Chiral Carbon Dots as Nanoantennas for Amplification of Molecular Chirality

We present herein a previously unreported chiroptical phenomenon, leveraging the intrinsic optical nanoscale-originated properties of chiral (l- and d-cysteine derived) carbon dots (C-Dots), specifically, their surface (low-lying electronic excited) states. We show here that these structures generate an exceptional chiroptical response that, furthermore, can be transferred to molecularly chiral entities interacting with C-Dots. In such assemblies, C-Dots behave as nanoantennas, losing their own chiral identity to the advantage of the newly formed chiral (nano)assemblies that show at least 20-times higher intensity of vibrational optical activity compared to the molecular chirality signal. In a conceptual way, the observed phenomenon is similar to surface-enhanced Raman and Raman optical activity (ROA) spectroscopies, in which nanoparticles, in resonance with the incoming light, enhance the electromagnetic field around analyzed molecules, amplifying their Raman or ROA signal. Our findings enable the application of C-Dots as highly efficient chirality nanosensors which, in light of their rich surface chemistry, translates to the broad potential for the development of C-Dots-based nanoprobes with tailored properties as well as for the rational design of next-generation chiral nanomaterials.