DNA Electrochemical Aptasensor for Detecting Fumonisins B1 Based on Graphene and Thionine Nanocomposite

In this paper, a novel aptasensor was designed by with the dual amplification of Au nanoparticles (AuNPs) and graphene/thionine nanocomposites (GS‐TH) for sensitive determination of fumonisins B₁ (FB₁). AuNPs is modified at the electrode surface to increase the electrical conductivity and fabricate specific recognition interface for FB₁ through the hybridization of capture DNA and its aptamer. Large number of TH molecules were loaded at the surface of graphene sheet to served as electrochemical probe and increase its electrochemical signal due to the excellent conductivity and large surface area of graphene sheet. This type of nanocomposites is then assembled to the single strand section of FB₁ aptamer at electrode surface by π–π stacking interactions between them, leading to an enhanced electrochemical signal. After the specific combination between FB₁ aptamer and its target (FB₁) in solution, GS–TH was released from electrode surface, resulting in a decreased electrochemical signal. The result demonstrated that the decreased currents were proportional to the FB₁ concentration in the range of 1–10⁶ pg/mL with a detection limit of 1 pg/mL. Besides, the developed aptasensor was also applied successfully for the determination of FB₁ in feed samples. The result shows this aptasensor has a higher sensitivity and selectivity.     

Label‐Free Electrochemical Aptasensor for Determination of Chloramphenicol Based on Gold Nanocubes‐Modified Screen‐Printed Gold Electrode

An ultrasensitive label‐free electrochemical aptasensor was developed for selective detection of chloramphenicol (CAP). The aptasensor was made using screen‐printed gold electrode modified with synthesized gold nanocube/cysteine. The interactions of CAP with aptamer were studied by cyclic voltammetry, square wave voltammetry (SWV) and electrochemical impedance spectroscopy. Under optimized conditions, two linear calibration curves were obtained for CAP determination using SWV technique, from 0.03 to 0.10 µM and 0.25–6.0 µM with a detection limit of 4.0 nM. The aptasensor has the advantages of good selectivity and stability and applied to the determination of CAP in human blood serum sample.     

Electrochemical aptasensor for detection of copper based on a reagentless signal-on architecture and amplification by gold nanoparticles

A highly sensitive and specific electrochemical aptasensor for Cu(2+) detection based on gold nanoparticles (AuNPs) is presented. In this work, AuNPs offered a big surface area to immobilize a large number of aptamers and excellent electrochemical signal transduction. Its high sensitivity, low detection limit, and wide detection range are the main advantages over our former copper aptasensor. The peak current increased proportionally to the Cu(2+) concentration over the range from 0.1 nM to 10 μM with a detection limit of 0.1 pM. The presence of other divalent metal ions did not affect the detection of Cu(2+), which indicates a high specificity of Cu(2+) detection could be detected. Rapidity, simplicity, and excellent selectivity make it suitable for practical use in determination of Cu(2+) from lake samples.     

A Hairpin Electrochemical Aptasensor for Sensitive and Specific Detection of Thrombin Based on Homogenous Target Recognition

An electrochemical aptasensor was developed for sensitive and specific detection of thrombin by combining homogenous recognition strategy and gold nanoparticles (AuNPs) amplification. Streptavidin‐alkaline phosphatase was used as reporter molecule. Compared with the traditional hairpin aptasensor monitoring the distance of the redox molecule from the electrode surface, the proposed aptasensor successfully overcome the limitations of distance and improved the stability and high affinity of the aptamer hairpin through homogenous recognition, which enhanced the sensitivity and selectivity of the sensors effectively. Additionally, AuNPs were employed to increase the active area and conductivity of the electrode, thus, improving the sensitivity of the aptasensor. As a result, the designed thrombin detection sensor obtained a lower detection limit of 0.52 pM in buffer and 6.9 pM in blood serum.     

Label‐free Electrochemical Aptasensor for Carcino‐embryonic Antigen Based on Ternary Nanocomposite of Gold Nanoparticles,Hemin and Graphene

In this report, a label‐free electrochemical aptasensor for carcino‐embryonic antigen (CEA) was successfully developed based on a ternary nanocomposite of gold nanoparticles, hemin and graphene nanosheets (AuNPs‐HGNs). This nanocomposite was prepared by decorating gold nanoparticles on the surface of hemin functionalized graphene nanosheets via a simple wet‐chemical strategy. The aptamer can be assembled on the surface of AuNPs‐HGNs/GCE (glassy carbon electrode) through Au‐S covalent bond to form the sensing interface. Hemin absorbed on the graphene nanosheets not only acts as a protective agent of graphene sheets, but also as an in situ probe base on its excellent redox properties. Gold nanoparticles provide with both numerous binding sites for loading CEA binding aptamer (CBA) and good conductivity to promote the electron transfer. The current changes, which are caused by CEA specifically binding on the modified electrode, are exploited for the label‐free detection of CEA in a very rapid and convenient protocol. Therefore, the method has advantages of high sensitivity, wide linear range (0.0001–10 ng mL^?1), low detection limit (40 fg mL^?1) and attractive specificity. The results illustrate that the proposed label‐free electrochemical aptasensor has a potential application in the biological or clinical target analysis for its simple operation and low cost.     

A highly selective and sensitive cocaine aptasensor based on covalent attachment of the aptamer-functionalized AuNPs onto nanocomposite as the support platform

Based on the conformational changes of the aptamer-functionalized gold nanoparticles (AuNPs) onto MWCNTs/IL/Chit nanocomposite as the support platform, we have developed a sensitive and selective electrochemical aptasensor for the detection of cocaine. The 5′-amine-3′-AuNP terminated aptamer is covalently attached to a MWCNTs/IL/Chit nanocomposite. The interaction of cocaine with the aptamer functionalized AuNP caused the aptamer to be folded and the AuNPs with negative charge at the end of the aptamer came to the near of electrode surface therefore, the electron transfer between ferricyanide (K₃Fe(CN)₆) as redox probe and electrode surface was inhibited. A decreased current of (K₃Fe(CN)₆) was monitored by differential pulse voltammetry technique. In an optimized condition the calibration curve for cocaine concentration was linear up to 11 μM with detection limit (signal-to-noise ratio of 3) of 100 pM. To test the selectivity of the prepared aptasensor sensing platform applicability, some analgesic drugs as the interferes were examined. The potential of the aptasensor was successfully applied for measuring cocaine concentration in human blood serum. Based on our experiments it can be said that the present method is absolutely beneficial in developing other electrochemical aptasensor.     

A Multifunctional N-Doped Cu–MOFs (N–Cu–MOF) Nanomaterial-Driven Electrochemical Aptasensor for Sensitive Detection of Deoxynivalenol

Deoxynivalenol (DON) is one of the most common mycotoxins in grains, causing gastrointestinal inflammation, neurotoxicity, hepatotoxicity and embryotoxicity, even at a low quantity. In this study, a facile electrochemical aptasensor was established for the rapid and sensitive determination of DON based on a multifunctional N-doped Cu-metallic organic framework (N–Cu–MOF) nanomaterial. The N–Cu–MOF, with a large specific surface area and good electrical conductivity, served not only as an optimal electrical signal probe but also as an effective supporting substrate for stabilizing aptamers through the interactions of amino (-NH₂) and copper. Under the optimal conditions, the proposed sensor provided a wide linear concentration range of 0.02–20 ng mL⁻¹ (R² = 0.994), showing high sensitivity, with a lower detection limit of 0.008 ng mL⁻¹, and good selectivity. The sensor’s effectiveness was also verified in real spiked wheat samples with satisfactory recoveries of 95.6–105.9%. The current work provides a flexible approach for the rapid and sensitive analysis of highly toxic DON in food samples and may also be easily extended to detect other hazardous substances with alternative target-recognition aptamers.     

Aptamer-based highly sensitive electrochemical detection of thrombin via the amplification of graphene

Herein, we successfully fabricated a highly sensitive label-free electrochemical aptasensor for thrombin based on the amplification of graphene (Gra). The excellent electrochemical probe of nickel hexacyanoferrate nanoparticles (NiHCFNPs) was introduced to form Nafion-Graphene-NiHCFNPs (Nf-Gra-NiHCFNPs) nanocomposites membrane on the gold electrode. The employment of graphene not only enhanced the surface area of the electrode with increased NiHCFNPs immobilization, but also improved the conductivity of the electrode, which further effectively improved the sensitivity of this proposed aptasensor. Subsequently, AuNPs layer was formed to immobilize the thrombin aptamer (TBA) and enhance the stability of the composite monolayer mentioned above. Then, thiol-modified TBA was assembled onto the AuNPs layer. Thereafter, hexanethiol (HT) was employed to block the possible remaining active sites. With the dual amplification of Gra and AuNPs, the resulting aptasensor exhibited good current response to target thrombin with a wide linear range extended from 1 pM to 80 nM (the detection limit was 0.3 pM). Additionally, the morphologies of bare Au substrate, nickel hexacyanoferrate nanoparticles (NiHCFNPs) and nanocomposites were successfully characterized by atomic force microscopy (AFM).     

A novel colorimetric aptasensor for detection of chloramphenicol based on lanthanum ion–assisted gold nanoparticle aggregation and smartphone imaging

A label-free, rapid response colorimetric aptasensor for sensitive detection of chloramphenicol (CAP) was proposed, which was based on the strategy of ssDNA-modified gold nanoparticle (AuNP) aggregation assisted by lanthanum (La³⁺) ions. The AuNPs generated a color change that could be monitored in the red, green, and blue and analyzed by the smartphone imaging app. La³⁺, as a trigger agent, strongly combined with the phosphate groups of the surface of ssDNA-AuNPs probe, which helps create AuNP aggregation and the color change of AuNPs from red to blue. On the contrary, when mixing with CAP, the aptamer (Apt) bound to CAP to form a rigid structure of the Apt-CAP complex, and La³⁺ attached to the phosphate groups of the complex, which prevented the aptamer from binding to the surface of the AuNPs. As a result, the color of the AuNPs changed to violet-red. Finally, UV-vis absorption spectroscopy and the smartphone imaging app were employed to determine CAP with a lower detection limit of 7.65 nM and 5.88 nM, respectively. The proposed strategy featuring high selectivity and strong anti-interference ability for detection of CAP in practical samples was achieved. It is worth mentioning that the simple and portable colorimetric aptasensor will be used for facilitating on-site detection of food samples.

     

Dopamine-loaded Liposomes-amplified Electrochemical Immunoassay Based on MXene (Ti3C2)−AuNPs

A simple and novel electrochemical immunoassay based on MXene (Ti₃C₂)−Au nanoparticles (AuNPs) was designed for sensitive screening of a disease-related biomarker, prostate-specific antigen (PSA), by using dopamine-loaded liposomes (DLL) for signal amplification. The system involves two parts, namely, sandwich-type immunoreaction to capture DLL and electrochemical measurement of dopamine. The target PSA can cause a specific antigen-antibody reaction and DLL are enriched in the enzyme-labeled pores. After Triton X-100 is injected into the detection cell, the carried DLL was quickly cracked to release dopamine wrapped in the cavity. A nanocomposite consisting of MXene (Ti₃C₂) support to immobilize Au nanoparticles (Ti₃C₂−Au) was utilized to modify a glassy carbon electrode, which gives a strongly enhanced differential pulse voltammetric (DPV) signals for dopamine. In this case, the change of DPV signal depends on the amount of dopamine released by liposomes, which is further positively correlated with the concentration of the analyte PSA. Combining the of MXene (Ti₃C₂)−AuNPs nanomaterials (large specific surface area, excellent electrical conductivity, and good electrocatalytic properties) with the liposome signal amplification strategy, the electrochemical immunoassay exhibited excellent performance toward PSA determination with a broad linear range of 1 pg/mL to 50 ng/mL and limit of detection down to 0.31 pg/mL (S/N=3) under the optimized testing conditions. High specificity for PSA over other disease-related biomarkers and acceptable nanocomposite/electrode stability were acquired. The excellent analytical performance shows that the current strategy provides an effective detection platform for clinical sample analysis.     

Sensitive determination of hydrazine using poly(phenolphthalein), Au nanoparticles and multiwalled carbon nanotubes modified glassy carbon electrode

This study reports a detailed analysis of an electrode material containing poly(phenolphthalein), carbon nanotubes and gold nanoparticles which shows superior catalytic effect towards to hydrazine oxidation in Britton–Robinson buffer (pH 10.0). Glassy carbon electrode was modified by electropolymerization of phenolphthalein (PP) monomer (poly(PP)/GCE) and the multiwalled carbon nanotubes (MWCNTs) was dropped on the surface. This modified surface was electrodeposited with gold nanoparticles (AuNPs/CNT/poly(PP)/GCE). The fabricated electrode was analysed the determination of hydrazine using cyclic voltammetry, linear sweep voltammetry and amperometry. The peak potential of hydrazine oxidation on bare GCE, poly(PP)/GCE, CNT/GCE, CNT/poly(PP)/GCE, and AuNPs/CNT/poly(PP)/GCE were observed at 596 mV, 342 mV, 320 mV, 313 mV, and 27 mV, respectively. A shift in the overpotential to more negative direction and an enhancement in the peak current indicated that the AuNPs/CNT/poly(PP)/GC electrode presented an efficient electrocatalytic activity toward oxidation of hydrazine. Modified electrodes were characterized with High-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Amperometric current responses in the low hydrazine concentration range of 0.25–13 µM at the AuNPs/CNT/poly(PP)/GCE. The limit of detection (LOD) value was obtained to be 0.083 µM. A modified electrode was applied to naturel samples for hydrazine determination.     

Label-free aptasensor for thrombin using a glassy carbon electrode modified with a graphene-porphyrin composite

We report on an electrochemical aptasensor for the ultrasensitive determination of thrombin. A glassy carbon electrode modified with a graphene-porphyrin nanocomposite exhibits excellent electrochemical activity and can be used as a redox probe in differential pulse voltammetry of the porphyrin on its surface. The thrombin aptamer is then immobilized via p-stacking interactions between aptamer and graphene and π-π stacking with porphyrin simultaneously. The resulting electrochemical aptasensor displays a linear response to thrombin in the 5–1,500 nM concentration range and with a limit of detection of 0.2 nM (at an S/N of 3). The sensor benefits from the synergetic effects of graphene (with its high conductivity and high surface area), of the porphyrin (possessing excellent electrochemical activity), and of the aptamer (with its high affinity and specificity). This kind of aptasensor conceivably represents a promising tool for bioanalytical applications.

Electrochemical impedance spectroscopy detection of lysozyme based on electrodeposited gold nanoparticles

A simple, highly sensitive, and label-free electrochemical impedance spectroscopy (EIS) aptasensor based on an anti-lysozyme-aptamer as a molecular recognition element, was developed for the detection of lysozyme. Improvement in sensitivity was achieved by utilizing gold nanoparticles (AuNPs), which were electrodeposited onto the surface of a gold electrode, as a platform for immobilization of the aptamer. To quantify the amount of lysozyme, changes in the interfacial electron transfer resistance (R_et) of the aptasensor were monitored using the redox couple of an [Fe(CN)₆]^3−/4− probe. The R_et increased with lysozyme concentration. The plot of R_et against the logarithm of lysozyme concentration is linear over the range from 0.1 pM to 500 pM with a detection limit of 0.01 pM. The aptasensor also showed good selectivity for lysozyme without being affected by the presence of other proteins.     

A sensitive, label free electrochemical aptasensor for ATP detection

A sensitive, label free electrochemical aptasensor for small molecular detection has been developed in this work based on gold nanoparticles (AuNPs) amplification. This aptasensor was fabricated as a tertiary hybrid DNA-AuNPs system, which involved the anchored DNA (ADNA) immobilized on gold electrode, reporter DNA (RDNA) tethered with AuNPs and target-responsive DNA (TRDNA) linking ADNA and RDNA. Electrochemical signal is derived from chronocoulometric interrogation of [Ru(NH₃)₆]³⁺ (RuHex) that quantitatively binds to surface-confined DNA via electrostatic interaction. Using adenosine triphosphate (ATP) as a model analyte and ATP-binding aptamer as a model molecular reorganization element, the introduction of ATP triggers the structure switching of the TRDNA to form aptamer-ATP complex, which results in the dissociation of the RDNA capped AuNPs (RDNA-AuNPs) and release of abundant RuHex molecules trapped by RDNA-AuNPs. The incorporation of AuNPs in this strategy significantly enhances the sensitivity because of the amplification of electrochemical signal by the RDNA-AuNPs/RuHex system. Under optimized conditions, a wide linear dynamic range of 4 orders of magnitude (1 nM-10 μM) was reached with the minimum detectable concentration at sub-nanomolar level (0.2 nM). Those results demonstrate that our nanoparticles-based amplification strategy is feasible for ATP assay and presents a potential universal method for other small molecular aptasensors.     

Amperometric aptasensing of chloramphenicol at a glassy carbon electrode modified with a nanocomposite consisting of graphene and silver nanoparticles

A nanocomposite prepared from reduced graphene oxide (rGO) and silver nanoparticles (AgNPs) is used in an electrochemical aptasensor for the sensitive and selective determination of the antibiotic chloramphenicol (CAP). The nanocomposite was obtained by electrostatic assembly of AgNPs on the surface of polyelectrolyte-functionalized rGO and then used to modify a glassy carbon electrode. The biosensor is then obtained by immobilizing the aptamer against CAP. When incubated with solutions of CAP, the sensor surface is loaded with CAP due to aptamer recognition. The captured CAP can be electrochemically reduced to yield a current that is strongly enhanced as a result of the excellent electrocatalysis property of the graphene/AgNP-nanocomposite. Under optimum conditions, the calibration plot is linear in the 0.01 to 35 μM concentration range, with a 2 nM detection limit (at 3σ). The sensor is reproducible, stable, selective over homologous interferents, and performs excellently when analyzing CAP in milk samples.

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Graphical Abstract A graphene/silver nanoparticle-based electrochemical aptasensor is designed for the selective determination of the antibiotic chloramphenicol (CAP). The excellent electrocatalytic reduction of CAP specifically captured onto the electrode surface enables the sensitive electrochemical signal transduction of the biosensor by linear sweep voltammetry (LSV).

     

Fabrication and characterization of enhanced hydrazine electrochemical sensor based on gold nanoparticles decorated on the vanadium oxide,ruthenium oxide nanomaterials,and carbon nanotubes composites

This work describes the synthesis of mixed oxide film of vanadium and ruthenium by pulsed deposition technique on multiwall carbon nanotubes and the decoration of gold nanoparticles on the mixed film. A ternary electrocatalyst has been developed for the electrochemical oxidation of hydrazine by combining two metal oxide mixtures with Au nanoparticles. Surface morphology and chemical composition of the electrode have been examined with SEM, EDX, HRTEM, EIS, and XRD. The peak current of hydrazine increased 9 times at the AuNPs/(VOx-RuOx)/CNT/GCE compared to the bare GCE, and the peak potential shifted to negative 848 mV. Linear sweep voltammetry (LSV) and amperometric techniques revealed that the AuNPs/(VOx-RuOx)/CNT/GCE displays linear concentration range 2.5–10000 µM (LSV) and the concentration range 0.03–100 µM (amperometry). The limit of detection (LOD) is 0.5 μM and 0.1 μM at (S/N = 3) for LSV and amperometric technique, respectively. The results obtained show a good RSD% of 2.1%–3.2% and reasonable recovery of 97%–108% of hydrazine detection.     

A bifunctional electrochemical aptasensor based on AuNPs-coated ERGO nanosheets for sensitive detection of adenosine and thrombin

A simple and sensitive bifunctional electrochemical aptasensor for detection of adenosine and thrombin has been developed using gold nanoparticles–electrochemically reduced graphene oxide (AuNPs-ERGO) composite film-modified electrode. Firstly, the reduced graphene oxide film and AuNPs were sequentially immobilized on glassy carbon electrode (GCE) surface. Secondly, thrombin aptamer was immobilized on the modified electrode. Finally, adenosine aptamer was hybridized with it to serve as a recognition element and methylene blue (MB) as electrochemical signal indicator. In the presence of adenosine or thrombin, the sensor recognized it and a conformational change was induced in aptamer, resulting in decrease of the peak current of MB. The linear relation between concentration of adenosine or thrombin and peak current of MB allowed quantification of them. Thanks to the special electronic characteristic of AuNPs-ERGO composite film, sensitivity of sensor was greatly improved. Under optimal conditions, the proposed aptasensor presented an excellent performance in a linear range of 25 nM to 750 nM for adenosine and 0.5 nM to 10 nM for thrombin. Detection limits were estimated to be 8.3 nM for adenosine and 0.17 nM for thrombin, respectively. Moreover, dual-analyte detection of adenosine and thrombin was achieved without potentially increasing the complexity and cost of the assay.

     

Electrochemical aptasensor for the determination of bisphenol A in drinking water

We present an electrochemical aptasensor for rapid and ultrasensitive determination of the additive bisphenol A (BPA) and for screening drinking water for the presence of BPA. A specific aptamer against BPA and its complementary DNA probe were immobilized on the surface of a gold electrode via self-assembly and hybridization, respectively. The detection of BPA is mainly based on the competitive recognition of BPA by the immobilized aptamer on the surface of the electrode. The electrochemical aptasensor enables BPA to be detected in drinking water with a limit of detection as low as 0.284 pg?mL^?1 in less than 30 min. This extraordinary sensitivity makes the method a most powerful tool for on-site monitoring of water quality and food safety.

Preparation of Epirubicin Aptasensor Using Curcumin as Hybridization Indicator: Competitive Binding Assay between Complementary Strand of Aptamer and Epirubicin

The present work explains the fabrication of a novel electrochemical aptasensor for identifying and measuring the epirubicin (Epi) by using curcumin (Cur) as an anticancer electrochemical indicator. The aptasensor prepared by immobilizing the thiolated aptamer on the surface of graphite screen‐printed electrode modified with gold nanoparticles/functionalized multiwall carbon nanotubes, ionic liquid and chitosan nanocomposite (AuNPs/FMWCNTs‐IL‐Chit/SPE). To evaluate the willingness of aptamer to interaction with Epi in the presence of complementary strand DNA, competitive binding assay between the complementary strand of aptamer and Epi were used. Cur tends to bound to the grooves of two strands DNA. With increasing the concentration of Epi in the range of 0.007–7.0 μM, the peak current of Cur decreased, due to the formation of aptamer‐Epi complex and decreasing the amount of complementary strand DNA. Through the control experiments, we examined the response of fabricated aptasensor for some anticancer drugs, which have a structure similar to the Epi. The results showed that using the thiol‐terminated aptamer as a recognition layer led to a sensor with a high tendency for Epi compared to other anticancer drugs.     

Highly sensitive electrochemical label-free aptasensor based on dual electrocatalytic amplification of Pt-AuNPs and HRP

In this work, a label-free electrochemical aptamer-based sensor (aptasensor) was constructed on account of the direct immobilization of redox probes on an electrode surface. For this proposed aptasensor, a gold nanoparticles (AuNPs)-coated electrode was firstly modified with redox probes-nickel hexacyanoferrates nanoparticles (NiHCFNPs) through chemisorption and electrostatic adsorption. Then, platinum-gold alloy nanoparticles (Pt-AuNPs) and horseradish peroxidase (HRP) were respectively assembled onto the modified electrode surface, which formed the multilayer films for amplifying the electrochemical signal of NiHCFNPs and immobilizing thiolated thrombin aptamers (TBAs). In the presence of target thrombin, the TBA on the multilayer could catch the thrombin onto the electrode surface, which resulted in a barrier for electro-transfer, leading to the decrease of the electrochemical signal of NiHCFNPs amplified by the Pt-AuNPs and HRP toward H(2)O(2). The proposed method avoided the redox probes labeling process, increased the amount of redox probes, and further amplified the electrochemical signal. Thus, the approach showed a high sensitivity and a wider linearity to thrombin in the range between 0.01 nM and 50 nM with a detection limit of 6.3 pM.