AVS 49th International Symposium
    Biomaterials Thursday Sessions
       Session BI+HS+SS-ThM

Paper BI+HS+SS-ThM2
Chemical Sensing Using Ultra-Fast Micro-Boiling

Thursday, November 7, 2002, 8:40 am, Room C-201

Session: Biosensors and Biodiagnostics
Presenter: O. Thomas, National Institute of Standards and Technology
Authors: O. Thomas, National Institute of Standards and Technology
R.E. Cavicchi, National Institute of Standards and Technology
M.J. Tarlov, National Institute of Standards and Technology
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We report a novel liquid sensing method that exploits micro-boiling phenomena on the surface of rapidly heated thin film heaters. The heaters are thin films of platinum and gold-plated platinum that are approximately tens of micrometers in width and hundreds in length. The micro-heaters are immersed in solutions where they are rapidly heated to high temperature with short, 5 - 40 microsecond, square voltage pulses. The temperature-time responses of the micro-heaters are obtained by measuring their resistance during the application of the heating pulse. The bubble nucleation event associated with boiling is signaled in the temperature-time transient by an inflection point that results from a change in heat transfer when a vapor film forms on the heater. Because of the extremely high heating rates, superheating is observed where nucleation temperatures approaching 300°C have been measured for aqueous solutions. The bubble nucleation temperature and average heater temperature during the micro-boiling process have been found to be highly dependent on the surface wettability of the heater, as well as the presence of surfactant molecules. We will report on the use of alkanethiol self-assembled monolayers to investigate the effect of surface wettability on micro-boiling. We will demonstrate that temperature-time transients of hydrophobic SAMs are distinct from those of hydrophilic SAMs and that information on SAM stability can be gleaned from transient data. We will also present preliminary results on using the micro-boiling phenomenon to detect surface binding events such as DNA hybridization and biotin-avidin coupling.