Analytical applications of acousto-optic tunable filters

The Acousto-Optic Tunable Filter (AOTF) is considered to be the new generation monochromator. These optical devices have many advantages which are not available in other wavelength dispersive devices. Namely, AOTFs are compact, have an all solid-state construction, no moving parts, rapid scanning ability (μs), high spectral resolution (3 angstroms at 632.8 nm) and high efficiency (\u3e90%). In addition, AOTFs are available from the ultraviolet (UV) through the infrared (IR) regions. Attributes such as these make it possible to develop spectroscopic instruments that are not possible with other dispersive devices. We have developed several AOTF-based instruments in our laboratory. Two of these instruments were designed for the measurement of molecular fluorescence. The first of these fluorimeters is based on a non-collinear TeO2 AOTF and bright blue Superluminescent Light Emitting Diodes (SLED). This instrument has been used for the simultaneous determination of Chlorophylls a and b in organized media. Using this instrument in conjunction with the Partial Least Squares technique make it possible to detect the chlorophylls at nanomolar concentrations. Further, a second fluorimeter has been developed for the simultaneous detection of two types of fluorescence spectroscopy. Namely, two-photon excited (TPE) fluorescence and near infrared fluorescence (NIRF). TPE fluorescence spectroscopy was used to probe a visible fluorophore labeled oligonucleotide while a NIR fluorophore labeled oligonucleotide was detected by the NIRF technique. This detection system is based on a visible as well as NIR TeO2 AOTF and uses a tunable Titanium: Sapphire laser as the excitation source. Using this instrument, it is possible to excite both samples with a single laser line and detect both 20-mer oligonucleotides simultaneously. The high throughput capability of the AOTF makes it possible to develop multispectral imaging systems. We have constructed a NIR multispectral imager based on a non-collinear TeO2 AOTF and 256 x 320 pixel InSb focal plane array (FPA). This instrument has been used to measure the NIR absorption spectra of peptides synthesized by the Combinatorial Chemistry mediated solid-phase peptide synthesis method. Using this instrument in conjunction with the Partial Least Squares Regression technique it is possible to determine the constituent amino acids of these resin-bound peptides