A novel printed graphene electrode modified with electrochemically reduced graphene oxide was developed for the detection of a specific oligonucleotide sequence. The graphene oxide was immobilized onto the surface of a graphene electrode via π-π bonds and electrochemical reduction of graphene oxide was achieved by cyclic voltammetry. A much higher redox current was observed from the reduced graphene oxide-graphene double-layer electrode, a 42% and 36.7% increase, respectively, in comparison with that of a bare printed graphene or reduced graphene oxide electrode. The good electron transfer activity is attributed to a combination of the large number of electroactive sites in reduced graphene oxide and the high conductivity nature of graphene. The probe ssDNA was further immobilized onto the surface of the reduced graphene oxide-graphene double-layer electrode via π-π bonds and then hybridized with its target cDNA. The change of peak current due to the hybridized dsDNA could be used for quantitative sensing of DNA concentration. It has been demonstrated that a linear range from 10(-7)M to 10(-12)M is achievable for the detection of human immunodeficiency virus 1 gene with a detection limit of 1.58 × 10(-13)M as determined by three times standard deviation of zero DNA concentration.

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Flexible electronic materials combined with micro-3D fabrication present new opportunities for wearable biosensors and medical devices. This Research Article introduces a novel carbonnanotube-coated force sensor, successfully combining the advantages of flexible conductive nanomaterials and the versatility of two photon polymerization technologies for creating functional 3D microstructures. The device employs carbon-nanotube-coated microsprings with varying configurations and geometries for real-time force sensing. To demonstrate its practical value, the device has first been embodied as a patch sensor for transcutaneous monitoring of human arterial pulses, followed by the development of a multiple-point force-sensitive catheter for real-time noninvasive intraluminal intervention. The results illustrate the potential of leveraging advanced nanomaterials and micro-3D-printing for developing new medical devices.

Real-time monitoring of intrabody pressures can benefit from the use of miniaturized force sensors during surgical interventions or for the recovery period thereafter. Herein, we present a force sensor made of poly(vinylidene fluoride)-cotrifluoroethylene (P(VDF-TrFE)) with a simple fabrication process that has been integrated into the tip of a medical catheter for intraluminal pressure monitoring, as well as into an implantable device with a power consumption of 180 μW obtained by the nearfield communication (NFC) interface to monitor the arterial pulse at the subcutaneous level (≤1 cm). The pressure range supported by the sensor is below 40 kPa, with a signal responsivity of 0.63 μV/Pa and a mean lifetime expectancy of 400 000 loading cycles inside physiological conditions (12 kPa). The proposed sensor has been tested experimentally with synthetic anatomical models for the lungs (bronchoscopy) and subcutaneous tissue, as well as directly above the human carotid and radial arteries. Information about these pressure levels can provide insights about tissue homeostasis inside the body as fluid dynamics are altered in some health conditions affecting the hemodynamic and endocrine body systems, whereas for surgical interventions, precise control and estimation of the pressure exerted by a catheter over the internal walls are necessary to avoid endothelium injuries that lead to bleeding, liquid extravasation, or flow alteration associated with atheroma formation.

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Polymer residue from Polymethyl methacrylate (PMMA) on transferred graphene is a common issue for graphene devices. This residue affects the properties of graphene. Herein, we have introduced an improved technique to reduce the effect of this residue by deep UV (DUV) exposure of PMMA coated graphene samples within the wet transfer process. This technique has systematically been evaluated by optical microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and electrical measurements. The results show that this residue is effectively reduced on the graphene surface after DUV treatment. In addition, the electrical characteristics of transferred graphene confirm that the sheet resistance and contact resistance are reduced by about 60 and 80%, respectively, after the DUV exposure. Electrical current transport characteristics also show that minimizing this residue on the graphene surface gives less hysteresis of electronic transport in back-gate graphene field-effect transistors. Furthermore, repeating electrical tests and aging shift the neutral point voltage of graphene. We attribute these improvements to cleaving of the chemical bonds in PMMA by DUV exposure and hence increasing the solubility of PMMA in acetone for subsequent processing steps. This work provides a unique route to enhance the electrical properties of transferred graphene after the fabrication process.

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