SARS-CoV-2 virus label-free electrochemical nanohybrid MIP-aptasensor based on Ni3(BTC)2 MOF as a high-performance surface substrate.

A dual recognition biosensor was developed via introducing aptamer strings and molecular imprinting polymer (MIP) for the selective detection of intact SARS-CoV-2 virus based on screen printed carbon electrode (SPCE) modified with nickel-benzene tricarboxylic acid-metal-organic framework (Ni3(BTC)2 MOF) synthesized by in situ growth method, SARS-CoV-2 S protein-specific amino-aptamer and electropolymerization of dopamine (ePDA). The proposed biosensor showed an excellent linear relationship between charge transfer resistance (Rct) and increase in virus concentration in the range 10 to 108 plaque-forming units/mL (PFU/mL) with a low detection limit of 3.3 ± 0.04 PFU/mL and response time of 20 min. Compared with single-element sensors (aptamer or MIP), it showed higher selectivity for  the SARS-CoV-2 virus and facilitated detection in real samples.

Label-free electrochemical aptasensor for rapid detection of SARS-CoV-2 spike glycoprotein based on the composite of Cu(OH)2 nanorods arrays as a high-performance surface substrate.

The development of advanced electrode materials and the combination of aptamer with them have improved dramatically the performance of aptasensors. Herein, a new architecture based on copper hydroxide nanorods (Cu(OH)2 NRs) are directly grown on the surface of screen printed carbon electrode (SPCE) using a two-step in situ, very simple and fast strategy and was used as a high-performance substrate for immobilization of aptamer strings, as well as an electrochemical probe to development a label-free electrochemical aptasensor for SARS-CoV-2 spike glycoprotein measurement. The Cu(OH)2 NRs was characterized using X-ray Diffraction (XRD) and electron microscopy (FESEM). In the presence of SARS-CoV-2 spike glycoprotein, a decrease in Cu(OH)2 NRs-associated peak current was observed that can be owing to the target-aptamer complexes formation and thus blocking the electron transfer of Cu(OH)2 NRs on the surface of electrode. This strategy exhibited wide dynamic range in of 0.1 fg mL-1 to 1.2 µg mL-1 and with a high sensitivity of 1974.43 µA mM-1 cm-2 and low detection limit of 0.03 ± 0.01 fg mL-1 of SARS-CoV-2 spike glycoprotein deprived of any cross-reactivity in the presence of possible interference species. In addition, the good reproducibility, repeatability, high stability and excellent feasibility in real samples of saliva and viral transport medium (VTM) were found from the provided aptasensor. Also, the aptasensor efficiency was evaluated by real samples of sick and healthy individuals and compared with the standard polymerase chain reaction (PCR) method and acceptable results were observed.

Hierarchical nickel hydroxide nanosheets grown on hollow nitrogen doped carbon nanoboxes as a high-performance surface substrate for alpha-fetoprotein cancer biomarkers electrochemical aptasensing.

During recent decades, we have witnessed a great improvement in the performance of aptamer-based sensors, specifically when aptamers are combined with new nanomaterials; as a platform for biosensors. The design of hollow carbon-based materials has also received a lot of attention due to its excellent properties in various applications. Herein, we aim at designing hierarchical porous Ni(OH)2 nanosheets on hollow N-doped carbon nanoboxes Ni(OH)2@N-C n-box). In this sense, we obtained the hollow N-C n-box skeletons from the Fe2O3 nanocubes template. The development of label-free electrochemical aptasensor was carried out using the covalently immobilizing NH2-functionalized aptamer on Ni(OH)2@N-C n-box as an efficient substrate. The Ni(OH)2@N-C n-box was characterized using scanning fourier transform infrared spectroscopy (FTIR), X-ray Diffraction (XRD), Brunauer, Emmett and Teller (BET), transmission electron microscopes (TEM) and electron microscopy (FESEM). The electrochemical evaluations clarified the fact that a linear relationship exists between the alpha-fetoprotein (AFP) contents and the charge transfer resistance (Rct) (from 1 fg mL-1 to 100 ng mL-1) with a low detection limit of 0.3 fg mL-1. Moreover, regarding the aptasensor, the superior detection recoveries were experienced in real biological samples, illustrating its great detection performance and practical feasibility. Considering the aptasensor application, these studies showed that Ni(OH)2@N-C n-box possesses different enhanced electrochemical features, making it appropriate as an electrode material for aptasensor application.

An electrochemical immunosensor using SARS-CoV-2 spike protein-nickel hydroxide nanoparticles bio-conjugate modified SPCE for ultrasensitive detection of SARS-CoV-2 antibodies.

As a promising approach for serological tests, the present study aimed at designing a robust electrochemical biosensor for selective and quantitative analysis of SARS-CoV-2-specific viral antibodies. In our proposed strategy, recombinant SARS-CoV-2 spike protein antigen (spike protein) was used as a specific receptor to detect SARS-CoV-2-specific viral antibodies. In this sense, with a layer of nickel hydroxide nanoparticles (Ni(OH)2 NPs), the screen-printed carbon electrode (SPCE) surface was directly electrodeposited to ensure better loading of spike protein on the surface of SPCE. The differential pulse voltammetry (DPV) showed signals which were inversely proportional to the concentrations of the antibody (from 1 fg mL-1 L to 1 µg mL-1) via a specific and stable binding reaction. The assay was performed in 20 min with a low detection limit of 0.3 fg mL-1. This biodevice had high sensitivity and specificity as compared to non-specific antibodies. Moreover, it can be regarded as a highly sensitive immunological diagnostic method for SARS-CoV-2 antibody in which no labeling is required. The fabricated hand-held biodevice showed an average satisfactory recovery rate of ~99-103% for the determination of antibodies in real blood serum samples with the possibility of being widely used in individual serological qualitative monitoring. Also, the biodevice was tested using real patients and healthy people samples, where the results are already confirmed using the enzyme-linked immunosorbent assay (ELISA) procedure, and showed satisfactory results.

Electrochemical immunosensor with Cu2O nanocube coating for detection of SARS-CoV-2 spike protein.

Severe acute respiratory syndrome SARS-CoV-2 has caused a global pandemic starting in 2020. Accordingly, testing is crucial for mitigating the economic and public health effects. In order to facilitate point-of-care diagnosis, this study aims at presenting a label-free electrochemical biosensor as a powerful nanobiodevice for SARS-CoV-2 spike protein detection. Utilizing the IgG anti-SARS-CoV-2 spike antibody onto the electrode surface as a specific platform in an ordered orientation through staphylococcal protein A (ProtA) is highly significant in fabricating the designed nanobiodevice. In this sense, the screen-printed carbon electrode modified with Cu2O nanocubes (Cu2O NCs), which provide a large surface area in a very small space, was applied in order to increase the ProtA loading on the electrode surface. Accordingly, the sensitivity and stability of the sensing platform significantly increased. The electrochemical evaluations proved that there is a very good linear relationship between the charge transfer resistance (Rct) and spike protein contents via a specific binding reaction in the range 0.25 fg mL-1 to 1 µg mL-1. Moreover, the assay when tested with influenza viruses 1 and 2 was performed in 20 min with a low detection limit of 0.04 fg mL-1 for spike protein without any cross-reactivity. The designed nanobiodevice exhibited an average satisfactory recovery rate of ~ 97-103% in different artificial sample matrices, i.e., saliva, artificial nasal, and universal transport medium (UTM), illustrating its high detection performance and practicability. The nanobiodevice was also tested using real patients and healthy samples, where the results had been already obtained using the standard polymerase chain reaction (PCR) procedure, and showed satisfactory results. Graphical abstract.

Electrochemical immunosensor for determination of Staphylococcus aureus bacteria by IgY immobilized on glassy carbon electrode with electrodeposited gold nanoparticles.

A new ultrasensitive immunosensor is proposed based on the covalently attached anti-protein A antibody (IgY) on deposited gold nanoparticle (AuNP)-modified glassy carbon electrode (GCE) for the electrochemical measurement of Staphylococcus aureus (S. aureus). Chicken IgY as a capture antibody provides highly selective and specific binding to the target bacteria and selectively captures the S. aureus in its three-dimensional space. Due to that it can eliminate the interference from protein G-producing Streptococcus. In addition, the electron-transfer characteristic of [Fe(CN)6]4-/3- is hindered by this combination; as it is reflected on the electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) curves. The proposed immunosensor displays a wide linear dynamic range from 10 to 107 CFU mL-1 with a detection limit of 3.3 CFU mL-1 with RSD 3.0%. It is capable to accurately determine S. aureus in milk and human blood serum as a complex matrix sample with satisfactory recovery of ∼ 97-103%. The immunosensor also displays high selectivity over other bacteria and acceptable stability. Presumably, our study can be regarded as the first one to report chicken IgY in order to detect S. aureus based on an electrochemical method.Graphical abstract.

The development of an electrochemical nanoaptasensor to sensing chloramphenicol using a nanocomposite consisting of graphene oxide functionalized with (3-Aminopropyl) triethoxysilane and silver nanoparticles.

In the present research, a nanoaptasensor is proposed for electrochemical measurement of chloramphenicol (CAP). To this purpose, the nanocomposite prepared from graphene oxide and functionalized with (3-Aminopropyl) triethoxysilane/silver nanoparticles to the abbreviated AgNPs/[NH2-Si]-f-GO, was utilized to modify the glassy carbon electrode (GCE). Furthermore, the modified electrode was also investigated using the electrochemical methods such as electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The AgNPs/[NH2-Si]-f-GO nanocomposite was investigated by UV-Vis spectrophotometry. Fourier transform infrared (FT-IR) spectrometry and transmission electron microscopy (TEM). Moreover, [Fe(CN)6]3-/4 solution in the role of an electrochemical probe was applied. The AgNPs/[NH2-Si]-f-GO nanocomposite was confirmed as a good layer to covalent immobilization of aptamer (Apt) onto the GCE surface. In this sense, the DPV was used as a sensitive electrochemical technique for the measurement of CAP with an appropriate linear concentration range which was found to be between 10 pM and 0.2 µM and, with a low limit of detection, it equaled 3.3 pM. CAP which was identified in the presence of other usual antibiotics existed in the real samples.

Impedimetric ultrasensitive detection of chloramphenicol based on aptamer MIP using a glassy carbon electrode modified by 3-ampy-RGO and silver nanoparticle.

In this research work, a biosensor with a dual recognition system was fabricated and founded on a combination of aptasensing and the molecular imprinting union of the chloramphenicol (CAP) selective detection. CAP, is an antibiotic, was applied in veterinary and human in order to treat gram-positive and gram-negative infections. It is worth mentioning that CAP residue brings about earnest side effects on human health. According to this, in this sensing system, 3-aminomethyl pyridine functionalized graphene oxide (GO) (3-ampy-RGO) has been coated on the surface of GCE. Afterwards, the silver nanoparticle (AgNPs) was coated on the 3-ampy-RGO/GCE and, then, the CAP complex-amino-aptamer (NH2-Apt[CAP]) was attached to the AgNP/3-ampy-RGO/GCE using a kind of bonding formation of Ag-N. In this sense, it is worth noting that the resorcinol electropolymerization around the complex of aptamer/CAP would confine the complex and, then, retain the aptamer. Following the CAP removal, the MIP cavity, as it was supposed, synergistically acted with that of the embedded aptamer in order to construct a nanohybrid receptor. Interestingly, the double exact property of the molecular imprinting polymers and aptamers led to the superb sensing properties. In the mentioned system it was illustrated that the linear range was from 1.0 pM to 1.0 nM with the detection limit of 0.3 pM; consequently, as observed, it was better than or as good as other similar assays. Moreover, the mentioned system whose activity was observed in the various interferences presence showed great selectivity in detected the CAP. Finally, the designed sensor exhibited outstanding results when applied to detect CAP in milk samples.