Abstract
The purpose of this study was to explore the use of surface-enhanced Raman spectroscopy (SERS) to image the distribution of epidermal growth factor receptor (EGFR) in cells. To accomplish this task, 30-nm gold nanoparticles (AuNPs) tagged with antibodies to EGFR (1012 per mL) were incubated with cells (106 per mL) of the A431 human epidermoid carcinoma and normal human bronchial epithelial cell lines. Using the 632.8-nm excitation line of a He-Ne laser, Raman spectroscopy measurements were performed using a point mapping scheme. Normal cells show little to no enhancement. SERS signals were observed inside the cytoplasm of A431 cells with an overall enhancement of 4 to 7 orders of magnitude. Raman intensity maps of the 1450 and 1583 cm−1 peaks correlate well with the expected distribution of EGFR and AuNPs, aggregated following uptake by endosomes and lysosomes. Spectral features from tyrosine and tryptophan residues dominate the SERS signals.
Highlights
A number of cancers are characterized by overexpression of the epidermal growth factor receptor (EGFR), a membrane protein which mediates cell growth, proliferation, and differentiation in multiple tissues
To overcome the limited contrast, we explore the use of surface-enhanced Raman spectroscopy (SERS)
The gold colloidal solution was characterized by UV-visible spectroscopy (UV-Vis) spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS)
Summary
A number of cancers are characterized by overexpression of the epidermal growth factor receptor (EGFR), a membrane protein which mediates cell growth, proliferation, and differentiation in multiple tissues. Many epithelial tumors have been found to express high numbers of EGF receptors,[1,2,3,4,5,6,7] and the receptor levels are associated with poor clinical prognosis in cancers of the bladder,[4] lung,[5] and breast.[4,6] Antibodies for EGFR tagged with fluorescent probes have been used as contrast agents to image EGFR overexpression.[8] The EGFR-induced shift in the plasmon resonance has been used as an image contrast method.[9] Both of these methods provide at most a 10-fold intensity contrast factor. To overcome the limited contrast, we explore the use of surface-enhanced Raman spectroscopy (SERS). By exciting a sample with laser light, energy is transferred to (Stokes process) or lost (anti-Stokes process) by the medium in an inelastic scattering process referred to as Raman spectroscopy. By tuning the incident laser frequency to the plasma frequency of the nanoparticle assembly, an overall enhancement of 7 to 8 orders of magnitude of the Journal of Nanophotonics
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