## 1 Introduction
In the recent times, ionic-liquid-anchored silica particles have been used in making polymer nanocomposites with enhanced properties, especially mechanical, thermal, and proton conductivity, for polymer electrolyte membrane fuel cell applications [33; 34; 35]. Moreover, immobilizing ionic liquids on xerogel silica helped researchers to achieve a solid-gas system for CO\({}_{2}\) capture [36]. In most cases, imidazolium-based ionic liquids were used as templates and structure-directing agents for the preparation of sol-gel-derived silica aerogels and ionogels [12]. However, [PERSON] et al. [37] used an ionic liquid as an additive to prevent the inactivation of enzymes during the sol-gel process, which retains 80% of the enzyme activity compared with enzymes encapsulated in gel without an ionic liquid. The enhanced activity and thermal stability of the horseradish peroxidase enzyme were achieved by encapsulating it in a room temperature ionic-liquid-based sol-gel matrix [38]. In the recent past, [PERSON] et al. [9] demonstrated the preparation of a red fluorescent protein encapsulated bio-aerogel using1-butyl-3-methylimidazololium chloride ionic liquid as a solvent and pore-forming agent. Here, 85% fluorescent activity of the protein was retained. Most of the ILs comprising imidazolium cations have been found to exhibit toxicity, sometimes more toxic than conventional organic solvents [39]. ILs containing imidazolium, pyridinium cations, and halide anions have been found to be highly toxic and less biodegradable, which can create aquatic environmental problems due to leaching into water resources [40]. Recently, researchers have focused on the use of ionic liquids prepared from cations and anions of biological components with well-studied biological and biodegradation properties [34; 35; 41; 42], in particular, a choline-cation-based ionic liquid, which is an important cation present in the liver that regulates biological metabolism in the human body [41; 42; 43; 44]. There are several ionic liquids reported to have different anions such as formate, lactate, dihydrogen phosphate, levulinate, and so forth, in combination with choline cations. Naturally, choline and phosphate ions are present in the human body, so the combination of these cations and anions is of interest. Choline dihydrogen phosphate (CDHP) is an important bio-ionic liquid reported to have the combination of chaotropic cations and kosmotropic anions, which can stabilize proteins in aqueous solutions [45]. Moreover, [PERSON] et al. [46] also reported a series of choline-based ionic liquids that can dissolve proteins and retain their secondary structure at high temperatures. The structural stability and activity of cytochrome \(c\) in the hydrated form of choline dihydrogen phosphate IL was clearly demonstrated by [PERSON] et al. [47] using different techniques. According to [PERSON] et al. [48], cytochrome \(c\) retains its native state and remains active for 18 months during storage at room temperature in hydrated choline dihydrogen phosphate IL compared to ILs from various anions such as dibutyl phosphate, acetate, lactate, and methane sulfonate. The high solubility of DNA from salmon testes was achieved by dissolving it in choline-based ionic liquids, and the recyclability of IL was found to be very good (95%) [49]. Specifically, CDHP is an important candidate for the encapsulation of biomolecules into a silica gel matrix [50]. The hydrated form of CDHP ionic liquid greatly improved the thermodynamic stability of DNA duplex, which opens up a new pathway for the development of biomaterials from DNA base pair switches [51]. Recently, we reported for the first time the use of a choline formate IL for preparing biocompatible and surface-active silica aerogels with 90% cell viability and proliferation compared with control gel without IL [52; 53]. In this study, our main approach was to prepare silica-based ionogels using biocompatible CDHP ionic liquid as a green solvent and to study the role of ionic liquid concentration on its properties.