Biocompatible sensor particles with high nitric oxide (NO) sensitivity were fabricated by a combination of layer-by-layer assembly and acid-free chitosan dissolving techniques. The sensor particles encapsulating 4,5-diaminofluorescein (DAF-2), an NO fluorescent probe, can detect 5-500 nM NO and had higher cytocompatibility as compared to DAF-2 molecules. These sensor particles will be useful for quantitative and spatial analyses of extracellular NO molecules from living cells.