Publications
214 results found
Xu L, Ramadan S, Rosa BG, et al., 2022, On-chip integrated graphene aptasensor with portable readout for fast and label-free COVID-19 detection in virus transport medium., Sens Diagn, Vol: 1, Pages: 719-730
Graphene field-effect transistor (GFET) biosensors exhibit high sensitivity due to a large surface-to-volume ratio and the high sensitivity of the Fermi level to the presence of charged biomolecules near the surface. For most reported GFET biosensors, bulky external reference electrodes are used which prevent their full-scale chip integration and contribute to higher costs per test. In this study, GFET arrays with on-chip integrated liquid electrodes were employed for COVID-19 detection and functionalized with either antibody or aptamer to selectively bind the spike proteins of SARS-CoV-2. In the case of the aptamer-functionalized GFET (aptasensor, Apt-GFET), the limit-of-detection (LOD) achieved was about 103 particles per mL for virus-like particles (VLPs) in clinical transport medium, outperforming the Ab-GFET biosensor counterpart. In addition, the aptasensor achieved a LOD of 160 aM for COVID-19 neutralizing antibodies in serum. The sensors were found to be highly selective, fast (sample-to-result within minutes), and stable (low device-to-device signal variation; relative standard deviations below 0.5%). A home-built portable readout electronic unit was employed for simultaneous real-time measurements of 12 GFETs per chip. Our successful demonstration of a portable GFET biosensing platform has high potential for infectious disease detection and other health-care applications.
Noori YJ, Thomas S, Ramadan S, et al., 2022, Electrodeposited WS<sub>2</sub> monolayers on patterned graphene, 2D MATERIALS, Vol: 9, ISSN: 2053-1583
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- Citations: 2
Li B, Xu L, Ramadan S, et al., 2021, Detection of glial fibrillary acidic protein in patient plasma using on-chip graphene field-effect biosensors, in comparison with ELISA and single molecule array, ACS Sensors, Vol: 7, Pages: 253-262, ISSN: 2379-3694
Glial fibrillary acidic protein (GFAP) is a discriminative blood biomarker for many neurological diseases, such as traumatic brain injury. Detection of GFAP in buffer solutions using biosensors has been demonstrated, but accurate quantification of GFAP in patient samples has not been reported, yet in urgent need. Herein, we demonstrate a robust on-chip graphene field-effect transistor (GFET) biosensing method for sensitive and ultrafast detection of GFAP in patient plasma. Patients with moderate–severe traumatic brain injuries, defined by the Mayo classification, are recruited to provide plasma samples. The binding of target GFAP with the specific antibodies that are conjugated on a monolayer GFET device triggers the shift of its Dirac point, and this signal change is correlated with the GFAP concentration in the patient plasma. The limit of detection (LOD) values of 20 fg/mL (400 aM) in buffer solution and 231 fg/mL (4 fM) in patient plasma have been achieved using this approach. In parallel, for the first time, we compare our results to the state-of-the-art single-molecule array (Simoa) technology and the classic enzyme-linked immunosorbent assay (ELISA) for reference. The GFET biosensor shows competitive LOD to Simoa (1.18 pg/mL) and faster sample-to-result time (<15 min), and also it is cheaper and more user-friendly. In comparison to ELISA, GFET offers advantages of total detection time, detection sensitivity, and simplicity. This GFET biosensing platform holds high promise for the point-of-care diagnosis and monitoring of traumatic brain injury in GP surgeries and patient homes.
Ramadan S, Lobo R, Zhang Y, et al., 2021, Carbon-dot-enhanced graphene field-effect transistors for uitrasensitive detection of exosomes, ACS Applied Materials and Interfaces, Vol: 13, Pages: 7854-7864, ISSN: 1944-8244
Graphene field-effect transistors (GFETs) are suitable building blocks for high-performance electrical biosensors, because graphene inherently exhibits a strong response to charged biomolecules on its surface. However, achieving ultralow limit-of-detection (LoD) is limited by sensor response time and screening effect. Herein, we demonstrate that the detection limit of GFET biosensors can be improved significantly by decorating the uncovered graphene sensor area with carbon dots (CDs). The developed CDs-GFET biosensors used for exosome detection exhibited higher sensitivity, faster response, and three orders of magnitude improvements in the LoD compared with nondecorated GFET biosensors. A LoD down to 100 particles/μL was achieved with CDs-GFET sensor for exosome detection with the capability for further improvements. The results were further supported by atomic force microscopy (AFM) and fluorescent microscopy measurements. The high-performance CDs-GFET biosensors will aid the development of an ultrahigh sensitivity biosensing platform based on graphene for rapid and early diagnosis of diseases.
Ramadan S, Zhang Y, Tsang DKH, et al., 2021, Enhancing structural properties and performance of graphene-based devices using self-assembled HMDS monolayers, ACS Omega, Vol: 6, Pages: 4767-4775, ISSN: 2470-1343
The performance of graphene devices is often limited by defects and impurities induced during device fabrication. Polymer residue left on the surface of graphene after photoresist processing can increase electron scattering and hinder electron transport. Furthermore, exposing graphene to plasma-based processing such as sputtering of metallization layers can increase the defect density in graphene and alter the device performance. Therefore, the preservation of the high-quality surface of graphene during thin-film deposition and device manufacturing is essential for many electronic applications. Here, we show that the use of self-assembled monolayers (SAMs) of hexamethyldisilazane (HMDS) as a buffer layer during the device fabrication of graphene can significantly reduce damage, improve the quality of graphene, and enhance device performance. The role of HMDS has been systematically investigated using surface analysis techniques and electrical measurements. The benefits of HMDS treatment include a significant reduction in defect density compared with as-treated graphene and more than a 2-fold reduction of contact resistance. This surface treatment is simple and offers a practical route for improving graphene device interfaces, which is important for the integration of graphene into functional devices such as electronics and sensor devices.
Xu L, Li D, Ramadan S, et al., 2020, Facile biosensors for rapid detection of COVID-19, Biosensors and Bioelectronics, Vol: 170, Pages: 1-13, ISSN: 0956-5663
Currently the world is being challenged by a public health emergency caused by the coronavirus pandemic (COVID-19). Extensive efforts in testing for coronavirus infection, combined with isolating infected cases and quarantining those in contact, have proven successful in bringing the epidemic under control. Rapid and facile screening of this disease is in high demand. This review summarises recent advances in strategies reported by international researchers and engineers concerning how to tackle COVID-19 via rapid testing, mainly through nucleic acid- and antibody- testing. The roles of biosensors as powerful analytical tools are emphasized for the detection of viral RNAs, surface antigens, whole viral particles, antibodies and other potential biomarkers in human specimen. We critically review in depth newly developed biosensing methods especially for in-field and point-of-care detection of SARS-CoV-2. Additionally, this review describes possible future strategies for virus rapid detection. It helps researchers working on novel sensor technologies to tailor their technologies in a way to address the challenge for effective detection of COVID-19.
Noori YJ, Thomas S, Ramadan S, et al., 2020, Large-Area Electrodeposition of Few-Layer MoS<sub>2</sub> on Graphene for 2D Material Heterostructures, ACS APPLIED MATERIALS & INTERFACES, Vol: 12, Pages: 49786-49794, ISSN: 1944-8244
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- Citations: 19
Song W, Stein Scholtis E, sherrel P, et al., 2020, Electronic Structure Influences on the Formation of the Solid Electrolyte Interphase, Energy and Environmental Science, ISSN: 1754-5692
Watts C, Hanham S, Armstrong J, et al., 2020, Microwave dielectric sensing of free-flowing, single, living cells in aqueous suspension, IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology, Vol: 4, Pages: 97-208, ISSN: 2469-7249
Dielectric measurements offer the possibility of highly sensitive detection of physical cell properties, and are of interest for clinical applications due to their non-destructive nature and the lack of need for cell labelling. Here we report sensitive measurements on single, living, free-flowing cells (not electrostatically or dielectrophoretically trapped, cultured or fixed directly on sensing elements) in aqueous medium at ~9.8 GHz taken using a coupled dielectric-split ring resonator assembly. Inductive coupling between the two resonators enabled separation of microfluidic chips from RF connectors and allowed for time-resolved continuous-wave measurements on flowing single cells via the coaxial ports of a dielectric-loaded microwave cavity. Analysis via an equivalent circuit model showed that the novel resonator assembly maintained the permittivity-dependent sensitivity of a split ring resonator while operating at quality factors >1000 with lossy aqueous media (typically ~1900). Using a microfluidic channel with a 300 x 300 μm cross section, at a water-loaded resonant amplitude of ~-22 dB at 0 dBm input power level, shifts in amplitude due to individual cells passing through the sensing region of up to -0.0015 dB were observed. Correlations between averaged amplitude shifts and cell size as well as material properties demonstrate the diagnostic potential of this technique.
Gajewski K, Ramadan S, Kunicki P, et al., 2020, Microscale surface potential gradient disturbances observed in bilayer graphene, APPLIED SURFACE SCIENCE, Vol: 510, ISSN: 0169-4332
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- Citations: 3
Klein N, 2020, Evidence for modified Newtonian dynamics from Cavendish-type gravitational constant experiments, Classical and Quantum Gravity, Vol: 37, Pages: 1-21, ISSN: 0264-9381
Recent experimental results for the gravitational constant G from Cavendish-type experiments were analysed in the framework of Modified Newtonian Dynamics (MOND). MOND corrections were applied to the equation of motion of a pendulum, under the assumption that the magnitude of the horizontal time dependent gravitational acceleration determines the amount of MOND corrections. The large vertical component of the local gravitational field of the earth is fully compensated by the alignment of the torsion pendulum in accordance with Newton's third law and therefore not considered for MOND corrections. From the analysis of the MOND corrected equation of motion of a realistic torsion pendulum with mixed gravitational and electromagnetic restoring torque simple rules for meaningful MOND corrections of measured G values determined by different operational modes of Cavendish type G experiments were derived. Based on this analysis the reported discrepancies for G determined by "static deflection" and "electrostatic servo" methods of the "BIPM" experiment by Quinn et al. and between time-of-swing and angular acceleration feedback methods for the "HUST" experiment by Li et al. could be fully resolved by MOND corrections using one common MOND interpolation function, determined by a one parameter fit. The MOND corrected "BIPM" and "HUST" results, along with other "single method" results from G experiments by Gundlach and Merkovitz, Schlamminger et al. and Newman et al. lead to an average G value of 6.6742210-11 m3kg-1 s-2 with a standard deviation of 12.5 ppm only. The applied MOND correction procedure and the fitted interpolation function employed for the G experiments were found to be consistent with the most viable MOND fits to galaxy rotation curves.
Kwong Hong Tsang D, Lieberthal T, Watts C, et al., 2019, Chemically functionalised graphene FET biosensor for the label-free sensing of exosomes, Scientific Reports, Vol: 9, ISSN: 2045-2322
A graphene field-effect transistor (gFET) was non-covalently functionalised with 1-pyrenebutyric acid N-hydroxysuccinimide ester and conjugated with anti-CD63 antibodiesfor the label-free detection of exosomes.Using a microfluidic channel, part of a graphene film was exposed to solution. The change in electrical properties of the exposed graphene created anadditional minimum alongside the original Dirac point inthe drain-source current(Ids)-back-gate voltage (Vg) curve. When phosphate buffered saline (PBS) was present in the channel, the additional minimum was present at a Vglower than the original Dirac point and shifted with time when exosomes were introduced into the channel.Thisshift of the minimum from the PBS reference point reached saturationafter 30 minutesand was observed for multiple exosome concentrations. Upon conjugation with an isotype control, sensor responsetothe highest concentration ofexosomes was negligible in comparison to that with anti-CD63antibody, indicatingthat thefunctionalised gFETcan specifically detect exosomes at least down to 0.1μg/mLand is sensitive to concentration. Such a gFET biosensor has not been used before for exosome sensing and could be an effective tool for the liquid-biopsy detection of exosomes as biomarkers for early-stage identification of diseases such as cancer.
Hanham S, Watts C, Ahmad M, et al., 2019, Photonic crystal resonators as bio-liquid sensing platforms in the terahertz band, META 2019
We describethe development of high quality(Q)factor photonic crystal resonators(PCRs)integrated with microfluidic systems to formthe basis ofhighly sensitive liquid sensing platformsforthe terahertz band.The strong confinement of the terahertz fieldincombinationwith the high Q-factor provided bythe PCR allows the measurement of thedielectric properties of sub-nanoliter liquid volumes. We demonstrate the utility of thisapproach by measuring the complex permittivity of several bio-liquids at 100 GHz.
Gajewski K, Kunicki P, Sierakowski A, et al., 2019, High-resolution, spatially-resolved surface potential investigations of high-strength metallurgical graphene using scanning tunnelling potentiometry, MICROELECTRONIC ENGINEERING, Vol: 212, Pages: 1-8, ISSN: 0167-9317
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- Citations: 2
Delle LE, Pachauri V, Sharma S, et al., 2018, ScFv-modified graphene-coated IDE-arrays for 'label-free' screening of cardiovascular disease biomarkers in physiological saline, BIOSENSORS & BIOELECTRONICS, Vol: 102, Pages: 574-581, ISSN: 0956-5663
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- Citations: 19
Hanham S, Watts C, Ahmad M, et al., 2018, Photonic crystal resonators for terahertz sensing applications, Progress in Electromagnetics Research Symposium, Publisher: IEICE, Pages: 803-803
Ma Z, Hanham SM, Huidobro PA, et al., 2017, Terahertz particle-in-liquid sensing with spoof surface plasmon polariton waveguides, APL Photonics, Vol: 2, ISSN: 2378-0967
We present a highly sensitive microfluidic sensing technique for the terahertz (THz) region of the electromagnetic spectrum based on spoof surface plasmon polaritons (SPPs). By integrating a microfluidic channel in a spoof SPP waveguide, we take advantage of these highly confined electromagnetic modes to create a platform for dielectric sensing of liquids. Our design consists of a domino waveguide, that is, a series of periodically arranged rectangular metal blocks on top of a metal surface that supports the propagation of spoof SPPs. Through numerical simulations, we demonstrate that the transmission of spoof SPPs along the waveguide is extremely sensitive to the refractive index of a liquid flowing through a microfluidic channel crossing the waveguide to give an interaction volume on the nanoliter scale. Furthermore, by taking advantage of the insensitivity of the domino waveguide’s fundamental spoof SPP mode to the lateral width of the metal blocks, we design a tapered waveguide able to achieve further confinement of the electromagnetic field. Using this approach, we demonstrate the highly sensitive detection of individual subwavelength micro-particles flowing in the liquid. These results are promising for the creation of spoof SPP based THz lab-on-a-chip microfluidic devices that are suitable for the analysis of biological liquids such as proteins and circulating tumour cells in buffer solution.
Adabi M, Lischner J, Hanham SM, et al., 2017, Microwave study of field-effect devices based on graphene/aluminum nitride/graphene structures, Scientific Reports, Vol: 7, ISSN: 2045-2322
Metallic gate electrodes are often employed to control the conductivity of graphene based field effect devices. The lack of transparency of such electrodes in many optical applications is a key limiting factor. We demonstrate a working concept of a double layer graphene field effect device that utilizes a thin film of sputtered aluminum nitride as dielectric gate material. For this system, we show that the graphene resistance can be modified by a voltage between the two graphene layers. We study how a second gate voltage applied to the silicon back gate modifies the measured microwave transport data at around 8.7 GHz. As confirmed by numerical simulations based on the Boltzmann equation, this system resembles a parallel circuit of two graphene layers with different intrinsic doping levels. The obtained experimental results indicate that the graphene-aluminum nitride-graphene device concept presents a promising technology platform for terahertz- to- optical devices as well as radio-frequency acoustic devices where piezoelectricity in aluminum nitride can also be exploited.
Goniszewski S, Adabi M, Shaforost O, et al., 2017, Corrigendum: Correlation of p-doping in CVD graphene with substrate surface charges., Scientific Reports, Vol: 7, ISSN: 2045-2322
Hanham SM, Ahmad MM, Lucyszyn S, et al., 2017, LED-switchable High-Q Packaged THz Microbeam Resonators, IEEE Transactions on Terahertz Science and Technology, Vol: 7, Pages: 199-208, ISSN: 2156-342X
This paper describes the design, fabrication and experimental characterization of photonic crystal microbeam cavity resonators for the terahertz band implemented using suspended dielectric rectangular waveguide (DRW) in high resistivity silicon. Electrical quality factors of up to 11,900, combined with small modal volumes of 0.28 mm3 and 0.077 mm3, are demonstrated for devices operating at 100 and 200 GHz, respectively. The devices are found to be extremely light-sensitive, opening up new opportunities for light-controlled switching devices at terahertz frequencies. It is shown that the quality factor of the resonator can be tuned and the resonance extinguished through photo-illumination with an infrared light-emitting diode (IR LED). Additionally, the questions of thermal tunability and thermal stability of the resonators are examined. The demonstrated resonators are inherently suited to integration with DRW and by silicon bulk micromachining represent an attractive approach for realizing microphotonic integrated circuits for terahertz systems-on-a-substrate.
Watts C, Hanham SM, Ahmad MM, et al., 2017, Coupled Dielectric-Split Ring Microwave Resonatorfor Liquid Measurements in Microfluidic Channels atNanoliter Volumes, European Microwave Conference, Publisher: IEEE
A microwave dielectric resonator based sensor system has been investigated with respect to its sensitivity for the assessment of aqueous liquids. The system exploits the field enhancement of a split ring structure while retaining high and tunable quality factors due to weak and adjustable coupling between a planar split-ring and a dielectric resonator. The proposed sensor with integrated microfluidic channel allows investigation of volumes of liquids less than 1 nL and is capable of detecting small changes in relative permittivity, as demonstrated by measurements of water-ethanol solutions.
Klein N, Watts C, Hanham SM, et al., 2016, Microwave-to-terahertz dielectric resonators for liquid sensing in microfluidic systems, Conference on Terahertz Emitters, Receivers, and Applications VII, Publisher: Society of Photo-optical Instrumentation Engineer, ISSN: 0277-786X
The microwave-to-terahertz frequency range offers unique opportunities for the sensing of liquids based on the degree of molecular orientational and electronic polarization, Debye relaxation due to intermolecular forces between (semi-)polar molecules and collective vibrational modes within complex molecules. Methods for the fast dielectric characterization of (sub-)nanolitre volumes of mostly aqueous liquids and biological cell suspensions are discussed, with emphasis on labon- chip approaches aimed towards single-cell detection and label-free flow cytometry at microwave-to-terahertz frequencies. Among the most promising approaches, photonic crystal defect cavities made from high-resistivity silicon are compared with metallic split-ring resonant systems and high quality factor (Q-factor) whispering gallery-type resonances in dielectric resonators. Applications range from accurate haemoglobin measurements on nanolitre samples to label-free detection of circulating tumor cells. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Petrov PK, Zou B, Walker C, et al., 2016, Growth of Epitaxial Oxide Thin Films on Graphene, Scientific Reports, Vol: 6, ISSN: 2045-2322
The transfer process of graphene onto the surface of oxide substrates is well known.However, for many devices, we require high quality oxide thin films on the surface ofgraphene. This step is not understood. It is not clear why the oxide should adopt theepitaxy of the underlying oxide layer when it is deposited on graphene where there isno lattice match. To date there has been no explanation or suggestion of mechanismswhich clarify this step. Here we show a mechanism, supported by first principlessimulation and structural characterisation results, for the growth of oxide thin films ongraphene. We describe the growth of epitaxial SrTiO3 (STO) thin films on a grapheneand show that local defects in the graphene layer (e.g. grain boundaries) act as bridgepillarspots that enable the epitaxial growth of STO thin films on the surface of thegraphene layer. This study, and in particular the suggestion of a mechanism forepitaxial growth of oxides on graphene, offers new directions to exploit thedevelopment of oxide/graphene multilayer structures and devices.
Wang R, Pearce R, Gallop J, et al., 2016, Investigation of CVD graphene topography and surface electrical properties, SURFACE TOPOGRAPHY-METROLOGY AND PROPERTIES, Vol: 4, ISSN: 2051-672X
Hanham SM, Watts C, Otter WJ, et al., 2016, Probing the THz response of biological cells using photonic crystal resonators, Energy Materials Nanotechnology (EMN) Meeting on Terahertz
Goniszewski S, Adabi M, Shaforost O, et al., 2016, Correlation of p-doping in CVD Graphene with Substrate Surface Charges, Scientific Reports, Vol: 6, ISSN: 2045-2322
Correlations between the level of p-doping exhibited in large area chemical vapour deposition (CVD) graphene field effect transistor structures (gFETs) and residual charges created by a variety of surface treatments to the silicon dioxide (SiO2) substrates prior to CVD graphene transfer are measured. Beginning with graphene on untreated thermal oxidised silicon, a minimum conductivity (σmin) occurring at gate voltage Vg = 15 V (Dirac Point) is measured. It was found that more aggressive treatments (O2 plasma and UV Ozone treatments) further increase the gate voltage of the Dirac point up to 65 V, corresponding to a significant increase of the level of p-doping displayed in the graphene. An electrowetting model describing the measured relationship between the contact angle (θ) of a water droplet applied to the treated substrate/graphene surface and an effective gate voltage from a surface charge density is proposed to describe biasing of Vg at σmin and was found to fit the measurements with multiplication of a correction factor, allowing effective non-destructive approximation of substrate added charge carrier density using contact angle measurements.
Otter W, Hu F, Hanham S, et al., 2016, Terahertz metamaterial devices, International Conference on Semiconductor Mid-IR and THz Materials and Optics (SMMO2016)
Gregory AP, Blackburn JF, Lees K, et al., 2016, Measurement of the permittivity and loss of high-loss a Near-Field Scanning Microwave Microscope, ULTRAMICROSCOPY, Vol: 161, Pages: 137-145, ISSN: 0304-3991
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- Citations: 14
Gajewski K, Goniszewski S, Szumska A, et al., 2016, Raman Spectroscopy and Kelvin Probe Force Microscopy characteristics of the CVD suspended graphene, Diamond and Related Materials, Vol: 64, Pages: 27-33, ISSN: 0925-9635
In this work we present combined Kelvin probe force microscopy and Raman spectroscopy studies of supported and suspended structures formed out of chemical vapor deposition (CVD) grown graphene. Work function of both suspended and supported graphene was -4.81 ± 0.06eV and -4.92 ± 0.06eV respectively. By G and 2D modes correlation we showed, that CVD graphene was influenced by biaxial strain. Increased contact potential difference (CPD) on the suspended graphene in comparison with the areas of the supported graphene was the sign of increased strain (from 0.05% to ~ 0.12%) rather than decreased doping (p-doping decreased from ~ 5.5 × 1012cm-2 to ~ 4.5 × 1012cm-2).
Otter WJ, Hanham SM, Klein N, et al., 2016, Millimeter-wave negative group delay network, URSI Asia-Pacific Radio Science Conference (URSI AP-RASC), Publisher: IEEE, Pages: 1205-1207
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- Citations: 2
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