Preparation of paper-based devices for reagentless electrochemical (bio)sensor strips

Vertical-Flow Paper Sensor for On-Site and Prompt Evaluation of Chloride Contamination in Concrete Structures

Corrosion occurring in reinforced concrete has turned into a primary concern of the current century, concrete being the most ubiquitous and predominant material used in the construction industry. Among the many interrelated processes that trigger corrosion of metallic reinforcements, the penetration of chloride ions into the concrete matrix is the most insidious threat. Herein, we developed the first electrochemical device entirely made of paper that allows for the direct, prompt, and noninvasive evaluation of free chloride ion contamination in concrete-based constructions. Our device is based on a three-layer wax-modified filter paper, consisting of two Ag/AgCl screen-printed electrodes that are interfaced by a junction pad in a sandwich-like configuration. Filter paper allows for generating a vertical-flow potentiometric device capable of measuring the electrochemical potential between two solutions containing different concentrations of chloride ions, which are separately drop-cast on the top and bottom layers. After demonstrating the analytical performance of the device, the same principle was applied to the evaluation of the chloride contents in different concrete samples, exploiting paper as a suitable interfacing material for potentiometric measurements on the cement solid surface. Laboratory-prepared concrete samples with known chloride contents were first assessed, and then, the paper-based vertical-flow device was applied to real concrete structures at the Giacomo Manzù Museum (Ardea, Italy) for the evaluation of chloride contamination caused by the proximity to the seaside. The capability of our device to provide timely warning of the risk conditions of concrete-based artifacts was demonstrated.

The Food-Materials Nexus: Next Generation Bioplastics and Advanced Materials from Agri-Food Residues

The most recent strategies available for upcycling agri-food losses and waste (FLW) into functional bioplastics and advanced materials are reviewed and the valorization of food residuals are put in perspective, adding to the water-food-energy nexus. Low value or underutilized biomass, biocolloids, water-soluble biopolymers, polymerizable monomers, and nutrients are introduced as feasible building blocks for biotechnological conversion into bioplastics. The latter are demonstrated for their incorporation in multifunctional packaging, biomedical devices, sensors, actuators, and energy conversion and storage devices, contributing to the valorization efforts within the future circular bioeconomy. Strategies are introduced to effectively synthesize, deconstruct and reassemble or engineer FLW-derived monomeric, polymeric, and colloidal building blocks. Multifunctional bioplastics are introduced considering the structural, chemical, physical as well as the accessibility of FLW precursors. Processing techniques are analyzed within the fields of polymer chemistry and physics. The prospects of FLW streams and biomass surplus, considering their availability, interactions with water and thermal stability, are critically discussed in a near-future scenario that is expected to lead to next-generation bioplastics and advanced materials.

Origami Paper-Based Electrochemical (Bio)Sensors: State of the Art and Perspective

In the last 10 years, paper-based electrochemical biosensors have gathered attention from the scientific community for their unique advantages and sustainability vision. The use of papers in the design the electrochemical biosensors confers to these analytical tools several interesting features such as the management of the solution flow without external equipment, the fabrication of reagent-free devices exploiting the porosity of the paper to store the reagents, and the unprecedented capability to detect the target analyte in gas phase without any sampling system. Furthermore, cost-effective fabrication using printing technologies, including wax and screen-printing, combined with the use of this eco-friendly substrate and the possibility of reducing waste management after measuring by the incineration of the sensor, designate these type of sensors as eco-designed analytical tools. Additionally, the foldability feature of the paper has been recently exploited to design and fabricate 3D multifarious biosensors, which are able to detect different target analytes by using enzymes, antibodies, DNA, molecularly imprinted polymers, and cells as biocomponents. Interestingly, the 3D structure has recently boosted the self-powered paper-based biosensors, opening new frontiers in origami devices. This review aims to give an overview of the current state origami paper-based biosensors, pointing out how the foldability of the paper allows for the development of sensitive, selective, and easy-to-use smart and sustainable analytical devices.

Electrochemical Biosensors for Tracing Cyanotoxins in Food and Environmental Matrices

The adoption of electrochemical principles to realize on-field analytical tools for detecting pollutants represents a great possibility for food safety and environmental applications. With respect to the existing transduction mechanisms, i.e., colorimetric, fluorescence, piezoelectric etc., electrochemical mechanisms offer the tremendous advantage of being easily miniaturized, connected with low cost (commercially available) readers and unaffected by the color/turbidity of real matrices. In particular, their versatility represents a powerful approach for detecting traces of emerging pollutants such as cyanotoxins. The combination of electrochemical platforms with nanomaterials, synthetic receptors and microfabrication makes electroanalysis a strong starting point towards decentralized monitoring of toxins in diverse matrices. This review gives an overview of the electrochemical biosensors that have been developed to detect four common cyanotoxins, namely microcystin-LR, anatoxin-a, saxitoxin and cylindrospermopsin. The manuscript provides the readers a quick guide to understand the main electrochemical platforms that have been realized so far, and the presence of a comprehensive table provides a perspective at a glance.

Multi-array wax paper-based platform for the pre-concentration and determination of silver ions in drinking water

In this work, a wax-patterned chromatographic paper has been utilized as a holistic platform to 1) synthesize Prussian Blue Nanoparticles (sensing species), 2) load the reagents for the assay, 3) concentrate the sample through multistep, and 4) visualize the determination of silver ions. Waters are continuously affected by changes in the composition, thus the utilization of reagent-free analytical tools is of huge interest for smart drinking water monitoring. Herein, we report the characterization and application of a multi-array paper-based platform for the colorimetric determination of silver ions based on the conversion from Prussian Blue to its silver-based analogue, namely Ag₄[Fe(CN)₆]. In particular, the platform highlights the increase of sensitivity due to paper pre-concentration of sample, that can be easily adapted to the analytical necessities. Within the proposed experimental setup, Ag⁺ is visualized down to a detection limit of 0.9 μM, with high repeatability and satisfactory recoveries in the range comprised between 90 and 113%.

Merging office/filter paper-based tools for pre-concentring and detecting heavy metals in drinking water

A novel miniaturized and sustainable platform exploiting two merged paper-based substrates has been applied for the programmable pre-concentration of analytes of interest and electrochemical detection of mercury traces in drinking water using printable sensor strips. This strategy represents a novel versatile possibility in merging humble materials maximizing their impacts on analytical and remediation challenges.

Office Paper-Based Electrochemical Strips for Organophosphorus Pesticide Monitoring in Agricultural Soil

Although the use of pesticides has highlighted obvious advantages on agricultural yields, intensive and widespread pesticide use raises serious environmental and health concerns. In particular, organophosphate pesticides represent >40% of the totality used in the field of agriculture, and developing countries face the issue of agricultural poisoning, also due to scarce monitoring programs. In this work, a decentralized, miniaturized, sustainable, and portable paper-based electrochemical biosensor for the quantification of organophosphorus pesticides' level has been realized. The proposed approach highlights the use of a very common paper-based substrate, namely, office paper. Office paper offers several advantages due to its nature: it allows one to print conductive strips for electrochemical connection, loading bio-hybrid nanosized probes (Prussian blue, carbon black, and butyrylcholinesterase), evaluating pesticides and reducing waste disposal compared to plastic-based strips. The portable system has been characterized by a low detection limit of 1.3 ng/mL, and accordingly to total discovered pesticide contents in EU agricultural soils, up to ca. 3 μg/mL, it can offer a valuable tool for fast monitoring. To demonstrate its effectiveness, soil and fruit vegetables have been used to perform in situ quantification. Good recovery percentages between 90 and 110% have been achieved in different matrices, highlighting to be suitable for field measurements, and a good correlation has been obtained in comparison with LC-MS analysis.

Integrating programmable DNAzymes with electrical readout for rapid and culture-free bacterial detection using a handheld platform

The detection and identification of bacteria currently rely on enrichment steps such as bacterial culture and nucleic acid amplification to increase the concentration of target analytes. These steps increase assay time, cost and complexity, making it difficult to realize a truly rapid point-of-care test. Here we report the development of an electrical assay that uses electroactive RNA-cleaving DNAzymes (e-RCDs) to identify specific bacterial targets and subsequently release a DNA barcode for transducing a signal onto an electrical chip. Integrating e-RCDs into a two-channel electrical chip with nanostructured electrodes provides the analytical sensitivity and specificity needed for clinical analysis. The e-RCD assay is capable of detecting 10 CFU (equivalent to 1,000 CFU ml^-1) of Escherichia coli selectively from a panel containing multiple non-specific bacterial species. Clinical evaluation of this assay using 41 patient urine samples demonstrated a diagnostic sensitivity of 100% and specificity of 78% at an analysis time of less than one hour compared with the several hours needed for currently used culture-based methods.

ASSURED Point-of-Need Food Safety Screening: A Critical Assessment of Portable Food Analyzers

Standard methods for chemical food safety testing in official laboratories rely largely on liquid or gas chromatography coupled with mass spectrometry. Although these methods are considered the gold standard for quantitative confirmatory analysis, they require sampling, transferring the samples to a central laboratory to be tested by highly trained personnel, and the use of expensive equipment. Therefore, there is an increasing demand for portable and handheld devices to provide rapid, efficient, and on-site screening of food contaminants. Recent technological advancements in the field include smartphone-based, microfluidic chip-based, and paper-based devices integrated with electrochemical and optical biosensing platforms. Furthermore, the potential application of portable mass spectrometers in food testing might bring the confirmatory analysis from the laboratory to the field in the future. Although such systems open new promising possibilities for portable food testing, few of these devices are commercially available. To understand why barriers remain, portable food analyzers reported in the literature over the last ten years were reviewed. To this end, the analytical performance of these devices and the extent they match the World Health Organization benchmark for diagnostic tests, i.e., the Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free, and Deliverable to end-users (ASSURED) criteria, was evaluated critically. A five-star scoring system was used to assess their potential to be implemented as food safety testing systems. The main findings highlight the need for concentrated efforts towards combining the best features of different technologies, to bridge technological gaps and meet commercialization requirements.

Woven Electroanalytical Biosensor for Nucleic Acid Amplification Tests

Fiber-based biosensors enable a new approach in analytical diagnostic devices. The majority of textile-based biosensors, however, rely on colorimetric detection. Here a woven biosensor that integrates microfluidics structures in combination with an electroanalytical readout based on a thiol-self-assembled monolayer (SAM) for Nucleic Acid Amplification Testing, NAATs is shown. Two types of fiber-based electrodes are systematically characterized: pure gold microwires (bond wire) and off-the-shelf plasma gold-coated polyester multifilament threads to evaluate their potential to form SAMs on their surface and their electrochemical performance in woven textile. A woven electrochemical DNA (E-DNA) sensor using a SAM-based stem-loop probe-modified gold microwire is fabricated. These sensors can specifically detect unpurified, isothermally amplified genomic DNA of Staphylococcus epidermidis (10 copies/µL) by recombinase polymerase amplification (RPA). This work demonstrates that textile-based biosensors have the potential for integrating and being employed as automated, sample-to-answer analytical devices for point-of-care (POC) diagnostics.

A paper-based electrochemical sensor for H2O2 detection in aerosol phase: Measure of H2O2 nebulized by a reconverted ultrasonic aroma diffuser as a case of study

The outbreak of COVID-19 is caused by high contagiousness and rapid spread of SARS-CoV-2 virus between people when an infected person is in close contact with another one. In this overall scenario, the disinfection processes have been largely improved. For instance, some countries have approved no-touch technologies by vaporizing disinfectants such as hydrogen peroxide, with the overriding goal to boost the safety of the places. In the era of sustainability, we designed an electrochemical paper-based device for the assessment of hydrogen peroxide nebulized by a cost-effective ultrasonic aroma diffuser. The paper-based sensor was fabricated by modifying via drop-casting a filter paper-based screen-printed electrode with a dispersion of carbon black-Prussian Blue nanocomposite, to assess the detection of hydrogen peroxide at −0.05 V vs Ag/AgCl. The use of paper-based modified screen-printed electrode loaded with phosphate buffer allowed for monitoring the concentration of hydrogen peroxide in aerosol, without any additional sampling instrument to capture the nebulized solution of hydrogen peroxide at a concentration up to 7% w/w. Hydrogen peroxide, a reconverted ultrasonic aroma diffuser, and the paper-based electrochemical sensor assisted by smartphone have demonstrated how different low-cost technologies are able to supply an useful and cost-effective solution for disinfection procedures.

Electroanalytical Sensor Based on Gold-Nanoparticle-Decorated Paper for Sensitive Detection of Copper Ions in Sweat and Serum

The growth of (bio)sensors in analytical chemistry is mainly attributable to the development of affordable, effective, portable, and user-friendly analytical tools. In the field of sensors, paper-based devices are gaining a relevant position for their outstanding features including foldability, ease of use, and instrument-free microfluidics. Herein, a multifarious use of filter paper to detect copper ions in bodily fluids is reported by exploiting this eco-friendly material to (i) synthesize AuNPs without the use of reductants and/or external stimuli, (ii) print the electrodes, (iii) load the reagents for the assay, (iv) filter the gross impurities, and (v) preconcentrate the target analyte. Copper ions were detected down to 3 ppb with a linearity up to 400 ppb in standard solutions. The applicability in biological matrices, namely, sweat and serum, was demonstrated by recovery studies and by analyzing these biofluids with the paper-based platform and the reference method (atomic absorption spectroscopy), demonstrating satisfactory accuracy of the novel eco-designed analytical tool.

Highly sensitive electrochemical detection of the marine toxins okadaic acid and domoic acid with carbon black modified screen printed electrodes

A novel electrochemical immunosensor for the detection of the important marine biotoxins domoic acid (DA) and okadaic acid (OA) was developed. The sensors used carbon black modified screen-printed electrodes (CB-SPE) obtained using a high-throughput method. The electrochemical performance and stability of CB modified SPEs and bare carbon SPEs (c-SPEs) were compared using cyclic voltammetry and electrochemical impedance spectroscopy. CB-SPEs showed improved long-term (at least six months) stability and electro-catalytic properties compared with c-SPEs. The CB-SPEs were bio-functionalized with DA or OA protein-conjugates and used to develop two indirect competitive immunosensors using differential pulse voltammetry (DPV). The DPV signals obtained for the OA and DA immunosensors fitted well to four-parameter dose-response curves (R² > 0.98) and showed excellent LODs (LOD = 1.7 ng mL^-1 for DA in buffer; LOD = 1.9 ng mL^-1 for DA in mussel extract; LOD = 0.15 ng mL^-1 for OA in buffer; LOD = 0.18 ng mL^-1 for OA in mussel extract). No significant interference of the naturally co-occurring marine toxins saxitoxin, tetrodotoxin and OA was detected for the DA immunosensor. Similarly, for the OA immunosensor saxitoxin, tetrodotoxin and DA did not cross-react and very limited interference was observed for the dinophysis toxins DTX-1, DTX-2 and DTX-3 (OA congeners). Moreover, both immunosensors remained stable after at least 25 days of storage at 4 °C. This work demonstrates the potential of affordable, mass-produced nanomaterial-modified SPEs for marine toxin detection in shellfish.

A semi-dry chemistry hydrogel-based smart biosensing platform for on-site detection of metal ions

Balancing operability and performance has long been a focus of research in bioanalysis and biosensing. In this work, between the traditional wet chemistry and dry chemistry, we develop a semi-dry smart biosensing platform with favourable operability and performance for metal ions detection. This platform is based on the integration of a stimuli-responsive hydrogel with intelligent image recognition. The hydrogel consists of agarose as a matrix and well-designed fluorescent DNA probes as response elements. Target metal ions in a test sample can diffuse into the hydrogel and activate the DNA probes, outputting fluorescence signals for intelligent imaging. In this way, sensitive and convenient detection of metal ions such as potassium ions (K+) and mercury ions (Hg2+) can be achieved without the assistance of huge instruments and professional workers. The detection limits for K+ and Hg2+ are 0.34 mM and 5.6 nM, respectively. Detection of ions in serum and lake water is also available. Moreover, the hydrogel-based biosensing platform exhibits favorable selectivity, anti-degradation ability, and long-term stability. High-throughput testing can be also achieved by punching multiple test microwells in a single piece of hydrogel. The concept and successful practice of a semi-dry chemistry-based strategy make up for the shortcomings of wet chemistry and dry chemistry, and provide a promising approach for on-site testing.

Recent advances in sensitivity enhancement for lateral flow assay

Conventional lateral flow assay (LFA) is typically performed by observing the color changes in the test lines by naked eyes, which achieves considerable commercial success and has a significant impact on the fields of food safety, environment monitoring, disease diagnosis, and other applications. However, this qualitative detection method is not very suitable for low levels of disease biomarkers' detection. Although many nanomaterials are used as new labels for LFA, additional readers limit their application to some extent. Fortunately, a lot of work has been done for improving the sensitivity of LFA. In this review, currently reported LFA sensitivity enhancement methods with an objective evaluation are summarized, such as sample pretreatment, the change of flow rate, and label evolution, and future development direction and challenges of LFAs are discussed.

A disposable paper-based hydrophobic substrate for highly sensitive surface-enhanced Raman scattering detection

Detection of target analytes with high sensitivity and reproducibility remains a challenge for surface-enhanced Raman scattering (SERS) due to the lack of cost-effective and highly sensitive substrates. In this study, a hydrophobic SERS substrate capable of concentrating nanoparticles and analytes was prepared by spin-coating lubricating liquid onto commercial paper. The condensation effect of the paper-based hydrophobic substrate induced aggregation of gold nanoparticles (Au NPs) to generate ''hot spots'' for SERS and to drive analytes to the hot-spot areas for more sensitive detection. The obtained SERS signal intensity was 5-fold higher than that obtained using common paper, and a detection limit (LOD) of 4.3 × 10^-10 M for rhodamine 6G (R6G) was achieved. Randomly selected points on the substrate and different batches of substrates all exhibited high reproducibility, and the relative standard deviation (RSD) at 1362 cm^-1 is approximately 11%. A further application of the hydrophobic substrate was demonstrated by the detection of cytochrome C within a linear detection range of 3.90 × 10^-8 M-1.25 × 10^-6 M. In addition, the prepared substrate can obtain identifiable SERS spectra of cancer cells and non-cancer cells because a large number of AuNP or Au NPs clusters can adhere to cells, resulting in the construction of a 3D hotspot matrix. The disposable hydrophobic paper substrate eliminates the problem of solution diffusion, and also provides an effective platform for biomolecular screening detection.

Printed Electrochemical Biosensors: Opportunities and Metrological Challenges

Printed electrochemical biosensors have recently gained increasing relevance in fields ranging from basic research to home-based point-of-care. Thus, they represent a unique opportunity to enable low-cost, fast, non-invasive and/or continuous monitoring of cells and biomolecules, exploiting their electrical properties. Printing technologies represent powerful tools to combine simpler and more customizable fabrication of biosensors with high resolution, miniaturization and integration with more complex microfluidic and electronics systems. The metrological aspects of those biosensors, such as sensitivity, repeatability and stability, represent very challenging aspects that are required for the assessment of the sensor itself. This review provides an overview of the opportunities of printed electrochemical biosensors in terms of transducing principles, metrological characteristics and the enlargement of the application field. A critical discussion on metrological challenges is then provided, deepening our understanding of the most promising trends in order to overcome them: printed nanostructures to improve the limit of detection, sensitivity and repeatability; printing strategies to improve organic biosensor integration in biological environments; emerging printing methods for non-conventional substrates; microfluidic dispensing to improve repeatability. Finally, an up-to-date analysis of the most recent examples of printed electrochemical biosensors for the main classes of target analytes (live cells, nucleic acids, proteins, metabolites and electrolytes) is reported.

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

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.

Paper-based electrochemical peptide nucleic acid (PNA) biosensor for detection of miRNA-492: a pancreatic ductal adenocarcinoma biomarker

Pancreatic ductal adenocarcinoma is the predominant neoplastic disease of the pancreas and it represents the fourth most frequent cause of death in cancer-related disease, with only 8% of survivors after 5-year to the diagnosis. The main issues of this type of cancer rely on fast progress (i.e. 14 months from T1 to a T4 stage), nonspecific symptoms with delay in diagnosis, and the absence of effective screening strategies. To address the lack of early diagnosis, we report a cost-effective paper-based biosensor for the detection of miRNA-492, which is recognised as a biomarker for pancreatic ductal adenocarcinoma. To design a miniaturised, sensitive, and robust paper-based platform, an electrochemical sensor was screen-printed on office paper previously wax-patterned via wax-printing technique. The paper-based sensor was then engineered with a novel and highly specific peptide nucleic acid (PNA) as the recognition element. The formation of PNA/miRNA-492 adduct was evaluated by monitoring the interaction between the positively charged ruthenium (III) hexamine with uncharged PNA and/or negatively charged PNA/miRNA-492 duplex by differential pulse voltammetry. The paper-based biosensor provided a linear range up to 100 nM, with a LOD of 6 nM. Excellent selectivity towards one- and two-base mismatches (1MM, 2MM) or scrambled (SCR) sequences was highlighted and the applicability for biomedical analyses was demonstrated, measuring miRNA-492 in undiluted serum samples.

Novel bio-lab-on-a-tip for electrochemical glucose sensing in commercial beverages

The development of portable and user-friendly sensing platforms is a hot topic in the field of analytical chemistry. Among others, electroanalytical approaches exhibit a high amenability for reaching this purpose, i.e. the commercial strips for diabetes care are an obvious success. However, providing fully-integrated and reagent-free methods is always a leitmotiv. In this work, we evaluated the use of a disposable pipette tip, opportunely configured to demonstrate the first example of an electrochemical biosystem in a pipette tip, namely bio-lab-on-a-tip. The combination of a pipette tip, wire electrodes, enzyme, and cotton wool filter, allows the fabrication of a novel electroanalytical platform that does not need expertise-required tasks. To demonstrate the feasibility of this novel method, glucose is detected in beverages by means of chronoamperometry. The experimental setup, entirely built inside the pipette tip, is able to 1) block impurities/interferences from matrix, 2) load/release reagents for the bio-assay, 3) reduce the operating task to zero, and 4) perform electrochemical detection. With optimized experimental parameters, the bio-lab-on-a-tip is able to detect glucose linearly up to 10 mM with a detection limit of 170 μM. The effectiveness of the platform was confirmed by testing commercial beverages, e.g. Coca-Cola and Coca-Cola Zero, with high accuracy. In addition, the shelf-life of the novel device was evaluated, highlighting the role of cotton wool filter for providing a suitable environment for glucose oxidase stability. The novel concept can be easily generalized for further applications in the field of non-invasive clinical diagnostics and in-situ environmental monitoring.

Sustainable Printed Electrochemical Platforms for Greener Analytics

The development of miniaturized electrochemical platforms holds considerable importance for the in situ analytical monitoring of clinical, environmental, food, and forensic samples. However, it is crucial to pay attention to the sustainability of materials chosen to fabricate these devices, in order to decrease the amount and the impact of waste coming from their production and use. In the framework of a circular economy and an environmental footprint reduction, the electrochemical sensor production technology must discover the potentiality of innovative approaches based on techniques and materials that can satisfy the needs of environmental-friendly and greener analytics. The aim of this review is to describe some of the printing technologies most used for sensor production, including screen-printing, inkjet-printing, and 3D-printing, and the low-impact materials that are recently proposed for these techniques, such as polylactic acid, cellulose, silk proteins, biochar.

Metal sensing-carbon dots loaded TiO2-nanocomposite for photocatalytic bacterial deactivation and application in aquaculture

Nowadays, bioactive nanomaterials have been attracted the researcher's enthusiasm in various fields. Herein, Diplocyclos palmatus leaf extract-derived green-fluorescence carbon dots (DP-CDs) were prepared using the hydrothermal method. Due to the strong fluorescence stability, the prepared DP-CDs were coated on filter-paper to make a fluorometric sensor-strip for Fe3+ detection. After, a bandgap-narrowed DP-CDs/TiO2 nanocomposite (DCTN) was prepared using the methanolic extract of D. palmatus. The prepared DCTN exhibited improved photocatalytic bacterial deactivation under sunlight irradiation. The DCTN-photocatalysis slaughtered V. harveyi cells by the production of reactive oxygen species, which prompting oxidative stress, damaging the cell membrane and cellular constituents. These results suggest the plausible mode of bactericidal action of DCTN-photocatalysis under sunlight. Further, the DCTN has shown potent anti-biofilm activity against V. harveyi, and thereby, DCTN extended the survival of V. harveyi-infected shrimps during the in vivo trial with Litopenaeus vannamei. Notably, this is the first report for the disinfection of V. harveyi-mediated acute-hepatopancreatic necrosis disease (AHPND) using nanocomposite. The reduced internal-colonization of V. harveyi on the hepatopancreas as well as the rescue action of the pathognomonic effect in the experimental animals demonstrated the anti-infection potential of DCTN against V. harveyi-mediated AHPND in aquaculture.

A Review on the Use of Impedimetric Sensors for the Inspection of Food Quality

This paper exhibits a thorough review of the use of impedimetric sensors for the analysis of food quality. It helps to understand the contribution of some of the major types of impedimetric sensors that are used for this application. The deployment of impedimetric sensing prototypes has been advantageous due to their wide linear range of responses, detection of the target analyte at low concentrations, good stability, high accuracy and high reproducibility in the results. The choice of these sensors was classified on the basis of structure and the conductive material used to develop them. The first category included the use of nanomaterials such as graphene and metallic nanowires used to form the sensing devices. Different forms of graphene nanoparticles, such as nano-hybrids, nanosheets, and nano-powders, have been largely used to sense biomolecules in the micro-molar range. The use of conductive materials such as gold, copper, tungsten and tin to develop nanowire-based prototypes for the inspection of food quality has also been shown. The second category was based on conventional electromechanical circuits such as electronic noses and other smart systems. Within this sector, the standardized systems, such as electronic noses, and LC circuit -based systems have been explained. Finally, some of the challenges posed by the existing sensors have been listed out, along with an estimate of the increase in the number of sensors employed to assess food quality.

Carbon black as an outstanding and affordable nanomaterial for electrochemical (bio)sensor design

Advances in cutting-edge technologies including nanotechnology, microfluidics, electronic engineering, and material science have boosted a new era in the design of robust and sensitive biosensors. In recent years, carbon black has been re-discovered in the design of electrochemical (bio)sensors thanks to its interesting electroanalytical properties, absence of treatment requirement, cost-effectiveness (c.a. 1 €/Kg), and easiness in the preparation of stable dispersions. Herein, we present an overview of the literature on carbon black-based electrochemical (bio)sensors, highlighting current trends and possible challenges to this rapidly developing area, with a special focus on the fabrication of carbon black-based electrodes in the realisation of sensors and biosensors (e.g. enzymatic, immunosensors, and DNA-based).

Long-Term Stability Monitoring of Printed Proteins on Paper-Based Membranes

Monitoring of long-term stability of proteins on paper-based membranes is important as it is directly related to paper-based sensor fabrication. By using a simple piezo printhead inkjet printer, recombinant proteins and antibodies were printed on paper-based membranes to test their stability and sensitivity under varying lengths of storage and temperature conditions. Our data show that a printed IgG-HRP antibody on simple printing paper maintains >50% functionality up to ∼2 months under 4 and -20 °C storage. Antibodies printed on polyvinylidene difluoride (PVDF) and nitrocellulose showed 5.3 and 9.7% decreases, respectively, in initial signal intensities compared to printing paper. Prostate-specific membrane antigen and tumor necrosis factor alpha recombinant proteins printed on paper-based membranes can be detected by antibodies, and antibody signal intensities can be detected up to 28 days after storage at 4 and -20 °C when printed on PVDF membrane or printing paper. These data suggest that printed proteins on simple printing paper and PVDF membrane can maintain their functionality up to few months when stored at 4 °C or lower and can be potentially applied in paper-based sensor development.