Hydrogen sulfide (H2S) has been recognized as one of most important gaseous signaling molecules mediated by a variety of physiological and pathological processes. Yet, its functions remain largely elusive due to the lack of potent monitoring methods. Hereby this issue is addressed with a powerful new platform - dye-assembled upconversion nanoparticles (UCNPs). A series of chromophores with different absorption bands and fast responses towards H2S is combined with UCNPs and results in a library of H2S sensors with responsive emission signals ranging from the visible to the near-infrared (NIR) region. These nanoprobes demonstrate highly selective and rapid responses to H2S in vitro and in cells. Furthermore, H2S levels in blood can be detected using the developed nanoprobes. Hence the reported H2S sensing platform can serve as a powerful diagnostic tool to research H2S functions and to investigate H2S-related diseases. The request of powerful sensor probes for environmental and bioimaging fields has attracted intensive and enthusiastic research during the past decades. Hereby a new dye-assembled H2S sensing platform - dye-assembled upconversion nanoparticles (UCNPs) - is designed. These probes with emission spectra ranging from visible to near-infrared (NIR) are applicable for H2S detection in cells and mice serum. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.