Vertically Aligned Gold Nanorod Monolayer on Arbitrary Substrates: Self-Assembly and Femtomolar Detection of Food Contaminants

TLDR

Food scandals have highlighted the urgent need for reliable contaminant detection, yet current methods rely on liquid chromatography, mass spectrometry, or colorimetry, which are sophisticated and time‑consuming. We develop a facile strategy to assemble vertically aligned Au nanorod monolayers with ~0.8 nm gaps and use them for rapid femtomolar detection of plasticizers and melamine via SERS. The method assembles vertically aligned Au nanorod monolayers with ~0.8 nm gaps, enabling SERS‑based detection of plasticizers and melamine at femtomolar concentrations. The SERS platform detects plasticizers down to 0.9 fM in orange juice, a 7‑order‑of‑magnitude improvement over the 6 ppb US standard, and the vertical arrays provide reproducible SERS sites on diverse substrates from silicon to flexible PET.

Abstract

Public attention to the food scandals raises an urgent need to develop effective and reliable methods to detect food contaminants. The current prevailing detections are primarily based upon liquid chromatography, mass spectroscopy, or colorimetric methods, which usually require sophisticated and time-consuming steps or sample preparation. Herein, we develop a facile strategy to assemble the vertically aligned monolayer of Au nanorods with a nominal 0.8 nm gap distance and demonstrate their applications in the rapid detection of plasticizers and melamine contamination at femtomolar level by surface-enhanced Raman scattering spectroscopy (SERS). The SERS signals of plasticizers are sensitive down to 0.9 fM concentrations in orange juices. It is the lowest detection limit reported to date, which is 7 orders of magnitude lower than the standard of United States (6 ppb). The highly organized vertical arrays generate the reproducible "SERS-active sites" and can be achieved on arbitrary substrates, ranging from silicon, gallium nitride, glass to flexible poly(ethylene naphthalate) substrates.