SERS-based chip for discrimination of formaldehyde and acetaldehyde in aqueous solution using silver reduction

A method is described for surface-enhanced Raman scattering (SERS) discrimination of formaldehyde (FA) and acetaldehyde (AA) in aqueous sample solutions. It is based on the use of a paper strip containing 4-aminothiophenol (Atp)-modified reduced graphene oxide (rGO)/[Ag(NH ₃ ) ₂ ] ⁺ (rGO/[Ag(NH ₃ ) ₂ ] ⁺ /Atp). The addition of FA or AA induces the conversion of [Ag(NH ₃ ) ₂ ] ⁺ complex to silver nanoparticles (AgNPs) because of aldehyde-induced silver reduction reaction. The AgNPs possess strong SERS activity. The average interparticle gaps between the AgNPs can be fine-tuned by controlling the experimental conditions, this leading to the formation of optimized SERS hot spots. It is also found that the changes in the spectral shapes and the relative intensity ratio of the bands at 1143 and 1072 cm ⁻¹ result from the difference in the pH value of the surrounding solution. This effect enables the selective discrimination of FA and AA. The paper strip can be used as a SERS dipstick and swab for on-site determination of FA or AA in wine and human urine via the differences in the intensity of the SERS peaks. The assay works over a wide range of concentrations (0.45 ng·L ⁻¹ to 480 μg·L ⁻¹ ) for FA and AA, and the respective detection limits are 0.15 and 1.3 ng·L ⁻¹ . [Figure not available: see fulltext.].