Session: ASME Undergraduate Student Design Expo

Paper Number: 173341

Investigating Ionic Conditions for Reliable Alzheimer's Biomarker Detection in Poc Biosensors 

     Alzheimer’s disease is a progressive neurodegenerative disorder affecting more than 7.2 million Americans in 2025. The Alzheimer’s Association projects this number to rise to nearly 13 million by 2050. Alzheimer’s disease leads to cognitive and behavioral decline in an individual, placing an immense emotional and financial burden on patients, families, and healthcare systems. While there is no cure for the disease currently, it is understood that early detection is critical in slowing disease progression. Unfortunately, current early diagnostic methods such as PET scans and cerebrospinal fluid (CSF) analysis are invasive, expensive, and often highly specialized. These limitations emphasize the urgent need for an accessible and easy-to-use point-of-care (POC) diagnostic device for Alzheimer’s disease.
     In developing a POC device, it is critical to investigate how exposure to physiological environments may affect device performance. This study will contribute to understanding the operation of a POC device under physiologically relevant ionic conditions. This is vital in ensuring that data collected as baseline measurements for commercial use are more accurate and transferable in real-world applications. 
     In this study, an electrochemical POC diagnostic device is used to detect Alzheimer’s disease biomarkers, antigen Amyloid-beta 42, found in plasma from a simple finger-stick blood sample. The device features microfluidic channels capable of separating plasma from whole blood, with an integrated electrode. Detection is achieved by measuring capacitance changes resulting from antigen-antibody conjugation on the electrode surface, recognizing real-time changes in antigen concentration levels. For data collection, antigens are diluted in phosphate buffer solution (PBS) instead of blood plasma. When mimicking the physiological conditions of plasma in electrochemical settings, it is important to consider ionic strength, or the measure of a solution’s ion concentration, in relation to Debye length. When an electric potential is applied to the electrode, an electric field is created. Once in contact with an ion-containing solution, this field is screened, resulting in “charge screening.” This distance from the charged surface before the electric field is screened is quantified as the Debye length. In other words, due to the concentration of ions in plasma, the electrode is limited in its ability to detect surface interactions, diminishing the measurable capacitance change caused by biomolecular interactions, a critical factor in capacitive biosensing. Thus, it is imperative to systematically evaluate the effect of the Debye length and charge screening on the POC device.
     To achieve this, antigens will be diluted in phosphate buffer solutions of varying ionic strengths. Comparing the fabricated biosensor’s capacitance responses across these conditions will deepen our understanding of the interplay between ionic strength and biosensor signal detection. Preliminary findings suggest that the ionic strength of a solution significantly impacts biosensor sensitivity. In solutions of high ionic strength, the Debye length decreases, reducing the sensor’s ability to detect capacitance changes from antigen-antibody binding. This is seen with experimental data using PBS, an electrode experiencing a difference of only a few hundred picofarads from a 0.500 microliter drop of PBS to a PBS-diluted drop of antigens, picking up on only a few antigen-antibody interactions. However, over-diluted phosphate buffer solutions may not adequately mimic the physiological conditions, changing biomolecular behavior and baseline data. An optimal ionic concentration range must be determined, one that more accurately mimics physiological conditions and increases sensor sensitivity to detecting antigen-antibody interactions.
     This research considers ionic strength and Debye screening effects in the design and implementation of biosensors for early Alzheimer’s disease detection. Improving the understanding of these fundamental interactions supports the broader effort to engineer clinically viable biosensors for neurodegenerative disease detection, helping to realize a future where a practical and accessible diagnostic solution is available for early detection of a disease that poses one of the most significant public health challenges of the 21st century.

Presenting Author: Kinjal Gupta New Jersey Institute of Technology

Presenting Author Biography: Kinjal Gupta is an undergraduate sophomore majoring in Chemical Engineering at the New Jersey Institute of Technology (NJIT) and an Honors College student. She conducts undergraduate research at the Advanced Energy Systems and Microdevices Laboratory, where her work centers on increasing detection sensitivity of biomarker-based point-of-care diagnostic devices and microfluidic biosensors. Her academic interests lie at the intersection of chemical and mechanical engineering, with a particular focus on biomedical devices and materials science.

Authors:

Kinjal Gupta New Jersey Institute of Technology
Yudong Wang Georgia Institute of Technology
Eon Soo Lee New Jersey Institute of Technology