# BODIPY-Based Nanomaterials--Sensing and Biomedical Applications
## 1 Introduction
### Brief Characterization of Selected Nanoparticles  
The selected nanoparticles below were introduced and discussed in terms of the most important physicochemical features of potential applicability in nanomedicine. There is no doubt that gold nanoparticles are among the most frequently applied metallic nanoparticles for various purposes, especially in medicine. They are produced via the reduction reaction of gold salts and are stabilized by phosphines, alkanethiols or citrates. The surface of gold nanoparticles can easily be chemically modified with ligands containing functional groups such as thiols, phosphines, and amines [21]. The functional groups of the surface ligands allow some other moieties to be attached, such as oligonucleotides, proteins, and antibodies, to modify the functionality of such hybrids. For example, coating of Ag nanoparticles with thiolated PEG or incorporation into liposomes can lead to species that can evade the opsonization and bypass the immune system. Gold nanoparticles can be widely used in nanomedicine, particularly in cancer therapy [22; 23]. Gold nanoparticles reveal a significant feature-surface plasmon resonance, which means the ability to absorb and scatter light of wavelengths considerably larger than the size of a particle. The treatment method that employs plasmon resonance is photothermal therapy (PTT), where irradiation with light from the wavelength range of 800-1200 nm causes heat release resulting in tumor cells destruction, which is based on protein denaturation and damage of nucleic acids and cell membrane, as well as the generation of reactive oxygen species (ROS) [24]. As drug carriers, gold nanoparticles can be utilized as passive and/or active transporters. When they act as passive carriers, their absorption and accumulation are based on the EPR effect. As active carriers, gold nanoparticles can be combined with antibodies providing their desired localization [23]. However, application of gold nanoparticles in the treatment can lead to some toxic effects, depending on their size and surface modification. As mentioned above, apart from the heat release, when irradiated with light or ultrasounds, gold nanoparticles can also generate cytotoxic ROS. For this reason, gold nanoparticles can also be considered as photo- and sonosensitizers for photodynamic therapy (PDT) and sonodynamic therapy (SDT), respectively [23; 25; 26; 27]. Moreover, conjugation of gold nanoparticles with photosensizers can significantly increase the concentration of photosensizers in tumor tissue in comparison to the accumulation of photosensitizer alone. What is more, after light irradiation, the energy transfer from photoexcited electrons is elevated between photosensitizer (PS) and gold nanoparticles [27]. Frequent usage of antibiotics results in an increase in drug resistance among bacteria and forces the need to search for alternative sources for antimicrobial treatment. Silver nanoparticles (AgNPs) seem to meet these requirements as they were developed as promising, efficacious inhibitors of microorganisms' growth with potential medical applications in ophthalmology, dermatology, orthopedics, and dentistry [13; 28; 29]. Similar to gold nanoparticles, silver nanoparticles can be synthesized by reducing silver salts. Furthermore, the silver core is usually coated with polyvinylpyrrolidone (PVP) or citrate to increase its stability [13]. The antimicrobial effect of the AgNPs is based on many mechanisms: (i) they attach to the cell wall of bacteria or fungi and cause damage to the structure of the cell membrane and leakage of intracellular components, (ii) they bind to DNA, thus hampering replication, and finally, (iii) silver ions can produce radicals that can decrease the activity of enzymes [28]. The main obstacle to the development of antimicrobial effects of silver nanoparticles is the determination of proper concentration for selected pathogens and the establishment of treatment algorithms [29].