This invention describes a new system and method for performing surface-selective spectroscopic detection with high sensitivity and low detection limits particularly in the visible and fingerprint mid-infrared spectral regions. The method offers a substantial improvement, 10-fold or more, over existing techniques. This invention has already been reduced to a working prototype and demonstrated utility investigating numerous systems. Unlike other spectrometers in its class, this invention achieves superior performance without the need for surface enhancements, use of additional substrates or fluorescent labels. The novel HD-SFG signal detection method is capable of detection of a few percent of a monolayer level while simultaneously providing phase information on the molecular vibrations.
Applications:
Detection of absorbed molecules at interfaces is of vital importance in many areas of chemistry, physics and biology. Current applications of this technology relate to surface functionalization chemistry, semiconductor passivation, biofouling and cell membrane biology. Existing commercial Sum Frequency Generation (SFG) and Second Harmonic Generation (SHG) spectrometers could be adapted to incorporate this invention without significant additional expense as an optional accessory. Enhancement of the detection signal extends the capabilities of these spectrometers to include ultrasensitive noninvasive chemicals and biological sensing as well as to microscopy and imaging applications. This technology has the potential to broaden the market into emerging materials characterization and biomedical research applications.
Benefits:
Method significantly amplifies the signal and linearizes it with respect to the surface coverage, allowing greatly improved sensitivity and detection limits.
· Substantially lower detection limits (Few % of a monolayer)
· Works on any transparent dielectric substrate
· No surface enhancements needed (not limited to metal surfaces)
· Probes both vibrational and electronic transitions
· No fluorescent labels needed
· Provides phase information
References:
“Heterodyne-detected Vibrational Sum Frequency Generation Spectroscopy", J. Am. Chem. Soc. 130, 2271 -2275 (2008).
"Molecular Order in Langmuir- Blodgett Monolayers of Metal-Ligand Surfactants Probed by Sum Frequency Generation" Langmuir 25, 6880-6886 (2009).
“Hydrogen bonding at the water surface revealed by isotopic dilution spectroscopy", Nature 474, 192 (2011)