Design and development of novel fluorescence-based detection methods for bio-analytes

• Main Author: Ng, Shue Mei
• Other Authors: Xing Bengang
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: DRNTU::Science::Chemistry
• Online Access: https://hdl.handle.net/10356/89647; http://hdl.handle.net/10220/47715
• Institution: Nanyang Technological University

Fluorescence-based detection methods are advantageous because of their high sensitivity, rapidity and simplicity. Furthermore, various fluorescent materials and sensing mechanisms can be used in the rational design of these methods, which also demonstrate the versatility of such methods to be tailored to detect various targets with high sensitivity and selectivity. In Chapter 1, we focused our discussion on two fluorescent materials, organic dyes and upconversion nanoparticles, as well as two commonly applied sensing mechanisms, namely photoinduced electron transfer (PET) and fluorescence resonance energy transfer (FRET). These would be used in the design and development of novel detection methods for a first-line antibiotic vancomycin (Van; Chapters 2 and 3) and an important neurotransmitter epinephrine (EP; Chapter 4). Toward the end of Chapter 1, a comprehensive and detailed discussion on current methods reported for Van detection is included to serve as a bridge for the introduction of our proposed method in Chapters 2 and 3. In Chapters 2 and 3, two organic PET-based probes were prepared and their ability to sense Van in a fluorescence “turn-on” manner were tested. The first probe consists of a triad made up of a squaraine dye conjugated to two anthraquinone molecules via Van-specific peptide sequences, i.e. Lys-D-Ala-D-Ala (Chapter 2). In the absence of Van, an energetically favourable electron transfer from the excited dye to anthraquinone resulted in fluorescence quenching of the triad, which was recovered upon the addition and binding of Van to the -D-Ala-D-Ala ligands. The detection mechanism of the triad was investigated using time-resolved spectroscopy. The second probe consists of the triad made up of a cyanine dye conjugated to two ferrocene moieties via Lys-D-Ala-D-Ala peptides (Chapter 3). In this case, fluorescence quenching in the absence of Van takes place via a hole-transfer process from the excited dye to ferrocene. An investigation of the influence of linker length between the cyanine dye and ferrocene on the hole-transfer quenching efficiency was also conducted. In Chapter 4, a novel FRET-based probe utilizing o-phenylenediamine (OPD)-conjugated upconversion nanoparticles was proposed for the detection of EP. The preparation of the conjugated nanoparticles and its application to sense EP are described in this chapter.