Development of Carbon-based Nano-structural Fluorescent Biosensor

Yingqi Zhang, The University of Western Ontario

Abstract

Detection systems with high sensitivity and selectivity are critical for daily health monitoring and clinical diagnostics. Nanomaterials have shown great potentials in user-friendly biomedical devices, such as biosensors, because of their special chemical and physical properties. Recently, carbon-based nanostructures have attracted great attentions in the application of miniaturized biomedical devices because of their enhanced optical properties and biocompatibility. Herein, this thesis focuses on developing carbon-based nanostructured biosensing systems by employing advanced fluorescence technologies.

Gene detection is vital for early-stage diagnosis of diseases, e.g., breast cancer. The first sensing system has been developed to quantitatively detect breast cancer-associated gene by using fluorescence resonance energy transfer (FRET) quenching mechanism. Carbon quantum dots (CQDs) acted as the FRET donor to generate the emission, λ_em=510nm, which can be quenched by graphene oxide nanosheets (GONSs) which is used as the FRET quencher. In the presence of the target DNA sequence, the fluorescence intensity (I_max) can be restored. The detection range of this DNA sensing system is from 0.25 to 2.5 μM. The limit of the detection (LOD) is around 0.24 μM. The carbon-based FRET sensing system can be further developed to detect monosaccharide, e.g. D-glucose. Concanavalin A (Con A) has been conjugated on CQDs which are linked to the dextran-conjugated GONSs. Due to the competitive reaction between the dextran and the glucose with Con A, the homogeneous carbon-based sensing system can measure glucose from 0.02 mM to 0.1 mM with the LOD around 0.0127 mM. In addition, carbon-based biosensing systems have been used to quantitatively measure lactoferrin (LF), one of the major functional proteins in maintaining human health due to its antioxidant, antibacterial, antiviral, anti-inflammatory activities. Two different fluorescence technologies have been employed in the design of carbon nanostructure-based LF biosensors; (1) FRET quenching and (2) fluorescence polarization (FP). Due to a stronger binding affinity between LF and a chosen aptamer, the GONSs coupled with the aptamer-conjugated CQDs can be replaced by LF which results in the restoration of I_max. LF can be detected from 4 μg/mL to 18 μg/mL which have an ability to diagnose Alzheimer’s disease by using salivary LF as biomarker. On the other hand, LF bonded to the aptamer-conjugated CQDs can make the degree of fluorescence polarization changed in the solution-based carbon nanostructured biosensing system. The results indicate that this FP-based biosensor can be used to detect tear LF, considered as biomarker of dye eye disease.

In summary, carbon nanostructured-based biosensing systems integrating with advanced fluorescence technologies have been developed for quantitatively detecting different biomolecules. The high sensitivity and selectivity of the developed carbon nanostructured-based biosensing systems could benefit in early-stage diagnosis of diseases.