Bio-PEDOT: Modulating Carboxyl Moieties in Poly(3,4-ethylenedioxythiophene) for Enzyme-Coupled Bioelectronic Interfaces.

Modulation of chemical functional groups on conducting polymers (CPs) provides an effective way to tailor the physicochemical properties and electrochemical performance of CPs, as well as serves as a functional interface for stable integration of CPs with biomolecules for organic bioelectronics (OBEs). Herein, we introduced a facile approach to modulate the carboxylate functional groups on the PEDOT interface through a systematic evaluation on the effect of a series of carboxylate-containing molecules as counterion dopant integrated into the PEDOT backbone, including acetate as monocarboxylate (mono-COO), malate as dicarboxylate (di-COO), citrate as tricarboxylate (tri-COO), and poly(acrylamide--acrylate) as polycarboxylate (poly-COO) bearing different amounts of molecular carboxylate moieties to create tunable PEDOT:COO interfaces with improved polymerization efficiency. We demonstrated the modulation of PEDOT:COO interfaces with various granulated morphologies from 0.33 to 0.11 μm, tunable surface carboxylate densities from 0.56 to 3.6 μM cm, and with improved electrochemical kinetics and cycling stability. We further demonstrated the effective and stable coupling of an enzyme model lactate dehydrogenase (LDH) with the optimized PEDOT:poly-COO interface via simple covalent chemistry to develop biofunctionalized PEDOT (Bio-PEDOT) as a lactate biosensor. The biosensing mechanism is driven by a sequential bioelectrochemical signal transduction between the bio-organic LDH and organic PEDOT toward the concept of all-polymer-based OBEs with a high sensitivity of 8.38 μA mM cm and good reproducibility. Moreover, we utilized the LDH-PEDOT biosensor for the detection of lactate in spiked serum samples with a high recovery value of 91-96% and relatively small RSD in the range of 2.1-3.1%. Our findings provide a new insight into the design and optimization of functional CPs, leading to the development of new OBEs for sensing, biosensing, bioengineering, and biofuel cell applications.