Surface-enhanced Raman scattering biomedical applications of plasmonic colloidal particles

Abstract

This review article presents a general view of the recent progress in the fast developing area of surface-enhanced Raman scattering spectroscopy as an analytical tool for the detection and identification of molecular species in very small concentrations, with a particular focus on potential applications in the biomedical area. We start with a brief overview of the relevant concepts related to the choice of plasmonic nanostructures for the design of suitable substrates, their implementation into more complex materials that allow generalization of the method and detection of a wide variety of (bio)molecules and the strategies that can be used for both direct and indirect sensing. In relation to indirect sensing, we devote the final section to a description of SERS-encoded particles, which have found wide application in biomedicine (among other fields), since they are expected to face challenges such as multiplexing and high-throughput screening.

Figure 1.

(a) Evolution of extinction spectra over a wide range of particle sizes for gold nanospheres in water, normalized to the maximum extinction for each value of the diameter, 2R. (b–h) Near-field enhancement maps for dipolar, quadrupolar and octupolar modes in particles of different diameters, corresponding to the symbols superimposed in the upper contour plot. Adapted from Myroshnychenko et al. (2008). Copyright © RSC Publishing (2008).

Figure 2.

High-resolution scanning transmission electron microscopy (STEM) dark-field image, electron energy loss spectroscopy (EELS) intensity mapping and calculated EELS intensity map of (a) a single Ag triangle and (b) an Au nanostar. Adapted from (a) Nelayah et al. (2007) and (b) Rodriguez-Lorenzo et al. (2009). Copyright © Nature Publishing Group (2007) and ACS Publishing (2009).

Figure 3.

(a) UV/vis spectra of e-LBL films infiltrated with Ag nanoparticles, as a function of immersion time of the e-LBL film in a silver colloid. Inset: digital photographs of the films after 12 and 24 h of immersion time. (b) SERS spectra of 1-naphthalenethiol (1NAT) from an LBL Ag film using different excitation laser lines. (c) SERS mapping of 1NAT (1553 cm⁻¹) on the films with different excitation laser lines. Adapted from Abalde-Cela et al. (2009). Copyright © Wiley Interscience (2009).

Figure 4.

(a) SEM image of Au–PEG/PS bead. (b) Cross-sectional TEM image and electron diffraction pattern of the bead crust. (c) SERS mapping of one Au–PEG/PS microbead, showing the distribution of serotonin (5-HT) (at 1531 cm⁻¹). (d) Raman spectra of 5-HT obtained with different excitation wavelengths. (e) SERS spectra of 5-HT on Au colloids and on Au–PEG/PS microbeads (Raman scattering spectrum of PEG/PS with the same concentration of 5-HT is also shown). Adapted from Farah et al. (2009). (f,g) TEM images of Au nanostars with superparamagnetic cores (bar = 50 nm), with the approximate position of the Fe₃O₄ core outlined by a dashed circle. Adapted from Wei et al. (2009). Copyright © Wiley Interscience (2009) and ACS Publishing (2009).

Figure 5.

Comparison of empirically predicted (red) and directly measured experimental (black) spectra of penetratin. (a) Molecular model of penetratin peptide, including one phenylalanine (purple) and two tryptophans (green). (b) Raman spectra. (c) SERS spectra. (b) Red lines, predicted Raman; black lines, experimental Raman. (c) Black lines, predicted SERS; red lines, experimental SERS. Adapted from Wei et al. (2008). Copyright © ACS Publishing (2008).

Figure 6.

Bacillus anthracis Sterne spore (a) without and (b) with silver nanoparticle coating. (c) SERS-processed RGB image of a complex bacterial mixture overlaid on BFI. (d) Comparison of extracted Raman spectra from single spores (thin coloured lines), average spectrum (black line) and a library spectrum of BASP (thick red line); (e) extracted Raman spectra from single cells (thin coloured lines), average spectrum (black line) and a library spectrum of BCVG (thick green line). Adapted from Guicheteau et al. (in press). Copyright © Wiley Interscience (2010).

Figure 7.

(a) Schematic image illustrating the fabrication of SERS-encoded particles; (b) strategy for the detection of analytes of interest, i.e. pathogenic antigen, with suspension experiments; (c) detection route through microarray patterning.

Figure 8.

(a) Preparation of targeted SERS nanoparticles; (b) SERS imaging of H9c2 cardiac myocytes. (i) SERS image of the normalized CN intensity map of a fixed H9c2 cell. (ii) Multivariate deconvolution of the MMBN SERS spectra for fixed H9c2. (iii) SERS spectrum of MMBN (4-(mercaptomethyl)benzonitrile) Raman reporter molecule. (iv) Cell Raman spectrum taken from the nucleus region of the cell shown in the inset. (a) Adapted from Qian et al. (2008); (b) Adapted from Kennedy et al. (2009). Copyright © Nature Publishing Group (2008) and ACS (2009).