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Working Towards Ultrasensitive, Affordable Sensors for Glucose and Glyphosate

byZEISS Microscopy 8 November 2021 3 min read

Introduction

Researchers develop a new method to produce nanoporous gold particles on a transparent substrate using scanning electron microscopy.

The fabrication of micro and nano metallic structures, including nanoparticles, nanoholes and nanofibers, presents a challenging area especially in the material science domain.

Dr. Francesco Ruffino is an Associate Professor of Experimental Physics at the University of Catania, Italy. His research is focused on the study and fabrication of metal-based nanostructures, nanomaterials and nanocomposites and on their applications in some important technological fields connected to the challenges of human society.

In C. Awada et al., he presents findings on optical enhancement in gold/silver (Ag/Au) alloys and porous gold nanostructures. Scanning electron microscopy was one tool he used to develop this research.

One of our goals is to produce ultrasensitive, low-cost, stable, selective sensors for various chemical agents with improved characteristics. We recently developed a graphene-gold nanocomposite which can be used as a non-enzymatic electrochemical sensor for glucose. This could be important in the reliable diagnosis and treatment of diabetic pathologies.

Dr. Francesco Ruffino Associate Professor of Experimental Physics at the University of Catania, Italy

A New Method to Produce Nanoporous Gold Particles on a Transparent Substrate

Morphology Analyzed by Scanning Electron Microscopy

Scanning electron microscopy image of alloy Au/Ag particles produced by the melting, alloying and dewetting processes of a nanoscale-thick Au-Ag bilayers irradiated by a nanosecond-pulsed laser.

Production of Nanoporous Gold Particles on a Transparent Substrate

Their recent work results from an international collaboration with the University of Catania, the Institute for Microelectronics and Microsystems of the Italian National Research Council, the King Faisal University in Saudi Arabia and the University of Montréal in Canada.

They developed a new method to produce nanoporous gold particles on a transparent substrate. This method is based on the ultrafast laser processing of a nanoscale-thick gold-silver bilayer deposited on the substrate to induce the gold and silver melting, alloy and nanoparticle formation by a dewetting process. This is followed by the silver removal from the nanoparticles by an opportune chemical etching with the consequent rearrangement of gold in the form of nanoporous particles.

Raman spectra of methylene blue molecules on porous gold and glass substrate (a) and Au/Ag alloys (b)

Nanoporosity Gives Peculiar Optical Properties

This nanoporosity gives the particles peculiar optical properties as was tested at the King Faisal University by the Surface Enhanced Raman Spectroscopy technique. In brief, the plasmonic properties of gold in combination with the nanoporosity leads to the enhancement, by orders of magnitude, of the local electromagnetic field. This enhancement affects the Raman response of the material and this can be used for the ultrasensitive sensing of very small amounts of molecules adsorbed on the gold surface. These results were supported by an extensive simulation work performed at the University of Montréal.

Morphology of Nanoporous Gold Particles

Analyzed using Scanning Electron Microscopy

Scanning electron microscopy image of nanoporous Au particles obtained by the dealloying process of AuAg particles resulting from the chemical etching (in HNO3 solution) of the Ag atoms from the alloy particles. — Scanning electron microscopy image of nanoporous Au particles obtained by the dealloying process of AuAg particles resulting from the chemical etching (in HNO₃ solution) of the Ag atoms from the alloy particles.

Scanning Electron Microscopy in this Research

All the properties of nanostructures and nanomaterials are strongly dependent on their morphology. In this specific case, the surface enhanced Raman properties of the nanoporous gold particles are strongly determined, as suggested by the simulation work, by the particles’ morphology including porosity, pore size and gold ligament size. At each step of the fabrication process, microscopic analysis is fundamental to image the nanoparticles and to quantify the corresponding morphological characteristics. To this end, scanning electron microscopy was used.

Dr. Ruffino is planning to expand on this result to fabricate some prototypes of ultrasensitive optical sensors, for example in glucose and glyphosate sensing.

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