In accordance with the microscopy studies on uranyl biosorption by yeast cells, excitation of G. sulfurreducens in the presence of uranium with a pulsed, NIR laser (810 nm) resulted in metal-based emission. The use of 2PE has distinct advantages in the microscopy of biological systems, several of which are demonstrated here. From a technical standpoint, the large anti-Stokes shift (~300 nm between λex and λem for 2PE compared to ~100 nm for 1PE) facilitates the selection of optics such as dichroic mirrors, allowing for more efficient separation of emission from incident light. Additionally, the images also demonstrated excellent resolution, without the need for an additional pinhole as in confocal microscopy, allowing the visualisation of distinct areas of shorter-and longer-lived emission (Fig. ) spread over the cell surface. Control experiments using Escherichia coli, a bacterium which is known to absorb, but not reduce, U VI O2 2+ showed an increase in the intensity of fluorescence but consistent lifetimes over the surface of the cell (ESI). In our previous work, the increase in fluorescence intensity and the associated emission spectrum of Geobacter cells demonstrated the sorption of U VI O2 2+ . The extremely short lifetime of this emission was attributed to the presence of electron donating species localised on the outer membrane of the cell as it is well established that transitory reduction to U V is a significant quenching mechanism of U VI emission. It is possible that even in the absence of light (which can also reduce U VI O2 2+ , albeit slowly) these reducing species are involved in the electron transfer chain in which U VI O2 2+ acts as the terminal electron acceptor and that the species are unevenly distributed over the surface of the cell. Previous studies have highlighted the involvement of OmcB 75 and OmcS 76 cytochromes as playing key roles in electron transfer to Fe(III) and hence potentially other metals including U(VI) at the periphery of the Geobacter cell, while the potential orientation of these proteins at the cell surface was discussed in detail by Liu et al.