In-situ monitoring of etching of bovine serum albumin using low-temperature atmospheric plasma jet

Direct Exposure of Dry Enzymes to Atmospheric Pressure Non-Equilibrium Plasmas: The Case of Tyrosinase

“…Therefore, Tyr seems to display remarkable resistance upon plasma exposure, i.e., considerable activity retention is observed also when very low enzyme amounts are used, with very weak dependence on the exposed amount. Upon drying, due to the so-called coffee-ring effect, the droplet of Tyr solution deposited on the glass slide leaves a ring-shaped solid structure with a diameter of 3.4 ± 0.4 mm and a horizontal width of ∼0.15 mm (Figure 3b) [40,43]. As a consequence, the major fraction of the enzyme is confined in a thick annular deposit of area 1.53 mm 2 with an effective protein surface density (total protein amount divided by the area occupied by the coffee-ring) of 3.27 μg‧mm 2 .…”

“…The twodimensional width and radius of the coffee-ring do not seem to vary appreciably with the deposited Tyr amount (as evaluated by the naked eye), so that the thickness of the deposit should depend mainly on the amount of protein. Within the above described approximation, 10 μg and 2 μg Tyr Upon drying, due to the so-called coffee-ring effect, the droplet of Tyr solution deposited on the glass slide leaves a ring-shaped solid structure with a diameter of 3.4 ± 0.4 mm and a horizontal width of ~0.15 mm (Figure 3b) [40,43]. As a consequence, the major fraction of the enzyme is confined in a thick annular deposit of area 1.53 mm 2 with an effective protein surface density (total protein amount divided by the area occupied by the coffee-ring) of 3.27 µg•mm 2 .…”

“…This increase can be explained considering that these atomic species, present as contaminants in the pristine Tyr deposit, cannot be etched away by the oxygen-containing plasma. As reported in the literature on low pressure and atmospheric pressure plasma etching of dry proteins (e.g., bovine serum albumin [40,60]), the building up of inorganic compounds at the surface of protein deposits can provide passivation effect and limit the action of reactive oxygen species present in the plasma in terms of etching efficiency. Interestingly, the fact that the total concentration of Na, K, P, and S significantly increases from 1.5 to 11.5 at % after 30 min of plasma exposure (Table 2), and that both residual thickness and activity do not decrease appreciably when process duration exceeds 30 min (Figure 3a), suggests that the formation on the deposit surface of a layer enriched in inorganic compounds protects Tyrosinase from further etching and damage.…”

“…Indeed, they can afford the desired surface modification with easier, faster, and more cost-effective plasma processes [27,[32][33][34]. Moreover, considerable efforts have been devoted to investigate the direct interaction of AP non-equilibrium plasmas with various biomolecules (e.g., proteins and nucleic acids) both in the dry state and in aqueous solutions, focusing on many different biomedical, biotechnological, and pharmaceutical applications [28,[35][36][37][38][39][40][41][42][43][44][45].…”

“…They induce extensive surface chemical modifications as well as considerable etching of carbon-based materials with formation of volatile products [27,55]. Importantly, ROSs are widely known to cause biomolecule damage [36,38,40,43]. The investigation of this feed mixture allows also evaluating possible detrimental effects induced by the presence of a severe O 2 contamination in the plasma.…”