We have developed a biochip platform technology suitable for controlled cell-free gene expression at the micrometer scale. A new hybrid molecule, "Daisy", was designed and synthesized to form in a single step a biocompatible lithographic interface on silicon dioxide. A protocol is described for the immobilization of linear DNA molecules thousands of base pairs long on Daisy-coated surfaces with submicrometer spatial resolution and up to high densities. On-chip protein synthesis can be obtained with a dynamic range of up to four orders of magnitude and minimal nonspecific activity. En route to on-chip artificial gene circuits, a simple two-stage gene cascade was built, in which the protein synthesized at the first location diffuses to regulate the synthesis of another protein at a second location. We demonstrate the capture of proteins from crude extract onto micrometer-scale designated traps, an important step for the formation of miniaturized self-assembled protein chips. Our biochip platform can be combined with elastomeric microfluidic devices, thereby opening possibilities for isolated and confined reaction chambers and artificial cells in which the transport of products and reagents is done by diffusion and flow. The Daisy molecule and described approach enables groups not proficient in surface chemistry to construct active biochips based on cell-free gene expression.

The cover picture shows an image of fluorescent‐labeled double‐stranded DNA molecules encoded for entire genes some 2000 base‐pairs long. The molecules were immobilized on a silicon dioxide chip at one of their ends. The brightest regions of the image correspond to a high density of genes on the surface with 30 nm between molecules. Such gene chips can now be prepared using a new single‐step biocompatible photolithographic interface. This interface provides an adequate and simple‐to‐use platform for biosynthetic reactions localized to submicrometer resolution. The ability to fabricate gene layouts on a chip opens many new possibilities to explore artificial biological systems based on cell‐free gene expression at the scale of a living cell. For more information, please read the Full Paper, “A Single‐Step Photolithographic Interface for Cell‐Free Gene Expression and Active Biochips” by R. Bar‐Ziv and co‐workers on page 500 ff.