A comparison of inkjet-printed amperometric and transistor-based biosensors towards continuous glucose monitoring

Continuous glucose monitoring (CGM) is a technologically challenging topic, whose global medical relevance drives research efforts in several scientific fields. In this study, we analyze the potential of fully-ink-jet printed, flexible electrochemical biosensors for glucose monitoring with particular emphasis on the systematic comparison between two complementary device architectures. Specifically, amperometric and organic electrochemical transistor (OECT) structures entirely made of ink-jet printed poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) are equipped with a biosensing interface modified with Pt nanoparticles and a membrane immobilizing glucose oxidase, where glucose is detected through the oxidation of hydrogen peroxide. The analytical performance of the two sensing configurations is systematically evaluated upon miniaturization, guiding the adjustment of both printing and functionalization strategies. Morphological, electrochemical and electrical characterizations are used to investigate the transduction mechanisms, characterize the key performance indexes and highlight the advantages of each sensing structure. On one hand, the intrinsic amplification provided by the transistor architecture results in higher sensitivity in the micromolar range (12 vs 0.43 mA M-1, for OECT and amperometric sensors respectively). On the other hand, the lower S/N ratio exhibited by the OECT negatively impacts on the detection limit (66 µM for the transistor and 18 µM for the amperometric sensor). Overall, both sensor types are promising for the real-time glucose monitoring in biofluids like saliva and extracted interstitial fluid. Moreover, the miniaturized ink-jet printed devices outperform current state-of-the-art ink-jet printed glucose biosensors, most of which are not fully printed and flexible, or do not include the immobilized enzyme-containing layer in a compact layout.