# Quantum Leap from Gold and Silver to Aluminum Nanoplasmonics for Enhanced Biomedical Applications
## 3 Applications
### Plasmonic Medicine
#### 3.2.2 Plasmonic Antibacterial Treatment  
Over the past years, the number of infections associated with bacteria has increased, many of which are accompanied by the formation of biofilms [97; 105; 106; 107; 191]. Some of the common bacterial pathogens, which cause diseases in humans, are _E. coli, S. aureus, V. cholerae, P. aeruginosa, E. faecalis, S. epidermidis, S. viridans, K. pneumoniae, and P. mirabilis_. Many bacteria developed tolerance/resistance against common organic antibacterial agents and continue to be one of the serious health challenges worldwide. Therefore, developing point-of-care devices for direct and early detection and treatment of  
Figure 4: Mechanisms of hot electron generation by Au NPs and their applications. (**a**) Mechanism for the treatment of HeLa cells under visible and NIR radiation using TiO\({}_{2}\) Au NR conjugates. (**b**) A combination of visible and IR radiation shows stronger green fluorescence than visible light only, implying enhanced reactive oxygen species (ROS) generation by synergistic effect of visible light and heat generation, leading to high cell death efficacy. (Adapted from [PERSON] et al. [180]). (**c**) Schematic of singlet oxygen generation upon laser irradiation of naked Au NPs. (Adapted from [PERSON] et al. [181]). infections is the need of the hour. In this context, NPs with unique physicochemical characteristics have proven effectiveness for imaging, diagnosis, and therapy. However, real-time detection/diagnosis and quantitative evaluation of the type of pathogens are still a challenging task. Nevertheless, certain properties of some metal NPs, such as Al, Ag, and Au NPs, can be combined with smart optical techniques, such as handheld fluorescence and Raman spectroscopy, to develop affordable and routine diagnosis tools for early pathogen detection and treatment effectiveness assessment. Microorganisms form complex biofilm structures via self-produced extracellular matrix composed of hydrated extracellular polymeric substances (EPS), which include proteins, lipids, nucleic acids, and polysaccharides [192]. Biofilms are bacterial microenvironments that are widely found in nature, including the human body, and present multiple negative consequences such as energy losses, equipment damage, imbalance in the ecosystem and human diseases [193; 194]. EPS serves many crucial roles through providing not only mechanical stability for the biofilm but also acting as an external digestive system [195]. Cystic fibrosis (CF) is one of the genetic disorders that affect lungs causing bacterial infection and biofilm formation. The clinical treatment of other types of biofilm infections related to fungi or yeast, such as, for example, oral candidiasis [196], could also benefit from the plasmonic NPs. Bacterial infections are often associated with biofilms in catheters, valves, and surgery. Microorganisms in biofilms are a common reason for medical device-caused infections, estimating up to 80% of infections in hospitals related to biofilms [197]. Biofilm-encapsulated bacteria show more than three orders of magnitude larger antibiotic resistance compared to their planktonic counterparts [198]. As a result, biofilm treatment presents a big challenge both for traditional antibiotic [199] and alternative plasmonic NP treatments. Various plasmonic metal (such as Au, Ag, Cu, Al) and metal oxide (such as TiO\({}_{2}\), ZnO, and MgO) NPs were investigated for bacterial cell and biofilm inactivation [200]. Au and Ag NPs have been most widely studied separately and in combined antibiotic treatments [201; 202]. However, there are limitations that need to be addressed to translate the Au and Ag treatments to a broad range of bacterial and environmental conditions. For example, _Pseudomonas_ and _E. coli_ bacteria were shown to develop resistance to Ag NPs after multiple exposures [203]. TiO\({}_{2}\) NPs showed toxicity to healthy cells and tissues via oxidative DNA damage in human cells even without photoactivation [204].