Band-gap-tunable carbon quantum dots for surface-enhanced Raman scattering

Carbon quantum dots (CQDs) with photoluminescence properties have been widely recognized, however, their inherent surface-enhanced Raman scattering (SERS) activity is rare reported. Herein, we propose a type of band-gap-tunable CQDs derived from metal-phenolic network (MPN) that exhibits excellent SERS performance. MPN-CQDs may be the ideal nonmetallic SERS substrates to accurately elucidate the chemical mechanism (CM) due to their simply controllable bandgap structure. By screening the doped metal elements of MPN, MPN-CQDs can realize the optimal SERS effect with the maximum Raman enhancement factor of 5.5×10 ⁴ , also exhibit outstanding SERS reproducibility and stability. We then systematically disclose the interfacial photo-induced charge transfer process and corresponding migration pathways between band-gap-tunable MPN-CQDs and analyte. This class of nonmetallic SERS substrates is finally applied for detection of hemoglobin with high sensitivity; further combined with machine learning algorithm, we have successfully achieved precise identification of the heterogeneity of hemoglobin. This is the first evidence for the tunable SERS performance in CQDs, which also offers the facile avenue for in-depth understanding of CM in nonmetallic materials.