Figure 4.

SERRS detection of pyocyanin produced by P. aeruginosa PA14 strains grown in planktonic culture. (A) UV–visible–near-infrared spectrum of aqueous pyocyanin solution (10⁻⁴ M) and molecular structure of pyocyanin (inset). The dotted line indicates 785 nm, corresponding to the excitation wavelength used for SERRS. (B) Resonance Raman and SERRS spectra of pyocyanin measured in solid state and in aqueous solution (1 μM, Au@pNIPAM hydrogel), respectively. Raman measurement was carried out with a 50× objective, a maximum power of 54.22 kW cm⁻² and an acquisition time of 10 s. SERRS measurement was carried out with a 20× objective, a maximum power of 4.24 kW cm⁻² and an acquisition time of 10 s. (C) SERRS spectra of commercial pyocyanin (PYO) and of pyocyanin produced by the wild-type (WT) and the phenazine-null phz1/2 (Δphz) strains. (D) SERRS spectra of pyocyanin produced by wild-type and the indicated phenazine mutant strains. (E) Photographs of the phenazine-containing samples obtained from the wild type PA14 (wt) and the different mutants (PhzH, PhzS and PhzM), as labeled, under visible light illumination. (F) UV-Vis-NIR spectra of the samples containing different phenazines; pyocyanin (wt and PhzH), 1-hydroxyphenazine (1-HO-PHZ, wt, PhzM, and PhzH) and phenazine-1-carboxamide (PCN, wt, PhzS, and PhzM). All SERRS measurements were performed with a 785 nm laser line employing a 20× objective, maximum power between 1.72 kW cm⁻² and an acquisition time of 10 s (intensity at 418 cm⁻¹) employing Au@pNIPAM hydrogels. Images reproduced with permission from Bodelón et al. (2016).