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      Strong Magneto-Optical Response of Nonmagnetic Organic Materials Coupled to Plasmonic Nanostructures

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          Abstract

          Plasmonic nanoparticles (PNPs) can significantly modify the optical properties of nearby organic molecules and thus present an attractive opportunity for sensing applications. However, the utilization of PNPs in conventional absorption, fluorescence, or Raman spectroscopy techniques is often ineffective due to strong absorption background and light scattering, particularly in the case of turbid solutions, cell suspensions, and biological tissues. Here we show that nonmagnetic organic molecules may exhibit magneto-optical response due to binding to a PNP. Specifically, we detect strong magnetic circular dichroism signal from supramolecular J-aggregates, a representative organic dye, upon binding to silver-coated gold nanorods. We explain this effect by strong coupling between the J-aggregate exciton and the nanoparticle plasmon, leading to the formation of a hybrid state in which the exciton effectively acquires magnetic properties from the plasmon. Our findings are fully corroborated by theoretical modeling and constitute a novel magnetic method for chemo- and biosensing, which (upon adequate PNP functionalization) is intrinsically insensitive to the organic background and thus offers a significant advantage over conventional spectroscopy techniques.

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          Most cited references40

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          Biosensing with plasmonic nanosensors.

          Recent developments have greatly improved the sensitivity of optical sensors based on metal nanoparticle arrays and single nanoparticles. We introduce the localized surface plasmon resonance (LSPR) sensor and describe how its exquisite sensitivity to size, shape and environment can be harnessed to detect molecular binding events and changes in molecular conformation. We then describe recent progress in three areas representing the most significant challenges: pushing sensitivity towards the single-molecule detection limit, combining LSPR with complementary molecular identification techniques such as surface-enhanced Raman spectroscopy, and practical development of sensors and instrumentation for routine use and high-throughput detection. This review highlights several exceptionally promising research directions and discusses how diverse applications of plasmonic nanoparticles can be integrated in the near future.
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            Is Open Access

            JC-1: alternative excitation wavelengths facilitate mitochondrial membrane potential cytometry

            Mitochondrial membrane potential provides a valuable indicator of cells' health and functional status. Cytometry- and microscopy-based analyses, in combination with fluorescent probes, are widely used to study mitochondrial behavior related to cellular pathways, most notably – apoptosis. The cyanine dye JC-1 (5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimi- dazolylcarbocyanine iodide) facilitates discrimination of energized and deenergized mitochondria because the normally green fluorescent dye forms red fluorescent aggregates when concentrated in energized mitochondria in response to their higher membrane potential. JC-1 fluorescence is usually excited by the 488 nm laser wavelength common in flow cytometers. In this study, we show that in practice this approach is not optimal for monitoring mitochondrial behavior. Investigation of fluorescence of JC-1 in solution and in cells using spectrofluorimetry, microscopy and flow cytometry reveals that excitation at 405 nm wavelength, now available on standard instruments, produces signals from aggregate fluorescence with considerably less spillover from dye monomer fluorescence than can be obtained using 488 nm excitation. The improved data are more accurate and eliminate the necessity for fluorescence compensation, making the use of the alternative excitation wavelengths beneficial for mitochondria-related biological and biomedial research.
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              Plasmonic enhancement of molecular fluorescence.

              Metallic nanoparticles are known to dramatically modify the spontaneous emission of nearby fluorescent molecules and materials. Here we examine the role of the nanoparticle plasmon resonance energy and nanoparticle scattering cross section on the fluorescence enhancement of adjacent indocyanine green (ICG) dye molecules. We find that enhancement of the molecular fluorescence by more than a factor of 50 can be achieved for ICG next to a nanoparticle with a large scattering cross section and a plasmon resonance frequency corresponding to the emission frequency of the molecule.
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                Author and article information

                Journal
                Nano Lett
                Nano Lett
                nl
                nalefd
                Nano Letters
                American Chemical Society
                1530-6984
                1530-6992
                03 February 2017
                08 March 2017
                03 February 2018
                : 17
                : 3
                : 1808-1813
                Affiliations
                []CIC NanoGUNE , Avenida Tolosa 76, 20018 Donostia-San Sebastián, Spain
                []National University of Ireland Galway , University Road, Galway, Ireland
                [§ ]CIC biomaGUNE , Paseo de Miramón 182, 20014 Donostia-San Sebastián, Spain
                []Centro de Física de Materiales (MPC, CSIC-UPV/EHU) Paseo Manuel de Lardizabal 5, Donostia-San Sebastián, 20018, Spain
                []Donostia International Physics Center (DIPC) , Paseo Manuel de Lardizabal 4, Donostia-San Sebastián, 20018, Spain
                [# ]IKERBASQUE, Basque Foundation for Science , 48013, Bilbao, Spain
                []Biomedical Research Networking Center in Bioengineering Biomaterials and Nanomedicine, Ciber-BBN , Paseo de Miramón 182, 20014 Donostia-San Sebastián, Spain
                Author notes
                Article
                10.1021/acs.nanolett.6b05128
                5744660
                28157323
                5b30a1fc-e4d5-4125-927f-42943dfd38a6
                Copyright © 2017 American Chemical Society

                This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.

                History
                : 10 December 2016
                : 25 January 2017
                Categories
                Letter
                Custom metadata
                nl6b05128
                nl-2016-05128j

                Nanotechnology
                sensing,magneto-optical activity,magneto-plasmonics,j-aggregates,plexciton,strong coupling

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