## 1 Introduction  
The far infrared is a region in the infrared spectrum of electromagnetic radiation, defined as any radiation with a wavelength of 3-1000 \(\upmu\)m. Owing to its long wavelength, far infrared radiation (FIR) can penetrate up to 40 mm beneath the skin [1]. Furthermore, FIR allows even transmission of energy as heat [2, 3], applying rotational and vibrational modes to the molecule-forming bonds. This motion can alter cell membrane potential and mitochondrial metabolism [4]. Therefore, FIR can serve as a non-invasive and convenient therapeutic modality through its thermal and non-thermal effects [5, 6]. FIR reportedly improves blood flow, endothelial function, and ventricular arrhythmias, reducing the frequency of cardiovascular diseases, and improving the patency of arteriovenous fistulas in patients with hemodialysis [6, 7, 8, 9]. FIR also increased angiogenesis in mice with hindlimb ischemia by upregulating arterial endothelial nitric oxide synthase (eNOS) [6]. Besides, FIR stimulated cell signaling as a non-thermal effect. For instance, FIR stimulated platelet-derived growth factor-mediated skeletal muscle cell migration through extracellular matrix-integrin signaling [10]. FIR can also promote ischemia-induced angiogenesis in diabetic mice, restoring high glucose-suppressed endothelial progenitor cell functions both in vitro and in vivo [11]. Moreover, FIR exposure attenuated high-grade glycosylation end-product-induced damage in vascular endothelial cells activated by promyelocytic leukemia zinc finger protein and alleviated ischemia-reperfusion injury induced by heme oxygenase-1 in rat testis [12, 13].  
In contrast, FIR has also been known to exert inhibitory effects on cells. FIR exposure curbed the vascular endothelial growth factor (VEGF)-induced proliferation and phosphorylation of extracellular signal-regulated kinases in human umbilical vein endothelial cells (HUVEC) and the proliferation of human tongue squamous carcinoma cells (HSC3) and human epidermoid carcinoma cells (A431) via overexpression of a 70 kDa heat shock protein (HSP70) [14; 15]. In cancer therapy, FIR reportedly inhibits murine melanoma cell growth [16]. FIR inhibited the proliferation, migration, and angiogenesis of HUVEC via decreasing secretory clustering [17]. In addition, FIR inhibited breast cancer cell proliferation via increased nuclear Ca\({}^{2+}\)/calmodulin binding-modulated activation of checkpoint kinase 2 and suppressed the proliferation of human lung cancer cells by activating transcription factor 3 (ATF3) [18; 19]. Consequently, FIR exerts excitatory or inhibitory effects on cells. The FIR energy density used in these studies [1; 15] ranged from 0.1-13 mW/cm\({}^{2}\), suggesting that these effects do not depend on the density of FIR but on the cellular signals specifically triggering FIR. Cell signaling can be classified into two kinds: anabolism and catabolism. FIR affects cells via anabolism. During anabolism, FIR is absorbed by mitochondrial cytochrome c oxidase in the form of photons similar to near-infrared radiation [20; 21; 22]. These accepted photons activate the enzyme by photodissociating the inhibitory molecule (NO) from the copper B site [23]. The loss of NO yields a marked elevation in mitochondrial membrane potential, which increases electron transport, oxygen consumption, and adenosine triphosphate (ATP), leading to the activation of transcription factors [24], ultimately benefiting cells and tissues. However, which FIR exposure affects the cellular plasma membrane to trigger anabolism is still unknown. The mechanism related to anabolism likely involves the mitochondrial membrane, particularly mitochondrial calcium channels [25]. Therefore, this study aimed to investigate the inhibitory effect of FIR on cancer cells via the complement membrane attack complex (MAC) in the plasma membrane. To this end, we fabricated a tourmaline-based powder and induced an FIR-inhibitory effect on cells.