Poly-and oligothiophenes : Optical probes for multimodal fluorescent assessment of biological processes

Abstract

IICover: Fibroblasts and melanoma cells stained with a fluorescent thiophene probe called p-HTIm, DAPI and antibodies against ER, proteasomes, α-tubulin, fibronectin, or mitotracker against mitochondria.During the course of the research underlying this thesis, Karin Magnusson was enrolled in Forum Scientium, a multidisciplinary doctoral program at Linköping University, Sweden. ABSTRACTOne interesting class of molecules in the research field of imaging biological processes is luminescent conjugated polythiophenes, LCPs. These fluorescent probes have a flexible backbone consisting of repetitive thiophene units. Due to this backbone, the probes possess unique abilities to give rise to different spectral signatures depending on their target and environment. LCPs are a polydispersed material meaning there is an uneven distribution of lengths of the probe. Recently, monodispersed chemically well-defined material denoted luminescent conjugated oligothiophenes, LCOs, with an exact number of repetitive units and distinct sidechain functionalities along the backbone has been developed. LCOs have the advantages of being smaller which leads to higher ability to cross the blood brain barrier. The synthesis of minor chemical alterations is also more simplified due to the well-defined materials. During my doctoral studies I have used both LCPs and LCOs to study biological processes such as conformational variation of protein aggregates in prion diseases and cellular uptake in normal cells and cancer cells. The research has generally been based on the probes capability to emit light upon irradiation and the interaction with their targets has mainly been assessed through variations in fluorescence intensity, emission-and excitation profiles and fluorescence lifetime decay. These studies verified the utility of LCPs and LCOs for staining and discrimination of both prion strains and cell phenotypes. The results also demonstrated the pronounced influence minor chemical modifications have on the LCO´s staining capacity. IV POPULÄRVETENSKAPLIG SAMMANFATTNING LYSANDE MOLEKYLER FÖR STUDIER AV BIOLOGISKA PROCESSERLuminiscenta konjugerade polytiofener, LCPs, är en väldigt intressant typ av molekyl som kan användas för att studera processer i biologiska system. Strukturen hos dessa fluorescerande molekyler kan liknas vid olika element som är fästa vid en ryggrad. De olika elementen ger molekylen dess affinitet för sin målmolekyl, medan ryggraden är mest ansvarig för molekylens optiska egenskaper. Ryggraden ändrar sin struktur beroende på målmolekylen och resultatet kan avläsas med ett flertal fluorescens-metoder. Längden på ryggraden hos LCPs varierar och varje parti av en LCP består därmed av en blandning längder och storlekar. De senaste åren har Peter Nilssons forskargrupp utvecklat LCPs till molekyler med väldefinierad längd på ryggraden som då betecknas luminiscenta konjugerade oligotiofener, LCOs. Dessa mindre molekyler har större möjlighet att passera blodhjärnbarriären samt att syntesen för små kemiska modifieringar av elementen ...

A Perspective on Polythiophenes as Conformation Dependent Optical Reporters for Label-Free Bioanalytics

“…These LCOs are synthesized by adding required units one-by-one. Although during the synthesis of LCOs, few purification steps are required, unlike PT synthesis, LCOs have reported several advantages compared to PTs, ,, because LCOs with a monodisperse size have consistent absorption and emission spectra. PT optical response is mainly dependent on the electrostatic interactions between the analyte and PT.…”

“…Thus, changes in the conjugation length directly affect the band gap of PTs, which eventually causes significant changes in absorption and emission. Moreover, stacking of PT chains results in aggregation, causing abrupt changes in optical response; a red shift in the emission spectrum and a decrease in fluorescence intensity due to the nonradiative energy transfer. − ,,,− The collective response of PTs in the form of backbone conformational rearrangement or aggregation is the fundamental sensing mechanism of PTs, making them highly sensitive and responsive to their surroundings.…”

“…Employing the PTs with unique side chains R, Figure A, that specifically interact with a target and bring about a conformational change in its backbone offers an attractive avenue for developing biosensors to detect various analytes. The interactions between side chains and the analyte induce conformational changes in the PT backbone or a change in the aggregation state of PTs in solution and in solid-state, further modulating the optical spectra. ,,,,,,− …”