Simultaneous Second Harmonic Generation and Multiphoton Excited Photoluminescence in Samarium-Doped BaTiO3 Nanoparticles Functionalized with Poly(ethylene glycol)

Abstract

In this work, samarium-doped BaTiO₃ (BT:Sm) nanoparticles (NPs) were prepared and coated with poly(ethylene glycol) (PEG) to investigate their optical characteristics and compatibility with biological systems. The structure, particle morphology, optical properties, and biological compatibility of the NPs were assessed. The results demonstrated the formation of BT:Sm and [(BT:Sm)-PEG]. The relative intensities and positions of peaks in the X-ray diffraction (XRD) are consistent with an average crystallite size of ∼75 nm. The Raman spectra showed that Sm doping produced the typical tetragonal peaks at around 306 and 715 cm^-1, and Fourier transform infrared (FTIR) spectroscopy showed that the PEGylation process was effective. Also, our investigation demonstrates the potential of these NPs as very temperature-sensitive nanosensors with a resolution exceeding 0.5 °C, which is achievable through optical excitation. We also analyze their emission properties. Finally, we present a study related with the mitochondrial activity of naked and PEG-coated NPs. The results indicate that neither naked nor PEG-coated NPs exhibit changes in mitochondrial metabolism, as indicated by quantitative cell viability and morphological visualization. The PEG-coated NPs prevented the formation of aggregates in cell culture compared to naked NPs, demonstrating the significance of PEG as a stabilizing agent.

Figure 1

XRD patterns of BT and BT:Sm (a, b); FTIR spectra BT:Sm and [(BT:Sm)-PEG] 5 mol % (c); Raman spectra BT and BT:Sm 5 mol % (d).

Figure 2

SEM patterns BT:Sm and [(BT:Sm)-PEG] 5 mol % (a, b); elemental map BT:Sm 5 mol %; (c) EDS analysis BT:Sm 5 mol % (d); Ti 2p (e) and Sm 3d (f) XPS spectra of BT:Sm 5 mol %.

Figure 3

pH effect on Size distribution: (a) accumulate volume fraction; (b) frequency; and (c) ζ potential measurements of [(BT:Sm)-PEG] 5 mol % NPs.

Figure 4

(a) Normalized emission spectra of Samarium and SGH of the sample as a function of temperature, measured using a double excitation with a continuous laser at 473 nm (≈0.6 KW·cm^–2) and a pulse laser at 1064 nm (≈1 W·cm^–2). (b) Determined band intensity ratios 532 nm/604 nm as a function of temperature. (c) Relative sensitivity and (d) temperature distribution obtained using 100 measurements in the same conditions at 30.0 °C.

Figure 5

(a) DC emission spectra of the sample as a function of temperature, measured at λ_ex = 473 nm and ≈0.6 KW·cm^–2. (b) Determined band intensity ratios 596 nm/643 nm as a function of temperature. (c) Relative sensitivity and (d) temperature distribution were obtained using 100 measurements in the same conditions at 30.0 °C.

Figure 6

(a, b) SGH emission obtained using different excitation wavelengths for the BT:Sm 5 mol % NPs.

Figure 7

Effect of naked and PEG-coated BT:Sm NPs on the cell viability of HEK293-T cells. Data represent mean ± SEM of viable cells (as a percentage of control; 0 μg/mL) treated 24 h with naked (black bars) or PEG-coated BT:Sm NPs (red bars) doped with (a) Sm 1, (b) Sm 3, and (c) Sm 5 mol %. (d) Representative images of HEK293-T cells exposed to different concentrations of naked and PEG-coated BT:Sm 5 mol %.