Design, Fabrication, and Testing of Graphene Oxide-Based Biosensing Platforms

Abstract

Timely and accurate disease diagnosis remains a cornerstone of effective healthcare delivery, but many current diagnostic tools, such as PCR and ELISA, require centralized laboratory infrastructure, trained personnel, and extensive processing times. These constraints limit their accessibility and scalability, especially in resource-limited settings. Biosensors offer a promising alternative; providing rapid, label-free detection with potential for point-of-care deployment. However, despite extensive academic research, most biosensor platforms struggle to transition beyond proof-of-concept due to fabrication complexity, low yield, and limited integration into scalable systems.

This thesis explores two nanomaterial-based strategies designed to address these challenges. First, I use femtosecond laser ablation to fabricate a reduced graphene oxide and gold nanocomposite substrate for surface-enhanced Raman spectroscopy (SERS). Using a 24-mer DNA sequence as a target analyte, this platform achieves a limit of detection (LOD) of 10\textsuperscript{-7} M of its complementary DNA. Compared to conventional colloidal SERS substrates, this nanocomposite demonstrates improved hotspot distribution and substrate uniformity, indicating its promise for scalable nucleic acid detection.

Second, I investigate boron nitride–doped reduced graphene oxide field-effect transistor (FET) biosensors, focusing on device yield and fabrication reproducibility. Across multiple batches of devices, I identify failure modes including fabrication inconsistencies, gel synthesis variability, and passivation requirements. By analyzing these trends and benchmarking our device performance against current market diagnostic tools for COVID-19, I propose practical modifications to enhance reliability and consistency.

Collectively, these projects demonstrate how laser ablation–based defect engineering of graphene materials can advance biosensor platforms from experimental prototypes toward scalable, clinically relevant technologies. By emphasizing fabrication scalability, electrical reliability, and molecular sensitivity, this work contributes to the growing effort to align high-performance biosensing with real-world applicability.