Maneesh K. Gupta

Ultra-Robust Graphene Oxide-Silk Fibroin Nanocomposite Membranes

Nanocomposite materials in forms of membranes, fi lms, and coatings are gaining surging interests in structural and functional applications, because they are more effi cient in loading transfer than conventional composites and can substantially eliminate catastrophic failure caused by poor loading transfer between components. To enhance the mechanical properties of polymeric nanocomposites, carbon nanotubes, intercalated clay, graphene, and graphene oxide are added as high-performance reinforcing nanofi llers. For example, ultrahigh toughness was reported for polyvinyl alcohol nanocomposite fi lms fi lled with single-walled carbon nanotubes; [ 1 ] and ultrahigh modulus was reported for crosslinked nanoclay containing nanocomposites. [ 2 ] However, improving toughness is usually achieved by increasing the ultimate strain and compromising the strength, which is not desired for high-performance applications. [ 3 ]

3D Printed Quantum Dot Light-Emitting Diodes

Developing the ability to 3D print various classes of materials possessing distinct properties could enable the freeform generation of active electronics in unique functional, interwoven architectures. Achieving seamless integration of diverse materials with 3D printing is a significant challenge that requires overcoming discrepancies in material properties in addition to ensuring that all the materials are compatible with the 3D printing process. To date, 3D printing has been limited to specific plastics, passive conductors, and a few biological materials. Here, we show that diverse classes of materials can be 3D printed and fully integrated into device components with active properties. Specifically, we demonstrate the seamless interweaving of five different materials, including (1) emissive semiconducting inorganic nanoparticles, (2) an elastomeric matrix, (3) organic polymers as charge transport layers, (4) solid and liquid metal leads, and (5) a UV-adhesive transparent substrate layer. As a proof of concept for demonstrating the integrated functionality of these materials, we 3D printed quantum dot-based light-emitting diodes (QD-LEDs) that exhibit pure and tunable color emission properties. By further incorporating the 3D scanning of surface topologies, we demonstrate the ability to conformally print devices onto curvilinear surfaces, such as contact lenses. Finally, we show that novel architectures that are not easily accessed using standard microfabrication techniques can be constructed, by 3D printing a 2 × 2 × 2 cube of encapsulated LEDs, in which every component of the cube and electronics are 3D printed. Overall, these results suggest that 3D printing is more versatile than has been demonstrated to date and is capable of integrating many distinct classes of materials.

Morphological control and assembly of zinc oxide using a biotemplate.

Zinc oxide is a wide band gap material that has significant applications in photovoltaics, piezoelectrics and optoelectronics. Traditionally, ZnO has been synthesized using high temperatures and harsh reaction conditions. Recently, benign reaction conditions have been used to synthesize ZnO using amine and citrate additives. In this study, peptide phage display was performed to identify a peptide, termed Z1, that binds to and directs the growth of ZnO hexagonal nanocrystals. By altering the concentration of Z1 peptide, the ZnO nanocrystal morphology can be tailored. Additionally, Z1 peptide was used to direct the growth of ZnO structures on free-standing silk films. The results presented here demonstrate the utility of peptides in controlling the structure and deposition of ZnO.

Silk-on-silk layer-by-layer microcapsules.

A IO N Silks are made of proteins produced naturally by silkworms and spiders and are known as biocompatible, biodegradable, and extraordinarily robust biomaterials frequently utilized in biomaterial composites. [ 1 , 2 ] The versatility of silk proteins, along with their favorable characteristics and potential for processing in aqueous solution under ambient conditions, make silk-based materials excellent candidates for biomedical applications such as drug delivery systems and scaffolds for tissue engineering. [ 3 ]

In situ Growth of Silver Nanoparticles in Porous Membranes for Surface-Enhanced Raman Scattering

We demonstrate the in situ growth of silver nanoparticles in porous alumina membranes (PAMs) for use as a surface-enhanced Raman scattering (SERS) detection substrate. This fabrication method is simple, cost-effective, and fast, while providing control over the size of silver nanoparticles through the entire length of the cylindrical nanopores with uniform particle density inside the pores unachievable by the traditional infiltration technique. The in situ growth of silver nanoparticles was conducted from electroless-deposited nanoscale seeds on the interior of the PAM and resulted in the formation of numerous hot spots, which facilitated significantly higher SERS enhancement for these substrates compared with previously reported porous substrates.

Plasmonic Biofoam: A Versatile Optically Active Material

Owing to their ability to confine and manipulate light at the nanoscale, plasmonic nanostructures are highly attractive for a broad range of applications. While tremendous progress has been made in the synthesis of size- and shape-controlled plasmonic nanostructures, their integration with other materials and application in solid-state is primarily through their assembly on rigid two-dimensional (2D) substrates, which limits the plasmonically active space to a few nanometers above the substrate. In this work, we demonstrate a simple method to create plasmonically active three-dimensional biofoams by integrating plasmonic nanostructures with highly porous biomaterial aerogels. We demonstrate that plasmonic biofoam is a versatile optically active platform that can be harnessed for numerous applications including (i) ultrasensitive chemical detection using surface-enhanced Raman scattering; (ii) highly efficient energy harvesting and steam generation through plasmonic photothermal heating; and (iii) optical control of enzymatic activity by triggered release of biomolecules encapsulated within the aerogel. Our results demonstrate that 3D plasmonic biofoam exhibits significantly higher sensing, photothermal, and loading efficiency compared to conventional 2D counterparts. The design principles and processing methodology of plasmonic aerogels demonstrated here can be broadly applied in the fabrication of other functional foams.

pH-Triggered SERS via Modulated Plasmonic Coupling in Individual Bimetallic Nanocobs

Abstract : In this Communication, we demonstrate the pH-triggered SPR and SERS properties of silver nanowires functionalized with gold nanoparticles in both solution and dry states. In contrast with previous examples of such bimetallic nanocobs, we utilize here a responsive polyacrylic acid (PAA) nanocoating that acts as a linker between the nanoparticles and nanowire. The pH-responsive nature of the PAA nanocoating, which is sensitive to the environmental pH, is employed to vary the separation distance between the gold nanoparticles and the silver nanowire and thus control plasmon coupling. Moreover, placing nanoparticles inside a polymer-gel layer in close proximity to the nanowire surface effectively prevents any potential aggregation of nanoparticles under variable environmental conditions, in contrast with regular nanoparticle solutions, which easily precipitate with changing conditions.

Using Amphiphilic Nanostructures to Enable Long-Range Ensemble Coalescence and Surface Rejuvenation in Dropwise Condensation

Controlling coalescence events in a heterogeneous ensemble of condensing droplets on a surface is an outstanding fundamental challenge in surface and interfacial sciences, with a broad practical importance in applications ranging from thermal management of high-performance electronic devices to moisture management in high-humidity environments. Nature-inspired superhydrophobic surfaces have been actively explored to enhance heat and mass transfer rates by achieving favorable dynamics during dropwise condensation; however, the effectiveness of such chemically homogeneous surfaces has been limited because condensing droplets tend to form as pinned Wenzel drops rather than mobile Cassie ones. Here, we introduce an amphiphilic nanostructured surface, consisting of a hydrophilic base with hydrophobic tips, which promotes the periodic regeneration of nucleation sites for small droplets, thus rendering the surface self-rejuvenating. This unique amphiphilic nanointerface generates an arrangement of condensed Wenzel droplets that are fluidically linked by a wetted sublayer, promoting previously unobserved coalescence events where numerous droplets simultaneously merge, without direct contact. Such ensemble coalescences rapidly create fresh nucleation sites, thereby shifting the overall population toward smaller droplets and enhancing the rates of mass and heat transfer during condensation.

SERS Effects in Silver‐Decorated Cylindrical Nanopores

Optimization of pore diameter, the placement of nanoparticles, and the transmission of surface-enhanced Raman scattering (SERS) substrates are found to be very critical for achieving high SERS activity in porous alumina-membrane-based substrates. SERS substrates with a pore diameter of 355 nm incorporating silver nanoparticles show very high SERS activity with enhancement factors of 10(10) .

Nondestructive In Situ Identification of Crystal Orientation of Anisotropic ZnO Nanostructures

We present a novel method for direct, fast, nonambiguous, and nondestructive identification of the growth direction and orientation of individual ZnO nanostructures in the device-ready environment by exploiting high-resolution confocal Raman mapping. Various features of the Raman spectrum of ZnO nanostructures, vapor deposition grown nanobelts and peptide-assisted vertical nanorods, were found to be sensitive to the relative orientation of the crystal plane. Furthermore, we discovered that the waveguiding property of the ZnO nanobelt is also orientation dependent and results in either apparent enhancement or suppression of Raman scattering from the underlying substrate. We demonstrate that various features of Raman spectrum of ZnO and the modulation of the substrate signal can be employed for the rapid and nondestructive identification of the crystal growth direction and orientation of these nanostructures even after integration into devices, which is impossible with current electron microscopy and diffraction techniques. We believe that the general features observed here are equally applicable to other wurtzite nanostructures (ZnS, GaN) which are critical in optoelectronics, lasing, and piezotronic applications.