Utilization of nanoporous membranes as a filter for SERS detection

The aim of the project is to work parallely on two very different techniques in order to improve the detection of a particular charged molecules. The first subject deals with SERS (Surface Enhanced Raman Spectroscopy) sensors. Exploiting the Raman effect it’s possible to create a fingerprint of specific molecules collecting the energy exchange after the irradiation with a monochromatic flux. This analysis makes possible the detection of particular molecules in heterogeneus analytes. The main drawback of the Raman technique is the poor sensitivity, making necessary to find enhancement ways. For this purpose it’s possible to exploit the high power of the localized surface plasmons. Plasmons waves are coming from the excitation of collective vibrations of electrons that are propagating at the surface between a metal and a dielectric material. In the resonant condition and if the plasmons are confined in metal nanostructures the enhancement becomes really powerful and available for non-linear optical processes as Raman. For this reasons and their huge potentiality, SERS sensors have been widely investigated during the last years and many improvements have been carried out also due to the parallel growth in fabrication techniques of well defined nanostructures; the great advantage is that they can be designed with specific characteristics according to the investigated sample. In this work the sensor will be tested with two different proteins, BSA (Bovine Serum Albumin) and Lysozyme. The second investigated way is related to the increase of concentration of a charged molecule exploiting a polycarbonate mebrane characterized by nanopores with a conical shape. Applying an alternate voltage, zero in average, it’s possible to exchange the ions between the two sides of the membrane, anyway creating a favorite direction due to the particular shape of the pores. This property is based on the fact that molecules are facilitated to go on one side while they have some resistance to go back, leading to an asymmetry in the flux that can be appreciated with a rectification in the IV curves. The device working is tested with a charged polymer, Polystyrene Sulfonate (PSS) in order to characterize the energy variation created by the conical pores. Many possible applications can be furtherly investigated with this kind of effect in order to regulate the ions transport, in particular because the membrane acts in different ways for ions that vary in terms of size and diffusivity. The idea of the project is try to combine these two very different techniques: in fact the membrane in the best case can be used in order to increase the concentration of a charged molecule, to pump it on one compartment permitting to increase its detection with the sensor.