The development of graphene-based devices requires control over the functionalization and modification of the graphene surface. We studied the modification of the monolayer graphene surface with downstream oxygen plasma treatment to form graphene oxide (GO) for use in glucose biosensors. Amperometric and voltammetric methods were applied to GO for glucose oxidase (GOx) immobilization with a simultaneous reduction of GO to reduce graphene oxide. The fabricated glucose sensor shows a sensitivity of 0.118 μA mM −1 cm −2 and a detection limit of 0.0526 mM of glucose. This method provides fast and simultaneous immobilization of GOx and reduction of GO, and can be used in the fabrication of other electrochemical biosensors. Glucose oxidase has been recognized as an enzyme for monitoring glucose. In amperometric biosensors for glucose detection, GOx is immobilized on a nanomaterial surface and catalytically oxidizes glucose for high sensitivity and selectivity.9-11 However, enzyme immobilization is complicated by poor electrical communication of the active sites of the enzyme and the electrode surface, and by enzyme leaching. [12][13][14][15] Recently, graphene has been used to modify biosensors, offering advantages for enzyme immobilization on graphene surfaces. [16][17][18] Pristine graphene (PrG), a monolayer structure composed of one-atom thick two-dimensional honeycomb lattices of sp 2 carbon atoms, has extraordinary properties such as high intrinsic mobility and excellent thermal and electrical conductivity. [19][20][21][22] Although the bulk properties of graphene are very promising for a variety of applications, the development of graphene-based devices requires great control over the functionalization and modification of the graphene surface. Graphene oxide (GO) is one branch of functionalized graphene. GO is typically covalently functionalized with hydroxyl, epoxy, carbonyl, and carboxyl groups on its basal planes and at its edges, 23 resulting in a hybrid structure comprising a mixture of sp 2 and sp 3 hybridized carbon atoms. 24 GO sheets synthesized from graphite powders by the modified Hummers method 25 have been coated on carbon and Pt electrodes and used to immobilize GOx to develop glucose sensors. [26][27][28][29] On the other hand, monolayer graphene has been fabricated by chemical vapor deposition (CVD) on Cu and Ni substrates then transferred to other substrates for chemical and gas sensors. [30][31][32] Monolayer graphene has also been utilized for glucose sensor after immobilizing GOx to its surface through linker molecules. 33,34 With the aid of lithography and plasma etch techniques, monolayer-graphene-based devices can be patterned into arrays 32 and integrated with Si microelectronics technology. 35,36 In this work we synthesized GO from monolayer graphene by a downstream oxygen plasma. 37,38 The plasma-assisted technique has the advantages of short treatment time, an environmentally friendly manufacturing process, and the generation of numerous active species. 39 The immobilization of GOx en...

We have prepared graphene quantum dots (GQDs) and boron-doped GQDs (BGQDs) utilizing spent coffee grounds (SCGs) via a simple one-step hydrothermal process for glucose sensor application. FTIR and XPS characterizations reveal that the boron atoms have been successfully doped into graphene structures. BGQDs on glassy carbon electrode (GCE) in PBS were found to be two times as active compared to GCE/GQDs electrodes. The significant difference in electrochemical activity shown by BGQDs is evidence that boron from boric acid was doped into the graphene dominion. The generation of boronic acid groups on the boron-doped graphene quantum dots (BGQDs) surfaces facilitates the application of GQDs as a new photoluminescence (PL) probe for label-free glucose sensing. The photoluminescence of developed GQDs showed a linear response to glucose over a concentration range of 5–45 mM with a limit of detection of 12.45 mM whereas BGQDs biosensor was found to exhibit a higher sensitivity over the same concentration range with limit of detection of 3.23 mM towards glucose sensing. These results demonstrate that the synthesized BGQD has a promising potential in electrochemical activity and efficient to the PL enhancement mechanism determination of glucose.