Toxic heavy metal ions in the environment are detrimental hazards to aquatic ecosystems and human life. Among such metal ions, the Cu2 + is a particularly important divalent cation that plays a critical role as a catalytic cofactor for a variety of metalloenzymes, including superoxide dismutase, cytochrome c oxidase, tyrosinase and nuclease . However, under overloading conditions, copper exhibits toxicity and can cause oxidative stress and disorders associated with neurodegenerative diseases (e.g. Alzheimer’s and Wilson’s diseases) . Hence, designing and developing innovative materials for simple, sensitive and rapid monitoring and sensing of heavy metals is necessary, even in trace amounts [6, 7, 24]. In this respect, enormous efforts have been dedicated to develop analytical methods for the detection of heavy metal ions [24, 9]. Yet, the most common techniques, e.g., atomic emission spectrometry, atomic absorption spectrometry and X-ray fluorescence spectrometry are still suffering from the time-consuming process, expensive instruments, and intensive labor. To overcome these problems, different means of colorimetric, optical, and electrochemical platforms have been broadly investigated for the installation of simple, sensitive, selective, and cost-effective approaches [22, 16]. More attempts have been particularly dedicated to the progress of smart and innovative fluorophores for heavy metal ions detection. Despite these efforts, there are still plenty of challenges with fabricating and developing a cost-effective and highly selective and sensitive chemo-sensor for monitoring heavy metal ions. The optical methods based on graphene-based nanosensors have recently been proposed as one of the promising methods for the detection of heavy metal ions owing to their potential benefits of easy design and sensitive recognition of metal ions .
The graphene oxide presents a unique feature such as easy functionalization, high electronic conductivity, large specific surface area, exclusive optical properties, chemical stability, and mechanical and photonic properties that deliver a talented platform for the construction and design of innovative nanomaterials. In addition, graphenes as rapidly developing nanomaterials have attracted great attention owing to their possible applications in clinical medicine, biomedical field, and in sensors particularly in electrochemical sensors and fluorescence sensors.
Graphen usually does not have flurocence property but through surface modification by some materials itcan cause fluorescence [28, 2].Typically, these methods can be categorized into “grafting from” and “grafting to” strategy. “Grafting from” methods are talented to grow polymers on the surface of the support with adjustable grafting dimension and controlled functionality [9, 23, 18, 14]. In this regard, a diversity of methods, for instance, coupling reaction , surface-initiated controlled radical polymerization (SI-CRP) such as atom transfer radical polymerization (ATRP) and RAFT polymerization [1, 25] have been developed to functionalize GO.
Some recent studies[10, 20, 19] have reported heavy metal characterization through quenching the intensity of florescence. For instance, Hua et al  for determination of mercury in river utilized sio2 modified by graphene quantum dot CdTe.
The major objectives of the present study are to develop effective chelating groups on the surface of the GO for the sensing of heavy metal ions from the aqueous media. For this purpose, the design strategy of the nanosensor was motivated based on “grafting from” method through surface modification of GO with PMAM via RAFT polymerization strategy (Scheme 1). This polymeric material with amide functional groups on the surface of GO could be employed as an agent to complex and chelate heavy metal ions from the aqueous media . Therefore, the potentiality of prepared GOLP/PMAM-hydrogel as an effective nanosensor for the detecting of heavy metal ions from aqueous media was investigated.