# Recent Advances in Intrinsically Fluorescent
## 3 Application
### Detection of Bacteria  
In recent years, public health safety issues have received widespread attention from countries around the world. According to estimates by the World Health Organization, 70% of foodborne disease instances worldwide are caused by pathogenic microorganisms each year. Therefore, the development of a sensitive and efficient method for pathogenic bacteria is essential to improve the protection of public health and ensure the safety of people. Fluorescence biosensors are receiving increasing interest recently due to their excellent sensitivity and portability for use on-site compared with conventional polymerase chain reaction (PCR)-based and immunology-based methods, giving them the potential to be used in the rapid and sensitive detection of pathogens [97]. [PERSON] et al. synthesized PDA-PEI copolymer dots with green emission and great photostability using a facile one-pot method (Figure 6) [36]. Because of the rich carboxyl groups on the surface of PDA, connecting PDA-PEI to the aptamers can specifically recognize _Pseudomonas aeruginosa_ (_P. aeruginosa_) by the common method of EDC/NHS connection. The amino group on PDA-PEI and the phosphate group on the cell wall form a strong ionic complex, causing fluorescence to be quenched. The experimental results showed high specificity to _P. aeruginosa_, and the fluorescence intensity was hardly affected by other types of bacteria to use dual-aptamers. The limit of detection (LOD) was calculated to be 1 CFU mL\({}^{-1}\) and applied for the detection of _P. aeruginosa_ in real samples (skim milk, orange juice, and a popsicle). In addition to detecting bacteria, fluorescent biosensors also show potential for therapy. As we all know, PDA exhibits strong absorption of ultraviolet and near-infrared (NIR) light and high photothermal conversion efficiency. Therefore, it is also used as a photothermal agent in photothermal therapy for clinical cancer treatment [22; 30]. It has been reported that PDA, as a photothermal agent, generates heat under near-infrared light to denature bacterial proteins and kill bacteria [98; 99]. [PERSON] et al. synthesized PDA-PEI copolymer dots with the sensitive detection of gram bacteria. Since both PEI and PDA are positively charged, PDA-PEI and the negatively charged cell wall are connected by electrostatic action, which leads to strong \(\pi\)-\(\pi\) stacking interactions and quenches fluorescence [100]. It is worth noting that the photothermal effect of the PDA-PEI copolymer dots under near-infrared irradiation leads to a rise in temperature, which inhibits the growth of bacteria and some basic physiological activities [101; 102]. Compared with traditional therapies, it displays the advantages of simplicity, convenience, and no drug resistance problems. However, it needs to be pointed out that the specificity of binding to Gram bacteria through electrostatic interaction is not strong enough, and the use of an aptamer connection may result in a distance between the PDA and bacteria and affect heat transfer to the cells. It may be a good idea to choose peptides or proteins that can specifically recognize and enter the bacteria, and the heat in the cell will have a greater impact on the bacteria, leading to a better sterilization effect.