a, Schematic illustration of synthesis of serum albumin-coated Ag2S nanoparticles. b,c, In vivo tumour detection via near-infrared-II fluorescence imaging (part b) and photoacoustic imaging (part c). d, Infrared thermography of tumours showing elevated temperature when irradiated with a near-infrared laser. NDs, nanodots; NHS, N-hydroxysuccinimide; PBS, phosphate-buffered saline. Adapted with permission from ref. 220. Copyright 2017 American Chemical Society.