Intracellular SERS

Table 3.1 Comparison of Raman shifts in single cell and intracellular SERS measurements. Values in columns a to e are taken from corresponding spectra in Fig. 3.11 [56] ...

As has long been practiced in various cell biology applications (23 - 25) gold nanoparticles can be delivered into live cells (see also Experimental section). Figure 3 illustrates the basic concept of intracellular SERS probes. Large nanoparticle aggregates can easily be visualized by standard bright field microscopy inside the cells, here, in the lysosomal structures of a fibroblast cell. 

Figure 3, Basic concept of intracellular SERS probes Gold nanoparticles are transferred into cells. Aggregates which provide optimum SERS enhancement and are typically utilized in the live cell experiments are shown in the transmission electron micrograph and the schematic drawing. During excitation with laser light in the near-infrared (h VjJ, such gold nanoaggregates provide enhanced local optical fields in their nm-scaled vicinity, leading to surface-enhanced Stokes (h and anti Stokes...

Fig. 6.1 Summary of different strategies for intracellular SERS. a Au NPs or aggregate provide molecular information from their immediate surroundings, b Hybrid SERS tag constructed from the Au NPs and RRMs that serve to identify the tag. It generates SERS signal from both the cell and RRM. c Au NPs with pH-sensitive RRM can serve as a pH sensor (adapted with permission from Kneipp 2011. Copyright 2011 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim)...

Fig. 6.2 Basic scheme of intracellular SERS experiment, a Scheme for the delivery of Au NPs into eukaryotic cells from the culture medium. Parallel samples were prepared for biological assays, electron microscopy and Raman microspectroscopy, b Cell lines NIH/3T3 upper panel) and J774 lower panel) after several hours of incubation with Au NPs (scale bar 20 pm) (adapted with permission from Kneipp 2006. Copyright 2006 Springtar)...

In the case of intrinsic intracellular SERS studies without RRMs, there is no analytically significant SERS response of intrinsic molecules (Chourpa et al. 2008). A particularly high number of NPs per cell should be used to obtain intrinsic SERS spectra. Typical SERS intrinsic spectra from cells of the immortalized rat renal proximal tubule cells are shown in Fig. 6.3 as an example (Kneipp et al. 2006). The spectra obtained after 120 min incubation with Au NPs provided the best SERS... 

In fact, the possibility of obtaining molecular structural information from the target analyte inside the cell is the most important characteristic of SERS. Until now this has not been possible by any other techniques. On the other hand, the limitation of intracellular SERS spectroscopy exists due to the complex matrix of molecules present in the cell that can produce SERS. Consequentiy, very complicated SERS spectra are acquired from the cells. Such SERS spectra provide only general information about the types of molecules present inside the cell. Therefore, in order to obtain a specific and known SERS spectmm from cells functionalization of the SERS tags with a RRM is required. 

Fig. 6.4 Intracellular SERS using RRM (ICG). A Examples of SERS spectra measured in single living cells incubated with the ICG-Au NPs at 830 nm excitation. ICG bands are marked with an asterisk, while an asterisk in parentheses indicates contribution of both ICG and cell. Spectmm (a) represents the ICG signature. Spectrum (c) shows the difference between spectra (b) and (a). B Spectral map of the ICG-Au tag in a cell based on 1147 cm ICG line and of two ICG lines at 1147 and 945 cm. Intensities are colour-scaled to the highest value in each area. A photomicrograph of the cell, indicating the studied area, is shown for comparison. Scale bar 20 pm (adapted with permission from Kneipp et al. 2005. Copyright 2005 American Chemical Society)...

Intracellular SERS Monitoring of Drug Release In Vivo... 

---