Staff directory Ruslan Raulevich Álvarez Diduk

Ruslan Raulevich Álvarez Diduk

Postdoctoral Researcher
Nanobioelectronics and Biosensors



  • A Novel Ratiometric Fluorescent Approach for the Modulation of the Dynamic Range of Lateral Flow Immunoassays

    Sena-Torralba A., Torné-Morató H., Parolo C., Ranjbar S., Farahmand Nejad M.A., Álvarez-Diduk R., Idili A., Hormozi-Nezhad M.R., Merkoçi A. Advanced Materials Technologies; 7 (8, 2101450) 2022. 10.1002/admt.202101450. IF: 7.848

    The majority of lateral flow assays (LFAs) use single-color optical labels to provide a qualitative naked-eye detection, however this detection method displays two important limitations. First, the use of a single-color label makes the LFA prone to results misinterpretation. Second, it does not allow the precise modulation of the sensitivity and dynamic range of the test. To overcome these limitations, a ratiometric approach is developed. In particular, using anti-HIgG functionalized red-fluorescent quantum dots on the conjugate pad (as target dependent labels) and blue-fluorescent nanoparticles fixed on the test line (as target independent reporters), it is possible to generate a wide color palette (blue, purple, pink, red) on the test line. It is believed that this strategy will facilitate the development of LFAs by easily adjusting their analytical properties to the needs required by the specific application. © 2022 The Authors. Advanced Materials Technologies published by Wiley-VCH GmbH.

  • A Programmable Electrochemical Y-Shaped DNA Scaffold Sensor for the Single-Step Detection of Antibodies and Proteins in Untreated Biological Fluids

    Idili A., Bonini A., Parolo C., Alvarez-Diduk R., Di Francesco F., Merkoçi A. Advanced Functional Materials; 2022. 10.1002/adfm.202201881.

    Proteins and antibodies are key biomarkers for diagnosing and monitoring specific medical conditions. Currently, gold standard techniques used for their quantification require laborious multi-step procedures, involving high costs and slow response times. It is possible to overcome these limitations by exploiting the chemistry and programmability of DNA to design a reagentless electrochemical sensing platform. Specifically, three DNA single strands are engineered that can self-assemble into a Y-shaped DNA nanostructure that resembles one of the IgGs. In order to convert this DNA nanostructure into a responsive DNA-scaffold bioreceptor, it is modified including two recognition elements, two redox tag molecules, and a thiol group. In the absence of the target, the scaffold receptor can efficiently collide with the electrode surface and generate a strong electrochemical signal. The presence of the target induces its bivalent binding, which produces steric hindrance interactions that limit the receptor's collisional activity. In its bound state, the redox tags can therefore approach the surface at a slower rate, leading to a signal decrease that is quantitatively related to the target concentration. The Y-shape DNA scaffold sensor can detect nanomolar concentrations of antibodies and proteins in <15 min with a single-step procedure directly in untreated biological fluids. © 2022 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH.

  • An innovative autonomous robotic system for on-site detection of heavy metal pollution plumes in surface water

    De Vito-Francesco E., Farinelli A., Yang Q., Nagar B., Álvarez R., Merkoçi A., Knutz T., Haider A., Stach W., Ziegenbalg F., Allabashi R. Environmental Monitoring and Assessment; 194 (2, 122) 2022. 10.1007/s10661-021-09738-z. IF: 2.513

    Smart monitoring has been studied and developed in recent years to create faster, cheaper, and more user-friendly on-site methods. The present study describes an innovative technology for investigative monitoring of heavy metal pollution (Cu and Pb) in surface water. It is composed of an autonomous surface vehicle capable of semiautonomous driving and equipped with a microfluidic device for detection of heavy metals. Detection is based on the method of square wave anodic stripping voltammetry using carbon-based screen-printed electrodes (SPEs). The focus of this work was to validate the ability of the integrated system to perform on-site detection of heavy metal pollution plumes in river catchments. This scenario was simulated in laboratory experiments. The main performance characteristics of the system, which was evaluated based on ISO 15839 were measurement bias (Pb 75%, Cu 65%), reproducibility (in terms of relative standard deviation: Pb 11–18%, Cu 6–10%) and the limit of detection (4 µg/L for Pb and 7 µg/L for Cu). The lowest detectable change (LDC), which is an important performance characteristic for this application, was estimated to be 4–5 µg/L for Pb and 6–7 µg/L for Cu. The life span of an SPE averaged 39 measurements per day, which is considered sufficient for intended monitoring campaigns. This work demonstrated the suitability of the integrated system for on-site detection of Pb and Cu emissions from large and medium urban areas discharging into small water bodies. © 2022, The Author(s).

  • Graphene Nanobeacons with High-Affinity Pockets for Combined, Selective, and Effective Decontamination and Reagentless Detection of Heavy Metals

    Panáček D., Zdražil L., Langer M., Šedajová V., Baďura Z., Zoppellaro G., Yang Q., Nguyen E.P., Álvarez-Diduk R., Hrubý V., Kolařík J., Chalmpes N., Bourlinos A.B., Zbořil R., Merkoçi A., Bakandritsos A., Otyepka M. Small; 18 (33, 2201003) 2022. 10.1002/smll.202201003.

    Access to clean water for drinking, sanitation, and irrigation is a major sustainable development goal of the United Nations. Thus, technologies for cleaning water and quality-monitoring must become widely accessible and of low-cost, while being effective, selective, sustainable, and eco-friendly. To meet this challenge, hetero-bifunctional nanographene fluorescent beacons with high-affinity pockets for heavy metals are developed, offering top-rated and selective adsorption for cadmium and lead, reaching 870 and 450 mg g-1, respectively. The heterobifunctional and multidentate pockets also operate as selective gates for fluorescence signal regulation with sub-nanomolar sensitivity (0.1 and 0.2 nm for Pb2+ and Cd2+, respectively), due to binding affinities as low as those of antigen-antibody interactions. Importantly, the acid-proof nanographenes can be fully regenerated and reused. Their broad visible-light absorption offers an additional mode for water-quality monitoring based on ultra-low cost and user-friendly reagentless paper detection with the naked-eye at a limit of detection of 1 and 10 ppb for Pb2+ and Cd2+ ions, respectively. This work shows that photoactive nanomaterials, densely-functionalized with strong, yet selective ligands for targeted contaminants, can successfully combine features such as excellent adsorption, reusability, and sensing capabilities, in a way to extend the material's applicability, its life-cycle, and value-for-money. © 2022 The Authors. Small published by Wiley-VCH GmbH.

  • Low-Cost, User-Friendly, All-Integrated Smartphone-Based Microplate Reader for Optical-Based Biological and Chemical Analyses

    Bergua J.F., Álvarez-Diduk R., Idili A., Parolo C., Maymó M., Hu L., Merkoçi A. Analytical Chemistry; 94 (2): 1271 - 1285. 2022. 10.1021/acs.analchem.1c04491. IF: 6.986

    The quantitative detection of different molecular targets is of utmost importance for a variety of human activities, ranging from healthcare to environmental studies. Bioanalytical methods have been developed to solve this and to achieve the quantification of multiple targets from small volume samples. Generally, they can be divided into two different classes: point of care (PoC) and laboratory-based approaches. The former is rapid, low-cost, and user-friendly; however, the majority of the tests are semiquantitative, lacking in specificity and sensitivity. On the contrary, laboratory-based approaches provide high sensitivity and specificity, but the bulkiness of experimental instruments and complicated protocols hamper their use in resource-limited settings. In response, here we propose a smartphone-based device able to support laboratory-based optical techniques directly at the point of care. Specifically, we designed and fabricated a portable microplate reader that supports colorimetric, fluorescence, luminescence, and turbidity analyses. To demonstrate the potential of the device, we characterized its analytical performance by detecting a variety of relevant molecular targets (ranging from antibodies, toxins, drugs, and classic fluorophore dyes) and we showed how the estimated results are comparable to those obtained from a commercial microplate reader. Thanks to its low cost (<$300), portability (27 cm [length] × 18 cm [width] × 7 cm [height]), commercially available components, and open-source-based system, we believe it represents a valid approach to bring high-precision laboratory-based analysis at the point of care. © 2022 The Authors. Published by American Chemical Society

  • Selection and characterisation of bioreceptors to develop nanoparticle-based lateral-flow immunoassays in the context of the SARS-CoV-2 outbreak

    Hu L., Calucho E., Fuentes-Chust C., Parolo C., Idili A., Álvarez-Diduk R., Rivas L., Merkoçi A. Lab on a Chip; 22 (16): 2938 - 2943. 2022. 10.1039/d2lc00486k.

    This manuscript aims at raising the attention of the scientific community to the need for better characterised bioreceptors for fast development of point-of-care diagnostic devices able to support mass frequency testing. Particularly, we present the difficulties encountered in finding suitable antibodies for the development of a lateral flow assay for detecting the nucleoprotein of SARS-CoV-2. © 2022 The Royal Society of Chemistry.


  • Attomolar analyte sensing techniques (AttoSens): A review on a decade of progress on chemical and biosensing nanoplatforms

    Usha S.P., Manoharan H., Deshmukh R., Álvarez-Diduk R., Calucho E., Sai V.V.R., Merkoçi A. Chemical Society Reviews; 50 (23): 13012 - 13089. 2021. 10.1039/d1cs00137j. IF: 54.564

    Detecting the ultra-low abundance of analytes in real-life samples, such as biological fluids, water, soil, and food, requires the design and development of high-performance biosensing modalities. The breakthrough efforts from the scientific community have led to the realization of sensing technologies that measure the analyte's ultra-trace level, with relevant sensitivity, selectivity, response time, and sampling efficiency, referred to as Attomolar Analyte Sensing Techniques (AttoSens) in this review. In an AttoSens platform, 1 aM detection corresponds to the quantification of 60 target analyte molecules in 100 μL of sample volume. Herein, we review the approaches listed for various sensor probe design, and their sensing strategies that paved the way for the detection of attomolar (aM: 10-18 M) concentration of analytes. A summary of the technological advances made by the diverse AttoSens trends from the past decade is presented. This journal is © The Royal Society of Chemistry.

  • Development of a Heavy Metal Sensing Boat for Automatic Analysis in Natural Waters Utilizing Anodic Stripping Voltammetry

    Qiuyue Yang,Bhawna Nagar,Ruslán Alvarez-Diduk,Marc Balsells,Alessandro Farinelli,Domenico Bloisi, Lorenzo Proia, Carmen Espinosa, Marc Ordeix, Thorsten Knutz,Elisabetta De Vito-Francesco, Roza Allabashi, Arben Merkoçi Acs Es&t Water; 1 (12): 2470 - 2476. 2021. 10.1021/acsestwater.1c00192. IF: 0.000

    Determination of the levels of heavy metal ions would support assessment of sources and pathways of water pollution. However, traditional spatial assessment by manual sampling and off-site detection in the laboratory is expensive and time-consuming and requires trained personnel. Aiming to fill the gap between on-site automatic approaches and laboratory techniques, we developed an autonomous sensing boat for on-site heavy metal detection using square-wave anodic stripping voltammetry. A fluidic sensing system was developed to integrate into the boat as the critical sensing component and could detect ≤1 μg/L Pb, ≤6 μg/L Cu, and ≤71 μg/L Cd simultaneously in the laboratory. Once its integration was completed, the autonomous sensing boat was tested in the field, demonstrating its ability to distinguish the highest concentration of Pb in an effluent of a galena-enriched mine compared to those at other sites in the stream (Osor Stream, Girona, Spain).

  • Electrochromism: An emerging and promising approach in (bio)sensing technology

    Farahmand Nejad M.A., Ranjbar S., Parolo C., Nguyen E.P., Álvarez-Diduk R., Hormozi-Nezhad M.R., Merkoçi A. Materials Today; 50: 476 - 498. 2021. 10.1016/j.mattod.2021.06.015. IF: 31.041

    Electrochromism (EC) is a unique property of certain materials that undergo an electrochemical-induced change in colouration. During the last decades, electrochromic materials (ECMs) have been applied in a variety of technologies ranging from smart windows to information displays and energy storage devices. More recently, ECMs have attracted the attention of the (bio)sensing community thanks to their ability to combine the sensitivity of electrochemical methods with the intuitive readout of optical sensors. Although still a nascent technology, EC-based sensors are on the rise with several targets (e.g. cancer biomarkers, bacteria, metabolites and pesticides), which have already been detected by (bio)sensors using ECMs as transducers. In this review, we provide the reader with all the information to understand EC and its use in the development of EC-based biosensors. © 2021 Elsevier Ltd

  • Improved Aliivibrio fischeri based-toxicity assay: Graphene-oxide as a sensitivity booster with a mobile-phone application

    Bergua J.F., Álvarez-Diduk R., Hu L., Hassan A.H.A., Merkoçi A. Journal of Hazardous Materials; 406 (124434) 2021. 10.1016/j.jhazmat.2020.124434. IF: 10.588

    Recently, many bioluminescence-based applications have arisen in several fields, such as biosensing, bioimaging, molecular biology, and human health diagnosis. Among all bioluminescent organisms, Aliivibrio fischeri (A. fischeri) is a bioluminescent bacterium used to carry out water toxicity assays since the late 1970s. Since then, several commercial A. fischeri-based products have been launched to the market, as these bacteria are considered as a gold standard for water toxicity assessment worldwide. However, the aforementioned commercial products rely on expensive equipment, requiring several reagents and working steps, as well as high-trained personnel to perform the assays and analyze the output data. For these reasons, in this work, we have developed for the first time a mobile-phone-based sensing platform for water toxicity assessment in just 5 min using two widespread pesticides as model analytes. To accomplish this, we have established new methodologies to enhance the bioluminescent signal of A. fischeri based on the bacterial culture in a solid media and/or using graphene oxide. Finally, we have addressed the biocompatibility of graphene oxide to A. fischeri, boosting the sensitivity of the toxicity assays and the bacterial growth of the lyophilized bacterial cultures for more user-friendly storage. © 2020 Elsevier B.V.

  • Lateral flow device for water fecal pollution assessment: From troubleshooting of its microfluidics using bioluminescence to colorimetric monitoring of genericEscherichia coli

    Bergua J.F., Hu L., Fuentes-Chust C., Álvarez-Diduk R., Hassan A.H.A., Parolo C., Merkoçi A. Lab on a Chip; 21 (12): 2417 - 2426. 2021. 10.1039/d1lc00090j. IF: 6.799

    Water is the most important ingredient of life. Water fecal pollution threatens water quality worldwide and has direct detrimental effects on human health and the global economy. Nowadays, assessment of water fecal pollution relies on time-consuming techniques that often require well-trained personnel and highly-equipped laboratories. Therefore, faster, cheaper, and easily-used systems are needed toin situmonitor water fecal pollution. Herein, we have developed colorimetric lateral flow strips (LFS) able to detect and quantifyEscherichia colispecies in tap, river, and sewage water samples as an indicator of fecal pollution. The combination of LFS with a simple water filtration unit and a commercially available colorimetric reader enhanced the assay sensitivity and enabled more accurate quantification of bacteria concentration down to 104CFU mL−1in 10 minutes, yielding recovery percentages between 80% and 90% for all water samples analyzed. Overall, this system allows for monitoring and assessing water quality based onE. colispecies as a standard microbiological indicator of fecal pollution. Furthermore, we have developed a novel bioluminescent, bacteria-based method to quickly characterize the performance of a great variety of LFS materials. This new method allows evaluating the flow rate of big analytes such as bacteria through the LFS materials, as a suggestive means for selecting the appropriate materials for fabricating LFS targeting big analytes (≈2 μm). As a whole, the proposed approach can accelerate and reduce the costs of water quality monitoring and pave the way for further improvement of fecal pollution detection systems. © The Royal Society of Chemistry 2021.

  • Nanodiagnostics to Face SARS-CoV-2 and Future Pandemics: From an Idea to the Market and beyond

    Rosati G., Idili A., Parolo C., Fuentes-Chust C., Calucho E., Hu L., Castro E Silva C.D.C., Rivas L., Nguyen E.P., Bergua J.F., Alvárez-Diduk R., Muñoz J., Junot C., Penon O., Monferrer D., Delamarche E., Merkoçi A. ACS Nano; 15 (11): 17137 - 17149. 2021. 10.1021/acsnano.1c06839. IF: 15.881

    The COVID-19 pandemic made clear how our society requires quickly available tools to address emerging healthcare issues. Diagnostic assays and devices are used every day to screen for COVID-19 positive patients, with the aim to decide the appropriate treatment and containment measures. In this context, we would have expected to see the use of the most recent diagnostic technologies worldwide, including the advanced ones such as nano-biosensors capable to provide faster, more sensitive, cheaper, and high-throughput results than the standard polymerase chain reaction and lateral flow assays. Here we discuss why that has not been the case and why all the exciting diagnostic strategies published on a daily basis in peer-reviewed journals are not yet successful in reaching the market and being implemented in the clinical practice. ©

  • Paper-based electrophoretic bioassay: Biosensing in whole blood operating via smartphone

    Merkoçi A., Sena-Torralba A., Alvarez-Diduk R., Parolo C., Torné-Morató H., Müller A. Analytical Chemistry; 93 (6): 3112 - 3121. 2021. 10.1021/acs.analchem.0c04330. IF: 6.986

    Point-of-care (PoC) tests are practical and effective diagnostic solutions for major clinical problems, ranging from the monitoring of a pandemic to recurrent or simple measurements. Although, in recent years, a great improvement in the analytical performance of such sensors has been observed, there is still a major issue that has not been properly solved: The ability to perform adequate sample treatments. The main reason is that normally sample treatments require complicated or long procedures not adequate for deployment at the PoC. In response, a sensing platform, called paperbased electrophoretic bioassay (PEB), that combines the key characteristics of a lateral flow assay (LFA) with the sample treatment capabilities of electrophoresis is developed. In particular, the ability of PEB to separate different types of particles and to detect human antibodies in untreated spiked whole blood is demonstrated. Finally, to make the platform suitable for PoC, PEB is coupled with a smartphone that controls the electrophoresis and reads the optical signal generated. It is believed that the PEB platform represents a much-needed solution for the detection of low target concentrations in complex media, solving one of the major limitations of LFA and opening opportunities for point-of-care sensors. © 2021 American Chemical Society.

  • Rapid and Efficient Detection of the SARS-CoV-2 Spike Protein Using an Electrochemical Aptamer-Based Sensor

    Idili A., Parolo C., Alvarez-Diduk R., Merkoçi A. ACS Sensors; 6 (8): 3093 - 3101. 2021. 10.1021/acssensors.1c01222. IF: 7.711

    The availability of sensors able to rapidly detect SARS-CoV-2 directly in biological fluids in a single step would allow performing massive diagnostic testing to track in real time and contain the spread of COVID-19. Motivated by this, here, we developed an electrochemical aptamer-based (EAB) sensor able to achieve the rapid, reagentless, and quantitative measurement of the SARS-CoV-2 spike (S) protein. First, we demonstrated the ability of the selected aptamer to undergo a binding-induced conformational change in the presence of its target using fluorescence spectroscopy. Then, we engineered the aptamer to work as a bioreceptor in the EAB platform and we demonstrated its sensitivity and specificity. Finally, to demonstrate the clinical potential of the sensor, we tested it directly in biological fluids (serum and artificial saliva), achieving the rapid (minutes) and single-step detection of the S protein in its clinical range. © 2021 American Chemical Society.


  • Lab in a Tube: Point-of-Care Detection of Escherichia coli

    Amin N., Torralba A.S., Álvarez-Diduk R., Afkhami A., Merkoçi A. Analytical Chemistry; 92 (6): 4209 - 4216. 2020. 10.1021/acs.analchem.9b04369. IF: 6.785

    Significant levels of infectious diseases caused by pathogenic bacteria are nowadays a worldwide matter, carrying considerable public health care challenges and huge economic concerns. Because of the rapid transmission of these biothreat agents and the outbreak of diseases, a rapid detection of pathogens in early stages is crucial, particularly in low-resources settings. To this aim, we developed for the first time a new sensing approach carried out in a single step for Escherichia coli O157:H7 detection. The detection principle is based on Förster resonance energy transfer using gold nanoclusters as a signal reporter and gold nanoparticles conjugated with antibodies as a quencher. The sensing platform includes an ultraviolet-light-emitting diode to provide the proper excitation and consists of a microtube containing two pieces of fiber glass; one of them is embedded with label-free gold nanoclusters and the other one with gold nanoparticles conjugated with antibodies. Upon the addition of the sample containing bacteria, the florescence of gold nanoclusters is recovered. The assay was evaluated by the naked eye (on/off) and quantitatively with use of a smartphone camera. The biosensor proved to be highly specific and sensitive, achieving a limit of detection as low as 4.0 cfu mL-1. Additionally, recoveries of 110% and 95% were obtained when the platforms in spiked river and tap water, respectively, were evaluated. Copyright © 2020 American Chemical Society.

  • Lateral flow assay modified with time-delay wax barriers as a sensitivity and signal enhancement strategy

    Sena-Torralba A., Ngo D.B., Parolo C., Hu L., Álvarez-Diduk R., Bergua J.F., Rosati G., Surareungchai W., Merkoçi A. Biosensors and Bioelectronics; 168 (112559) 2020. 10.1016/j.bios.2020.112559. IF: 10.257

    The ease of use, low cost and quick operation of lateral flow assays (LFA) have made them some of the most common point of care biosensors in a variety of fields. However, their generally low sensitivity has limited their use for more challenging applications, where the detection of low analytic concentrations is required. Here we propose the use of soluble wax barriers to selectively and temporarily accumulate the target and label nanoparticles on top of the test line (TL). This extended internal incubation step promotes the formation of the immune-complex, generating a 51.7-fold sensitivity enhancement, considering the limit of quantification, and up to 96% signal enhancement compared to the conventional LFA for Human IgG (H-IgG) detection. © 2020 Elsevier B.V.

  • Nano-lantern on paper for smartphone-based ATP detection

    Calabretta M.M., Álvarez-Diduk R., Michelini E., Roda A., Merkoçi A. Biosensors and Bioelectronics; 150 (111902) 2020. 10.1016/j.bios.2019.111902. IF: 10.257

    ATP-driven bioluminescence relying on the D-luciferin-luciferase reaction is widely employed for several biosensing applications where bacterial ATP detection allows to verify microbial contamination for hygiene monitoring in hospitals, food processing and in general for cell viability studies. Several ATP kit assays are already commercially available but an user-friendly ATP biosensor characterized by low-cost, portability, and adequate sensitivity would be highly valuable for rapid and facile on site screening. Thanks to an innovative freeze-drying procedure, we developed a user-friendly, ready-to-use and stable ATP sensing paper biosensor that can be combined with smartphone detection. The ATP sensing paper includes a lyophilized “nano-lantern” with reaction components being rapidly reconstituted by 10 μL sample addition, enabling detection of 10−14 mol of ATP within 10 min. We analysed urinary microbial ATP as a biomarker of urinary tract infection (UTI), confirming the capability of the ATP sensing paper to detect the threshold for positivity corresponding to 105 colony-forming units of bacteria per mL of urine. © 2019 Elsevier B.V.

  • Nanomaterials for Nanotheranostics: Tuning Their Properties According to Disease Needs

    Wong X.Y., Sena-Torralba A., Álvarez-Diduk R., Muthoosamy K., Merkoçi A. ACS Nano; 14 (3): 2585 - 2627. 2020. 10.1021/acsnano.9b08133. IF: 14.588

    Nanotheranostics is one of the biggest scientific breakthroughs in nanomedicine. Most of the currently available diagnosis and therapies are invasive, time-consuming, and associated with severe toxic side effects. Nanotheranostics, on the other hand, has the potential to bridge this gap by harnessing the capabilities of nanotechnology and nanomaterials for combined therapeutics and diagnostics with markedly enhanced efficacy. However, nanomaterial applications in nanotheranostics are still in its infancy. This is due to the fact that each disease has a particular microenvironment with well-defined characteristics, which promotes deeper selection criteria of nanomaterials to meet the disease needs. In this review, we have outlined how nanomaterials are designed and tailored for nanotheranostics of cancer and other diseases such as neurodegenerative, autoimmune (particularly on rheumatoid arthritis), and cardiovascular diseases. The penetrability and retention of a nanomaterial in the biological system, the therapeutic strategy used, and the imaging mode selected are some of the aspects discussed for each disease. The specific properties of the nanomaterials in terms of feasibility, physicochemical challenges, progress in clinical trials, its toxicity, and their future application on translational medicine are addressed. Our review meticulously and critically examines the applications of nanotheranostics with various nanomaterials, including graphene, across several diseases, offering a broader perspective of this emerging field. © 2020 American Chemical Society.

  • Selective stamping of laser scribed rGO nanofilms: From sensing to multiple applications

    Giacomelli C., Álvarez-Diduk R., Testolin A., Merkoçi A. 2D Materials; 7 (2, 024006) 2020. 10.1088/2053-1583/ab68a7. IF: 7.140

    A rapid low-cost technology to produce highly conductive laser-scribed reduced-graphene oxide (rGO) thin films on flexible substrates is developed. Isolated rGO films, up to 30 nm thick and with a conductivity of 102 S m-1 are produced at room temperature in a three-step process: filtering the graphene oxide (GO) solution through nitrocellulose membranes, reduction of GO surface using a DVD-burner laser and solvent-free transfer of the resulting rGO pattern onto new substrates via pressure-based mechanism. The loss of density in the reduced part produces an increase in the thickness enabling the transfer of rGO only. The rGO is characterized with several analytical techniques, and its reduction degree, thickness, morphology, electrochemical and electromechanical properties are investigated and optimized. The validation of the technology is tested using a wide variety of substrates, and its applicability as a sensing platform for dopamine detection and back electrode in an electroluminescent lamp is demonstrated, opening the venue for a plethora of other new applications. © 2020 IOP Publishing Ltd.

  • Tutorial: design and fabrication of nanoparticle-based lateral-flow immunoassays

    Parolo C., Sena-Torralba A., Bergua J.F., Calucho E., Fuentes-Chust C., Hu L., Rivas L., Álvarez-Diduk R., Nguyen E.P., Cinti S., Quesada-González D., Merkoçi A. Nature Protocols; 15 (12): 3788 - 3816. 2020. 10.1038/s41596-020-0357-x. IF: 10.419

    Lateral-flow assays (LFAs) are quick, simple and cheap assays to analyze various samples at the point of care or in the field, making them one of the most widespread biosensors currently available. They have been successfully employed for the detection of a myriad of different targets (ranging from atoms up to whole cells) in all type of samples (including water, blood, foodstuff and environmental samples). Their operation relies on the capillary flow of the sample throughout a series of sequential pads, each with different functionalities aiming to generate a signal to indicate the absence/presence (and, in some cases, the concentration) of the analyte of interest. To have a user-friendly operation, their development requires the optimization of multiple, interconnected parameters that may overwhelm new developers. In this tutorial, we provide the readers with: (i) the basic knowledge to understand the principles governing an LFA and to take informed decisions during lateral flow strip design and fabrication, (ii) a roadmap for optimal LFA development independent of the specific application, (iii) a step-by-step example procedure for the assembly and operation of an LF strip for the detection of human IgG and (iv) an extensive troubleshooting section addressing the most frequent issues in designing, assembling and using LFAs. By changing only the receptors, the provided example procedure can easily be adapted for cost-efficient detection of a broad variety of targets. © 2020, The Author(s), under exclusive licence to Springer Nature Limited.


  • Electrochromic Molecular Imprinting Sensor for Visual and Smartphone-Based Detections

    Capoferri D., Álvarez-Diduk R., Del Carlo M., Compagnone D., Merkoçi A. Analytical Chemistry; 90 (9): 5850 - 5856. 2018. 10.1021/acs.analchem.8b00389. IF: 6.042

    Electrochromic effect and molecularly imprinted technology have been used to develop a sensitive and selective electrochromic sensor. The polymeric matrices obtained using the imprinting technology are robust molecular recognition elements and have the potential to mimic natural recognition entities with very high selectivity. The electrochromic behavior of iridium oxide nanoparticles (IrOx NPs) as physicochemical transducer together with a molecularly imprinted polymer (MIP) as recognition layer resulted in a fast and efficient translation of the detection event. The sensor was fabricated using screen-printing technology with indium tin oxide as a transparent working electrode; IrOx NPs where electrodeposited onto the electrode followed by thermal polymerization of polypyrrole in the presence of the analyte (chlorpyrifos). Two different approaches were used to detect and quantify the pesticide: direct visual detection and smartphone imaging. Application of different oxidation potentials for 10 s resulted in color changes directly related to the concentration of the analyte. For smartphone imaging, at fixed potential, the concentration of the analyte was dependent on the color intensity of the electrode. The electrochromic sensor detects a highly toxic compound (chlorpyrifos) with a 100 fM and 1 mM dynamic range. So far, to the best of our knowledge, this is the first work where an electrochromic MIP sensor uses the electrochromic properties of IrOx to detect a certain analyte with high selectivity and sensitivity. © 2018 American Chemical Society.

  • Screen-Printed Electroluminescent Lamp Modified with Graphene Oxide as a Sensing Device

    Yakoh A., Álvarez-Diduk R., Chailapakul O., Merkoçi A. ACS Applied Materials and Interfaces; 10 (24): 20775 - 20782. 2018. 10.1021/acsami.8b04883. IF: 8.097

    A screen-printed electroluminescent display with different sensing capabilities is presented. The sensing principle is based on the direct relationship between the light intensity of the lamp and the conductivity of the external layers. The proposed device is able to detect the ionic concentration of any conductive species. Using both top and bottom emission architectures, for the first time, a humidity sensor based on electroluminescent display functionalized by a graphene oxide nanocomposite is introduced. In this regard, just by coupling the display to a smartphone camera sensor, its potential was expanded for automatically monitoring human respiration in real time. Besides, the research includes a responsive display in which the light is spatially turned on in response to pencil drawing or any other conductive media. The above mentioned features together with the easiness of manufacturing and cost-effectiveness of this electroluminescent display can open up great opportunities to exploit it in sensing applications and point-of-care diagnosis. Copyright © 2018 American Chemical Society.


  • Paper strip-embedded graphene quantum dots: A screening device with a smartphone readout

    Álvarez-DIduk R., Orozco J., Merkoçi A. Scientific Reports; 7 (1, 976) 2017. 10.1038/s41598-017-01134-3. IF: 4.259

    Simple, inexpensive and rapid sensing systems are very demanded for a myriad of uses. Intrinsic properties of emerging paper-based analytical devices have demonstrated considerable potential to fulfill such demand. This work reports an easy-to-use, low cost, and disposable paper-based sensing device for rapid chemical screening with a smartphone readout. The device comprises luminescent graphene quantum dots (GQDs) sensing probes embedded into a nitrocellulose matrix where the resonance energy transfer phenomenon seems to be the sensing mechanism. The GQDs probes were synthesized from citric acid by a pyrolysis procedure, further physisorbed and confined into small wax-traced spots on the nitrocellulose substrate. The GQDs were excited by an UV LED, this, is powered by a smartphone used as both; energy source and imaging capture. The LED was contained within a 3D-printed dark chamber that isolates the paper platform from external light fluctuations leading to highly reproducible data. The cellulose-based device was proven as a promising screening tool for phenols and polyphenols in environmental and food samples, respectively. It opens up new opportunities for simple and fast screening of organic compounds and offers numerous possibilities for versatile applications. It can be especially useful in remote settings where sophisticated instrumentation is not always available. © 2017 The Author(s).


  • Nanostructured Ti thin films by magnetron sputtering at oblique angles

    Alvarez R., Garcia-Martin J.M., Garcia-Valenzuela A., Macias-Montero M., Ferrer F.J., Santiso J., Rico V., Cotrino J., Gonzalez-Elipe A.R., Palmero A. Journal of Physics D: Applied Physics; 49 (4, 045303) 2015. 10.1088/0022-3727/49/4/045303. IF: 2.721

    The growth of Ti thin films by the magnetron sputtering technique at oblique angles and at room temperature is analysed from both experimental and theoretical points of view. Unlike other materials deposited in similar conditions, the nanostructure development of the Ti layers exhibits an anomalous behaviour when varying both the angle of incidence of the deposition flux and the deposition pressure. At low pressures, a sharp transition from compact to isolated, vertically aligned, nanocolumns is obtained when the angle of incidence surpasses a critical threshold. Remarkably, this transition also occurs when solely increasing the deposition pressure under certain conditions. By the characterization of the Ti layers, the realization of fundamental experiments and the use of a simple growth model, we demonstrate that surface mobilization processes associated to a highly directed momentum distribution and the relatively high kinetic energy of sputtered atoms are responsible for this behaviour. © 2016 IOP Publishing Ltd.


  • Deprotonation mechanism and acidity constants in aqueous solution of flavonols: A combined experimental and theoretical study

    Álvarez-Diduk, R.; Ramírez-Silva, M.T.; Galano, A.; Merkoçi, A. Journal of Physical Chemistry B; 117 (41): 12347 - 12359. 2013. 10.1021/jp4049617. IF: 3.607