Development of a photoelectrochemical current microscope

This thesis describes the activity that I carried out during the internship at the Department of Physics and Astronomy (DIFA) of the University of Bologna, which focused on the development of a photoelectrochemical current (PEC) microscope. PEC microscopy is an emerging technique that aims at monitoring chemical and biological processes in real-time using the tools of photoelectrochemistry. At the core of the herein presented PEC microscope lies a three-dimensional actuator system, a focused light source, a lock-in amplifier and a photoelectrochemical cell. The novelty of the developed PEC mi- croscope is the photoelectrode, i.e the p-n organic heterojunction (H2Pc/PTCDI), which is highly biocompatible, stable in physiological solution and does not require an external bias. The p-n junction devices were fabricated at the Central European Institute of Technology (CEITEC) by the group of Dr. Eric D. Glowacki. The actuator system consists in two Physik Intrumente (PI) linear stages that controls the in-plane motion by performing either one/two dimensional scans in continuous/discrete fashion with a sub-micron accuracy. The focused light source was crafted using Thorlabs optical components, following optical simulations and experimental criteria, resulting in a 2.59 ± 0.03 μm radius circular light spot at the focus. Several experiments were carried out to assess the performances of the PEC microscope, such as an imaging test with SiO2 microbeads that confirmed the synchronism of the imaging system as well as the spatial resolution of the microscope, which was evaluated to be at least of 5.7 ± 0.2 μm. Lastly, experiments with the living cells (glioma cell line, T98G) seeded on the pn electrodes allowed to resolve cells position by changes in the photocurrent phase, for the first time. The proposed microscope is very general and can be used with any photoactive material for scanning photocurrent microscopy applications.