Highlighted articles (October 29, 2014)

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We recommend the following articles that deal with different aspects related to sample preparation.

1. Coumarins as turn on/off fluorescent probes for detection of residual acetone in cosmetics following headspace single-drop microextraction. This article presents an interesting application of HS-SDME for the indirect determination of acetone residues in cosmetics. The method takes advantage of the special characteristics of the native fluorescence of coumarins whose intensity depends, among other factors, on the chemical composition of the medium where they are dissolved. In fact, the fluorescence intensity of an ethanol/water solution of 7-diethylamino-4- methylcoumarin (MDAC) increases in the presence of acetone while the intensity of an ethanol/water solution of 7-hydroxy-4-methylcoumarin (4-MU) decreases when acetone is dissolved in that medium. These are the so-called turn-on and turn-off fluorescent effects. In short, the method comprises different steps. First of all, a defined amount of cosmetic is located in a vial which is sealed. In a second step, a small drop of an ethanol/water solution containing the probe (MDAC or 4-MU) is exposed to the sample headspace. During this exposure, acetone is transferred from the sample to the headspace, and from there to the drop inducing a final modification of the fluorescence intensity. The increase (when MDAC is used as probe) or the decrease (when 4-MU is employed as probe) of the fluorescence intensity is directly related to the acetone concentration. The article describes in depth all the theoretical considerations, the overall optimization process and the analytical validation of the method where the selectivity study can be highlighted. Link to the article


2. Development of aptamer-conjugated magnetic graphene/gold nanoparticle hybrid nanocomposites for specific enrichment and rapid analysis of thrombin by MALDI-TOF MS. In this article, a nanocomposite containing a selective aptamer towards thrombin, a protein that can used as tumor biomarker, is presented and applied for the isolation of this target and its final determination by MALDI-TOF-MS. Magnetic graphene, which is the core of the composite, is obtained by the dispersion of magnetic nanoparticles over the graphene nanosheets. In a second step, gold nanoparticles are deposited on the surface of the core using a polyelectrolyte [poly (diallyldimethylammonium chloride] as reagent. In the final step the thrombin-aptamer, previously thiolated, is simply conjugated to the gold nanoparticles surface. This composite presents the ability to isolate thrombin in a selective way from a complex matrix. After the extraction, the composite is digested with trypsin and the final digestion medium is analyzed by MALDI-TOF-MS. This proposal allows the detection of thrombin at concentration levels as low as 0.085 ng/L. Link to the article

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