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Biomedical Imaging and Instrumentation

Biomedical Imaging and Instrumentation - Poster Session C

Poster G1 - Laser-Induced Graphene for Electrochemical Sensing for Low-Cost Point of Care Devices

Friday, October 25, 2024

10:00 AM – 11:00 AM EST

Location: Exhibit Hall E, F & G

Presenting Author(s)

Julia J. Szela

Undergraduate Research Assistant
Purdue University
Wayne, Pennsylvania, United States

Co-Author(s)

Barrett Davis

Graduate Researcher
Purdue University - Weldon School of Biomedical Engineering, Indiana, United States

Primary Investigator(s)

TK

Tamara Kinzer-Ursem, PhD (she/her/hers)

Professor, Associate Dean
Purdue University, United States

Introduction: Point-of-care (PoC) health screening tools, particularly paper-based lateral flow immunoassays (LFIA), are widely used for the categorical detection of viral infections. However, compared to electrochemical assays, LFIA are ill-suited for the robust quantification of sample analyte concentration, lacking appropriate specificity and limits of detection. Enhancing current paper-based methods through the integration of electrochemical sensing capabilities would allow for the earlier detection of sample analytes and any changes in their concentration over time with serial testing. Here we designed a paper-based capacitive biosensor comprising of interdigitated sensing, counter, and reference electrodes with the goal of functionalizing the sensing electrode by antibodies or nucleic acid probes. Where previous works that sought to include electrical sensing modalities into PoC platforms relied on supplemental measurement equipment, our new biosensor design directly interfaces with USB-type C receptacles to leverage the integrated analog-to-digital conversion hardware of smartphones or portable computers for this purpose.

Materials and

Methods: To circumvent the need for specialized inks or metal deposition processes, we used a one-step CO2 laser treatment process to create electrically conductive, laser-induced graphene (LIG) traces atop a paper cardstock substrate. The same laser was used to cut individual biosensors into a USB type-C compatible form factor in the X and Y dimensions, and a hydraulic press was used to ensure an appropriate thickness in the Z dimension. The dimensional accuracy of manufactured biosensors was verified by manual inspection with calipers. The effect of laser fluence on the sheet resistivity of the induced graphene traces was investigated by adjusting laser power, focus and dwell-time. Observations from this step were used to create a computational model to guide future trace resistivity minimization. The electrical compatibility of manufactured biosensors with USB-type C receptacles was verified by measuring signal fidelity across a test design inserted into a USB-C breakout board via an oscilloscope. Effective capacitances of the biosensor electrodes were measured by pipetting 50 microliters of PBS onto the device, applying a 48 kHz square wave, and fitting the measured charge and discharge curves to first-order exponential functions. The suitability of this platform for on-chip heating was also assessed by applying a 5V DC signal and recording temperature changes through infrared thermography.

Results, Conclusions, and Discussions: We demonstrated that laser-induced graphene traces could be created on a paper cardstock substrate and directly integrated into a USB type-C receptacle. After treating the cardstock with an effective laser fluence of 38 Joules per square centimeter, we recorded a minimum sheet resistance of approximately 1 Ohms square. We also found that this sheet resistance could be tuned between 1 to 18 Ohms square by changing the pre-programmed CO2 laser cutter settings to output effective laser fluences between 25 to 50 Joules per square centimeter. Initial measurements of capacitance for the platform’s non-functionalized sensing and counter electrodes revealed repeatable differences of 300 to 400 fF which we attribute to small differences in interface lengths along the reference electrode. By pre-calibrating these differences, we expect to be able to distinguish between changes in capacitance from target analyte binding and non-specific binding with a functionalized sensing electrode. Additionally, while testing the platform’s capability as a standalone heater, we recorded a maximum temperature change of 109 degrees Celsius over 4.5 seconds with a constant 5V power supply. This rapid change in temperature was achieved with an average current draw of approximately 20 mA and demonstrates strong potential for use in low-power nucleic acid amplification. Future work will include conducting an XPS study to analyze the chemical composition of the electrode surfaces. Additionally, we intend to conjugate the sensing electrode with HIV1 p24 monoclonal antibodies to test the biosensor’s specificity and sensitivity against dilute analyte solutions. Ultimately, we will develop a smartphone app interface to integrate with the USB-C biosensor and provide user-friendly output information.

Acknowledgements (Optional):