High-affinity Fe₃O₄/Au probe with synergetic effect of surface plasmon resonance and charge transfer enabling improved SERS sensing of dopamine in biofluids

Abstract

Development of analytical methods allowing sensitive detection of neurotransmitters in various biofluids is vital. However, limitations of these methods include interference of impurities and stringent requirements concerning sample purity. In the current work, we developed a strategy for the rapid and sensitive analysis of dopamine (DA) in various biofluids with a smart surface-enhanced Raman spectroscopy (SERS) probe composed of magnetite Fe₃O₄ and Au nanoparticles (Fe₃O₄/Au NPs). Besides the simple and quick separation of DA from the specimen, Fe₃O₄ not only enabled a specific chemical interaction with DA molecules, but also acted as a SERS substrate capable of electromagnetically enhancing the Raman signal of DA. Therefore, the Fe₃O₄/Au NP composite with its coexisting electric-field effect and charger transfer (CT) enhancement was found to be beneficial for capturing the target molecules in biological environments and then enhancing the DA sensitivity. To understand the strong binding interaction between Fe₃O₄/Au and DA, X-ray photoelectron spectroscopy (XPS) was carried out, specifically to illuminate the chemical adsorption or possible CT complex. Moreover, a rapid purification strategy for further separating DA from serum was developed, and thus a high nanometer-level sensitivity was achieved. In addition, the feasibility of using Fe₃O₄/Au combined with the developed purification method was also verified using various tissue homogenates spiked with DA molecules. Such a nanocomposite can offer the possibility of efficiently separating DA from the complex specimen and then providing the sensitive detection of DA for various tissues. Accordingly, the smart SERS Fe₃O₄/Au nanocomposite probe, with its advantages of simple pre-treatment and synergetic enhanced mechanisms, shows great promise for the rapid and sensitive detection of DA in complicated specimens.