Ag nanorod based surface-enhanced Raman spectroscopy applied to bioanalytical sensing

Abstract

Recent progress in substrate nanofabrication has led to the development of Ag nanorod arrays as uniform, reproducible, large area SERS-active substrates with high signal enhancement. These novel nanostructures fabricated by oblique angle vapor deposition (OAD) offer a robust platform for the rapid detection of biological agents and open new perspectives for the development and integration of biomedical diagnostic for clinical and therapeutic applications. Ag nanorod arrays have been investigated as SERS-active substrates for the detection and identification of pathogens, including bacteria and viruses, as well as to evaluate the potential of this biosensing platform for bio-recognition of high affinity events using oligonucleotide-modified substrates. This review summarizes the various nanostructured substrates designed for SERS-based applications, highlights the nanofabrication methodology used to produce Ag nanorod arrays, outlines their morphological and physical properties, and provides a summary of the most recent uses of these substrates for clinical diagnostic and biomedical applications.

Figure 1

(A) Schematic of the Ag nanorod array with approximate dimensions. (B) Top-view micrograph (40K) of a Ag nanorod array depositied onto a glass slide using the OAD method. The scale bar represents 200nm.

Figure 2

(a) Five SERS spectra for M. pneumonia collected from different locations on the substrate. (B) The first derivative spectra of the data plotted in (A).

Figure 3

SERS spectra of the RSV strains (a) strain A/Long (A/Long), (b) strain B1 (B1), (c) strain A2 with a G gene deletion (ΔG), and (d) strain A2 (A2), collected from several spots on multiple substrates and normalized to the peak intensity of the most intense band (1045 cm⁻¹) and overlaid to illustrate the reproducibility on the Ag nanorod substrate.

Figure 4

Rotavirus SERS spectra. (A) Average SERS spectra for eight strains of rotavirus and the negative control (MA104 cell lysate). Spectra were baseline corrected, normalized to the band at 633cm⁻¹, and offset for visualization. (B) Difference SERS spectra for eight strains after subtraction of MA104 spectrum.

Figure 5

Overlaid average SERS spectra (n=18) for each unrelated miRNA. The spectra have been baseline corrected and unit-vector normalized for visualization of spectral differences.

Figure 6

PLS-DA Y predicted plots. Each plot predicts a sample as belonging to or not belonging to the specified miRNA class. Let-7a (●), miR-16(), miR-21 (), miR-24a (), and miR-133a (◇).

Figure 7

SERS spectrum of the anti-influenza aptamer (1000 nM) - PEG spacer (100 nM) complex on a Ag nanorod substrate, (b) anti-influenza aptamer complex and binding buffer blank control, (c) anti-influenza aptamer complex and RSV (10⁵ PFU/mL) negative control, (d) anti-influenza aptamer complex and nucleoproteins from A/Uruguay, (e) anti-influenza aptamer complex and nucleoproteins from A/Brisbane, and (f) anti-influenza aptamer complex and nucleoproteins from B/Brisbane. Virus concentrations in (d) – (f) were adjusted to 1μg/mL (relative to HA content). Each spectrum shown is an average of 10 individual spectra for each particular sample. The dashed vertical lines in (a), (b), and (c) indicate the characteristic oligonucleotide bands for the influenza aptamer and its controls. The dashed vertical lines in (d), (e), and (f) indicate the oligonucleotide bands that changed after binding of the nucleoproteins. Asterisks indicate the presence of new bands in the aptamer complex corresponding to binding of the protein target.