Since 2004, NevadaNano has been developing the Molecular Property Spectrometer (MPS™)—a robust, low-cost, silicon-chip-based, micro-electro-mechanical system (MEMS). Its low power consumption, small size, light weight and near-imperviousness to high g-force trauma make the MPS™ an attractive solution for a wide range of applications. The MPS™ uses multiple sensor elements incorporated into a compact, flow-through, solid-state silicon chip. The sensing elements measure a variety of thermodynamic and electrostatic molecular properties of sampled vapors, liquids, and particles, thereby providing a highly orthogonal analysis of the sample. When used in the standard analysis mode, the MPS™ utilizes these measurements to analyze an unknown sample and identify the types of molecules present.
The key components used to operate the MPS™ all fit in your hand.
To analyze a sample, air is first passed through a metal mesh filter to remove dust and debris. In field testing conducted to date, this filter has not clogged or significantly limited flow-through even after hundreds of liters of air were sampled through it. The filtered air then passes through the MPS™ chip. The sensors protrude over a flow-through window in the center of the chip, enabling vapors to drift directly over and then past the sensors, maximizing the interaction of the sample with the sensing elements.
The MPS™ sensor chip incorporates a patented array of frequency-differentiated microcantilevers with integrated piezoelectric sensing elements that provide electrical actuation and sensing of resonance frequency. Resonance frequency is proportional to sensor mass. Monitoring the resonance is therefore a highly sensitive way of measuring very small masses (picogram-level) of adsorbed analyte. The unique piezoelectric configuration of the MPS™ allows an array of sensors to be electrically monitored in a low-cost, robust fashion rather than using an optical readout (which is more common but more expensive and less robust). The sensors also have built-in resistive heaters for thermal analysis and also for cleaning each sensor after processing a sample; when necessary, these resistors also enable temperature and flow compensation in order to minimize noise and drift and further enhance sensitivity.
MPS™ operation exploits the inherent advantages of this MEMS device, which can heat to hundreds of degrees Celsius and back to room temperature in milliseconds—both for cleaning the sensors for re-use and for conducting thermal analyses of samples as a sample-characterization protocol. The system can detect picogram-scale masses and measure temperature with sub-degree precision. These capabilities make the MPS™ a precise and flexible environmental sensor platform.
One major application for which the MPS™ has thus far been developed is shipping container screening, whereby the MPS™ serves as the sensor platform of a system that “sniffs” the headspace of a shipping container for explosive and chemical threats. In this application, the MPS™ was mated to an RF transmitter for wireless communication of field results. The shipping container security application demands a compact, low-power system, and the ability to operate in relatively extreme environmental conditions (e.g., temperatures from -40°C to 70°C and relative humidities from 20% to 95%, non-condensing).