# Microbial-Based Biotechnology: Production and Evaluation of Selenium-Tellurium Nanoalloys
## 1 Introduction  
In the world, a huge risk to public health in the 21 st century is multi-drug-resistant (MDR) bacterial infections [1] and MDR malignancies. More than 90% of deaths in cancer patients are due to drug resistance [2]. Unrestricted and unlicensed use of antibiotics has led to the rapid development of antibiotic resistance in bacterial strains [3]. [PERSON] et al. predict that by 2050, MDR will put 10 million lives and $100 trillion in total economic output at risk annually [4]. Therefore, developing new and effective anticancer and antibacterial agents is of great importance. Nanotechnology involves creating materials at the atomic level that are stabilized by hydrophobic, electrostatic, coordinative, or hydrogen bonds. Stable nanoparticles (NPs)can be generated in polymer solutions by reducing agents using several transformation methods. Volatile or toxic chemicals are commonly used for the synthesis of NPs. But recently, green synthesis of NPs and quantum dots (QDs) has become a trend due to their high bioavailability and low toxicity. NPs and QDs are popular as anticancer and antibacterial agents. QDs are small, spherical, light-emitting nanocrystalline particles. They are smaller than 10 nm and contain about 200 to 10,000 atoms. NPs can penetrate the bacterial cell wall and disrupt biochemical processes by disrupting organelles, ultimately destroying the bacterium [5]. [PERSON] discovered tellurium (Te) in 1783 in the Feis Banya mine in the Zartona region of Transylvania, Romania (formerly Hungary). There is an exciting story about the discovery of tellurium involving the famous music composer [PERSON]. After 250 years, despite advances in nanotechnology, little research has been conducted on Te and tellurium nanoparticles (Te-NPs). Similar to other nanoparticle transformations, Te-NPs can be obtained using any conversion method. Generally, Te-NPs exhibit excellent anticancer and antibacterial properties. For example, ultrathin tellurium nanosheets combining photothermal effects and chemotherapy showed anticancer effects [6]. Also, aloe vera-mediated Te-NPs have shown anticancer activity against melanoma cells. This can be explained by damage to cellular proteins, lipids, nucleic acids, organelles, and membranes due to increased reactive oxygen species (ROS) levels [7]. [PERSON] discovered selenium in a sample of pyrite in 1817 while producing sulfuric acid at the Falun mine in Stockholm, Sweden. Since then, many studies have been conducted on Se. NPs from selenium have presented many potential opportunities over the past 200 years. Se-NPs can also be prepared using other reductions such as \(\gamma\)-radiolysis, chemical, and biological reduction [8]. Actually, bacterial and plant metabolites mainly cause the biological transformation of NPs, strengthening and enhancing the reduction process, which is the most effective as it is cheap, rapid, and highly pure [9]. Se-NPs have several important characteristics including small size, atomic arrangement, shape, complex internal structure, and high surface area-to-volume ratio. Therefore, they can be used in a variety of applications including nanomedicine [10; 11; 12], food packaging [13; 14], and food supplementation [15; 16]. The size of Se-NPs determines their physical and biological properties. Smaller particle size always results in higher bioactivity. Their most important advantages are higher bioavailability and lower toxicity than organic and inorganic forms [17]. Se-NPs have been shown to have high antioxidant [18], detoxification [19; 20], antibacterial [21; 22], antifungal [23; 24], antiviral [25], and antidiabetic effects [26]. For example, biosynthesized Se-NPs inhibited the growth of _Staphylococcus aureus (S. aureus)_[22; 27], _Escherichia coli (E. coli)_[27], _Saccharomyces cerevisiae_ (S. cerevisiae) [28], _Steinrenema feltiae_ (S. feltiae) [28], _Pseudomonas aeruginosa (P. aeruginosa)_[29], _Streptococcus pyogenes (S. pyogenes)_[27], and _Apergillus clavatus (A. clavatus)_[27].