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Graphene metrology needs to keep up with the fast pace of developments in graphene growth and transfer. Terahertz time-domain spectroscopy (THz-TDS) is a non-contact, fast, and non-destructive characterization technique for mapping the electrical properties of graphene. Here we show several case studies of graphene characterization on a range of different substrates that highlight the versatility of THz-TDS measurements and its relevance for process optimization in graphene production scenarios.

Real-time, high resolution, simultaneous measurement of multiple ionic species is challenging with existing chromatographic, spectrophotometric and potentiometric techniques. Potentiometric ion sensors exhibit limitations in both resolution and selectivity. Herein, we develop wafer scale graphene transistor technology for overcoming these limitations. Large area graphene is an ideal material for high resolution ion sensitive field effect transistors (ISFETs), while simultaneously enabling facile fabrication as compared to conventional semiconductors. We develop the ISFETs into an array and apply Nikolskii–Eisenman analysis to account for cross-sensitivity and thereby achieve high selectivity. We experimentally demonstrate real-time, simultaneous concentration measurement of K+, Na+, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\rm{NH}}}_{4}^{+}$$\end{document}NH4+, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\rm{NO}}}_{3}^{-}$$\end{document}NO3−, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\rm{SO}}}_{4}^{2-}$$\end{document}SO42−, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\rm{HPO}}}_{4}^{2-}$$\end{document}HPO42− and Cl− with a resolution of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim\! 2\times 1{0}^{-3}\,{\mathrm{log}}\,$$\end{document}~2×10−3log concentration units. The array achieves an accuracy of ±0.05 log concentration. Finally, we demonstrate real-time ion concentration measurement in an aquarium with lemnoideae lemna over three weeks, where mineral uptake by aquatic organisms can be observed during their growth., The authors demonstrate wafer-scale, graphene-based ion sensitive field effect transistors arrays for simultaneous concentration measurement of K+, Na+, NH4+, NO3−, SO42−, HPO42− and Cl−, and use their technology for real-time ion concentration measurements in an aquarium with lemnoideae lemna over a period of three weeks.

2D Materials ACCEPTED MANUSCRIPT • The following article is Open access Mass spectrometry of carbohydrate-protein interactions on a glycan array conjugated to CVD graphene surfaces Juan Pedro Merino1, Sonia Serna2 , Alejandro Criado3, Alba Centeno4 , Ilargi Napal5, Javier Calvo1, Amaia Zurutuza6, Niels Reichardt1 and Maurizio Prato7 Accepted Manuscript online 11 December 2019 • © 2019 IOP Publishing Ltd What is an Accepted Manuscript? Download Accepted Manuscript PDF Turn on MathJax Share this article Article information Abstract Mass spectrometry (MS) is a valuable tool for functional genomic, proteomic, and glycomic studies. Particularly, the combination of MS with microarrays is a powerful technique for analyzing the activity of carbohydrate processing enzymes and for the identification of carbohydrate-binding proteins (lectins) in complex matrices. On the other hand; graphene exhibits high desorption/ionization efficiency, good conductivity and optical transparency, specifications of a high-performance component for matrix-assisted laser desorption/ionization (MALDI) platforms. Besides, the chemical functionalization of graphene increases the adsorption capability of functional biomolecules (e.g. receptors), resulting in very stable interfaces. Taking advantage of the properties of graphene, we developed several modified chemical vapor deposited graphene (CVDG)-based glycan arrays on different substrates including ITO and bare glass, as a potential sensing platform for carbohydrate-lectin interactions, which are involved in a plethora of biological processes The glycan arrays were fully characterized by MALDI-MS analysis and, in some cases, optical microscopy.

The discovery of the field effect in graphene initiated the development of graphene field effect transistor (FET) sensors, wherein high mobility surface conduction is readily modulated by surface adsorption. For all graphene transistor sensors, low-frequency 1/f noise determines sensor resolution, and the absolute measure of 1/f noise is thus a crucial performance metric for sensor applications. Here we report a simple method for reducing 1/f noise by scaling the active area of graphene FET sensors. We measured 1/f noise in graphene FETs with size 5 μm × 5 μm to 5.12 mm × 5.12 mm, observing more than five orders of magnitude reduction in 1/f noise. We report the lowest normalized graphene 1/f noise parameter observed to date, 5 × 10−13, and we demonstrate a sulfate ion sensor with a record resolution of 1.2 × 10−3 log molar concentration units. Our work highlights the importance of area scaling in graphene FET sensor design, wherein increased channel area improves sensor resolution.

Flicker noise or 1/f noise refers to processes in which the power spectral density (PSD) is inversely proportional to frequency and is typically the dominant noise source in transistors at low frequency. We report our work on measurements of unprecedentedly low 1/f noise in graphene field effect transistors, which we attribute to large device area. Large area graphene grown by chemical vapor deposition (CVD) has potential for a variety of applications including biomolecular sensors, bolometric photodetectors and ion sensitive field effect transistors (ISFET) [1]. For all these applications, low-frequency 1/f noise is found to be the dominant factor that determines sensor resolution limits. Hence, the absolute value of 1/f noise PSD serves as a crucial performance metric for graphene sensor applications. Previous studies of 1/f noise in graphene devices has been performed using both CVD grown graphene and exfoliated graphene. Balandin et al [2] has studied 1/f noise in exfoliated graphene and how it varies with substrate and charge carrier concentration. Karnatak et al [3] has shown that contact resistance can play a dominant role in 1/f noise. To date, there has been no experimental study of 1/f as the graphene channel is scaled up to mm lengths. We report here our work on 1/f noise measurement of graphene field effect transistors with varying channel and contact geometries. In our experiments, CVD grown graphene on copper was transferred onto fused silica coated with 100 nm of parylene using a standard wet transfer process. Parylene was used as an interface between the graphene and fused silica, which has been shown by Fakih et al [1] to reduce both drift and hysteresis in graphene ISFETs. The transferred graphene was processed with two photolithography steps to fabricate devices with areas ranging from 12µm2 to 36mm2. Electrical contact to the graphene was made directly with Au. The 1/f noise was measured by first applying a dc bias using a low noise lithium-ion battery, and the generated voltage fluctuations were then measured using a low noise voltage pre-amplifier and a 24-bit digitizer. The voltage PSD of 1/f noise in graphene, will typically have the form of SV=Vo 2K/f. Where Vo is the dc voltage applied across the device, f is the frequency, and K is the unitless noise constant. K is experimentally approximated to be (1/N)∑nSVnfn/Vo 2, where SVn is the voltage PSD measured at n different frequencies fn. The work from Balandin et al [2] demonstrates typical K values of 10-8, and work from Karnatak et al [3] shows values as low as 10-9. Our devices have unprecedented low measured K values of 10-14, which we attribute to the large device area of 36 mm2. Our results experimentally demonstrate that the noise parameter can be decreased by orders of magnitude by working with large area devices. Our work suggests that for graphene based sensor applications, large device area is favourable for improved sensor resolution. References: 1. Fakih, I., et al., High resolution potassium sensing with large-area graphene field-effect transistors. Sensors and Actuators B: Chemical, 2019. 291: p. 89-95. 2. Balandin, A.A., Low-frequency 1/f noise in graphene devices. Nature nanotechnology, 2013. 8(8): p. 549-55. 3. Karnatak, P., et al., Current crowding mediated large contact noise in graphene field-effect transistors. Nature Communications, 2016. 7(1).

Electrolyte-gated graphene field-effect transistors are here proposed for biosensing applications. To this end, a label-free immunosensor based on this technology is employed for the sensitive and selective detection of IgG. Differently from the typical approach based on the bioreceptor immobilization onto a graphene layer, in this work sensitivity in the lower femtomolar range can be reached thanks to the formation of a closely packed layer of anti-IgG receptors anchored to the gold gate electrode.