Differential labeling of closely spaced biosensor electrodes via electrochemical lithography

Electrochemical biosensors offer the promise of exceptional scalability and parallelizability. To achieve this promise, however, will require the development of new methods for the differential labeling of closely spaced electrodes with specific biomolecules such as DNA or proteins. Here we report a simple, highly selective method for passivating and differentially labeling closely separated gold electrodes with oligonucleotides or other biomolecules. Analogous to photolithography, where a light-sensitive resist is selectively removed to expose specific surfaces to further modification, we passivate gold electrodes with a self-assembled alkanethiol monolayer that protects them from modification. The monolayer is then electrochemically desorbed at relatively low potentials, allowing for the subsequent labeling of the now exposed array element with a specific sensing biomolecule. The observed passivation is highly efficient: using a C11-OH monolayer as the passivating agent, we do not observe any detectable cross-contamination of adjacent electrodes (95 microm separation) upon labeling with a stem-loop DNA probe. Critically, the conditions employed are sufficiently gentle that depassivation reduces the DNA load on adjacent electrodes by only approximately 1%, allowing for the sequential labeling of multiple, closely spaced electrodes. This technology paves the way for labeling multiple array elements sequentially without observable cross-contamination in a fast and controlled manner.