Biomedical subjects

Imants Zudans

Publications and source records attributed to Imants Zudans.

5 recordsLinked to original sources

PubMed2007

Simultaneous maximization of cell permeabilization and viability in single-cell electroporation using an electrolyte-filled capillary.

A549 cells were briefly exposed to Thioglo-1, which converts thiols to fluorescent adducts. The fluorescent cells were exposed to short (50-300 ms) electric field pulses (500 V across a 15 cm capillary) created at the tip of an electrolyte-filled capillary. Fluorescence microscopy revealed varying degrees of cell permeabilization depending on the conditions. Longer pulses and a shorter cell-capillary tip distance led to a greater decrease in the cell's fluorescence. Live/dead (calcein AM and propidium iodide) testing revealed that a certain fraction of cells died. Longer pulses and shorter cell-capillary tip distances were more deadly. An optimum condition exists at a cell-capillary tip distance of 3.5-4.5 microm and a pulse duration of 120-150 ms. At these conditions, >90% of the cells are permeabilized and 80-90% survive.

Biosensing Techniques↗

PubMed2005

Electrochemical investigation of Pb2+ binding and transport through a polymerized crystalline colloidal array hydrogel containing benzo-18-crown-6.

The transport of Pb2+ through a sensory gel, a polymerized crystalline colloidal array hydrogel with immobilized benzo-18-crown-6, is important for understanding and optimizing the sensor. Square wave voltammetry at a Hg/Au electrode reveals many parameters. The partition coefficient for Pb2+ into a control gel (no crown ether), K(p), is 1.00 +/- 0.018 (errors reported are SEM). The porosity, epsilon, of the gel is 0.90 +/- 0.01. Log K(c) for complexation in the gel is 2.75 +/- 0.014. Log K(c) in aqueous solution for Pb2+ with the ligand 4-acryloylamidobenzo-18-crown-6 is 3.01 +/- 0.010 with dissociation rate k(d) = (8.34 +/- 0.45) x 10(2) s(-1) and association rate k(f) = (8.79 +/- 0.025) x 10(7) M(-1) s(-1). The partition coefficient of the ligand 4-acryloylamidobenzo-18-crown-6 into the control gel, K(p,L) is 2.07 +/- 0.15. The diffusion coefficient of Pb2+ in the control gel is 6.72 x 10(-6) +/- 0.12 cm(2)/s. For the sensor gel, but not control gel, diffusion coefficients are location dependent. The range of diffusion coefficients for Pb2+ in the probed locations was found to be (6.11-12.60) x 10(-7) cm(2)/s for 0.91 mM Pb2+ and (2.84-9.39) x 10(-7) cm(2)/s for 0.35 mM Pb2+. Lead binding in the sensor gel is slightly less avid than in solution. This is attributed, in part, to the demonstrated affinity of the ligand 4-acryloylamidobenzo-18-crown-6 to the gel. Diffusion coefficients determined for the sensor gel were found to be location dependent. This is attributed to heterogeneities in the crown concentration in the gel. Analysis of diffusion coefficients and rate constants show that diffusion and not chemical relaxation will limit the time response of the material.

Colloids↗

PubMed2004

Spectroelectrochemical sensing based on multimode selectivity simultaneously achievable in a single device. 17. Improvement in detection limits using ultrathin perfluorosulfonated ionomer films in conjunction with continuous sample flow.

We report herein an attenuated total reflectance (ATR) absorbance-based spectroelectrochemical sensor for tris(2,2'-bipyridyl)ruthenium(II) ion [Ru(bpy)(3)(2+)] that employs ultrathin (24-50 nm) Nafion films as the charge-selective layer. This film serves to sequester and preconcentrate the analyte at the optically transparent electrode surface such that it can be efficiently detected optically via electrochemical modulation. Our studies indicate that use of ultrathin films in tandem with continuous flow of sample solution through the cell compartment leads to a 100-500-fold enhancement in detection limit (10 nM) compared to earlier absorbance-based spectroelectrochemical sensors ( approximately 1-5 microM); markedly shorter analysis times also result. We report the dependence of the measured absorbance on sample flow rate and Nafion film thickness, and also provide calibration curves that illustrate the linear range and detection limits of the sensor using a 24 nm film at a constant sample flow rate of 0.07 mL/min.

Journal Article↗

PubMed2004

Further investigations on a poly(vinyl alcohol)- polyelectrolyte chemically selective optical film.

The ionomer poly(vinylbenzyltrimethylammonium chloride) has been blended with cross-linked poly(vinyl alcohol) to form optically clear composites that can be covalently linked as thin films to oxide surfaces. Films are characterized using spectroscopic ellipsometry with refractive index (n) and extinction coefficient (k) data presented for wavelengths 300 to 1100 nm. A refractive index of 1.54 and average thickness of 709 nm are typical of an air dry film prepared by spin-coating. Dynamic in situ ellipsometry results for films exposed to 0.1 M KNO(3) and 1.0 mM Fe(CN)(6)(-3) are presented. Upon initial exposure to 0.1 M KNO(3), an air dry film expands by about 160% and stabilizes in size and refractive index at about 18 hours. Ion exchange of film cationic groups with ferricyanide is marked by slight film contraction, presumably due to electrostatic cross-linking by the multivalent anion. These films are useful in the spectroelectrochemical sensor with our newly developed fluorescence detection mode, as demonstrated by results of the reversible incorporation of the fluorescent anion fluorescein.

Journal Article↗

PubMed2002

Spectroelectrochemical sensing based on multimode selectivity simultaneously achievable in a single device. 13. Detection of aqueous iron by in situ complexation with 2,2'-bipyridine.

A spectroelectrochemical sensor with attenuated total reflectance at an indium-doped tin oxide (ITO) optically transparent electrode coated with a thin film of Nafion has been demonstrated for the determination of aqueous iron ion. The novelty of this sensor stems from its ability to take up colorless iron ion (Fe2+) from solution and complex it with an organic ligand, 2,2'-bipyridine (bipy), that has been previously loaded in the optically transparent charge-selective Nafion film coating the electrode. The resulting complex ion, tris(2,2'-bipyridyl)iron(II), Fe(bipy)3(2+), absorbs strongly, making it easily detectable via optical spectroscopy. Fe(bipy)3(2+) loaded into the selective film is oxidized to colorless Fe(bipy)3(3+), which gives rise to an absorbance change for quantifying iron. This paper maps the development of this sensor, from the spectroelectrochemical characterization of the complex ion at an ITO optically transparent electrode to an analysis of the uptake, retention, and optical response of the complex ion in the Nafion film. Finally, an evaluation of the uptake of aqueous Fe2+ by the bipy-loaded Nafion film is reported. These data include preliminary results illustrating the dependence of the sensor response on differing concentrations of Fe2+ in solution.

Journal Article↗