Investigation of light-addressable potentiometric sensors for electrochemical imaging based on different semiconductor substrates

Abstract

Light-addressable potentiometric sensors (LAPS) and scanning photo-induced impedance microscopy (SPIM) have been extensively applied as chemical sensors and biosensors. This thesis focuses on the investigation of LAPS and SPIM for electrochemical imaging based on two different semiconductor substrates, silicon on sapphire (SOS) and indium tin oxide (ITO) coated glass. Firstly, SOS substrates were modified with 1,8-nonadiyne self-assembled organic monolayers (SAMs), which served as the insulator. The resultant alkyne terminals provided a platform for the further functionalization of the sensor substrate with various chemicals and biomolecules by Cu(I)-catalyzed azide alkyne cycloaddition (CuAAC) ‘click’ reactions. The CuAAC reaction combined with microcontact printing (μCP) was successfully used to create chemical patterns on alkyne-terminated SOS substrates. The patterned monolayers were found to be contaminated with the copper catalyst used in the click reaction as visualized by LAPS and SPIM. Different strategies for avoiding copper contamination were tested. Only cleaning of the silicon surfaces with an ethylenediaminetetraacetic acid tetrasodium salt (EDTA) solution containing trifluoroacetic acid after the ‘click’ modification proved to be an effective method as confirmed by LAPS and SPIM results, which allowed, for the first time, the impedance of an organic monolayer to be imaged. Furthermore, the 1,8-nonadiyne modified SOS substrate was functionalized and patterned with an RGD containing peptide, which was used to improve the biocompatibility of the substrate and cell adhesion. By seeding cells on the peptide patterned sensor substrate, cell patterning was achieved. Single cell imaging using LAPS and SPIM was attempted on the RGD containing peptide modified SOS substrate Finally, an ITO coated glass substrate was used as a LAPS substrate for the first time. The photocurrent response, the pH response, LAPS and SPIM imaging and its lateral resolution using ITO coated glass without any modification were investigated. Importantly, single cell images were obtained with this ITO-based LAPS system