Sol-Gel Dipping Devices for H2S Visualization

Abstract

In this contribution we report the synthesis and full characterization, via a combination of different spectroscopies (e.g., ¹H NMR, UV-vis, fluorescence, MALDI), of a new family of fluorescent zinc complexes with extended π-conjugated systems, with the final aim of setting up higher performance H₂S sensing devices. Immobilization of the systems into a polymeric matrix for use in a solid-state portable device was also explored. The results provided proof-of-principle that the title complexes could be successfully implemented in a fast, simple and cost-effective H₂S sensing device.

Keywords: fluorescence; hydrogen sulfide; portable sensors.

Scheme 1

Structures of the complexes studied in this work.

Figure 1

Electronic absorption spectra of complexes 1–4 with and without the addition of 50 µM of NaSH. Spectra were recorded in DMSO at room temperature. [complexes] = 10 µM.

Figure 2

Emission spectra of complexes 1−4 before and after the addition of 5 equiv of NaSH. [Complexes 1−4] = 1 × 10⁻⁵ M; [NaSH] = 5 × 10⁻⁵ M. All spectra were measured in DMSO with λ_exc = 481 nm for complex 1; λ_exc = 513 nm for complex 2; λ_exc = 516 nm for complex 3; λ_exc = 598 nm for complex 4.

Figure 3

Emission spectrum of complex 1 (λ_ex = 481 nm; λ_em = 550 nm), upon addition of 5 equiv of NaSH and upon addition of 10 equiv of acetic acid. [Complex 1] = 1 × 10⁻⁵ M; [NaSH] = 5 × 10⁻⁵ M. Spectrum was measured in DMSO.

Figure 4

(Left) Emission spectra of complex 1 (λ_exc = 481 nm) when titrated with NaSH. [Complex 1] = 1 × 10⁻⁵ M; end concentration of NaSH varied in the range (1−5) × 10⁻⁵ M. (Right) The fluorescence intensity values of complex 1 at 565 nm have been plotted as a function of the HS⁻ concentration.

Figure 5

Structure of a model complex.

Figure 6

Real color images of a cropped area of the model complex—reported in Figure 5—(a) and complex 1 (b) loaded in sol-gel matrices after adding increasing amounts of HS⁻ dissolved in H₂O (0, 1.78, and 10 mM). Non-treated matrices are indicated as FREE.

Figure 7

Real color images of a cropped area of the model complex—reported in Figure 5—(a) and complex 1 (b) loaded in sol-gel matrices after adding increasing amounts of HS⁻ dissolved in HBSS (0, 17.8 µM, 178 µM, and 1.78 mM). Non-treated matrices are indicated as FREE.

Figure 8

Real color images of a cropped area of the model complex—reported in Figure 5—(a) and complex 1 (b) loaded in sol-gel matrices after adding cell-conditioned HBSS media. Matrices treated with non-conditioned HBSS (HBSS); non-conditioned medium +800 µM H₂O₂ (HBSS+ H₂O₂); cell-conditioned HBSS (Cond. HBSS); and cell-conditioned HBSS after 1 h treatment of the HepG2 cells with 800 µM H₂O₂ (Cond. HBSS+ H₂O₂).

Figure 9

Optimized geometries for complex 1 (left) and its adduct with HS^– (right).

Figure 10

Computed energies (E, eV) of the ground state (S₀) first excited singlet (S₁), and four lowest energy triplet states, evaluated at the S₀ geometry for complex 1 and complex 4, and their HS^– adducts.