Polymer-based micro/nanoelectromechanical systems have attracted a great deal of interest from industries and academia. The common polymer fabrication methods involve either organic solvents or temperatures above the glass transition temperature, which is undesirable, particularly at the nanoscale. On the basis of different properties near polymer surfaces from those in the bulk, we introduce subcritical fluids [particularly carbon dioxide (CO2)] into polymer surfaces to manipulate the polymer properties at the nanoscale so that we can achieve low temperature polymer nanofabrication. Guided by CO2-enhanced surface dynamics of polymers, we developed a CO2 bonding technique to succeed in low temperature assembly of polymeric nanostructures. This CO2 bonding technique has been applied to seal polymeric nanofluidic biochips and construct well-defined three-dimensional biodegradable polymeric scaffolds for tissue engineering. (c) 2005 American Vacuum Society.