Reusable graphite-based electrochemical sensors for L-dopa and dopamine detection.

A fully reusable electrochemical device is proposed for the first time made from laser cutting and a homemade conductive ink composed of carbon and nail polish. As a sensor substrate, we applied polymethyl methacrylate, which allows the surface to be renewed by simply removing and reapplying a new layer of ink. In addition to the ease of renewing the sensor's conductive surface, the design of the device has allowed for the integration of different forms of analysis. The determination of L-Dopa was performed using DPV, which presented a linear response range between 5.0 and 1000.0 µmol L-1, and a LOD of 0.11 µmol L-1. For dopamine, a flow injection analysis system was employed, and using the amperometric technique measurements were performed with a linear ranging from 2.0 to 100.0 µmol L-1 and a LOD of 0.26 µmol L-1. To demonstrate its applicability, the device was used in the quantification of analytes in pharmaceutical drug and synthetic urine samples.

Lab-made disposable screen-printed electrochemical sensors and immunosensors modified with Pd nanoparticles for Parkinson's disease diagnostics.

A new conductive ink based on the addition of carbon black to a poly(vinyl alcohol) matrix is developed and investigated for electrochemical sensing and biosensing applications. The produced devices were characterized using morphological and electrochemical techniques and modified with Pd nanoparticles to enhance electrical conductivity and reaction kinetics. With the aid of chemometrics, the parameters for metal deposition were investigated and the sensor was applied to the determination of Parkinson's disease biomarkers, specifically epinephrine and α-synuclein. A linear behavior was obtained in the range 0.75 to 100 µmol L-1 of the neurotransmitter, and the device displayed a limit of detection (LOD) of 0.051 µmol L-1. The three-electrode system was then tested using samples of synthetic cerebrospinal fluid. Afterward, the device was modified with specific antibodies to quantify α-synuclein using electrochemical impedance spectroscopy. In phosphate buffer, a linear range was obtained for α-synuclein concentrations from 1.5 to 15 µg mL-1, with a calculated LOD of 0.13 µg mL-1. The proposed immunosensor was also applied to blood serum samples, and, in this case, the linear range was observed from 6.0 to 100.5 µg mL-1 of α-synuclein, with a LOD = 1.3 µg mL-1. Both linear curves attend the range for the real diagnosis, demonstrating its potential application to complex matrices.

Electrochemical immunosensors using electrodeposited gold nanostructures for detecting the S proteins from SARS-CoV and SARS-CoV-2.

This paper reports the development of a low-cost (< US$ 0.03 per device) immunosensor based on gold-modified screen-printed carbon electrodes (SPCEs). As a proof of concept, the immunosensor was tested for a fast and sensitive determination of S proteins from both SARS-CoV and SARS-CoV-2, by a single disposable device. Gold nanoparticles were electrochemically deposited via direct reduction of gold ions on the electrode using amperometry. Capture antibodies from spike (S) protein were covalently immobilized on carboxylic groups of self-assembled monolayers (SAM) of mercaptoacetic acid (MAA) attached to the gold nanoparticles. Label-free detection of S proteins from both SARS-CoV and SARS-CoV-2 was performed with electrochemical impedance spectroscopy (EIS). The immunosensor fabricated with 9 s gold deposition had a high performance in terms of selectivity, sensitivity, and low limit of detection (LOD) (3.16 pmol L-1), thus permitting the direct determination of the target proteins in spiked saliva samples. The complete analysis can be carried out within 35 min using a simple one-step assay protocol with small sample volumes (10 µL). With such features, the immunoplatform presented here can be deployed for mass testing in point-of-care settings.

Development of low-cost planar electrodes and microfluidic channels for applications in capacitively coupled contactless conductivity detection (C4 D).

Electrochemical techniques are commonly applied to micro total analysis system (µTAS) devices mainly due to its high sensitivity and miniaturization capacity. Among many electrochemical techniques, capacitively coupled contactless conductivity detection (C4 D) stands out for not requiring direct electrode-solution contact, avoiding several problems such as electrolysis, bubble formation, and metal degradation. Furthermore, the instrumentation required for C4 D measurements is compact, low cost, and easy to use, allowing in situ measurements to be performed even by nonspecialized personal. Contrarily, the production of metallic electrodes and microchannels adequate for C4 D measurements commonly requires specialized facilities and workers, increasing the costs of applying these methods. We propose alternatives to batch manufacture metallic electrodes and polymeric microchannels for C4 D analysis using more straightforward equipment and lower-cost materials. Three devices with different dielectric layer compositions and electrode sizes were tested and compared regarding their analytical performance. The constructed platforms have shown a reduction of more than 64% in cost when compared to traditional techniques and displayed good linearity (R2 ≥ 0.994), reproducibility (RSD ≤ 4.07%, n = 3), and limits of detection (≤0.26 mmol/L) when measuring standard NaCl samples. Therefore, the proposed methods were successfully validated and are available for further C4 D applications such as diagnosis of dry-eye syndrome.

The use of biological fluids in microfluidic paper-based analytical devices (µPADs): Recent advances, challenges and future perspectives.

The use of microfluidic paper-based analytical devices (µPADs) for aiding medical diagnosis is a growing trend in the literature mainly due to their low cost, easy use, simple manufacturing, and great potential for application in low-resource settings. Many important biomarkers (proteins, ions, lipids, hormones, DNA, RNA, drugs, whole cells, and more) and biofluids are available for precise detection and diagnosis. We have reviewed the advances µPADs in medical diagnostics have achieved in the last few years, focusing on the most common human biofluids (whole blood/plasma, sweat, urine, tears, and saliva). The challenges of detecting specific biomarkers in each sample are discussed, along with innovative techniques that overcome such limitations. Finally, the difficulties of commercializing µPADs are considered, and future trends are presented, including wearable devices and integrating multiple steps in a single platform.

Low-cost precision agriculture for sustainable farming using paper-based analytical devices.

The United Nations estimates that by 2030, agricultural production must increase by 70% to meet food demand. Precision agriculture (PA) optimizes production through efficient resource use, with soil fertility being crucial for nutrient supply. Traditional nutrient quantification methods are costly and time-consuming. This study introduces a rapid (15 min), user-friendly, paper-based platform for determining four essential macronutrients-nitrate, magnesium, calcium, and ammonium-using colorimetric methods and a smartphone for data reading and storage. The sensor effectively detects typical soil nutrient concentrations, showing strong linearity and adequate detection limits. For nitrate, the RGB method resulted in an R 2 of 0.992, a detection range of 0.5 to 10.0 mmol L-1, and an LOD of 0.299 mmol L-1. Calcium quantification using grayscale displayed an R 2 of 0.993, a detection range of 2.0 to 6.0 mmol L-1, and an LOD of 0.595 mmol L-1. Magnesium was best quantified using the hue color space, with an R 2 of 0.999, a detection range of 1.0 to 6.0 mmol L-1, and an LOD of 0.144 mmol L-1. Similarly, ammonium detection using the hue color space had an R 2 of 0.988, a range of 0.5 to 2.5 mmol L-1, and an LOD of 0.170 mmol L-1. This device enhances soil fertility assessment accessibility, supporting PA implementation and higher food production.

Strategies Employed to Design Biocompatible Metal Nanoparticles for Medical Science and Biotechnology Applications.

The applicability of nanomaterials has evolved in biomedical domains thanks to advances in biocompatibility strategies and the mitigation of cytotoxic effects, allowing diagnostics, imaging, and therapeutic approaches. The application of nanoparticles (NP), particularly metal nanoparticles (mNPs), such as gold (Au) and silver (Ag), includes inherent challenges related to the material characteristics, surface modification, and bioconjugation techniques. By tailoring the surface properties through appropriate coating with biocompatible molecules or functionalization with active biomolecules, researchers can reach a harmonious interaction with biological systems or samples (mostly fluids or tissues). Thus, this review highlights the mechanisms associated with the obtention of biocompatible mNP and presents a comprehensive overview of methods that facilitate safe and efficient production. Therefore, we consider this review to be a valuable resource for all researchers navigating this dynamic field.

Flexible Label-Free Platinum and Bio-PET-Based Immunosensor for the Detection of SARS-CoV-2.

The demand for new devices that enable the detection of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) at a relatively low cost and that are fast and feasible to be used as point-of-care is required overtime on a large scale. In this sense, the use of sustainable materials, for example, the bio-based poly (ethylene terephthalate) (Bio-PET) can be an alternative to current standard diagnostics. In this work, we present a flexible disposable printed electrode based on a platinum thin film on Bio-PET as a substrate for the development of a sensor and immunosensor for the monitoring of COVID-19 biomarkers, by the detection of L-cysteine and the SARS-CoV-2 spike protein, respectively. The electrode was applied in conjunction with 3D printing technology to generate a portable and easy-to-analyze device with a low sample volume. For the L-cysteine determination, chronoamperometry was used, which achieved two linear dynamic ranges (LDR) of 3.98-39.0 µmol L-1 and 39.0-145 µmol L-1, and a limit of detection (LOD) of 0.70 µmol L-1. The detection of the SARS-CoV-2 spike protein was achieved by both square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) by a label-free immunosensor, using potassium ferro-ferricyanide solution as the electrochemical probe. An LDR of 0.70-7.0 and 1.0-30 pmol L-1, with an LOD of 0.70 and 1.0 pmol L-1 were obtained by SWV and EIS, respectively. As a proof of concept, the immunosensor was successfully applied for the detection of the SARS-CoV-2 spike protein in enriched synthetic saliva samples, which demonstrates the potential of using the proposed sensor as an alternative platform for the diagnosis of COVID-19 in the future.

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.

Biosensing strategies for the electrochemical detection of viruses and viral diseases - A review.

Viruses are the causing agents for many relevant diseases, including influenza, Ebola, HIV/AIDS, and COVID-19. Its rapid replication and high transmissibility can lead to serious consequences not only to the individual but also to collective health, causing deep economic impacts. In this scenario, diagnosis tools are of significant importance, allowing the rapid, precise, and low-cost testing of a substantial number of individuals. Currently, PCR-based techniques are the gold standard for the diagnosis of viral diseases. Although these allow the diagnosis of different illnesses with high precision, they still present significant drawbacks. Their main disadvantages include long periods for obtaining results and the need for specialized professionals and equipment, requiring the tests to be performed in research centers. In this scenario, biosensors have been presented as promising alternatives for the rapid, precise, low-cost, and on-site diagnosis of viral diseases. This critical review article describes the advancements achieved in the last five years regarding electrochemical biosensors for the diagnosis of viral infections. First, genosensors and aptasensors for the detection of virus and the diagnosis of viral diseases are presented in detail regarding probe immobilization approaches, detection methods (label-free and sandwich), and amplification strategies. Following, immunosensors are highlighted, including many different construction strategies such as label-free, sandwich, competitive, and lateral-flow assays. Then, biosensors for the detection of viral-diseases-related biomarkers are presented and discussed, as well as point of care systems and their advantages when compared to traditional techniques. Last, the difficulties of commercializing electrochemical devices are critically discussed in conjunction with future trends such as lab-on-a-chip and flexible sensors.

Applications of biosensors in Alzheimer's disease diagnosis.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive and irreversible cognitive decline. Currently, it affects 36 million people and due to population ageing it is estimated that in 2030 disease incidence will reach 60 million individuals. The precise diagnosis of AD is still a complex task, being mainly performed by cerebrospinal fluid (CSF) analysis or neuroimaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI). Despite being effective these techniques are expensive, time-consuming and not accessible for most part of the population. In this scenario biosensors are presented as promising alternatives for simple, rapid and low cost diagnosis of AD. In this revision we summarize the recent advances on biosensors that brings more accessibility to AD diagnosis. We introduce the most used biorecognition elements in miniaturized biosensing systems as well as AD biomarkers present in CSF, in plasma and in genetic material which can be used for disease identification even in early stages. The recent developed biosensors for AD diagnosis using optical, electrochemical and colorimetric techniques as well as their strategies and analytical performances are discussed. Advancements in signal amplification methodologies with nanomaterials to increase biosensors sensitivity are also presented. This review highlights the potential of biosensors to be used as an accurate and portable tool to improve the early AD diagnosis.

Flexible platinum electrodes as electrochemical sensor and immunosensor for Parkinson's disease biomarkers.

In this study, platinum electrodes were fabricated on the bio-based poly(ethylene terephthalate) (Bio-PET) substrates for the development of flexible electrochemical sensors for the detection of Parkinson's disease biomarkers. Dopamine was detected by voltammetric measurements, displaying a 3.5 × 10-5 mol L-1 to 8.0 × 10-4 mol L-1 linear range with a limit of detection of 5.1 × 10-6 mol L-1. Parkinson's disease protein 7 (PARK7/DJ-1) was successfully detected by electrochemical impedance spectroscopy after electrode functionalization with specific anti-PARK7/DJ-1 antibodies. In this case, analytical curves presented a linear behavior from 40 ng mL-1 to 150 ng mL-1 of PARK7/DJ-1 with a limit of detection of 7.5 ng mL-1. Besides, the electrodes did not suffer any change in the electrochemical response after manual tests of mechanical tension. The proposed sensor and immunosensor were applied for the determination of Parkinson's disease biomarkers concentrations found in the human body, being adequate as an alternative method to diagnose this disease.

Eyeglasses-based tear biosensing system: Non-invasive detection of alcohol, vitamins and glucose.

We report on a wearable tear bioelectronic platform, integrating a microfluidic electrochemical detector into an eyeglasses nose-bridge pad, for non-invasive monitoring of key tear biomarkers. The alcohol-oxidase (AOx) biosensing fluidic system allowed real-time tear collection and direct alcohol measurements in stimulated tears, leading to the first wearable platform for tear alcohol monitoring. Placed outside the eye region this fully wearable tear-sensing platform addresses drawbacks of sensor systems involving direct contact with the eye as the contact lenses platform. Integrating the wireless electronic circuitry into the eyeglasses frame thus yielded a fully portable, convenient-to-use fashionable sensing device. The tear alcohol sensing concept was demonstrated for monitoring of alcohol intake in human subjects over multiple drinking courses, displaying good correlation to parallel BAC measurements. We also demonstrate for the first time the ability to monitor tear glucose outside the eye and the utility of wearable devices for monitoring vitamin nutrients in connection to enzymatic flow detector and rapid voltammetric scanning, respectively. These developments pave the way to build an effective eyeglasses system capable of chemical tear analysis.