**Abstract**

The present chapter aims to overview the application of silver nanoparticles (AgNPs) in photocatalysis and biomedical field. Firstly, the relevance of AgNPs will be addressed. Then, the discussion about the photocatalytic activity of the AgNPs (either in suspension or impregnation), and correlation with your properties and its potential application to organic pollutants degradation under UV and visible/solar radiation will be described. Thus, applications of the AgNPs as antimicrobial agents, such as *Escherichia coli, Schizophyllum commune, Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Haemophilus influenzae, Bacillus subtilis, Bacillus cereus* and *Enterobactor faecalis*, and in the development of biosensors will be discussed. Therefore, the present work will be important to contextualize different scenarios to AgNPs mainly to wastewater treatment and diagnosis/therapeutic applications.

**Keywords:** nanotechnology, metallic nanoparticles, heterogeneous photocatalysis, antimicrobial properties, biosensors

#### **1. Introduction**

Nanotechnology involves the manipulation of materials at nanometric scale (10−9 m) and have evolved to novel solutions for water/wastewater treatment as well as biomedical applications [1]. These applications fields are possible due to the unique properties of nanomaterials, such as high surface area, high reactivity and considerable porosity and morphological, electrical, magnetic and/or optical properties, which turn them into useful materials in catalysis, adsorption, sensing and optic-electronic applications [2]. Succinctly, nanomaterials can be divided into 2D, 1D, 0D, according to the number if dimensions the electrons are confined [3]. Metallic nanoparticles are 0D materials, that is, they have the three dimensions within the nanoscale [4]. Among metallic nanoparticles, silver nanoparticles (AgNPs) are largely investigated due to versatility in synthesis, easy processing, fast kinetic reaction rate, high thermal and chemical stability and so forth [5]. Both related to water/wastewater treatment and biomedical applications, AgNPs features allows them to control the interaction with bacteria and, in the case of wastewater

**Figure 1.** *Number of published papers involving AgNPS in photocatalysis and biomedical applications [7, 8].*

treatment, this control can be applied to several pollutants (dyes, hydrocarbons, pesticides, pathogens, and so forth) [6]. Based on that, AgNPs can be applied to photocatalysis and to biomedical applications, such as antimicrobial agents and biosensing [7, 8]. **Figure 1** shows the number of published papers involving AgNPs applied to photocatalysis and biomedical applications.

According to the **Figure 1**, it is possible to notice an increasing tendency of works related to application of AgNPs in the last 5 five years, mainly due to great efficiency of these nanoparticles in sensing applications.
