Interface Modulation of Fluorescent and Raman-active Nanomaterials for the Selective Detection of Cancer and Dementia Biomarkers

Abstract

Nanomaterials-based biosensors (denoted “nanobiosensors”) have exhibited the improved sensitivity and selectivity for the detection of biomarkers, including proteins and oligonucleotides specific to human diseases, as compared to conventional biosensing systems. The sensing performance such as sensitivity and selectivity of nanobiosensors for the biomarkers depends strongly on their interfacial structures in nanobiosensors as well as nanomaterials’ intrinsic properties. The interfacial structures of the nanomaterials employed in nanobiosensors are varied by the types and coverages of wrapping molecules, specifically, and recognition ligands, covertures, and surface charge balance etc. Hence, it is of great significance to control the interfaces of nanomaterials by adjusting the aforementioned factors in nanoscale to improve the sensing sensitivity and selectivity of nanobiosensors. However it still remains a big challenge to develop a facile and effective approach for the modulation of the interfaces of nanomaterials to provide nanobiosensors with reproducible sensing sensitivity and selectivity in clinical trials.

In this thesis, the several approaches for the effective modulation of the interfaces of nanomaterials, including transition metal dichalcogenides (TMDs), silica nanoparticles (Si-NPs), and carbon nanotubes (CNTs), were investigated to develop the novel nanobiosensors with improved sensing sensitivity and selectivity for the detection of biomarkers specific to cancer or dementia.

Specifically, in Chapter 1, the interface of WS2 nanosheets (WS2-NSs) was tuned by varying the functional groups of a dextran polymer for the selective and sensitive detection of micro-RNA (miR-29a) known as a biomarker for Alzheimer’s disease. WS2-NSs were exfoliated and functionalized with the dextran polymers bearing hydroxyl, phenoxy, carboxylic acid, or trimethylamonium group through ultra-sonication in water, providing four different functional dextran/WS2 nanohybrids (f-dex-WS2). The f-dex-WS2 exhibited unique binding affinities toward single-stranded DNA labelled with a fluorescent dye FAM (ssDNA-FAM): Especially, the WS2 with a carboxyl group (CM-dex-WS2) had the highest binding affinity of 0.38 nM to ssDNA-FAM while the WS2 with a trimethylamonium group (TMA-dex-WS2) showed 6.13 nM, leading to the fluorescence quenching of FAM. In addition, desorption of the double-stranded DNA consisting of a probe DNA and miR-29a (dsDNA-miR-29a) was controlled by the different polymeric interfaces: Specifically, TMD-dex-WS2 showed the highest desorption efficiency of dsDNA-miR-29a, resulting in restoration in the quenched fluorescence for the detection of miR-29a. Finally, this interface modulation allowed TMA-dex-WS2 to successfully detect miR-29a at the concentration as low as 10 nM in human serum.

In Chapter 2, the interface of silica nanoparticles was modified with Ag nanogap shells (denoted “Ag-NGSs”) as a surface-enhanced Raman scattering (SERS) nanoprobe for the sensitive and selective detection of Aβ42 peptide for diagnosis of Alzheimer’s disease. The surface of Si-NPs was functionalized with thiol group, followed by reduction of Ag ions to produce Ag nanoparticles on their surface. When the Ag ions were reduced on the Si-NPs, a Raman chemical, 4-bromobenzenethiol (4-BBT), was simultaneously added to generate the nanogap between the grown Ag nanoparticles. In the nanogap of Ag-NGSs, 4-BBT was entrapped, giving rise to the generation of unique, stable, and very strong SERS signals with enhancement of more than 104. Subsequently, the Ag-NGSs were functionalized with self-assembled monolayer and anti-Aβ42 antibody for the specific detection of Aβ42, denoted “a Ag-NGS nanoprobe”. Finally, the Ag-NGS nanoprobe was able to detect Aβ42 peptide at the concentration as low as 113 ng/mL in human serum.

In Chapter 3, single-walled carbon nanotubes were modified with an antibody (denoted “SBA”) through a biorthogonal conjugation method using cotinine and an anti-cotinine tandem antibody for the effective detection of a cancer biomarker. The effective control over antibody orientation and density on the surface of carbon nanotubes was achieved by site-specific binding between the anti-cotinine domain of the bispecific tandem antibody and the cotinine group of the functionalized carbon nanotubes. The SBA showed an enhanced binding affinity (4.7 nM) against HER2, which was three times larger than that of the CNT bearing a randomly conjugated tandem antibody prepared by EDC coupling (1.5 μM). Finally, the SBA was successfully applied to detection of HER2 on living breast cancer cells through its strong Raman signals.