## 1 Introduction  
Combining nanoparticles and proteins results in new nanomaterials with multiple possible applications [1; 2; 3; 4]. The way of junction building may define the future function, as it influences the protein-nanoparticle interaction routes. There are several ways to achieve such a junction, and a final product might be a colloid (not strictly called \"a solution\") or deposited on a solid substrate. The last may lead to the creation of 2D materials, with a nanosize in one of its dimensions and several centimeters or even meters in two other dimensions. The type of 2D material is graphene, which might be produced in sheets with huge surfaces [5]. The other known examples are molybdenum disulfide nanosheets, boron nitride nanolayers, and metal oxide layers, as well as 2D versions of silica or gold. In this understanding, 2D materials are of nonbiological origin, and their further interaction with protein has been already exploited [6; 7]. It is known, for example, that the direct interaction of a protein and an inorganic surface may lead to protein refolding, denaturation, and the loss of protein-specific properties. However, the composite of nonbiological structures and a nanolayer of proteins still fits into the definition of a 2D nanomaterial; therefore, we will use this term with its broader meaning. Here, we investigated the type of 2D nanomaterial created by the sequential deposition of monolayers made of fluorescent proteins (FPs) and colloidal quantum dots (QDs) on a stable support of polyvinylidene diluoride (PVDF) membrane. Fluorescent proteins (FPs), such as a green fluorescent protein (GFP), an mCherry, or an mBanana, are the product of the biotechnological modification of fluorescent proteins found in nature [8; 9]. They are engineered to have better stability, as well as desired extinction and emission spectra. They are also easily expressed in heterologous bacterial systems, which leads to the relatively cheap production of high amounts of those proteins. Simple gene engineering might be used to introduce additional polypeptide fragments to a main FP sequence. Such peptides might be a specific tag, such as a HisTag (six-ten histidine residues in a row), used for single-step protein purification, as well as for specific junctions in nanoassemblies [10; 11; 12]. QDs are nanocrystals (with a typical diameter of 1-10 nm) of semiconductor materials. They may be composed of a single material (such as CdTe, as used here) or consist of a core and shell, such as CdSe/ZnS QDs [13]. Additionally, the surface of nanocrystals is stabilized by a small organic ligand, deciding the charge of the nanoparticle in a water-based solution [14]. QDs are well known for their fluorescence ability, resulting from a quantum confinement effect during size reduction starting from a bulk material [15; 16]. The maximum emission of QD fluorescence depends on the diameter of the nanoparticle, which means that a nanoparticle of the same material (e.g., CdTe) but of a different size, shows a different color of fluorescence. Therefore, achieving a desired color of a QD emission is a simple task of slightly longer or shorter synthesis time. The absorption spectrum of QD is very broad; hence, their extinction may be realized by a broad spectrum of light sources, which is the advantage over conventional fluorophores. QDs are also very resistant to photobleaching. On the other hand, they are toxic to biological organisms, which reduces their actual application to in vitro assays [17; 18]. Poly-L-Lysines (PLLs), used in our study as modifiers for sequential monolayers, are frequently used as a matrix, facilitating the adhesion of various elements (living cells, organelles, and carbon nanotubes, etc.) to surfaces (glass and mica) and making covered surfaces or scaffolds compatible [19; 20]. PLL-coated graphene quantum dots were shown to be useful in the detection of cysteine and homocysteine [21]. PLLs are polypeptides, which are varied in length and size and composed of an amino acid, lysine.