Publications by authors named "Nicholas A Kotov"

231 Publications

Broad Chiroptical Activity from Ultraviolet to Short-Wave Infrared by Chirality Transfer from Molecular to Micrometer Scale.

ACS Nano 2021 Sep 14. Epub 2021 Sep 14.

Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea.

Chiral nanomaterials provide a rich platform for versatile applications. Tuning the wavelength of polarization rotation maxima in the broad range including short-wave infrared (SWIR) is a promising candidate for infrared neural stimulation, imaging, and nanothermometry. However, the majority of previously developed chiral nanomaterials reveal the optical activity in a relatively shorter wavelength range (ultraviolet-visible, UV-vis), not in SWIR. Here, we demonstrate a versatile method to synthesize chiral copper sulfides using cysteine, as the stabilizer, and transferring the chirality from molecular- to the microscale through self-assembly. The assembled structures show broad chiroptical activity in the UV-vis-NIR-SWIR region (200-2500 nm). Importantly, we can tune the chiroptical activity by simply changing the reaction conditions. This approach can be extended to materials platforms for developing next-generation optical devices, metamaterials, telecommunications, and asymmetric catalysts.
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http://dx.doi.org/10.1021/acsnano.1c05888DOI Listing
September 2021

Single-Molecule Binding Assay Using Nanopores and Dimeric NP Conjugates.

Adv Mater 2021 Jul 29:e2103067. Epub 2021 Jul 29.

Department of Chemistry, Molecular Science Research Hub, Imperial College London, White City Campus, 82 Wood Lane, London, W12 0BZ, UK.

The ability to measure biomarkers, both specifically and selectively at the single-molecule level in biological fluids, has the potential to transform the diagnosis, monitoring, and therapeutic intervention of diseases. The use of nanopores has been gaining prominence in this area, not only for sequencing but more recently in screening applications. The selectivity of nanopore sensing can be substantially improved with the use of labels, but substantial challenges remain, especially when trying to differentiate between bound from unbound targets. Here highly sensitive and selective molecular probes made from nanoparticles (NPs) that self-assemble and dimerize upon binding to a biological target are designed. It is shown that both single and paired NPs can be successfully resolved and detected at the single-molecule nanopore sensing and can be used for applications such as antigen/antibody detection and microRNA (miRNA) sequence analysis. It is expected that such technology will contribute significantly to developing highly sensitive and selective strategies for the diagnosis and screening of diseases without the need for sample processing or amplification while requiring minimal sample volume.
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http://dx.doi.org/10.1002/adma.202103067DOI Listing
July 2021

Structural Analysis of Nanoscale Network Materials Using Graph Theory.

ACS Nano 2021 Jul 27. Epub 2021 Jul 27.

Many materials with remarkable properties are structured as percolating nanoscale networks (PNNs). The design of this rapidly expanding family of composites and nanoporous materials requires a unifying approach for their structural description. However, their complex aperiodic architectures are difficult to describe using traditional methods that are tailored for crystals. Another problem is the lack of computational tools that enable one to capture and enumerate the patterns of stochastically branching fibrils that are typical for these composites. Here, we describe a computational package, , to automatically produce a graph theoretical (GT) description of PNNs from various micrographs that addresses both challenges. Using nanoscale networks formed by aramid nanofibers as examples, we demonstrate rapid structural analysis of PNNs with 13 GT parameters. Unlike qualitative assessments of physical features employed previously, allows researchers to quantitatively describe the complex structural attributes of percolating networks enumerating the network's morphology, connectivity, and transfer patterns. The accurate conversion and analysis of micrographs was obtained for various levels of noise, contrast, focus, and magnification, while a graphical user interface provides accessibility. In perspective, the calculated GT parameters can be correlated to specific material properties of PNNs (.., ion transport, conductivity, stiffness) and utilized by machine learning tools for effectual materials design.
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http://dx.doi.org/10.1021/acsnano.1c04711DOI Listing
July 2021

Reconfigurable Chirality of DNA-Bridged Nanorod Dimers.

ACS Nano 2021 Jul 22. Epub 2021 Jul 22.

Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, United States.

Gold nanorods assembled in a side-by-side chiral configuration have potential applications in sensing due to their strong chiroptical surface plasmon resonances. Recent experiments have shown that dimers of gold nanorods bridged by double-stranded DNA exhibit variable chiral configurations depending on the chemical and ionic properties of the solvent medium. Here, we uncover the underlying physics governing this intriguing chiral behavior of such DNA-bridged nanorods by theoretically evaluating their configurational free energy landscape. Our results reveal how chiral configurations emerge from an interplay between the twist-stretch coupling of the intervening DNA and the intermolecular interactions between the nanorods, with dimers exhibiting left-handed chirality when the interparticle interactions are dominated by attractive depletion or van der Waals forces and right-handed chirality when dominated by repulsive electrostatic or steric forces. We demonstrate how changes in the depletant or ion concentration of the solvent medium lead to different classes of configurational responses by the dimers, including chirality-switching behavior, in good agreement with experimental observations. Based on extensive analyses of how material properties like nanorod aspect ratio, DNA length, and graft height modulate the free energy landscape, we propose strategies for tuning the environmentally responsive reconfigurability of the nanorod dimers. Overall, this work should help control the chirality and related optical activity of nanoparticle dimers and higher-order assemblies for various applications.
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http://dx.doi.org/10.1021/acsnano.1c04326DOI Listing
July 2021

X-ray-Based Techniques to Study the Nano-Bio Interface.

ACS Nano 2021 03 2;15(3):3754-3807. Epub 2021 Mar 2.

Mathematics, Informatics, and Natural Sciences (MIN) Faculty, University of Hamburg, 20354 Hamburg, Germany.

X-ray-based analytics are routinely applied in many fields, including physics, chemistry, materials science, and engineering. The full potential of such techniques in the life sciences and medicine, however, has not yet been fully exploited. We highlight current and upcoming advances in this direction. We describe different X-ray-based methodologies (including those performed at synchrotron light sources and X-ray free-electron lasers) and their potentials for application to investigate the nano-bio interface. The discussion is predominantly guided by asking how such methods could better help to understand and to improve nanoparticle-based drug delivery, though the concepts also apply to nano-bio interactions in general. We discuss current limitations and how they might be overcome, particularly for future use .
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http://dx.doi.org/10.1021/acsnano.0c09563DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7992135PMC
March 2021

Enhanced optical asymmetry in supramolecular chiroplasmonic assemblies with long-range order.

Science 2021 03 25;371(6536):1368-1374. Epub 2021 Feb 25.

State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun, China.

Chiral assemblies of plasmonic nanoparticles are known for strong circular dichroism but not for high optical asymmetry, which is limited by the unfavorable combination of electrical and magnetic field components compounded by strong scattering. Here, we show that these limitations can be overcome by the long-range organization of nanoparticles in a manner similar to the liquid crystals and found in helical assemblies of gold nanorods with human islet amyloid polypeptides. A strong, polarization-dependent spectral shift and the reduced scattering of energy states with antiparallel orientation of dipoles activated in assembled helices increased optical asymmetry -factors by a factor of more than 4600. The liquid crystal-like color variations and the nanorod-accelerated fibrillation enable drug screening in complex biological media. Improvement of long-range order can also provide structural guidance for the design of materials with high optical asymmetry.
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http://dx.doi.org/10.1126/science.abd8576DOI Listing
March 2021

Photocatalytic Hedgehog Particles for High Ionic Strength Environments.

ACS Nano 2021 Mar 19;15(3):4226-4234. Epub 2021 Feb 19.

Jiangsu Collaborative Innovation Center for Ecological Building Material and Environmental Protection Equipment, Yancheng Institute of Technology, Yancheng 224051, China.

High ionic strength environments can profoundly influence catalytic reactions involving charged species. However, control of selectivity and yield of heterogeneous catalytic reactions involving nano- and microscale colloids remains hypothetical because high ionic strength leads to aggregation of particle dispersions. Here we show that microscale hedgehog particles (HPs) with semiconductor nanoscale spikes display enhanced stability in solutions of monovalent/divalent salts in both aqueous and hydrophobic media. HPs enable tuning of photocatalytic reactions toward high-value products by adding concentrated inert salts to amplify local electrical fields in agreement with Derjaguin, Landau, Verwey, and Overbeek theory. After optimization of HP geometry for a model photocatalytic reaction, we show that high salt conditions increase the yield of HP-facilitated photooxidation of 2-phenoxy-1-phenylethanol to benzaldehyde and 2-phenoxyacetophenone by 6 and 35 times, respectively. Depending on salinity, electrical fields at the HP-media interface increase from 1.7 × 10 V/m to 8.5 × 10 V/m, with high fields favoring products generated intermediate cation radicals rather than neutral species. Electron transfer rates were modulated by varying the ionic strength, which affords a convenient and hardly used reaction pathway for engineering a multitude of redox reactions including those involved in the environmental remediation of briny and salty water.
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http://dx.doi.org/10.1021/acsnano.0c05992DOI Listing
March 2021

Self-Assembly of Asymmetrically Functionalized Titania Nanoparticles into Nanoshells.

Materials (Basel) 2020 Oct 29;13(21). Epub 2020 Oct 29.

Department of Molecular Sciences, Swedish University of Agricultural Sciences (SLU), Box 7015, 75007 Uppsala, Sweden.

Titania (anatase) nanoparticles were anisotropically functionalized in water-toluene Pickering emulsions to self-assemble into nanoshells with diameters from 500 nm to 3 μm as candidates for encapsulation of drugs and other compounds. The water-phase contained a hydrophilic ligand, glucose-6-phosphate, while the toluene-phase contained a hydrophobic ligand, n-dodecylphosphonic acid. The addition of a dilute sodium alginate suspension that provided electrostatic charge was essential for the self-limited assembly of the nanoshells. The self-assembled spheres were characterized by scanning electron microscopy, elemental mapping, and atomic force microscopy. Drug release studies using tetracycline suggest a rapid release dominated by surface desorption.
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http://dx.doi.org/10.3390/ma13214856DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7662802PMC
October 2020

Penetration of Carbon Nanotubes into the Retinoblastoma Tumor after Intravitreal Injection in LH T Transgenic Mice Reti-noblastoma Model.

J Ophthalmic Vis Res 2020 Oct-Dec;15(4):446-452. Epub 2020 Oct 25.

Electrical Engineering and Computer Science, University of Michigan Ann Arbor, MI, USA.

Purpose: To evaluate the penetration of carbon nanotubes (CNTs) throughout retinoblastoma in a transgenic mice model.

Methods: CNTs functionalized with fluorescein isothiocyanate and targeting ligands biotin (CTN-FITC-Bio, 0.5mg/ml), or folic acid (CNT-FITC-FA, 0.5mg/ml) were injected into the vitreous of one eye of LH T transgenic mice. Other eye did not receive any injection and was used as control. Three mice were sacrificed at days 1, 2, and 3. Eyes were enucleated and stained with 4,6-diamidino-2-phenylindole. The sections were imaged by fluorescent microscope. The images were transformed into grey-scale in MATLAB for intensity analysis. Background intensity was normalized by marking squares outside the eyeball and using the mean intensity of these squares. Fluorescent intensity (FI) for each image was measured by calculating the intensity of a same-sized square within retinoblastoma.

Results: Nine eyes of nine mice were included in each CNT-FITC-Bio and CNT-FITC-FA groups. The mean FI in CNT-FITC-Bio was 52.08 6.33, 53.62 9.00, and 65.54 5.14 in days 1, 2, and 3, respectively. The mean FI in CNT-FITC-FA was 50.28 7.37, 59.21 6.43, and 58.38 2.32 on days 1, 2, and 3, respectively. FI was significantly higher in eyes injected with CNT-FITC-Bio and CNT-FITC-FA compared to the control eyes ( = 0.02). There was no difference in FI between eyes with CNT-FITC-Bio and CNT-FITC-FA, and FI remained stable on days 1-3 in CNT-FITC-Bio, CNT-FITC-FA, and control eyes ( 0.05).

Conclusion: We observed higher FI in eyes with CNT-FITC-Bio and CNT-FITC-FA compared to control eyes, showing penetration of CNTs throughout retinoblastoma. CNTs can be a carrier candidate for imaging or therapeutic purposes in retinoblastoma.
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http://dx.doi.org/10.18502/jovr.v15i4.7778DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7591833PMC
October 2020

Stimulation of neural stem cell differentiation by circularly polarized light transduced by chiral nanoassemblies.

Nat Biomed Eng 2021 01 26;5(1):103-113. Epub 2020 Oct 26.

Key Laboratory of Synthetic and Biological Colloids, International Joint Research Laboratory for Biointerface and Biodetection, Jiangnan University, Wuxi, Jiangsu, China.

The biological effects of circularly polarized light on living cells are considered to be negligibly weak. Here, we show that the differentiation of neural stem cells into neurons can be accelerated by circularly polarized photons when DNA-bridged chiral assemblies of gold nanoparticles are entangled with the cells' cytoskeletal fibres. By using cell-culture experiments and plasmonic-force calculations, we demonstrate that the nanoparticle assemblies exert a circularly-polarized-light-dependent force on the cytoskeleton, and that the light-induced periodic mechanical deformation of actin nanofibres with a frequency of 50 Hz stimulates the differentiation of neural stem cells into the neuronal phenotype. When implanted in the hippocampus of a mouse model of Alzheimer's disease, neural stem cells illuminated following a polarity-optimized protocol reduced the formation of amyloid plaques by more than 70%. Our findings suggest that circularly polarized light can guide cellular development for biomedical use.
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http://dx.doi.org/10.1038/s41551-020-00634-4DOI Listing
January 2021

Biomorphic structural batteries for robotics.

Sci Robot 2020 08;5(45)

Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109, USA.

Batteries with conformal shape and multiple functionalities could provide new degrees of freedom in the design of robotic devices. For example, the ability to provide both load bearing and energy storage can increase the payload and extend the operational range for robots. However, realizing these kinds of structural power devices requires the development of materials with suitable mechanical and ion transport properties. Here, we report biomimetic aramid nanofibers-based composites with cartilage-like nanoscale morphology that display an unusual combination of mechanical and ion transport properties. Ion-conducting membranes from these aramid nanofiber composites enable pliable zinc-air batteries with cyclic performance exceeding 100 hours that can also serve as protective covers in various robots including soft and flexible miniaturized robots. The unique properties of the aramid ion conductors are attributed to the percolating network architecture of nanofibers with high connectivity and strong nanoscale filaments designed using a graph theory of composite architecture when the continuous aramid filaments are denoted as edges and intersections are denoted as nodes. The total capacity of these body-integrated structural batteries is 72 times greater compared with a stand-alone Li-ion battery with the same volume. These materials and their graph theory description enable a new generation of robotic devices, body prosthetics, and flexible and soft robotics with nature-inspired distributed energy storage.
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http://dx.doi.org/10.1126/scirobotics.aba1912DOI Listing
August 2020

Chiral Nanoceramics.

Adv Mater 2020 Oct 5;32(41):e1906738. Epub 2020 Jun 5.

Department of Chemical Engineering and Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.

The study of different chiral inorganic nanomaterials has been experiencing rapid growth during the past decade, with its primary focus on metals and semiconductors. Ceramic materials can substantially expand the range of mechanical, optical, chemical, electrical, magnetic, and biological properties of chiral nanostructures, further stimulating theoretical, synthetic, and applied research in this area. An ever-expanding toolbox of nanoscale engineering and self-organization provides a chirality-based methodology for engineering of hierarchically organized ceramic materials. However, fundamental discoveries and technological translations of chiral nanoceramics have received substantially smaller attention than counterparts from metals and semiconductors. Findings in this research area are scattered over a variety of sources and subfields. Here, the diversity of chemistries, geometries, and properties found in chiral ceramic nanostructures are summarized. They represent a compelling materials platform for realization of chirality transfer through multiple scales that can result in new forms of ceramic materials. Multiscale chiral geometries and the structural versatility of nanoceramics are complemented by their high chiroptical activity, enantioselectivity, catalytic activity, and biocompatibility. Future development in this field is likely to encompass chiral synthesis, biomedical applications, and optical/electronic devices. The implementation of computationally designed chiral nanoceramics for biomimetic catalysts and quantum information devices may also be expected.
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http://dx.doi.org/10.1002/adma.201906738DOI Listing
October 2020

Enantiomeric Discrimination by Surface-Enhanced Raman Scattering-Chiral Anisotropy of Chiral Nanostructured Gold Films.

Angew Chem Int Ed Engl 2020 Aug 21;59(35):15226-15231. Epub 2020 Jun 21.

School of Chemical Science and Engineering, Tongji University, 1239 Siping Road, Shanghai, 200092, P. R. China.

A surface-enhanced Raman scattering-chiral anisotropy (SERS-ChA) effect is reported that combines chiral discrimination and surface Raman scattering enhancement on chiral nanostructured Au films (CNAFs) equipped in the normal Raman scattering Spectrometer. The CNAFs provided remarkably higher enhancement factors of Raman scattering (EFs) for particular enantiomers, and the SERS intensity was proportional to the enantiomeric excesses (ee) values. Except for molecules with mesomeric species, all of the tested enantiomers exhibited high SERS-ChA asymmetry factors (g), ranging between 1.34 and 1.99 regardless of polarities, sizes, chromophores, concentrations and ee. The effect might be attributed to selective resonance coupling between the induced electric and magnetic dipoles associated with enantiomers and chiral plasmonic modes of CNAFs.
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http://dx.doi.org/10.1002/anie.202006486DOI Listing
August 2020

Plasmonic nanoparticles assemblies templated by helical bacteria and resulting optical activity.

Chirality 2020 07 22;32(7):899-906. Epub 2020 Apr 22.

Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan, USA.

Plasmonic nanoparticles (NPs) adsorbing onto helical bacteria can lead to formation of NP helicoids with micron scale pitch. Associated chiroptical effects can be utilized as bioanalytical tool for bacterial detection and better understanding of the spectral behavior of helical self-assembled structures with different scales. Here, we report that enantiomerically pure helices with micron scale of chirality can be assembled on Campylobacter jejuni, a helical bacterium known for severe stomach infections. These organisms have right-handed helical shapes with a pitch of 1-2 microns and can serve as versatile templates for a variety of NPs. The bacteria itself shows no observable rotatory activity in the visible, red, and near-IR ranges of electromagnetic spectrum. The bacterial dispersion acquires chiroptical activity at 500-750 nm upon plasmonic functionalization with Au NPs. Finite-difference time-domain simulations confirmed the attribution of the chiroptical activity to the helical assembly of gold nanoparticles. The position of the circular dichroism peaks observed for these chiral structures overlaps with those obtained before for Au NPs and their constructs with molecular and nanoscale chirality. This work provides an experimental and computational pathway to utilize chiroplasmonic particles assembled on bacteria for bioanalytical purposes.
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http://dx.doi.org/10.1002/chir.23225DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7849023PMC
July 2020

Emergence of complexity in hierarchically organized chiral particles.

Science 2020 05 9;368(6491):642-648. Epub 2020 Apr 9.

Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109, USA.

The structural complexity of composite biomaterials and biomineralized particles arises from the hierarchical ordering of inorganic building blocks over multiple scales. Although empirical observations of complex nanoassemblies are abundant, the physicochemical mechanisms leading to their geometrical complexity are still puzzling, especially for nonuniformly sized components. We report the self-assembly of hierarchically organized particles (HOPs) from polydisperse gold thiolate nanoplatelets with cysteine surface ligands. Graph theory methods indicate that these HOPs, which feature twisted spikes and other morphologies, display higher complexity than their biological counterparts. Their intricate organization emerges from competing chirality-dependent assembly restrictions that render assembly pathways primarily dependent on nanoparticle symmetry rather than size. These findings and HOP phase diagrams open a pathway to a large family of colloids with complex architectures and unusual chiroptical and chemical properties.
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http://dx.doi.org/10.1126/science.aaz7949DOI Listing
May 2020

Chiral 2D Organic Inorganic Hybrid Perovskite with Circular Dichroism Tunable Over Wide Wavelength Range.

J Am Chem Soc 2020 Mar 21;142(9):4206-4212. Epub 2020 Feb 21.

Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea.

The effect of chemical-composition modification on the chiroptical property of chiral organic ammonium cation-containing organic inorganic hybrid perovskite (chiral OIHP) is investigated. Varying the mixing ratio of bromide and iodide anions in - or -CHCH(CH)NH)PbIBr modifies the band gap of chiral OIHP, leading to a shift of the circular dichroism (CD) signal from 495 to 474 nm. However, it is also found that an abrupt crystalline structure transition occurs, and the CD signal is turned off when iodide-determinant phases are transformed into the bromide-determinant phase. To obtain CD in the wavelength range where the bromide-determinant phase is supposed to exhibit chiroptical activity, that is, <474 nm, - or -CHCH(CH)NH with a larger spacer group can be adopted; thus, the CD signal can be further blue-shifted to ∼375 nm. Here, we show that chemical-composition modification of chiral OIHP affects the chiroptical properties of chiral OIHP in two ways: (1) tuning the wavelength of CD by modulating the excitonic band structure and (2) switching the CD on and off by inducing a crystalline-structure change. These properties can be utilized for structural engineering of high-performance chiroptical materials for spin-polarized light-emitting devices and polarization-based optoelectronics.
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http://dx.doi.org/10.1021/jacs.9b11453DOI Listing
March 2020

Chemo- and Thermomechanically Configurable 3D Optical Metamaterials Constructed from Colloidal Nanocrystal Assemblies.

ACS Nano 2020 Feb 31;14(2):1427-1435. Epub 2019 Dec 31.

Department of Materials Science and Engineering , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States.

Nanofabrication has limited most optical metamaterials to 2D or, often with multiple patterning steps, simple 3D meta-atoms that typically have limited built-in tunability. Here, with a one-step scalable patterning process, we exploit the chemical addressability and structural adaptability of colloidal Au nanocrystal assemblies to transform 2D nanocrystal/Ti bilayers into complex, 3D-structured meta-atoms and to thermally direct their shape morphing and alter their optical properties. By tailoring the length, number, and curvature of 3D helical structures in each meta-atom, we create large-area metamaterials with chiroptical responses of as high as ∼40% transmission difference between left-hand (LCP) and right-hand (RCP) circularly polarized light (Δ = - ) that are suitable for broadband circular polarizers and, upon thermally configuring their shape, switch the polarity of polarization rotation. These 3D optical metamaterials provide prototypes for low-cost, large-scale fabrication of optical metamaterials for ultrathin lenses, polarizers, and waveplates.
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http://dx.doi.org/10.1021/acsnano.9b08452DOI Listing
February 2020

Single- and multi-component chiral supraparticles as modular enantioselective catalysts.

Nat Commun 2019 10 23;10(1):4826. Epub 2019 Oct 23.

Department of Chemical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.

Nanoscale biological assemblies exemplified by exosomes, endosomes and capsids, play crucial roles in all living systems. Supraparticles (SP) from inorganic nanoparticles (NPs) replicate structural characteristics of these bioassemblies, but it is unknown whether they can mimic their biochemical functions. Here, we show that chiral ZnS NPs self-assemble into 70-100 nm SPs that display sub-nanoscale porosity associated with interstitial spaces between constituent NPs. Similarly to photosynthetic bacterial organelles, these SPs can serve as photocatalysts, enantioselectively converting L- or D-tyrosine (Tyr) into dityrosine (diTyr). Experimental data and molecular dynamic simulations indicate that the chiral bias of the photocatalytic reaction is associated with the chiral environment of interstitial spaces and preferential partitioning of enantiomers into SPs, which can be further enhanced by co-assembling ZnS with Au NPs. Besides replicating a specific function of biological nanoassemblies, these findings establish a path to enantioselective oxidative coupling of phenols for biomedical and other needs.
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http://dx.doi.org/10.1038/s41467-019-12134-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6811642PMC
October 2019

Origin of chiroptical activity in nanorod assemblies.

Science 2019 09;365(6460):1378-1379

Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109, USA.

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http://dx.doi.org/10.1126/science.aay7776DOI Listing
September 2019

Present and Future of Surface-Enhanced Raman Scattering.

ACS Nano 2020 01 8;14(1):28-117. Epub 2019 Oct 8.

Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences , Nanyang Technological University , 21 Nanyang Link , Singapore 637371 , Singapore.

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.
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http://dx.doi.org/10.1021/acsnano.9b04224DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6990571PMC
January 2020

Diverse Nanoassemblies of Graphene Quantum Dots and Their Mineralogical Counterparts.

Angew Chem Int Ed Engl 2020 May 8;59(22):8542-8551. Epub 2019 Oct 8.

Department of Chemical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.

Complex structures from nanoparticles are found in rocks, soils, and sea sediments but the mechanisms of their formation are poorly understood, which causes controversial conclusions about their genesis. Here we show that graphene quantum dots (GQDs) can assemble into complex structures driven by coordination interactions with metal ions commonly present in environment and serve a special role in Earth's history, such as Fe and Al . GQDs self-assemble into mesoscale chains, sheets, supraparticles, nanoshells, and nanostars. Specific assembly patterns are determined by the effective symmetry of the GQDs when forming the coordination assemblies with the metal ions. As such, maximization of the electronic delocalization of π-orbitals of GQDs with Fe leads to GQD-Fe-GQD units with D symmetry, dipolar bonding potential, and linear assemblies. Taking advantage of high electron microscopy contrast of carbonaceous nanostructures in respect to ceramic background, the mineralogical counterparts of GQD assemblies are found in mineraloid shungite. These findings provide insight into nanoparticle dynamics during the rock formation that can lead to mineralized structures of unexpectedly high complexity.
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http://dx.doi.org/10.1002/anie.201908216DOI Listing
May 2020

Stretchable batteries with gradient multilayer conductors.

Sci Adv 2019 Jul 26;5(7):eaaw1879. Epub 2019 Jul 26.

Department of Chemistry, Yonsei University, Seoul 03722, Republic of Korea.

Stretchable conductors are essential components in next-generation deformable and wearable electronic devices. The ability of stretchable conductors to achieve sufficient electrical conductivity, however, remains limited under high strain, which is particularly detrimental for charge storage devices. In this study, we present stretchable conductors made from multiple layers of gradient assembled polyurethane (GAP) comprising gold nanoparticles capable of self-assembly under strain. Stratified layering affords control over the composite internal architecture at multiple scales, leading to metallic conductivity in both the lateral and transversal directions under strains of as high as 300%. The unique combination of the electrical and mechanical properties of GAP electrodes enables the development of a stretchable lithium-ion battery with a charge-discharge rate capability of 100 mAh g at a current density of 0.5 A g and remarkable cycle retention of 96% after 1000 cycles. The hierarchical GAP nanocomposites afford rapid fabrication of advanced charge storage devices.
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http://dx.doi.org/10.1126/sciadv.aaw1879DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6660205PMC
July 2019

Terahertz circular dichroism spectroscopy of biomaterials enabled by kirigami polarization modulators.

Nat Mater 2019 08 1;18(8):820-826. Epub 2019 Jul 1.

Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, USA.

Terahertz circular dichroism (TCD) offers multifaceted spectroscopic capabilities for understanding the mesoscale chiral architecture and low-energy vibrations of macromolecules in (bio)materials. However, the lack of dynamic polarization modulators comparable to polarization optics for other parts of the electromagnetic spectrum is impeding the proliferation of TCD spectroscopy. Here we show that tunable optical elements fabricated from patterned plasmonic sheets with periodic kirigami cuts make possible the polarization modulation of terahertz radiation under application of mechanical strain. A herringbone pattern of microscale metal stripes enables a dynamic range of polarization rotation modulation exceeding 80° over thousands of cycles. Following out-of-plane buckling, the plasmonic stripes function as reconfigurable semi-helices of variable pitch aligned along the terahertz propagation direction. Several biomaterials, exemplified by an elytron of the Chrysina gloriosa, revealed distinct TCD fingerprints associated with the helical substructure in the biocomposite. Analogous kirigami modulators will also enable other applications in terahertz optics, such as polarization-based terahertz imaging, line-of-sight telecommunication, information encryption and space exploration.
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http://dx.doi.org/10.1038/s41563-019-0404-6DOI Listing
August 2019

Anti-Biofilm Activity of Graphene Quantum Dots via Self-Assembly with Bacterial Amyloid Proteins.

ACS Nano 2019 04 4;13(4):4278-4289. Epub 2019 Apr 4.

Biointerfaces Institute , University of Michigan , Ann Arbor , Michigan 48109 , United States.

Bacterial biofilms represent an essential part of Earth's ecosystem that can cause multiple ecological, technological, and health problems. The environmental resilience and sophisticated organization of biofilms are enabled by the extracellular matrix that creates a protective network of biomolecules around the bacterial community. Current anti-biofilm agents can interfere with extracellular matrix production but, being based on small molecules, are degraded by bacteria and rapidly diffuse away from biofilms. Both factors severely reduce their efficacy, while their toxicity to higher organisms creates additional barriers to their practicality. In this paper, we report on the ability of graphene quantum dots to effectively disperse mature amyloid-rich Staphylococcus aureus biofilms, interfering with the self-assembly of amyloid fibers, a key structural component of the extracellular matrix. Mimicking peptide-binding biomolecules, graphene quantum dots form supramolecular complexes with phenol-soluble modulins, the peptide monomers of amyloid fibers. Experimental and computational results show that graphene quantum dots efficiently dock near the N-terminus of the peptide and change the secondary structure of phenol-soluble modulins, which disrupts their fibrillation and represents a strategy for mitigation of bacterial communities.
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http://dx.doi.org/10.1021/acsnano.8b09403DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6528478PMC
April 2019

Quantitative zeptomolar imaging of miRNA cancer markers with nanoparticle assemblies.

Proc Natl Acad Sci U S A 2019 02 11;116(9):3391-3400. Epub 2019 Feb 11.

State Key Lab of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu 214122, China;

Multiplexed detection of small noncoding RNAs responsible for posttranscriptional regulation of gene expression, known as miRNAs, is essential for understanding and controlling cell development. However, the lifetimes of miRNAs are short and their concentrations are low, which inhibits the development of miRNA-based methods, diagnostics, and treatment of many diseases. Here we show that DNA-bridged assemblies of gold nanorods with upconverting nanoparticles can simultaneously quantify two miRNA cancer markers, namely miR-21 and miR-200b. Energy upconversion in nanoparticles affords efficient excitation of fluorescent dyes via energy transfer in the superstructures with core-satellite geometry where gold nanorods are surrounded by upconverting nanoparticles. Spectral separation of the excitation beam and dye emission wavelengths enables drastic reduction of signal-to-noise ratio and the limit of detection to 3.2 zmol/ng (0.11 amol or 6.5 × 10 copies) and 10.3 zmol/ng (0.34 amol or 2.1 × 10 copies) for miR-21 and miR-200b, respectively. Zeptomolar sensitivity and analytical linearity with respect to miRNA concentration affords multiplexed detection and imaging of these markers, both in living cells and in vivo assays. These findings create a pathway for the creation of an miRNA toolbox for quantitative epigenetics and digital personalized medicine.
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http://dx.doi.org/10.1073/pnas.1810764116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6397542PMC
February 2019

Spontaneous Formation of Cold-Welded Plasmonic Nanoassemblies with Refracted Shapes for Intense Raman Scattering.

Langmuir 2019 Mar 5;35(11):4110-4116. Epub 2019 Mar 5.

Department of Physical Chemistry, Biomedical Research Center, Southern Galicia Institute of Health Research and Biomedical Research Networking Center for Mental Health , Universidade de Vigo , 36310 Vigo , Spain.

Nanostructures with concave shapes made from continuous segments of plasmonic metals are known to dramatically enhance Raman scattering. Their synthesis in solutions is hindered, however, by their thermodynamic instability due to large surface area and high curvature of refracted geometries with nanoscale dimensions. Herein, we show that nanostructures with concave geometries can spontaneously form via self-organization of gold nanoparticles (NPs) at the air-water interface. The weakly bound surface ligands on the particle surface make possible their spontaneous accumulation and self-assembly at the air-water interface, forming monoparticulate films. Upon heating to 80 °C, the NPs further assemble into concave nanostructures where NPs are cold-welded to each other. Furthermore, the nanoassemblies effectively adsorb molecular analytes during their migration from the bulk solution to the surface where they can be probed by laser spectroscopies. We demonstrate that these films with local concentration of analytes increased by orders of magnitude and favorable plasmonic shapes can be exploited for surface-enhanced Raman scattering for high-sensitivity analysis of aliphatic molecules.
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http://dx.doi.org/10.1021/acs.langmuir.9b00234DOI Listing
March 2019

Biomimetic Solid-State Zn Electrolyte for Corrugated Structural Batteries.

ACS Nano 2019 02 23;13(2):1107-1115. Epub 2019 Jan 23.

Department of Chemical Engineering , University of Michigan , Ann Arbor , Michigan 48109 , United States.

Batteries based on divalent metals, such as the Zn/Zn pair, represent attractive alternatives to lithium-ion chemistry due to their high safety, reliability, earth-abundance, and energy density. However, archetypal Zn batteries are bulky, inflexible, non-rechargeable, and contain a corrosive electrolyte. Suppression of the anodic growth of Zn dendrites is essential for resolution of these problems and requires materials with nanoscale mechanics sufficient to withstand mechanical deformation from stiff Zn dendrites. Such materials must also support rapid transport Zn ions necessary for high Coulombic efficiency and energy density, which makes the structural design of such materials a difficult fundamental problem. Here, we show that it is possible to engineer a solid Zn electrolyte as a composite of branched aramid nanofibers (BANFs) and poly(ethylene oxide) by using the nanoscale organization of articular cartilage as a blueprint for its design. The high stiffness of the BANF network combined with the high ionic conductivity of soft poly(ethylene oxide) enable effective suppression of dendrites and fast Zn transport. The cartilage-inspired composite displays the ionic conductance 10× higher than the original polymer. The batteries constructed using the nanocomposite electrolyte are rechargeable and have Coulombic efficiency of 96-100% after 50-100 charge-discharge cycles. Furthermore, the biomimetic solid-state electrolyte enables the batteries to withstand not only elastic deformation during bending but also plastic deformation. This capability make them resilient to different type of damage and enables shape modification of the assembled battery to improve the ability of the battery stack to carry a structural load. The corrugated batteries can be integrated into body elements of unmanned aerial vehicles as auxiliary charge-storage devices. This functionality was demonstrated by replacing the covers of several small drones with corrugated Zn/BANF/MnO cells, resulting in the extension of the total flight time. These findings open a pathway to the design and utilization of corrugated structural batteries in the future transportation industry and other fields of use.
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http://dx.doi.org/10.1021/acsnano.8b05068DOI Listing
February 2019

Best Practices for Reporting Electrocatalytic Performance of Nanomaterials.

ACS Nano 2018 10;12(10):9635-9638

Institut Européen des Membranes , Université Montpellier, ENSCM, CNRS.

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http://dx.doi.org/10.1021/acsnano.8b07700DOI Listing
October 2018

Nanoporous aramid nanofibre separators for nonaqueous redox flow batteries.

Nat Commun 2018 10 10;9(1):4193. Epub 2018 Oct 10.

Department of Chemical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.

Redox flow batteries are attractive for large-scale energy storage due to a combination of high theoretical efficiencies and decoupled power and energy storage capacities. Efforts to significantly increase energy densities by using nonaqueous electrolytes have been impeded by separators with low selectivities. Here, we report nanoporous separators based on aramid nanofibres, which are assembled using a scalable, low cost, spin-assisted layer-by-layer technique. The multilayer structure yields 5 ± 0.5 nm pores, enabling nanofiltration with high selectivity. Further, surface modifications using polyelectrolytes result in enhanced performance. In vanadium acetylacetonate/acetonitrile-based electrolytes, the coated separator exhibits permeabilities an order of magnitude lower and ionic conductivities five times higher than those of a commercial separator. In addition, the coated separators exhibit exceptional stability, showing minimal degradation after more than 100 h of cycling. The low permeability translates into high coulombic efficiency in flow cell charge/discharge experiments performed at cycle times relevant for large-scale applications (5 h).
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http://dx.doi.org/10.1038/s41467-018-05752-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6180111PMC
October 2018
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