Electrical and optical properties of a gradient microplasma for microfluidic chips

The influence of the electrical and optical properties of a spatially varying He microplasma on the gradient surface modification of an adsorbed protein layer inside a microfluidic chip was investigated. Microplasma was generated inside a native polydimethylsiloxane (PDMS) microchannel. Excited and metastable states of He and N2 (from air) potentially played a major role in the removal/modification of protein during the discharge period. In‐between discharge events, N2(A) metastables can also induce bond breaking and surface modification. The purge time of the feed gas was shown to be important in the use of small scale microplasma sources for surface processing or protein modification. We report on how the intrinsic properties of a spatially varying microplasma might influence the gradient surface modification of an adsorbed protein layer inside a microfluidic chip. The temporal evolution of selected He and nitrogen (N2) emission lines suggest that excited and metastable states of He and N2 can play a major role in the removal/modification of protein during the discharge period. In‐between discharge events, the N2(A) metastables can also induce bond‐breaking and surface modification. However, the role of He in the modification of protein inside the microchannel is only relevant if the process gas (He) is flushed through the microchannel.