Direct electrodeposition of adherent ultra-thin polypyrrole films on minimally pretreated silicon for localized biofunctionalization

Abstract

Silicon is a valuable substrate for the design of biosensors and for micro/nanofluidic device fabrication, yet it remains challenging to achieve localized, tunable and robust surface functionalization. Existing methods such as hydrosylilation, silanization and electrografting often require multistep processing and harsh reagents like hydrofluoric acid. In this work, we introduce a one-step, aqueous electropolymerization strategy for directly functionalizing native oxide-bearing silicon with ultrathin polypyrrole (PPy) films. This is made possible by a simple dual pretreatment (plasma and oven) that enables stable, adherent PPy film formation using silicon as the working electrode. This film could be furtherly overoxidized to tune its conductivity and electroactivity. Homogeneous films with thicknesses ranging from 9 to ∼70 nm were obtained and characterized by AFM, SEM, ellipsometry, XPS, Raman spectroscopy, and FTIR/ATR. Furthermore, the films were biofunctionalized with oligonucleotides or antibodies via co-electropolymerization with pyrrole conjugates. Fluorescence-based assays confirmed both the specificity and stability of biomolecule grafting. This approach offers scalable and biocompatible strategy for the fabrication of silicon-based biosensors and nanofluidic platforms requiring precise control of film morphology, surface charge, electrical properties, and functional groups.