"Measuring the Conductivity of Ultrathin Water Layers as a Prelude to Experiments on DNA-Porphyrin Complexes"
I have always had an interest in physics and biology, and this project was a great way to combine the two in a new way. I first started on this project while working in a lab at Haverford over the summer before my senior year, and I enjoyed it so much that I decided to pursue it as a senior thesis.
A set of control experiments testing the conductivity of water layers that form on oxidized silicon substrates was performed. Illumination from a 445 nm laser was found to have no effect on the conductivity, suggesting that the photoconductivity observed in previous experiments on DNA-Porphyrin complexes is a property of the complexes rather than an adsorbed water film on the substrate. In I-V curves measured on the blank substrates, significant non-linear behavior was observed around 1.2V bias voltage, which is thought to be due to the electrolysis of the water layer. In addition, the application of gate voltage on the silicon substrates was found to increase the current through the substrate to unmeasurably high levels. This effect was observed in samples that had the gate voltage wire connected with an indium dot and also in samples for which this connection was made with silver paint. This effect was hypothesized to be the result of an electrochemical reaction between the connecting substance and the silicon substrate but requires further testing to be fully understood.