Single bacteria identification with second-harmonic generation in MoS2

Transition-metal dichalcogenides exhibit extraordinary optical nonlinearities, making them promising candidates for advanced photonic applications. Here, we present the microbial control over second-harmonic generation (SHG) in monolayer MoS2 and the identification of single-cell bacteria. Bacteria deposited on monolayer MoS2 induce a change in the SHG signal, in the form of anisotropic polarization responses that depend on the relative orientation of the bacteria with respect to the MoS2 crystallographic direction. The anisotropic enhancement is consistent with the presence of a tensile stress along the lateral direction of bacteria axis; SHG imaging is highly effective in monitoring biomaterial strain as low as 0.1%. We also investigate the ultravioletinduced removal of single bacteria, through the SHG imaging of MoS2. By monitoring the transient SHG signals, we determine the rupture times for bacteria, which varies noticeably for each species. This allows us to distinguish specific bacteria that share habitats; SHG imaging is useful for label free identification of pathogens at the single cell levels such as E. coli and L. casei. This label-free detection and identification of pathogens at the singlecell level can have a profound impact on the development of diagnostic tools for various applications.

Automated summary

Transition-metal dichalcogenides have extraordinary optical nonlinearities, making them potential candidates for advanced photonic applications. This study demonstrates the control of second-harmonic generation (SHG) in monolayer MoS2 by single-cell bacteria. The presence of bacteria induces anisotropic polarization responses in the SHG signal, which depends on the relative orientation of the bacteria and the MoS2 crystallographic direction. This research contributes to the monitoring of biomaterial strain and the label-free detection and identification of pathogens at the single-cell level.