Maria Anita Rampi

University of Ferrara, Ferrare, Emilia-Romagna, Italy

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Publications (46)353.82 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Gold nano-islands (Au NIs) deposited on solid surfaces exhibit localized surface plasmon resonance (LSPR) extinction bands, which are sensitive, among other parameters, to the morphology of the island and to the dielectric properties of the surrounding medium. The variation of LSPR maximum energy (lambda(max)) reflects then refractive index changes occurring at the surface of the Au NIs under the condition that they have reached a stable morphology. In this context we have quantified the morphological stability of Au NIs by measuring Delta lambda(max) by UV-vis spectroscopy in transmission mode. In particular, we have studied the stability of Au NIs (i) of different dimensions (3, 5, 10 nm), (ii) when deposited on substrates of different porosity as quartz and FTO, (iii) upon incubation in different solvents (EtOH, ButOH, MeOH, DMF, CHCl3), and (iv) upon the widely used process of washing and drying (WD). As expected, annealed Au NIs of larger size (10 nm) show good stability in all tested solvents. It is a general believe that unannealed Au NIs are unsuitable materials for LSPR based sensors because of large restructuring processes upon solvent incubation. In contrast, we found that unannealed NIs, even of small dimensions (3, 5 nm), show an excellent stability when incubated in more viscous solvents as EtOH and ButOH. These results indicate that the restructuring process can be reduced by increasing the viscosity of the incubation solvent. In addition, we proved that the sensitivity to formation of organic SAMs of unannealed 5 nm Au NIs is much higher (10 times) as compared to the annealed ones. Electromagnetic simulations support the experimental findings showing how the morphology of NIs may affect the plasmon peak position, and confirming the different sensitivity of unannealed and annealed Au NIs samples. Published by Elsevier B.V.
    Sensors and Actuators B Chemical 02/2014; 191:356-363. DOI:10.1016/j.snb.2013.09.026 · 3.84 Impact Factor
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    ABSTRACT: In the framework of bioanalytics and multiple array detection, we developed a fully portable and low-cost detection system based on Localized Surface Plasmon Resonance (LSPR) in a transmission configuration (T-LSPR). The transmission approach is suitable to be scaled to small dimension systems and to enable high-density array measurements on the same platform. Our setup is made out of off-the-shelf components and consists of a set of discrete light sources and a couple of light-detectors which enable a differential measurement setup. An algorithm fits the measured data and extracts the information of the plasmon peak position in the spectrum. The performance of our T-LSPR measurement system has been characterized on a set of Fluorinated Tin Oxide-coated glass slides covered with gold Nanoislands (NIs). The samples have been modified with a single-stranded DNA layer and a real-time DNA hybridization experiment has been performed. Here we demonstrate that the proposed T-LSPR device, based on the characterization of the plasmon peak with a differential approach, is able to monitor real-time DNA hybridization on surface, and to precisely measure the position of the peak with a standard deviation in wavelength of 0.2 nm.
    MRS Online Proceeding Library 08/2012; 1479:27-32. DOI:10.1557/opl.2012.1593
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    ABSTRACT: In recent years, the characterization of surface molecular layers by Localized Surface Plasmon Resonance (LSPR) has attracted a lot of interest thanks to its ability to provide a higher spatial resolution with respect to standard SPR. LSPR can be observed as a peak in the extinction spectrum of metal nanoparticles such as gold non-connected surface patterns. A Plasmon peak red shift is caused both by the presence of molecular layers on the gold surface and by molecular binding events. The current study presents a portable transmission system to observe the LSPR phenomenon that extracts the peak location employing a discrete number of light sources. The peak location extraction is performed by an algorithm that takes into account the spectral characteristics of all the components. The performance of our LSPR measurement system has been characterized on a set of FluorinatedTinOxide-coated slides covered with nanoislands with a diameter of approximately 30 nm. The samples have been modified with a single-stranded DNA layer and the plasmonic peak location has been determined before and after surface treatment. The samples have been characterized in parallel with a high-end spectrophotometer. The results presented demonstrated the performance of our measurement system in determining the peak location with 1 nm precision.
    Sensors and Actuators B Chemical 01/2012; 176(in press). DOI:10.1016/j.snb.2012.07.085, · 3.84 Impact Factor
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    ABSTRACT: The study of charge transport processes through organic molecules by using molecular junctions has generated great attention in the last few years, partially triggered by the possibility of developing molecular electronic devices to be implemented somehow into current silicon-based technology. As experimental tools, a large variety of conceptually and geometrically different metal-molecule(s)-metal junctions has been proposed. While the intrinsic conductivity of a molecule is still elusive, parameters crucial for molecular electronics have been extracted by using a variety of junctions. Significantly, the results extracted from molecular junctions and those obtained by the kinetic approach in supramolecular D-B-A systems are complementary. For the sake of a practical discussion, a distinction is made between "active junctions" and "non-active junctions". Active junctions are those aimed at switching the electrical response by an external stimulus acting "in situ" to modify the electronic structure of the molecular system. Non-active junctions are those aimed at studying different conduction regimes by incorporating molecules of different electronic structures. Depending on their geometry, the junctions can incorporate different numbers of molecules. Large area molecular junctions present two main advantages: (1) a simpler assembly, by requiring less sophisticated fabrication and (2) a higher versatility, relative to single molecule junctions, towards potential applications in organic electronics. The present chapter focuses on the fabrication of a variety of large-area molecular junctions and summarizes and compares the experimental results.
    Topics in current chemistry 09/2011; 313:85-119. DOI:10.1007/128_2011_221 · 4.61 Impact Factor
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    ABSTRACT: Metal nanoislands (NIs) deposited on transparent surfaces can be a convenient plasmonic material for bio/organic sensors, under the condition that a stable morphology is reached. Plasmonic materials suitable for the fabrication of low cost biosensors based on localized surface plas-mon resonance (LSPR) UV–Vis spectroscopy, are fabricated by a simple methodology based on thermal evaporation of Au on commercially available, transparent fluorine-doped tin oxide (FTO) surfaces. The LSPR UV–Vis spectroscopy performed in transmittance mode reveals: (i) a small energy shift, max , of the LSPR band under immersion both in organic solvent, and significantly in aqueous media, and (ii) a sensible and reproducible max under formation of organic SAMs on the NIs surface. These data indicate that the Au NIs when deposited on FTO substrate exhibit (i) strong adhesion and a high stability, and (ii) a good sensitivity to molecular interaction. The samples also show that the LSPR bands recover the original feature after being exposed to different type of SAMs. Significantly, the absorption maximum, max of the Au-NIs LSPR spectra shows a red shift when SAMs incorporating single strands DNA are exposed to the complementary strands. The plasmonic system based on Au NI deposited on FTO surfaces because of (i) the inexpensive fabrication of stable NIs, (ii) the easy way to detect the molecular interaction occurring at their surface, and (iii) the sensitivity of their LSPR to molecular interaction represents a convenient platform for biosensors.
    Sensors and Actuators B Chemical 03/2011; 152(2-152). DOI:10.1016/j.snb.2010.12.008 · 3.84 Impact Factor
  • Felice Carlo Simeone, Maria Anita Rampi
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    ABSTRACT: Junctions based on mesoscopic Hg electrodes are used to characterize the electrical properties of the organic molecules organized in self-assembled monolayers (SAMs). The junctions M-SAM//SAM-Hg are formed by one electrode based on metals (M) such as Hg, Ag, Au, covered by a SAM, and by a second electrode always formed by a Hg drop carrying also a SAM. The electrodes, brought together by using a micromanipulator, sandwich SAMs of different nature at the contact area (approximately = 0.7 microm2). The high versatility of the system allows a series of both electrical and electrochemical junctions to be assembled and characterized: (i) The compliant nature of the Hg electrodes allows incorporation into the junction and measurement of the electrical behavior of a large number of molecular systems and correlation of their electronic structure to the electrical behavior; (ii) by functionalizing both electrodes with SAMs exposing different functional groups, X and Y, it is possible to compare the rate of electron transfer through different X...Y molecular interactions; (iii) when the junction incorporates one of the electrode formed by a semitransparent film of Au, it allows electrical measurements under irradiation of the sandwiched SAMs. In this case the junction behaves as a photoswitch; iv) incorporation of redox centres with low lying, easily reachable energy levels, provides electron stations as indicated by the hopping mechanism dominating the current flow; (v) electrochemical junctions incorporating redox centres by both covalent and electrostatic interactions permit control of the potential of the electrodes with respect to that of the redox state by means of an external reference electrode. Both these junctions show an electrical behavior similar to that of conventional diodes, even though the mechanism generating the current flow is different. These systems, demonstrating high mechanical stability and reproducibility, easy assembly, and a wide variety of produced results, are convenient test-beds for molecular electronics and represent a useful complement to physics-based experimental methods.
    CHIMIA International Journal for Chemistry 06/2010; 64(6):362-9. DOI:10.2533/chimia.2010.362 · 1.35 Impact Factor
  • ChemInform 06/2010; 24(23):no-no. DOI:10.1002/chin.199323304
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    ABSTRACT: One of the main goals of molecular electronics is to achieve electronic functions from devices consisting of tailored organic molecules connecting two metal electrodes. The fabrication of nanometre-scale spaced electrodes still results in expensive, and often scarcely reproducible, devices. On the other hand, the 'conductance' of long organic molecules--generally dominated by the tunnelling mechanism--is very poor. Here, we show that by incorporating a large number of metal centres into rigid molecular backbones we can obtain very long (up to 40 nm) and highly 'conductive' molecular wires. The metal-centre molecular wires are assembled in situ on metal surfaces via a sequential stepwise coordination of metal ions by terpyridine-based ligands. They form highly ordered molecular films of elevated mechanical robustness. The electrical properties, characterized by a junction based on Hg electrodes, indicate that the 'conductance' of these metal-centre molecular wires does not decrease significantly even for very long molecular wires, and depends on the nature of the incorporated redox centre. The outstanding electrical and mechanical characteristics of these easy-to-assemble molecular systems open the door to a new generation of molecular wires, able to bridge large-gap electrodes, and to form robust films for organic electronics.
    Nature Material 03/2009; DOI:10.1038/nmat2401 · 36.43 Impact Factor
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    ABSTRACT: This paper describes the formation and electrical properties of a new Hg-based metal-molecules-metal junction that incorporates charged redox sites into the space between the electrodes. The junction is formed by bringing into contact two mercury-drop electrodes whose surfaces are covered by COO(-)-terminated self-assembled monolayers (SAMs) and immersed in a basic aqueous solution of Ru(NH(3))(6)Cl(3). The electrical behavior of the junction, which is contacted at its edges by aqueous electrolyte solution, has been characterized electrochemically. This characterization shows that current flowing through the junction on the initial potential cycles is dominated by a redox-cycling mechanism and that the rates of electron transport can be controlled by controlling the potentials of the mercury electrodes with respect to the redox potential of the Ru(NH(3))(6)(3+/2+) couple. On repeated cycling of the potential across the junction, the current across it increases by as much as a factor of 40, and this increase is accompanied by a large (>300 mV) negative shift in the formal potential for the reduction of Ru(NH(3))(6)(3+). The most plausible rationalization of this behavior postulates a decrease in the size of the gap between the electrodes with cycling and a mechanism of conduction dominated by physical diffusion of Ru(NH(3))(6)(3+/2+) ions (at larger interelectrode spacing), with a possible contribution of electron hopping to charge transport (at smaller interelectrode spacing). In this rationalization, the negative shift in the formal potential plausibly reflects extrusion of the solution of electrolyte from the junction and an increase in the effective concentration of negatively charged species (surface-immobilized COO(-) groups) in the volume bounded by the electrodes. This junction has the characteristics required for use in screening and in exploratory work, involving nanogap electrochemical systems, and in mechanistic studies involving these systems. It does not have the stability needed for long-term technological applications.
    Journal of the American Chemical Society 02/2009; 131(6):2141-50. DOI:10.1021/ja804075y · 11.44 Impact Factor
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    ABSTRACT: One of the main goals of molecular electronics is to achieve electronic functions from devices consisting of tailored organic molecules connecting two metal electrodes. The fabrication of nanometre-scale spaced electrodes still results in expensive, and often scarcely reproducible, devices. On the other hand, the `conductance' of long organic molecules-generally dominated by the tunnelling mechanism-is very poor. Here, we show that by incorporating a large number of metal centres into rigid molecular backbones we can obtain very long (up to 40nm) and highly `conductive' molecular wires. The metal-centre molecular wires are assembled in situ on metal surfaces via a sequential stepwise coordination of metal ions by terpyridine-based ligands. They form highly ordered molecular films of elevated mechanical robustness. The electrical properties, characterized by a junction based on Hg electrodes, indicate that the `conductance' of these metal-centre molecular wires does not decrease significantly even for very long molecular wires, and depends on the nature of the incorporated redox centre. The outstanding electrical and mechanical characteristics of these easy-to-assemble molecular systems open the door to a new generation of molecular wires, able to bridge large-gap electrodes, and to form robust films for organic electronics.
    Nature Material 01/2009; 8(1). DOI:10.1038/nmat2332 · 36.43 Impact Factor
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    ABSTRACT: Aiming at modulating the packing density within functional self-assembled monolayers (SAMs), two azo-biphenyl derivatives AZO1 and AZO2 comprising a terminal sulfur anchor group have been designed and synthesized. While AZO1 allows for a coplanar arrangement of both biphenyl subunits, additional steric repulsion due to two methyl side groups attached to the footing biphenyl of AZO2 results in an increased intermolecular distance within the SAM, providing additional free volume. SAMs of both derivatives on gold and platinum substrates have been formed and thoroughly investigated by photoelectron (XPS) and near-edge absorption fine structure (NEXAFS) spectroscopy as well as cyclic voltammetry and scanning tunneling microscopy. These measurements confirmed the formation of tightly packed SAMs for AZO1, while AZO2 formed SAMs consisting of less organized and more loosely packed molecules. Optical investigations of both azo derivatives in solution as well as their SAMs displayed efficient photoisomerization in solution and in SAMs. Comparable maximal cis/trans ratios of ca. 0.9 have been observed in all cases upon irradiation at λ = 370 and 360 nm for AZO1 and AZO2, respectively. The thermally induced cis → trans back reaction on AZO1 was found to be slower by a factor of 3 in SAMs as compared to solution, while AZO2 displayed comparable rates of the back reaction in both environments. This behavior can be explained by the different nature of molecular isomerization in the two SAM systems: whereas the isomerization in AZO1 SAMs takes place in a highly coordinated, collective way and involves many adjacent molecules, AZO2 species behave rather individually even packed in SAMs, such that their isomerization process is similar in SAMs and in solutions.
    Advanced Functional Materials 10/2008; 18(19):2972 - 2983. DOI:10.1002/adfm.200800652 · 11.81 Impact Factor
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    ABSTRACT: Conductance switching associated with the photoisomerization of azobenzene-based (Azo) molecules was observed in nanoscopic metal-molecule-metal junctions. The junctions were formed by using a conducting atomic force microscope (C-AFM) approach, where a metallic AFM tip was used to electrically contact a gold-supported Azo self-assembled monolayer. The measured 30-fold increase in conductance is consistent with the expected decrease in tunneling barrier length resulting from the conformational change of the Azo molecule.
    Journal of the American Chemical Society 08/2008; 130(29):9192-3. DOI:10.1021/ja8018093 · 11.44 Impact Factor
  • Electron Transfer in Chemistry, 04/2008: pages 337 - 408; , ISBN: 9783527618248
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    Angewandte Chemie International Edition 02/2008; 47(18):3407-9. DOI:10.1002/anie.200705339 · 11.34 Impact Factor
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    ABSTRACT: The electrical properties of two molecular wires-a novel aryl moiety, 6-(5-pyridin-2-ylpyrazin-2-yl)pyridine-3-thiol (PPPT), and the well studied 1,1';4',1."-terphenyl-4-thiol (TPT)-organized in self-assembled monolayers (SAMs) are measured using metal-molecule-metal (MMM) mercury-drop junctions. Current measured at the same bias voltage through PPPT is found to be more than one order of magnitude lower than through TPT. To interpret and understand these results, characterization of the structure, organization of the SAMs, and theoretical analyses of the molecular systems are discussed. X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS) indicate that although PPPT forms high-quality SAMs on both Au and Ag substrates, it exhibits a lower packing density (by 20 %) and less orientational order than TPT. In addition, electronic structure calculations with density functional theory (DFT) reveal that the electron-withdrawing nitrogen atoms in the PPPT aryl backbone stabilize the valence molecular electronic structure and pull negative charge from the thiol sulfur. This behavior can influence both charge-injection barriers and metal-molecule binding interactions in the MMM junctions. The current-voltage data are interpreted on the basis of a hole-tunneling, through-bond mechanism. Conductance analysis through a model for off-resonant tunneling transport suggests that a comparatively small difference in the charge-injection barrier can explain the factor of ten difference in observed conduction.
    Advanced Functional Materials 11/2007; 17(18):3816 - 3828. DOI:10.1002/adfm.200700459 · 11.81 Impact Factor
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    ABSTRACT: Photochromic systems can convert light energy into mechanical energy, thus they can be used as building blocks for the fabrication of prototypes of molecular devices that are based on the photomechanical effect. Hitherto a controlled photochromic switch on surfaces has been achieved either on isolated chromophores or within assemblies of randomly arranged molecules. Here we show by scanning tunneling microscopy imaging the photochemical switching of a new terminally thiolated azobiphenyl rigid rod molecule. Interestingly, the switching of entire molecular 2D crystalline domains is observed, which is ruled by the interactions between nearest neighbors. This observation of azobenzene-based systems displaying collective switching might be of interest for applications in high-density data storage.
    Proceedings of the National Academy of Sciences 07/2007; 104(24):9937-42. DOI:10.1073/pnas.0703748104 · 9.81 Impact Factor
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    ABSTRACT: This paper compares the structural and electrical characteristics of self-assembled monolayers (SAMs) of n-alkanethiolates, SCn (n = 10, 12, 14), on two types of silver substrates: one used as-deposited (AS-DEP) by an electron-beam evaporator, and one prepared using the method of template-stripping. Atomic force microscopy showed that the template-stripped (TS) silver surfaces were smoother and had larger grains than the AS-DEP surfaces, and reflectance-absorbance infrared spectroscopy showed that SAMs formed on TS substrates were more crystalline than SAMs formed on AS-DEP substrates. The range of current densities, J (A/cm2), measured through mercury-drop junctions incorporating a given SAM on AS-DEP silver was, on average, several orders of magnitude larger than the range of J measured through the same SAM on TS silver, and the AS-DEP junctions failed, on average, 3.5 times more often within five current density-voltage (J-V) scans than did TS junctions (depending on the length of the alkyl chains of the molecules in the SAM). The apparent log-normal distribution of J through the TS junctions suggests that, in these cases, it is the variability in the effective thickness of the insulating layer (the distance the electron travels between electrodes) that results in the uncertainty in J. The parameter describing the decay of current density with the thickness of the insulating layer, beta, was either 0.57 A-1 at V = +0.5 V (calculated using the log-mean of the distribution of values of J) or 0.64 A-1 (calculated using the peak of the distribution of values of J) for the TS junctions; the latter is probably the more accurate. The mechanisms of failure of the junctions, and the degree and sources of uncertainty in current density, are discussed with respect to a variety of defects that occur within Hg-drop junctions incorporating SAMs on silver.
    Journal of the American Chemical Society 05/2007; 129(14):4336-49. DOI:10.1021/ja0677261 · 11.44 Impact Factor
  • ChemPhysChem 03/2007; 8(4):493-493. DOI:10.1002/cphc.200790007 · 3.36 Impact Factor
  • ChemPhysChem 03/2007; 8(4):515-8. DOI:10.1002/cphc.200600672 · 3.36 Impact Factor
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    ABSTRACT: The electrochemical characterization of a series of redox sites absorbed at Hg surface by different interactions is reported. The redox centers, based on Fe(II) and Ru(II), are incorporated, respectively, in the molecules Fe(C5H5)(C5H4)(CH2)(4)SH and [Ru(NH3)(5-)NC5H4CH2NHCO(CH2)(10)SH](PF6), and are anchored on the Hg surface in one component self-assembled monolayers. The electrochemical behaviour of these systems indicates that redox centers are located onto a uniform, homogeneous environment at the external surface of the monolayer. We also report the electrochemical behaviour of the positively charged redox species [Ru(NH3)(6)](3+) when the Hg electrode surface is functionalized with a negatively charged SAM. The SAM is formed by 11-mercaptoundecanoic acid that exposes carboxylic acid groups to solutions of different pH values. At a pH lower than 4, the cyclic voltammograms show negligible current, and pH from 5 to 9, the voltammograms are essentially identical and show a well-defined redox wave. From a study of the voltammetric responses of the Ru(NH3)(6)(3+/2+) couple as a function of the electrolyte composition and concentration at pH 9, we suggest that the redox reaction takes place at the defects of the SAMs created by the repulsion of the -COO- head groups and that the current is determined by a diffusion-controlled mechanism. (c) 2006 Elsevier B.V. All rights reserved.
    Inorganica Chimica Acta 02/2007; 360(3):1095-1101. DOI:10.1016/j.ica.2006.08.030 · 2.04 Impact Factor

Publication Stats

2k Citations
353.82 Total Impact Points

Institutions

  • 1993–2014
    • University of Ferrara
      • Department of Chemical and Pharmaceutical Sciences
      Ferrare, Emilia-Romagna, Italy
  • 1999–2010
    • Harvard University
      • Department of Chemistry and Chemical Biology
      Cambridge, Massachusetts, United States
  • 2009
    • University of Catania
      • Department of Chemical Sciences
      Catania, Sicily, Italy
  • 1998
    • Max Planck Institute for Biophysical Chemistry
      Göttingen, Lower Saxony, Germany
  • 1996
    • New University of Lisbon
      • Faculty of Sciences and Technology
      Lisboa, Lisbon, Portugal