An iterative algorithm for background removal in spectroscopy by wavelet transforms.

Wavelet transforms are an extremely powerful tool when it comes to processing signals that have very "low frequency" components or non-periodic events. Our particular interest here is in the ability of wavelet transforms to remove backgrounds of spectroscopic signals. We will discuss the case of surface-enhanced Raman spectroscopy (SERS) for illustration, but the situation it depicts is widespread throughout a myriad of different types of spectroscopies (IR, NMR, etc.). We outline a purpose-built algorithm that we have developed to perform an iterative wavelet transform. In this algorithm, the effect of the signal peaks above the background is reduced after each iteration until the fit converges close to the real background. Experimental examples of two different SERS applications are given: one involving broad backgrounds (that do not vary much among spectra), and another that involves single molecule SERS (SM-SERS) measurements with narrower (and varying) backgrounds. In both cases, we will show that wavelet transforms can be used to fit the background with a great deal of accuracy, thus providing the framework for automatic background removal of large sets of data (typically obtained in time-series or spatial mappings). A MATLAB((R)) based application that utilizes the iterative algorithm developed here is freely available to download from http://www.victoria.ac.nz/raman/publis/codes/cobra.aspx.

Ultrafast nonradiative decay rates on metallic surfaces by comparing surface-enhanced Raman and fluorescence signals of single molecules.

By the simultaneous observation of surface-enhanced Raman scattering and surface-enhanced fluorescence signals from a single molecule, we can measure and quantify the modification of the total decay rate of emitters in very close proximity to metals, even down to adsorbed molecules. This modified decay rate is shown to be largely dominated by its nonradiative component, which would be extremely difficult to estimate with conventional approaches. The method provides an indirect measurement of ultrafast (approximately 25 fs) mechanisms, which would be impossible to gain with time-resolved spectroscopy of a single molecule.

Single-molecule vibrational pumping in SERS.

Single-molecule vibrational pumping in surface-enhanced Raman scattering (SERS) is demonstrated rigorously using the bi-analyte SERS method at low temperatures. These experiments reveal a systematic difference between the radiative SERS cross section estimated from the Stokes intensity and that obtained by pumping itself (from the anti-Stokes-to-Stokes ratio), the latter being always larger. This difference can only be reliably demonstrated in the single-molecule SERS regime, for it is otherwise affected by complications of the averaging (over the enhancement distribution) of the signals of several molecules. The findings in this paper highlight the limitations of the pumping cross-section, which cannot (in general) be taken as a reliable measure of the SERS cross-section itself. We provide a discussion of the main possible explanations for the systematic difference of the two estimates.

Vibrational pumping in surface enhanced Raman scattering (SERS).

In this tutorial review, the underlying principles of vibrational pumping in surface enhanced Raman scattering (SERS) are summarized and explained within the framework of their historical development. Some state-of-the-art results in the field are also presented, with the aim of giving an overview on what has been established at this stage, as well as hinting at areas where future developments might take place.

Fructose 2,6-bisphosphate inhibition of phosphoglucomutase.

Fructose 2,6-bisphosphate inhibits phosphoglucomutase noncompetitively with respect to the cofactor glucose 1,6-bisphosphate. Previous studies from our laboratory had shown that phosphoglucomutase was activated by fructose 2,6-bisphosphate in the absence of added glucose 1,6-bisphosphate. The fructose 2,6-bisphosphate activation previously reported was due to the presence of glucose 1,6-bisphosphate in the commercial preparation of fructose 2,6-bisphosphate.

Effects of Dimethyl Sulfoxide and pH on Indoleacetic Acid-Induced Lateral Root Formation in the Radish Seedling Root.

Segments (2.5 cm) cut from 3-day-old seedling roots of radish (Raphanus sativus L. ;Scarlet Globe') were cultured in medium with or without indoleacetic acid (IAA). Lateral root primordia frequency, determined for the central centimeter of segments, was dependent on IAA concentration and on conditions affecting IAA uptake. Dimethyl sulfoxide treatment, or a relatively low medium pH, greatly enhanced the response to exogenous IAA. It was concluded that a permeation barrier exists between the external medium and the hormone responsive sites within the radish seedling root.

In vitro activation of phosphoglucomutase by fructose 2,6-bisphosphate.

The hexose bisphosphate activation of phosphoglucomutase was investigated with both plant (pea and mung bean) and animal (rabbit muscle) sources of the enzyme. Plant phosphoglucomutase was purified about 50-fold from seeds, and to a lesser extent, from seedlings of Pisum sativum L. cv Grenadier and seedlings of Phaseolus aureus. It was found that the plant enzyme was isolated in a mostly dephosphorylated form while commercial rabbit muscle phosphoglucomutase was predominantly in the phosphorylated form. Activation studies were done using the dephosphorylated enzymes. The range of activation constant (K(a)) values were obtained for each bisphosphate were: for glucose 1-6-P(2), 0.5 to 1.8; fructose 2,6-P(2), 6 to 11.7; and fructose 1,6-P(2), 7 micromolar, respectively. Fructose 2,6-P(2) is known to occur in both plant and animal tissues at changing levels encompassing the K(a) values found in this study; hence, these results implicate fructose 2,6-P(2) as a natural activator of phosphoglucomutase, particularly in plants. Also, glucose 1,6-P(2) has not been found in plants, and the method for measuring glucose 1,6-P(2) by monitoring the activation of phosphoglucomutase is not specific.