Electrochemical DNA-based sensors for measuring cell-generated forces

Mechanical forces play an important role in cellular communication and signaling. We developed in this study novel electrochemical DNA-based force sensors for measuring cell-generated adhesion forces. Two types of DNA probes, i.e., tension gauge tether and DNA hairpin, were constructed on the surface of a smartphone-based electrochemical device to detect piconewton-scale cellular forces at tunable levels. Upon experiencing cellular tension, the unfolding of DNA probes induces the separation of redox reporters from the surface of the electrode, which results in detectable electrochemical signals. Using integrin-mediated cell adhesion as an example, our results indicated that these electrochemical sensors can be used for highly sensitive, robust, simple, and portable measurements of cell-generated forces.

A portable electrochemical DNA sensor for sensitive and tunable detection of piconewton-scale cellular forces

Cell-generated forces are a key player in cell biology, especially during cellular shape formation, migration, cancer development, and immune response. A new type of label-free smartphone-based electrochemical DNA sensor is developed here for cellular force measurement. When cells apply tension forces to the DNA sensors, the rapid rupture of DNA duplexes allows multiple redox reporters to reach the electrode and generate highly sensitive electrochemical signals. The sensitivity of these portable sensors can be further enhanced by incorporating a CRISPR-Cas12a system. Meanwhile, the threshold force values of these DNA-based sensors can be rationally tuned based on the force application geometries and also DNA intercalating agents. Overall, these highly sensitive, portable, cost-efficient, and easy-to-use electrochemical sensors can be powerful tools for detecting different cell-generated molecular forces.

Electrochemical DNA-based sensors for measuring cell-generated forces

Mechanical forces play an important role in cellular communication and signaling. We developed in this study novel electrochemical DNA-based force sensors for measuring cell-generated adhesion forces. Two types of DNA probes, i.e., tension gauge tether and DNA hairpin, were constructed on the surface of a smartphone-based electrochemical device to detect piconewton-scale cellular forces at tunable levels. Upon experiencing cellular tension, the unfolding of DNA probes induces the separation of redox reporters from the surface of the electrode, which results in detectable electrochemical signals. Using integrin-mediated cell adhesion as an example, our results indicated that these electrochemical sensors can be used for highly sensitive, robust, simple, and portable measurement of cell-generated forces.

A Facile Method for the Fabrication of the Microneedle Electrode and Its Application in the Enzymatic Determination of Glutamate

Herein, a simple method has been used in the fabrication of a microneedle electrode (MNE). To do this, firstly, a commercial self-dissolving microneedle patch has been used to make a hard-polydimethylsiloxane-based micro-pore mold (MPM). Then, the pores of the MPM were filled with the conductive platinum (Pt) paste and cured in an oven. Afterward, the MNE made of platinum (Pt-MNE) was characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). To prove the electrochemical applicability of the Pt-MNE, the glutamate oxidase enzyme was immobilized on the surface of the electrode, to detect glutamate, using the cyclic voltammetry (CV) and chronoamperometry (CA) methods. The obtained results demonstrated that the fabricated biosensor could detect a glutamate concentration in the range of 10-150 µM. The limits of detection (LODs) (three standard deviations of the blank/slope) were also calculated to be 0.25 µM and 0.41 µM, using CV and CA, respectively. Furthermore, the Michaelis-Menten constant (KMapp) of the biosensor was calculated to be 296.48 µM using a CA method. The proposed biosensor was finally applied, to detect the glutamate concentration in human serum samples. The presented method for the fabrication of the mold signifies a step further toward the fabrication of a microneedle electrode.

An electrochemical PNA-based sensor for the detection of the SARS-CoV-2 RdRP by using surface-initiated-reversible-addition−fragmentation-chain-transfer polymerization technique

Coronavirus disease 2019 is one of the global health problems. Herein, a highly sensitive electrochemical biosensor has been designed to detect the RNA-dependent RNA polymerase (RdRP) of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) (SARS-CoV-2 RdRP). Herein, the surface-initiated reversible-addition-fragmentation-chain-transfer polymerization was used to amplify the electrochemical signal. To do that, the thiol-terminated peptide nucleic acid (PNA) probes were first immobilized on the surface of a screen-printed electrode modified with reduced graphene oxide-gold nanocomposite and then the fixed concentration of the SARS-CoV-2 RdRP was added to the electrode surface to interact with PNA probes. Subsequently, the Zr ⁴⁺ ions were added to interact with the phosphate groups of the SARS-CoV-2 RdRP. It allowed us to polymerase the ferrocenylmethyl methacrylate (FcMMA) and 4-cyano-4-(phenylcarbonothioylthio)-pentanoic acid on the SARS-CoV-2 RdRP chain. Since the poly-FcMMA has an electrochemical signal, the response of the PNA-based sensor to SARS-CoV-2 RdRP was increased in the range of 5-500 aM. The limit of detection was calculated to be 0.8 aM which is lower than the previous sensor for SARS-CoV-2 RdRP detection. The proposed PNA-based sensor showed high selectivity to the SARS-CoV-2 RdRP in the presence of the gene fragments of influenza A and Middle East respiratory syndrome coronavirus.

Highly sensitive aptasensor for the detection of SARS-CoV-2-RBD using aptamer-gated methylene blue@mesoporous silica film/laser engraved graphene electrode

Herein, an aptasensor was designed to detect the receptor-binding domain of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2-RBD) based on the encapsulation of the methylene blue (MB) inside the mesoporous silica film (MPSF), and an aptamer as an electrochemical probe, a porous matrix, and a bio-gatekeeper, respectively. The signal analysis of the proposed aptasensor indicated that the surface coverage of the encapsulated MB inside the MPSF (MB@MPSF) was 1.9 nmol/cm². Aptamers were capped the MB@MPSF, avoiding the release of MB into the solution via the electrostatic attraction between the positively charged amino groups of the MPSF and negatively charged phosphate groups of the aptamers. Therefore, the electrochemical signal of the encapsulated MB in the absence of the SARS-CoV-2-RBD was high. In the presence of SARS-CoV-2-RBD, the aptamers that had a high affinity to the SARS-CoV-2-RBD molecules were removed from the electrode surface to interact with SARS-CoV-2-RBD. It gave rise to the release of the MB from the MPSF to the solution and washed away on the electrode surface. Therefore, the electrochemical signal of the aptasensor decreased. The electrochemical signal was recorded with a square wave voltammetry technical in the range of 0.5-250 ng/mL of SARS-CoV-2-RBD in a saliva sample. The limit of detection was found to be 0.36 ng/mL. Furthermore, the selectivity factor values of the proposed aptasensor to 32 ng/mL SARS-CoV-2-RBD in the presence of C-reactive protein, hemagglutinin, and neuraminidase of influenza A virus were 35.9, 11.7, and 17.37, respectively, indicating the high selectivity of the proposed aptasensor.

An electrochemical membrane-based aptasensor for detection of severe acute respiratory syndrome coronavirus-2 receptor-binding domain

Herein, we report an electrochemical membrane-based aptasensor for the determination of the SARS-CoV-2 receptor-binding domain (SARS-CoV-2-RBD). For this purpose, the nanoporous anodic aluminium oxide membrane (NPAOM) was first fabricated electrochemically. The NPAOM was then functionalized with 3-mercaptopropyl trimethoxysilane (NPAOM-Si-SH). After that, the NPAOM-Si-SH was decorated with gold nanoparticles by using gold ion and sodium borohydride. The NPAOM-Si-S-Au_nano was then attached to the surface of the working electrode of a laser-engraved graphene electrode (LEGE). Subsequently, the LEGE/NPAOM-Si-S-Au_nano was fixed inside a flow cell that was made by using a three-dimensional (3D) printer, and then thiolated aptamer was transferred into the flow cell using a pump. The electrochemical behavior of the LEGE/NPAOM-Si-S-Au_nano-Aptamer was studied using square wave voltammetry (SWV) in the presence of potassium ferrocyanide as a redox probe. The response of the LEGE/NPAOM-Si-S-Au_nano-Aptamer to the different concentrations of the SARS-CoV-2-RBD in human saliva sample was investigated in the concentration range of 2.5-40.0 ng/mL. The limit of the detection was found to be 0.8 ng/mL. The LEGE/NPAOM-Si-S-Au_nano-Aptamer showed good selectivity to 5.0 ng/mL of SARS-CoV-2-RBD in the presence of five times of the interfering agents like hemagglutinin and neuraminidase as the influenza A virus major surface glycoproteins.

An Electrochemical Impedance Spectroscopy-Based Aptasensor for the Determination of SARS-CoV-2-RBD Using a Carbon Nanofiber-Gold Nanocomposite Modified Screen-Printed Electrode

Worldwide, human health is affected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Hence, the fabrication of the biosensors to diagnose SARS-CoV-2 is critical. In this paper, we report an electrochemical impedance spectroscopy (EIS)-based aptasensor for the determination of the SARS-CoV-2 receptor-binding domain (SARS-CoV-2-RBD). For this purpose, the carbon nanofibers (CNFs) were first decorated with gold nanoparticles (AuNPs). Then, the surface of the carbon-based screen-printed electrode (CSPE) was modified with the CNF-AuNP nanocomposite (CSPE/CNF-AuNP). After that, the thiol-terminal aptamer probe was immobilized on the surface of the CSPE/CNF-AuNP. The surface coverage of the aptamer was calculated to be 52.8 pmol·cm^-2. The CSPE/CNF-AuNP/Aptamer was then used for the measurement of SARS-CoV-2-RBD by using the EIS method. The obtained results indicate that the signal had a linear-logarithmic relationship in the range of 0.01-64 nM with a limit of detection of 7.0 pM. The proposed aptasensor had a good selectivity to SARS-CoV-2-RBD in the presence of human serum albumin; human immunoglobulins G, A, and M, hemagglutinin, and neuraminidase. The analytical performance of the aptasensor was studied in human saliva samples. The present study indicates a practical application of the CSPE/CNF-AuNP/Aptamer for the determination of SARS-CoV-2-RBD in human saliva samples with high sensitivity and accuracy.

Highly Sensitive RNA-Based Electrochemical Aptasensor for the Determination of C-Reactive Protein Using Carbon Nanofiber-Chitosan Modified Screen-Printed Electrode

C-reactive protein (CRP) is one of the biomarkers related to coronavirus disease 2019 (COVID-19). Therefore, it is crucial to develop a highly sensitive, selective, and cost-effective biosensor for the determination of CRP. In this study, we designed an electrochemical aptasensor. For this purpose, the surface of a carbon screen-printed electrode was first modified with a carbon nanofiber-chitosan (CNFs-CHIT) nanocomposite. After that, the amino-terminal RNA aptamer probes were linked to the amino groups of CHIT via glutaraldehyde as the cross-linker. Finally, methylene blue (MB) as a redox probe was self-assembled on the surface of the aptasensor. The obtained results indicated that the CNFs-CHIT nanocomposite increased the surface coverage of the aptamer up to 5.9 times. The square-wave voltammetry was used for the measurement of CRP concentration in the linear range of 1.0–150.0 pM. The obtained results indicated that the signal had a logarithmic relationship with the concentration of CRP. The limit of detection (LOD) was obtained to be 0.37 pM. The dissociation constant (K_d) that demonstrates the affinity of the aptamer probe to its target was found to be 0.93 pM. The analytical performances of the proposed RNA aptasensor were better than the previously reported aptasensors for CRP. The proposed aptasensor was also applied for the determination of CRP in the human plasma samples. The obtained results indicated that there were no statistically significant differences between the responses of the proposed RNA aptasensor and an enzyme-linked immunosorbent assay kit (ELISA). The analytical performances of the proposed RNA aptasensor described in this paper are better than previously reported aptasensors for CRP determination.

An ultrasensitive molecularly imprinted polymer-based electrochemical sensor for the determination of SARS-CoV-2-RBD by using macroporous gold screen-printed electrode

Herein, a novel molecularly imprinted polymer (MIP) based electrochemical sensor for the determination of the receptor-binding domain of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2-RBD) has been developed. For this purpose, first, a macroporous gold screen-printed electrode (MP-Au-SPE) has been fabricated. The MIP was then synthesized on the surface of the MP-Au-SPE through the electro-polymerization of ortho-phenylenediamine in the presence of SARS-CoV-2-RBD molecules as matrix polymer, and template molecules, respectively. During the fabrication process, the SARS-CoV-2-RBD molecules were embedded in the polymer matrix. Subsequently, the template molecules were removed from the electrode by using alkaline ethanol. The template molecules removal was studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), and attenuated total reflectance spectroscopy (ATR). The fabricated MIP film acted as an artificial recognition element for the measurement of SARS-CoV-2-RBD. The EIS technique was used for the measurement of the SARS-CoV-2-RBD in the saliva solution. The electron transfer resistance (R_et) of the MIP-based sensor in a ferri/ferrocyanide solution increased as the SARS-CoV-2-RBD concentration increased due to the occupation of the imprinted cavities by the SARS-CoV-2-RBD. The MIP-based sensor exhibited a good response to the SARS-CoV-2-RBD in the concentration range between 2.0 and 40.0 pg mL^-1 with a limit of detection of 0.7 pg mL^-1. The obtained results showed that the fabricated MIP sensor has high selectivity sensitivity, and stability.

A photo-electrochemical aptasensor for the determination of severe acute respiratory syndrome coronavirus 2 receptor-binding domain by using graphitic carbon nitride-cadmium sulfide quantum dots nanocomposite

Herein, a photoelectrochemical aptasensor for the quantitive measurement of the severe acute respiratory syndrome coronavirus-2 receptor-binding domain (Sars-Cov-2 RBD) has been reported for the first time. For this purpose, first, graphitic carbon nitride and (gC₃N₄) and cadmium sulfide (CdS) quantum dots were fabricated and characterized. After that, gC₃N₄ and CdS were mixed well. The fabricated nanomaterials were characterized by scanning transmission electron microscopy. Then, the CdS QDs-gC₃N₄ nanocomposite was added to the solution containing chitosan as an amine-rich polymer to generate a Chitosan/CdS-gC₃N₄ nanocomposite. Subsequently, the surface of the ITO electrode was modified with Chitosan/CdS-gC₃N₄. After that, the amine-terminal aptamer probes were immobilized on the surface of the Chitosan/CdS QDs-gC₃N₄/ITO electrode by using glutaraldehyde as an amine-amine crosslinker. The electrochemical performances of the electrodes were studied using cyclic voltammetry (CV), electrochemical Impedance Spectroscopy (EIS), and photo-electrochemistry (PEC). The surface coverage of the immobilized aptamer probe was founded to be 26.2 pmol.cm^-2. The obtained results demonstrated that the proposed photo-electrochemical aptasensor can be used for the measurement of Sars-Cov-2 RBD within 0.5-32.0 nM. The limit of detection (LOD) was obtained to be 0.12 nM (at 3σ/slope). The affinity of the Aptamer/Chitosan/CdS QDs-gC₃N₄/ITO was also founded to be 3.4 nM by using Langmuir-typical adsorption systems. The proposed photo-electrochemical aptasensor was applied for the measurement of the spiked Sars-Cov-2 RBD in human saliva samples at two concentrations. The effect of the interfering biomaterials such as human immunoglobulin G human immunoglobulin A, human immunoglobulin M, and human serum albumin was also studied.

Novel enzyme-based electrochemical and colorimetric biosensors for tetracycline monitoring in milk

Recently, there has been a growing demand to develop portable devices for the fast detection of contaminants in food safety, healthcare, and environmental fields. Herein, two biosensing methods were designed by the use of nicotinamide adenine dinucleotide phosphate (NAD(P)H)-dependent TetX2 enzyme activity and thionine as an excellent electrochemical and colorimetric mediator/probe to monitor tetracycline (TC) in milk. The nanoporous glassy carbon electrode (NPGCE) modified with polythionine was first prepared by electrochemically and then TetX2 was immobilized onto the NPGCE using polyethyleneimine. The prepared biosensor provided a high electrocatalytic response toward NAD(P)H by significantly reducing its overpotential. The proposed biosensor exhibited a detection limit of 40 nM with a linear range of 0.1-0.8 μM for TC determination. Besides, the thionine probe was used to develop a novel colorimetric assay using a simple enzymatic color reaction within a few minutes. The limit of detection for TC was experimentally achieved as 60 nM, which was lower than the safety levels established by the World Health Organization (225 nM). The correlation between change in the color of the solution and the concentration of TC was used for quality control of milk samples, as confirmed by the standard high-performance liquid chromatography method. The results show the great potential of the proposed assays as portable instruments for on-site TC measurements.

Magnetic nanoparticle decorated anodic alumina nanotubes for fluorescent detection of cathepsin B

In this work, we present the process to provide anodic alumina nanotubes with magnetic responsivity based on magnetic nanoparticles. We demonstrate the possibility to cause the motion of these composite nanotubes under magnetic field, providing them with guided mobility. The obtained magnetic anodic alumina nanotubes are completely characterized and their potential to undergo selective and effective functionalization, and stimuli-responsive load release is demonstrated. For this purpose, protease-triggered release of fluorescent molecules loaded inside the magnetic anodic alumina nanotubes (MAANTs) by selective functionalization is performed. The inner walls of the MAANTs were selectively covered with protein padding of albumin-fluorescein isothiocyanate conjugate (FITC-BSA) through means of silanization. Protein functionalization was designed to undergo proteolytic hydrolysis in presence of cathepsin B- protease highly expressed during growth and initial stages of tumor metastasis - in order to cleave peptide bond of albumin and release fluorescent fragments of the protein. Proteolytic reaction with the enzyme is performed under acidic conditions. Presented arrangement is an exemplary combination of functionalities - which are vast - and of value for applications like drug delivery and biosensing applications.

Advances in Optical Biosensors and Sensors Using Nanoporous Anodic Alumina

This review paper focuses on recent progress in optical biosensors using self-ordered nanoporous anodic alumina. We present the fabrication of self-ordered nanoporous anodic alumina, surface functionalization, and optical sensor applications. We show that self-ordered nanoporous anodic alumina has good potential for use in the fabrication of antibody-based (immunosensor), aptamer-based (aptasensor), gene-based (genosensor), peptide-based, and enzyme-based optical biosensors. The fabricated optical biosensors presented high sensitivity and selectivity. In addition, we also showed that the performance of the biosensors and the self-ordered nanoporous anodic alumina can be used for assessing biomolecules, heavy ions, and gas molecules.

Application of metal-organic framework as redox probe in an electrochemical aptasensor for sensitive detection of MUC1

In this work, an electrochemical aptasensor was developed for sensitive detection of MUC1 based on metal-organic framework-reduced graphene oxide nanocomposite (Cu-MOF-RGO). Cu- MOF-RGO appeared to be suitable as a platform for immobilization of MUC1 aptamer, and also as an electrochemical probe, which exhibited well-defined peaks with good stability and reproducibility. Cu-MOF-graphene oxide (Cu-MOF-GO) nanocomposite was prepared and cast on the electrode surface, then in order to increase the conductivity of the electrode, GO was electrochemically reduced to RGO. In the presence of MUC1, the peak current of Cu in the nanocomposite decreased, which could be explained based on the formation of MUC1-aptamer complexes on the electrode, and consequence blocking the electron transfer of Cu at the electrode surface. Under optimum experimental conditions, a linear calibration curve was obtained by differential pulse voltammetry in the concentration range of 0.1 pM-10 nM (25 pg mL^-1 - 2500 ng mL^-1) with a limit of detection (LOD) of 0.033 pM (7.5 pg mL^-1) of MUC1. The proposed aptasensor offers acceptable selectivity, stability, and reproducibility in the determination of MUC1 spiked to human blood serum samples.

Highly sensitive aptasensor based on interferometric reflectance spectroscopy for the determination of amyloid β as an Alzheimer's disease biomarkers using nanoporous anodic alumina

It is well known that Alzheimer's disease is one of the global challenges for the 21st century. Therefore, it is urgent to develop a reliable biosensor for the detection of this disease. Here in, we have developed for the first time, an aptasensor based on interferometric reflectance spectroscopy (IRS) for the determination of amyloid β (Aβ) oligomers that is an Alzheimer's disease biomarker. For this purpose, the nanoporous anodic alumina (NAA) was first fabricated. After that, the pore walls of the NAA were modified with (3-aminopropyl) trimethoxysilane (NAA-NH₂). The amino-terminal aptamers probe were then attached to the pore walls of the NAA-NH₂ by using glutaraldehyde (GA) as the cross-linking agent. Subsequently, methylene blue (MB) was immobilized into the aptamer as the photo-probe, generating the MB/G-quadruplex complex. Since MB has a high absorption coefficient, the intensity of the reflected white light to the charge-coupled device (CCD) detector decreased. In the presence of the Aβ oligomers that have high affinity to the immobilized aptamer, the MB/quadruplex complex broke and MB washed away from the aptasensor. Therefore, the intensity of the reflected white light to the CCD detector increased. The increased signal intensity of the aptasensor has a logarithmic relationship with the concentration of Aβ oligomers. The proposed aptasensor exhibited a good response to the concentration of Aβ oligomers in the range of 0.5-50.0 μg × mL^-1. The experimental detection limit was of 0.02 μg × mL^-1 (at 3σ/S). The proposed optical aptasensor exhibited good selectivity, linear range, and stability.

Isolation of HL-60 cancer cells from the human serum sample using MnO2-PEI/Ni/Au/aptamer as a novel nanomotor and electrochemical determination of thereof by aptamer/gold nanoparticles-poly(3,4-ethylene dioxythiophene) modified GC electrode

Herein, aptamer-modified self-propelled nanomotors were used for transportation of human promyelocytic leukemia cells (HL-60) from a human serum sample. For this purpose, the fabricated manganese oxide nanosheets-polyethyleneimine decorated with nickel/gold nanoparticles (MnO₂-PEI/Ni/Au) as nanomotors were added to a vial containing thiolated aptamer KH1C12 solution as a capture aptamer to attach to the gold nanoparticles on the surface of nanomotors covalently. The aptamer-modified self-propelled nanomotors (aptamer_KH1C12/nanomotors) were then separated by placing the vial in a magnetic stand. The aptamer-modified self-propelled nanomotors were rinsed three times with water to remove the non-attached aptamers. Then, the resulting aptamer_KH1C12/nanomotors were applied for the on-the-fly" transporting of HL-60 cancer cell from a human serum sample. To release of the captured HL-60 cancer cells, the complementary nucleotide sequences of KH1C12 aptamer solution (releasing aptamer) that has a with capture aptamer was added to phosphate buffer solution (1 M, pH 7.4) containing HL-60/aptamer_KH1C12/nanomotors. Because of the high affinity of capture aptamer to complementary nucleotide sequences of aptamer_KH1C12, the HL-60 cancer cells released on the surface of aptamer_KH1C12/nanomotors into the solution. The second goal of the present work was determining the concentration of HL-60 cancer cell in the human serum samples. The electrochemical impedance spectroscopy technique (EIS) was used for the determination of HL-60 cancer cell. The concentration of separated cancer cell was determined by aptamer/gold nanoparticles-poly(3,4-ethylene dioxythiophene) modified GC electrode (GC/PEDOT-Au_nano/aptamer _KH1C12). The proposed aptasensor exhibited a good response to the concentration of HL-60 cancer cells in the range of 2.5 × 10¹ to 5 × 10⁵ cells mL^-1 with a low limit of detection of 250 cells mL^-1.

An electrochemical aptamer-based assay for femtomolar determination of insulin using a screen printed electrode modified with mesoporous carbon and 1,3,6,8-pyrenetetrasulfonate

The authors describe an electrochemical method for aptamer-based determination of insulin at femtomolar concentrations. The surface of a screen printed electrode was modified with ordered mesoporous carbon that was chemically modified with 1,3,6,8-pyrenetetrasulfonate (TPS). The amino-terminated aptamer was then covalently linked to TPS via reactive sulfonyl chloride groups. Subsequently, the redox probe Methylene Blue (MB) was interacted into the aptamer. The MB-modified binds to insulin and this results in the release of MB and a decreased signal as obtained by differential pulse voltammetry, best at a working voltage of -0.3 V (versus silver pseudo-reference electrode). Insulin can be quantified by this method in the 1.0 fM to 10.0 pM concentration range, with a 0.18 fM limit of detection (at 3σ/slope). The assay was applied to the determination of insulin in spiked human serum samples. The method is highly sensitive, selective, stable, and has a wide analytical range. Graphical abstract The surface of a screen printed electrode was modified with ordered mesoporous carbon-1,3,6,8-pyrenetetrasulfonate. The amino-terminated aptamer was then linked to the 1,3,6,8-pyrenetetrasulfonate. Then, the Methylene Blue was interacted into the aptamer. The modified electrode was applied to the determination of insulin.

CdTe amplification nanoplatforms capped with thioglycolic acid for electrochemical aptasensing of ultra-traces of ATP

A "signal off" voltammetric aptasensor was developed for the sensitive and selective detection of ultra-low levels of adenosine triphosphate (ATP). For this purpose, a new strategy based on the principle of recognition-induced switching of aptamers from DNA/DNA duplex to DNA/target complex was designed using thioglycolic acid (TGA)-capped CdTe quantum dots (QDs) as the signal amplifying nano-platforms. Owing to the small size, high surface-to-volume ratio and good conductivity, quantum dots were immobilized on the electrode surface for signal amplification. In this work, methylene blue (MB) adsorbed to DNA was used as a sensitive redox reporter. The intensity of voltammetric signal of MB was found to decrease linearly upon ATP addition over a concentration range of 0.1nM to 1.6μM with a correlation coefficient of 0.9924. Under optimized conditions, the aptasensor was able to selectively detect ATP with a limit of detection of 45pM at 3σ. The results also demonstrated that the QDs-based amplification strategy could be feasible for ATP assay and presented a potential universal method for other small biomolecular aptasensors.

A high sensitive electrochemical aptasensor for the determination of VEGF(165) in serum of lung cancer patient

Herein, a label free electrochemical aptasensor based on ordered mesoporous carbon-gold nanocomposite modified screen printed electrode has been fabricated for the detection of vascular endothelial growth factor (VEGF165) as a tumor marker. The electrochemical behavior of prepared biosensor was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The principle of operation of the proposed aptasensor is based on the changes in the interfacial properties of the electrode due to interaction of the immobilized antiVEGF165 aptamer at the electrode surface with VEGF165 tumor marker in the sample solution, which results in a change in the interfacial charge transfer resistance as detected by electrochemical impedance spectroscopy. The calibration curve for VEGF165 determination was linear over 10.0-300.0 pg mL(-1) with a limit of detection (3σ/S) of 1.0 pg mL(-1). The prepared aptasensor exhibited high sensitivity and good selectivity and reproducibility. The aptasensor was successfully applied to the determination of VEGF165 in serum sample of a lung cancer patient.

Highly sensitive label free electrochemical detection of VGEF165 tumor marker based on "signal off" and "signal on" strategies using an anti-VEGF165 aptamer immobilized BSA-gold nanoclusters/ionic liquid/glassy carbon electrode

In this work, a label free electrochemical aptasensor for the detection of ultra-traces of vascular endothelial growth factor (VEGF165) based on "signal off" and "signal on" mechanisms of response was developed. The BSA-gold nanoclusters/ionic liquid (BSA-AuNCs/IL) was used as a suitable nanocomposite platform for immobilization of the aptamer on a glassy carbon electrode. In "signal off" mechanism, the interaction of VEGF165 with its anti-VEGF165 aptamers, resulted in desorption of methylene blue (MB) probe from aptamer and its release into solution. Consequently, the decrease in current intensity of the differential pulse voltammogram of adsorbed MB was monitored and found to be linearly proportional with increasing concentration of VEGF165 in sample solution in the range of 1-120 pM with a limit of detection of 0.32p M. While, in "signal on" mechanism, the interaction of immobilized anti-VEGF165 aptamers on the electrode surface with VEGF165, led to more mass-transfer limiting of the [Fe(CN)6](3-/4-) probe to the electrode surface. Therefore, the charge transfer resistance (Rct) of the probe was increased linearly with increasing concentration of VEGF165 in the range of 2.5-250 pM with a limit of detection of 0.48 pM. The experimental results demonstrated that both of these mechanisms are suitable for determination of low levels of the VEGF165 tumor marker in serum samples.

A simple method for the fabrication of nanomotors based on a gold nanosheet decorated with CoPt nanoparticles

In this communication we present an extremely rapid, simple and template-free method for the electrochemical fabrication of CoPt/gold nanosheet motors (NSMs) via a three-step applied potential process.

Eco-synthesis of graphene and its use in dihydronicotinamide adenine dinucleotide sensing

In this paper, we report a green and eco-friendly approach to synthesize reduced graphene oxide (rGO) via a mild hydrothermal process using malt as a reduced agent. The proposed method is based on the reduction of graphene oxide (GO) in malt solution by making use of the reducing capability of phenolic compounds contained in malt solution. The obtained rGO was characterized by atomic force microscopy (AFM), ultraviolet-visible (UV-vis) absorption spectroscopy, X-ray diffraction spectroscopy (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Electrochemical impedance spectroscopy analysis revealed that the charge transfer resistance of rGO modified glassy carbon (GC) electrode was much lower than that of the GC electrode. The electrochemical behavior of dihydronicotinamide adenine dinucleotide (NADH) on rGO modified GC electrode was investigated by cyclic voltammetry and amperometry. Electrochemical experiments indicated that rGO/GC electrode exhibited excellent electrocatalytic activity toward the NADH, which can be attributed to excellent electrical conductivity and high specific surface area of the rGO composite. The resulting biosensor showed highly sensitive amperometric response to NADH with a low detection limit (0.33μM).

Imidazolium or guanidinium/layered manganese (III, IV) oxide hybrid as a promising structural model for the water-oxidizing complex of Photosystem II for artificial photosynthetic systems

Photosystem II is responsible for the light-driven biological water-splitting system in oxygenic photosynthesis and contains a cluster of one calcium and four manganese ions at its water-oxidizing complex. This cluster may serve as a model for the design of artificial or biomimetic systems capable of splitting water into oxygen and hydrogen. In this study, we consider the ability of manganese oxide monosheets to self-assemble with organic compounds. Layered structures of manganese oxide, including guanidinium and imidazolium groups, were synthesized and characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectrometry, and atomic absorption spectroscopy. The compounds can be considered as new structural models for the water-oxidizing complex of Photosystem II. The overvoltage of water oxidation for the compounds in these conditions at pH = 6.3 is ~0.6 V. These compounds may represent the first step to synthesize a hybrid of guanidinium or imidazole together with manganese as a biomimetic system for the water-oxidizing complex of Photosystem II.

A 2-(2-hydroxyphenyl)-1H-benzimidazole-manganese oxide hybrid as a promising structural model for the tyrosine 161/histidine 190-manganese cluster in photosystem II

In this communication, we report the synthesis, characterization, and electrochemistry of a 2-(2-hydroxyphenyl)-1H-benzimidazole-manganese oxide hybrid. Our results suggest that this compound is a promising model for the manganese cluster together with tyrosine-161 and histidine-190 in photosystem II of plants, algae and cyanobacteria.

Design, synthesis, DNA binding, and biological evaluation of water-soluble hybrid molecules containing two pyrazole analogues of the alkylating cyclopropylpyrroloindole (CPI) subunit of the antitumor agent CC-1065 and polypyrrole minor groove binders

We have synthesized and evaluated a series of hybrids, denoted 22--27, for in vitro cytotoxic activity against a variety of cancer cell lines. These hybrids represent a molecular combination of polypyrrole minor groove binders structurally related to the natural antitumor agent distamycin A and two pyrazole analogues of the left-hand segment called cyclopropylpyrroloindole (CPI) of the potent antitumor antibiotic (+)-CC-1065. These novel water-soluble hybrids have been designed to enhance the minor groove binding ability of alkylating units 20 and 21, which should increase their clinical appeal by overcoming the administration problems of (+)-CC-1065 derivatives. The DNA alkylating and cytotoxic activities against several tumor cell lines are reported and discussed in terms of their structural differences in relation to both the number of N-methyl pyrrole rings and the type of the alkylating unit tethered to the oligopeptidic frame. It may be noted that, in general, and especially for 22--24, the cytotoxicity of the hybrids was much greater than that of the alkylating units alone. In only one case, compound 27, did the hybrid have cytotoxic activity comparable to that of the alkylating unit alone against FM3A/0 cells. The broadest spectrum of activity and greatest potency was shown by the hybrid 24, in which the alkylating unit 20 and the deformyl distamycin A are tethered by 1-methyl 2,5-dicarbonyl pyrazole, with IC(50) values for the different tumor cell lines ranging from 7 to 71 nM. For compounds 22--24, the increase of the length of the pseudopeptidic moiety from one to three N-methylpyrrole residues led to an increased cytotoxicity. Among the hybrids tested for their inhibitory effects on the proliferation of murine L1210 leukemia cell line, compound 24 proved to be the most active (IC(50) = 7.4 nM), and in the sequencing gel experiments, it showed the strongest and most highly sequence-specific DNA alkylation activity. For compounds 22-24, the sequence specificity of DNA alkylation appears to be affected by the modification of the number of pyrrole rings, and the correlation between cytotoxicity and alkylation pattern suggests that 24 exerts its cytotoxicity through DNA sequence-specific alkylation of the third adenine located in the sequence 5'-ACAAAAATCG-3'. The two other hybrids 22 and 23 were slightly less active for tumor cell proliferation, with IC(50) values of 58 and 19 nM, respectively. With only one exception, none of the compounds was endowed with antiviral activity at subtoxic concentrations. Compound 24 inhibited the effect of vaccinia virus at a concentration that was significantly lower than its minimum cytotoxic concentration for the E(6)SM host cells. These compounds gave distinct patterns of alkylation in AT-rich sequences, indicating that minor structural changes produced marked alterations in sequence selectivity.

Synthesis and biological effects of a new series of 2-amino-3-benzoylthiophenes as allosteric enhancers of A1-adenosine receptor

New derivatives of PD 81,723, an allosteric enhancer of agonist binding to the A1-adenosine receptor, have been synthesized and evaluated in an intact cell assay. Compounds 3a, 3o and 3p appeared to be more potent than PD 81,723 and at a concentration of 0.1 microM caused significant reductions of cAMP content of CHO cells expressing the human A1-adenosine receptor. Compounds 4e and 4o appeared to be allosteric enhancers at a low concentration and antagonists at a higher concentration, whereas compounds 3c, 3g, 3s and 4l appeared to be weak antagonists that are also allosteric enhancers at the higher concentration of 10 microM.

Synthesis of conformationally constrained analogues of KN62, a potent antagonist of the P2X7-receptor

Conformationally constrained analogues of KN62 containing 1,2,3,4-tetrahydro-7-hydroxyisoquinoline-3-carboxylic acid with S configuration in position 3 were synthesized and their antagonist activities were tested on human macrophage cells. While KN62 is a potent antagonist of the P2X7 receptor, these analogues were inactive as antagonists and only one compound showed appreciable activity as P2X7 antagonist, which was 30 times weaker than that reported for KN62.

Geiparvarin analogues. 3. Synthesis and cytostatic activity of 3(2H)-furanone and 4,5-dihydro-3(2H)-furanone congeners of geiparvarin, containing a geraniol-like fragment in the side chain

Continuing our study on the structural features of geiparvarin (1), responsible for cytostatic activity, a series of 4,5-dihydro-3(2H)-furanones 10a-f and of 3(2H)-furanones 11a-f as well as 2",3"-dihydrogeiparvarin (14) have been designed and synthesized. Their cytostatic activity was evaluated against proliferation of murine (L1210, FM3A) and human (Raji, Molt/4F, and MT4) tumor cells. Modifications in the region of the olefinic double bond by introduction of the characteristic alkenyl side chain of ascofuranone (compounds 10a-f and 11a-f) markedly decreased the cytostatic activity as compared to geiparvarin itself, but this effect does not seem to be correlated to the presence of the furanone moiety linked to the alkenyl chain or to the ability to afford Michael type adducts. Replacement of the coumarin portion by other aromatic rings did not alter the cytostatic activity. The essential inactivity of 2",3"-dihydrogeiparvarin (14) points to the importance of the 3(2H)-furanone ring system in the cytostatic activity; consequently, this moiety may be considered as the determinant pharmacophore for antitumor activity, while the side chain plays a rather modulatory role.

New isoxazole derivatives of retinoids: synthesis and activity on growth and differentiation of tumor cells

The effects of several newly synthesized isoxazole analogues of retinoids on differentiation and proliferation of 'in vitro' cultured tumor cell lines are reported. Some of the tested compounds exhibit significative differentiating action, inducing adipogenic conversion of the Chinese hamster FH06T1-1 cell line in a range of 2-10 times the activity of retinoic acid and retinol. In addition, most of the compound tested display antiproliferative activity comparable to that of natural retinoids. The reported data could be of interest for experimental anticancer therapy.

Geiparvarin analogues. 2. Synthesis and cytostatic activity of 5-(4-arylbutadienyl)-3(2H)-furanones and of N-substituted 3-(4-oxo-2-furanyl)-2-buten-2-yl carbamates

In an attempt to determine some of the structural features of geiparvarin (1) that account for its cytostatic activity in vitro, a series of geiparvarin analogues (10a-i, 1, 12, and 14-16) which contain novel modifications in the region of the olefinic double bond and of the coumarin moiety have been designed and synthesized. Among the derivatives containing a carbamate moiety, only the analogues containing a carbamate group linked to an alkyl moiety 10b-i were endowed with potent cytostatic activity, whereas the corresponding benzene derivative 10a was devoid of any antiproliferative activity. 6-Methoxygeiparvarin 101 proved equally effective as geiparvin (1), while compounds containing an additional double bond at the side chain (12 and 14-16) were invariably 5-100-fold less effective than geiparvarin. Diene derivative 15, bearing a coumarin moiety, was essentially inactive against murine (L1210, FM3A) tumor cells but exhibited good activity against human (Molt/4F, MT-4) tumor cells.