Davide Ricci

Atomic Force Microscopy in Biomedical Research

This chapter aims at giving a quick but precise introduction of the atomic force microscope from the working principle point of view. It is intended to provide a useful starting point to those who first approach the instrument giving a general sketch of the working principles and technical implementations as well as last improvements. Subheading 1 is introductory: it gives an overview of what the instrument does and why it has been developed. Subheading 2 is focused on measurement ranges and on the comparison with scanning electron microscope (SEM) and transmission electron microscope (TEM) which have similar ranges and resolutions but different sample interactions and applications. Subheading 3 gives an overview of the working principles and the most diffused technical implementations on which most of the commercial microscopes rely, as we think it gives the useful base knowledge to understand possible applications, instrument capabilities, and results. In particular, technical improvements taking place over the past few years are highlighted. Despite of the simple and not very technical approach, it has a key importance in understanding concepts at the base of Chapter 3, which is, on the other side, useful for beginners and experienced users as well. Subheading 4 compares different instrument architectures and can, therefore, be useful for those who are going to choose an instrument having clear final applications. Latest solutions are once more highlighted. Subheading 5 gives an overview and some suggestions to start working, both in air and in liquid. Following the general philosophy of the book, it follows more an “how to do” concept than a general theoretical approach. Subheading 6 contains the future developments of the techniques.

The neuron-transistor junction: linking equivalent electric circuit models to microscopic descriptions

Abstract This paper deals with a detailed analysis of the junction that develops whenever a neuron is cultured directly on the top of a planar substrate microtransducer consisting of an insulated field effect transistor (FET). The equivalent circuit description for a patch of excitable membrane sealed to the insulating layer of a FET is provided. The patch is described according to the Hodgkin-Huxley model. Various ranges of capacitance and resistance values have been considered, under physico-chemical assumptions concerning the junction local microenvironment. Different recorded signals of neuronal activity have been simulated as a function of these values. The signals well reproduce the experimental data reported in the literature, thus suggesting the appropriateness of the analysis for the characterization of hybrid neuro-electronic systems.

Assembling thiolated gold nanoparticles in compact patterns: a transmission electron microscopy and scanning probe microscopy investigation

We present results from a study of the deposition of synthesized dodecanethiol capped gold clusters onto solid substrates investigated using Transmission Electron Microscopy (TEM) and Scanning Probe Microscopy (SPM). TEM imaging of films prepared onto carbon coated grids using the drop cast method from cluster solutions that have undergone an increasing number of selective size separation steps show the efficacy of the vapor transfer technique in narrowing down the particle size distribution. In order to assemble the gold clusters in compact patterns and investigate their organization using SPM, we have prepared 1,4-benzenedimethanethiol self-assembled films onto heteroepitaxial gold on mica to be used as a substrate. A comparison of results obtained on this substrate using gold cluster films prepared with the drop cast method and the Langmuir-Blodgett (LB) technique is made. In the case of LB films made from size-selected nanoparticles, we present room temperature scanning tunneling images of clusters arranged in compact patterns.

Imaging Bacterial Shape, Surface, and Appendages Before and After Treatments With Antibiotics

Antibiotics are particular type of drugs that are able to interfere in different ways to the metabolic -pathways of bacteria. This causes also morphostructural alterations of cell wall and surface appendages (flagella, fimbriae or pili, and filaments).Atomic force microscopy (AFM) is extremely useful for analyzing the three-dimensional structure of the surface of biological specimens, particularly bacteria. A step-by-step AFM methodology to be applied to different type of bacteria is reported and visual examples of the action of antibiotics are shown. Although scanning electron microscopy is still frequently used, the introduction of the AFM technique offers substantial benefits in real quantitative data acquisition in three dimensions, minimal sample preparation times, flexibility in ambient operating conditions (i.e., no vacuum is necessary), and effective three-dimensional magnification at submicron level.

Scanning electron microscopy and atomic force microscopy of alkanethiol monolayers on gold

Abstract Alkanethiolates are adsorbed rapidly at gold and silver surfaces, forming monomolecular layers. These structures find applications in non-linear optics, molecular electronics, biosensors, adhesion and wetting. With the aim of studying the surface morphology of such structures at various magnifications, gold film surfaces covered with 1-octadecanethiol monolayers were inspected by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The evaporated gold films were covered using both the Langmuir-Blodgett (LB) and self-assembly methods. SEM images of films deposited by the vertical-dipping method show ridges roughly perpendicular to the dipping direction. The self-assembled (SA) monolayers have a more uniform aspect. Both LB and SA films can be distinguished from the gold surface by larger heap-shaped structures. Patchwork structures appear in films partially removed. AFM images with a magnification similar to that of the SEM images reveal more details of the surface morphology. Thioalkane monolayers appear less well defined than gold films, but the quantitative evaluation of the roughness of both surfaces brings about very similar results. Molecular resolution images of octadecanethiol monolayers show periodical structures attributed to vertically oriented alkane tails.

High Resolution Imaging of Physisorbed Organic Monolayers by Scanning Tunneling Microscopy

Abstract Scanning Tunneling Microscopy (STM) reveals details down to the molecular and submolecular scale. This paper presents STM images taken under solution of three well known organic compounds deposited on highly oriented pyrolitic graphite. Dotriacontane, stearic acid and tetracosanoic acid showed to form highly organized monolayers that have a characteristic two-dimensional structure. Conditions for high resolution and optimal contrast are discussed. Different monolayer packing for stearic acid in correspondence of two concentration values are also reported.

Strategies for tuning carbon nanotube plastic actuator performance through material hybridization and the thickness effect: a proof of principle

Bucky gel actuators are a kind of electrochemical actuator based on carbon nanotubes having interesting features. They are intrinsically safe because are operated at low voltage, they are lightweight and they are able to work in air without any liquid electrolyte. One key aspect that needs improvement is their actuation speed which is strongly dependent on their ability of being efficiently charged and discharged without exceeding the electrochemical stability window of the electrolyte. By proper material processing, we have successfully addressed this issue. An actuator thickness reduction to one third of the original size results in a one order of magnitude increase of both the strain at higher frequencies and the maximum operating frequency. The strain improvement at high frequency due to thinning has the sole drawback of decreasing the maximum strain that can be achieved in quasi-static conditions. We addressed this second issue by using a proper combination of actuating materials. Oxidative polymerization of pyrrole was carried out directly on preformed bucky gel slurry in order to combine the remarkable properties of ionic actuators based on carbon nanotubes and polypyrrole. A small amount of polypyrrole is sufficient to dramatically improve the overall actuator performance, and by using this hybrid it is possible to obtain thin actuators (about 0.1xa0mm) with superior performance even at lower frequencies.

Investigating Schottky Barriers Effects in Carbon Nanotube FETs

The paper addresses the issue of Schottky barrier effects in carbon Nanotube field effect transistors and outlines some solutions to tackle such problem. Microfabricated test patterns have been designed to allow the deposition in a controlled way of single wall nanotubes between different couples of source and drain electrodes in a backgate device architecture. Current‐voltage characteristics depending on the back gate applied voltage have been recorded and briefly discussed. Through a proper exploitation of ad‐hoc developed contact arrays for CNFET fabrication, a strategy for the direct measurement of metal‐CN and CN‐CN junction characteristics has been described.

Hybrid Nanostructures: Organic Interconnections and Device Applications

Silicon technology is rapidly progressing toward device sizes in the range of 10 nm. The evolution rate of silicon technology in next decades will require the use of new materials and processes to develop revolutionary CMOS devices. Organic nanostructures onto semiconductors or metals may provide interesting solutions to address the technological issues of nanoscale devices. In particular, technologies and devices based on organic nanostructures such as carbon nanotubes, semiconductor or metallic nanoparticles, DNA-templated nanowires may supply solutions for on-chip interconnections. The aim of this work is to present recent results on hybrid nanostructures based on gold nanoparticles stabilized by organic coating. Particular emphasis is devoted to the problem of the interconnections at the nanoscale. The resulting hybrid devices are suitable to develop single electron transistors and memories

SPM Investigation of Thiolated Gold Nanoparticle Patterns Deposited on Different Self-Assembled Substrates

We present the results of a Scanning Probe Microscopy (SPM) investigation of ordered nanosized metallo-organic structures. Our aim is to investigate the organization and stability of thiolated gold nanoparticles in a compact pattern when deposited onto gold substrates functionalized with self-assembled monolayers made from two molecules that differ essentially in their terminating group: 1,4-benzenedimethanethiol and 4-methylbenzylthiol.