Direct and sensitive SERS detection of aflatoxin B1 based on aggregated silver nanocages

Aflatoxin B1 (AFB1), a highly toxic and potent carcinogenic contaminant, necessitates rapid and sensitive detection to ensure food safety. While conventional techniques like HPLC and HPLC-MS are confined to laboratory settings, rapid biosensor-based approaches often suffer from limited sensitivity and poor anti-interference capability. Developing sensitive and robust analytical platforms for rapid screening of AFB1 in food matrices remains a critical challenge. Surface enhanced Raman scattering (SERS) has gained prominence due to its ultrahigh sensitivity, rapid detection capability, and molecular fingerprinting capabilities. However, existing SERS-based sensors for AFB1 detection still face critical technical limitations, such as insufficient sensitivity or poor selectivity.

This study develops a SERS sensor based on aggregated silver nanocages (a-AgNCs) for direct, label-free detection of AFB1. The obtained a-AgNCs have dense nano gaps of ∼1 nm, which generate electromagnetic "hotspots" under 532 nm laser excitation, thereby achieving significant electromagnetic enhancement (EM) effect. Simultaneously, the Fermi level of a-AgNCs (-4.21 eV) aligns with the molecular orbitals of AFB1 (HOMO: 6.11 eV, LUMO: 2.13 eV), facilitating chemical enhancement (CM) effect through photo-induced charge transfer (PICT). The synergistic effect of EM and CM endows the SERS sensor a quite low detection limit of ≤0.5 ng/mL for AFB1 without requiring derivatization or bio-recognition elements. Furthermore, the SERS sensor demonstrates a high selectivity for AFB1 against coexisting substances (e.g., amino acids, sugars), and satisfactory spiked recoveries of AFB1 in real samples (from 81 % to 112 %).

Thus, the developed sensor combines high sensitivity, selectivity, and practicality, offering an innovative solution for detection of trace AFB1 in food. Moreover, this work can serve as a typical case study to illustrate how to enhance the response activity of SERS substrates toward target molecules by coordinating EM and CM effects, thereby facilitating the application of SERS in detecting certain molecules with low activity.