Highly Specific and Sensitive SERS Detection of Putrescine Using Au Nanobowls@Cu‐MOF Embedded in a Hydrogel Nanoreactor

Putrescine is of concern due to its toxicity and applications in monitoring food spoilage and water quality. However, it is difficult to realize highly selective and sensitive detection of putrescine with interferences from other biogenetic amines with similar molecular structures. In this work, Au nanobowls modified by Cu-MOF (core-shell Au bowl@Cu MOF) together with o-phthalaldehyde (OPA) are embedded into sodium alginate hydrogel to construct a unique SERS substrate (OPA-Au bowl@Cu MOF/hydrogel) for sensing of putrescine. In the confined space of porous hydrogel, the Schiff base reaction between OPA and putrescine resulted in the product of N, N-dibenzylidene-n-butylenediamine (OPA-Putrescine), which is easily captured by Cu-MOF via copper-nitrogen coordination and then detected thanks to the high SERS activity of Au nanobowls and the large Raman scattering cross-section of OPA-Putrescine. The above reaction contributed to a high selectivity to greatly suppress the interferences from many amino group-containing molecules. The limit of detection (LOD) of gaseous and liquid putrescine is 1.2 × 10^-9 and 6.3 × 10^-10 mol L^-1, respectively. Further, the application potential of this SERS-sensor in food and environmental fields are demonstrated by the successful detection of putrescine in salmon and seawater samples.