An integrated array of silicon field-effect transistor structures is used for electronic detection of label-free DNA. Measurements of the dc current–voltage characteristics of the transistors gives us access to reproducible detection of single- and double-stranded DNA, locally adsorbed on the surface of the device. We combine this approach with allele-specific polymerase chain reaction, to test for the 35delG mutation, a frequent mutation related to prelingual nonsyndromic deafness.

A double-tweezer setup is used to induce mechanical stress in systems of molecular biology. A double strand of DNA is first stretched and the data is compared to precedent experiments to check the experimental setup. Then a short foldable fragment of RNA is probed; the typical unfolding/refolding hysteresis behaviour of this kind of construction is shown and followed by a study of its elasticity and a comparison to a worm-like chain model. Eventually, we describe the unfolding of a larger RNA structure, which unfolds by multiple steps. We show that this unfolding is not reversible and that it presents numerous unfolding pathways.

The dc electrical conductivity of double stranded DNA is investigated experimentally. Single DNA molecules are manipulated with subpiconewton force and deposited on gold nanoelectrodes by optical traps. The DNA is modified at its ends for specific bead attachments and along the chain to favor charge transfer between the DNA base pair stack and the electrodes. For an electrode separation of 70 nm we find, in aqueous environment, electrical resistances above 100 G Omega indicating that even for weak stretching the double helix is almost insulating at this length scale.

An integrated array of field-effect transistor structures is used to detect two oppositely charged biopolymers: poly(L-lysine) and DNA. Local deposition of polymer solutions on part of the array induces sizeable variations in the dc current-voltage characteristics of the transistors exposed to the molecular charge. The whole transistor array is measured in the presence of a common electrolyte. Differential signals are studied as a function of electrolyte salt and polymer concentrations. The measurements provide information on the interface electrostatic potentials of the (semiconductor/biopolymer/electrolyte) system and the experimental data are compared to an analytical model which accounts for screening of the adsorbed charge by mobile ions.

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