Functionalized graphene oxide for the fabrication of paraoxon biosensors

• We developed functionalized graphene oxide (FGO) as a platform for biosensors.
• Abundant affinity groups on FGO resulted in an excellent enzyme loading.
• The modified electrodes exhibited great short-term and long-term stability.
• The FGO biosensors showed a detection limit of 0.65 nM to paraoxon.

There is an increasing need to develop biosensors for the detection of harmful pesticide residues in food and water. Here, we report on a versatile strategy to synthesize functionalized graphene oxide nanomaterials with abundant affinity groups that can capture histidine (His)-tagged acetylcholinesterase (AChE) for the fabrication of paraoxon biosensors. Initially, exfoliated graphene oxide (GO) was functionalized by a diazonium reaction to introduce abundant carboxyl groups. Then, Nα,Nα-bis(carboxymethyl)-l-lysine hydrate (NTA-NH2) and Ni2+ were anchored onto the GO based materials step by step. AChE was immobilized on the functionalized graphene oxide (FGO) through the specific binding between Ni-NTA and His-tag. A low anodic oxidation potential was observed due to an enhanced electrocatalytic activity and a large surface area brought about by the use of FGO. Furthermore, a sensitivity of 2.23 μA mM−1 to the acetylthiocholine chloride (ATChCl) substrate was found for our composite covered electrodes. The electrodes also showed a wide linear response range from 10 μM to 1 mM (R2 = 0.996), with an estimated detection limit of 3 μM based on an S/N = 3. The stable chelation between Ni-NTA and His-tagged AChE endowed our electrodes with great short-term and long-term stability. In addition, a linear correlation was found between paraoxon concentration and the inhibition response of the electrodes to paraoxon, with a detection limit of 6.5 × 10−10 M. This versatile strategy provides a platform to fabricate graphene oxide based nanomaterials for biosensor applications.

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