Recently, photoelectrochemical (PEC) signal transduction, with optical excitation and electronic readout, has been identified as a powerful transduction strategy for bioanalysis due to its high sensitivity and low limit-of-detection. Semiconductive materials have been used as the building blocks of PEC transducers, while plasmonic nanoparticles (NPs) are frequently used as signal amplifiers in these biosensors. Though these approaches have been previously used in PEC biosensing, the interaction between plasmonic and semiconductors NPs linked together through biomolecules are not currently well-understood. Herein, we developed new strategies for preparing photoelectrodes using solution-based methods to enhance the photocurrent of PEC transducers. These transducers were then used to investigate the interaction mechanisms between plasmonic NPs and the photoelectrodes with the goal of enhancing the limit-of-detection of PEC biosensors.
In order to create photoelectrodes that were fabricated using facile benchtop methods designed to enhance the photocurrent of PEC transducers, wrinkled scaffolds were used to fabricate photoelectrodes that show an order of magnitude enhancement in photocurrent compared to the planar electrodes. These electrodes were further used in label-free signal-off DNA biosensing without any amplification steps. Limit-of-detection of 200 times lower were reported using these wrinkled photoelectrodes, than planar electrodes.
Gold (Au) and TiO2¬ NPs were used as model materials to investigate the interaction between plasmonic and semiconductor NPs on a photoelectrode. The modulation of photocurrent was examined by varying the concentration of Au NPs and under different optical excitation wavelengths. UV light excitation provided larger photocurrent enhancement – at low concentration of Au NP – than visible light excitation. Furthermore, anodic photocurrent generation efficiencies by the photoelectrodes, which were prepared by using only Au NPs, were compared between interband and intraband excitation. The Au NP photoelectrodes demonstrated higher anodic photocurrent at interband excitation than intraband excitation and were further optimized by varying the size and deposition time of the Au NPs. Following this, Au NP- labeled DNA was used to study the effect of the distance between Au NPs and TiO2 NPs on the magnitude of the measured photocurrent. When Au NPs were in proximity with TiO2, they increased the generated photocurrent; however, they reduced the measured photocurrent when they were positioned further away from TiO2 NPs. Utilizing this switching behavior of PEC signals, a differential signal generation strategy was adopted to achieve a biosensor with enhanced sensitivity and signal-to-noise ratio.
Ultimately, we designed a PEC signal transduction strategy to detect nucleic acids without target labeling. In this assay, Au NP-labeled DNA was used as a signal-amplification-barcode that was introduced to the assay following target binding. This label-free PEC biosensor showed a low limit-of-detection (3 fM), broad (1 fM – 100 pM) linear range, and capability to detect single and double base-mismatched sequences of DNA. Thus, this work presents materials and signal transduction innovations that enhance the performance metrics of biosensors. / Dissertation / Doctor of Philosophy (PhD) / Detection and quantification of biomolecules is of utmost importance in early diagnosis, disease monitoring, prognosis, and disease management. In the past few decades, enormous efforts have been put towards utilizing photoelectrochemical (PEC) processes for biomolecular detection due to their high sensitivity. Gold nanoparticles are frequently being used to amplify the signal in the PEC bio-detection assay due to their plasmonic properties. However, the exact nature of the interaction between gold nanoparticles and the electrode material has not been determined. In this thesis, we investigated the interaction of gold nanoparticles with photoelectrode materials when they are separated by nucleic-acid sequences. Excitation energy and nucleic-acid length were varied to modulate the PEC current. The improved understanding of this interaction was further utilized to achieve a programmable response of nucleotide sensor from the photoelectrodes upon detecting the analyte of interest. We further developed different types of biosensing assay designs and examined their performance in terms of limit-of-detection, sensitivity, and specificity. Finally, we developed a new class of biosensor for detecting nucleic acids in bodily fluid and assessed the assay by using both electrochemical and PEC signal readout.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/26172 |
| Date | January 2021 |
| Creators | Saha, Sudip |
| Contributors | Soleymani, Leyla, Biomedical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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