Sensitive and Label-Free SERS Detection of Single-Stranded DNA Assisted by Silver Nanoparticles and Gold-Coated Magnetic Nanoparticles.

An efficient surface-enhanced Raman scattering (SERS) method combined with DNA ligation is demonstrated in this proof-of-concept study for the detection of the single-strand DNA associated with BRAF V600E mutation. Gold-coated magnetic nanoparticles with 6-mercaptopyridine-3-carboxylic acid (MPCA) as internal reference attached on the surface (MNP@SiO2@Au-MPCA) and silver nanoparticles with Raman reporter 4-mercaptobenzonic acid (4-MBA) on the surface (Ag@4-MBA) are used as the SERS substrates. Rationally designed DNA probes are conjugated to these two types of nanoparticles, respectively. The single-stranded DNA containing the BRAF V600E mutation is the target analyte, which would act as the substrate for MNP@SiO2@Au-MPCA and Ag@4-MBA to be linked together through ligation. After multiple cycles of DNA ligation, more Ag@4-MBA are brought to the surface of MNP@SiO2@Au-MPCA. The resulting nanoparticles are easily isolated by a magnet rapidly from the mixture and redispersed in aqueous solution for homogeneous SERS measurement. The detection sensitivity is improved by the enhancement of the SERS peaks of 4-MBA between the plasmonic nanoparticles, and the detection quantification is improved by the use of internal reference, MPCA, for signal normalization. The intensity ratio of 4-MBA/MPCA increases linearly in the 1-100 fmol range of the matched DNA (BRAF mutation). Different ratios of matched DNA in the background of a large number of the single-base mismatched DNA (BRAF normal) are used to mimic real samples, and the intensity ratios of 4-MBA/MPCA are linear in the 0.02-1% range of matched DNA/mismatched DNA. The high sensitivity and specificity of the method demonstrate its potential for clinical use.

Ratiometric SERS detection of polycyclic aromatic hydrocarbons assisted by ß-cyclodextrin-modified gold nanoparticles.

A surface-enhanced Raman scattering (SERS) method is described for the determination of trace polycyclic aromatic hydrocarbons (PAHs) in the environment efficiently and economically. Detection sensitivity is improved by modifying gold nanoparticles (AuNPs) with 4-mercaptophenylboronic acid (4-MPBA) conjugated to ß-cyclodextrin (ß-CD) as a new method for ratiometric determination of PAHs in solution. Pyrene (with a Raman band at 580 cm-1) and anthracene (750 cm-1) were used as the model analytes, while 4-MPBA (1570 cm-1) was used as the internal reference to normalize the SERS signals. The intensity ratios of pyrene/4-MPBA increase linearly in the 2 to 10 nM pyrene concentration range, and the intensity ratios of anthracene/4-MPBA increase linearly in the 10 to 100 nM anthracene concentration range. The detection limits are 0.4 nM for pyrene and 4.4 nM for anthracene. This method was applied to the determination of the two analytes in soil sample extracts and the recoveries of pyrene (at levels of 236 ng∙g-1 and 170 ng∙g-1) and anthracene (334 ng∙g-1 and 510 ng∙g-1) agreed well with the results from GC-MS analyses. The good recovery rates (101.8% and 102.5% for pyrene and 106.4% and 101.7% for anthracene) confirmed the reliability of the method. Graphical abstract Schematic illustration of SERS signal enhancement of pyrene, as an example of polycyclic aromatic hydrocarbons, by ß-cyclodextrin modified gold nanoparticles.