This Small Business Technology Transfer (STTR) Phase I project will result in the fabrication and validation of an optically-detected magnetic resonance sensor for determining the chemical composition of trace quantities of liquid and powder samples. This is critical in numerous industries ranging from defense forensics and environmental safety, to materials synthesis and petroleum exploration. The desire for chemically-specific detection of trace analytes has spurred the growth of a large and diverse market, served by techniques such as Raman spectroscopy and high-field benchtop nuclear magnetic resonance (NMR). These are already sizeable markets (on the order of $1 billion) with annual growth rates of 5-10%, depending on product type and geography. This new sensor will have a direct and broad impact on public security and defense, for example in airport and border security checks. The reliable detection and analysis of small quantities of potentially-threatening chemicals and materials are essential for simultaneously meeting the increased demands for security and eliminating the need to test large quantities of analyte. An impact on science education is also anticipated, based on the anticipated development of an affordable turnkey system, which can be used in instructional and research settings.
The intellectual merit of this project lies in the application of the basic physics of solid-state defects in diamond to create a device with unique properties desirable for chemical trace analysis. Unlike many NMR systems, this spectrometer operates at ambient temperature, in a range of magnetic fields easily generated by small permanent magnets, and with sub-microliter sample volumes. The analyte is delivered via a microfluidic chip to a sensor region consisting of a nanostructured diamond doped with nitrogen-vacancy (NV) color centers. By applying pulses of laser light and microwaves, the magnetic field from the analyte's precessing nuclear magnetization becomes encoded in the NV fluorescence signal. Analysis of the fluorescence signal reveals the NMR spectrum of the analyte, from which the chemical composition can be extracted based on established libraries. This platform bypasses two common problems that hinder NMR sensitivity using traditional coil-based approaches. First, it does not rely on thermal polarization and thus allows operation at ambient temperature and low magnetic field without affecting the signal strength. Second, it uses a magnetometer to directly measure the nuclear magnetization and thus avoids the poor sensitivity that is fundamental to frequency-dependent flux detection.