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. Author manuscript; available in PMC: 2022 Apr 15.
Published in final edited form as: ACS Nano. 2021 Nov 19;15(12):19956–19969. doi: 10.1021/acsnano.1c07470

Figure 2.

Figure 2.

Synthesis and characterization of multispectral NIR-SERRS nanoparticles. (a) A schematic of gold nanoparticle core-Raman reporters-silica shell-structured NIR-SERRS nanoparticles. (b) A TEM image of the NIR-SERRS nanoparticles. The average size of the gold nanoparticle core is 60 nm in diameter, which is coated with a 40 nm-thick silica shell. The nanoparticles are mixtures of monomeric (single gold core in a silica shell), dimeric (double gold core in a silica shell), and oligomeric (multiple gold core in a silica shell) structures. Scale bar: 500 nm. (c) Raman spectra of the NIR-SERRS nanoparticles of 3,3’-diethylthiatricarbocyanine iodide (red, DTTC-SERRS, 160 ± 40 nm) and the nonresonant SERS nanoparticles of 1,2-bis(4-pyridyl)ethylene (black, BPE-SERS, S440, Oxonica Materials Inc., 180 ± 50 nm, see Supporting Information Figure S1) at the same nanoparticle concentration of 10 pM. (d–f) Controlled oligomerization of the nanoparticles upon the increase of the added DTTC dyes amount during the DTTC-coded SERRS nanoparticles syntheses: 10 nmol (160 ± 40 nm, black), 15 nmol (185 ± 50 nm, red), to 20 nmol (245 ± 70 nm, blue). The dose-dependent change in the number of gold nanoparticle cores in a single NIR-SERRS nanoparticle (d, see Supporting Information Figure S3), hydrodynamic diameter (e), and the Raman intensity (f) of the DTTC-coded SERRS nanoparticles. (g) Normalized standard curves of Raman intensities of the DTTC-coded SERRS nanoparticles (red, DTTC-SERRS, 185 ± 50 nm) and the BPE-coded SERS nanoparticles (black, BPE-SERS, 180 ± 50 nm), and the NIR fluorescence intensity of the Cy7 dye-doped silica nanoparticles (blue, Cy7-FSN, 215 ± 20 nm, see Supporting Information Figure S5). The LOD calculated from the curves were 3.8 ± 0.38 fM (red), 21.2 ± 6.6 fM (blue), and 650 ± 29 fM (black) concentrations of the nanoparticles, respectively (see Supporting Information Figure S6). (h) The Raman scattering brightness of the 9 NIR-SERRS nanoparticles with respect to the BPE-coded SERS nanoparticles (S440, Oxonica Materials), measured at 10 pM. The error bars (g and h) represent the standard deviations of the Raman intensities collected from multiple points (n = 300) scanning per measurement.