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In the present study, an alternative platform for trace copper ions (Cu(II)) determination using a diamond electrode in combination with a disposable paper‐based analytical device (d‐PAD) has been proposed. First, the complexation between Cu(II) and 1,10‐phenanthroline ligand was adsorptively accumulated onto a paper that is directly in contact with the diamond electrode and measured via square wave anodic stripping voltammetry. Under the optimal experimental conditions, the peak current was proportional to the concentration of Cu(II) in the range of 0.4–70 ng mL−1, and the detection limit was found to be 0.1 ng mL−1. Most importantly, this platform can be successfully applied to detect trace Cu(II) in different water samples (drinking water, tap water, groundwater and river water) with satisfactory results. Thus, the proposed d‐PAD could be a highly efficient platform for trace Cu(II) determination in environmental samples. [ABSTRACT FROM AUTHOR]

To provide new choices and to replace the complicated steps of synthesizing modified electrodes, this research reports the systematic investigation of the effects of different supporting electrolytes on the electrochemical behavior of vitamin B2 (VB2), vitamin B6 (VB6), and vitamin C (VC) using a common screen-printed carbon electrode (SPCE) to achieve simultaneous detection. The roles of various well-known supporting electrolytes, including Britton–Robinson buffer solution (BRBS), acetate buffer solution (ABS), and phosphate buffer solution (PBS), in the electrochemical oxidation of VB2, VB6, and VC were carefully evaluated by square wave voltammetry (SWV). From a successive investigation based on the ionic conductivity of the species contained in the supporting electrolytes, PBS at pH 3.5 was selected as a suitable supporting electrolyte for the simultaneous detection of VB2, VB6, and VC. Under the optimized conditions, the simultaneous detection of VB2, VB6, and VC provided satisfactory sensitivity, selectivity, and reproducibility even when using a common electrode. To demonstrate the practicality and reliability of the proposed analytical procedure, the simultaneous detection of VB2, VB6, and VC was performed in mixed vegetable and fruit juice samples and urine samples by SWV, and the results were compared with those obtained by chromatographic detection. Therefore, this method was found to be simple and may be a new alternative for the simultaneous determination of VB2, VB6, and VC in practical applications. [ABSTRACT FROM AUTHOR]

This work presents a simple and sensitive electrochemical sensor for the determination of total vitamin K (K1 and K2) using a disposable screen-printed graphene electrode (SPGE). The application for the determination of vitamin K1 in green vegetables by this sensor was developed. The proposed method is based on controlling of negative potential for seconds and scanning it to a positive for oxidation analysis. The capacitance of SPGE was studied and it showed a higher sensitivity for vitamin K determination in comparison to carbon. The parameters, such as the pH of electrolytes, accumulation potential, accumulation time, etc. were investigated. The limit of detection was observed at 0.099 µgmL-1. This method was successfully applied for the determination of the vitamin K1 in various green vegetables. Therefore, the proposed method can be used for quality control of vitamin K1 in natural samples to create the food composition table. [ABSTRACT FROM AUTHOR]

The development of simple fluorescent and colorimetric assays that enable point-of-care DNA and RNA detection has been a topic of significant research because of the utility of such assays in resource limited settings. The most common motifs utilize hybridization to a complementary detection strand coupled with a sensitive reporter molecule. Here, a paper-based colorimetric assay for DNA detection based on pyrrolidinyl peptide nucleic acid (acpcPNA)-induced nanoparticle aggregation is reported as an alternative to traditional colorimetric approaches. PNA probes are an attractive alternative to DNA and RNA probes because they are chemically and biologically stable, easily synthesized, and hybridize efficiently with the complementary DNA strands. The acpcPNA probe contains a single positive charge from the lysine at C-terminus and causes aggregation of citrate anion-stabilized silver nanoparticles (AgNPs) in the absence of complementary DNA. In the presence of target DNA, formation of the anionic DNA-acpcPNA duplex results in dispersion of the AgNPs as a result of electrostatic repulsion, giving rise to a detectable color change. Factors affecting the sensitivity and selectivity of this assay were investigated, including ionic strength, AgNP concentration, PNA concentration, and DNA strand mismatches. The method was used for screening of synthetic Middle East respiratory syndrome coronavirus (MERS-CoV), Mycobacterium tuberculosis (MTB), and human papillomavirus (HPV) DNA based on a colorimetric paper-based analytical device developed using the aforementioned principle. The oligonucleotide targets were detected by measuring the color change of AgNPs, giving detection limits of 1.53 (MERS-CoV), 1.27 (MTB), and 1.03 nM (HPV). The acpcPNA probe exhibited high selectivity for the complementary oligonucleotides over single-base-mismatch, two-base-mismatch, and noncomplementary DNA targets. The proposed paper-based colorimetric DNA sensor has potential to be an alternative approach for simple, rapid, sensitive, and selective DNA detection. [ABSTRACT FROM AUTHOR]

A boron-doped diamond (BDD) electrode coupled to flow injection analysis (FIA) was firstly developed for determination of N-acetyl- L-cysteine (NAC) in drug formulations. The effects of experimental parameters including pH, applied potential and scan rate on the response were investigated. FIA amperometry was applied as an automatic method for the quantitative detection of trace amounts of NAC. A wide linear range of 0.5-50 µmol/L and a low detection limit of 10 nmol/L were obtained. The results of amperometric determinations show a very good reproducibility, and the RSD for the measurement based on 10 measurements was <3.7 % and <4.1 % for intra- and inter-day, respectively. The benefits of the proposed method are fast, simple, sensitive and no requirement of complicated operational steps. [ABSTRACT FROM AUTHOR]

A disposable gas-sensing paper-based device (gPAD) was fabricated in origami design which integrates the gas adsorbent and the electrochemical detection zone in a single device. The gPAD for the determination of NOx gas uses a screen-printed graphene electrode modified with copper nanoparticles (CuNP/SPGE) to achieve high sensitivity and selectivity. The gPAD detects both, NO and NO 2 (as NOx) with same current responses. The measurement could be performed directly through differential pulse voltammetry (DPV) with a detection limit as low as 0.23 vppm and 0.03 vppm with exposure times of 25 min and 1 h, respectively. The reproducibility in terms of relative standard deviation was less than 5.1% (n = 7 devices) at 25, 75 and 125 vppm NO 2 and the life-time of this device was more than 30 days. The gPAD was applied to detect NOx in air and exhaust gases from cars. In comparison with spectrophotometry, there are no significant differences between both methods using a paired t -test of the results on a 95% confidence level. The designed gPAD can provide a new template model for other gas sensors with features of disposability and portability for fieldwork analysis at low cost. Image 1 • A disposable gas-sensing paper-based device (gPAD) for electrochemical detection of NOx was demonstrated for the first time. • Electrochemical detection using CuNP/SPGE coupled with gas adsorber was integrated into a one-shot gPAD sensor. • Simplicity in preparation and handling of the sensor, low-cost and low limit of detection are high-lighted features. [ABSTRACT FROM AUTHOR]

A simple and low cost method for rapid detection of Pb 2+ was developed in this study using a simple fluorescent probe, biotin-4-fluorescein. The presence of Pb 2+ induced the color change of fluorescein from yellow to pink which can be detected visually by naked eyes. The color change of biotin-4-fluorescein was not observed while testing with other metal ions, such as Fe 3+ , Cu 2+ , Ca 2+ , Co 2+ and Cd 2+ , indicating the selectivity of fluorescein derivative with Pb 2+ . Moreover, the color change was observed at pH above 7.0, and the pink color got more intense when increasing pH. Adding EDTA, a chelating reagent, into the solution of biotin-4-fluorescein/Pb 2+ resulted to the rebound of the color to the original color of free biotin-4-fluorescein. The fluorescence spectra of fluorescein decreased with increasing Pb 2+ concentration, and the quenching was enhanced at higher pH. The association constant (K a ) of 2.00 × 10 4  M -1 was calculated from the fluorescence spectra with the limit of detection (LOD) and the limit of quantitation (LOQ) of 1.38 × 10 -5  M (2.86 ppm) and 4.61 × 10 -5  M (9.55 ppm), respectively. Job's plot analysis indicated 2:1 ratio of binding interaction. Pb 2+ in untreated wastewater was quantified for 24.99 ppm using this method. This quick analysis can be beneficial for the application of lead detection in real sample solutions, such as wastewater from industrial factories., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

A novel sensing material for L-hydroxyproline (Hyp) detection was developed by synthesizing a bismuth film (BiF) and poly(L-hydroxyproline) (Poly(Hyp)) on a screen-printed graphene electrode (SPGE). Initially, the BiF electrodeposition was produced on the SPGE surface, followed by the Poly(Hyp) electropolymerization, resulting in the obtained Poly(Hyp)/BiF/SPGE. The morphology of a sponge-like thin film of Poly(Hyp)/BiF on SPGE had uniform nanometer-sized cavities on the graphene surface, offering a large electroactive area for interaction with the target substance. Cyclic and differential pulse voltammetry was used to examine the sensing performance of the proposed sensor, which revealed that the Poly(Hyp)/BiF/SPGE had the highest response toward Hyp detection. This was attributed to BiF and Poly(Hyp) can facilitate the transfer of electrons at an electrode/solution interface, resulting in an effective sensor for the detection of Hyp. Under the optimal conditions, the quantification of the proposed sensor was found to be linearly related to Hyp concentrations in the range of 0.01-5.0 mM with a limit of detection of 9.2 μM. Moreover, the interference of other substances detected in biological fluids showed no effect based on the ±5% error, indicating good selectivity for Hyp detection. In real applications, the proposed assay successfully analyzed Hyp in human urine samples, yielding satisfactory results with recoveries in the acceptable range of 98%-102%. Therefore, this facilely synthesized approach could be a suitable candidate to obtain a material to fabricate a new sensor for the measurement of Hyp, an important biomarker in the human body., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Discovering alternative analytical techniques is crucial for practical applications; thus, this work aims to develop an innovative and simple electrochemical sensor for melanoma and the clinical diagnosis of related disorders by the simultaneous determination of 3,4-dihydroxy-L-phenylalanine (L-DOPA) and L-tyrosine (L-Tyr). The fabrication is based on the layer-by-layer electrodeposition of poly L-proline (poly(L-pro)) and nanodiamond (ND) onto a screen-printed graphene electrode (SPGE). The poly(L-pro)/ND/SPGEs were morphologically characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, and Raman spectroscopy followed by electrochemical investigation using cyclic voltammetry, differential pulse voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. These modifier-based electrodes pave a feasible way to unlock the coexisting interfering substances from screen-printing ink composition and improve the sensitivity. Additionally, computational chemistry calculations were performed to fully comprehend the sensing behavior on both target analytes. Under optimal conditions, the developed sensor provided linear concentration ranges of 0.075-50 μM, with a detection limit of 0.021 μM for L-DOPA, and 2.5-120 μM with a detection limit of 0.74 μM for L-Tyr. To demonstrate the reliability of the poly(L-pro)/ND/SPGE in practical application, it was successfully applied to the determination of these analytes in human urine and blood serum samples, with satisfactory recovery ranges (81.73-110.62% for L-DOPA and 82.17-110.01% for L-Tyr) and relative standard deviations (0.69-9.90% for L-DOPA and 0.40-9.55% for L-Tyr). Due to its simplicity, long-term stability (> 87.8% of their initial currents after 35 days), and portability, the developed sensor is a promising alternative analytical method for on-site clinical monitoring., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

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., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

1-Hydroxypyrene (1-OHP), a metabolite of polycyclic aromatic hydrocarbons (PAHs), is a frequently used biomarker for assessing human exposure to PAHs. Therefore, the technology that provides a quick, simple, cost-effective, portable, accurate, precise, and reliable test is still in great demand. To the best of our knowledge, the creation of an electrochemical device based on poly(l-glutamic acid)-modified a screen-printed graphene electrode (poly(L-GA)/SPGE) for 1-OHP detection was described for the first time. The developed sensor was simply and rapidly manufactured via only a single step of electropolymerization. All the concerned parameters and electroanalytical conditions were studied to obtain the best performance of the methodology. Under optimal conditions, the 1-OHP sensing provided a linear range of 1-1000 nM with the limits of detection and quantification of 0.95 and 3.16 nM, respectively. Moreover, this developed sensor was successfully utilized by determining 1-OHP in human urine samples. In comparison with conventional methods, this newly proposed electrochemical methodology might be tremendously valuable for 1-OHP evaluation in environmental and occupational applications, leading to the early detection of illness risk linked to PAHs in the human body., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

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., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

This work presents an all-in-one origami paper-based electrochemical platform for simple and inexpensive l-cysteine (Cys) detection using Cys as a monomer for modifying electrode surfaces. The proposed method combines the steps of electropolymerization and detection into a single device to offer a highly convenient method for the end-user. In comparison, the sensitivity toward Cys detection is a significantly increased using this modified electrode. The developed device provided a linear concentration range of 10-800 μM with a limit of detection of 5.5 μM. For application, the device was successfully applied to detect Cys in different food products such as wheat flour, bread, and cake with satisfactory results, yielding excellent intra-day and inter-day relative standard deviations (1.5-4.9%) and recoveries (84.2-110.8%). This discovery is important from the viewpoint of the development of Cys detection in other applications in the future., (Copyright © 2021 Elsevier B.V. All rights reserved.)

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., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

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., (Copyright © 2021 Elsevier B.V. All rights reserved.)

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., (Copyright © 2021 Elsevier B.V. All rights reserved.)

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.

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.

The simultaneous detection of multiple analytes from a single sample is a critical tool for the analysis of real world samples. However, this is challenging to accomplish in the field by current electroanalytical techniques, where tuning assay conditions towards a target analyte often results in poor selectivity and sensitivity for other species in the mixture. In this work, an electrochemical paper-based analytical device (ePAD) capable of performing simultaneous electrochemical experiments in different solution conditions on a single sample was developed for the first time. We refer to the system as a Janus-ePAD after the two-faced Greek god because of the ability of the device to perform electrochemistry on the same sample under differing solution conditions at the same time with a single potentiostat. In a Janus-ePAD, a sample wicks down two channels from a single inlet towards two discreet reagent zones that adjust solution conditions, such as pH, before flow termination in two electrochemical detection zones. These zones feature independent working electrodes and shared reference and counter electrodes, facilitating simultaneous detection of multiple species at each species' optimal solution condition. The device utility and applicability are demonstrated through the simultaneous detection of two biologically relevant species (norepinephrine and serotonin) and a common enzymatic assay product (p-aminophenol) at two different solution pH conditions. Janus-ePADs show great promise as an inexpensive and broadly applicable platform which can reduce the complexity and/or number of steps required in multiplexed analysis, while also operating under the optimized conditions of each species present in a mixture., (Copyright © 2019 Elsevier B.V. All rights reserved.)

A label-free electrochemical DNA sensor based on pyrrolidinyl peptide nucleic acid (acpcPNA)-immobilized on a paper-based analytical device (PAD) was developed. Unlike previous PNA-based electrochemical PAD (ePAD) sensors where the capture element was placed directly on the electrode, acpcPNA was covalently immobilized onto partially oxidized cellulose paper allowing regeneration by simple PAD replacement. As an example application, a sensor probe was designed for Mycobacterium tuberculosis (MTB) detection. The ePAD DNA sensor was used to determine a synthetic 15-base oligonucleotide of MTB by measuring the fractional change in the charge transfer resistance (R ct ) obtained from electrochemical impedance spectroscopy (EIS). The R ct of [Fe(CN) 6 ] 3-/4- before and after hybridization with the target DNA could be clearly distinguished. Cyclic voltammetry (CV) was used to verify the EIS results, and showed an increase in peak potential splitting in a similar stepwise manner for each immobilization step. Under optimal conditions, a linear calibration curve in the range of 2-200 nM and the limit of detection 1.24 nM were measured. The acpcPNA probe exhibited very high selectivity for complementary oligonucleotides over single-base-mismatch, two-base-mismatch and non-complementary DNA targets due to the conformationally constrained structure of the acpcPNA. Moreover, the ePAD DNA sensor platform was successfully applied to detect PCR-amplified MTB DNA extracted from clinical samples. The proposed paper-based electrochemical DNA sensor has potential to be an alternative device for low-cost, simple, label-free, sensitive and selective DNA sensor., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In this present work, a novel electrochemical immunosensor employing a screen-printed graphene electrode (SPGE) for a simple and highly sensitive determination of C-reactive protein (CRP) in a sandwich-type format was proposed. The sensor comprised of two CRP-specific antibodies: an unlabeled capture primary antibody (Anti-1°Ab) and an electrochemically detectable anthraquinone-labeled signaling secondary (AQ-2°Ab) antibody. The Anti-1°Ab was first covalently anchored onto an L-cysteine/gold-modified disposable SPGE (L-Cys/Au/SPGE) to create the anti-CRP surface. After binding of the CRP and the AQ-2°Ab, the electrochemical signal response was measured using differential pulse voltammetry (DPV). In the presence of CRP, the sensor exhibited a significant increase in the AQ current at AQ-2°Ab compared to the negative control. The CRP concentration was detected in the range of 0.01-150 µg/mL, and the limit of detection (LOD) (S/N = 3) and limit of quantitation (LOQ) (10 SD/Slope) were 1.5 ng/mL and 10 ng/mL, respectively. This sensor exhibited very high sensitivity in determining CRP and was successfully applied to detect CRP in certified human serum with satisfactory results. The developed sensor is suitable as an alternative method for determination of CRP and the same principle may be further applied to determine other clinically important target molecules., (Copyright © 2018 Elsevier B.V. All rights reserved.)