Reactive Hydrogel Patch for SERS Detection of Environmental Formaldehyde

The tobacco epidemic is a public health threat that has taken a heavy toll of lives around the globe each year. As one of the poison species from smoking, formaldehyde (FA) affects both the smokers and nearby persons who are exposed to second-hand smoke. Therefore, on-site tracking of FA exposure could evaluate the public environmental safety and mitigate the potential hazards. Herein, we first prepare SiO₂-shelled AuAg alloy nanoparticles (AuAg@SiO₂) and then embed AuAg@SiO₂ within agarose hydrogel to construct the three-dimensional (3D) surface-enhanced Raman scattering (SERS) substrate. A reagent of 3-methyl-2-benzothiazolinone hydrazine (MBTH) with reaction activity toward FA is loaded in the 3D substrate to obtain the selective SERS patch (designated as M-hydrogel patch). Based on a marker Raman peak at 1273 cm^-1 from the reaction product of MBTH-FA, the M-hydrogel patch is used to realize SERS detection of FA in smoke. A good linear relationship from 5 × 10^-4 to 5 mg/m³ and a limit of detection (LOD) of 2.92 × 10^-5 mg/m³ could be reached. While for detection of FA in aqueous, a linear range of 1 × 10^-7-1 × 10^-3 mg/mL with an LOD of 1.46 × 10^-8 mg/mL could be achieved. As the real application, the proposed M-hydrogel patch could be placed anywhere indoor to SERS evaluate the spatial distribution of FA in tobacco smoke, which is in connection with the second-hand smoke effect on children and adults. Such M-hydrogel patch-based SERS assay is exerted for on-field detection of FA in water and furniture panels by using a portable Raman system, showing satisfactory selectivity and reproducibility.