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      Label-Free Direct Detection of Saxitoxin Based on a Localized Surface Plasmon Resonance Aptasensor

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      , , , *
      Toxins
      MDPI
      marine-toxins, saxitoxin, LSPR, aptamer, aptasensor

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          Abstract

          Seafood is an emerging health food, and interest in improving the quality of seafood is increasing. Saxitoxin (STX) is a neurotoxin produced by marine dinoflagellates that is accumulated in seafood. It can block the neuronal transmission between nerves and muscle cell membranes, resulting in the disturbance of neuromuscular transmission and subsequent voluntary muscle paralysis. Here, we developed a new aptamer for the detection of STX using graphene oxide–systematic evolution of ligands by exponential enrichment (GO-SELEX). Furthermore, we confirmed sensitivity and selectivity of the developed aptamer specific to STX using a localized surface plasmon resonance (LSPR) sensor. The sensing chip was fabricated by fixing the new STX aptamer immobilized on the gold nanorod (GNR) substrate. The STX LSPR aptasensor showed a broad, linear detection range from 5 to 10,000 μg/L, with a limit of detection (LOD) of 2.46 μg/L (3σ). Moreover, it was suitable for the detection of STX (10, 100, and 2000 μg/L) in spiked mussel samples and showed a good recovery rate (96.13–116.05%). The results demonstrated that the new STX aptamer-modified GNR chip was sufficiently sensitive and selective to detect STX and can be applied to real samples as well. This LSPR aptasensor is a simple, label-free, cost-effective sensing system with a wide detectable range.

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          Most cited references40

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          Quantitation of metal content in the silver-assisted growth of gold nanorods.

          The seed-mediated approach to making gold nanorods in aqueous surfactant solutions has become tremendously popular in recent years. Unlike the use of strong chemical reductants to make spherical gold nanoparticles, the growth of gold nanorods requires weak reducing conditions, leading to an unknown degree of gold reduction. The metal content of gold nanorods, made in high yield in the presence of silver ion, is determined by inductively coupled plasma atomic emission spectroscopy. Through the use of the known gold concentration in nanorods, molar extinction coefficients are calculated for nanorods of varying aspect ratios from 2.0 to 4.5. The extinction coefficients at the longitudinal plasmon band peak maxima for these nanorods vary from 2.5x10(9) to 5.5x10(9) M-1 cm-1, respectively, on a per-particle basis. Many of the gold ions present in the growth solution remain unreacted; insights into the growth mechanism of gold nanorods are discussed.
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            Sensitivity of metal nanoparticle surface plasmon resonance to the dielectric environment.

            Electrodynamic simulations of gold nanoparticle spectra were used to investigate the sensitivity of localized surface plasmon band position to the refractive index, n, of the medium for nanoparticles of various shapes and nanoshells of various structures. Among single-component nanoparticles less than 130 nm in size, sensitivities of dipole resonance positions to bulk refractive index are found to depend only upon the wavelength of the resonance and the dielectric properties of the metal and the medium. Among particle plasmons that peak in the frequency range where the real part of the metal dielectric function varies linearly with wavelength and the imaginary part is small and slowly varying, the sensitivity of the peak wavelength, lambda, to refractive index, n, is found to be a linearly increasing function of lambda, regardless of the structural features of the particle that determine lambda. Quasistatic theory is used to derive an analytical expression for the refractive index sensitivity of small particle plasmon peaks. Through this analysis, the dependence of sensitivity on band position is found to be determined by the wavelength dependence of the real part, epsilon', of the particle dielectric function, and the sensitivity results are found to extend to all particles with resonance conditions of the form, epsilon' = -2chin(2), where chi is a function of geometric parameters and other constants. The sensitivity results observed using accurate computational methods for dipolar plasmon bands of gold nanodisks, nanorods, and hollow nanoshells extend, therefore, to particles of other shapes (such as hexagonal and chopped tetrahedral), composed of other metals, and to higher-order modes. The bulk refractive index sensitivity yielded by the theory serves as an upper bound to sensitivities of nanoparticles on dielectric substrates and sensitivities of nanoparticles to local refractive index changes, such as those associated with biomolecule sensing.
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              Circular dichroism spectroscopy of DNA: from duplexes to quadruplexes.

              Nucleic acids bear the genetic information and participate in its expression and evolution during replication, repair, recombination, transcription, and translation. These phenomena are mostly based on recognition of nucleic acids by proteins. The major factor enabling the specific recognition is structure. Circular dichroism (CD) spectroscopy is very useful to study secondary structures of nucleic acids, in general, and DNA, in particular. CD sensitively reflects isomerizations among distinct conformational states. The isomerizations may operate as molecular switches regulating various physiological or pathological processes. Here, we review CD spectra of nucleic acids, beginning with early studies on natural DNA molecules through analyses of synthetic polynucleotides to study of selected genomic fragments. Copyright © 2012 Wiley Periodicals, Inc.
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                Author and article information

                Journal
                Toxins (Basel)
                Toxins (Basel)
                toxins
                Toxins
                MDPI
                2072-6651
                15 May 2019
                May 2019
                : 11
                : 5
                : 274
                Affiliations
                Department of chemistry, school of physics and chemistry, Gwangju Institute of Science and Technology (GIST), 123 Cheomdangwagi-ro, Buk-Gu, Gwangju 500-712, Korea; suji1420@ 123456naver.com (S.-J.H.); jhp1223@ 123456gist.ac.kr (J.-H.P.); bb7896@ 123456gist.ac.kr (B.L.)
                Author notes
                [* ]Correspondence: mkim@ 123456gist.ac.kr ; Tel.: +82-62-715-3330; Fax: +82-62-715-2887
                [†]

                Equally contributed to this work.

                Article
                toxins-11-00274
                10.3390/toxins11050274
                6563244
                31096619
                41ca2c4a-ed32-4af1-a647-0fa2010934ef
                © 2019 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 12 April 2019
                : 14 May 2019
                Categories
                Article

                Molecular medicine
                marine-toxins,saxitoxin,lspr,aptamer,aptasensor
                Molecular medicine
                marine-toxins, saxitoxin, lspr, aptamer, aptasensor

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