Cell Suspension as a Model System for Electrochemical Analysis

Cell suspensions of marine phytoplankton Dunaliella tertiolecta in 0.1 M NaCl solution are proposed as a suitable model monodispersed system (particle diameter 6-10 μm) for the calibration of electrochemical response in natural aquatic samples containing organic surface-active particles. The electrochemical analysis is performed by direct recording of chronoamperometric curves of oxygen reduction in suspensions using a fast dropping mercury electrode. The electrode acts as adhesion sensor. The adhesion of individual surface-active particles suspended in natural seawater, analogously to Dunaliella tertiolecta cells in model suspensions, results in well resolved attachment signals in amperometric curves. The calibration curve presents dependence of attachment frequency on cell densities in the concentration range 106 to 2.5 x 107 particles L-1 and it can be used for the determination of particle abundance in a seawater sample. The advantage of the electrochemical approach over more conventional methodologies for particle analysis is discussed

Diatom Polysaccharides: Extracellular Production, Isolation and Molecular Characterization

The extracellular polysaccharide production by marine diatoms is a significant route by which photosynthetically produced organic carbon enters the trophic web and may influence the physical environment in the sea as observed for example when massive aggregation events on basin scale occur. Many papers showed that the aldose signatures of marine DOM obtained from different seawater samples around the world is similar to that determined on cultured phytoplankton DOM and that the carbohydrate production could be very different among the species selected, growth and environmental conditions. These results are very important in order to understand the role of algal exudation in the aggregation processes observed in all of the seas and in general in carbon cycling in the euphotic zone. Many authors showed that cultured diatoms growth in P-limiting condition determines an increase of polysaccharides exudated by different diatoms species both pelagic and benthic

Elektrokemijska detekcija mikročestica gela u morskoj vodi

We present the first atomic force microscopy (AFM) images of the native marine gel network and a new type of electrochemical signals of individual gel microparticles in seawater. Gel microparticles in seawater are selectively detected through specific amperometric signals using a dropping mercury electrode (DME) as a sensor. We have demonstrated that organic microparticles naturally present in Northern Adriatic seawater can be detected as single particles and sorted at the DME/seawater interface according to their hydrophobicity and supramolecular organization.Prvi puta prikazana je nanostruktura morskog gela oslikana mikroskopijom atomskih sila i nova vrsta elektrokemijskih signala mikročestica gela u morskoj vodi. Čestice gela u morskoj vodi selektivno se detektiraju kao specifični amperometrijski signali primjenom živine kapajuće elektrode kao senzora. Svaki signal je rezultat sudara mikročestice gela s rastućom površinom živine elektrode. Primjenom amperometrijske tehnike i živine kapajuće elektrode kao senzora organske mikročestice detektiraju se na dinamičkoj međupovršini živina elektroda/morska voda temeljem svojstava hidrofobnosti i supramolekulske organizacije kao površinski-aktivne i gel čestice