@article{khanwalker_hatada_labelle_sode_2024, title={Development of an electrochemical impedance spectroscopy immunosensor for insulin monitoring employing pyrroloquinoline quinone as an ingestible redox probe}, volume={250}, ISSN={["1873-4235"]}, url={https://doi.org/10.1016/j.bios.2024.116049}, DOI={10.1016/j.bios.2024.116049}, abstractNote={Contemporary electrochemical impedance spectroscopy (EIS)-based biosensors face limitations in their applicability for in vivo measurements, primarily due to the necessity of using a redox probe capable of undergoing oxidation and reduction reactions in solution. Although previous investigations have demonstrated the effectiveness of EIS-based biosensors in detecting various target analytes using potassium ferricyanide as a redox probe, its unsuitability for blood or serum measurements, attributed to its inherent toxicity, poses a significant challenge. In response to this challenge, our study adopted a unique approach, focusing on the use of ingestible materials, by exploring naturally occurring substances within the body, with a specific emphasis on pyrroloquinoline quinone (PQQ). Following an assessment of PQQ's electrochemical attributes, we conducted a comprehensive series of EIS measurements. This involved the thorough characterization of the sensor's evolution, starting from the bare electrode and progressing to the immobilization of antibodies. The sensor's performance was then evaluated through the quantification of insulin concentrations ranging from 1 pM to 100 nM. A single frequency was identified for insulin measurements, offering a pathway for potential in vivo applications by combining PQQ as a redox probe with EIS measurements. This innovative approach holds promise for advancing the field of in vivo biosensing based on the EIS method.}, journal={BIOSENSORS & BIOELECTRONICS}, author={Khanwalker, Mukund and Hatada, Mika and LaBelle, Jeffery T. and Sode, Koji}, year={2024}, month={Apr} }
 @article{lee_kane_khanwalker_sode_2022, title={Development of an electrochemical impedance spectroscopy based biosensor for detection of ubiquitin C-Terminal hydrolase L1}, volume={208}, ISSN={["1873-4235"]}, url={https://doi.org/10.1016/j.bios.2022.114232}, DOI={10.1016/j.bios.2022.114232}, abstractNote={Year over year, the incidence of traumatic brain injury (TBI) in the population is dramatically increasing; thus, timely diagnosis is crucial for improving patient outcomes in the clinic. Ubiquitin C-terminal hydrolase L1 (UCH-L1), a blood-based biomarker, has been approved by the FDA as a promising quantitative indicator of mild TBI that arises in blood serum shortly after injury. Current gold standard techniques for its quantitation are time-consuming and require specific laboratory equipment. Hence, development of a hand-held device is an attractive alternative. In this study, we report a novel system for rapid, one-step electrochemical UCH-L1 detection. Electrodes were functionalized with anti-UCH-L1 antibody, which was used as a molecular recognition element for selective sensing of UCH-L1. Electrochemical impedance spectroscopy (EIS) was used as a transduction method to quantify its binding. When the electrode was incubated with different concentrations of UCH-L1, impedance signal increased against a concentration gradient with high logarithmic correlation. Upon single-frequency analysis, a second calibration curve with greater signal to noise was obtained, which was used to distinguish physiologically relevant concentrations of UCH-L1. Notably, our system could detect UCH-L1 within 5 min, without a washing step nor bound/free separation, and had resolution across concentrations ranging from 1 pM to 1000 pM within an artificial serum sample. These attributes, together with the miniaturization potential afforded by an impedimetric sensing platform, make this platform an attractive candidate for scale-up as a device for rapid, on-site detection of TBI. These findings may aid in the future development of sensing systems for quantitative TBI detection.}, journal={BIOSENSORS & BIOELECTRONICS}, publisher={Elsevier BV}, author={Lee, Jinhee and Kane, Bryant J. and Khanwalker, Mukund and Sode, Koji}, year={2022}, month={Jul} }
 @article{hatada_loew_okuda-shimazaki_khanwalker_tsugawa_mulchandani_sode_2021, title={Development of an Interdigitated Electrode-Based Disposable Enzyme Sensor Strip for Glycated Albumin Measurement}, volume={26}, ISSN={["1420-3049"]}, DOI={10.3390/molecules26030734}, abstractNote={Glycated albumin (GA) is an important glycemic control marker for diabetes mellitus. This study aimed to develop a highly sensitive disposable enzyme sensor strip for GA measurement by using an interdigitated electrode (IDE) as an electrode platform. The superior characteristics of IDE were demonstrated using one microelectrode of the IDE pair as the working electrode (WE) and the other as the counter electrode, and by measuring ferrocyanide/ferricyanide redox couple. The oxidation current was immediately reached at the steady state when the oxidation potential was applied to the WE. Then, an IDE enzyme sensor strip for GA measurement was prepared. The measurement of fructosyl lysine, the protease digestion product of GA, exhibited a high, steady current immediately after potential application, revealing the highly reproducible measurement. The sensitivity (2.8 nA µM−1) and the limit of detection (1.2 µM) obtained with IDE enzyme sensor strip were superior compared with our previously reported sensor using screen printed electrode. Two GA samples, 15 or 30% GA, corresponding to healthy and diabetic levels, respectively, were measured after protease digestion with high resolution. This study demonstrated that the application of an IDE will realize the development of highly sensitive disposable-type amperometric enzyme sensors with high reproducibility.}, number={3}, journal={MOLECULES}, author={Hatada, Mika and Loew, Noya and Okuda-Shimazaki, Junko and Khanwalker, Mukund and Tsugawa, Wakako and Mulchandani, Ashok and Sode, Koji}, year={2021}, month={Feb} }