11-mercaptoundecyl trimethylammonium bromide gold nanorod (MTAB-GNR) coated with tannic acid (TA), useful for biological cellular imaging. A method of synthesizing tannic acid-coated 11-mercaptoundecyl trimethylammonium bromide gold nanorods (MTAB-TA GNRs) comprising presenting 11-mercaptoundecyl trimethylammonium bromide gold nanorods (MTAB-GNRs) in solution; functionalizing the MTAB-GNRs with tannic acid (TA) added to the MTAB-GNRs, the tannic acid configured to form a coating around the MTAB-GNRs forming MTAB-TA GNRs. The functionalizing step may further comprise adding a sodium chloride solution to the MTAB-TA GNR solution, and/or adding a MOPS buffer to the solution of tannic acid with MTAB-GNRs, and the tannic acid MTAB-GNR solution may be vortexed after each step. The MTAB-TA GNR solution may be centrifuged to separate the MTAB-TA GNRs from residual tannic acid and supernatant, and sterile water may be added to the MTAB-TA GNR solution and centrifuging performed to remove residual tannic acid from the MTAB-TA GNRs.