## 1 Introduction  
Astaxanthin (3,3\({}^{\prime}\)-dihydroxy-\(\beta\),\(\beta^{\prime}\)-carotene-4,4\({}^{\prime}\)-dione), a secondary ketocarotenoid phytopgment, is widely used in the cosmetic, aquaculture, food, and pharmaceutical industries [1, 2]. The potent antioxidant activity of astaxanthin has preventive effects against cancer, diabetes, cardiovascular disease, ulcers, and inflammation through the enhancement of the immune response [3, 4]. Astaxanthin has been proposed as a potential georoprotector that may affect the rate of human aging and extend cell longevity [5]. This biomolecule can induce the synthesis of hyaluron (hyaluronic acid), which is related to skin hydration [6]. _Haematococcus Iacustis_ (formerly, _H. pluvialis_; [7]), a unicellular freshwater green microalga, is considered an important source of astaxanthin because of its high astaxanthin content (~4% of dry weight) and potential for mass cultivation in open-pond and photobioreactor systems [8, 9]. Astaxanthin accumulates in _H. lacustis_ as neutral lipid bodies, primarily in mono- and di-ester forms with fatty acids, during the physiological development of dormant alphasopores (cysts) from vegetative palmella cells under conditions of stress, such as nutrient deprivation, pH shock, high salinity, strong light irradiance, and nanoparticleexposure [4; 10; 11]. In particular, cell encrystment is accompanied by the formation of a rigid multilayered cell wall structure. The cell wall thickness (\(\sim\)4 \(\upmu\)m) of \(H\). _lacustris_ cysts is significantly greater than that of _Chlamydomonas_ (\(\sim\)351 nm), which is extensively used in various algal biorefineries [12; 13; 14]. To destroy the cell wall of mature _H. lacustris_ cysts, harsh chemical treatments, such as hydrochloric acid administered at high temperatures [15], and highly energy-intensive mechanical methods, such as high-pressure homogenization [16], are applied extensively. However, excessive physicochemical stress can degrade the molecular structure of as-taxanthin, significantly reducing its antioxidative activity [3; 17]. Therefore, efficient cell disruption and astaxanthin extraction are considered important technical issues affecting the overall economics of _H. lacustris_ biorefineries [9; 18]. Ionic liquids (ILs) are new \"green\" solvents with several unique properties, such as good thermal and chemical stability, low volatility, and high hydrolytic activity [19; 20]. In particular, ILs can be custom-designed and synthesized as asymmetric organic cations and inorganic or organic anions, and they have been widely applied in lignocellulosic and algal bioenergy biorefineries. However, ILs generally require high-temperature operating conditions (\(\sim\)140 \({}^{\circ}\)C) to decompose the cell walls of various algal species, including _Chlamydomonas_, _Chorella_, _Nannochloropsis_, and _Haematococcus_[17; 19; 20; 21; 22; 23]. This implies that despite the strong cell-wall-disrupting effect of ILs, their use is not always feasible in the extraction of heat-sensitive bioactive algal products, including astaxanthin. For example, [PERSON] et al. [17] found that the extraction yields of lipids and astaxanthin were significantly different, at 60-82% and 11-17%, respectively, when 1-ethyl-3-methylimidazolium [Emim]-based ILs with bis(trifluoromethylsulfonyl)imide and acetate anions were applied to _H. lacustris_ cyst biomass at 80 \({}^{\circ}\)C.  
Recently, we reported the synthesis of ultrathin \(\upalpha\)-quartz nanoplates (NPLs) using a novel template-free hydrothermal method; we demonstrated their disruptive effect on algal cell walls for subsequent dichloromethane/methanol (DCM/MeOH) solvent extraction [13]. Here, we aimed to investigate the technical feasibility of room-temperature IL-based astaxanthin extraction from rigid _H. lacustris_ cysts using \(\upalpha\)-quartz NPLs as cell-wall disrupters.