Gold Nanotubes For Smart Biosensors: Synthesis And Characterization

The development of reliable electrochemical biosensors is a field of great importance in nowadays technology since they are very promising to replace a wide range of analytical techniques thanks to their unique and specific properties and characteristics. In recent years biosensors have been developed and used as reliable miniaturized devices able to perform sophisticated controls interesting many areas like nanotechnology, biology, environmental quality, and more specifically the general areas of rapid diagnostic essays. Rapid detection of many organic compounds depends to a large extent on the ability of biosensors to specifically and selectively recognize a target molecule, even in a complex or harsh environment. A crucial problem in the commercial development of electrochemical biosensors is the ability to immobilize an enzyme on an electrode surface without incurring in the loss of its biological activity. Many methods have been proposed to overcome this problem, among which the use of self-assembling monolayer as anchor layers for the enzyme molecules has been extensively studied by many research groups. However, the main problem with the use of monolayers is that only a very small amount of enzyme is immobilized and this will turn to a very low amperometric response of the biosensor. The use of gold nanotubes as electrodes provides a huge surface area per unit volume thus allowing the immobilization of a large amount of enzyme. In this work we report the preparation and characterization of gold nanotubes arrays to be used as a starting point for the realization of electrochemical biosensors. The specificity of this work is the characterization performed after each step of deposition, giving a complete analysis of the different phases of nanotube nucleation and evolution. Gold nanotubes were prepared by electroless deposition of the metal within the pores of polycarbonate particle track-etched membranes (PTM). The template method is particularly interesting, because it allows to include metallic constituents inside the void spaces of nanoporous host materials: nanomaterials with monodisperse diameters and controlled lengths are obtained. Different synthesis parameters, such as membrane pore diameters and different deposition time have been investigated. After each synthesis step, a complete chemical and morphological characterization was performed using techniques as Atomic Force Microscopy (AFM), Field Emission Gun Scanning Electron Microscopy (FEG-SEM), and X-Ray Photoelectron Spectroscopy (XPS). The results provide several interesting information about the growth mechanism of gold nanotubes, from the early stages of nucleation up to a 3-D structure. This offers excellent opportunities to select the best morphology of gold nanotube arrays for the assembling of smart electrochemical sensors and biosensors.