A novel disposable self-adhesive inked paper device for electrochemical sensing of dopamine and serotonin neurotransmitters and biosensing of glucose

In situ monitoring of cytoplasmic dopamine levels by noble metals decorated carbon fiber tips

Dopamine (DA), a catecholamine neurotransmitter, is crucial in brain signal transmission. Monitoring cytoplasmic DA levels can reflect changes in metabolic factors and provide valuable information for researching the mechanisms involved in neurodegenerative diseases. However, the in-situ detection of intracellular DA is constrained by its low contents in small-sized single cells. In this work, we report that noble metal (Au, Pt)-modified carbon fiber micro-nanoelectrodes are capable of real-time detection of DA in single cells with excellent sensitivity, selectivity, and anti-contamination capabilities. Notably, noble metals can be modified on the electrode surface through electrochemical deposition to enhance the conductivity of the electrode and the oxidation current of DA by 50 %. The nanosensors can work stably and continuously in rat adrenal pheochromocytoma cells (PC12) to monitor changes in DA levels upon K+ stimulation. The functionalized carbon fibers based nanosensors will provide excellent prospects for DA analysis in the brains of living animals.

The Role of Catecholamines in the Pathogenesis of Diseases and the Modified Electrodes for Electrochemical Detection of Catecholamines: A Review

Catecholamines (CAs), which include adrenaline, noradrenaline, and dopamine, are neurotransmitters and hormones that critically regulate the cardiovascular system, metabolism, and stress response in the human body. The abnormal levels of these molecules can lead to the development of various diseases, including pheochromocytoma and paragangliomas, Alzheimer's disease, and Takotsubo cardiomyopathy. Due to their low cost, high sensitivity, flexible detection strategies, ease of integration, and miniaturization, electrochemical techniques have been extensively employed in the detection of CAs, surpassing traditional analytical methods. Electrochemical detection of CAs in real samples is challenging due to the tendency of poisoning electrode. Chemically modified electrodes have been widely used to solve the problems of poor sensitivity and selectivity faced by bare electrodes. There are a few articles that provide an overview of electrochemical detection and efficient enrichment of CAs, but there is a dearth of updates on the role of CAs in the pathogenesis of diseases. Additionally, there is still a lack of systematic synthesis with a focus on modified electrodes for electrochemical detection. Thus, this review provides a summary of the recent clinical pathogenesis of CAs and the modified electrodes for electrochemical detection of CAs published between 2017 and 2022. Moreover, challenges and future perspectives are also highlighted. This work is expected to provide useful guidance to researchers entering this interdisciplinary field, promoting further development of CAs pathogenesis, and developing more novel chemically modified electrodes for the detection of CAs.

Preparation of self-supporting vertically/horizontally grown graphene microelectrodes for neurotransmitter determination

The development of microelectrodes for the rapid in situ detection of neurotransmitters and their metabolic levels in human biofluids has considerable significance in biomedical research. In this study, self-supported graphene microelectrodes with B-doped, N-doped, and B- and N-co-doped vertical graphene (BVG, NVG, and BNVG, respectively) nanosheets grown on horizontal graphene (HG) were fabricated for the first time. The high electrochemical catalytic activity of BVG/HG on monoamine compounds was explored by investigating the influence of B and N atoms and the VG layer thickness on the response current of neurotransmitters. Quantitative analysis using the BVG/HG electrode in a blood-like environment with pH 7.4 indicated that the linear concentration ranges were 1-400 and 1-350 μM for dopamine (DA) and serotonin (5-HT), with limits of detection (LODs) of 0.271 and 0.361 μM, respectively. For tryptophan (Trp), the sensor measured a wide linear concentration range of 3-1500 μM over a wide pH range of 5.0-9.0, with the LOD fluctuating between 0.58 and 1.04 μM. Furthermore, the BVG/HG microelectrodes could be developed as needle- and pen-type sensors for the detection of DA, 5-HT, and Trp in human blood and gastrointestinal secretion samples.

Paper-based analytical devices for point-of-need applications

Paper-based analytical devices (PADs) are powerful platforms for point-of-need testing since they are inexpensive devices fabricated in different shapes and miniaturized sizes, ensuring better portability. Additionally, the readout and detection systems can be accomplished with portable devices, allying with the features of both systems. These devices have been introduced as promising analytical platforms to meet critical demands involving rapid, reliable, and simple testing. They have been applied to monitor species related to environmental, health, and food issues. Herein, an outline of chronological events involving PADs is first reported. This work also introduces insights into fundamental parameters to engineer new analytical platforms, including the paper type and device operation. The discussions involve the main analytical techniques used as detection systems, such as colorimetry, fluorescence, and electrochemistry. It also showed recent advances involving PADs, especially combining optical and electrochemical detection into a single device. Dual/combined detection systems can overcome individual barriers of the analytical techniques, making possible simultaneous determinations, or enhancing the devices' sensitivity and/or selectivity. In addition, this review reports on distance-based detection, which is also considered a trend in analytical chemistry. Distance-based detection offers instrument-free analyses and avoids user interpretation errors, which are outstanding features for analyses at the point of need, especially for resource-limited regions. Finally, this review provides a critical overview of the practical specifications of the recent analytical platforms involving PADs, demonstrating their challenges. Therefore, this work can be a highly useful reference for new research and innovation.

A portable electrochemical sensing platform for serotonin detection based on surface-modified carbon fiber microelectrodes

Serotonin (5-HT) is one of the key neurotransmitters in the human body, regulating numerous physiological functions. A disruption in 5-HT homeostasis could result in serious health problems, including neurodegenerative disorders, depression, and 5-HT syndrome. Detection of 5-HT concentrations in biological fluids, such as urine, is a potential solution for early diagnosis of these diseases. In this study, we developed a novel, simple, and low-cost electrochemical sensing platform consisting of a portable workstation with customized electrodes for 5-HT detection in artificial biological fluids. Nafion/carbon nanotubes (CNTs) and electrochemically modified carbon fiber microelectrodes (Nafion-CNT/EC CFMEs) displayed improved 5-HT sensitivity and selectivity. Together with a customized Ag/AgCl reference electrode and Pt counter electrode, the portable 5-HT sensing platform had a sensitivity of 0.074 μA μM^-1 and a limit of detection (LOD) of 140 nM. This system was also assessed to measure 5-HT spiked in artificial urine samples, showing nearly full recovery rates. These satisfactory results demonstrated that the portable system exhibits outstanding performance and confirmed the feasibility of 5-HT detection, which can be used to provide point-of-care analysis in actual biological samples.

A Disposable Screen Printed Electrodes with Hexagonal Ni(OH)2 Nanoplates Embedded Chitosan Layer for the Detection of Depression Biomarker

Serotonin (5-hydroxytryptamine (5-HT)) is one of the important neurotransmitters which is released from the endocrine system. An abnormal level of this biomarker leads to several neurological diseases. The accurate assessment of serotonin is the utmost option to start treatment in the early stages of the disease. The current work is focused on the development of a disposable, screen-printed electrochemical sensor for the depression biomarker, serotonin in the physiological pH medium (pH 7.4) with the aid of a hexagonal, Ni(OH)₂-nanoplate (NH-HNP)-embedded chitosan (Chit) and modified, screen-printed carbon electrode (SPCE). Initially, hexagonal nanoplates of Ni(OH)₂ were synthesized by an eco-friendly and simple hydrothermal method. The prepared materials were well characterized by advanced analytical techniques to examine the physicochemical properties of the synthesized Ni(OH)₂ hexagonal nanoplates. From the cyclic voltametric (CV) analysis, it was found that the oxidative current response of 5-HT at a NH-HNP-modified SPCE has about fivefold higher current values than over bare SPCE. The scan rate studies of NH-HNP-Chit/SPCE electrodes revealed that the oxidation mechanism of 5-HT is controlled by the diffusion behavior of the analyte. Differential pulse voltammetric tests of the NH-HNP-Chit/SPCE electrode exhibited a linear response in the dynamic concentration range of 0.1 to 30 µM, with a detection limit of about 60 nM. The sensor response is very reproducible from electrode to electrode, and the deactivation or surface-fouling of the sensor was not observed within the several experimental measurements. The sensor exhibited excellent storage stability over a period of twenty days. Finally, the fabricated, disposable SPCE sensor has shown respectable activity for the detection of depression biomarker 5-HT from synthetic urine and saliva samples.

A pencil graphite-based disposable device for electrochemical monitoring of sulfanilamide in honey and water samples

The present paper reports a simple, fast, and inexpensive process of manufacturing a disposable pencil graphite electrode (PGE) from widely available materials, which showed a reproducibility of at least 7.5%. The electrode was compared to the commercial glassy carbon electrode (GCE) and showed superior electroanalytical performance for sulfanilamide (SFA) with approximately 3.9-fold higher current density. Additionally, a displacement of the oxidation peak from approximately 80 mV to more cathodic regions was observed. Therefore, a method based on square wave voltammetry (SWV) was developed for the determination of the antimicrobial SFA in honey and tap water samples using the proposed sensor. The optimized method presented good detectability (LOD = 2.37 μmol L^-1), with excellent precision and accuracy (relative standard deviation < 4.2%) and percent recovery from spiked samples ranging from 92 to 97%. In addition, the sensor did not suffer significant interference from sample matrix components and other commonly evaluated antimicrobials, which demonstrates the potential of these electrodes for implementation in routine analysis and quality control.

Development of New Simple Compositions of Silver Inks for the Preparation of Pseudo-Reference Electrodes

Silver materials are known to present excellent properties, such as high electrical and thermal conductivity as well as chemical stability. Silver-based inks have drawn a lot of attention for being compatible with various substrates, which can be used in the production uniform and stable pseudo-reference electrodes with low curing temperatures. Furthermore, the interest in the use of disposable electrodes has been increasing due to the low cost and the possibility of their use in point-of-care and point-of-need situations. Thus, in this work, two new inks were developed using Ag as conductive material and colorless polymers (nail polish (NP) and shellac (SL)), and applied to different substrates (screen-printed electrodes, acetate sheets, and 3D-printed electrodes) to verify the performance of the proposed inks. Measurements attained with open circuit potential (OCP) attested to the stability of the potential of the pseudo-reference proposed for 1 h. Analytical curves for β-estradiol were also obtained using the devices prepared with the proposed inks as pseudo-references electrodes, which presented satisfactory results concerning the potential stability (RSD < 2.6%). These inks are simple to prepare and present great alternatives for the development of pseudo-reference electrodes useful in the construction of disposable electrochemical systems.

Application and Progress of Chemometrics in Voltammetric Biosensing

The voltammetric electrochemical sensing method combined with biosensors and multi-sensor systems can quickly, accurately, and reliably analyze the concentration of the main analyte and the overall characteristics of complex samples. Simultaneously, the high-dimensional voltammogram contains the rich electrochemical features of the detected substances. Chemometric methods are important tools for mining valuable information from voltammetric data. Chemometrics can aid voltammetric biosensor calibration and multi-element detection in complex matrix conditions. This review introduces the voltammetric analysis techniques commonly used in the research of voltammetric biosensor and electronic tongues. Then, the research on optimizing voltammetric biosensor results using classical chemometrics is summarized. At the same time, the incorporation of machine learning and deep learning has brought new opportunities to further improve the detection performance of biosensors in complex samples. Finally, smartphones connected with miniaturized voltammetric biosensors and chemometric methods provide a high-quality portable analysis platform that shows great potential in point-of-care testing.

Rapid Detection of Anti-SARS-CoV-2 Antibodies with a Screen-Printed Electrode Modified with a Spike Glycoprotein Epitope

BACKGROUND

The coronavirus disease of 2019 (COVID-19) is caused by an infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It was recognized in late 2019 and has since spread worldwide, leading to a pandemic with unprecedented health and financial consequences. There remains an enormous demand for new diagnostic methods that can deliver fast, low-cost, and easy-to-use confirmation of a SARS-CoV-2 infection. We have developed an affordable electrochemical biosensor for the rapid detection of serological immunoglobulin G (IgG) antibody in sera against the spike protein.

MATERIALS AND METHODS

A previously identified linear B-cell epitope (EP) specific to the SARS-CoV-2 spike glycoprotein and recognized by IgG in patient sera was selected for the target molecule. After synthesis, the EP was immobilized onto the surface of the working electrode of a commercially available screen-printed electrode (SPE). The capture of SARS-CoV-2-specific IgGs allowed the formation of an immunocomplex that was measured by square-wave voltammetry from its generation of hydroquinone (HQ).

RESULTS

An evaluation of the performance of the EP-based biosensor presented a selectivity and specificity for COVID-19 of 93% and 100%, respectively. No cross-reaction was observed to antibodies against other diseases that included Chagas disease, Chikungunya, Leishmaniosis, and Dengue. Differentiation of infected and non-infected individuals was possible even at a high dilution factor that decreased the required sample volumes to a few microliters.

CONCLUSION

The final device proved suitable for diagnosing COVID-19 by assaying actual serum samples, and the results displayed good agreement with the molecular biology diagnoses. The flexibility to conjugate other EPs to SPEs suggests that this technology could be rapidly adapted to diagnose new variants of SARS-CoV-2 or other pathogens.

New conductive filament ready-to-use for 3D-printing electrochemical (bio)sensors: Towards the detection of SARS-CoV-2

The 3D printing technology has gained ground due to its wide range of applicability. The development of new conductive filaments contributes significantly to the production of improved electrochemical devices. In this context, we report a simple method to producing an efficient conductive filament, containing graphite within the polymer matrix of PLA, and applied in conjunction with 3D printing technology to generate (bio)sensors without the need for surface activation. The proposed method for producing the conductive filament consists of four steps: (i) mixing graphite and PLA in a heated reflux system; (ii) recrystallization of the composite; (iii) drying and; (iv) extrusion. The produced filament was used for the manufacture of electrochemical 3D printed sensors. The filament and sensor were characterized by physicochemical techniques, such as SEM, TGA, Raman, FTIR as well as electrochemical techniques (EIS and CV). Finally, as a proof-of-concept, the fabricated 3D-printed sensor was applied for the determination of uric acid and dopamine in synthetic urine and used as a platform for the development of a biosensor for the detection of SARS-CoV-2. The developed sensors, without pre-treatment, provided linear ranges of 0.5-150.0 and 5.0-50.0 μmol L^-1, with low LOD values (0.07 and 0.11 μmol L^-1), for uric acid and dopamine, respectively. The developed biosensor successfully detected SARS-CoV-2 S protein, with a linear range from 5.0 to 75.0 nmol L^-1 (0.38 μg mL^-1 to 5.74 μg mL^-1) and LOD of 1.36 nmol L^-1 (0.10 μg mL^-1) and sensitivity of 0.17 μA nmol^-1 L (0.01 μA μg^-1 mL). Therefore, the lab-made produced and the ready-to-use conductive filament is promising and can become an alternative route for the production of different 3D electrochemical (bio)sensors and other types of conductive devices by 3D printing.

High performance electrochemical method for simultaneous determination dopamine, serotonin, and tryptophan by ZrO2-CuO co-doped CeO2 modified carbon paste electrode

In this research, a paste containing ZrO₂-CuO-CeO₂ ternary nanocomposite and graphene (Gr) was used in constructing a carbon paste sensor for monitoring biomolecules including dopamine (Dop), serotonin (Ser) and tryptophan (Trp). The scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were utilized for ZrO₂-CuO-CeO₂ ternary nanocomposite characterization. The obtained data show that, the ZrO2-CuO-CeO₂/Gr and synergetic effect of using these three-metal oxide nanoparticles, could effectively improve the electron transfer kinetic and exhibit a high electrocatalytic activity, making it serve as a powerful tool for biomolecules analysis. The differential pulse (DP) and cycle voltammetry (CV) methods were applied for investigating electrochemical treatment of the analytes. In comparison to all of the previous voltammetric reports, this research has the lowest detection limit and widest linear range. The calibration curves in the optimum conditions were linear over the range of 0.008-7.2 and 7.2-185 μM for Dop, 0.008-7.9 and 7.9-205 μM for Ser and 0.009-8.6 and 8.6-194 μM for Trp. The calculated limit of detection (LOD) was 3.09, 3.49 and 5.32 nM for Dop, Ser and Trp, respectively. The applicability of this sensing device was tested by monitoring Dop, Ser and Trp in the human urine and plasma samples. The recovery percentage of the analysis in the real samples was between 95.6 and 104.74; also, the data of determination of Dop, Ser and Trp with ZrO₂-CuO-CeO₂/Gr/CPE was well close to HPLC data. The obtained result demonstrates that the ZrO₂-CuO-CeO₂/Gr/CPE has good selectivity, stability, reproducibility, and repeatability, and can be used for the routine analysis of Dop, Ser and Trp.

A Pencil-Lead Immunosensor for the Rapid Electrochemical Measurement of Anti-Diphtheria Toxin Antibodies

Diphtheria is a vaccine-preventable disease, yet immunization can wane over time to non-protective levels. We have developed a low-cost, miniaturized electroanalytical biosensor to quantify anti-diphtheria toxin (DTx) immunoglobulin G (anti-DTx IgG) antibody to minimize the risk for localized outbreaks. Two epitopes specific to DTx and recognized by antibodies generated post-vaccination were selected to create a bi-epitope peptide, biEP, by synthesizing the epitopes in tandem. The biEP peptide was conjugated to the surface of a pencil-lead electrode (PLE) integrated into a portable electrode holder. Captured anti-DTx IgG was measured by square wave voltammetry from the generation of hydroquinone (HQ) from the resulting immunocomplex. The performance of the biEP reagent presented high selectivity and specificity for DTx. Under the optimized working conditions, a logarithmic calibration curve showed good linearity over the concentration range of 10-5-10-1 IU mL-1 and achieved a limit of detection of 5 × 10-6 IU mL-1. The final device proved suitable for interrogating the immunity level against DTx in actual serum samples. Results showed good agreement with those obtained from a commercial enzyme-linked immunosorbent assay. In addition, the flexibility for conjugating other capture molecules to PLEs suggests that this technology could be easily adapted to the diagnoses of other pathogens.

Carbon fiber microelectrode array loaded with the diazonium salt-single-walled carbon nanotubes composites for the simultaneous monitoring of dopamine and serotonin in vivo

Carbon fiber microelectrode arrays based on diazonium salt and single-walled carbon nanotubes composites (DS-SWCNT/CFMEA) have been fabricated, and it developed for the simultaneous monitoring of dopamine (DA) and serotonin (5-HT) with differential pulse voltammary (DPV). The diazonium salt can improve the water-solubility of single-walled carbon nanotubes and show good selectivity to DA, thus DS-SWCNT/CFMEA exhibits enhanced electrocatalytic activity for the oxidation of DA and 5-HT, and well antifouling ability to the other biomolecules. Moreover, DS-SWCNT/CFMEA shows the wider liner range, and the good performance of precision, reproducibility and biocompatibility. The excellent characteristics of the prepared microsensor array make it to be used to monitor the release of DA and 5-HT in the mouse brain striatum of different group over time. Meanwhile, the results of in vivo on line assay further confirmed the pharmacological effects of Uncaria alkaloid extract solution on DA and 5-HT. This research may provide a new method for monitoring the release of neurobiomolecules, and the microsensor array are expected to be a tool for the study of pharmacological and physiological processes on line in vivo.

Lab-on-Paper Devices for Diagnosis of Human Diseases Using Urine Samples-A Review

In recent years, microfluidic lab-on-paper devices have emerged as a rapid and low-cost alternative to traditional laboratory tests. Additionally, they were widely considered as a promising solution for point-of-care testing (POCT) at home or regions that lack medical infrastructure and resources. This review describes important advances in microfluidic lab-on-paper diagnostics for human health monitoring and disease diagnosis over the past five years. The review commenced by explaining the choice of paper, fabrication methods, and detection techniques to realize microfluidic lab-on-paper devices. Then, the sample pretreatment procedure used to improve the detection performance of lab-on-paper devices was introduced. Furthermore, an in-depth review of lab-on-paper devices for disease measurement based on an analysis of urine samples was presented. The review concludes with the potential challenges that the future development of commercial microfluidic lab-on-paper platforms for human disease detection would face.

Recent Advances in Enzymatic and Non-Enzymatic Electrochemical Glucose Sensing

The detection of glucose is crucial in the management of diabetes and other medical conditions but also crucial in a wide range of industries such as food and beverages. The development of glucose sensors in the past century has allowed diabetic patients to effectively manage their disease and has saved lives. First-generation glucose sensors have considerable limitations in sensitivity and selectivity which has spurred the development of more advanced approaches for both the medical and industrial sectors. The wide range of application areas has resulted in a range of materials and fabrication techniques to produce novel glucose sensors that have higher sensitivity and selectivity, lower cost, and are simpler to use. A major focus has been on the development of enzymatic electrochemical sensors, typically using glucose oxidase. However, non-enzymatic approaches using direct electrochemistry of glucose on noble metals are now a viable approach in glucose biosensor design. This review discusses the mechanisms of electrochemical glucose sensing with a focus on the different generations of enzymatic-based sensors, their recent advances, and provides an overview of the next generation of non-enzymatic sensors. Advancements in manufacturing techniques and materials are key in propelling the field of glucose sensing, however, significant limitations remain which are highlighted in this review and requires addressing to obtain a more stable, sensitive, selective, cost efficient, and real-time glucose sensor.

Serotonin level as a potent diabetes biomarker based on electrochemical sensing: a new approach in a zebra fish model

Serotonin (5-HT) levels have been associated with several exclusively metabolic disorders. Herein, a new approach for 5-HT level as a novel biomarker of diabetes mellitus is considered using a simple nanocomposite and HPLC method. Reduced graphene oxide (rGO) comprising gold nanoparticles (AuNPs) was decorated with 18-crown-6 (18.Cr.6) to fabricate a simple nanocomposite (rGO-AuNPs-18.Cr.6). The nanocomposite was positioned on a glassy carbon electrode (GCE) to form an electrochemical sensor for the biomarker 5-HT in the presence of L-tryptophan (L-Trp), dopamine (DA), ascorbic acid (AA), urea, and glucose. The nanocomposite exhibited efficient catalytic activity for 5-HT detection by square-wave voltammetry (SWV). The proposed sensor displayed high selectivity, excellent reproducibility, notable anti-interference ability, and long-term stability even after 2 months. SWV defined a linear range of 5-HT concentration from 0.4 to 10 μg L^-1. A diabetic animal model (diabetic zebrafish model) was then applied to investigate 5-HT as a novel biomarker of diabetes. A limit of detection (LOD) of about 0.33 μg L^-1 was found for the diabetic group and 0.15 μg L^-1 for the control group. The average levels of 5-HT obtained were 9 and 2 μg L^-1 for control and diabetic groups, respectively. The recovery, relative standard deviation (RSD), and relative error (RE) were found to be about 97%, less than 2%, and around 3%, respectively. The significant reduction in 5-HT level in the diabetic group compared to the control group proved that the biomarker 5-HT can be applied for the early diagnosis of diabetes mellitus.

Structural refinement and electrochemical properties of one dimensional (ZnO NRs)1-x(CNs)x functional hybrids for serotonin sensing studies

Herein, the efficient serotonin (5-HT) sensing studies have been conducted using the (ZnO NRs)1-x(CNs)x nanocomposites (NCs) having appropriate structural and electrochemical properties. Initially, the different compositions of ZnO nanorods (NRs), with varying content of carbon nanostructures (CNs=MWCNTs and RGO), are prepared using simple in-situ wet chemical method and thereafter these NCs have been characterized for physico-chemical properties in correlation to the 5-HT sensing activity. XRD Rietveld refinement studies reveal the hexagonal Wurtzite ZnO NRs oriented in (101) direction with space group 'P63mc' and both orientation as well as phase of ZnO NRs are also retained in the NCs due to the small content of CNs. The interconnectivity between the ZnO NRs with CNs through different functional moieties is also studied using FTIR analysis; while phases of the constituents are confirmed through Raman analysis. FESEM images of the bare/NCs show hexagonal shaped rods with higher aspect ratio (4.87) to that of others. BET analysis and EIS measurements reveal the higher surface area (97.895 m2/g), lower charge transfer resistance (16.2 kΩ) for the ZCNT 0.1 NCs to that of other NCs or bare material. Thereafter, the prepared NCs are deposited on the screen printed carbon electrode (SPCE) using chitosan as cross-linked agent for 5-HT sensing studies; conducted through cyclic voltammetry (CV) and square wave voltammetry (SWV) measurements. Among the various composites, ZCNT0.1 NCs based electrodes exhibit higher sensing activity towards 5-HT in accordance to its higher surface area, lower particle size and lower charge transfer resistance. SWV measurements provide a wide linear response range (7.5-300 μM); lower limit of detection (0.66 μM), excellent limit of quantification (2.19 μM) and good reproducibility to ZCNT 0.1 NCs as compared to others for 5-HT sensing studies.

Design of A Low-Cost and Disposable Paper-Based Immunosensor for the Rapid and Sensitive Detection of Aflatoxin B1

We report a paper-based electrochemical immunosensor made with sustainable materials to detect aflatoxin B1 (AFB1), a highly toxic, carcinogenic mycotoxin found in food. The immunosensor was prepared with a waterproof paper substrate and low-cost graphite-based conductive ink through a simple cut-printing method. The working electrode was functionalized with a drop-cast film of multiwalled carbon nanotubes (MWCNT)/chitosan on which a layer of anti-AFB1 monoclonal antibodies was immobilized covalently. The architecture of the immunosensor was confirmed with polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and electrochemical impedance spectroscopy (EIS), including the effective immobilization of the active layer of anti-AFB1. With EIS as the principle of detection, the immunosensor could detect AFB1 in the range from 1 to 30 ng·mL−1, and detection limit of 0.62 ng·mL−1. This sensitivity is sufficient to detect AFB1 in food according to regulatory agencies. The immunosensor exhibited good repeatability, reproducibility, stability, and selectivity in experiments with a possible interferent. Furthermore, detection of AFB1 in maize flour samples yielded recovery of 97–99%, in a demonstration of the possible use of the paper-based immunosensor to detect AFB1 using extraction solutions from food samples.

Fully-printed electrochemical sensors made with flexible screen-printed electrodes modified by roll-to-roll slot-die coating

The manufacture of sensors using large-scale production techniques, such as roll-to-roll (R2R) processing, may fulfill requirements of low-cost disposable devices. Herein, we report the fabrication of fully-printed electrochemical sensors using screen-printed carbon electrodes coated with carbon black inks through slot-die coating within an R2R process. As a proof of concept, sensors were produced to detect the neurotransmitter dopamine with high reproducibility and low limit of detection (0.09 μmol L^-1). Furthermore, fully-printed biosensors made with a tyrosinase-containing ink were used to detect catechol in natural water samples. Since slot-die deposition enables printing enzymes without significant activity loss, the biosensors exhibited high stability over a period of several weeks. Even more important, R2R slot-die coating may be extended to any type of sensors and biosensors with the possibility of large-scale manufacturing.

Development of a Pencil Drawn Paper-based Analytical Device to Detect Lysergic Acid Diethylamide (LSD)*, †

The need for agile and proper identification of drugs of abuse has encouraged the scientific community to improve and to develop new methodologies. The drug lysergic acid diethylamide (LSD) is still widely used due to its hallucinogenic effects. The use of voltammetric methods to analyze narcotics has increased in recent years, and the possibility of miniaturizing the electrochemical equipment allows these methods to be applied outside the laboratory; for example, in crime scenes. In addition to portability, the search for affordable and sustainable materials for use in electroanalytical research has grown in recent decades. In this context, employing paper substrate, graphite pencil, and silver paint to construct paper-based electrodes is a great alternative. Here, a paper-based device comprising three electrodes was drawn on 300 g/m² watercolor paper with 8B pencils, and its efficiency was compared to the efficiency of a commercially available screen-printed carbon electrode. Square wave voltammetry was used for LSD analysis in aqueous medium containing 0.05 mol/L LiClO₄ . The limits of detection and quantification were 0.38 and 1.27 μmol/L, respectively. Both electrodes exhibited a similar voltammetric response, which was also confirmed during analysis of a seized LSD sample, with recovery of less than 10%. The seized samples were previously analyzed by GCMS technique, employing the full scan spectra against the software spectral library. The electrode selectivity was also tested against 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine. It was possible to differentiate these compounds from LSD, indicating that the developed paper-based device has potential application in forensic chemistry analyses.