Another important and unique advantage of the photolithographic approach is that it is largely substrate agnostic. While electrochemical synthesis particularly, but also ink-jet-based synthesis, require complex substrate structuring, the substrates needed for the photolithographic approach are undemanding, and multiple alternative materials and surface functionalizations have been successfully implemented to enable enhanced performance as well as new applications. The default substrate has been borosilicate glass functionalized using silane chemistry to provide reactive surface groups for the initial phosphoramidite coupling reaction. Typically this functionalization provides hydroxyl groups , but amino and epoxy groups have also been used . To improve array hydrolytic stability and reusability, several carbon-based substrates have also been developed. These include diamond films , amorphous and glassy carbon , carbon-on-metal , and polymers . Direct synthesis on conductive substrates such as indium tin oxide on glass enables detection and quantification of isotopically enriched RNA via secondary ion mass spectrometry, a high throughput approach for associating biogeochemical function and identity in mixed bacterial communities .