Inflammatory biomarkers detection in saliva samples by printed graphene immunosensors

The combination of novel materials/techniques and consolidated tools for electronic (bio)sensor devices applications, is nowadays a paradigm largely pursued by worldwide researchers interested in applications in the flexible (bio)electronics field. Starting from graphene, 2D materials allow to tune with a certain degree of control the properties of related devices. The main goals in using 2D materials consist of enhancing the sensing performance and adapting prototypes to reliable applications, as well as of extending their fabrication into the domain of simple and rapid prototyping tools that respond to criteria of industrial scalability. In this respect, the present talk focuses on the design and fabrication of a portable and fast responding biochemical sensor based on the Screen Printed Electrode (SPE) concept and applied for detecting a popular inflammatory biomarker, i.e. the interleukin-6 (IL-6), in whole human saliva samples. A Thermally Exfoliated Graphene Oxide (TEGO) layer printed by the state of art method for 3D printed electronics, i.e. the Aerosol Jet Printing (AJP) technique, is demonstrated to be defective, due to the presence of functional groups as required to host IL-6 antibodies upon an easy biochemical functionalization; all this, being possible without recurring to long-lasting and expensive methods aimed at promoting the required defectivity by the graphene layer. The control of biosensor fabrication routes implies a well-accomplished device fabrication in terms of device-to-device reproducibility, while the method introduced for evaluating the sensor response allows to define a calibration curve showing a high degree of reproducibility of the biosenrors’ response for IL-6 concentrations falling within the ‘cytokine storm’ range. As a result, we show how the proposed biosensors display a dynamic range also comprising IL-6 concentrations falling within the normal IL-6 levels in saliva. In addition, we also show an extensive analysis of the device performance performed by assessing the sensor Limit of Detection (LoD) by means of two conceptually correct different models. Our work aims at providing a contribution towards applications in real environment, going beyond a proof of concept or prototyping at lab scale. In this respect, the device-to-device reproducibility in case of Il-6 concentrations indicating a strong inflammation, has been verified upon acquiring multiple experimental points along the calibration curve by using different individual devices for each point and by using real saliva samples with and without IL-6 aliquots spike in.