Optical emission spectroscopic diagnostics of a non-thermal atmospheric pressure helium-oxygen plasma jet for biomedical applications

摘要

In this work, we have applied optical emission spectroscopy diagnostics to investigate the characteristics of a non-thermal atmospheric pressure helium plasma jet. The discharge characteristics in the active and afterglow region of the plasma jet, that are critical for biomedical applications, have been investigated. The voltage-current characteristics of the plasma discharge were analyzed and the average plasma power was measured to be around 18W. The effect of addition of small fractions of oxygen at 0.1%-0.5% on the plasma jet characteristics was studied. The addition of oxygen resulted in a decrease in plasma plume length due to the electronegativity property of oxygen. Atomic and molecular lines of selected reactive plasma species that are considered to be useful to induce biochemical reactions such as OH transitions A~2∑~+ (v = 0, 1) → X~2Π(Δ_v = 0) at 308nm and A~2∑~+ (v = 0, 1) → X~2Π(Δ_v = 1)at 287nm, O 1 transitions 3p~5P→3s~5S~0 at 777.41 nm, and 3p~3P→3s~3S~0 at 844.6 nm, N_2(C-B) second positive system with electronic transition C~3Π_u→ B~3Π in the range of 300-450 nm and N_2~+(B-X) first negative system with electronic transition B~2∑_u~+ → X~2∑_g~+(Δ_v = 0) at 391.4nm have been studied. The atomic emission lines of helium were identified, including the He I transitions 3p~3P~0→2s~3S at 388.8 nm, 3p~1P~0→ 2s~1S at 501.6nm, 3d~3D→2p~3P~0 at 587.6nm, 3d~1D→2p~1P~0 at 667.8nm, 3s~3S~1→2p~3P~0 at 706.5 nm, 3s~1S~0→2p~1P~0 at 728.1 nm, and H_x transition 2p-3d at 656.3 nm. Using a spectral fitting method, the OH radicals at 306-312 nm, the rotational and vibrational temperatures equivalent to gas temperatures of the discharge was measured and the effective non-equilibrium nature of the plasma jet was demonstrated. Our results show that, in the entire active plasma region, the gas temperature remains at 310 ± 25 K and 340 ± 25 K and it increases to 320 ± 25 K and 360 ± 25 K in the afterglow region of the plasma jet for pure helium and helium/oxygen (0.1%) mixture, respectively. Additionally, the vibrational temperatures range from 2200 ± 100K and 2500 ± 100K for pure helium and helium/oxygen (0.1%) mixture, respectively. The plasma jet was tested on heat sensitive polymer films used in biomedical applications such as polyethylene terephthalate and poly-L-lactide samples continuously for several minutes without causing any physical or thermal damage to the films. The plasma jet produces significant reactive species of interest while the gas temperatures remain very low demonstrating its potential for a range of biomedical applications.