Influence of light-emitting diodes (LEDs) on the 2,4-diclorophenoxyacetic acid phytoremediation by plectranthus neochilus.

2,4-Dichlorophenoxyacetic acid (2,4-D) is an herbicide widely used in crops against broadleaf weeds. However, 2,4-D residues are considered an environmental pollutant in bodies of water. Phytoremediation with Plectranthus neochilus is a substantial strategy to remove 2,4-D from the aquatic environment. The objective of this study was to verify the efficiency of the association of the photostimulus by Light Emitting Diodes (LED) with P. neochilus to improve phytoremediation of 2,4-D in water. Phytoremediation was evaluated with the following samples: natural light, white LED, blue LED, and red LED, with and without the plant as controls. The data corresponding to the validation of the method were in accordance with the required parameters: R2: 0.9926; RSD: 1.74%; LOD: 0.075 mg.L-1; LOQ: 0.227 mg.L-1 and recovery by SPE was 76.57%. The efficiency of the association of LED with P. neochilus in the 28 days was: ambient light + plant (47.0%); white light + plant (37.10%); blue light + plant (26.80%); red light + plant (3.32%). This study demonstrated, for the first time, the efficiency of using LEDs light in association with P. neochilus for the phytoremediation of 2,4-D in water.

Phytoremediation of organic compounds in water is a time-consuming process and generally unfavorable to the plant. This study demonstrated that the photostimulation with blue and red LED lights can accelerate the phytoremediation of the herbicide by P. neochilus, decreasing the t_1/2 of 2,4-D in water by 2 and 5 times, respectively. We equate the time of this process to physical-chemical degradation methods, but without the use of reagents, creating a green strategy to accelerate the decontamination of water resources contaminated with pesticides.

Detachment of Dunaliella tertiolecta Microalgae from a Glass Surface by a Near-Infrared Optical Trap.

We report on the observation of the detachment in situ and in vivo of Dunaliella tertiolecta microalgae cells from a glass surface using a 1064 nm wavelength trapping laser beam. The principal bends of both flagella of Dunaliella were seen self-adhered to either the top or bottom coverslip surfaces of a 50 µm thick chamber. When a selected attached Dunaliella was placed in the trapping site, it photoresponded to the laser beam by moving its body and flagellar tips, which eventually resulted in its detachment. The dependence of the time required for detachment on the trapping power was measured. No significant difference was found in the detachment time for cells detached from the top or bottom coverslip, indicating that the induced detachment was not due solely to the optical forces applied to the cells. After detachment, the cells remained within the optical trap. Dunaliella detached from the bottom were seen rotating about their long axis in a counterclockwise direction, while those detached from the top did not rotate. The rotation frequency and the minimal force required to escape from the trap were also measured. The average rotation frequency was found to be independent of the trapping power, and the swimming force of a cell escaping the laser trap ranged from 4 to 10 picoNewtons. Our observations provide insight into the photostimulus produced when a near-infrared trapping beam encounters a Dunaliella. The microalgae frequently absorb more light than they can actually use in photosynthesis, which could cause genetic and molecular changes. Our findings may open new research directions into the study of photomovement in species of Dunaliella and other swimming microorganisms that could eventually help to solve technological problems currently confronting biomass production. In future work, studies of the response to excess light may uncover unrecognized mechanisms of photoprotection and photoacclimation.

Photostimulus-Responsive Large-Area Two-Dimensional Covalent Organic Framework Films.

Using an external stimulus to modulate the electronic structure of covalent organic frameworks (COFs) is very important because such a response will endow them with additional functions. A two-dimensional (2D) COF, constructed from a photo-responsive unit (1,2-bis(5-formyl-2-methylthien-3-yl)cyclopentene), can reversibly switch its electrical conductivity 200 times from low state (the open form) to high state (the closed form) upon irradiation with UV light and reversible with visible light. This reversible phenomenon can be monitored through a circuit containing a light-emitting diode (LED). Photoinduced ring-closing/opening reactions do not destroy the integrity of the frameworks, and both processes follow logarithmic carrier generation with time. Moreover, the correlation between COFs electronic properties and changes in photoinduced kinetics and absorption curves has been demonstrated.

Photoinduced morphological transformations of soft nanotubes.

In water, synthetic amphiphiles composed of a photoresponsive azobenzene moiety and an oligoglycine hydrogen-bonding moiety selectively self-assembled into nanotubes with solid bilayer membranes. The nanotubes underwent morphological transformations induced by photoisomerization of the azobenzene moiety within the membranes, and the nature of the transformation depended on the number of glycine residues in the oligoglycine moiety (i.e., on the strength of intermolecular hydrogen bonding). Upon UV-light irradiation of nanotubes prepared from amphiphiles with the diglycine residue, trans-to-cis isomerization induced a transformation from nanotubes (inner diameter (i.d.) 7 nm), several hundreds of nanometers to several tens of micrometers in length, to imperfect nanorings (i.d. 21-38 nm). The cis-to-trans isomerization induced by continuous visible-light irradiation resulted in the stacking of the imperfect nanorings to form nanotubes with an i.d. of 25 nm and an average length of 310 nm, which were never formed by a self-assembly process. Time-lapse fluorescence microscopy enabled us to visualize the transformation of nanotubes with an i.d. of 20 nm (self-assembled from amphiphiles with the monoglycine residue) to cylindrical nanofibers with an i.d. of 1 nm; shrinkage of the hollow cylinders started at the two open ends with simultaneous elongation in the direction of the long axis.