# BODIPY-Based Nanomaterials--Sensing and Biomedical Applications
## 2 Metallic Nanoparticles@BODIPY
### Sensing Applications
#### 2.1.3 Other Metallic Nanoparticles  
[PERSON] and co-workers developed a ratiometric pH nanosensor based on the fluorescence phenomenon [67]. They employed NaYF4: Yb3+, Tm3+ nanoparticles with deposited BODIPY dye (Figure 13). This UCN revealed pH-sensitive fluorescence ON/OFF properties depending on H+ concentration. Ratiometric sensors revealed serious advantages. It was observed that, once performed, optimization of calibration gives further reproducible results. The principle of pH measurement with this nanoparticle is based on its excitation of the nanoparticle with 980 nm. Ytterbium ions are excited and transfer their energy to the thulium ion Tm3+, which emits light at 451, 475, 646 (R-red), and 805 nm. Light emitted at 475 nm is absorbed by BODIPY dye, which is undergoing excitation and, depending on the pH (protonation of the phenolic component), emits light in the range of 500-600 nm (G-green). The BODIPY fluorescence is turned off at pH values above 9 and turned on during acidification. The G/R ratio gives detailed information on the pH value. The authors deposited the developed nanoparticles onto HydroMed D4 hydrogel, which possesses the capability for water uptake and protons diffusion. The response of the obtained sensor for pH is independent of layer homogeneity and excitation power. The usability of this system was determined according to the measurement of the pH in the biological system. The bacteria _Escherichia coli_ was cultured, which acidify their surrounding environment via acid fermentation. Linear dependency was noticed in the sensor working pH range 5-9 [67].  
Figure 12: The chemical structure of gold nanoparticles functionalized with pyridine-BODIPY moieties [66].  
[PERSON] and co-workers developed an arsenate nanosensor based on BODIPY and CeO\({}_{2}\) nanowires (Figure 14) [68]. Arsenates cause severe life-threatening effects on the body. Therefore, their concentration in drinking water, especially in spring water, has to be strictly controlled. The World Health Organization regulates the maximal acceptable content of arsenates up to 10 ppb (130 nM). There are a few arsenate quantification methods, but they are expensive, limited by the interferences, time-consuming, etc. The proposed nanoprobe was based on the BODIPY fluorescence and its quenching by the nanowire. BODIPY fluorescence quenching by CeO\({}_{2}\) is caused by oxidative electron transfer from the excited dye to the nanowire. The studied nanowire revealed dimensions of 120 \(\pm\) 15 nm \(\times\) 8.0 \(\pm\) 2.5 nm. BODIPY dye was deposited on these surfaces via an ATP linker. The nanosensor needed only 10 min to respond, which is based on the competitive sorption of BODIPY and arsenates. In the presence of arsenates, the BODIPY was released, and the fluorescence signal increased. The linear dependence between the concentration of arsenates and the intensity of BODIPY fluorescence in the ranges of 20-150 and 150-1000 nM was determined at the detection limit estimated to be 7 nM. Moreover, the authors assessed the stability of the response in the pH range of 3-7 as well as selectivity for arsenates in the presence of arsenate or phosphate ions. Recognition of arsenates and phosphates was provided by an ATP linker with optimal phosphate chain length [68].  
To sum up:  
* Different strategies were used for conjugation of BODIPY dyes to metallic nanoparticles through direct coordination or through indirect attachment via silica or thiolate linkers.
* BODIPY/metallic nanoparticles sensors can act as fluorescent probes.
* BODIPY dyes in conjugation with gold and magnetic nanoparticles were mostly used to determine heavy metal ions in aqueous solutions.  
Figure 14: The chemical structure of cerium(IV) oxide nanowires conjugated with BODIPY dye by ATP linker [68].  
Figure 13: The chemical structure of NaYF\({}_{4}\): Yb\({}^{3+}\), Tm\({}^{3+}\) nanoparticles with deposited BODIPY dye 1-4 [67].  
* Upconverted nanoparticles surface functionalized with BODIPY dyes can be potentially used as pH sensors.