Molecularly Imprinted Polymers (MIPs) in Sensors for Environmental and Biomedical Applications: A Review.

Molecular imprinted polymers are custom made materials with specific recognition sites for a target molecule. Their specificity and the variety of materials and physical shapes in which they can be fabricated make them ideal components for sensing platforms. Despite their excellent properties, MIP-based sensors have rarely left the academic laboratory environment. This work presents a comprehensive review of recent reports in the environmental and biomedical fields, with a focus on electrochemical and optical signaling mechanisms. The discussion aims to identify knowledge gaps that hinder the translation of MIP-based technology from research laboratories to commercialization.

Enhancement of the Fouling Resistance of Zwitterion Coated Ceramic Membranes.

Ceramic membranes suffer from rapid permeability loss during filtration of organic matter due to their fouling propensity. To address this problem, iron oxide ultrafiltration membranes were coated with poly(sulfobetaine methacrylate) (polySBMA), a superhydrophilic zwitterionic polymer. The ceramic-organic hybrid membrane was characterized by scanning electron microscopy (SEM) and optical profilometry (OP). Membranes with and without polySBMA coating were subjected to fouling with bovine serum albumin solution. Hydraulic cleaning was significantly more effective for the coated membrane than for the non-coated one, as 56%, 66%, and 100% of the fouling was removed for the first, second, and third filtration cycle, respectively. Therefore, we can highlight the improved cleaning due to an increased fouling reversibility. Although some loss of polymer during operation was detected, it did not affect the improved behavior of the tested membranes.

Abatement of 2,4-D by H2O2 solar photolysis and solar photo-Fenton-like process with minute Fe(III) concentrations.

The Photo-Fenton-like (PF-like) process with minute Fe(III) concentrations and the Hydrogen Peroxide Photolysis (HPP), using Xe-lamp or solar light as sources of irradiation, were efficiently applied to eliminate the herbicide 2,4-D from water. PF-like experiments concerning ferric and H2O2 concentrations of 0.6 mg L-1 and 20 mg L-1 respectively, using Xenon lamps (Xe-lamps) as a source of irradiation and 2,4-D concentrations of 10 mg L-1 at pH 3.6, exhibited complete 2,4-D degradation and 77% dissolved organic carbon (DOC) removal after 30 min and 6 h of irradiation respectively whereas HPP (in absence of ferric ions) experiments showed a 2,4-D reduction and DOC removal of 90% and 7% respectively after 6 h of irradiation. At pH 7.0, HPP process achieved a 2,4-D abatement of approximately 75% and a DOC removal of 4% after 6 h. PF-like exhibited slightly improved 2,4-D and DOC removals (80% and 12% respectively) after the same irradiation time probably due to the low pH reduction (from 7.0 to 5.6). Several chlorinated-aromatic intermediates were identified by HPLC-MS. These by-products were efficiently removed by PF at pH 3.6, whereas at neutral PF-like and acid or neutral HPP, they were not efficiently degraded. With natural solar light irradiation, 10 and 1 mg L-1 of 2,4-D were abated using minor H2O2 concentrations (3, 6, 10 and 20 mg L-1) and iron at 0.6 mg L-1 in Milli-Q water. Similar results to Xe-lamp experiments were obtained, where solar UV-B + A light H2O2 photolysis (HPSP) and solar photo-Fenton-like (SPF-like) played an important role and even at low H2O2 and ferric concentrations of 3 and 0.6 mg L-1 respectively, 2,4-D was efficiently removed at pH 3.6. Simulated surface water at pH 3.6 containing 1 mg L-1 2,4-D, 20 mg L-1 H2O2 and 0.6 mg L-1 Fe(III) under natural sunlight irradiation efficiently removed the herbicide and its main metabolite 2,4-DCP after 30 min of treatment while at neutral pH, 40% of herbicide degradation was achieved. In the case of very low iron concentrations (0.05 mg L-1) at acid pH, 150 min of solar treatment was required to remove 2,4-D.

Enhanced retention of bacteria by TiO2 nanoparticles in saturated porous media.

The simultaneous transport of TiO2 nanoparticles and bacteria Pseudomonas aeruginosa in saturated porous media was investigated. Nanoparticle and bacterium size and surface charge were measured as a function of electrolyte concentration. Sand column breakthrough curves were obtained for single and combined suspensions, at four different ionic strengths. DLVO and classical filtration theories were employed to model the interactions between particles and between particles and sand grains. Attachment of TiO2 to the sand was explained by electrostatic forces and these nanoparticles acted as bonds between the bacteria and the sand, leading to retention. Presence of TiO2 significantly increased the retention of bacteria in the sand bed, but microorganisms were released when nanomaterial influx ceased. The inclusion of nanomaterials in saturated porous media may have implications for the design and operation of sand filters in water treatment.

An experimental study on the aggregation of TiO2 nanoparticles under environmentally relevant conditions.

The eventual future scenario of a release of nanomaterials into the environment makes it necessary to assess the risk involved in their use by studying their behavior in natural waters. NanoTiO2 is one of the most commonly employed nanomaterials. In the present work we studied the aggregation rates, aggregate size and aggregate morphology of NanoTiO2 under the presence of inert electrolytes, divalent cations, and these two combined with natural organic matter, in an effort to provide a comprehensive investigation of the phenomena of interaction of nanomaterials and natural waters and elucidate some of the conflicting information reported in the literature. The stability of nanoparticles could be explained in all cases, at least qualitatively, in terms of classical DLVO interactions (Electrical Double Layer, Van der Waals). Divalent cations were adsorbed to the surface of the nanoparticles, neutralizing the negative charge at pH values greater than the point of zero charge and inducing aggregation. Natural organic matter (NOM) adsorbed to the particles and made their zeta potential more negative, hence stabilizing them by lowering the pH of maximum aggregation. Divalent cations partially neutralized the adsorbed NOM, and at high concentrations aggregation was observed with Ca(2+) but not Mg(2+), suggesting the presence of specific Ca(2+)-NOM bridges. SEM images visually revealed a fractal-like morphology of the aggregates formed under unfavorable conditions.