As a new category of nanomaterials, fluorescent carbon nanodots (CNDs) have outstanding optical properties, good biocompatibility, and surface functional division of regulatory and other characteristics; and they have the extensive applications in photocatalysis, biochemical analysis, bioimaging, drug delivery, and tracing the toxic metal ions sensitively, etc. In this project, we will develop an effective and quantified methodology based on fluorescent carbon nanodots (CNDs) for tracing the toxic metal ions, such as Hg(II), Pb(II), Cd (II) and Cu(II), etc.. CNDs as fluorescent probe in solution are easily quenched efficiently by electron acceptor and thus can effectively detect metal ions in solution and determine the concentration of metal ions in a certain concentration range, to achieve the trace analysis of metal ions. Hg(II) ion is one of the most toxic heavy metal ions in environment, has received the attention of scientific researchers. Currently, based on CNDs as sensor, scientists have developed a variety of methods to detect Hg(II). It was reported that the as-received CNDs with excellent fluorescent stability by the polyethylene glycol (PEG) refluxed with NaOH, can specifically detect Hg(II) in solution and the detection limit reaches 1 nM. This test method successfully detected Hg(II) in the rivers, lakes, and tap water samples. In addition to the detection of Hg(II), lots of publications have also reported a variety of methods to detect Cu(II), Fe(III), and Pb(II). Due to the rich type of carbon sources, it is still challenge to develop the new methodology for the preparations of CNDs with the sensitivity and selectivity for the detection of toxic metal ions in environment. Herein, we prepared the water-soluble, fluorescent carbon nanodots derived from β-lactoglobulin (LG) by hydrothermal method. In this case, the advantage of our LG-derived CNDs mainly came from the participation of EDA in the formation of CNDs. Due to the consuming of carboxyl groups by EDA, a uniform coverage of -NH2 groups on the surface of CNDs was achieved. It indicates that the as-received CNDs would be doped with large amount of nitrogen, responsible for the high quantum yield and high intensive photoluminescence. It is efficient way to trace the metal ions by using the CNDs immobilized on optical fiber as fluorescent device. Gonçalvesa et. al reported a sol-gel method to immobilized CNDs on optical fiber as device to detect Hg(II) ions. However, the sensitivity is relative low due to the lower fluorescent intensity of embedded CNDs in silica hydrogels. In our case, we will design and fabricate the printable PAAm/PNIPAM–CNDs hybrid hydrogels, and manage to coat it on optical fiber for fluorescent device. The ink-like hybrid hydrogels would show the reversible and temperature-dependent on–off photoluminescence with high intensity on optical fiber. PNIPAM hydrogel spheres were prepared by surfactant-free radical polymerization. The photoluminescent PAAm/PNIPAM–CND hydrogels were prepared by radical copolymerization of AAM, PNIPAM and MBA in the presence of TEMED as catalyst, and KPS as initiator in water. The optical fiber coated with fluorescent N-doped CNDs were prepared by immersing the prepared fiber tips in the PAAm/PNIPAM–CND hybrid hydrogels for six hours, and left to dry for overnight at room temperature. Afterwards, the repeated procedures would conducted two or more times. To investigate the tracing effect of metal ions by using the optical fiber with the fluorescence N-CNDs, we will select the different kinds of metal ions solutions for testing the sensitivity and selectivity. The selected metal ions solutions are listed as follows: Zn(NO3)2, FeCl2, FeCl3, Cu(NO3)2, Hg(NO3)2, Pb(NO3)2, Mg(NO3)2, CdCl2, CaCl2. The developed fluorescent probes with N-doped CNDs would perform the high sensitivity and selectivity for tracing metal ions in nM range, and exhibit the great potential for analysis of environmental water samples.