## 1 Introduction  
Protection against flames is a key issue in the industry [1, 2]. Over 2 million tonnes of flame-retardant chemicals were used in 2020 [3]. Flame retardants cover a highly diverse range of substances, materials and areas of application [4, 5, 6]. Areas of application include personal protective equipment (PPE) and fire curtains, used, for example, in airports for the purpose of separating fire compartments [7, 8, 9, 10]. In particular, these textiles are impregnated with flame retardants [8, 11]. Many of the flame retardants commonly used today are applied to textiles with adhesion promoters [12, 13]. The flame retardants as well as the adhesion promoters are harmful to health and the environment [13, 14]. The European Union's REACH regulation (Registration, Evaluation, Authorization and Restriction of Chemicals) will ban around 1400 chemicals over the next few years [15, 16]. Around 220 chemicals are already banned. The banned chemicals are used for flame retardancy, among other things [5, 17, 18, 19, 20, 21, 22]. The banned substances have properties that are harmful to health and the environment [2, 14]. Brominated flame retardants are one of the substances that are harmful to health and the environment and had a market share of around 18 % in 2020 [3, 23]. The use of brominated flame retardants is still subject to a time limit until the use of these substances is banned [24; 25]. It is therefore necessary to develop alternatives to conventional flame retardant/adhesion promoter combinations that are less harmful to the environment than conventional flame retardants and do not fall under the REACH bans. In addition to the REACH regulation, the sustainability concept is also crucial [14; 26]. The use of innovative bio-based adhesion promoters, such as anchor peptides, extends the period until a new finish is required for the textiles [27; 28; 29; 30; 31]. As the flame retardant remains on the textiles for longer, less flame retardant is required. Extending the time interval for reimpregnation is particularly interesting in the context of maintaining PPE, e.g., in blast furnace protection [32]. Material-binding peptides (MBPs) are highly diverse in terms of their small amino acid sequence, ranging from 30 to 100 amino acids in length. MBPs have a specific material-binding ability to a broad portfolio of materials including polymers, metals, ceramics, glass, textiles, and other natural surfaces [33]. The affinity and efficient binding of MBPs to material surfaces rely on non-covalent multiple-site interactions (e.g., electrostatic, hydrophobic, \(\pi\)-\(\pi\) interactions, and hydrogen bonds), enabling highly selective and intensive binding under mild conditions [34]. For example, a mere 1 g of MBPs covering up to 250 m\({}^{2}\), at a cost of less than one cent per square meter, further solidifies their application [28]. Moreover, the binding properties can be tailored by directed evolution (e.g., KnowVolution) to meet varied formulation and application requirements [35]. The diverse binding affinities of MBPs bring a wide range of applications in plant/human health, the immobilization of catalysts, bioactive coatings, accelerated polymer degradation and analytics for micro/nanoplastic quantification [36]. To date, no industrial process is known for the sustainable finishing of textiles with material-binding peptides (MBPs) [37; 38]. Due to the high specificity of MBPs, the bifunctional peptide, constructed by fusing two MBPs, brings new strategies for surface functionalization. The bifunctional peptide comprises two MBPs connected by a linker to prevent intermolecular interactions [39]. One MBP binds specifically to a material surface (e.g., textiles), while the other MBP selectively interacts with the desired functional molecule (e.g., flame-retardant additives). Applying bifunctional peptides to treat textiles is both cost-effective and resource-efficient.