Graphene oxide wrapped SERS tags: multifunctional platforms toward optical labeling, photothermal ablation of bacteria, and the monitoring of killing effect.

As novel optical nanoprobes, surface-enhanced Raman scattering (SERS) tags have drawn growing interests in the application of biomedical imaging and phototherapies. Herein, we demonstrated a novel in situ synthesis strategy for GO wrapped gold nanocluster SERS tags by using a tris(2,2'-bipyridyl)ruthenium(II) chloride (Rubpy)/GO nanohybrid as a complex Raman reporter, inspired by the role of GO as an artificial receptor for various dyes. The introduction of GO in the synthesis procedure provided systematic solutions for controlling several key parameters of SERS tags, including reproducibility, sensitivity, and colloidal and signal stability. An additional interesting thermal-sensitive SERS property (SERS intensity decreased upon increasing the temperature) was also achieved due to the heat-induced release/redistribution of reporter molecules adsorbed on GO. Combining the synergic effect of these features, we further fabricated multifunctional, aldehyde group conjugated Au@Rubpy/GO SERS tags for optical labeling and photothermal ablation of bacteria. Sensitive Raman imaging of gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria could be realized, and satisfactory photothermal killing efficacy for both bacteria was achieved. Our results also demonstrated the correlation among the SERS intensity decrease ratio, bacteria survival rate, and the terminal temperature of the tag-bacteria suspension, showing the possibility to use SERS assay to measure antibacterial response during the photothermal process using this tag.