The ability to transform two-dimensional (2D) materials into a three-dimensional (3D) structure while preserving their unique inherent properties might offer great enticing opportunities in the development of diverse applications for next generation micro/nanodevices. Here, a self-assembly process is introduced for building free-standing 3D, micro/nanoscale, hollow, polyhedral structures configured with a few layers of graphene-based materials: graphene and graphene oxide. The 3D structures have been further modified with surface patterning, realized through the inclusion of metal patterns on their 3D surfaces. The 3D geometry leads to a nontrivial spatial distribution of strong electric fields (volumetric light confinement) induced by 3D plasmon hybridization on the surface of the graphene forming the 3D structures. Due to coupling in all directions, resulting in 3D plasmon hybridization, the 3D closed box graphene generates a highly confined electric field within as well as outside of the cubes. Moreover, since the uniform coupling reduces the decay of the field enhancement away from the surface, the confined electric field inside of the 3D structure shows two orders of magnitude higher than that of 2D graphene before transformation into the 3D structure. Therefore, these structures might be used for detection of target substances (not limited to only the graphene surfaces, but using the entire volume formed by the 3D graphene-based structure) in sensor applications.

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The self-assembly of 3D nanostructures is a promising technology for the fabrication of next generation nanodevices and the exploration of novel phenomena. However, the present techniques for assembly of 3D nanostructures are invisible and have to be done without physical contact, which bring great challenges in controlling the shapes with nanoscale precision. This situation leads to an extremely low yield of self-assembly, especially in 3D nanostructures built with metal and semiconductor materials. Here, an in situ self-assembly process using a focused ion beam (FIB) microscopy system has been demonstrated to realize 3D polyhedral nanostructures from 2D multiple pieces. An excited ion beam in the FIB microscopy system offers not only a visualization of the nanoscale self-assembly process but also the necessary energy for inducing the process. Because the beam energy that induces the self-assembly can be precisely adjusted while monitoring the status of the self-assembly, it is possible to control the self-assembly process with sub-10 nm scale precision, resulting in the realization of diverse 3D nanoarchitectures with a high yield. This approach will lead to state-of-the-art applications utilizing properties of 3D nanostructures in diverse fields.

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A microbial biosensor is an analytical device that immobilizes microorganisms onto a transducer for the detection of target analytes. With the development of nanotechnology, nanomaterials have been used to achieve better immobilization for developing a more reliable and selective microbial biosensor. Also, significant progress has been made in the development of transducer technology leading to higher sensitivity. Microbial biosensors have become one of the most useful means of monitoring environmental, food and clinical samples. In this review, we focus on the newly developed technologies and applications of microbial biosensors in recent years.

Thermal reflow of polymers is a well-established phenomenon that has been used in various microfabrication processes. However, present techniques have critical limitations in controlling the various attributes of polymer reflow, such as the position and extent of reflow, especially at the nanoscale. These challenges primarily result from the reflow heat source supplying heat energy to the entire substrate rather than a specific area. In this work, a focused ion beam (FIB) microscope is used to achieve controllable localized heat generation, leading to precise control over the nanoscale polymer reflow. Through the use of the patterning capability of FIB microscopy, dramatically different reflow performances within nanoscale distances of each other are demonstrated in both discrete periodic and continuous polymer structures. Further, we utilize a self-assembly process induced by nanoscale polymer reflow to realize 3D optical devices, specifically, vertically aligned nanoresonators and graphene-based nanocubes. HFSS and Comsol simulations have been carried out to analyze the advantages of the polymer-based 3D metamaterials as opposed to those fabricated with a metallic hinge. The simulation results clearly demonstrate that the polymer hinges have a dual advantage; first, the removal of any interference from the transmission spectrum leading to strong and distinct resonance peaks and, second, the elimination of parasitic leeching of the enhanced field by the metallic hinge resulting in stronger volumetric enhancement. Thus, the 2-fold advantages existing in 3D polymer-hinge optical metamaterials can open pathways for applications in 3D optoelectronic devices and sensors, vibrational molecular spectroscopy, and other nanoscale 3D plasmonic devices.

Sequence plays an important role in self-assembly of 3D complex structures, particularly for those with overlap, intersection, and asymmetry. However, it remains challenging to program the sequence of self-assembly, resulting in geometric and topological constrains. In this work, a nanoscale, programmable, self-assembly technique is reported, which uses electron irradiation as "hands" to manipulate the motion of nanostructures with the desired order. By assigning each single assembly step in a particular order, localized motion can be selectively triggered with perfect timing, making a component accurately integrate into the complex 3D structure without disturbing other parts of the assembly process. The features of localized motion, real-time monitoring, and surface patterning open the possibility for the further innovation of nanomachines, nanoscale test platforms, and advanced optical devices

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