Phase-sensitive detection in Raman Tweezers: biological applications

To tackle this problem, during my PhD work, I have implemented a novel method that allows acquiring Raman spectra of a single trapped particle free from any background contribution. The method is based on the use of two collinear and copropagating laser beams. The first is devoted to trapping (trap laser), while the second one is used to excite the Raman transitions (pump laser). The trap laser moves the trapped particle periodically, by means of a galvomirror, back and forth across the pump laser. The back-scattered photons are analyzed by a spectrometer and detected by a photomultiplier. Then, the resulting signal is sent to a lock-in amplifier for phase-sensitive detection. The obtained results demonstrate that our Raman Tweezers system may find valuable applications in rapid sensing of biological samples in aqueous solutions. Finally, it has been demonstrated the potential of the developed Raman Tweezers system as a diagnostic tool to study a specific disease related to oxygenation capability of individual red blood cells, known as thalassemia. Thalassemia is the name of a group of genetic blood disorders. In thalassemia, the genetic defect results in reduced rate of synthesis of one of the globin chains that make up the Hb. If there is a reduced synthesis of one of the globin chains, the RBCs do not form properly and cannot carry sufficient oxygen. By way of a resonant excitation of Hb Raman bands, it has been examined the oxygenation capability of both normal and thalassemic erythrocytes. A reduction of this fundamental erythrocyte function for thalassemia has been shown. Raman spectroscopy has been also used to draw hemoglobin