*4.4. Plasma-Based Synthesis*

This technique can be combined with those based on mechanical exfoliation to minimize the aforementioned problems. Plasma engraving obtained with Ar<sup>+</sup> gas glow discharge ensures considerable advantages, notably: (i) the reduction of all impurities typically on the adhesive tape; and (ii), this technique can lead to better precision of the proportions of the BP layers. This is possible thanks to the modulation of engraving times, which would allow us to better control the production stage [25].

### *4.5. CVT (Chemical Vapor Transport) Synthesis*

Among the bottom-up techniques, CVT is the one which shows the most promise in the synthesis of BP. This technique needs a chemical reaction to occur between a solid and a gas, resulting in the formation of mono-layers of BP after precipitation [26]. More in detail, the molecules of BP are used as precursors within a tube filled with argon. Once both temperature and time have been set, there is the further step: deposition. To remove impurities, several baths in toluene or acetone are suggested. Therefore, as previously described, numerous production techniques will produce BP nanosheets which are characterized by different and specific chemical-physical properties. Currently, Raman spectroscopy is used to evaluate the purity of the BP samples, using a laser operating at 514 nm. Then, using techniques such as HRTEM (high-resolution electron transmission microscopy), AFM (atomic force microscopy), and XPS (X-ray photonic spectroscopy), the structures of BP can be investigated at high resolution [22].

### **5. Biomedical Applications of BP**
