Potentiometric Biosensor Research Articles

A Novel Low Unity-Gain Frequency and Low Power Consumption Instrumentation Amplifier Design for RuO₂ Uric Acid Biosensor Measurement

In this study, a novel low unity-gain frequency and low power consumption instrumentation amplifier (UGFPCIA) was designed and applied to the readout circuit of the potentiometric biosensor measurement system. The proposed UGFPCIA was developed using the Taiwan Semiconductor Manufacturing Company (TSMC) 0.18- $\mu \text{m}$ process technology, and simulated in a Laker analog design environment, and had a 1.5-V supply voltage for reduced power consumption. The uric acid (UA) biosensor based on RuO2 thin film was fabricated in this study. The sensing characteristics of the RuO2 UA biosensor were measured by the proposed UGFPCIA and the LT1167, a commercial instrumentation amplifier; then, their readout circuits were compared. According to the chip measurement results, the proposed UGFPCIA achieved a common-mode gain of −54 dB and a unity-gain frequency (UGF) of 588 kHz. Its power consumption was $397.92~\mu \text{W}$ . Moreover, the measurement results showed that the sensitivity and linearity of the flexible arrayed RuO2 UA biosensor were 7.15 mV/(mg/dL) and 0.997, respectively. The LT1167 used a 2.3-V minimum supply voltage, while the proposed UGFPCIA used a 1.5-V minimum supply voltage; the power consumption is 84% lower than the former. This indicates that UGFPCIA was more stable during the measurement process and consumes lesser power.

Organic and inorganic mixed phase modification of a silver surface for functionalization with biomolecules and stabilization of electromotive force

A solid-state potentiometric biosensor based on the organic and inorganic mixed phase modification of a silver surface is proposed. Stabilization of the electromotive force and functionalization with biomolecules on the sensing surface were simultaneously achieved using silver chloride chemically deposited with 1,3-diaminopropanetetraacetic acid ferric ammonium salt monohydrate and a self-assembled monolayer with oligonucleotide probes, respectively. The formation of silver chloride and adsorption of alkanethiol on the silver surface were confirmed with X-ray photoelectron spectroscopy. The resulting modified surface reduced the nonspecific binding of interfering biomolecules and achieved a high signal to noise ratio. The electromotive forces of the modified silver thin film electrodes were stable under constant chloride ion concentrations. Hybridization assays were performed to detect microRNA 146. The lower limit of detection was 0.1 pM because of the small standard deviation. The proposed biosensor could be useful as a disposable single-use sensor in medical fields such as liquid biopsies.

Aptamer-based nanofilter interface for small-biomarker detection with potentiometric biosensor

In this paper, we report the concept of an aptamer (Ap)-based nanofilter interface for the suppression of nonspecific signals generated by interfering species in biological samples. As a model of the target small biomolecule, l-3,4-dihydroxyphenylalanine (l-DOPA) is used to demonstrate its electrical discrimination from dopamine (DA) despite their similar chemical structures using a DA–Ap nanofilter-coated Au gate field-effect transistor (FET). A Au gate electrode is employed to assess the electrical response of the FET to l-DOPA on the basis of oxidative reactions. In particular, the proposed nanofilter interface is based on the DA–Ap layer immobilized at the aryl-diazonium-based anchor monolayer, which is electrochemically grafted on the Au gate electrode via diazonium chemistry. As a result, the electrical signal from l-DOPA is clearly discriminated from that from DA at a concentration of 1 μM or higher using the DA–Ap nanofilter-coated Au gate FET. That is, DA is trapped by the DA–Ap nanofilter through the formation of complexes, the molecular charges of which are shielded by counter ions that are not in contact with the Au gate surface, whereas l-DOPA reaches and electrochemically reacts with the Au gate surface, generating an electrical signal regardless of the nanofilter. The surface properties of the DA–Ap nanofilter modified on the Au gate electrode are investigated by cyclic voltammetry, chronocoulometry, atomic force microscopy, and X-ray photoelectron spectroscopy. A platform based on the FET biosensor with the Ap-based nanofilter interface contributes to the electrical monitoring of small biomarkers while suppressing the nonspecific signals of interfering species in biological samples.

Polyaniline-based field effect transistor for DNA/RNA biomarker sensing: Comparison to electrochemical impedance and inorganic layer

One relevant aspect of the research in materials science focus on studying materials properties for applications in the field of sensing and biosensing devices aiming to obtain portable, stable, sensitive, and low-cost detection systems for a broad range of diseases, traumas, and infections. We report a polyaniline (PANI)-based extended-gate field effect transistor DNA/RNA (DNA-EGFET) biosensor. The biosensor is based on a functionalized Au reference electrode with thiolated bio-receptor single-strand DNA (ssDNA) corresponding to the μDNA-224, an overexpressed DNA biomarker sample for rectal colon cancer, and the transduction system is based on an electrodeposited PANI thin film as sensing stage. Variations on net surface charge of the hybridized single strand DNA led to changes of the output voltage from the FET system, which could be correlated to the concentration of the detected complementary DNA. Comparison between the potentiometric EGFET biosensor and the electrochemical impedance spectroscopy (EIS) biosensor used for DNA/RNA measurements and the use of organic and inorganic (metal oxide) semiconducting sensing materials were performed. This DNA-EGFET biosensor offered fast response, sensitivity of 3.3 ± 0.3 mV/log[tDNA], linearity of 96 % in a detection range from 1 pmol/L to 1 μmol/L and LoD of 9.77 pmol/L in buffer solution. The application and comparison of the PANI based DNA-EGFET for measurements of DNA biomarkers was demonstrated as a proof-of-concept of the advantages and easy fabrication of the device.

Magnetic-Field-Driven Extraction of Bioreceptors into Polymeric Membranes for Label-Free Potentiometric Biosensing.

We report here the concept of a magnetically controlled extraction of hydrophilic bioreceptors into polymeric membranes for bioassays. The potentiometric assay relies on the intrinsic charges of an antimicrobial peptide and its unique recognition abilities, which can eliminate the probe labeling and indicator addition. The target binding event could effectively prevent the extraction of the peptide into the polymeric membrane doped with an ion exchanger, thus resulting in a potential change. The potentiometric response properties of the peptide assembled on magnetic beads can be dynamically controlled and modulated by applying a magnetic field. Staphylococcus aureus, as a model of food-borne pathogens, was measured at levels down to 10 CFU mL-1 . Based on this sensing strategy, a potentiometric array was developed for the pattern recognition of bacteria. The proposed general platform can be used for potentiometric biosensing using other hydrophilic bioreceptors.

Magnetic‐Field‐Driven Extraction of Bioreceptors into Polymeric Membranes for Label‐Free Potentiometric Biosensing

AbstractWe report here the concept of a magnetically controlled extraction of hydrophilic bioreceptors into polymeric membranes for bioassays. The potentiometric assay relies on the intrinsic charges of an antimicrobial peptide and its unique recognition abilities, which can eliminate the probe labeling and indicator addition. The target binding event could effectively prevent the extraction of the peptide into the polymeric membrane doped with an ion exchanger, thus resulting in a potential change. The potentiometric response properties of the peptide assembled on magnetic beads can be dynamically controlled and modulated by applying a magnetic field. Staphylococcus aureus, as a model of food‐borne pathogens, was measured at levels down to 10 CFU mL−1. Based on this sensing strategy, a potentiometric array was developed for the pattern recognition of bacteria. The proposed general platform can be used for potentiometric biosensing using other hydrophilic bioreceptors.

Molecularly Imprinted Polymer Based GCE for Ultra-sensitive Voltammetric and Potentiometric Bio Sensing of Topiramate.

Topiramate (TOP) drug is classified as one of the most commonly used human drugs for anticonvulsants and antiepileptic, so its rapid detection and monitoring is of great importance. In this work, new potentiometric (MIP/PVC/GCE) and voltammetric (MIP/GO/GCE) sensors for the selective and sensitive determination of TOP were fabricated based on the molecularly imprinted polymer (MIP) approach. The MIP was synthesized by the polymerization of acrylamide and methacrylic acid as monomers, in the presence of TOP as a template and ethylene glycol dimethacrylate as a cross-linker. The obtained products were characterized by FT-IR, SEM, BET, and EDX. The MIP was embedded in a plasticized polyvinyl chloride membrane and used as a potentiometric sensor for sensing TOP. Alternatively, the synthesized MIP and graphene oxide (GO) were deposited layer-by-layer on the surface of GCE to construct a voltammetric sensor for studying the electrochemical behavior of the drug. Under optimized conditions, both electrochemical sensors showed excellent linear relationships between the concentration of TOP and the response signals of MIP/GO/GCE or MIP/PVC/GCE sensors in the 2.7 × 10-10 to 4.9 × 10-3 M and 1 × 10-9 to 3.4 × 10-3 M ranges, respectively. Also, both sensors have good reproducibility and high stability for up to 15 days for a voltammetric sensor and 28 days for a potentiometric sensor. The utility of these sensors was checked for TOP analysis in different real samples with good recovery (92.8 - 99%).

High stability potentiometric urea biosensor based on enzyme attached nanoparticles

Highly stable new urea biosensor was prepared by using poly(2-hydroxyethyl methacrylate-glycidyl methacrylate) nanoparticles, which was used as a nano-carrier for urease enzyme. The urea biosensor was prepared by an ammonium selective electrode along with the urease immobilized nanoparticles. Synthesized nanoparticles were characterized by SEM and attachment of the enzyme onto the nanoparticles was evaluated by EDX analysis. Potentiometric response of the biosensor was examined as a function of the different concentrations of urea solution, and linear concentration range of urea was demonstrated in the range of 0.01 mM-500 mM. The detection limit was also investigated and measured as 0.77 µM. Response time of the biosensor was also determined as 30 s. Repeatability of the urea biosensor system was found to be very high, and it was demonstrated that response of the urea sensor was protected by 95.7% at the end of the 170th reuse. This biosensor system protected 83% of its initial activity at the end of the 90 day storage. Additionally, interference profile of the urea biosensor was tested against the common interferents such as ascorbic acid (AA), uric acid (UR), glucose (GL) and sodium ions (Na+), and the response of these interfering agents was found to be as negligible. Also, applicability of the synthesized urea sensor for detection of urea from artificial human serum was demonstrated.

Development of potentıometrıc bıosensor for dıagnosıs of prostate cancer

Prostate cancer is an important public health problem in the world with its burden of disease, increase in fatality and incidence rates. Recently, naturally occurring amino acid sarcosine has been investigated as a recognized marker of prostate cancer. The aim of the study for the early detection of prostate cancer is to develop a method of high sensitivity, low cost and low concentration in the determination of sarcosine. High sensitive nano anti-sarcosine-antibody and nano anti-sarcosine antibody-GFOX polymer have been prepared for the potentiometric detection of sarcosine and its reusability as biosensors have investigated. Nano anti-sarcosine antibody and nano anti-sarcosine antibody-GFOX potentiometric biosensor have shown excellent detection performance. Nano anti-sarcosine antibody potentiometric biosensor and nano anti-sarcosine antibody-GFOX potentiometric biosensor have low detection limit (4.75 × 10−9 mM and 3.34 × 10−9mM, respectively), high selectivity, short response time, wide linear range, and satisfactory long-term stability (3–4 months) for sarcosine detection.

All-solid-state Potentiometric Biosensors Based on Electropolymerized Poly(3,4-ethylenedioxythiophene) as Solid Contact for Acetylcholine Determination in Artificial Cerebrospinal Fluid

All-solid-state Potentiometric Biosensors Based on Electropolymerized Poly(3,4-ethylenedioxythiophene) as Solid Contact for Acetylcholine Determination in Artificial Cerebrospinal Fluid

Modulating the mixed potential for developing biosensors: Direct potentiometric determination of glucose in whole, undiluted blood

The growing demand for tools to generate chemical information in decentralized settings is creating a vast range of opportunities for potentiometric sensors, since their combination of robustness, simplicity of operation and cost can hardly be rivalled by any other technique. In previous works, we have shown that the mixed potential of a Pt electrode can be controlled with analytical purposes using a coating of Nafion, thus providing a way to develop a potentiometric biosensor for glucose. Unfortunately, the linear range of this device did not match the relevant clinical range for glucose in blood.This work presents a novel strategy to control the mixed potential that allows the development of a potentiometric biosensor for the direct detection of glucose in whole, undiluted blood without any sample pretreatment. By changing the ionomer, the analytical response can be tuned, shifting the linear range while keeping the sensitivity. Aquivion, a polyelectrolyte from the same family as Nafion, is used to stabilize the mixed potential of a platinized paper-based electrode, to entrap the enzyme and to reduce the interference from negatively charged species. Factors affecting the generation of the signal and the principle of detection are discussed. Optimization of the biosensor composition was achieved with particular focus on the characterization of the linear range and sensitivity. The accurate measurement of blood sugar levels in a single drop of whole blood with excellent recovery is presented.

High-Density Immobilization of Tobacco Mosaic Virus Nanotubes As Enzyme Nanocarriers Onto Field-Effect Biosensor Structures

Introduction Viruses are not only infectious agents, they are also known as promising functional building blocks for application in nano- and biotechnologies. The tobacco mosaic virus (TMV) was the first studied plant virus and is widely distributed; it infects vegetables, like tomato, bell pepper, beans and other members of the family Solanaceae, while it is totally harmless for mammals [1]. It is one of the most studied plant viruses and its genome is completely sequenced, whereby genetical and chemical modification is easy. TMV has a nanotube-like shape with a length of 300 nm, an outer diameter of 18 nm and an inner diameter of 4 nm. Since it possesses a high chemical and physical robustness, it can be integrated with different electronic transducers for bio- and chemical sensing applications [2].Recently, we presented a TMV-based amperometric glucose biosensor [3] and a potentiometric penicillin biosensor [4]. TMV was used as enzyme nanocarrier for the enzyme glucose oxidase and penicillinase, respectively [3,4]. The sensitivity and detection limit of these biosensors, among others, depend on the density of TMVs on the sensor surface. The surface density of the immobilized TMVs is strongly influenced by the electrostatic interactions between the charged TMVs and sensor surface as well as by the inter-TMV-nanotubes repulsion, which could be changed by varying the pH value and the ionic strength of the TMV solution. In this study, we investigated an impact of the pH value and ionic strength of the TMV solution on the surface density of TMV nanotubes immobilized onto Ta2O5-gate capacitive field-effect electrolyte-insulator-semiconductor (EIS) sensors. Materials and Methods TMV particles modified with biotin-linker molecules (TMVBio), which serve as binding sites for streptavidin-conjugated enzymes, have been immobilized onto capacitive field-effect EIS sensors with Ta2O5 as transducer layer, as shown in Fig. 1. Immobilization was performed from TMVBiosolutions with different values of pH between pH 3.0 and pH 9.5 and ionic strength between 0.1 mM and 750 mM. The sensors have been electrochemically characterized before and after TMVBio immobilization by capacitance-voltage- and constant-capacitance methods, respectively. In addition, the density of the immobilized TMVs and morphology of the sensor surface has been investigated by means of scanning electron microscopy (SEM). Results and Conclusions The TMVBio density on the Ta2O5 sensor surface was influenced by varying the pH value (as exemplarily shown in Fig. 1) and ionic strength (not shown) of the TMVBio solution. The amplitude of the field-effect sensor signal correlates well with the density of the immobilized TMVBionanotubes. Thus, optimized conditions for the high-density immobilization of TMVBio nanotubes onto the Ta2O5 surface and thereby enhanced biosensing have been found. Details of the experiments and the obtained results will be presented and discussed.Figure 1: Measurement set-up with schematic layer structure of the capacitive EIS sensor modified with negatively charged TMVBio particles (a). SEM images of the Ta2O5-sensor surface modified with TMVBio nanotubes at pH 4.5 (b) and pH 7.0 (c), respectively. Acknowledgements The authors like to thank Dr. Claudia Koch and Rebecca Hummel, Stuttgart, for scientific and technical support.

Functionalization of Polymeric Nanofilter Biointerface for Small Biomarker Sensing

Small biomolecules contained in body fluids are often recognized as indicators of diseases and health conditions. Therefore, the development of biosensors capable of recognizing significant biomarkers from body fluids such as blood, sweat, tears, and saliva, leads to early diagnosis and contribute to the realization of next-generation medical care. In this regard, we have recently developed the potentiometric biosensor based on the extended-gate field-effect transistor (EG-FET) for small-biomolecule recognition. The catalytically active extended-Au electrodes have the capability to detect various small biomolecules with high sensitivity on the basis of the surface electrochemical reaction. However, since the Au electrode may react with various electrochemically active biomolecules, it is necessary to limit the interfering biomolecules from approaching the Au surface in order to enhance target selectivity. Therefore, a suitable polymeric nanofilter was developed on the Au electrode where interfering biomolecules are prevented from penetrating through the nanofilter, and only the target biomolecules can access the Au sensing surface to generate an electrical signal.1,2 The polymeric nanofilter biointerface is composed of two layers. The first layer is an anchor layer directly grafted on the Au surface, which controls the density of the polymeric nanofilter to make enough space for only small biomolecules to penetrate through and prevent large-biomolecule interferences from approaching the Au sensing surface. Then, a polymeric filter layer as the second layer is precisely grafted from the surface of the anchor layer by atom transfer radical polymerization (ATRP). The filter layer selectively captures the small-biomolecule interferences outside the Debye’s length; therefore, the interfering small-biomolecules will not cause the change in Au surface potential. In our previous study, we designed and developed the polymeric nanofilter by using aryldiazonium reduction chemistry and boronate affinity. Aryldiazonium reduction chemistry enabled the grafting of chemically stable multilayer film on the Au surface, having an adequate density in order to suppress the penetration of large biomolecules. Phenylboronic acid was included in the polymeric filter layer to capture the model interfering small biomolecule, L-DOPA, via a reversible PBA/diol boronate affinity binding. Resultantly, the polymeric nanofilter-coated EG-FET biosensor specifically detected the model target biomolecule, L-cysteine. In this study, we designed and developed the second polymeric layer on the polymeric nanofilter to give an additional function. Although the space-controlled nanofilter suppresses the penetration of the large biomolecules, the non-specific adsorption can cause severe fouling of the nanofilter surface. Therefore, in order to improve the anti-fouling function of the nanofilter interface, poly(2-methacryloyloxyethyl phosphorylcholine) (pMPC) was chosen as the second polymeric layer. PMPC is a bio-inspired polymer that has been widely used as a biocompatible, anti-fouling coating material. In order to investigate the anti-fouling function of pMPC coating, we firstly grafted the pMPC layer directly from the anchor layer surface via surface-initiated ATRP. Then, the response of pMPC-nanofilter coated EG-FET biosensor to human-serum albumin (HSA) was compared with the response of the control (unmodified) sensor. Resultantly, the pMPC-coated sensor suppressed the non-specific response up to 60% compared with the control sensor. Therefore, we verified the successful enhancement of the anti-fouling property on the nanofilter surface.Reference(1) Nishitani, S.; Sakata, T. ACS Appl. Mater. Interfaces 2019, 11 (5), 5561–5569.(2) Himori, S.; Nishitani, S.; Sakata, T. Langmuir 2019, 35 (10), 3701–3709.

Functionalization of Polymeric Nanofilter Biointerface for Small Biomarker Sensing

We propose a polymeric nanofilter biointerface with a multilayer that suppresses nonspecific signals caused by interfering species such as proteins and small biomolecules for potentiometric biosensors. In a previous work, we successfully prevented small biomolecules from reacting with the Au electrode using a polymeric nanofilter with a single polymeric layer, resulting in the suppression of nonspecific signals in an extended-Au-gate field-effect transistor (FET). In this study, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) is additionally employed as an antifouling nanofilter layer to suppress the nonspecific adsorption of proteins on the Au gate surface. We precisely graft the polymeric nanofilter on the Au electrode via diazonium chemistry and activators regenerated by electron transfer surface-initiated atom transfer radical polymerization (ARGET SI-ATRP). By impedimetric analysis, we found that the charge transfer resistance (R CT) of the Au electrode with the PMPC-based nanofilter hardly changes even when human serum albumin (HSA) is added onto the electrode. That is, the PMPC-based nanofilter effectively contributes to the prevention of the nonspecific adsorption of proteins such as HSA.

Retraction Note to: Effect of Urea on the Morphology of Fe3O4 Magnetic Nanoparticles and their Application in Potentiometric Urea Biosensors

The Editor-in-Chief has retracted this article [1] because Figure 4 and Figure 5 appear to show cobalt oxide nanoparticles and not iron oxide nanoparticles as stated in the article. The data reported in this article are therefore unreliable.

Enhancement of Signal-to-Noise Ratio for Serotonin Detection with Well-Designed Nanofilter-Coated Potentiometric Electrochemical Biosensor.

In this paper, we proposed to enhance a signal-to-noise (S/N) ratio for detecting a primary stress marker, serotonin, using a potentiometric biosensor modified by a well-designed nanofilter film. An extended-Au-gate field-effect transistor (EG-Au-gate FET) biosensor exhibits highly sensitive electrochemical detection toward various small biomolecules, including serotonin. Therefore, to enhance the S/N ratio for the serotonin detection, we designed an appropriate nanofilter film on the Au electrode by combining the aryldiazonium salt reduction strategy and boronate affinity. That is, only serotonin can approach the Au sensing surface to generate an electrical signal; interfering biomolecules are prevented from penetrating through the nanofilter, either because large interfering biomolecules cannot permeate through the highly dense, nanoporous multilayer film, or because phenylboronic acids included in the nanofilter captures small interfering biomolecules (e.g., catecholamines). The potentiometric biosensor modified by such a nanofilter film detected serotonin in a model sample solution containing catecholamines, cortisol, and human serum albumin with a high S/N ratio for the serotonin levels in the blood. Furthermore, we found that the effect of the nanofilter directly reflects the binding affinity of the receptors such as phenylboronic acids included in the nanofilter; thus, the selectivity and dynamic range of small target biomolecules can be tuned freely by designing the appropriate receptors for the nanofilter. The results show that a well-designed nanofilter biointerface can be a versatile biosensing platform for point-of-care testing, particularly for a simple stress check.

Enzymatically functionalized polyaniline thin films produced with one-step electrochemical immobilization and its application in glucose and urea potentiometric biosensors.

Glucose and urea enzymatic biosensors were fabricated. One-step electrochemical immobilization process was used to produce thin polyaniline films with entrapped enzymes. Chronopotentiometric analysis, scanning electron microscopy, electrochemical impedance spectroscopy and optical reflectance spectroscopy were used to determine the structure-property relationship of the functionalized polymeric thin films. The device has a recognition stage connected to a potentiometric field-effect-transistor stage and is based on the measurement of microenvironment pH variation or locally produced ions. Optimization of biosensor fabrication and effective measurement conditions were performed. The optimized films presented sensitivity, linearity and detection range to glucose of 14.6 ± 0.4mV/decade, 99.8% and from 10-4M to 10-1mol/L. Two different biosensors were produced based on the enzymatic reaction of urea with selectivity to ammonium or hydroxyl ions. For ammonium ion selective film, the sensor's parameters were 14.7 ± 0.9mV/decade, 98.2% and from 10-5 to 10-1mol/L. For the hydroxyl ion selective film, the same parameters were 7.4 ± 0.5mV/decade, 98.1% and from 10-5 to 10-1mol/L. The change in the oxidation state of the polymeric matrix explains: i) the large loss of functionality of glucose biosensor in time, ii) the conservation of functionality to the hydroxyl ions for urea biosensor and iii) the selectivity variation of the ammonium ion selective urea biosensor. The results indicate that the polymeric matrix has indeed changeable selectivity, what can be applied in different situations for biosensors production.

Potentiometric detection of ATP based on the transmembrane proton gradient generated by ATPase reconstituted on a gold electrode

Adenosine triphosphate (ATP) is a key molecule as energy vector for living organisms, therefore its detection reveals the presence of microbial colonies. Environments where the existence of microbial pathogens suppose a health hazard can benefit from real time monitoring of such molecule. We report a potentiometric biosensor based on ATP-synthase from Escherichia coli reconstituted in a floating phospholipid bilayer over gold electrodes modified with a 4-aminothiophenol self-assembled monolayer. The use of a pH-dependent redox probe on the electrode surface allows a simple, specific and reliable on site determination of ATP concentration from 1 μM to 1 mM. The broad range ATP biosensor can offer an alternative way of measuring in a few minutes the presence of microbial contamination.

A Facile Fabrication of a Potentiometric Arrayed Glucose Biosensor Based on Nafion-GOx/GO/AZO.

In this study, the potentiometric arrayed glucose biosensors, which were based on zinc oxide (ZnO) or aluminum-doped zinc oxide (AZO) sensing membranes, were fabricated by using screen-printing technology and a sputtering system, and graphene oxide (GO) and Nafion-glucose oxidase (GOx) were used to modify sensing membranes by using the drop-coating method. Next, the material properties were characterized by using a Raman spectrometer, a field-emission scanning electron microscope (FE-SEM), and a scanning probe microscope (SPM). The sensing characteristics of the glucose biosensors were measured by using the voltage–time (V-T) measurement system. Finally, electrochemical impedance spectroscopy (EIS) was conducted to analyze their charge transfer abilities. The results indicated that the average sensitivity of the glucose biosensor based on Nafion-GOx/GO/AZO was apparently higher than that of the glucose biosensor based on Nafion-GOx/GO/ZnO. In addition, the glucose biosensor based on Nafion-GOx/GO/AZO exhibited an excellent average sensitivity of 15.44 mV/mM and linearity of 0.997 over a narrow range of glucose concentration range, a response time of 26 s, a limit of detection (LOD) of 1.89 mM, and good reproducibility. In terms of the reversibility and stability, the hysteresis voltages (VH) were 3.96 mV and 2.42 mV. Additionally, the glucose biosensor also showed good anti-inference ability and reproducibility. According to these results, it is demonstrated that AZO is a promising material, which could be used to develop a reliable, simple, and low-cost potentiometric glucose biosensor.

A novel nano copper complex: potentiometry, DFT and application as a cancer prostatic biomarker for the ultrasensitive detection of human PSA.

Worldwide, prostate cancer is considered to be one of the three most commonly occurring cancers amongst the male population. Clinically, early detection of diverse forms of cancer before they spread and become incurable plays an important role in treatment strategy. Therefore, the development of fast, accurate, sensitive, and low-cost analytical methodologies and techniques for the detection of cancer biomarkers is an attractive research area for scientists globally. Herein, a Schiff base ligand (A1) was prepared via the refluxing of 3-aminobenzoic acid with 1,2-phenylenediamine. After that, a nano Cu complex (N1) was synthesized by reacting A1 with copper chloride. The produced A1 and N1 were characterized using several techniques to determine their physicochemical properties. A density functional theory study was carried out to rationalize the experimental work and support the obtained results. Moreover, the nano Cu complex (N1) was used for the fabrication of a potentiometric membrane biosensor for the early detection of the prostate-specific antigen (PSA). The results reveal that the electrode displays a stable Nernstian response of 29.26 ± 0.87 mV per decade for PSA in a linear dynamic range of 5.0 pg mL-1-10.0 ng mL-1, in a pH range of 6.5-9.2, with a short response time of 25 ± 5 s. The lifetime was between 5-7 weeks under different storage conditions. The detection (LOD) and quantification (LOQ) limits were 0.098 and 0.297 pg mL-1, respectively. The presence of different interfering species on the potentiometric biosensor response against PSA was investigated. The sensing mechanism of N1 toward PSA and the applicability of the developed electrode for the screening and quantification of PSA in real serum samples were also studied.