Graphene and 2D Nanomaterials for 3D Printing and Biosensing

Abstract

Designing 3D printed micro-architectures using electronic materials with well-understood electronic transport within such structures will potentially lead to accessible device fabrication for ‘on-demand’ applications. Here we show controlled nozzle-extrusion based 3D printing of a commercially available nano-composite of graphene/polylactic acid, enabling the fabrication of a tensile gauge functioning via the readjustment of the electron-tunneling barrier width between conductive graphene-centers. The electronic transport in the graphene/polymer 3D printed structure exhibited the Fowler Nordheim mechanism with a tunneling width of 0.79 – 0.95 nm and graphene centers having a carrier concentration of 2.66 ×10^12/cm2. Furthermore, a mechanical strain that increases the electron-tunneling width between graphene nanostructures (~38 nm) by only 0.19 Angstrom reduces the electron flux by 1e/s/nm2 (from 18.51 to 19.51 e/s/nm2) through the polylactic acid junctions in the 3D-printed heterostructure. This corresponds to a sensitivity of 2.59 Ω/Ω%, which compares well with other tensile gauges. We envision that the proposed electron-tunneling model for conductive 3D-printed structures with thermal expansion and external strain will lead to an evolution in the design of next-generation of ‘on-demand’ printed electronic and electromechanical devices. In addition, here we show gelation, 3D gel-printing and the resultant device’s characterization for six different concentration of graphene/MoS2 (100:0, 10:90,30:70, 50:50, 70:30, 90:10) and Graphene/BN (50:50) alloys. Rheology studies show the viscoelastic properties of the gels, including viscosity and yield stress. The shear-thinning behavior was engineered to provide the ability of fabricate 3D printed devices via an aligned controlled nozzle-extrusion based modified 3D printer, enabling the fabrication of composite electrodes. The 3D printed devices structure was arrested in place lyophilization induced water removal. These nanocomposites were analyzed for electron-tunneling barrier width between conductive graphene-centers; and structural and mechanical properties. The ordered graphitic region with sp2 hybridized carbon atoms in the graphene sheets is in the order of 8.28 ±0.23 nm. The temperature-dependent electronic transport of 3D printed electrodes structures exhibits a transport-barrier of 16.24 meV and a tunneling width of 0.45 nm (Fowler Nordheim electron tunneling) with graphene centers having a carrier concentration of 1.7*1011/cm2. By modifying the graphene/MoS2 concentration, the Young’s Modulus of the structure can be controlled between 0.6 and 1.6 N/cm2. We envision that the proposed 3D-printing of gels of nanomaterial will lead to an evolution in the design of next-generation of ‘on-demand’ printed electronic and electromechanical devices. Furthermore, Imaging modalities aimed at distinguishing Glioblastoma multiforme (GBM) tumor margins can be potentially applied intraoperatively towards maximal tumor resection and improve overall survival. Here we present a novel technique aimed at characterizing heterogeneity of GBM tissue to distinguishing necrosis, tumor, margin, and normal tissue. An ultrasensitive monolayer graphene sheet was interfaced with 11 GBM tissue samples, to study the resultant change in shift of Raman signal and doping, in relation to various H&E confirmed heterogenous regions. We showed that the second-order overtone of in-plane phonon vibration energies (2D) of graphene can sensitively differentiate various heterogenous regions within GBM tissue, as confirmed on H&E stain. Graphene interfaced with tumor tissue was significantly n-doped with a Raman shift of ~5 cm-1 in the 2D peak. This is attributed to the distinct surface chemistries of the heterogeneous tissue, which sensitively modified the phonon vibration energies of the interfaced graphene. Further, the molecular dipole moment arising from the different tissue sections coupled with the high quantum capacitance of graphene resulted in a doping density of ~9.40 x 10^12 cm-2 for tumor interfaced graphene. Raman based graphene platform is capable of identifying heterogeneity within GBM tissue. This can be applied to design ultrasensitive diagnostic, therapeutic and monitoring technology in GBM patients. Intraoperatively, not only can this technology be applied towards identification of tumor margins for maximal safe resection, but also, the characteristic signal can enhance or replace frozen histopathologic diagnosis. This research can open new avenues for studying various cancer tissues via a simple Raman based graphene platform.