Magnetically Optimized Surface - Enhanced Raman Spectroscopy And Its Application In Trace Analysis

Surface-enhanced Raman scattering(SERS) spectroscopy has shown the advantage of overcoming the low sensitivity of conventional Raman spectroscopy and molecular detection capabilities. SERS substrates are essential in the detection and metal nanoparticles are widely used as SERS substrates. In order to make multifunctional SERS substrates, magnetic Fe3O4 nanoparticles and metal nanoparticles are combined to form magnetic nanocomposites with both magnetic characteristics and optical properties. The magnetic nanocomposites can be developed as magnetically-optimized SERS substrate under an external magnetic force, having a huge sensitivity when detecting targets. In the preparation of magnetic nanocomposites, phytic acid(IP6) and its salts are used as a stabilizer and bridging agent. IP6 are economical and ‘green’ reagents and liable to chelate with metal ions because of its structure containing six phosphates separately on both sides of the cyclohexane. Therefore, a magnetically-optimized SERS approach combined with a portable Raman are used to monitor trace envinronmental pollutants or biomarker. The main contents of this article are as follows:A novel magnetically responsive and SERS active nanocomposite is designed and prepared by direct grafting of Au nanoparticles onto the surface of magnetic network nanostructure(MNN) with the help of a nontoxic and environmentally friendly reagent of inositol hexakisphosphate shortly named as IP6. The presence of IP6 as a stabilizer and a bridging agent could weave Fe3O4 nanoparticles(NPs) into magnetic network nanostructure, which is easily dotted with Au nanoparticles. It has been shown firstly that the huge Raman enhancement of Au-MNN is reached by an external magnetic collection. Au-MNN presenting the large surface and high detection sensitivity enables it to exhibit multifunctional applications involving sufficient adsorption of dissolved chemical species for enrichment, separation, as well as a Raman amplifier for the analysis of trace pesticide residues at femtomolar level by a portable Raman spectrometer. Therefore, such multifunctional nanocomposites can be developed as a smart and promising nanosystem that integrates SERS approach with an easy assay for concentration by an external magnet for the effective on-site assessments of agricultural and environmental safety.New developments in the fields of human healthcare and social security call for the exploration of an easy and on-field method to detect drug-related biomarkers. In this paper, Au nanoparticles dotted magnetic nanocomposites(AMN) modified with IP6 were used as SERS substrate to quickly monitor trace drug-related biomarkers in saliva and to on-site screen a trace drug biomarker in fingerprints. Due to inducing with an external magnet, such substrate presented a huge SERS activity, which has met the sensitivity requirement for assay to detect the drug biomarkers in saliva from the U.S. Substance Abuse and Mental Health Services Administration. And also the limit of detection for drug biomarker in fingerprint reached 100 n M. In addition, this AMN-based SERS assay was successfully conducted using a portable Raman spectrometer, which could be used to on-site and accurately differentiate between the smokers and drug addicts in near future.Adenosine plays a crucial role in the regulation of physiological activity in various tissues and organs. As adenosine is a possible biomarker for cancer, the determination of its level presents a demanding task for deeply monitoring progress of diseases. Through the synthesis of Fe3O4/Au/Ag nanocomposites weaved and stabilized by phytic acid and its salt, we develop a magnetically assisted SERS protocol to determine trace level adenosine in urine samples from both lung cancer patients and health human. The magnetic properties of the nanocomposites enable to realize the simple separation of targeted molecules from a complex matrix and the Au/Ag nanoparticles moieties act as the SERS platform. This label-free Fe3O4/Au/Agnanocomposites-based SERS protocol shows a good stability, reproducibility, timeefficiency(less than 20 min for one sample test) and huge sensitivity down to 10-10 M. The protocol also has high selectivity because SERS signal of adenosine provides the molecular fingerprint information as well as an azo coupling pretreatment is performed to remove the interference of urea. Furthermore, a SERS array is designed for on-site screening adenosine in urine samples in a massive way using a portable Raman. Such a magnetically assisted SERS method as a powerful alternative can be expected as a smart and promising tool for effective assessment of healthcare.