Browsing by Author "Bardhan, Neelkanth M."

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Enhanced Cell Capture on Functionalized Graphene Oxide Nanosheets through Oxygen Clustering
(2017-02)
Bardhan, Neelkanth M.
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Kumar, Priyank V.
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Li, Zeyang
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Ploegh, Hidde L.
;
Grossman, Jeffrey C.
With the global rise in incidence of cancer and infectious diseases, there is a need for the development of techniques to diagnose, treat, and monitor these conditions. The ability to efficiently capture and isolate cells and other bio-molecules from peripheral whole blood for downstream analyses is a necessary requirement. Graphene oxide (GO) is an attractive template nanomaterial for such biosensing applications. Favorable properties include its two-dimensional architecture and wide range of functionalization chemistries, offering significant potential to tailor affinity toward aromatic functional groups expressed in biomolecules of interest. However, a limitation of current techniques is that as-synthesized GO nanosheets are used directly in sensing applications, and the benefits of their structural modification on the device performance have remained unexplored. Here, we report a microfluidic-free, sensitive, planar device on treated GO substrates to enable quick and efficient capture of Class-II MHC-positive cells from murine whole blood. We achieve this by using a mild thermal annealing treatment on the GO substrates, which drives a phase transformation through oxygen clustering. Using a combination of experimental observations and MD simulations, we demonstrate that this process leads to improved reactivity and density of functionalization of cell capture agents, resulting in an enhanced cell capture efficiency of 92 +/- 7% at room temperature, almost double the efficiency afforded by devices made using as-synthesized GO (54 +/- 3%). Our work highlights a scalable, cost-effective, general approach to improve the functionalization of GO, which creates diverse opportunities for various next-generation device applications.
New insights into the thermal reduction of graphene oxide: Impact of oxygen clustering
(2016-04)
Kumar, Priyank V.
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Bardhan, Neelkanth M.
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Chen, Guan-Yu
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Li, Zeyang
;
Belcher, Angela M.
Graphene has attracted interest for a number of applications ranging from electronics, optoelectronics to membrane-based technologies. The thermal reduction of chemically exfoliated graphene oxide (GO) sheets represents an important step for large-scale, solution-based graphene synthesis. Therefore, understanding the reduction process and being able to provide new handles to control the resulting sheet properties is highly desirable. Using atomistic calculations combined with experiments, we study and demonstrate the impact of one such new handle - oxygen clustering on the graphene basal plane - on the structural and electrical properties of reduced GO (rGO) structures. Our calculations reveal that the number of oxygen and carbon atoms removed from the graphene plane during reduction can be tuned depending on the degree of oxygen clustering, without altering the reduction temperature. Further, we demonstrate that rGO thin films with improved sheet resistance (up to 2-fold smaller) can be obtained by facilitating oxygen clustering prior to reduction. Overall, our results highlight that oxygen clustering serves as a useful handle in controlling the structural and electrical properties of the resulting rGO structures, and could be potentially useful toward the synthesis of electrodes, graphene quantum dots and for different graphene-based thin film applications. (C) 2015 Elsevier Ltd. All rights reserved.