Absolute calibration-free quantitation of electroactive species on screen-printed electrodes under limited diffusion conditions. A proof of concept

Abstract

The advantages of the thin-layer diffusion regime introduced in the 1960’s can now be achieved through the simple spreading of a solution drop with an inert surface on a screen-printed electrode. Once a specific force threshold is exceeded, the solution volume remains virtually constant, while the micrometric volume of analyte and the limited diffusion ensure complete redox reactions. This allows for the direct quantification of soluble electroactive substances using Faraday's law, eliminating the need for calibration curves. This study includes 400 experimental results with four molecular probes (ferrocyanide, hexaamineruthenium (III), hexachloroiridic acid and carboxyTEMPO) and three techniques (chronoamperometry, cyclic voltammetry, and coulometry) to determine the necessary electrochemical cell volume for this configuration. Theoretical characterization of voltammetric and chronoamperometric responses established the conditions required for complete redox probe conversion. The data show that applying a typical force of 50 mN consistently creates a thin-layer cell of approximately 30 µm thick, independent of the solution amount on the electrode surface or the applied force. This method is expected to significantly impact the development of decentralized analysis across various applications.