Unleashing inkjet-printed nanostructured electrodes and battery-free potentiostat for the DNA-based multiplexed detection of SARS-CoV-2 genes

Following the global COVID-19 pandemic triggered by SARS-CoV-2, the need for rapid, specific and cost-effective point-of-care diagnostic solutions remains paramount. Even though COVID-19 is no longer a public health emergency, the disease still poses a global threat leading to deaths, and it continues to change with the risk of new variants emerging causing a new surge in cases and deaths. Here, we address the urgent need for rapid, cost-effective and point-of-care diagnostic solutions for SARS-CoV-2. We propose a multiplexed DNA-based sensing platform that utilizes inkjet-printed nanostructured gold electrodes and an inkjet-printed battery-free near-field communication (NFC) potentiostat for the simultaneous quantitative detection of two SARS-CoV-2 genes, the ORF1ab and the N gene. The detection strategy based on the formation of an RNA-DNA sandwich structure leads to a highly specific electrochemical output. The inkjet-printed nanostructured gold electrodes providing a large surface area enable efficient binding and increase the sensitivity. The inkjet-printed battery-free NFC potentiostat enables rapid measurements and real-time data analysis via a smartphone application, making the platform accessible and portable. With the advantages of speed (5 min), simplicity, sensitivity (low pM range, ∼450% signal gain) and cost-effectiveness, the proposed platform is a promising alternative for point-of-care diagnostics and high-throughput analysis that complements the COVID-19 diagnostic toolkit.

Nanomaterial-based Electrochemical Sensors for Multiplex Medicinal Applications

This review explores the advancements in nanomaterial-based electrochemical sensors for the multiplex detection of medicinal compounds. The growing demand for efficient and selective detection methods in the pharmaceutical field has prompted significant research into the development of electrochemical sensors employing nanomaterials. These materials, defined as functional materials with at least one dimension between 1 and 100 nanometers, encompass metal nanoparticles, polymers, carbon-based nanocomposites, and nano-bioprobes. These sensors are characterized by their enhanced sensitivity and selectivity, playing a crucial role in simultaneous detection and offering a comprehensive analysis of multiple medicinal complexes within a single sample. The review comprehensively examines the design, fabrication, and application of nanomaterial- based electrochemical sensors, focusing on their ability to achieve multiplex detection of various medicinal substances. Insights into the strategies and nanomaterials employed for enhancing sensor performance are discussed. Additionally, the review explores the challenges and future perspectives of this evolving field, highlighting the potential impact of nanomaterial-based electrochemical sensors on the advancement of medicinal detection technologies.

Toward the early diagnosis of tuberculosis: A gold particle-decorated graphene-modified paper-based electrochemical biosensor for Hsp16.3 detection

Tuberculosis (TB) currently remains a major life-threatening disease as it can be fatal if not treated properly or in a timely manner. Herein, we first describe a disposable and cost-effective paper-based electrochemical biosensor based on a gold particle-decorated carboxyl graphene (AuPs/GCOOH)-modified electrode for detecting heat shock protein (Hsp16.3), which is a specific biomarker indicating the onset of TB infection. The device pattern was first engineered to facilitate detection procedures and printed on low-cost filter paper to create hydrophobic and hydrophilic regions using a wax printing technique. Immunoassays proceeded in a half-sandwich format because it is a reagent-less approach and requires no labeling step. The fabrication of the immunosensor began with GCOOH drop casting, the electrochemical deposition of AuPs, and the establishment of a biorecognition layer against Hsp16.3 utilizing 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS)-sulfo standard chemistry. The appearance of Hsp16.3 resulted in a substantial decrease in the electrochemical signal response of the redox probe employed [Fe (CN)6]3-/4- due to the created immunocomplexes that possess insulation properties. GCOOH enables direct antibody immobilization, and AuPs enhance the electrochemical properties of the sensor. This proposed immunosensor, while requiring only a miniscule sample volume (5 μL), achieved superior performance in terms of the limit of detection, measuring at 0.01 ng/mL. Our platform was confirmed to be highly specific to Hsp16.3 and can rapidly detect TB-infected sera without necessitating any pre-enrichment (20 min), making it an alternative and particularly suitable for the early diagnosis of TB in resource-scarce countries.

A facile and automated microfluidic electrochemical platform for the in-field speciation analysis of inorganic arsenic

An automated microfluidic electrochemical platform was developed for the rapid in-field analysis of arsenic speciation. Herein, we integrated an electrochemical sensing and microfluidic channel for the simultaneous determination of As(III) and total inorganic As (total iAs) within a single device. The platform was fabricated by assembling a gold nanoparticle-modified screen-printed graphene electrode (AuNP/SPGE) on a hydrophilic polyethylene terephthalate (PET) sheet that was specially designed to enclose a microfluidic channel with dual flow channels for separate determination of the two species. While As(III) can be promptly detected with the AuNP/SPGE on one end, thioglycolic acid stored in glass fiber is employed on the other end to reduce As(V) before being electrochemically analyzed on the AuNP/SPGE as total iAs; the difference represents the amount of As(V). With a wireless potentiostat and a smartphone equipped with Bluetooth technology, the overall procedure can be fully automated and accomplished merely within 9 min. The linear ranges for the determination of As(III) and total iAs were found to be 50-1000 and 100-1500 ng/mL with detection limits of 3.7 and 17 ng/mL, respectively. The proposed method was validated and applied for the inorganic As speciation of various food samples with satisfactory results compared to those obtained with the standard HPLC-ICP‒MS protocol. This novel microfluidic electrochemical platform offers numerous advantages, notably for its simplicity, speed, low cost, and portability for on-site analysis, which conclusively makes it a highly promising analytical device for the speciation of inorganic arsenic.

Sequential Flow Controllable Microfluidic Device for G-Quadruplex DNAzyme-Based Electrochemical Detection of SARS-CoV-2 Using a Pyrrolidinyl Peptide Nucleic Acid

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been a significant health issue globally. Point-of-care (POC) testing that can offer a rapid and accurate diagnosis of SARS-CoV-2 at the early stage of infection is highly desirable to constrain this outbreak, especially in resource-limited settings. Herein, we present a G-quadruplex DNAzyme-based electrochemical assay that is integrated with a sequential flow controllable microfluidic device for the detection of SARS-CoV-2 cDNA. According to the detection principle, a pyrrolidinyl peptide nucleic acid probe is immobilized on a screen-printed graphene electrode for capturing SARS-CoV-2 DNA. The captured DNA subsequently hybridizes with another DNA probe that carries a G-quadruplex DNAzyme as the signaling unit. The G-quadruplex DNAzyme catalyzes the H2O2-mediated oxidation of hydroquinone to benzoquinone that can be detected using square-wave voltammetry to give a signal that corresponds to the target DNA concentration. The assay exhibited high selectivity for SARS-CoV-2 DNA and showed a good experimental detection limit at 30 pM. To enable automation, the DNAzyme-based assay was combined with a capillary-driven microfluidic device featuring a burst valve technology to allow sequential sample and reagent delivery as well as the DNA target hybridization and enzymatic reaction to be operated in a precisely controlled fashion. The developed microfluidic device was successfully applied for the detection of SARS-CoV-2 from nasopharyngeal swab samples. The results were in good agreement with the standard RT-PCR method and could be performed within 20 min. Thus, this platform offers desirable characteristics that make it an alternative POC tool for COVID-19 diagnosis.

Toward the rapid diagnosis of sepsis: dendritic copper nanostructure functionalized diazonium salt modified screen-printed graphene electrode for IL-6 detection

Sepsis, an infectious disease affecting millions of people's health worldwide each year, calls for urgent attention to an improvement of analytical devices. Chemiluminescence immunoassay is a typical diagnostic method utilized to assess the risk development of sepsis. However, due to its high-cost, delayed, and complicated procedure, the practical utilization is therefore undoubtedly limited, especially for point-of-care test. Herein, we fabricated for the first time an immunosensor based on dendritic copper nanostructures (CuNSs) combined with 4-aminobenzoic acid (4-AB, the diazonium salt) as antibody linker modified on a screen-printed graphene electrode for the early detection of the sepsis biomarker interleukin-6 (IL-6). The electrode fabrication is made by electrodeposition, thus eliminating the multistep of nanomaterial synthesis and time wasting. The resulting dendritic CuNSs significantly increase the effective surface area (1.2 times) and the sensor's performance. The morphology of this combination was characterized using CV, EIS, SEM, EDX, and FTIR techniques. In the detection process, the appearance of IL-6 suppresses the current response of the redox probe indicator measured by differential pulse voltammetry due to the antibody-antigen complex. The subtraction of signal (ΔI) was interpreted as IL-6 concentration. This sensor exhibited a linear range from 0.05 to 500 pg mL-1 with low detection limit of 0.02 pg mL-1, proving a possibility for early sepsis screening. In addition, the established immunosensor can successfully quantify IL-6 in human serum sample, in which the results agreed well with those achieved using the standard approach, further showing high practical applicability of this developed immunosensor.

Electrochemical capillary-driven microfluidic DNA sensor for HIV-1 and HCV coinfection analysis

Electrochemical DNA sensors can be operated in either static or flow-based detection schemes. In static schemes, manual washing steps are still necessary, resulting in a tedious and time-consuming process. In contrast, in flow-based electrochemical sensors, the current response is collected when the solution flows through the electrode continuously. However, the drawback of such a flow system is the low sensitivity due to the limited time for the interaction between the capturing element and the target. Herein, we propose a novel electrochemical capillary-driven microfluidic DNA sensor to combine the advantages of static and flow-based electrochemical detection systems into a single device by incorporating burst valve technology. The microfluidic device with a two-electrode configuration was applied for the simultaneous detection of two different DNA markers, human immunodeficiency virus-1 (HIV-1) and hepatitis C virus (HCV) cDNA, via the specific interaction between pyrrolidinyl peptide nucleic acids (PNA) probes and the DNA target. The integrated system, while requiring a small sample volume (7 μL for each sample loading port) and less analysis time, achieved good performance in terms of the limits of detection (LOD) (3SD_blank/slope) and quantification (LOQ) (10SD_blank/slope) at 1.45 nM and 4.79 nM for HIV and 1.20 nM and 3.96 nM for HCV, respectively. The simultaneous detection of HIV-1 and HCV cDNA prepared from human blood samples showed results that are in complete agreement with the RT‒PCR assay. The results qualify this platform as a promising alternative for the analysis of either HIV-1/HCV or coinfection that can be easily adapted for other clinically important nucleic acid-based markers.

Single-step electropolymerization on a printed sensor towards a conductive thin film polymer for the simultaneous determination of drug metabolites: 5-aminosalicylic acid and sulfapyridine

Amino acid conductive polymers can easily form a thin film on a sensor surface by an electrochemical process. Therefore, we are pioneers in reporting the electropolymerization of L-methionine on the surface of a screen-printed graphene electrode to obtain a disposable electrochemical sensor for determining drug metabolites (5-aminosalicylic acid (5-ASA) and sulfapyridine (SPD)) of sulfasalazine (SSZ) simultaneously. In this work, the developed sensor was facilely created through a single step of electropolymerization under mild conditions (0.1 M phosphate buffer pH 7.0) using cyclic voltammetry. Important parameters in the synthesis process were systematically investigated followed by surface composition and morphology studies. Then, analytical performances, comprising sensitivity, selectivity, stability, reproducibility, and sample preparation, were carefully evaluated. Under optimal conditions, the proposed methodology demonstrated a highly sensitive and selective simultaneous detection of 5-ASA and SPD with wide linear dynamic ranges of 1-50 μM and 80-250 μM and low detection limits of 0.60 and 0.57 μM for 5-ASA and SPD, respectively. To evaluate the potential of the designed sensor, it was successfully applied by simultaneously determining 5-ASA and SPD in real human urine samples on the same day (intra-day study) and on three different days (inter-day study).

Capillary driven microfluidic sequential flow device for point-of-need ELISA: COVID-19 serology testing

A capillary-driven microfluidic sequential flow device, designed for eventual at-home or doctor's office use, was developed to perform an enzyme-linked immunosorbent assay (ELISA) for serology assays. Serology assays that detect SARS-CoV-2 antibodies can be used to determine prior infection, immunity status, and/or individual vaccination status and are typically run using well-plate ELISAs in centralized laboratories, but in this format SARs-CoV-2 serology tests are too expensive and/or slow for most situations. Instead, a point-of-need device that can be used at home or in doctor's offices for COVID-19 serology testing would provide critical information for managing infections and determining immune status. Lateral flow assays are common and easy to use, but lack the sensitivity needed to reliably detect SARS-CoV-2 antibodies in clinical samples. This work describes a microfluidic sequential flow device that is as simple to use as a lateral flow assay, but as sensitive as a well-plate ELISA through sequential delivery of reagents to the detection area using only capillary flow. The device utilizes a network of microfluidic channels made of transparency film and double-sided adhesive combined with paper pumps to drive flow. The geometry of the channels and storage pads enables automated sequential washing and reagent addition steps with two simple end-user steps. An enzyme label and colorimetric substrate produce an amplified, visible signal for increased sensitivity, while the integrated washing steps decrease false positives and increase reproducibility. Naked-eye detection can be used for qualitative results or a smartphone camera for quantitative analysis. The device detected antibodies at 2.8 ng mL-1 from whole blood, while a well-plate ELISA using the same capture and detection antibodies could detect 1.2 ng mL-1. The performance of the capillary-driven immunoassay (CaDI) system developed here was confirmed by demonstrating SARS-CoV-2 antibody detection, and we believe that the device represents a fundamental step forward in equipment-free point-of-care technology.

Large-scale fabrication of ion-selective electrodes for simultaneous detection of Na+, K+, and Ca2+ in biofluids using a smartphone-based potentiometric sensing platform

A significant bottleneck exists for mass-production of ion-selective electrodes despite recent developments in manufacturing technologies. Here, we present a fully-automated system for large-scale production of ISEs. Three materials, including polyvinyl chloride, polyethylene terephthalate and polyimide, were used as substrates for fabricating ion-selective electrodes (ISEs) using stencil printing, screen-printing and laser engraving, respectively. We compared sensitivities of the ISEs to determine the best material for the fabrication process of the ISEs. The electrode surfaces were modified with various carbon nanomaterials including multi-walled carbon nanotubes, graphene, carbon black, and their mixed suspensions as the intermediate layer to enhance sensitivities of the electrodes. An automated 3D-printed robot was used for the drop-cast procedure during ISE fabrication to eliminate manual steps. The sensor array was optimized, and the detection limits were 10^-5 M, 10^-5 M and 10^-4 M for detection of K⁺, Na⁺ and Ca²⁺ ions, respectively. The sensor array integrated with a portable wireless potentiometer was used to detect K⁺, Na⁺ and Ca²⁺ in real urine and simulated sweat samples and results obtained were in agreement with ICP-OES with good recoveries. The developed sensing platform offers low-cost detection of electrolytes for point-of-care applications.

Label free electrochemical DNA biosensor for COVID-19 diagnosis

The COVID-19 pandemic has significantly increased the development of the development of point-of-care (POC) diagnostic tools because they can serve as useful tools for detecting and controlling spread of the disease. Most current methods require sophisticated laboratory instruments and specialists to provide reliable, cost-effective, specific, and sensitive POC testing for COVID-19 diagnosis. Here, a smartphone-assisted Sensit Smart potentiostat (PalmSens) was integrated with a paper-based electrochemical sensor to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A disposable paper-based device was fabricated, and the working electrode directly modified with a pyrrolidinyl peptide nucleic acid (acpcPNA) as the biological recognition element to capture the target complementary DNA (cDNA). In the presence of the target cDNA, hybridization with acpcPNA probe blocks the redox conversion of a redox reporter, leading to a decrease in electrochemical response correlating to SARS-CoV-2 concentration. Under optimal conditions, a linear range from 0.1 to 200 nM and a detection limit of 1.0 pM were obtained. The PNA-based electrochemical paper-based analytical device (PNA-based ePAD) offers high specificity toward SARS-CoV-2 N gene because of the highly selective PNA-DNA binding. The developed sensor was used for amplification-free SARS-CoV-2 detection in 10 nasopharyngeal swab samples (7 SARS-CoV-2 positive and 3 SARS-CoV-2 negative), giving a 100% agreement result with RT-PCR.

A simple and fast flow injection amperometry for the determination of methimazole in pharmaceutical preparations using an unmodified boron-doped diamond electrode

In this work, an automated flow injection analysis (FIA) connected to a boron-doped diamond electrode (BDDE) was originally developed for the analysis of methimazole in pharmaceutical preparations. At a modification-free BDDE, methimazole was easilly oxidized. For the analysis of the mechanisms occurring at the electrode surface, cyclic voltammetry was employed to evaluate the impact of fundamental experimental parameters, such as pH and scan rate, on the BDDE response. For the quantitative detection, the FIA amperometric approach was constructed and used as a fast and sensitive method. The suggested approach provided a broad linear range of 0.5-50 μmol/L and a low detection limit of 10 nmol/L (signal-to-noise ratio = 3). Furthermore, the BDDE was successfully utilized to quantify methimazole in genuine samples from a variety of medicines, and its performance remained steady after more than 50 tests. The findings of amperometric measurements exhibit excellent repeatability, with relative standard deviations of less than 3.9 and 4.7 % for intra-day and inter-day, respectively. The findings indicated that, compared with traditional approaches, the suggested method has the following advantages: quick analysis time, simplicity, highly sensitive output, and no need for complicated operational processes.

Silver-enhanced colloidal gold dip strip immunoassay integrated with smartphone-based colorimetry for sensitive detection of cardiac marker troponin I

Cardiac troponin I (cTnI) is a specific cardiac biomarker for diagnosis of acute myocardial infarction (AMI). A sensitive and simple point-of-care test (POCT) is still required for early detection of AMI. To address this need, we developed a dip strip assay based on sandwich immunoassay coupled with a silver enhancement system. Pre-incubation and silver enhancement were introduced to the dip strip to increase sensitivity. Due to the catalytic reaction of the silver enhancement solution, the red color of AuNPs changed to dark brown as silver ions precipitated and enlarged the AuNPs. The obtained results were easily seen by the naked eye. For quantitative analysis, the color intensity of the results was analyzed using a smartphone with RGB color picker application. The effects of operating parameters (volume of AuNP-Ab conjugate, volume of sample, incubation time, and analysis time) were investigated and optimized. Under optimal conditions, the limit of detection (LOD) by the naked eye was 0.5 ng/mL. The LOD with silver enhancement was 50-fold lower than without. For quantitative analysis using the smartphone, linearity of detection was observed through the range of 0.5-50 ng/mL (R² = 0.9952) and the LOD was 0.12 ng/mL. The developed method was successfully applied to detection of cTnI in serum samples, achieving analytical recoveries and %RSD in the ranges of 96.10-119.17% and 2.91-5.13%, respectively. Additionally, this developed assay was not cross reactive with the potentially interfering serum proteins. These results showed the great potential of this dip strip assay as an alternative POCT for detection of serum cTnI.

Microfluidic Paper-Based Device for Medicinal Diagnosis

BACKGROUND

The demand for point-of-care testing (POCT) devices has rapidly grown since they offer immediate test results with ease of use, makingthem suitable for home self-testing patients and caretakers. However, the POCT development has faced the challenges of increased cost and limited resources. Therefore, the paper substrate as a low-cost material has been employed to develop a cost-effective POCT device, known as "Microfluidic paper-based analytical devices (μPADs)". This device is gaining attention as a promising tool for medicinal diagnostic applications owing to its unique features of simple fabrication, low cost, enabling manipulation flow (capillarydriven flow), the ability to store reagents, and accommodating multistep assay requirements.

OBJECTIVE

This review comprehensively examines the fabrication methods and device designs (2D/3D configuration) and their advantages and disadvantages, focusing on updated μPADs applications for motif identification.

METHODS

The evolution of paper-based devices, starting from the traditional devices of dipstick and lateral flow assay (LFA) with μPADs, has been described. Patterned structure fabrication of each technique has been compared among the equipment used, benefits, and drawbacks. Microfluidic device designs, including 2D and 3D configurations, have been introduced as well as their modifications. Various designs of μPADs have been integrated with many powerful detection methods such as colorimetry, electrochemistry, fluorescence, chemiluminescence, electrochemiluminescence, and SER-based sensors for medicinal diagnosis applications.

CONCLUSION

The μPADs potential to deal with commercialization in terms of the state-of-the-art of μPADs in medicinal diagnosis has been discussed. A great prototype, which is currently in a reallife application breakthrough, has been updated.

Fully integrated colorimetric sensor based on transparency substrate for salbutamol determination

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Facile colorimetric method for the determination of salbutamol based on a simple redox reaction using permanganate as reagent was first investigated at the transparency-based analytical device (TAD).

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The colorimetric TAD sensor was in-lab constructed using a transparent PET-based substrate, showing good compatibility with the permanganate reagent which could result in a vivid color change, clearly observed by the naked eye.

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This proposed colorimetric TAD sensor was successfully applied for salbutamol determination in real drug samples with good accuracy and satisfactory recovery, highlighting the potential capability of this TAD-based colorimetric sensor in pharmaceutical application.

A facile colorimetric method based on a typical redox reaction was first developed for the determination of salbutamol (SAL) using a low-cost and portable transparency-based analytical device (TAD). The TAD was simply fabricated by wax-printing onto a transparent polymer-based substrate to create the hydrophobic barriers and the colorimetric reaction zones where the color changes could be easily observed with the naked eye. Potassium permanganate (KMnO₄), a common oxidizing agent, was deliberately used as a colorimetric reagent for SAL. Once SAL reacted with KMnO₄ in the acidified system, it could undergo oxidation and the color of KMnO₄ subsequently changed from light pink to orange. The color change corresponding to the SAL concentration could be clearly observed at the TAD sensor. In addition, the reaction color could be recorded using a digital camera and then analyzed by ImageJ for quantitative analysis. Under the optimized conditions, the developed method together with the TAD sensor exhibited high efficiency for SAL determination with linearity ranging from 0.5 to 40 mg·L⁻¹ and a limit of detection (LOD) of 0.05 mg·L⁻¹.

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This proposed TAD-based colorimetric method using permanganate as color reagent showed excellent performance in SAL detection with good accuracy and high precision.

Recent developments in microfluidic paper-based analytical devices for pharmaceutical analysis

In the last decade, due to the global increase in diseases, drugs for biomedical applications have increased dramatically. Therefore, there is an urgent need for analytical tools to monitor, treat, investigate, and control drug compounds in diverse matrices. The new and challenging task has been looking for simple, low-cost, rapid, and portable analytical platforms. The development of microfluidic paper-based analytical devices (µPADs) has garnered immense attention in many analytical applications due to the benefit of cellulose structure. It can be functionalized and serves as an ideal channel and scaffold for the transportation and immobilization of various substances. Microfluidic technology has been considered an effective tool in pharmaceutical analysis that facilitates the quantitative measurement of several parameters on cells or other biological systems. The µPADs represent unique advantages over conventional microfluidics, such as the self-pumping capability. They have low material costs, are easy to fabricate, and do not require external power sources. This review gives an overview of the current designs in this decade for µPADs and their respective application in pharmaceutical analysis. These include device designs, choice of paper material, and fabrication techniques with their advantages and drawbacks. In addition, the strategies for improving analytical performance in terms of simplicity, high sensitivity, and selectivity are highlighted, followed by the application of µPADs design for the detection of drug compounds for various purposes. Moreover, we present recent advances involving µPAD technologies in the field of pharmaceutical applications. Finally, we discussed the challenges and potential of µPADs for the transition from laboratory to commercialization.

Resistance-Based Lateral Flow Immunosensor with a NFC-Enabled Smartphone for Rapid Diagnosis of Leptospirosis in Clinical Samples

Leptospirosis is one of the most life-threatening tropical diseases caused by pathogenic Leptospira. To date, a diagnostic device that offers rapid and sensitive detection of leptospires has been still in demand for proper treatment to reduce the mortality rate. Herein, we create a resistance-based lateral flow immunosensor diagnosis device (R-LFI) that integrates near-field communication (NFC) with a portable smartphone for leptospiral detection in clinical samples. A specific monoclonal antibody against the pathogen was coated on a nitrocellulose membrane (NCM) where the test line was collocated. Two electrodes with a sandwich-like configuration were installed employing a conductive double-sided adhesive tape and connected with a NFC smartphone-based detection system. A half-sandwich immunocomplex formation induced high proton conduction, resulting in a considerable decrement in resistive response. The performance of the R-LFI sensor was evaluated using recombinant LipL32 (rLipL32), Leptospira interrogans, and clinical samples. The R-LFI device exhibited linear responses toward rLipL32 protein in phosphate buffer and L. interrogans-spiked healthy human serum samples within the concentration ranging from 1 to 1000 ng mL^-1 (limit of detection (LOD): 0.29 ng mL^-1) and from 10⁴ to 10⁶ cell mL^-1 (LOD: 4.89 × 10³ cell mL^-1), respectively. Our R-LFI sensor successfully detected L. interrogans-positive clinical samples as confirmed by polymerase chain reaction (PCR). This platform offers high specificity, selectivity, simplicity, miniscule sample volume, and no labeling element requirement. These desirable features make it particularly suitable for countries where medical facilities and resources are limited.

A novel delayed lateral flow immunoassay for enhanced detection of SARS-CoV-2 spike antigen

A new detection strategy was developed to improve the sensitivity of a lateral flow immunoassay platform utilizing a delayed hydrophobic barrier fabricated with trimethylsilyl cellulose (TMSC). The SARS-CoV-2 spike receptor-binding domain (SARS-CoV-2 SP RBD) antigen was chosen as a model analyte to demonstrate the superior detectability of this scheme. The novel device consists of 2 separate layers, so-called delayed lateral flow immunoassay (d-LFIA). The upper layer is intended for the analyte or sample flow path, where the test solution flows freely straight to the detection zone to bind with the primary antibody. The lower layer, located just underneath, is designed for the SARS-CoV-2 spike receptor-binding domain-conjugated gold nanoparticles (SARS-CoV-2 SP RBD-AuNPs) used for producing a colorimetric signal. This layer is fabricated with a TMSC barrier to time-delay the movement of SARS-CoV-2 SP RBD-AuNPs, thus allowing the antigen to bind with the primary antibody more efficiently. This platform exhibited a 2.6-fold enhancement in the sensitivity and 9.1-fold improvement in the limit of detection (LOD) as compared with the conventional LFIA. In addition, this d-LFIA device was satisfactorily applied to accurate screening of COVID-19 patients.

Electrochemical immunoassay for detection of hepatitis C virus core antigen using electrode modified with Pt-decorated single-walled carbon nanotubes

Pt nanoparticles deposited on single-walled carbon nanotubes (PtSWCNTs), synthesized via the deposition precipitation (DP) method, were introduced as a substrate for immobilizing antibodies on an electrode surface and then enhancing the electrochemical sensitivity. A PtSWCNT-modified paper-based screen-printed graphene electrode was successfully developed to diagnose hepatitis C virus (HCV) infection. The hepatitis C virus core antigen (HCV-cAg) level was determined by differential pulse voltammetry (DPV) using [Fe(CN)₆]^3-/4- as a redox solution. In the presence of HCV-cAg, the DPV current response decreased with increasing HCV-cAg concentration. Under the optimal conditions, the change in current response provides a good linear correlation with the logarithm of HCV-cAg concentration in the range 0.05 to 1000 pg mL^-1 (RSD < 5%), and the limit of detection was 0.015 pg mL^-1 (or 0.71 fmol L^-1). Furthermore, the proposed immunosensor has been utilized to quantify HCV-cAg in human serum samples with reliable results compared with standard immunoassays (% relative error < 10%). This sensor offers a simple, sensitive, selective, disposable, and inexpensive means for determination of HCV-cAg in human serum samples. The paper-based label-free immunosensor is versatile and feasible for clinical diagnosis.

Electrochemical paper-based antigen sensing platform using plant-derived monoclonal antibody for detecting SARS-CoV-2

The current approaches of diagnostic platforms for detecting SARS-CoV-2 infections mostly relied on adapting the existing technology. In this work, a simple and low-cost electrochemical sensing platform for detecting SAR-CoV-2 antigen was established. The proposed sensor combined the innovative disposable paper-based immunosensor and cost-effective plant-based anti-SARS-CoV-2 monoclonal antibody CR3022, expressed in Nicotiana benthamiana. The cellulose nanocrystal was modified on screen-printed graphene electrode to provide the abundant COOH functional groups on electrode surface, leading to the high ability for antibody immobilization. The quantification of the presence receptor binding domain (RBD) spike protein of SARS-CoV-2 was performed using differential pulse voltammetry by monitoring the changing current of [Fe(CN)₆]^3-/4- redox solution. The current change of [Fe(CN)₆]^3-/4- before and after the presence of target RBD could be clearly distinguished, providing a linear relationship with RBD concentration in the range from 0.1 pg/mL to 500 ng/mL with the minimum limit of detection of 2.0 fg/mL. The proposed platform was successfully applied to detect RBD in nasopharyngeal swab samples with satisfactory results. Furthermore, the paper-based immunosensor was extended to quantify the RBD level in spiked saliva samples, demonstrating the broadly applicability of this system. This electrochemical paper-based immunosensor has the potential to be employed as a point-of-care testing for COVID-19 diagnosis.

Simple manipulation of enzyme-linked immunosorbent assay (ELISA) using an automated microfluidic interface

Among lateral flow immunoassay (LFIA) platforms, enzyme-based LFIAs provide signal amplification to improve sensitivity. However, most enzyme-based LFIAs require multiple timed steps, complicating their utility in point-of-care testing (POCT). Here, we report a microfluidic interface for LFIAs that automates sample, buffer, and reagent addition, greatly simplifying operation while achieving the high analytical stringency associated with more complex assays. The microfluidic interface also maintains the low cost and small footprint of standard LFIAs. The platform is fabricated from a combination of polyester film, double-sided adhesive tape, and nitrocellulose, and fits in the palm of your hand. All reagents are dried on the nitrocellulose to facilitate sequential reagent delivery, and the sample is used as the wash buffer to minimize steps. After the sample addition, a user simply waits 15 min for a colorimetric result. This manuscript discusses the development and optimization of the channel geometry to achieve a simple step enzyme amplified immunoassay. As a proof-of-concept target, we selected lipoarabinomannan (LAM), a WHO identified urinary biomarker of active tuberculosis, to demonstrate the device feasibility and reliability. The results revealed that the device successfully detected LAM in phosphate buffer (PBS) as well as spiked urine samples within 15 min after sample loading. The minimum concentration of color change was achieved at 25 ng mL^-1.

Simple Portable Voltammetric Sensor Using Anodized Screen-Printed Graphene Electrode for the Quantitative Analysis of p-Hydroxybenzoic Acid in Cosmetics

Screen-printed graphene electrodes (SPGEs) have become a potential option in electrochemical applications because of their outstanding properties and disposable approach to miniaturize the electrodes for onsite analysis. Herein, the detection of para-hydroxybenzoic acid (PHBA) in cosmetics using the anodized SPGE has been pioneered and reported. The simple anodization of the SPGE surface was operated by anodic pretreatment at a constant potential on SPGE. The surface morphologies and electrochemical behaviors of anodized SPGEs in different anodization electrolytes were examined. Using anodized SPGE in a phosphate-buffered solution, a nontoxic solution, the sensitivity of PHBA detection was significantly improved compared with pristine SPGE owing to the increase of the polar oxygen-containing functional group during the anodization. The anodized SPGE could detect a PHBA down to 0.073 μmol/L. Finally, the developed anodized SPGE presented high ability and feasibility for PHBA detection in cosmetics. Furthermore, a facile electrode preparation step with a nontoxic solution can present high reproducibility and compatibility with a portable potentiostat for onsite PHBA detection during manufacturing.

Smartphone-based electrochemical analysis integrated with NFC system for the voltammetric detection of heavy metals using a screen-printed graphene electrode

The electrochemical determination of five heavy metals is demonstrated using a wireless and card-sized potentiostat coupled with a smartphone through near-field communication (NFC) technology. A smartphone application was customized to command the NFC potentiostat, collect real-time signals, process the data, and ultimately display the quantities of the selected elements. The screen-printed graphene electrode (SPGE) was simply fabricated and modified using different nanomaterials for each heavy metal. Using differential pulse voltammetry (DPV) mode on the smartphone, the signal peaks were presented at + 10 mV for As(III), + 350 mV for Cr(VI), 0 mV for Hg(II), - 900 mV for Cd(II), and - 680 mV vs. Ag/AgCl for Pb(II). The linear ranges were 25-500, 250-25,000, 100-1,500, 25-750, 25-750 ng mL^-1 with detection limits of 3.0, 40, 16, 2.0, and 0.95 ng mL^-1 for As(III), Cr(VI), Hg(II), Cd(II), and Pb(II), respectively. The reproducibility in terms of relative standard deviation was less than 8.8% (n = 5 devices) of the developed SPGE coupled with the NFC potentiostat. Various samples for different applications (e.g., food safety and environmental monitoring) were analyzed and quantified using the proposed sensors. The results from this sensor indicate that there is no significant difference (95% confidence level) compared with those obtained from the traditional ICP-OES method, while the recoveries were found in the acceptable range of 80-111%. Hence, it can be deduced that this recent advanced technology of the NFC potentiostat developed for heavy metal analysis offers a highly sensitive and selective detection, yet the sensor remains compact, low-cost, and readily accessible to end-users.

Integrated Lateral Flow Electrochemical Strip for Leptospirosis Diagnosis

LipL32 is an outer membrane protein present only on pathogenic Leptospira species, which is the causative agent of leptospirosis. Leptospirosis symptoms are often misdiagnosed with other febrile illnesses as the clinical manifestations are non-specific. Therefore, an accurate diagnostic tool for leptospirosis is indeed critical for proper and prompt treatment. Typical diagnosis via serological assays is generally performed to assess the antibodies produced against Leptospira. However, their delayed antibody response and complicated procedure undoubtedly limit the practical utilization especially in a primary care setting. Here, we demonstrate for the first time an early-stage detection of LipL32 by an integrated lateral-flow immunoassay with an electrochemical readout (eLFIA). A ferrocene trace tag was monitored via differential pulse voltammetry operated on a smartphone-based device, thus allowing for on-field testing. A superior performance in terms of the lowest detectable limit of detection of 8.53 pg/mL and broad linear dynamic range (5 orders of magnitude) among other sensors available thus far was established. Additionally, the developed test strip provided a straightforward yet sensitive approach for diagnosis of leptospirosis using the collected human sera from patients, in which the results were comparable to the real-time polymerase chain reaction technique.

A portable blood lactate sensor with a non-immobilized enzyme for early sepsis diagnosis

Early determination of blood lactate levels may accelerate the detection of sepsis, one of the most time-sensitive illnesses.

An automated fast-flow/delayed paper-based platform for the simultaneous electrochemical detection of hepatitis B virus and hepatitis C virus core antigen

Electrochemical paper-based analytical devices (ePADs) are useful analytical devices that serve as point-of-care testing (POCT) devices for various clinical biomarkers in view of their simplicity, portability, and low-cost format. However, multistep reagent manipulation usually restricts the performance of the device for end users. Herein, we developed a sequential ePAD for sequential immunosensing fluid delivery by integrating dual flow behaviors (fast-flow/delayed) within a single paper platform for the simultaneous detection of hepatitis B surface antigen (HBsAg) and hepatitis C core antigen (HCVcAg). In the present work, a fast-flow channel was used for the automated washing of unbound antigens, while a delayed channel was created to store a redox reagent for further electrochemical analysis with a single buffer loading (the analysis time can be completed within 500 s). Hence, the undesirable complex procedure of multi-step reagent manipulation is scarcely needed by the user. The detection limit of the proposed ePAD was as low as 18.2 pg mL^-1 for HBsAg and 1.19 pg mL^-1 for HCVcAg. In addition, this proposed ePAD was also proven to be effective in real clinical sera from patients to verify its biological applicability. The ePAD sensor shows high promise as an easy-to-use, portable, and extendable sensor for other multiplex biological assays.

Enzyme-free impedimetric biosensor-based molecularly imprinted polymer for selective determination of L-hydroxyproline

This study first reported enzyme-free impedimetric biosensor-based molecularly imprinted polymers for selective and sensitive determination of L-hydroxyproline (L-hyp), a biomarker for the early diagnosis of bone diseases. In recent study, utilizing a single 3-aminophenylboronic acid (3-APBA) to create imprinted surfaces could result in a strong interaction and difficulty in removal of a template molecule. Hence, a mixture of monomer solution containing 3-APBA and o-phenylenediamine (OPD) in the presence of the L-hyp molecule was co-electropolymerized onto the screen-printed electrode using cyclic voltammetry (CV) to eradicate this mentioned limitation. The detection principle of this sensor is relied on alteration of mediator's charge transfer resistance (R_ct) that could be obstructed by L-hyp occupied in imprinted surface. The successfully fabricated biosensor was explored by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and confocal scanning microscopy. Furthermore, the effect of polymer composition on the R_ct response was systematically investigated. The result exhibited that the mixture of monomers could provide the highest change of R_ct due to high selectivity from esterification of 3-APBA and from hydrogen bond of OPD surrounding the template. The sensor showed a significant increase in R_ct in the presence of L-hyp, whereas no observable resistance change was detected in the absence thereof. The calibration curve was obtained in the range from 0.4 to 25 μg mL^-1 with limits of detection (3SD_blank/Slope) and quantification (10SD_blank/Slope) of 0.13 and 0.42 μg mL^-1, respectively. This biosensor exhibited high selectivity and sensitivity and was successfully applied to determine L-hyp in human serum samples with satisfactory results.

An alternative label-free DNA sensor based on the alternating-current electroluminescent device for simultaneous detection of human immunodeficiency virus and hepatitis C co-infection

Coinfection of HIV/HCV is a significant public health issue globally, as it increases the risk of liver cancer in co-infected individuals. The point-of-care testing (POCT) device for HIV/HCV DNA detection is promptly needed for diagnosis and monitoring of the disease progression. Here, the alternating-current electroluminescence (ACEL) technique is proposed as a sensitive POCT sensing platform for HIV/HCV cDNA detection. A conductance-based light emission modulated by the hybridization between a pyrrolidinyl PNA probe and the DNA target enabled the DNA detection in a label-free format. Enhanced electroluminescence was observed in the presence of the target DNA due to the increased proton conductivity. Under the optimal conditions, the linearity range from 1 nM to 1 μM was achieved for HIV and HCV cDNA with LODs of 1.86 pM (HIV cDNA) and 1.96 pM (HCV cDNA). The spiked HIV/HCV cDNA in healthy human serum was successfully detected, demonstrating the feasibility of the developed device for the detection of cDNA in real biological samples. Additionally, simultaneous HIV/HCV cDNA detection on a single ACEL device employing a 2x2-array detection zone design. The cross-reactivity with other viral DNA was shown to be minimal due to the high specificity of the PNA probes used. Finally, the negative and positive samples from the patient's serum were tested and the results were in 100% agreement with the commercial kit based-on real-time PCR method, thus illustrating the high sensitivity and specificity of the developed sensor.

Enhanced and Selective MALDI-MS Detection of Peptides via the Nanomaterial-Dependent Coffee Ring Effect

Nanomaterials have been explored as alternative matrices in MALDI-MS to overcome some of the limitations of conventional matrices. Recently, we demonstrated a new means by which nanomaterials can improve peptide ionization and detection in MALDI-MS analyses by exploiting the tendency of nanomaterials to form "coffee rings" upon drying from liquids. In the current work, we investigate how nanomaterial size and composition affect the signal enhancement of peptides through the coffee-ring effect. From studies of eight different types of nanomaterials ranging in size and composition, we find that most nanomaterials can provide signal enhancement ranging from 2- to 10-fold for individual peptides, as long as a coffee ring is formed. However, when a mixture of peptides is present in a sample, the signal enhancement is the greatest for peptides whose net charge is complementary to the nanomaterial's surface charge. These results suggest that careful design of NM surface properties could allow for selective, enhanced MALDI-MS detection of specific peptides in complex mixtures.

A non-enzymatic disposable electrochemical sensor based on surface-modified screen-printed electrode CuO-IL/rGO nanocomposite for a single-step determination of glucose in human urine and electrolyte drinks

A non-enzymatic disposable electrochemical sensor coupled with an automated sample pretreatment paper-based device was developed to avoid an additional sample preparation step for glucose determination in human urine and electrolyte drinks. The automated sample pretreatment paper-based device was successfully fabricated by the simple coating of a strong alkaline solution on a patterned wax paper, and then attached on an electrochemical sensor. The nanocomposite of copper oxide nanoparticles, ionic liquid and reduced graphene oxide (CuO-IL/rGO) modified on the screen-printed carbon electrode (SPCE) was created and used as a non-enzymatic electrochemical glucose sensor. The presence of the CuO-IL/rGO nanocomposite on the screen-printed electrode surface was confirmed by transmission electron microscopy (TEM), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction spectroscopy (XRD). Under optimal conditions, glucose was measured by dropping 100 μL sample solution on the device and detected via chronoamperometry (CA) using a smartphone potentiostat controlled by Android app., providing a rapid current response within 20 s and linearity in a range of 0.03-7.0 mM with a limit of detection (LOD) of 0.14 μM. Furthermore, this developed device was successfully applied for determining glucose levels in human urine and electrolyte drinks, exporting satisfying results correlated with a commercial enzymatic glucose biosensor and labeled values of the commercial products. Therefore, this device could be an alternative device for a non-enzymatic glucose sensor with single-step sample loading, allowing for real-time analysis, low cost, portability, disposability, and on-field measurement.

Fluorescent paper-based DNA sensor using pyrrolidinyl peptide nucleic acids for hepatitis C virus detection

A novel fluorescent paper-based DNA sensor employing a highly specific pyrrolidinyl peptide nucleic acid (acpcPNA) probe was developed for the sensitive and selective detection of hepatitis C virus (HCV). The acpcPNA was covalently immobilized onto partially oxidized cellulose paper via reductive alkylation between the amine and the aldehyde groups. The fluorescence-based detection was performed by monitoring the fluorescence signal response of a fluorescent dye that selectively binds to the single-strand region of the DNA target over the PNA probe employing a custom-made portable fluorescent camera gadget in combination with a smartphone camera. Under the optimal conditions, a linear relationship between the fluorescence change in the green channel and the amount of HCV DNA from 5 to 100 pmol with a correlation coefficient of 0.9956, and the limit of detection of 5 pmol were obtained for short synthetic oligonucleotides. The acpcPNA probe exhibited very high selectivity for the complementary oligonucleotides over the single-base-mismatched, two-base-mismatched, and non-complementary DNA targets. Benefitting from the signal amplification achieved through the numerous binding sites for the dye provided by the overhanging tail of long ssDNA target sequences, this system was successfully applied to detect the HCV complementary DNA (cDNA) obtained from clinical samples with satisfactory results. The proposed fluorescent paper-based sensor demonstrated a great potential to be used as a low-cost, simple, label-free, sensitive, and selective DNA sensor for point-of-care applications.

Cost-effective paper-based electrochemical immunosensor using a label-free assay for sensitive detection of ferritin

Ferritin, a blood cell protein containing iron, is a crucial biomarker that is used to estimate the risk assessment of iron deficiency anemia. For point-of-care analysis, a reliable, cost-effective, selective, sensitive, and portable tool is extremely necessary. In this study, a label-free electrochemical immunosensor for detecting ferritin using a paper-based analytical device (ePAD) was created. The device pattern was custom designed onto filter paper to successfully fabricate a deliverable immunosensor. Graphene oxide was first modified onto the working electrode using an inkjet printing technique. An activation step of the electrode surface was then performed using standard 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/N-hydroxysulfosuccinimide (sulfo-NHS) chemistry. Anti-ferritin antibodies were covalently immobilized onto the amine-reactive ester surface. The amount of ferritin was monitored by observing the electrochemical signal of the selected redox couple by differential pulse voltammetry (DPV). In the presence of ferritin, the sensor showed a considerable decrease in electrochemical response in a concentration-dependent manner. In contrast, there was no observable change in current response detected in the absence of ferritin. The current response provided a good correlation with ferritin concentrations in the range of 1 to 1000 ng mL-1, and the limit of detection (3SD/slope) was found to be 0.19 ng mL-1. This fabricated immunosensor offered good selectivity, reproducibility, and long-term storage stability. In addition, this proposed immunosensor was successfully applied to detect ferritin in human serum with satisfactory results. The promising results suggested that this handmade paper-based immunosensor may be an alternative device for the diagnosis of iron deficiency anemia.

Toward the Rapid Diagnosis of Sepsis: Detecting Interleukin-6 in Blood Plasma Using Functionalized Screen-Printed Electrodes with a Thermal Detection Methodology

This paper reports the detection of the inflammatory and sepsis-related biomarker, interleukin-6 (IL-6), in human blood plasma using functionalized screen-printed electrodes (SPEs) in conjunction with a thermal detection methodology, termed heat-transfer method (HTM). SPEs are functionalized with antibodies specific for IL-6 through electrodeposition of a diazonium linking group and N'-ethylcarbodiimide hydrochloride (EDC) coupling, which was tracked through the use of cyclic voltammetry and Raman spectroscopy. The functionalized SPEs are mounted inside an additively manufactured flow cell and connected to the HTM device. We demonstrate the ability to detect IL-6 at clinically relevant concentrations in PBS buffer (pH = 7.4) with no significant interference from the similarly sized sepsis-related biomarker procalcitonin (PCT). The limit of detection (3σ) of the system is calculated to correspond to 3.4 ± 0.2 pg mL^-1 with a working range spanning the physiologically relevant concentration levels in both healthy individuals and patients with sepsis, indicating the sensitivity of the sensor is suitable for the application. Further experiments helped provide a proof-of-application through the detection of IL-6 in blood plasma with no significant interference observed from PCT or the constituents of the medium. Due to the selectivity, sensitivity, straightforward operation, and low cost of production, this sensor platform has the potential for use as a traffic light sensor for the multidetection of inflammatory biomarkers for the diagnosis of sepsis and other conditions in which the rapid testing of blood biomarkers has vital clinical application.

Laser engraved microapillary pump paper-based microfluidic device for colorimetric and electrochemical detection of salivary thiocyanate

A microcapillary grooved paper-based analytical device capable of dual-mode sensing (colorimetric and electrochemical detection) was demonstrated for analysis of viscous samples (e.g., human saliva). Herein, a hollow capillary channel was constructed via laser engraved micropatterning functions as a micropump to facilitate viscous fluidic transport, which would otherwise impede analysis on paper devices. Using salivary thiocyanate as a model analyte, the proposed device was found to exhibit a promising sensing ability on paper devices without the need for sample pretreatment or bulky instrumentation, as normally required in conventional methods used for saliva analysis. An extensive linear dynamic range covering detection of salivary thiocyanate for both high and trace level regimes (5 orders of magnitude working range) was collectively achieved using the dual-sensing modes. Under optimal conditions, the limit of detection was 6 μmol L^-1 with a RSD of less than 5%. An excellent stability for the μpumpPAD was also observed for over 30 days. Real sample analysis using the proposed device was found to be in line with the standard chromatographic method. Benefitting from simple fabrication and operation, portability, disposability, low sample volume (20 μL), and low cost (< 1 USD), the μpumpPAD is an exceptional alternative tool for the detection of various biomarkers in saliva specimens.

Impedimetric determination of cortisol using screen-printed electrode with aptamer-modified magnetic beads

A non-invasive aptamer-based electrochemical biosensor using disposable screen-printed graphene electrodes (SPGEs) was developed for simple, rapid, and sensitive determination of cortisol levels. Selective detection of cortisol based on a label-free electrochemical assay was achieved by specific recognition of the cortisol DNA aptamer (CApt). The CApt was modified with streptavidin magnetic beads (MBs) before simple immobilization onto the electrode surface using a neodymium magnet. The electrochemical behavior of the aptamer-based biosensor was assessed by using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) (vs Ag/AgCl). The specific binding between cortisol and CApt resulted in a decrease in charge transfer resistance (R_ct) from EIS using [Fe(CN)₆]^3-/4- with increasing cortisol concentration. Under optimal conditions, a linear range from 0.10 to 100 ng/mL with a low detection limit (3SD/slope) of 2.1 pg/mL was obtained. Furthermore, the proposed biosensing system exhibited a satisfactory recovery in the range 97.4-109.2% with 5.7-6.6% RSD in spiked artificial human sweat. Regarding the applications of this tool, the aptamer-based biosensor has potential to be a versatile and point-of-care (POC) device for simple, sensitive, selective, disposable, and low-cost cortisol detection.

Label-free anti-Müllerian hormone sensor based on polyaniline micellar modified electrode

A label-free electrochemical immunosensor based on polyaniline (PANI) micellar electrode was firstly fabricated for direct AMH detection. To control the size regularity of PANI, a micelle-based method using ammonium peroxydisulfate (APS) as a reducing agent was employed in the polymerization process. The Anti-AMH antibodies were readily immobilized onto PANI via peptide bond to enhance the sensor specificity and sensitivity. This sensor was applied for the detection of AMH, an ovarian response indicator in female related to residual eggs during a woman's monthly cycle. The sensor performances were systematically investigated by differential pulse voltammetry. The anodic peak current decreases with the increase of AMH concentration owing to blocking of electron transfer by AMH. Under the optimal conditions, this sensor offers high sensitivity with a low detection limit of 0.1 ng mL^-1 and a wide linear range of 0.1-4 ng mL^-1, which is sensitive enough to indicate the ability to produce eggs during a woman's monthly cycle. Furthermore, this system requires lower sample volume (5 μL), while offers the simple fabrication with low cost and no synthetic challenge and faster analysis compared with a standard ELISA. Ultimately, this sensor was successfully applied for the detection of AMH in human serum with satisfactory results. Thus, it might be an alternative tool for AMH screening in clinical setting.

Flow-based System: A Highly Efficient Tool Speeds Up Data Production and Improves Analytical Performance

In this review, we cite references from the period between 2015 and 2020 related to the use of a flow-based system as a tool to obtain a modern analytical system for speeding up data production and improving performance. Based on a great deal of concepts for automatic systems, there are several research groups introduced in the development of flow-based systems to increase sample throughput while retaining the reproducibility and repeatability as well as to propose new platforms of flow-based systems, such as microfluidic chip and paper-based devices. Additionally, to apply a developed system for on-site analysis is one of the key features for development. We believe that this review will be very interested and useful for readers because of its impact on developing novel analytical systems. The content of the review is categorized following their applications including quality control and food safety, clinical diagnostics, environmental monitoring and miscellaneous.

Paper-based DNA sensor enabling colorimetric assay integrated with smartphone for human papillomavirus detection

A colorimetric paper-based DNA sensor that relies on the inhibition of PNA-induced AuNPs aggregation was combined with a simple smartphone readout for the point-of-care detection of HPV type 16 DNA.

Miniaturized electrocoagulation approach for removal of polymeric pigments and selective analysis of non- and mono-hydroxylated phenolic acids in wine with HPLC-UV

Electrocoagulation (EC) approach was developed to allow fast sample cleanup step prior to selective analysis of non- and mono-hydroxylated phenolic acids in red wine samples with high performance liquid chromatography hyphenated with UV detection (HPLC-UV). EC system with the wine in KCl_(aq) electrolyte (1.5 mol L⁻¹) was employed removing the polymeric pigments with good recovery of 39 peaks from 64 peaks. The mechanisms mainly involve enrichment induced aggregation and reduction of the pigments at the cathode and the adsorption onto the EC sludge. The EC was further miniaturized employing two intercalated stainless steel spring electrodes at 9.0 V which allowed removal of >99% interference peak area from the pigments within 5 s. The recoveries of the target phenolic acids (p-hydroxybenzoic acid, vanillic acid, syringic acid and ferulic acid) were within the range of 86–102%. The repeated analysis of these standards revealed <2 and ≤10% RSD of the intra-day and inter-day precisions, respectively. The linearities of their calibration curves were observed with R² > 0.99. Their method detection limits were within the range of 0.02–0.20 mg L⁻¹.

Electrocoagulation (EC) approach was developed to allow fast sample clean-up step prior to selective analysis of non- and mono-hydroxylated phenolic acids in red wine samples with high performance liquid chromatography hyphenated with UV detection (HPLC-UV).

Paper-based electrochemical biosensor for diagnosing COVID-19: Detection of SARS-CoV-2 antibodies and antigen

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is emerging as a global pandemic outbreak. To date, approximately one million deaths and over 32 million cases have been reported. This ongoing pandemic urgently requires an accurate testing device that can be used in the field in a fast manner. Serological assays to detect antibodies have been proven to be a great complement to the standard method of reverse transcription-polymerase chain reaction (RT-PCR), particularly after the second week of infection. We have developed a specific and sensitive immunosensor for immunoglobulin detection produced against SARS-CoV-2. Unlike other lateral flow-based assays (LFAs) involving the utilization of multiple antibodies, we have reported a label-free paper-based electrochemical platform targeting SARS-CoV-2 antibodies without the specific requirement of an antibody. The presence of SARS-CoV-2 antibodies will interrupt the redox conversion of the redox indicator, resulting in a decreased current response. This electrochemical sensor was proven effective in real clinical sera from patients with satisfactory results. In addition, the proposed format was also extended to antigen detection (the spike protein of SARS-CoV-2), which presents new possibilities for diagnosing COVID-19.

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Electrochemical sensor for COVID-19 diagnostic.

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Serological assay for SARS-CoV-2 antibodies was demonstrated.

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Sensitivity enhancement compared to the traditional LFA devices.

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Applicable to real clinical sera with satisfactory results.

Development of an unmodified screen-printed graphene electrode for nonenzymatic histamine detection

The high requirement for food quality control has inspired the creation of high-performance sensing, cost-effectiveness, and ease to use. Therefore, the aim of this work is to develop nonenzymatic electrochemical platforms for direct detection of histamine using unmodified screen-printed graphene electrodes (SPGEs) for their applications such as evaluation of fish freshness. In alkaline media (0.2 M NaOH), unmodified SPGEs showed a very low oxidation potential of histamine at +0.58 V (vs. Ag/AgCl) avoiding perturbations from other biogenic amines. The developed method offers an excellent selectivity, sensitivity (a limit of detection (at 3SD/slope) of 0.62 mg L^-1) and wide working linear range (5-100 mg L^-1) for histamine detection. In addition, the proposed method was successfully applied to detect histamine in canned fish samples with recovery values ranging from 90.72% to 101.21%. Therefore, this newly proposed method is promising as an alternative choice for the determination of histamine in fish samples and related food products.

A new alternative assay for sensitive analysis of ethylenethiourea and propylenethiourea in fruit samples after their separation

Ultra-high-performance liquid chromatography (UHPLC) coupled with a cobalt phthalocyanine screen-printed carbon electrode (CoPc-SPCE) was developed and validated for quantitative analysis of ethylenethiourea (ETU) and propylenethiourea (PTU). CoPC-SPCE provided high catalytic properties for ETU and PTU oxidation. This fabricated electrode is inexpensive, disposable, and easy to prepare by an in-house screen-printing technique. The chromatographic separation was performed in isocratic mode on a reversed phase C18 (100 mm × 4.6 mm, 3 μm) column, using a 90 : 10 (v/v) ratio of 0.05 M phosphate buffer solution (pH 4) and methanol as the mobile phase with a flow rate of 1.0 mL min^-1 at an oxidation potential of +0.7 V vs. Ag/AgCl. The separation could be achieved within 3 min, and a wide linear range of 0.01-100 μg mL^-1 (r² > 0.99) was obtained for both analytes. The limits of detection (3 S/N) were found to be 0.006 and 0.009 μg mL^-1 for ETU and PTU, respectively. Furthermore, this proposed method was utilized to determine ETU and PTU in fruit samples with satisfactory results, yielding excellent intra-day and inter-day relative standard deviations and recoveries. These results demonstrated that the proposed assay can be used as a new alternative way for inexpensive, rapid, selective and sensitive determination of ETU and PTU in fruit samples.