Several studies have revealed that various diseases such as cancer have been associated with elevated phospholipase A₂ (PLA₂) activity. Therefore, the regulation of PLA₂ catalytic activity is undoubtedly vital. In this study, effective inactivation of PLA₂ due to reactive species produced from cold physical plasma as a source to model oxidative stress is reported. We found singlet oxygen to be the most relevant active agent in PLA₂ inhibition. A more detailed analysis of the plasma‐treated PLA₂ identified tryptophan 128 as a hot spot, rich in double oxidation. The significant dioxidation of this interfacial tryptophan resulted in an N‐formylkynurenine product via the oxidative opening of the tryptophan indole ring. Molecular dynamics simulation indicated that the efficient interactions between the tryptophan residue and phospholipids are eliminated following tryptophan dioxidation. As interfacial tryptophan residues are predominantly involved in the attaching of membrane enzymes to the bilayers, tryptophan dioxidation and indole ring opening leads to the loss of essential interactions for enzyme binding and, consequently, enzyme inactivation.

As a new field of oxidative stress-based therapy, cold physical plasma is a promising tool for several biomedical applications due to its potential to create a broad diversity of reactive oxygen and nitrogen species (RONS). Although proposed, the impact of plasma-derived RONS on the cell membrane lipids and properties is not fully understood. For this purpose, the changes in the lipid bilayer functionality under oxidative stress generated by an argon plasma jet (kINPen) were investigated by electrochemical techniques. In addition, liquid chromatography-tandem mass spectrometry was employed to analyze the plasma-induced modifications on the model lipids. Various asymmetric bilayers mimicking the structure and properties of the erythrocyte cell membrane were transferred onto a gold electrode surface by Langmuir-Blodgett/Langmuir-Schaefer deposition techniques. A strong impact of cholesterol on membrane permeabilization by plasma-derived species was revealed. Moreover, the maintenance of the barrier properties is influenced by the chemical composition of the head group. Mainly the head group size and its hydrogen bonding capacities are relevant, and phosphatidylcholines are significantly more susceptible than phosphatidylserines and other lipid classes, underlining the high relevance of this lipid class in membrane dynamics and cell physiology.

Cold physical plasma is a partially ionized gas operated at body temperature and utilized for heat-sensitive technical and medical purposes. Physical plasma is a multi-component system consisting of, e.g., reactive species, ions and electrons, electric fields, and UV light. Therefore, cold plasma technology is an interesting tool for introducing biomolecule oxidative modifications. This concept can be extended to anticancer drugs, including prodrugs, which could be activated in situ to enhance local anticancer effects. To this end, we performed a proof-of-concept study on the oxidative prodrug activation of a tailor-made boronic pinacol ester fenretinide treated with the atmospheric pressure argon plasma jet kINPen operated with either argon, argon–hydrogen, or argon–oxygen feed gas. Fenretinide release from the prodrug was triggered via Baeyer–Villiger-type oxidation of the boron–carbon bond based on hydrogen peroxide and peroxynitrite, which were generated by plasma processes and chemical addition using mass spectrometry. Fenretinide activation led to additive cytotoxic effects in three epithelial cell lines in vitro compared to the effects of cold plasma treatment alone regarding metabolic activity reduction and an increase in terminal cell death, suggesting that cold physical plasma-mediated prodrug activation is a new direction for combination cancer treatment studies.

The present study demonstrates the application of scanning electrochemical microscopy to follow the morphological changes of the lipid bilayer under oxidative stress or due to the action of membrane proteins or antimicrobial peptides.

Amphiphilic hydrogels from mixtures of 2-hydroxyethyl methacrylate and 2-(diethylamino)ethyl methacrylate p(HEMA-co-DEAEMA) with specific pH sensitivity and hydrophilic/hydrophobic structures were designed and polymerized via plasma polymerization. The behavior of plasma-polymerized (pp) hydrogels containing different ratios of pH-sensitive DEAEMA segments was investigated concerning possible applications in bioanalytics. In this regard, the morphological changes, permeability, and stability of the hydrogels immersed in solutions of different pHs were studied. The physico-chemical properties of the pp hydrogel coatings were analyzed using X-ray photoelectron spectroscopy, surface free energy measurements, and atomic force microscopy. Wettability measurements showed an increased hydrophilicity of the pp hydrogels when stored in acidic buffers and a slightly hydrophobic behavior after immersion in alkaline solutions, indicating a pH-dependent behavior. Furthermore, the pp (p(HEMA-co-DEAEMA) (ppHD) hydrogels were deposited on gold electrodes and studied electrochemically to investigate the pH sensitivity of the hydrogels. The hydrogel coatings with a higher ratio of DEAEMA segments showed excellent pH responsiveness at the studied pHs (pH 4, 7, and 10), demonstrating the importance of the DEAEMA ratio in the functionality of pp hydrogel films. Due to their stability and pH-responsive properties, pp (p(HEMA-co-DEAEMA) hydrogels are conceivable candidates for functional and immobilization layers for biosensors.