Graphene nanowalls for high-performance chemotherapeutic drug sensing and anti-fouling properties
Graphical abstract
Graphene nanowalls provide an ultrasensitive drug monitoring platform exhibiting excellent anti-fouling properties. Effective screening of etoposide is achieved at concentrations below and within the lowest values of the therapeutic window therefore enabling the estimation of the drug’s effectiveness.
Introduction
Cancer is a fatal malignant disease and a leading cause of death worldwide. Nevertheless, the systemic administration of anticancer drugs has laterally limited effectiveness in the treatment of solid tumors. In addition, the commonly applied therapeutic approaches signify invasive chemical treatments (chemotherapy) which are mainly toxic for the patient. As only a small fraction of the total dose of the drug reaches the tumor site, the remainder of the dose is distributed throughout healthy organs and tissues, causing undesirable side-effects. For dealing with this issue, the monitoring of the concentration of drug compounds in the patient’s circulating system is crucial for maintaining the drug concentrations within a targeted therapeutic window. This aims to the individualisation of the drug dosage regime for optimal efficacy and safety of the treatment, sparing expenses and side effects issues for the patients that the treatment would be harmful or inefficient. Furthermore, as opposed to traditional monitoring technologies, personalized therapy utilizing Point-of-Care (P.o.C) devices will provide a cutting-edge technology for economical and user-friendly monitoring of analytes directly available to patients. However, personalized therapy, presents some serious limitations and uncertainties while involving complexity when dealing with mass applications. Therefore, accurate techniques based on the quantitative monitoring of the drug response at any time after the administration is highly desirable.
Meanwhile, vertically-oriented graphene nanosheets (VGs) consisting of networks perpendicularly oriented to a substrate and demonstrating exposed sharp edges and pronounced surface-to-volume ratios, are recently reported in literature [[1], [2], [3], [4]]. VGs can be grown on a wide variety of materials [1] completely or selectively filling the substrate, and may consist of only few-layers, i.e. 4–6 atomic layers, of graphene [5] or being multi-layer graphene configurations forming wall-like networks known as graphene nanowalls (GNWs) [6]. GNWs have been leveraged in different applications, for example as enhancing materials for improving the interfacial strength of composites [7], or for ameliorating the electrochemical capabilities of electrodes, when the GNWs are coated on the electrode’s surface [8]. In addition, applications involving GNWs in combination with other nanostructures, such as nanoparticles [[9], [10]], or in conjugation with soft materials like Polydimethylsiloxane (PDMS) [11] are also reported for exhibiting improved performance. Nonetheless, very limited are the studies dedicated for implementation in the therapeutics field, and, most importantly, for the effective monitoring of chemotherapeutic drugs.
In this work, we demonstrated successful ultrasensitive detection of etoposide, one of the main drugs used in chemotherapy of cancer, achieving a Limit-of-Detection (LOD) down to 4.36 nM, by leveraging optimized graphene nanowalls developed by means of Thermal Chemical Vapor Deposition (TCVD) through a catalyst-free, direct-growth method. Graphene nanostructures were developed involving three different substrate materials and implementing different growth parameters with respect to growth time and gas flow ratios, and then compared for their sensing capabilities in monitoring electroactive compounds. The optimum configuration was then selected for the actual drug screening. The growth process was performed directly on the substrate that would shape the final electrochemical electrode, avoiding any complex transferring post-processes. The work targets at the crucial aspects of the therapeutics towards malignant diseases, such as improved sensitivity and detection within and below the concentrations of the therapeutic range. In addition, the aspect of the continuous drug monitoring is ensured by the excellent anti-fouling property exhibited by the graphene-based nanostructures.
Section snippets
Growth process of vertically-stacked graphene network
A two-zone furnace thermal CVD (TCVD RF100CA 2D growth tool from Graphene Square Inc.) with a special tubular furnace design was used to implement the catalyst-free method for the growth of the nanostructures. For the preparation of samples, standard 〈100〉 4” silicon wafers (Si-Mat) were employed as the starting substrate. A 300-nm oxide was grown using a thermal oxidation oven (Tempress TS6304) in the case of SiO2 substrates. For the Ni substrates, a 20 nm Ni layer was directly deposited on Si
GNWs morphological characterization
SEM characterization (bird-eye view of the surface morphology in lower and higher magnification imaging conditions) of the fabricated nanostructures (Fig. 1a) for the different growth parameters under consideration (Fig. 1b) reveals a “maze-like” configuration indicating the characteristic morphology and dimensions of GNWs. A further significant characteristic is the wavy geometry and the curled edges of the nanowalls that may be attributed to internal stress or/and to stress induced during the
Conclusions
The present work presents a first and innovative step towards the efficient detection of etoposide that is one of the widely used drugs in cancer chemotherapy that will also pave the way for further studies concerning interference and multiplexing aspects. The detection of etoposide is for the first time hereby reported by means of directly-grown GNW-structures. Different GNW configurations were developed implementing different substrate materials and growth parameters and studied through SEM,
Author contributions
T and N.A contributed equally. I.T and N.A performed all surface treatments, data acquisition, data analysis, SEM and TEM imaging and comparison with the literature. I.T, D.D and N.A performed fabrications and Raman analysis. I.T and N.A have prepared the manuscript. S.C and D.D gave suggestions on the manuscript. I.T, N.A, D.D, S.C, and G.d.M have revised the manuscript.
Acknowledgements
The authors thank D. Deiana for assisting with TEM characterization. The authors acknowledge financial support from European Commission FP7 Programme through the Marie Curie Initial Training Network ‘PROSENSE’ (Grant No. 317420, 2012–2016), and by H2020-ERC-2014-ADG669354 CyberCare.
Ioulia Tzouvadaki received her B.Sc. degree in physics, from National and Kapodistrian University of Athens (U.O.A), Greece, the M.Sc. degree in microsystems and nanodevices from National Technical University of Athens (N.T.U.A) and the doctorate degree from EPFL, Switzerland. During her postgraduate studies, she worked at the Clean Room Laboratory of the National Center for Scientific Research (NCSR) Demokritos in the field of experimental construction processes concerning integrated circuits
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Ioulia Tzouvadaki received her B.Sc. degree in physics, from National and Kapodistrian University of Athens (U.O.A), Greece, the M.Sc. degree in microsystems and nanodevices from National Technical University of Athens (N.T.U.A) and the doctorate degree from EPFL, Switzerland. During her postgraduate studies, she worked at the Clean Room Laboratory of the National Center for Scientific Research (NCSR) Demokritos in the field of experimental construction processes concerning integrated circuits and the experimental characterisation process of nanomaterials and nanodevices. Her M.Sc. thesis concerned the computational study and simulation of polymer nanocomposite materials, within the Computational Materials Science and Engineering (CoMSE) research group, of the School of Chemical Engineering at the NTUA. Her Ph.D. work at the Integrated System Laboratory (LSI) of EPFL, focused on the fabrication and characterisation of nanostructures and their implementation as ultrasensitive nano-bio-sensors in both diagnostics and therapeutics.
Nima Aliakbarinodehi has obtained his PhD from Integrated Systems Laboratory (LSI) at École Polytechnique Fédérale de Lausanne (EPFL), Switzerland. He is currently investigating the development of ultrasensitive electrochemical and field-effect biosensors for diseases theragnosis (diagnosis and therapy). Nima, born in Tehran on 1986, received his B.Sc. from Mazandaran University, Iran in Electronics. He continued his M.Sc. study in Politecnico di Torino, Italy in MEMS, where he achieved a scholarship from LSI for a 6 months master thesis exchange program at EPFL. During his master thesis he worked on the optimization of electrochemical biosensors with the aim of enhancing their sensing performance and reliability.
Diana Dávila Pineda is currently an Adv. Senior Engineer at the IBM Research – Zurich Lab. She received her B.Sc. in Electronic Engineering, from the Tecnológico de Monterrey, Mexico in 2004 and her M.S. in Micro and Nanoelectronic Engineering in 2008 and Ph.D. in Electronic Engineering in 2011 from the Universitat Autònoma de Barcelona, Spain. She has conducted research on fuel cells, nanomaterials, thermoelectricity, spintronics and MEMS devices in multidisciplinary environments such as the Microelectronics Institute of Barcelona (IMB-CNM, CSIC), the Catalonia Institute for Energy Research (IREC), the International Iberian Nanotechnology Laboratory (INL) and ETH Zurich.
Giovanni De Micheli is Professor and Director of the Institute of Electrical Engineering and of the Integrated Systems Centre at EPF Lausanne, Switzerland. He is program leader of the Nano-Tera.ch program. Previously, he was Professor of Electrical Engineering at Stanford University. He holds a Nuclear Engineer degree (Politecnico di Milano, 1979), a M.S. and a Ph.D. degree in Electrical Engineering and Computer Science (University of California at Berkeley, 1980 and 1983). Prof. De Micheli is a Fellow of ACM and IEEE, a member of the Academia Europaea and an International Honorary member of the American Academy of Arts and Sciences. His research interests include several aspects of design technologies for integrated circuits and systems, such as synthesis for emerging technologies, networks on chips and 3D integration. He is also interested in heterogeneous platform design including electrical components and biosensors, as well as in data processing of biomedical information. He is author of: Synthesis and Optimization of Digital Circuits, McGraw-Hill, 1994, co-author and/or co-editor of eight other books and of over 750 technical articles. His citation h-index is 93 according to Google Scholar. He is member of the Scientific Advisory Board of IMEC (Leuven, B), CfAED (Dresden, D) and STMicroelectronics.
Sandro Carrara is an IEEE Fellow for his outstanding record of accomplishments in the field of design of nanoscale biological CMOS sensors. He is also the recipient of the IEEE Sensors Council Technical Achievement Award in 2016 for his leadership in the emerging area of co-design in Bio/Nano/CMOS interfaces. He is a faculty member (MER) at the EPFL in Lausanne (Switzerland). He is former professor of optical and electrical biosensors at the Department of Electrical Engineering and Biophysics (DIBE) of the University of Genoa (Italy) and former professor of nanobiotechnology at the University of Bologna (Italy). He holds a PhD in Biochemistry & Biophysics from University of Padua (Italy), a Master degree in Physics from University of Genoa (Italy), and a diploma in Electronics from National Institute of Technology in Albenga (Italy). His scientific interests are on electrical phenomena of nano-bio-structured films, and include CMOS design of biochips based on proteins and DNA.
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These authors contributed equally.