Enhanced Stability and Sensitivity for CA-125 Detection\nUnder Microfluidic Shear Flow Using Polyethylene Glycol-Coated Biosensor

The microfluidic-based\npoint-of-care (POC) diagnostic tool has\ngarnered significant interest in recent years, offering rapid and\ncost-effective disease detection. There is a growing trend toward\nintegrating microfluidic platforms with biosensors, aligning lab-on-a-chip\ntechnologies with POC diagnostic devices. Despite numerous efforts\nto incorporate biosensors into microfluidic systems, researchers have\nperformed very limited investigations on the stability of biomarker\ndetection when biosensors operate under microfluidic shear flow conditions.\nGold nanoparticles (AuNPs) are a widely employed material in capacitive\nbiosensors for antibody immobilization and sensitivity enhancement.\nHowever, AuNPs have limitations in providing stable detection of biomarkers\nwithin microfluidic shear flow due to their agglomeration nature.\nThis study addresses these limitations by employing 2 kDa polyethylene\nglycol (PEG) as an intermediate biofunctional layer to immobilize\nCA-125 antibodies on gold-interdigitated electrodes for the stable\nand accurate detection of CA-125 antigens. The stabilities and sensitivities\nof AuNPs and PEG-coated biosensors are evaluated under both static\ndrop and microfluidic shear flow conditions for CA-125 antigen detection.\nThe experimental results demonstrate a capacitive signal response\n(5660 pF at 10 kHz) 2.2 times higher using the PEG-coated biosensor\nthan the signal (2551 pF at 10 kHz) measured by the AuNP-coated biosensor\nin the detection of CA-125 antigen–antibody conjugation under\nstatic drop conditions, indicating the higher sensitivity of the PEG-coated\nbiosensor. Additionally, the PEG-coated biosensor exhibits better\nconsistency for the CA-125 antigen detection between static drop and\nmicrofluidic shear flow conditions (Cp decrease in percentage (ΔCp%↓)\n= 2.9% at 10 kHz) compared to the electrical signals measured using\nthe AuNP-coated biosensor (ΔCp%↓ = 32.4% at 10 kHz),\nwhich suggests that the PEG-coated biosensor demonstrates higher stability\nfor CA-125 antigen detection under microfluidic shear flow conditions.\nWith these significant improvements brought by the PEG-coated biosensor,\nespecially under microfluidic conditions, a substantial hurdle in\ndeveloping electrical biosensors for POC diagnostic applications has\nbeen overcome, expediting further advancements in the field.