Development of biocompatible SERS nanotag with increased stability by chemisorption of reporter molecule for in vivo cancer detection.

Biocompatible surface-enhanced Raman scattering (SERS) nanotag has been developed by chemisorption of novel Raman reporters on gold colloid. We modified our previously published best five reporter molecules (B2, B7, C3, C7 and C9) from triphenylmethine (TM) library using lipoic acid (LA) as a linker to covalently attach the reporters on gold colloid. Among these TM-LA molecules, B2LA showed the highest SERS signal intensity and stability over time. Further, time course SERS intensity of B2LA was compared with currently popular Raman reporter malachite green isothiocyanate (MGITC). The results demonstrated that signal intensity from B2LA was even stable over a period of one month. In vitro SERS screening was performed in cancer cell lines using B2LA containing nanotag conjugated with selective antibodies recognizing HER2 and EGFR cancer proteins. We found reasonably strong SERS signals from both HER2 and EGFR positive cells whereas no signal was measured from respective negative cells. Moreover, we successfully proved this recognition by cell imaging using fluorescein isothiocyanate (FITC) labeled antibody conjugated nanotag. Both SERS and cell-imaging study further confirmed the selective binding of antibody conjugated nanotag to cancer cells over-expressing HER2 and EGFR. In addition, as a proof of concept, in vivo SERS measurement in a mouse model was carried out to detect the nanotag-anchored cancer cells that are subcutaneously injected to the animal.