Thermophoretic stretching of DNA in polymer nanochannels

We demonstrate that thermophoretic forces generated by light-induced local heating can enhance the extension of genomic-length DNA confined in a polymer nanochannel. By temperature control on the micron-scale, bacteriophage T4 DNA is locally stretched to 80{\%} of its contour length, although the cross-section of the nanochannel is as large as 250x250nm$^2$. A coarse-grained model of the forces at play captures the DNA-molecule's response to thermophoretic forces with accuracy and precision, and allows for fitting the density profile of the stretched DNA with only a single fit-parameter. The forces involved are relatively strong, because they add up along the molecule. They are measured by using the molecule as an entropic spring balance. Pending a calculation of these forces, this experiment might discriminate between the competing theories for thermophoretic forces.