Master of Science in Engineering, Youngstown State University, 2024, Department of Civil/Environmental and Chemical Engineering

Wearable biosensors have become a valuable tool for their promising applications in personalized medicine. Cortisol is a biomarker for various diseases and plays a key role in metabolism, blood pressure regulation, and glucose levels. In this study, we fabricated an interdigitated laser-induced graphene (LIG) biosensor for the non-faradaic impedimetric detection of cortisol in sweat. A direct laser writing technique was used to produce the LIG. Gold nanoparticles (AuNPs) were electrochemically deposited onto the surface to enhance impedance response. A Self-Assembled Monolayer (SAM) was formed with on the AuNPs via 3-Mercaptopropionic acid (MPA) thiol chemistry. The carboxylic acid (-COOH) groups of the MPA were activated using EDC/NHS chemistry. Following activation, anti-cortisol antibodies were immobilized on the surface. Lastly, the LIG was incubated in the blocking agent bovine serum albumin (BSA) to avoid unwanted detection. Surface characterization of the LIG was performed at each step of modification by Electrochemical impedance spectroscopy (EIS) in a phosphate buffered saline (PBS) solution containing a 5 mM Fe(CN)3-/4- (1:1) redox couple. Further characterization of the modified LIG electrode was achieved through Fourier transform infrared (FT-IR), surfaced-enhanced Raman spectroscopy (SERS), and X-ray diffraction (XRD). The detection experiment using EIS was conducted in increasing concentrations of cortisol (0.1 pM-100 nM) in PBS. The ZMod decreased logarithmically (R2=0.97) with a 0.0085 nM limit of detection. Reproducibility was examined by percent change of ZMod at 100 nM and a 5.93%RSD (n=5) was observed. Additional analysis of sensor specificity and interference studies showed no substantial effect on detection. This research establishes the feasibility of using the gold nanoparticle decorated LIG electrode for flexible, wearable cortisol sensing devices, which would pave the way towards an end-user easy-to-handle biosensors as point-of-care diagno (open full item for complete abstract)

Committee: Byung-Wook Park PhD (Advisor); Frank Li PhD (Committee Member); Jonathan Caguiat PhD (Committee Member) Subjects: Biochemistry; Chemical Engineering; Chemistry; Engineering