A Portable Electrochemical Sensing Platform for Early Screening of Chronic Kidney Disease

Introduction: Chronic Kidney Disease (CKD) is a major global health concern, affecting over 10% of the population. Left untreated, CKD can progress to kidney failure and other health complications. Timely diagnosis is crucial for implementing interventions that can prolong and improve patients' lives. Previous research suggests that Volatile Organic Compounds (VOCs) present in exhaled breath hold promise as biomarkers for CKD detection. Alterations in metabolic pathways due to the disease manifest in changes to the breath profile, offering a unique fingerprint for CKD detection. Hence, the development of a non-invasive, sensitive, and specific electrochemical sensor to detect these VOCs in exhaled breath is imperative.
Electrochemical sensors, comprising electrodes, electrolytes, and transducers, have gained traction for their efficiency and sensitivity. Room Temperature Ionic Liquids (RTILs) exhibit thermal stability and desirable chemical and electrochemical properties, making them ideal electrolytes for gas sensing applications. Nafion, serving as a binder, forms a thin film that enhances sensor stability and facilitates gas molecule diffusion towards the electrode surface.
Studies identify Ammonia, Isoprene, and Acetone as representative breath biomarkers for CKD detection. Healthy individuals exhibit an average range of 200PPB-800PPB for Ammonia, 100PPB-600PPB for Isoprene, and 300PPB-1000PPB for Acetone. In CKD patients, these VOC levels are elevated due to metabolic pathway alterations. Thus, analyzing the concentration of these VOCs in breath can indicate the presence of CKD. Leveraging the diffusion of these VOCs through the Nafion-RTIL thin film enables the analysis of transient diffusion currents in a dose-dependent manner, rendering the platform suitable for electrochemical gas sensing.

Materials and

Methods: Materials:
RTIL 1-ethyl-3-methylimidazolium bis(trifluoromethylsufonyl)imide ([EMIM][Tf2N]) with over 99% purity was used as received without any further purification. Nafion, used as a crosslinking polymer, a 5% wt solution in a mixture of lower aliphatic alcohols and 10% water was purchased from the Sigma-Aldrich. Nafion was mixed with RTIL to form a cross-linked polymer network of nafion-[EMIM][Tf2N]. Trace Source™ disposable permeation tubes for Ammonia, Isoprene and Acetone were purchased from KIN-TEK analytical.

Methods:
A computational study was performed to identify the interaction of the RTIL with each VOC. FT-IR spectroscopy was performed to identify the nafion-RTIL interactions. The sensors were procured from Vida Biotechnology where the design consists of a spiral gold working electrode, carbon counter electrode, an Ag/AgCl reference electrode. The electrode surface was modified by drop casting nafion-[EMIM][Tf2N] to cover all three electrodes. [EMIM][Tf2N] was used as the electrolyte and the transducer for gas sensing. The gas mixing system was placed inside the fume hood, with an in-house N2 supply as the diluent gas. Cyclic voltammetry was performed to understand the interaction of each VOC with the modified electrode interface. Chronocoulometry was performed to understand the charging effect at the electrode-electrolyte interface due to diffusion. The diffusion characteristics of the gases across the electrode-electrolyte interface was studied using chronoamperometry as the transduction principle. GC-MS has been performed as the validation technique.

Results, Conclusions, and Discussions:

Results:
For each VOC the results showed an increasing relative current output with increasing analyte concentration as a higher number of species is diffusing across the interface, showing the sensor's ability to detect a range of ammonia, isoprene, and acetone concentrations separately.

Conclusion:
CKD's widespread occurrence globally has become a significant public health issue, straining the economies of many nations with its high incidence rates. Consequently, there's a critical demand for affordable diagnostic methods to detect CKD early. This research focuses on building a real-time, multiplex electrochemical sensor platform to monitor levels of exhaled breath ammonia, isoprene and acetone which serves as biomarker for kidney function, providing insight into breath profile changes due to CKD making the prognosis of the disease easier. The result has shown the developed sensor’s capability to differentiate between concentrations even at very low levels of ammonia, isoprene and acetone demonstrating the functionality of the sensor chemistry and proving the concept.

Discussion:
With this proof of concept, ongoing research focuses on broadening the concentration ranges of each VOC to include levels observed in patients with CKD, and constructing a calibrated dose-dependent response curve. Future efforts will encompass multiplexing studies, further GC-MS studies, and human trials involving breath samples. Ultimately, this study aims to establish a sensing platform proficient in detecting these biomarkers across diverse concentration ranges and to assess the potential for non-invasive CKD diagnosis through breath analysis. This innovative approach could revolutionize early CKD detection, offering a practical and sensitive alternative to current diagnostic methods.

Acknowledgements (Optional): I extend my heartfelt gratitude to Dr. Shalini Prasad, my mentor, for her unwavering guidance and inspiration in bioengineering research. Her dedication and emphasis on continuous learning have fueled my passion for making an impact in the field. I also appreciate Dr. Anirban Paul and Dr. Ivneet Banga for their mentorship, and my colleagues for their support on this journey.