| The rapid and sensitive determination of environmental pollutants and disease biomarkers is of great practical significance.Surface-enhanced Raman spectroscopy(SERS)has been widely used to analyze the above substances due to its numerous advantages,including rapid response times,pinpoint accuracy,and noninvasive detection.The fabrication of the SERS substrate is the most critical step in the SERS measurement.In this study,three SERS substrates with excellent performance,low cost,and simple operation were developed for the detection of a variety of environmental pollutants and biomarkers.A poly(bisphenol A carbonate)(PC)/Ag hybrid nanofibers substrate with high-density of Raman“hotspots”was fabricated through the combination of electrospinning and in situ chemical reduction.When the volume ratio of tetrahydrofuran and dimethylformamide is6:4 as well as the mass fractions of PC and Ag NO3 are 14.0 wt%and 4.5 wt%,respectively in the spinning solution,the resultant nanofibers were uniform without beads.After 30 s of in situ reduction with 10 m M Na BH4,a large number of silver nanoparticles(Ag NPs)were generated on the fiber surface.Then,the nanofibers were modified with L-cysteine to capture TNT molecules by the formation of a Meisenheimer complex,after which positively charged 4-aminothiophenol-labelled Ag NPs were introduced to the system,which both improved the substrate surface roughness and led to extend the original planar hotspots to the spatial level.As a result,a good linear response ranging from 10-8 to 10-12M was achieved,and the detection limit for TNT was as low as 2.1×10-13 M.A flexible coralloid polyamide(PA)@Ag nanoarrays substrate was obtained through a simple self-assembly process under specific conditions.To maximize the amount of Raman hotspots generated,the spatial structure of the nanorod arrays,Ag NPs size,p H of the self-assembly environment,and self-assembly time were optimized in combination with finite difference time domain simulations.The results indicate that the prepared PA@Ag nanorod arrays(300-nm diameter,500-nm height,28-nm Ag NPs and 8 h of self-assembly)possess the best SERS performance.The characteristic peaks of R6G can be clearly observed even for concentrations as low as 10-13 M and the average relative standard deviation of the intensities at the 610 cm-1 peak was less than 9.8%.Meanwhile,the self-assembly process needs to be realized under specific conditions,and an inappropriate p H value will seriously affect the loading of Ag NPs on the substrate.Once the assembly process is completed,the connections between nanorods and Ag NPs are no longer affected by the surrounding p H,which gives the substrate a high degree of stability over a wide p H range of 1.25-12.00.In practical applications,the hybrid substrate was further applied for the label-free analysis of cell-targeting agent folic acid(1 n M),lung cancer biomarker adenosine(10-8 M),and highly toxic pesticide methyl parathion(10-8 M).A raspberry-like PA@Ag hybrid nanoarrays film with flexible cores was fabricated as a highly sensitive and disposable SERS substrate for sensing adenosine.Through the combination of Ag NPs self-assembly onto PA nanorod and in situ chemical reduction for further Ag NPs growth under specific conditions,a SERS-active metal shell with a large number of nanogaps was formed on the substrate surface.After adjusting the geometric construction and in situ reduction parameters of the nanoarray,the substrate exhibits good signal reproducibility and SERS activity.Besides,the Ag NPs size on the substrate increased to about 53 nm,which overcomes the problem that a single self-assembly method cannot load large-size Ag NPs on the polymer surface.4-mercaptophenylboronic acid-modified Ag NPs were introduced to form Ag-adenosine-Ag molecular bridges via the boronate affinity technique.As a result,additional Raman hotspots were generated on the active Ag“hat”surface,thereby achieving a secondary enhancement of the adenosine signal with a detection limit as low as 9.8×10-10 M. |
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