabrication of graphene micro-supercapacitors over large areas by direct laser writing on graphite oxide films using a standard LightScribe DVD burner. More than 100 micro-supercapacitors can be produced on a single disc in 30 min or less. The devices are built on flexible substrates for flexible electronics and on-chip uses that can be integrated with MEMS or CMOS in a single chip. Remarkably, miniaturizing the devices to the microscale results in enhanced charge-storage capacity and rate capability. These micro-supercapacitors demons...
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Biotemplated metal nanoclusters have garnered much attention owing to their wide range of potential applications in biosensing, bioimaging, catalysis, and nanomedicine. Here, we report the synthesis of stable, biocompatible,... more
Biotemplated metal nanoclusters have garnered much attention owing to their wide range of potential applications in biosensing, bioimaging, catalysis, and nanomedicine. Here, we report the synthesis of stable, biocompatible, water-soluble, and highly fluorescent bovine serum albumin-templated cadmium nanoclusters (Cd NCs) through a facile one-pot green method. We covalently conjugated hyaluronic acid (HA) to the Cd NCs to form a pH-responsive, tumor-targeting theranostic nanocarrier with a sustained release profile for doxorubicin (DOX), a model anticancer drug. The nanocarrier showed a DOX encapsulation efficiency of about 75.6%. DOX release profiles revealed that 74% of DOX was released at pH 5.3, while less than 26% of DOX was released at pH 7.4 within the same 24-h period. The nanocarrier selectively recognized MCF-7 breast cancer cells expressing CD44, a cell surface receptor for HA, whereas no such recognition was observed with HA receptor-negative HEK293 cells. Biocompatibility of the nanocarrier was evaluated through cytotoxicity assays with HEK293 and MCF-7 cells. The nanocarrier exhibited very low to no cytotoxicity, whereas the DOX-loaded nanocarrier showed considerable cellular uptake and enhanced MCF-7 breast cancer cell-killing ability. We also confirmed the feasibility of using the highly fluorescent nanoconjugate for bioimaging of MCF-7 and HeLa cells. The superior targeted drug delivery efficacy, cellular imaging capability, and low cytotoxicity position this nanoconjugate as an exciting new nanoplatform with promising biomedical applications.
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Building three-dimensional porous microstructures is an effective way to make use of the extraordinary nanoscale properties of individual graphene sheets. However, current 3D graphene films suffer from poor electrical conductivity, weak... more
Building three-dimensional porous microstructures is an effective way to make use of the extraordinary nanoscale properties of individual graphene sheets. However, current 3D graphene films suffer from poor electrical conductivity, weak mechanical strength, and chaotic porosity. Here, we demonstrate a method combining freeze-casting and filtration to synthesize 3D reduced graphene oxide (RGO) films with open porosity, high electrical conductivity (>1900 S m-1), and good tensile strength (18.7 MPa). Taking advantage of the abundant interconnected pathways for electrolyte/ion transport, the resulting supercapacitors based on the 3D porous RGO film exhibited extremely high specific power densities (>280 kW kg-1) and high energy densities (up to 9.9 Wh kg-1) in aqueous electrolyte. The fabrication process provides an effective means for controlling the pore size, electronic conductivity and loading mass of electrode materials, offering a good opportunity for the design of devices with high energy density. We envision these 3D porous films to be useful in a broad range of applications including energy conversion and storage, catalysis, sensing and environmental remediation.
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The global supercapacitor market has been growing rapidly during the past decade. Today, virtually all commercial devices use activated carbon. In this work, it is shown that laser treatment of activated carbon electrodes results in the... more
The global supercapacitor market has been growing rapidly during the past decade. Today, virtually all commercial devices use activated carbon. In this work, it is shown that laser treatment of activated carbon electrodes results in the formation of microchannels that can connect the internal pores of activated carbon with the surrounding electrolyte. These microchannels serve as electrolyte reservoirs that in turn shorten the ion diffusion distance and enable better interaction between the electrode surfaces and electrolyte ions. The capacitance can be further increased through fast and reversible redox reactions on the electrode surface using a redox-active electrolyte, enabling the operation of a symmetric device at 2.0 V, much higher than the thermodynamic decomposition voltage of water. This simple approach can alleviate the low energy density of supercapacitors which has limited the widespread use of this technology. This work represents a clear advancement in the processing of activated carbon electrodes toward the next-generation of low-cost supercapacitors.
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One of the fundamental issues with graphene for logic applications is its lack of a band gap. In this issue of ACS Nano, Shim and colleagues introduce an effective approach for modulating the current flow in graphene by forming pn... more
One of the fundamental issues with graphene for logic applications is its lack of a band gap. In this issue of ACS Nano, Shim and colleagues introduce an effective approach for modulating the current flow in graphene by forming pn junctions using lasers. The findings could lead to a new route for controlling the electronic properties of graphene-based devices. We highlight recent progress in the direct laser synthesis and patterning of graphene for numerous applications. We also discuss the challenges and opportunities in translating this remarkable progress toward the direct laser writing of grapheme electronics at large scales.