Fluorescence enhanced BA-LIFT for single cell detection and isolation.

Laser bioprinting is a term that refers to a group of laser-based techniques for printing living cells with high precision and good viability. Most of these techniques are based on modifications of the standard laser induced forward transfer technique (LIFT). When it comes to printing living material, direct laser irradiation should be avoided, therefore an indirect LIFT technique comprising an energy absorption layer should be used. This work presents a blister actuated-LIFT (BA-LIFT) technique which uses a commercial polyimide tape as a uniform energy absorption layer. To increase the potential of the technique for cell selection and printing accuracy, we take advantage of the high optical transmission of the polyimide layer to implement an in-line fluorescence and conventional imaging vision system coaxial with the laser path. With this system and using the appropriate staining methodology it is possible to track and identify different cell types, selecting those to be transferred and tracking cell survival both in the donor and acceptor substrates. We studied the BA-LIFT printability map for sodium alginate and methylcellulose hydrogels in the fluence range from 6.1 to 2.0 J cm-2 together with the cell viability assessment measured by our fluorescence system. The study has revealed that less concentrated, therefore less viscose hydrogel shows better results with lower fluences, whereas hydrogels with higher concentrations present better results at higher fluences. Also, at low fluences 98 % of cell viability was obtained, besides both primary cells and cell lines keep their integrity, proliferating and functional activity. The technique was tested by tracking and targeting mouse hematopoietic progenitor stem cells transferred to assess colony forming units; moreover, natural killer cells were isolated and its activation in a stimulation media was tracked with the fluorescence system.

Spectroscopic properties of the 1.4 microm emission of Tm3+ ions in TeO2-WO3-PbO glasses.

In this work, we report the spectroscopic properties of the infrared 3H4-->3F4 emission of Tm3+ ions in two different compositions of glasses based on TeO2, WO3, and PbO for three Tm2O3 concentrations (0.1,0.5, and 1 wt%). Judd-Ofelt intensity parameters have been determined and used to calculate the radiative transition probabilities and radiative lifetimes. The infrared emission at around 1490 nm corresponding to the 3H4-->F4 transition has two noticeable features if compared to fluoride glasses used for S-band amplifiers. On one hand, it is broader by nearly 30 nm, and on the other, the stimulated emission cross section is twice the value for fluoride glasses. Both the relative intensity ratio of the 1490 nm emission to 1820 nm and the measured lifetime of the 3H4 level decrease as concentration increases, due to the existence of energy transfer via cross-relaxation among Tm3+ ions. The analysis of the decays from the 3H4 level with increasing concentration indicates the presence of a dipole-dipole quenching process assisted by energy migration.