# BODIPY-Based Nanomaterials--Sensing and Biomedical Applications
## 2 Metallic Nanoparticles@BODIPY
### Sensing Applications
#### 2.1.2. Gold Nanoparticles  
[PERSON] and co-workers continued the above-presented research for new nanoprobes [64]. They developed a nanosensor based on gold nanoparticles and BODIPY dyes to detect Cu\({}^{2+}\) ions (Figure 10). Obtained nanoparticles also revealed a spherical shape at a small size equal to 7-10 nm. Quenching of fluorescence by sensor-copper particles was noted, and a detection limit at 1 \(\upmu\)M was determined, whereas the response time equaled 200 s to total quenching. The nanoprobe was active in the water environment and in the living cells. The selectivity was studied as well, and it was noticed that the response for copper ions is not affected in the presence of Li\({}^{+}\), Na\({}^{+}\), Mg\({}^{2+}\), K\({}^{+}\), Ca\({}^{2+}\), Pb\({}^{2+}\), Cu\({}^{2+}\), Zn\({}^{2+}\), Ag\({}^{+}\), Cd\({}^{2+}\), and Hg\({}^{2+}\)[64].  
Figure 9: The chemical structures of magnetite nanoparticles coated with silica, modified by aminopropyltrimethoxysilanes (APTMS) bound to \(p\)-tolyl BODIPY moieties [62].  
A nanoprobe for Hg\({}^{2+}\) ions based on fluorescence quenching was proposed by [PERSON] and co-workers [65]. They deposited a highly fluorescent BODIPY dye onto Au-Fe\({}_{3}\)O\({}_{4}\) nanoparticles (Figure 11). They found that in the presence of mercury ions, nanoprobe emission drops proportionally to the concentration of the analyte. The fluorescence quenching in BODIPYs via coordination with some metal ions such as Cu\({}^{2+}\), Hg\({}^{2+}\), or Cd\({}^{2+}\) was linked with reversed photoinduced electron transfer. The selectivity of the nanoprobe was confirmed through the fluorescence measurements in the presence of Na\({}^{+}\), Mg\({}^{2+}\), Ca\({}^{2+}\), Cu\({}^{2+}\), Fe\({}^{2+}\), Co\({}^{2+}\), Cd\({}^{2+}\), and Ni\({}^{2+}\). Moreover, the authors indicated no pH influence on the emission signal during the determination of the mercury ion level. The detection limit was assigned as 5 ppb [65].  
Another approach was presented by [PERSON] and co-workers, who used a ligand exchange displacement reaction for cysteine detection and determination [66]. The authors built Au nanoparticles with pyridine-BODIPY moieties (Figure 12). The main principle of cysteine detection relies on the nanoparticle ligand exchange due to the high affinity of Au nanoparticles to thiol groups. Weak fluorescent Au-BODIPY nanoparticles (\(\Phi\) < 0.01), after exchanging ligands to cysteine, release a fluorescent BODIPY molecule (\(\Phi\) = 0.17). The  
Figure 11: The chemical structure of thiolated Au/Fe\({}_{3}\)O\({}_{4}\) nanocomposite conjugated with BODIPY dye for mercury determination [65].  
Figure 10: The chemical structure of gold nanoparticle surface functionalized with BODIPY dyes as a copper sensor [64].  
authors determined a linear response in the range of 0.4-1.4 mM of cysteine, whereas the normal level of cysteine in blood plasma is placed between 240 and 360 uM. The detection limit was assessed as 1.2 uM. Moreover, the selectivity of the developed nanosensor was confirmed in the presence of other amino acids such as Ala, Arg, Asp, Glu, Gly, Hcy, His, Ile, Lys, Met Phe, Pro, Ser, Trp, Tyr, and Val. The authors checked the impact of the nanoprobe on living cells and noted 80% cellular viability after incubation of the nanosensor with RAW264.7 cells within 24 h [66].