Detection of Formaldehyde by Surface-Enhanced Raman Spectroscopy Based on PbBiO₂Br/Au₄Ag₄ Nanospheres

In this work, a portable surface-enhanced Raman spectroscopy (SERS) substrate based on perovskite-like PbBiO2Br/AuAg hybrid nanoalloys (PbBiO2Br/Au4Ag4 nanospheres) was fabricated for the rapid, sensitive, and selective detection of formaldehyde. PbBiO2Br nanospheres with thin nanosheets on the surface of the microsphere structure were synthesized via the hydrothermal method. The formation of nanospheres was controlled by an ionic liquid ([C16mim]+). [C16mim]+ can be simultaneously used as a solvent, reactant, and template for fabricating a porous microstructure of PbBiO2Br nanospheres. AuAg nanoalloys were grown on PbBiO2Br nanospheres in situ in the presence of Au3+ and Ag+. SERS performance was further optimized by adjusting the ratio of Au/Ag. PbBiO2Br/Au4Ag4 membranes as the SERS substrate were further obtained via simple filtration of the PbBiO2Br/Au4Ag4 nanospheres on filter paper. The PbBiO2Br/Au4Ag4 membranes displayed better SERS activity for molecules with an −SH group than for molecules with nonsulfhydryl targets owing to the high affinity between AuAg nanoalloys and −SH. Under optimum conditions, the method developed herein determined that the analytical enhancement factor of 4-mercaptobenzoic acid and 4-nitrothiophenol could reach 4.5 × 108 and 3.2 × 107, respectively. The proposed strategy showed a wide linear range (20.0–500.0 μg L–1) and a low limit of detection (2.6 μg L–1) for formaldehyde determination. The membrane-based substrate developed in this study offers a novel strategy for fabricating portable and reliable SERS substrates and provides a valid SERS method for rapid on-site monitoring of formaldehyde.