Micro Contact Printing of DNA Molecules

The development of DNA sensors has attracted substantial research efforts. Such devices could be used for the rapid identification of pathogens in humans, animals, and plant; in the detection of specific genes in animal and plant breeding; and in the diagnosis of human genetic disorders. The first step to fabricate the DNA sensors is the probe immobilization on the suitable substrate. Traditionally, the DNA probes are spotted on the substrate while the technique hardly controlled the small pattern and surface density of DNA probes. The main challenge here is to achieve probe layer uniformity and the nature of the probe layer itself in few micron and sub-micron feature range.

Ion irradiated polystyrene: transport and hardness Measurements

Thin films of polystyrene (PS) were modified using oxygen (0+) and helium (He+) ions and analyzed via diffusion and hardness measurements. One micron thick films were modified with 400 keV 0+ and He+ ions. The fluence was varied from 1.7 to 34.0 x 1013 ions/cm2 for both incident ions. Following irradiation, some samples were covered with a probe layer of deuterated PS, and annealed at 170°C. Using forward recoil spectrometry, the diffusion of d-PS and the PS hydrogen loss were measured as a function of incident ion species and dose. For all modified samples, d-PS diffusion was significantly retarded compared to the unmodified case. Atomic force microscopy measurements on the as-cast and irradiated PS samples suggest that the relative hardness of the 0+ modified PS was greater than that of the as-cast PS. The force-displacement curves of the modified PS displayed no hysteresis whereas the as-cast PS had a large hysteresis due to tip penetration and tip-polymer adhesion. These results indicate that ion irradiation decreases transport in PS and increases PS hardness.