We continue the development of two types of sensors: (1) those based on reporting to each other and to a central hub via spontaneous networks and (2) those that are standalone detectors and utilize local reporting. The applications range from border security and the safety of first-responders to the detection of disease marker molecules. Our project involves the development of miniature chemical/biological sensors of unprecedented selectivity and sensitivity usiing imprinted polymers as the sensing agent.  The sensing element uses either capacitance, conductance or the I-V curves of a monolayer of gold nanoparticles.

For capacitive sensors, the physical property associated with the target molecule is the peak in the loss curve as a function of frequency. Sensor functionality depends upon detecting differences in this property as a function of the insertion or removal of the target molecule from the sensor chip. A control sensor, constructed with an unimprinted polymer film, provides a reference level for the absence of the target molecule in the sensor.  A range of sensor production conditions were tested including variations on: electrode material, thickness, area, etching conditions, and configuration; inclusion of insulation layers between electrode and polymer; sensor post-production treatment (washing, baking, etc.) and treatment of the polymer layer.  Conductive sensors rely on the change in resistance in an imprinted conductive polymer. The presence of the analyte may enhance or reduce the background resistance, depending upon the material.

In recent years, the striking conductivity properties of nanometer-size metal particles have inspired a great deal of research. If the particles are made small enough, the capacitive charging energy for transferring a single electron becomes comparable to the thermal energy, kBT.  This results in a non-linear resistance. Alteration of the chemical environment of the nanoparticles has been shown to change the offset of the voltage steps.  It is this dependence that we exploit in using these nanoparticle films and arrays as sensors. Our work combines the single electron technique with molecular imprint selectivity to create a new generation of sensors. Integration of a nanoparticle layer into the MIP sensor involves a resistive measurement of the changes induced in the nanoparticle layer.