Sol–Gel and Electrospinning Synthesis of Silica–Hydroxyapatite–Silver Nanofibers for SEIRAS and SERS

Surface-enhanced Raman spectroscopy (SERS) and Surface-enhanced infrared absorption spectroscopy (SEIRAS) are both novel techniques favored by the excitation of surface plasmons onto metal nanostructures. The light emitted from the metal surface couples with the vibrational transitions of molecules in proximity, enhancing its spectral response and leading to more sensitive and effective spectroscopic analysis. The absence of inexpensive and reproducible substrates is among the major impediments to the accurate implementation and optimal performance of the technique. The development of a low-cost active substrate based on silica–hydroxyapatite through sol–gel synthesis and electrospinning is addressed in the present study. Fibers of 512 ± 199 nm diameter were produced after sintering at 1150 °C on the electrospun mats. The fibers are fixed to an indium tin oxide (ITO) glass base for electrodeposition with 10 and 20 mM AgNO3 at 1.5 and 3.3 V at different time periods. Electrodeposition produced silver nanorods and nanocubes on the fibers. The SERS and SEIRAS activity of each one of the nine supports was tested using pyridine 1 nM, comparing it with the spectrum of pyridine 1 mM. An enhancement factor of 2.01 × 106 for the band at 3335 cm−1 was obtained during a SEIRAS essay for the support doped for 2 min at 3.3 V with 10 mM silver nitrate solution. The highest SERS enhancement factor was 3.46 × 108, for the band at 1567 cm−1 in the substrate doped for 5 min at 1.5 V with silver nitrate solution at 10 mM. After testing both samples with 10−4 M violet crystal solution, no SERS enhancement factor was found, but higher band resolution in the spectra was observed.