Optical probes for molecular processes in live cells

Liquid chromatography/tandem mass spectrometry sensitivity enhancement via online sample dilution and trapping: applications in microdosing and dried blood spot (DBS) bioanalysis

A simple online sample dilution, enrichment, and cleanup technique was developed for sensitive microdosing and dried blood spot (DBS) liquid chromatography/tandem mass spectrometric (LC/MS/MS) bioanalysis. Samples are diluted online with water and enriched in a trap column which is subsequently switched inline with the analytical column. Excellent lansoprazole (in acetonitrile) peak shape is maintained even with an 80-microL injection. In comparison, similar chromatographic peaks were observed only when a small volume of the same solution, i.e., 1 microL, was injected on a regular high-performance liquid chromatography (HPLC) system, where an injection of 5 microL resulted in severe peak fronting. A substantial enhancement in sensitivity is realized in the trapping mode using large injection volumes. The trap column is washed at the beginning and at the end of each injection with aqueous and organic solvent respectively to remove matrix components. This ultimately leads to reduction of matrix effects and mass spectrometer noise, thus facilitating the utilization of protein precipitation as the sample preparation for plasma samples. A lower limit of quantitation (LLOQ) of 0.5 pg/mL was demonstrated for lansoprazole in human plasma with a signal-to-noise (S/N) ratio of 13 using a 100 microL injection. Excellent intra-day precision and accuracy were established for lansoprazole in human plasma with good linearity (R(2) > 0.999) from 0.5 to 500 pg/mL. This level of LLOQ makes LC/MS/MS a practical alternative for microdosing bioanalysis, where the dose is typically 100 times lower than the therapeutic dose. The same technique was applied to quantitate lansoprazole in human whole blood employing DBS technology. With a single 3-mm punch, i.e. approximately 2 microL of whole blood or approximately 1 microL plasma, a LLOQ of 0.1 ng/mL showed sufficient S/N ratio (40) for lansoprazole when 75 microL of extract was injected. In all, the online sample dilution, cleanup, and enrichment technique demonstrated the practical utility of LC/MS/MS in microdosing and DBS bioanalysis.

Validation of TPEN as a zinc chelator in fluorescence probing of calcium in cells with the indicator Fura-2

Fura-2 is widely used as a fluorescent probe to monitor dynamic changes in cytosolic free calcium in cells, where Ca(2+) can enter through several types of voltage-operated or ligand-gated channels. However, Fura-2 is also sensitive to other metal ions, such as zinc, which may be involved in ionic channels and receptors. There is interest, in particular, in studying the synapses between mossy fibers and CA3 pyramidal cells which contain both calcium and high quantities of free or loosely bound zinc. We have found, through fluorescence probing, that endogenous zinc inhibits mossy fiber calcium transients. However, since these results might be explained by an effect of the zinc chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) on the spectral properties of Fura-2, we have carried out a validation of the method through fluorescence excitation spectra of the complex Fura-2/calcium, and show that TPEN does not affect these spectra. This supports the idea that the observed calcium enhancement is related to a zinc inhibition of presynaptic calcium mechanisms, and confirms the use of the chelator TPEN as a general procedure for the biophysical study of Ca(II) in the presence of Zn(II) using Fura-2.

Two-parameter monitoring in a lab-on-valve manifold, applied to intracellular H2O2 measurements

This work introduces, for the first time, simultaneous monitoring of fluorescence and absorbance using Bead Injection in a Lab-on-valve format. The aim of the paper is to show that when the target species, cells immobilized on a stationary phase, are exposed to reagents under well-controlled reaction conditions, dual monitoring yields valuable information. The applicability of this technique is demonstrated by the development of a Bead Injection method for automated measurement of cell density and intracellular hydrogen peroxide.