Ff01 535 50

To obtain isolated Bi₄NbO₈Cl particles, a well-dispersed methanol suspension of Bi₄NbO₈Cl in low concentration was spin-coated onto a cleaned cover glass. The particle-coated cover glass was annealed at 363 K for 30 min to immobilize the particles on the glass surface, and then placed in a chamber filled with an Ar-saturated aqueous methanol solution of MS-DN-BODIPY (1 μM). A 488 nm CW laser (OBIS 488LX, Coherent; 10 mW cm⁻²) passing through an objective lens (CFI Plan Apo λ100 × H, Nikon; NA 1.45) after reflection by a dichroic mirror (Di02-R488, Semrock) was reflected completely at the cover glass–solution interface to generate an evanescent field, which made it possible to detect the fluorescent products selectively on the bottom surface of the crystal. The emission from the sample was collected by the same objective lens, after which it was magnified by a 1.5× built-in magnification changer, and passed through a band-pass filter (FF01-535/50, Semrock) to remove undesired scattered light. The emission images were recorded using an electron-multiplying charge-coupled device (EMCCD) camera (Evolve 512, Roper Scientific) using Micro-Manager (https://www.micro-manager.org/). All experimental data were obtained at room temperature.

Images of HEK293 cells or neurons were acquired with an inverted microscope (IX71, Olympus) equipped with a 100×/1.45-NA oil-immersion objective. Cells were illuminated with high-power light-emitting diodes with wavelength of 405 nm (M405LP1, Thorlabs), 450 nm (M450LP1, Thorlabs) and/or 470 nm (M470 L3, Thorlabs). 405-nm and 470-nm illumination light were filtered at the exit of LEDs with band-pass filters centered at 405 nm (FBH405–10, Thorlabs) and 475 nm (FF01–475/28, Semrock), respectively. 450 nm illumination was filtered with a band-pass filters centered at 434 nm to allow the 440-nm component passing through. The fluorescence was collected through a 495-nm dichroic mirror (FF495-Di03, Semrock) and a 535/50 emission filter (FF01–535/50, Semrock). Illumination intensity was 5 mW/mm² in all cases for 470-nm light and and 0.1~ 2.5 mW/mm² for 405-nm light at the specimen plane. In all experiments, images were acquired continuously unless described explicitly, at 200 Hz with a sCMOS camera (Zyla, Andor). The camera and the microscope were connected with a 0.35×-magnification adapter (Olympus). Synchronization of electrophysiology and imaging was implemented with a DAQ board (PCI-6229, National Instruments) interfaced with Igor Pro (Wavemetrics) and Micro-Manager [20 (link)].