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The aggregation of nanoparticles is the key factor to form hot spots for the flocculation-enhanced Raman spectroscopy (FLERS) method. However, the structure of flocculation is still not clear. It is therefore necessary to explore and analyze the aggregation process of nanoparticles more carefully, so as to realize a better application of FLERS. Here, we report the application of in situ liquid cell transmission electron microscopy (TEM) combined with an in situ high-speed camera to analyze the particle behaviors. The results showed that flocculation can exist stably and the gap between the nanoparticles in the flocculation always remained at 7–9 nm, which ensured the high stability and sensitivity of the FLERS method. We successfully applied FLERS to the in situ noninvasive probing of cupping effect substances. The results indicated the scientific principle behind the traditional Chinese medicine method to some extent, which thus provides a new and effective method for the in situ dynamic monitoring of biological systems. [ABSTRACT FROM AUTHOR]

A rapid and accurate method for the sensitive detection of illegal drug additives including atenolol (ATN), metformin hydrochloride (MET), and phenformin hydrochloride (PHE) in health products using solvent microextraction (SME) combined with surface-enhanced Raman spectroscopy (SERS) was developed. Various illegal drug additives in different health products were separated via microextraction and then detected in situ using a portable Raman spectrometer with Ag colloids acting as SERS-active substrates. The effects of experimental parameters on the detection sensitivity and producibility were evaluated, and the applications of illegal additives spiked into samples were systematically investigated with SME-SERS. It was demonstrated that the mixture of CH3OH and CHCl3 (v/v = 1 : 4) as the extractant was suitable for the rapid microextraction separation of illegal drug additives and also induced the distribution of the Ag colloids (2 M) on the CHCl3 surface. More importantly, CH3OH can carry the drug molecules to enter into the inter-particles of the Ag colloids in this process, and then significantly improve the detection sensitivity of illegal drug additives. Furthermore, the high-throughput and real-time detection of illegal drug additives spiked into health products with SME-SERS in multi-well 96 plates were achieved with the level of 0.1 μg mg−1. The results reveal that this rapid and convenient method could be used for the effective separation and sensitive detection of illegal additives in complex specimen. [ABSTRACT FROM AUTHOR]

The development of sensitive and rapid methods for analysis and detection of small molecules is highly desirable for medical diagnostics and therapeutics. We report an acupuncture needle functionalized with gold nanoparticles (Au NPs) and a macrocyclic amine (MA) Raman tag as the platform to realize the sensitive detection of adenosine triphosphate (ATP) by surface-enhanced Raman spectroscopy (SERS). The assembled Au NPs with abundant hot spots on the surface of the needle avoids the aggregation of Au NPs and results in a good signal response. Moreover, there is strong combination between ATP and MA through electrostatic adsorption, hydrogen-bonding interactions, and π–π stacking, and as a consequence, this functionalized needle can be used as a SERS platform for detection of ATP (25 nM) through a decrease of the Raman signal of MA resulting from the high chemical affinity of ATP for MA. Specially, the Au NP/MA-functionalized needle is conveniently used to monitor ATP (100 nM) added to serum, and demonstrates great promise in the study and detection of ATP in a complex sample, laying the foundation for SERS applications in complex acupuncture specimens with fast response and simple operation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]