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 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.

An Electrochemical Immunosensor for the Determination of Procalcitonin Using the Gold-Graphene Interdigitated Electrode.

Procalcitonin (PCT) is considered a sepsis and infection biomarker. Herein, an interdigitated electrochemical immunosensor for the determination of PCT has been developed. The interdigitated electrode was made of the laser-engraved graphene electrode decorated with gold (LEGE/Aunano). The scanning electron microscopy indicated the LEGE/Aunano has been fabricated successfully. After that, the anti-PTC antibodies were immobilized on the surface of the electrode by using 3-mercaptopropionic acid. The electrochemical performance of the fabricated immunosensor was studied using electrochemical impedance spectroscopy (EIS). The EIS method was used for the determination of PCT in the concentration range of 2.5-800 pg/mL with a limit of detection of 0.36 pg/mL. The effect of several interfering agents such as the C reactive protein (CRP), immunoglobulin G (IgG), and human serum albumin (HSA) was also studied. The fabricated immunosensor had a good selectivity to the PCT. The stability of the immunosensor was also studied for 1 month. The relative standard deviation (RSD) was obtained to be 5.2%.

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-Aunano was then attached to the surface of the working electrode of a laser-engraved graphene electrode (LEGE). Subsequently, the LEGE/NPAOM-Si-S-Aunano 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-Aunano-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-Aunano-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-Aunano-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 (Kd) 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 (Ret) 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.

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.

An optical biosensor for the determination of cathepsin B as a cancer-associated enzyme using nanoporous anodic alumina modified with human serum albumin-thionine.

An interferometric reflectance spectroscopy-based biosensor for the determination of cathepsin B (Cat B) as a cancer-related enzyme has been fabricated. For this purpose, the nanoporous anodic alumina (NAA) was fabricated electrochemically. The NAA was then modified with the amino-silane coupling agent. After that, human serum albumin (HSA) was immobilized into the NAA pores by using glutaraldehyde as a cross-linking agent. Subsequently, the carboxylic group of HSA was activated with N-ethyl-N'-(3-(dimethylamino)propyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) to attach to thionine (TH) as a photoprobe to fabricate the labeled HSA (HSA-TH). HSA-TH plays a significant role in this sensor to determine cathepsin B as a model analyte for the development of the interferometric reflectance spectroscopy-based biosensor for the measurement of protease. The attached TH adsorbed the illuminated white light on NAA modified with HSA-TH. Therefore, the intensity of the reflected light to the charge-coupled device (CCD) detector decreased in the wavelength range 450-1050 nm. In the presence of Cat B, HAS-TH cleaved into short peptide fragments and washed away by flow cell system. Since TH was removed from NAA, the intensity of the reflected light increased. The peak area has a logarithmic relationship with the concentration of Cat B in the range 0.5 to 64.0 nM. The limit of detection of the biosensor sensor was 0.08 nM. The optical sensor was used for the determination of Cat B in a human serum sample. Graphical abstract Schematic presentation of biosensor for the determination of the cathepsin B which is based on nanoporous anodic alumina modified with HSA-thionine. The principle response of the optical biosensor is based on detecting changes in the intensity of the reflected light after cleaving the immobilized HSA-thionine by cathepsin B into short peptide fragments.

Remote biosensor for the determination of trypsin by using nanoporous anodic alumina as a three-dimensional nanostructured material.

The determination of trypsin in the human real sample is a routine medical investigation to assess the pancreatic disease. Herein, we fabricated an interferometric reflectance spectroscopy based biosensor for the determination trypsin. For this purpose, urease and fluorescein 5(6)-isothiocyanate (FLITC) were immobilized on the nanoporous anodic alumina (NAA). The operation principle of the proposed biosensor is based on the change in the pH of the solution during the reaction of urease and urea and therefore change in the light-absorbing ability of FLITC in the presence of trypsin. The reaction of the urease enzyme with urea increased the pH of the solution because of producing ammonia. This increase in the pH of solution increased the light-absorbing ability of the immobilized FLITC on NAA and therefore the intensity of the reflected light from the NAA to the charge-coupled device detector decreased. In the presence of trypsin, the catalytic activity of immobilized urease on NAA decreased. This decrease in the activity of urease enzyme consequent on the decrease in the amount of the generated ammonia. Therefore, the immobilized FLITC on the NAA did not absorb more light and consciously, the intensity of the light reflected light into the detector increased. The proposed biosensor exhibited a good response to the concentration of trypsin in the range of 0.25-20 µg.mL-1 with the limit of detection of 0.06 µg.mL-1.

Highly sensitive IRS based biosensor for the determination of cytochrome c as a cancer marker by using nanoporous anodic alumina modified with trypsin.

The determination of cytochrome c in the human serum sample is a regular medical investigation performed to assess cancer diseases. Herein, we used interferometric reflectance spectroscopy (IRS) based biosensor for the determination of cytochrome c. For this purpose first, the nanoporous anodic alumina (NAA) was fabricated. Then, the NAA pore walls were functionalized with 3-aminopropyl trimethoxy silane (NAA-NH2). Subsequently, the trypsin enzyme was immobilized on the NAA pore walls. The sensing principle of proposed IRS sensor to cytochrome c is based on a change in the intensity of the reflected light to a charge-coupled device (CCD) detector after digesting of cytochrome c by immobilized trypsin enzymes on NAA-NH2 into the heme-peptide fragment. The heme-peptide fragment then oxidized 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) to green color ABTS·- anion radical in the presence of hydrogen peroxide. The generated green color ABTS·- anion radical solution adsorbed the white light and therefore the intensity of the reflected light from NAA to the CCD decreased. The decrease in the intensity of the white light had a logarithmic relationship with the concentration of the cytochrome c in the range of 1-100 nM. The limit of detections (LOD) for cytochrome c was 0.5 nM. The proposed biosensor exhibited high selectivity, sensitivity, and good stability.

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 ß 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 ß (Aß) 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 Aß 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 Aß oligomers. The proposed aptasensor exhibited a good response to the concentration of Aß 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 (aptamerKH1C12/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 aptamerKH1C12/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/aptamerKH1C12/nanomotors. Because of the high affinity of capture aptamer to complementary nucleotide sequences of aptamerKH1C12, the HL-60 cancer cells released on the surface of aptamerKH1C12/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-Aunano/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.

Flow injection amperometric sandwich-type aptasensor for the determination of human leukemic lymphoblast cancer cells using MWCNTs-Pdnano/PTCA/aptamer as labeled aptamer for the signal amplification.

In this research, we demonstrated a flow injection amperometric sandwich-type aptasensor for the determination of human leukemic lymphoblasts (CCRF-CEM) based on poly(3,4-ethylenedioxythiophene) decorated with gold nanoparticles (PEDOT-Aunano) as a nano platform to immobilize thiolated sgc8c aptamer and multiwall carbon nanotubes decorated with palladium nanoparticles/3,4,9,10-perylene tetracarboxylic acid (MWCNTs-Pdnano/PTCA) to fabricate catalytic labeled aptamer. In the proposed sensing strategy, the CCRF-CEM cancer cells were sandwiched between immobilized sgc8c aptamer on PEDOT-Aunano modified surface electrode and catalytic labeled sgc8c aptamer (MWCNTs-Pdnano/PTCA/aptamer). After that, the concentration of CCRF-CEM cancer cells was determined in presence of 0.1 mM hydrogen peroxide (H2O2) as an electroactive component. The attached MWCNTs-Pdnano nanocomposites to CCRF-CEM cancer cells amplified the electrocatalytic reduction of H2O2 and improved the sensitivity of the sensor to CCRF-CEM cancer cells. The MWCNT-Pdnano nanocomposite was characterized with transmission electron microscopy (TEM) and energy dispersive X-ray (EDX). The electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to confirm the stepwise changes in the electrochemical surface properties of the electrode. The proposed sandwich-type electrochemical aptasensor exhibited an excellent analytical performance for the detection of CCRF-CEM cancer cells ranging from 1.0 × 101 to 5.0 × 105 cells mL-1. The limit of detection was 8 cells mL-1. The proposed aptasensor showed high selectivity toward CCRF-CEM cancer cells. The proposed aptasensor was also applied to the determination of CCRF-CEM cancer cells in human serum samples.

A high sensitive visible light-driven photoelectrochemical aptasensor for shrimp allergen tropomyosin detection using graphitic carbon nitride-TiO2 nanocomposite.

Herein, for the first time a visible-light-driven photoelectrochemical (PEC) aptasensor for shrimp tropomyosin determination was fabricated by using graphitic carbon nitride (g-C3N4) and titanium dioxide (TiO2) as photoactive nanomaterials, ascorbic acid (AA) as electron donor and ruthenium (III) hexaammine (Ru(NH3)63+) as signal enhancer. The surface of an ITO electrode was first modified with g-C3N4, TiO2, and polyethyleneimine (PEI) and then the amine terminal aptamerTROP probe was attached to PEI by the use of glutaraldehyde (GA) as cross-linker. After that, Ru(NH3)63+ was adsorbed on aptamer to enhance the photocurrent signal. The principle of proposed PEC aptasensor is based on the formation of a selective complex between tropomyosin and immobilized aptamerTROP probe on the surface of ITO/g-C3N4-TiO2/PEI/aptamerTROP-Ru(NH3)6+3. After the incubation of tropomyosin with TROP aptamer probe, the photocurrent signal decreased due to releasing adsorbed Ru(NH3)63+ on aptamer and preventing AA from scavenging photogenerated holes to the photoactive modified electrode. Under the optimized conditions, the fabricated PEC aptasensor was used for the determination of shrimp tropomyosin in the concentration range of 1-400ngmL-1 with a limit of detection of 0.23ngmL-1. The proposed PEC aptasensor exhibited high selectivity, sensitivity, and good stability.

Functionalized Fe3O4/graphene oxide nanocomposites with hairpin aptamers for the separation and preconcentration of trace Pb2+ from biological samples prior to determination by ICP MS.

Lead (Pb) as a topically poisonous metal represents a serious threat to the ecological environment and especially to human beings. Therefore, it is urgent to develop a rapid and reliable monitoring technique for this heavy metal in the environmental samples. In the present study, we have designed a selective and sensitive method for the determination of ultratrace contents of Pb2+ in biological samples, based on the guanine (G)-quadruplex formed by the aptamer with hairpin structure and Pb2+. For this purpose, Pb2+ specific aptamer serving as affinity probe to capture and separate trace amounts of the analyte, was covalently linked to Fe3O4/graphene oxide (GO) surface by using a suitable cross-linking agent. Then, the G-quadruplex complex was formed by the opening of the "neck- ring" of the hairpin structure of aptamer in the presence of Pb2+. Inductively coupled plasma mass spectrometry (ICP-MS) was used for determination of Pb2+ in biological matrices. The analysis conditions were optimized and the performance of the proposed method was investigated. Under optimum conditions, the calibration curve was linear over the range of 0.3-867.5µgL-1 and an enrichment factor (EF) of 50 was obtained. The limit of detection (LOD) was 0.05µgL-1 and the relative standard deviation (RSD) for single-sorbent repeatability and sorbent-to-sorbent reproducibility were <4.7% and 8.8% (n=5), respectively. The accuracy of aptamer-based affinity purification method was confirmed by the analysis of quality control materials (QCMs, Seronorm™ Blood REF NO 201505 and Urine REF NO 2525).