A density gradient centrifugation method for rapid separation of nanoTiO2 and TiO2 aggregates from microalgal cells in complex mixtures with mercury

Abstract

In natural environment, the microorganisms are exposed to complex mixtures of contaminants, including manufactured nanoparticles and their aggregates. Evaluation of the toxicant accumulation in biota exposed to such cocktails is a challenging task because the microorganisms need to be separated from nanomaterial aggregates often of a comparable size. We propose a method for separation of TiO 2 aggregates from green microalga Chlamydomonas reinhardtii and subsequent determination of cellular Hg concentration in algae exposed to mixture of Hg with nanoTiO 2 , known also to adsorb Hg. The method is based on differences in specific weight of algae and TiO 2 aggregates, using medium speed centrifugation on a step gradient of sucrose. The efficiency of the separation method was tested with nanoTiO 2 of three different primary sizes at four concentrations: 2, 20, 100 and 200 mg L −1 . The method gives a possibility to separate nanoTiO 2 and their aggregates from the algae with a mean recovery of 83.3% of algal cells, thus allowing a reliable determination of Hg accumulation by microalgae when co-exposed to Hg and nanoTiO 2 . • A rapid and reliable method to separate algal cells and nanoparticle aggregates of comparable size. • A method to measure the cellular amount of Hg in green alga co-exposed to Hg and nanoTiO 2 .

Kinetic Aspects of the Interactions between TiO2 Nanoparticles, Mercury and the Green Alga Chlamydomonas reinhardtii

“…The bioavailability of Hg to C. reinhardtii was characterized following the intracellular and adsorbed Hg contents over the exposure time. Cellular and aqueous samples were prepared and analyzed following a previously described methodology [28]. Briefly, density gradient centrifugation was employed to allow for efficient separation of the algal cells from the nTiO 2 and more than 83.3% recovery of algal cells for further treatment.…”

The Encapsulation of Natural Organic Dyes on TiO2 for Photochromism Control

“…It should be noted that natural organic dyes are well dispersed in ammonia solutions [36]. Indeed, centrifugal separation was helpful for the separation of small TiO 2 particles with certain density gradients [37]. After rinsing with DI water, the mixtures were collected on filter paper and dried at 80 • C without a vacuum.…”