University of Massachusetts Amherst,
Keywords: SERS, gold nanoparticles, food materials
Summary:We developed an innovative surface enhanced Raman scattering (SERS)-active needle which is composed with an injection needle and a gold-nanoparticles coated fiber inside the injection needle. The SERS-active fiber was fabricated by reducing gold (III) on a chemically etched stainless-steel wire, resulting 100 nm gold nanoparticle uniformly coated on the surface. The SERS needle can be used to insert into the headspace and liquid sample for simultaneous multiphase sample preparation, or a soft tissue like a tomato fruit to detect the analyte inside of the tissue with minimum invasion. After the fiber absorbs the analyte, the fiber can be taken out of the injection needle and placed under a Raman spectroscope to measure the signal. The injection needle can still leave at the same place and another fiber can insert in the needle if needed. Using this invention, we successfully detected a volatile pesticide (i.e. fonofos) in a headspace of apple juice as low as 5 ppb within 30 min. We also applied this fiber containing needle for one-step simultaneous capture of red wine compounds that were in the gas, aqueous and organic phases. The obtained three phase spectra provide rich spectral details that can be used for identification and quality analysis of red wine. Similar approach was used to analyze three antioxidants, ascorbic acid, ascorbyl palmitate, and α-tocopherol in a multiphase system. In addition, the SERS needle was successfully applied for real-time monitoring the translocation of pesticide thiabendazole into tomato fruits with minimum invasion. This invention shows the great advantage of direct and sensitive multi-phase (gas and liquid) detection that traditionally requires the use of gas and liquid chromatography separately. The facile and rapid one-step sample preparation outperform the tedious chromatographic methods. The rich spectral characteristics provide solutions for identification and characterization. The use of an injection needle protected the fragile fiber and enable minimum invasive detection of analyte inside of a soft tissue. Overall, this invention opens a new field of SERS strategy for broad analytical applications.