Interactions of ultrashort laser pulses with hemoglobin: Photophysical aspects and potential applications.

Hemoglobin (Hb), a life-sustaining and highly abundant erythrocyte protein, is not readily fluorescent. A few studies have already reported Two-Photon Excited Fluorescence (TPEF) of Hb, however, the mechanisms through which Hb becomes fluorescent upon interaction with ultrashort laser pulses are not completely understood. Here, we characterized photophysically this interaction on Hb thin film and erythrocytes using fluorescence spectroscopy upon single-photon/two-photon absorption, and UV-VIS single-photon absorption spectroscopy. A gradual increase of the fluorescence intensity, ending up with saturation, is observed upon prolonged exposure of Hb thin layer and erythrocytes to ultrashort laser pulses at 730 nm. When compared to protoporphyrin IX (PpIX) and oxidized Hb by H2O2, TPEF spectra from a thin Hb film and erythrocytes showed good mutual agreement, broad peaking at 550 nm, supporting hemoglobin undergoes degradation and that same fluorescent specie(s) originating from the heme moiety are generated. The uniform square shaped patterns of the fluorescent photoproduct exhibited the same level of the fluorescence intensity even after 12 weeks from the formation, indicating high photoproduct stability. We finally demonstrated the full potential of the formed Hb photoproduct with TPEF scanning microscopy towards spatiotemporally controlled micropatterning in HTF and single human erythrocyte labelling and tracking in the whole blood.

Characterization and Optimization of Real-Time Photoresponsive Gelatin for Direct Laser Writing.

There is an abundance of plastic materials used in the widest range of applications, such as packaging, machine parts, biomedical devices and components, etc. However, most materials used today are non-decomposable in the environment, producing a huge burden on ecosystems. The search for better, safer alternatives is still on. Here we present a detailed analysis of a simple, cheap, non-toxic, even edible, eco-friendly material, which can be easily manufactured, laser patterned and used for the fabrication of complex structures. The base substance is gelatin which is made photoresponsive by adding plasticizers and sensitizers. The resulting films were analyzed with respect to their optical, thermal and mechanical properties, which can be modified by a slight variation of chemical composition. The material is optimized for rapid laser-manufacturing of elastic microstructures (lenses, gratings, cantilevers, etc.) without any waste or residues. Overall, the material properties were tailored to increase photothermal responsivity, improve the surface quality and achieve material homogeneity, transparency and long-term stability (as verified using electron microscopy, infrared spectroscopy and differential scanning calorimetry).