A Novel DNA Biosensor Based on a Pencil Graphite Electrode Modified with Polypyrrole/Functionalized Multiwalled Carbon Nanotubes for Determination of 6-Mercaptopurine Anticancer Drug

A label-free immunosensor for sensitive detection of RACK 1 cancer biomarker based on conjugated polymer modified ITO electrode

A new flexible biosensor based on conjugated polymer functionalized indium tin oxide (ITO) sheet was fabricated for Receptor for Activated C Kinase 1 (RACK 1) determination. Poly(3-thiophene acetic acid) (P(Thi-Ac)) was used as an immobilization matrix for construction of RACK 1 immunosensor. This polymer had a great number of carboxyl groups on its end site and these carboxyl ends provided anchoring points to the anti-RACK 1 antibodies. Anti-RACK 1 antibodies were covalently attached on the ITO electrode and recognized the RACK 1 antigens. Electrochemical characterizations were made by employing electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. Additionally, single frequency impedance method (SFI) was applied to follow the specific biointeraction between antibody and antigen. As a result of specific biointeraction, the designed immunosensor exhibited a wide linear detection range between 0.01 pg/mL and 2 pg/mL RACK 1 with a detection limit of 3.1 fg/mL. Scanning electron microscopy and atomic force microscopy analyses were employed for electrode surface morphology investigation. The designed RACK 1 biosensor had good repeatability (5.73 %, RSD), excellent reproducibility (2.5 %, RSD), long storage-stability and reusable property. In addition, the fabricated RACK 1 biosensor was applied to determine RACK 1 concentration in human serums and the recovery was ranging from 98.79%-100.22%. This work illustrated a new tool to construct a sensitive and low-cost disposable biosensor for applications in clinical monitoring.

A New Sensitive Method for Quantitative Determination of Cisplatin in Biological Samples by Kinetic Spectrophotometry

This study describes a kinetic spectrophotometric method for accurate, sensitive and rapid determination of cisplatin in biofluids. The developed method is based on the inhibitory effect of cisplatin on the oxidization of Janus Green by bromate in acidic media. The change in absorbance as the criteria of the oxidation reaction was followed spectrophotometrically. To obtain the highest rate of sensitivity, efficient reaction parameters were optimized. Under optimum experimental conditions, a calibration graph was obtained linearly over the range 10.0 - 5750.0 μg L^-1 and the limit of detection (3s_b/m) was 4.2 μg L^-1 of cisplatin. The interfering effect of diverse species was investigated. The developed method was used for the quantification of cisplatin in bio fluids of patients treated with cisplatin, spiked bio fluids and pharmaceutical samples and yielded satisfactory results.

Pen sensor made with silver nanoparticles decorating graphite-polyurethane electrodes to detect bisphenol-A in tap and river water samples

Rapid, on-site detection of emerging pollutants is critical for monitoring health threats and the environment, especially if performed through autonomous systems. In this paper, we report on a new design of a complete electrochemical system whose working (WE), auxiliary (AE) and reference (RE) electrodes were obtained on a pen (PEN Sensor) made with graphite:polyurethane (GPUE). Working electrodes were decorated with spherical, ca. 200 nm silver nanoparticles (AgNPs) reduced on graphite using the polyol method. Differential pulse voltammetry (DPV) was used to detect bisphenol-A (BPA) in a linear range from 2.5 to 15 μmol L^-1 with detection limit of 0.24 μmol L^-1. The PEN Sensor could also detect bisphenol-A in tap and river water samples, with satisfactory reproducibility and repeatability, while common interferents did not affect electrooxidation of bisphenol-A. The high sensitivity and rapid detection are suitable for real-time analysis and in loco monitoring of emerging pollutants. With their robustness and versatility, PEN Sensors such as those fabricated here may be integrated into futuristic smart robotic systems.

Ultrasensitive detection of ochratoxin A based on biomimetic nanochannel and catalytic hairpin assembly signal amplification

In this paper, an ultrasensitive nanochannel sensor has been proposed for label-free Ochratoxin A (OTA) assay in combination with graphene oxide (GO) and catalyzed hairpin assembly (CHA). The high-performance sensor is segmented into two parts. One is composed of graphene oxide (GO) and DNA probes. In the presence of target OTA, OTA works as a catalyst to trigger the self-assembly pathway of the two probes and initiate the cycling of CHA circuits, which results in numerous double-stranded DNAs (dsDNA) in solution. The excess ssDNA probes are removed by GO. The other part is composed of biomimetic nanochannel coated with polyethyleneimine (PEI) and Zr⁴⁺, which can quantify the concentration of OTA by detecting the dsDNA in solution. The nanofluidic device has a detection limit of as low as 6.2 pM with an excellent selectivity. The nanochannel based assay was used to analyse food samples (red wine) with satisfied results. Thus, the proposed analytical method will provide a new approach the detection of OTA and can be applied for quality control to ensure food safety.

A metal-organic framework/aptamer system as a fluorescent biosensor for determination of aflatoxin B1 in food samples

The demand of simple, sensitive, selective and reliable assay for aflatoxin B1 (AFB1) detection is ubiquitous in food safety, due to its high toxic. Herein, a novel fluorescent aptasensor using metal-organic frameworks (UiO-66-NH₂) and TAMRA label aptamer as sensing platform for AFB1 detection was developed. The TAMRA aptamer adsorbed on the surface of UiO-66-NH₂ via van der Waals force and its fluorescence was quenched for the charge transfer from fluorescence dye TAMRA to metal ions of UiO-66-NH₂. After introducing AFB1 to the system, the TAMRA aptamer binded to AFB1 and formed TAMRA aptamer/AFB1complex, making its conformation change and resulting in fluorescence recovery. Thus, the quantity of AFB1 could be analyzed according to the fluorescence signal change. Under optimize experimental conditions, the assay exhibited high sensitivity toward AFB1 in range of 0-180 ng mL^-1 with low limit of detection of 0.35 ng mL^-1 and good specificity against other toxins. Moreover, the aptamer/metal-organic frameworks sensing platform could be utilized to determine AFB1 content in food samples such as corn, rice and milk. It provided a reasonable method for other mycotoxin detection by changing the sequence of aptamer.

Sensitive and selective ctDNA detection based on functionalized black phosphorus nanosheets

Circulating tumor DNA (ctDNA) identification is one of the most meaningful approaches towards early cancer diagnosis. However, effective and practical methods for analyzing this emerging class of biomarkers are still lacking. In this work, a biosensor based on nitrophenyl functionalized black phosphorus nanosheets (NP-BPs) is fabricated for sensitive and selective detection of ctDNA. In this work, a nitrophenyl functionalized black phosphorus nanosheets (NP-BPs) biosensor is fabricated for sensitive and selective detection of ctDNA. Due to the successful nitrophenyl functionalization, the NP-BPs biosensor shows higher quenching efficiency and stronger affinity towards single-stranded DNA (ssDNA), as compared with double-stranded DNA (dsDNA). Therefore, the NP-BPs biosensor exhibits 5.4-fold fluorescence enhancement when dye-labelled ssDNA probe forms dsDNA in the presence of its specific ctDNA target. This biosensor exhibits a detection limit of 50 fM and a wide linear detection range of 50 fM-80 pM, provides reliable readout in a short time (15 min). Moreover, the NP-BPs-based biosensor could be applied to discriminate single nucleotide polymorphisms in clinical serum samples. It is envisioned that the NP-BPs-based sensing platform has great potentials in early cancer diagnosis and monitoring cancer progression.

A Facile Colorimetric Sensor for 6-Mercaptopurine Based on Silver Nanoparticles

A facile colorimetric method was developed for detecting 6-mercaptopurine (6-MP) using silver nanoparticles (AgNPs). The addition of 6-MP to AgNPs led to the aggregation of AgNPs with a color change from yellow to brown. The ratio between the absorbance at 394 and 530 nm (A394/A530) was used for a quantitative analysis of 6-MP. A linear range of 0 - 0.5 μM was obtained with a detection limit of 10 nM. The developed method is cost-effective and simple.

A facile biosensor for Aβ40O based on fluorescence quenching of prussian blue nanoparticles

Amyloid β peptide oligomeFrs (AβOs) have been proved to be crucial biomarkers of Alzheimer's disease (AD). To explore an applicable method for the determination of AβOs is significant for the early AD diagnosis. Prussian blue nanoparticles (PBNPs), as one excellent nanomaterials, have the advantages of good stability, favorable biocompatibility, low cost, easy preparation and controllable shape. PBNPs was found to be of the fluorescence quenching ability to fluorophores, and the adsorption of DNA onto PBNPs surface occurred via the binding of phosphate skeleton in DNA to Fe²⁺/Fe³⁺ in PBNPs. On basis of this, carboxyl fluorescein (FAM) modified Aβ₄₀O-targeting aptamer (FAM-Apt_Aβ) was adsorbed onto PBNPs. And FAM-Apt_Aβ@PBNPs-based fluorescent aptasensor for the determination of Aβ₄₀O was developed. Upon incubating FAM-Apt_Aβ@PBNPs with Aβ₄₀O, the fluorescence intensity of the FAM-Apt_Aβ@PBNPs obviously increased comparing to the initial fluorescence intensity of the FAM-Apt_Aβ@PBNPs. The changes in the fluorescence intensity of the FAM-Apt_Aβ@PBNPs were linear with the Aβ₄₀O concentrations ranging from 1.00 nM to 100 nM. Moreover, AD patients and healthy persons can be distinguished using this method to determine Aβ₄₀O concentrations in human cerebrospinal fluid samples from AD patients and healthy persons. It demonstrates that this PBNPs-based aptasensor is not only simple and cost-effective, but also sensitive, selective and more applicable. This fluorescent sensing strategy is promising for the development of aptasensor in clinical fields.

A multi-responsive crown ether-based colorimetric/fluorescent chemosensor for highly selective detection of Al3+, Cu2+ and Mg2

A novel multi-response chemosensor L based on coumarin-chalcone-crown ether was designed and synthesized, which exhibited a high selectivity for the colorimetric detecting Al³⁺ and Cu²⁺ and fluorescent recognizing Al³⁺ and Mg²⁺ in ethanol. L can monitor Al³⁺ and Cu²⁺ via distinct color changes from a slight yellow to pink and to orange, respectively. The sensor L can also monitor Al³⁺ and Mg²⁺ by fluorescence emission responses at 592 nm and 547 nm with low detection limits of 0.31 μM and 0.23 μM, respectively. The selectivity of L toward Al³⁺, Cu²⁺ and Mg²⁺ was not interfered by a large number of coexisting ions and was found to be reversible. By means of spectrometric titration, Job's plot, mass spectrometry, ¹H NMR titration and IR spectroscopy analysis, it was unanimously confirmed that the sensor L had a stoichiometric ratio of 1:1 with Cu²⁺ and Mg²⁺, and 1:2 with Al³⁺. The order of the stability of the complexes formed by L and Al³⁺, Cu²⁺, Mg²⁺ was as follows: L-Al³⁺ > L-Cu²⁺ > L-Mg²⁺. At the same time, some possible bonding modes and sensing mechanisms were further proposed, and the optimized structure of the sensor L and its sensing mechanism for Al³⁺, Cu²⁺ and Mg²⁺ were confirmed by the calculations of DFT/B3LYP and TD-DFT methods in a suite of Gaussian 09 programs.

L-cysteine modified silver nanoparticles for selective and sensitive colorimetric detection of vitamin B1 in food and water samples

The use of L-cysteine modified silver nanoparticles (Cys-capped AgNPs) as a colorimetric probe for determination of vitamin B1 (thiamine) is described in the present work. This method is based on the measurement of red shift of localized surface plasmon resonance (LSPR) band of Cys-capped AgNPs in the region of 200–800 nm. The color of Cys-capped AgNPs was changed from yellow to colorless by the addition of vitamin B1. The mechanism for detection of vitamin B1 is based on the electrostatic interaction between positively charged vitamin B1, which causes the red shift of LSPR band from 390 nm to 580 nm. The interaction between Cys-capped AgNPs and vitamin B1 was theoretically explored by density function theory (DFT) using LANL2DZ basis sets with help of Gaussian 09 (C.01) program. The morphology, size distribution and optical properties of Cys-capped AgNPs were characterized by transmission electron microscope (TEM), UV-Visible spectrophotometry, Fourier transform infrared spectroscopy (FTIR) and dynamic light scattering (DLS) techniques. The method is linear in the range of 25–500 μg mL⁻¹ with correlation coefficient (R²) 0.992 and limit of detection of 7.0 μg mL⁻¹. The advantages of using Cys-capped AgNPs as a chemical sensor in colorimetry assay are being simple, low cost and selective for detection of vitamin B1 from food (peas, grapes and tomato) and environmental (river, sewage and pond) water samples.

An electrochemical sensor based on chitosan capped with gold nanoparticles combined with a voltammetric electronic tongue for quantitative aspirin detection in human physiological fluids and tablets

Inflammatory diseases increase has recently sparked the research interest for drugs diagnostic tools development. At therapeutic doses, acetylsalicylic acid (ASA or aspirin) is widely used for these diseases' treatment. ASA overdoses can however give rise to adverse side effects including ulcers, gastric damage. Hence, development of simple, portable and sensitive methods for ASA detection is desirable. This paper reports aspirin analysis in urine, saliva and pharmaceutical tablet using an electrochemical sensor and a voltammetric electronic tongue (VE-Tongue). The electrochemical sensor was fabricated by self-assembling chitosan capped with gold nanoparticles (Cs + AuNPs) on a screen-printed carbon electrode (SPCE). It exhibits a logarithmic-linear relationship between its response and the ASA concentration in the range between 1 pg/mL and 1 μg/mL. A low detection limit (0.03 pg/mL), good selectivity against phenol and benzoic acid interference, and successful practical application were demonstrated. Qualitative analysis was performed using the VE-Tongue based unmodified metal electrodes combined with two chemometric approaches to classify urine samples spiked with different aspirin concentrations. Partial least squares (PLS) method provided prediction models obtained from the data of both devices with a regression correlation coefficient R² = 0.99. Correspondingly, the SPCE/(Cs + AuNPs) electrochemical sensor and VE-Tongue could be viable tools for biological analysis of drugs.

Synthesis of bifunctional cabbage flower-like Ho3+/NiO nanostructures as a modifier for simultaneous determination of methotrexate and carbamazepine

Cabbage flower-like Ho³⁺/NiO nanostructure (CFL-Ho³⁺/NiO NSs) with significant electrocatalytic oxidation has been published for the first time. First, structure and morphology of CFL-Ho³⁺/NiO-NSs have been described by XRD, SEM, and EDX methods. Then, CFL-Ho³⁺/NiO-NSs have been applied as a modifier for simultaneous electrochemical detection of methotrexate (MTX) and carbamazepine (CBZ). Functions of the modified electrode have been dealt with through electrochemical impedance spectroscopy (EIS). It has been demonstrated that the electrode response has been linear from 0.001-310.0 μM with a limit of detection of 5.2 nM and 4.5 nM (3 s/m) through DPV for MTX and CBZ. Diffusion coefficient (D) and heterogeneous rate constant (k_h) have been detected for MTX and CBZ oxidation at the surface of the modified electrode. Moreover, CFL-Ho³⁺/NiO-NS/GCE has been employed for determining MTX and CBZ in urine and drug specimens. Outputs showed the analyte acceptable recovery. Therefore, the electrode could be applied to analyze both analytes in drug prescription and clinical laboratories. Graphical abstract Electrochemical sensor based on bifunctional cabbage flower-like Ho³⁺/NiO nanostructures modified glassy carbon electrode for simultaneous detecting methotrexate and carbamazepine was fabricated.

Synergistic activity of binary metal sulphide WS2–RuS2 nanospheres for the electrochemical detection of the antipsychotic drug promazine

Schematic presentation for the synthesis of tungsten disulfide–ruthenium disulfide (WS₂–RuS₂) nanospheres and application for the electrochemical determination of antipsychotic drug promazine.

Electrochemical Sensors, a Bright Future in the Fabrication of Portable Kits in Analytical Systems

Analysis of food, pharmaceutical, and environmental compounds is an inevitable issue to evaluate quality of the compounds used in human life. Quality of drinking water, food products, and pharmaceutical compounds is directly associated with human health. Presence of forbidden additives in food products, toxic compounds in water samples and drugs with low quality lead to important problems for human health. Therefore, attention to analytical strategy for investigation of quality of food, pharmaceutical, and environmental compounds and monitoring presence of forbidden compounds in materials used by humans has increased in recent years. Analytical methods help to identify and quantify both permissible and unauthorized compounds present in the materials used in human daily life. Among analytical methods, electrochemical methods have been shown to have more advantages compared to other analytical methods due to their portability and low cost. Most of big companies have applied this type of analytical methods because of their fast and selective analysis. Due to simple operation and high diversity of electroanalytical sensors, these types of sensors are expected to be the future generation of analytical systems. Therefore, many scientists and researchers have focused on designing and fabrication of electroanalytical sensors with good selectivity and high sensitivity for different types of compounds such as drugs, food, and environmental pollutants. In this paper, we described the mechanism and different examples of DNA, enzymatic and electro-catalytic methods for electroanalytical determination of drug, food and environmental compounds.

Electrochemical sensor based on incorporation of gold nanoparticles, ionic liquid crystal, and β-cyclodextrin into carbon paste composite for ultra-sensitive determination of norepinephrine in real samples

A novel, reliable electrochemical sensor is fabricated for direct and sensitive determination of norepinephrine (NE) based on gold nanoparticles, ionic liquid crystal, and β-cyclodextrin modified carbon paste electrode, namely AuILCCDCPE. The ionic liquid crystal (ILC) played a key role in improving the current response of electro-oxidation of NE compared with other ionic liquids modified electrodes. The ILC increased the ionic conductivity of the paste and formed noncovalent interactions with both host (CD) and guest (NE) compounds. The solid state structure of the ILC helped in the formation of ordered films in the paste. Furthermore, CD and Au nanoparticles raised the stability and the electrocatalytic ability of the proposed sensor. Under optimized conditions, the fabricated electrochemical sensor showed a good electrochemical response towards NE in human urine in the linear dynamic ranges of 0.05–10 μmol/L and 20–300 μmol/L with a correlation coefficient of 0.999 and detection limit of 3.12 × 10−9 mol/L in the low concentration range. The practical analytical performance of the sensor was attained for determination of NE in real samples with satisfied recovery results. This sensor has great ability to be extended for electrochemical applications in assays of other drugs.

Monitor application of multi-electrochemical sensor in extracting bromine from seawater

In this paper, a set of online measurement devices of multi-electrochemical sensor was investigated. Combined with industrial distributed control system, it was first applied in extracting bromine from seawater to realize the real-time adjustment of production process parameters. In the process of extracting bromine from seawater, the pH value of acidified raw brine, the addition amount of Cl₂ in the oxidation stage and the addition amount of SO₂ in the absorption stage are key parameters to control the whole production process. The multi-electrochemical sensor realized a rapid and high-throughput detection of the above parameters by integrating an all-solid-stage bromide ion selective electrode (Br-ISE), Eh electrode and pH electrode. The Br-ISE and the pH electrode were self-developed electrodes and the Pt electrode was Eh electrode. The pH electrode was used to control the addition amount of H₂SO₄ during the acidification of the brine. The Eh electrode was used to control the addition amount of Cl₂ during the oxidation stage and the addition amount of SO₂ during the absorption stage. The Br-ISE was used to monitor the Br^- concentration change in the raw brine. Results showed the optimum range of Eh in the oxidation stage and absorption stage of brine were 950-1000 mV and 580-610 mV, respectively. The application of multi-electrochemical sensor in industrial bromine production can realize real-time control of material addition and save the cost of production.

Development of membrane electrodes for selective determination of lisinopril in pharmaceuticals

Background

Lisinopril (LNP) is an angiotensin-converting enzyme inhibitor used as anti-hypertensive, cardiovascular, in anti-prophylactic and anti-diabetic nephropathy drug. Development of two new, simple, low cost, and selective membrane-based ion-selective electrodes has been proposed for the determination of LNP in pharmaceuticals.

Methods

The electrodes are based on poly(vinyl)chloride membrane doped with LNP-phosphotungstic acid (LNP-PTA) and LNP-phosphomolybdic acid (LNP-PMA) ion-pairs as molecular recognition materials.

Results

The developed LNP-PTA and LNP-PMA electrodes are applicable for the determination of LNP over the linear range of 5 × 10−5–2.4 × 10−3 mol l−1. The working pH ranges to measure potentials were 2.5 to 6.4 and 2.3 to 6.0 for LNP-PTA and LNP-PMA ISEs, respectively. The electrodes displayed the rapid Nernstian responses as revealed by the values of slopes 55.06 and 52.39 mV/decade, with limit of detection (LOD) values of 1.2 × 10−5 and 1.18 × 10−5 mol l−1 for LNP-PTA and LNP-PMA electrodes, respectively. The limits of quantitation (LOQ) values have also been calculated for both the electrodes. The developed electrodes have potential stability for up to 1 month and emerged as highly selective for the determination of LNP over other spiked ions and compounds.

Conclusions

The proposed electrodes have been validated and found that they are suitable for the determination of LNP in pharmaceuticals in pure form and in dosage forms. The results obtained in the analysis of LNP using proposed electrodes have been compared statistically with reference method’s results to assess the accuracy and precision. Robustness and ruggedness of the developed electrodes have also been checked and found satisfactory. The recovery studies have been performed by standard addition procedure to assess the role of excipients in tablets containing LNP and the results obtained are satisfactory.

Colorimetric immunosensor for determination of prostate specific antigen using surface plasmon resonance band of colloidal triangular shape gold nanoparticles

In this work, we demonstrated the development of a colorimetric immunosensor using surface plasmon resonance band of gold nanoparticles for the detection of prostate specific antigen (PSA). To develop this biosensing tool, triangular gold nanoparticles (AuNPs) were synthesized using Tween-20 as a nonionic surfactant and then, conjugated with PSA capture antibody (Ab₁-AuNPs). When exposed to Ab₁-AuNPs, PSA antigens were found to be successfully captured by nanosystem (PSA)-Ab₁-AuNPs. Next, (PSA)-Ab₁-AuNPs were incubated with second PSA antibody (2)-decorated magnetite (Fe₃O₄-Ab₂) and separated by an external magnetic force to leave Ab₁-AuNPs in the supernatant solution to be directly analyzed using UV-Vis spectroscopy. It was found that the absorption intensity was directly proportional to the PSA concentration. As a result, the linear range for PSA detection was found to be 0.01-20 ng mL^-1 with a detection limit of 0.009 ng mL^-1. Because of significant stability of the prepared Ab₁-AuNPs and excellent selectivity to the PSA antigen, this simple and sensitive sensing system is proposed to be potentially effective in the fast and real-time analysis of clinical samples from prostate cancer patients. We believe that the simple platform of this immunosensor to be useful in the development of future point-of-care sensing tools, working on the quantification of biomarkers in a drop of blood.

A sensitive H2O2 biosensor based on carbon nanotubes/tetrathiafulvalene and its application in detecting NADH

Reduced nicotinamide adenine dinucleotide (NADH) plays a pivotal role in the electron-transfer chain of biological system. Analysis of many biological markers is based on the detection of the enzymatically generated NADH. In this paper, a sensitive hydrogen peroxide (H₂O₂) biosensor, fabricated by carbon nanotubes (CNTs)/tetrathiafulvalene (TTF)/horseradish peroxidase (HRP), was applied for detecting the NADH in a buffer containing methylene blue (MB) at low operating potential of - 0.3 V (vs. Ag/AgCl). Since the NADH could be oxidized by MB to release H₂O₂, the electrochemical biosensor enables to detect the NADH in the MB buffer. And the low working potential made the biosensor avoid the interference from other electroactive substances. Linear response ranges from 10 μM to 790 μM, with a sensitivity of 4.76 μA mM^-1 and a detection limit of 1.53 μM were obtained under the optimum conditions. The proposed sensor provided a promising approach for sensitively detecting the NADH.