Seeded-Growth Experiment Demonstrating Size- and Shape-Dependence on Gold Nanoparticle–Light Interactions

Gold nanoparticles are exciting materials in nanotechnology and nanoscience research and are being applied across a wide range of fields including imaging, chemical sensing, energy storage, and cancer therapies. In this experiment, students will synthesize two sizes of gold nanospheres (~20 nm and ~100 nm) and will create gold nanostars utilizing a seed-mediated growth synthetic approach. Students will compare how each sample interacts differently with light (absorption and scattering) based on the nanoparticles' size and shape. This experiment is ideal for high-school and early undergraduate students since all reagents are non-toxic, affordable, and no special characterization equipment is required

Extraction of Hidden Science from Nanoscale Images

Scanning probe microscopies and spectroscopies enable investigation of surfaces and even buried interfaces down to the scale of chemical-bonding interactions, and this capability has been enhanced with the support of computational algorithms for data acquisition and image processing to explore physical, chemical, and biological phenomena. Here, we describe how scanning probe techniques have been enhanced by some of these recent algorithmic improvements. One improvement to the data acquisition algorithm is to advance beyond a simple rastering framework by using spirals at constant angular velocity then switching to constant linear velocity, which limits the piezo creep and hysteresis issues seen in traditional acquisition methods. One can also use image-processing techniques to model the distortions that appear from tip motion effects and to make corrections to these images. Another image-processing algorithm we discuss enables researchers to segment images by domains and subdomains, thereby highlighting reactive and interesting disordered sites at domain boundaries. Lastly, we discuss algorithms used to examine the dipole direction of individual molecules and surface domains, hydrogen bonding interactions, and molecular tilt. The computational algorithms used for scanning probe techniques are still improving rapidly and are incorporating machine learning at the next level of iteration. That said, the algorithms are not yet able to perform live adjustments during data recording that could enhance the microscopy and spectroscopic imaging methods significantly

PHOTOABSORPTION OF Ag (N = 6 - 6000) CLUSTERS IN He DROPLETS: A TRANSITION FROM SINGLE- TO MULTI-CENTERED GROWTH

Author Institution: Department of Chemistry, University of Southern California, Los Angeles, CA 90089-0482; Department of Physics, University of Southern California, Los Angeles, CA 90089-0484Ag clusters with up to thousands of atoms were grown in large He droplets and studied by optical spectroscopy. For clusters smaller than about 10$^{3}$ the spectra are dominated by a surface plasmon resonance near 3.8 eV and a broad feature in the UV, consistent with the absorption of individual metallic particles. Larger Ag clusters reveal an unexpectedly strong, broad absorption extending to lower frequencies down to approximately 0.5 eV. This suggests a transition from single-center to multi-center formation, in agreement with estimates of the kinetics of Ag cluster growth in He droplets. Moreover, the spectra of large clusters develop a characteristic dispersion profile at 3.5-4.5 eV, indicative of the coexistence of localized and delocalized electronic excitations in composite clusters, as predicted theoretically. We also report on the characterization of He droplet beams, obtained in the supercritical expansion regime, comprised of large droplets of up to 10$^{11}$ atoms

Large-Scale Soft-Lithographic Patterning of Plasmonic Nanoparticles

Micro- and nanoscale patterned monolayers of plasmonic nanoparticles were fabricated by combining concepts from colloidal chemistry, self-assembly, and subtractive soft lithography. Leveraging chemical interactions between the capping ligands of pre-synthesized gold colloids and a polydimethylsiloxane stamp, we demonstrated patterning gold nanoparticles over centimeter-scale areas with a variety of micro- and nanoscale geometries, including islands, lines, and chiral structures (e.g., square spirals). By successfully achieving nanoscale manipulation over a wide range of substrates and patterns, we established a powerful and straightforward strategy, nanoparticle chemical lift-off lithography (NP-CLL), for the economical and scalable fabrication of functional plasmonic materials with colloidal nanoparticles as building blocks, offering a transformative solution for designing next-generation plasmonic technologies.The authors would like to thank the Nanoquim clean room facility at ICMAB-CSIC and, in particular, Dr. Luigi Morrone for help with the use of the microwriter for master preparation. We acknowledge the CNSI-EICN, ICMAB-CSIC, and ICN2 electron microscopy facilities for TEM and SEM imaging, WiTEC for access to their microscopy instrumentation, and Dr. Thomas Young and Michael Mellody for the preparation of silicon masters. Special thanks to Dr. Leonora Velleman for the fruitful discussion on nanoparticle self-assembly. L.S. research is supported by the Marie Sklodowska-Curie Actions SHINE (H2020-MSCA-IF-2019, grant agreement No. 894847) and the 2020 Post-doctoral Junior Leader-Incoming Fellowship by “la Caixa” Foundation (ID 100010434, fellowship code LCF/BQ/PI20/11760028). L.A.P. thanks the Marie Sklodowska-Curie Actions (H2020-MSCA-IF-2018) for grant agreement No. 839402, PLASMIONICO. L.S., L.A.P., C.D., and A.M. acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant Agreement No. 637116, ENLIGHTMENT). ICMAB acknowledges the Spanish Ministry of Economy and Competitiveness under grants PID2019-106860GB-I00 (AEI/FEDER, UE) and FUNFUTURE (CEX2019-000917-S) center of excellence Severo Ochoa program. This work has been performed in the framework of the doctorate in Materials Science of the Autonomous University of Barcelona. N.C. thanks the NIH NIBIB Pathway to Independence Award (K99EB028325) for support. S.J.J. is supported by the NIH Common Fund through a NIH Director’s Early Independence Award co-funded by the National Institute of Dental and Craniofacial Research and Office of the Director, NIH Grant DP5OD028181. S.J.J. also acknowledges Young Investigator Award funds from the Alex’s Lemonade Stand Foundation for Childhood Cancer Research and the Hyundai Hope on Wheels Foundation for Pediatric Cancer Research. P.S.W. thanks the National Science Foundation (2004238) for support of this work. Funds for core facility use were provided via a support voucher awarded to N.C. and S.J.J. via the UCLA Clinical and Translational Science Institute (CTSI) Core Voucher Program, which is administered through Grant Number UL1TR001881.Peer reviewe

Exploring the Bottom-Up Growth of Anisotropic Gold Nanoparticles from Substrate-Bound Seeds in Microfluidic Reactors

We developed an unconventional seed-mediated in situ synthetic method, whereby gold nanostars are formed directly on the internal walls of microfluidic reactors. The dense plasmonic substrate coatings were grown in microfluidic channels with different geometries to elucidate the impacts of flow rate and profile on reagent consumption, product morphology, and density. Nanostar growth was found to occur in the flow-limited regime and our results highlight the possibility of creating shape gradients or incorporating multiple morphologies in the same microreactor, which is challenging to achieve with traditional self-assembly. The plasmonic-microfluidic platforms developed herein have implications for a broad range of applications, including cell culture/sorting, catalysis, sensing, and drug/gene delivery.The authors acknowledge the use of instruments at the Electron Imaging Center for NanoMachines supported by NIH (1S10RR23057) and CNSI at UCLA and technical assistance by Ivo Atanasov. We also thank Ms. Lisa Kawakami for the fabrication of the channel masters. G.A.V.-W. thanks the UCLA graduate division for funding through the University of California Office of the President Dissertation Year Fellowship. N.C. acknowledges support from the National Institute of Biomedical Imaging and Bioengineering (R00EB028325). L.S. is supported by the 2020 Postdoctoral Junior Leader-Incoming Fellowship by “la Caixa” Foundation (ID 100010434, code LCF/BQ/PI20/11760028) and by a 2022 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation. S.J.J. acknowledges support from the National Institutes of Health (NIH) Common Fund through a NIH Director’s Early Independence Award, Grant DP5OD028181. S.J.J. and G.A.V.-W. acknowledge support through a Scholar Award from the Hyundai Hope on Wheels Foundation (20193309).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Exploring the Bottom-Up Growth of Anisotropic Gold Nanoparticles from Substrate-Bound Seeds in Microfluidic Reactors

We developed an unconventional seed-mediated in situ synthetic method, whereby gold nanostars are formed directly on the internal walls of microfluidic reactors. The dense plasmonic substrate coatings were grown in microfluidic channels with different geometries to elucidate the impacts of flow rate and profile on reagent consumption, product morphology, and density. Nanostar growth was found to occur in the flow-limited regime and our results highlight the possibility of creating shape gradients or incorporating multiple morphologies in the same microreactor, which is challenging to achieve with traditional self-assembly. The plasmonic-microfluidic platforms developed herein have implications for a broad range of applications, including cell culture/sorting, catalysis, sensing, and drug/gene delivery

Scalable Fabrication of Quasi-One-Dimensional Gold Nanoribbons for Plasmonic Sensing

Plasmonic nanostructures have a wide range of applications, including chemical and biological sensing. However, the development of techniques to fabricate submicrometer-sized plasmonic structures over large scales remains challenging. We demonstrate a high-throughput, cost-effective approach to fabricate Au nanoribbons via chemical lift-off lithography (CLL). Commercial HD-DVDs were used as large-area templates for CLL. Transparent glass slides were coated with Au/Ti films and functionalized with self-assembled alkanethiolate monolayers. Monolayers were patterned with lines via CLL. The lifted-off, exposed regions of underlying Au were selectively etched into large-area grating-like patterns (200 nm line width; 400 nm pitch; 60 nm height). After removal of the remaining monolayers, a thin In2O3 layer was deposited and the resulting gratings were used as plasmonic sensors. Distinct features in the extinction spectra varied in their responses to refractive index changes in the solution environment with a maximum bulk sensitivity of ∼510 nm/refractive index unit. Sensitivity to local refractive index changes in the near-field was also achieved, as evidenced by real-time tracking of lipid vesicle or protein adsorption. These findings show how CLL provides a simple and economical means to pattern large-area plasmonic nanostructures for applications in optoelectronics and sensing