Ratiometric SERS detection of N2H4 by porous Ag(i)-linked Waugh-type polyoxometalate as an efficient label-free substrate

Abstract

For quantitative analysis of SERS detection, the rational design of efficient substrates and stable internal standards are both key issues to realize reliable detection. In this paper, a novel three-dimensional (3D) silver(I)–polyoxometalate complex of Ag₆[MnMo₉O₃₂]·4H₂O (Ag₆MnMo₉) was designed and synthesized to realize the quantitative detection of N₂H₄, which is composed of Waugh-type polyoxoanions and silver (I)ions via Ag–O bonds to form a 3D structure with two-dimensional channels. For [MnMo₉O₃₂]⁶⁻, the central [MnO₆] group does not make contact with silver ions and can be used as internal standards. When Ag₆MnMo₉ is exposed to N₂H₄ vapor, Ag⁺ is partially reduced to Ag⁰ and the ratiometric I_Mo–O/I_Mn–O SERS signals are proportional to hydrazine concentrations, realizing the elusive label-free SERS quantitative analysis. In addition, compared with the similar 3D complex whose pore channels are completely filled, the Raman signal of Ag₆MnMo₉ is more sensitive and stable, indicating that the porous structure also facilitates the interactions of silver with the targeting molecules. This work opens up an innovative way to the rational synthesis of 3D label-free SERS substrates based on polyoxoanions and silver ions, which can be used for the detection of hazardous gas molecules.