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

An aptasensor for chloramphenicol determination based on dual signal output of photoelectrochemistry and colorimetry

In the present work, we developed an aptasensor to determine chloramphenicol (CAP) based on the dual signal output of photoelectrochemistry (PEC) and colorimetry. The Fe3+-doped porous tungsten trioxide was prepared by sol-gel method and coated on the ITO conductive glass to form ITO/p-W(Fe)O3. After assembling the captured DNA (cDNA) and the aptamer of CAP (apt) successively, the constructed ITO/p-W(Fe)O3-cDNA/apt aptasensor exhibited excellent photocurrent response under visible light irradiation in the presence of glucose, which provided the feasibility for PEC measurement with high sensitivity. In the presence of CAP, the apt left the ITO/p-W(Fe)O3 surface and AuNPs linked on the probe DNA would be assembled on it, which led to the decrease of photocurrent. Thanks to the oxidase-mimic catalytic performance of AuNPs and the recycling catalytic hydrolysis by exonuclease I, the measurement signal of the aptasensor could be amplified significantly, and the photocurrent decrease of the aptasensor was linearly related to the concentration of CAP in the range of 1.0 pM-10.0 nM and low detection limit was 0.36 pM. Meanwhile, the H2O2 produced from catalytic oxidation of glucose could oxidize TMB to blue oxTMB under HRP catalysis, which absorbance at 652 nm was linearly related to the concentration of CAP in the range of 5.0 pM-10.0 nM and low detection limit was 1.72 pM. Therefore, an aptasensor that determine CAP in real samples was successfully constructed with good precision of the relative standard deviation less than 5.7 % for PEC method and 7.3 % for colorimetric method, which can meet the analysis needs in different scenarios.

Flake-like structure of SrTiO3 nanoparticles dispersed on graphene oxide: A selective and sensitive electrochemical sensor for determination of chloramphenicol in milk and honey samples

The use of Chloramphenicol (CAP), a potent antibiotic with broad-spectrum capabilities in food-producing animals has been restricted by the European Union and several other countries due to its severe side effects. Thus, CAP must be detected quickly and sensitively. In this investigation, the preparation of SrTiO3 nanoparticles was carried out utilizing a hydrothermal technique. The as-synthesized strontium titanate was decorated on the graphene oxide (SrTiO3/GO) using an ultrasonication method. An electrochemical sensor was developed by employing a modified electrode consisting of SrTiO3/GO, which can accurately detect CAP in food samples. The synergistic effect of SrTiO3 and GO could improve the peak current response. Remarkably, the SrTiO3/GO-modified glassy carbon electrode has a LOD and sensitivity of 6.08 µM nM and 2.771 µA·μM-1·cm-2, respectively. This modified electrode was evaluated in food samples and had an outstanding reaction with a high percentage of recovery, which makes it a potential electrocatalyst for CAP detection.

A reusable screen-printed carbon electrode-based aptasensor for the determination of chloramphenicol in food and environment samples

An electrochemical aptasensor was developed for the determination of chloramphenicol (CAP) in fresh foods and food products. The aptasensor was developed using Prussian blue (PB) and chitosan (CS) film. PB acts as a redox probe for detection and CS acts as a sorption material. The aptamer (Apt) was immobilized on a screen-printed carbon electrode (SPCE) modified with gold nanoparticles (AuNPs). Under optimum conditions, the linearity of the aptasensor was between 1.0 and 6.0 × 106 ng L-1 with a detection limit of 0.65 and a quantification limit of 2.15 ng L-1. The electrode could be regenerated up to 24 times without the use of chemicals. The aptasensor showed good repeatability (RSD <11.2%) and good reproducibility (RSD <7.7%). The proposed method successfully quantified CAP in milk, shrimp pond water and shrimp meat with good accuracy (recovery = 88.0 ± 0.6% to 100 ± 2%). The proposed aptasensor could be especially useful in agriculture to ensure the quality of food and the environment and could be used to determine other antibiotics.

Novel nickel(II) phthalocyanine/reduced graphene oxide: an electrochemical sensing platform for analysis of hydroquinone and chloramphenicol in environmental samples

Novel tetra-2-(biphenyl-4-yl)-1,3-benzoxazol-carboxamide nickel(II) phthalocyanine (NiTBPBXCAPc) and rGO were confirmed using FT-IR, UV-vis, XRD, TGA and Raman spectra. The NiTBPBXCAPc and rGO nanocomposite has been developed to detect hydroquinone (HQN) and chloramphenicol (CPC). NiTBPBXCAPc has been examined using cyclic voltammetry (CV), linear sweep voltammetry (LSV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) analysis. The simultaneous CV analysis of HQN and CPC demonstrated the ability of NiTBPBXCAPc@rGO/GCE to execute simultaneous redox reactions. The voltammetric and amperometric limit of detection for HQN and CPC was determined to be 4.5 and 3.5 nM respectively, with a sensitivity of 0.446 and 0.416 μA M-1 cm-2. The amperometric LOD was observed to be 5 and 4 nM with a sensitivity of 0.235 and 0.288 μA M-1 cm-2. Additionally, the NiTBPBXCAPc@rGO/GC electrode is also used for real sample analysis with outstanding recovery. The long-term storage stability, reusability, and real-world sample analysis of the NiTBPBXCAPc@rGO/GC electrode demonstrated its use in environmental analysis.

Advances of aptamer-based small-molecules sensors in body fluids detection

The field of aptamer-based sensing has evolved considerably over the past three decades. The aptamer sensor-based detection of small-molecule targets in body fluids is designed for real-time or rapid, low-cost, non- or minimally invasive tracking and diagnosis of human health status. It can be achieved by specifically monitoring biomarkers or metabolites excreted from various body fluids, including blood, urine, cerebrospinal fluid, saliva, ect. This article reviews a comprehensive collection of aptamer-based sensors for detecting small-molecule in various body fluids. A comparative analysis of aptamer features, emerging chemistry, advanced sensing materials, transduction techniques, and detection performance is conducted, and the strengths and pitfalls of each approach are discussed. Finally, the development process and application challenges of aptamer-based sensors in the detection of small-molecule in body fluids are presented and discussed.

Effect of Aspect Ratio of a Gold-Nanorod-Modified Screen-Printed Carbon Electrode for Carbaryl Detection in Three Different Samples of Vegetables

In this study, three different sizes of gold nanorods (AuNRs) were synthesized using the seed-growth method by adding various volumes of AgNO3 as 400, 600, and 800 μL into the growth solution of gold nanoparticles. Three different sizes of AuNRs were then characterized using UV-vis spectroscopy, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) patterns, and atomic force microscopy (AFM) to investigate the surface morphology, topography, and aspect ratios of each synthesized AuNR. The aspect ratios from the histogram of size distributions of three AuNRs as 2.21, 2.53, and 2.85 can be calculated corresponding to the addition of AgNO3 volumes of 400, 600, and 800 μL. Moreover, each AuNR in three different aspect ratios was drop-cast onto the surface of a commercial screen-printed carbon electrode (SPCE) to obtain three different SPCE-modified AuNRs (SPCE-A400, SPCE-A600, and SPCE-A800, respectively). All SPCE-modified AuNRs were then evaluated for their electrochemical behavior using cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques and the highest electrochemical performance was shown as the order of magnitude of SPCE-A400 > SPCE-A600/SPCE-A800. The reason for the highest electrocatalytic activity of SPCE-A400 might be due to the smallest particle size and uniform distribution of AuNRs ∼ 2.2, which enhanced the charge transfer, thus providing the highest electroactive surface area (0.6685 cm2) compared to other electrodes. These results also confirm that the sensing mechanism for all SPCE-modified AuNRs is controlled by diffusion phenomena. In addition, the optimum pH was obtained as 4 for carbaryl detection for all SPCE-modified AuNRs with the highest current shown by SPCE-A400. Furthermore, SPCE-A400 has the highest fundamental parameters (surface coverage, catalytic rate constant, electron transfer rate constant, and adsorption capacity) for carbaryl detection, which were investigated using cyclic voltammetry and chronoamperometric techniques. The electroanalytical performances of all SPCE-modified AuNRs for carbaryl detection were also investigated with SPCE-A400 displaying the best performance among other electrodes in terms of its linearity (0.2-100 μM), limit of detection (LOD) ∼ 0.07 μM, and limit of quantification (LOQ) ∼ 0.2 μM. All SPCE-modified AuNRs were also subsequently evaluated for their stability, reproducibility, and selectivity in the presence of interfering species such as NaNO2, NH4NO3, Zn(CH3CO2)2, FeSO4, diazinon, and glucose and show reliable results as depicted from %RSD values less than 3%. At last, all SPCE-modified AuNRs have been employed for carbaryl detection using a standard addition technique in three different samples of vegetables (cabbage, cucumber, and Chinese cabbage) with its results (%recovery ≈ 100%) within the acceptable analytical range. In conclusion, this work demonstrates the great potential of a disposable device based on an AuNR-modified SPCE for rapid detection and high sensitivity in monitoring the concentration of carbaryl as a residual pesticide in vegetable samples.

Deciphering the Molecular Mechanism of Substrate-Induced Assembly of Gold Nanocube Arrays toward an Accelerated Electrocatalytic Effect Employing Heterogeneous Diffusion Field Confinement

The complex electrocatalytic performance of gold nanocubes (AuNCs) is the focus of this work. The faceted shapes of AuNCs and the individual assembly processes at the electrode surfaces define the heterogeneous conditions for the purpose of electrocatalytic processes. Topographic and electron imaging demonstrated slightly rounded AuNC (average of 38 nm) assemblies with sizes of ≤1 μm, where the dominating patterns are (111) and (200) crystallographic planes. The AuNCs significantly impact the electrochemical performance of the investigated electrode [indium-tin oxide (ITO), glassy carbon (GC), and bulk gold] systems driven by surface electrons promoting the catalytic effect. Cyclic voltammetry in combination with scanning electrochemical microscopy allowed us to decipher the molecular mechanism of substrate-induced electrostatic assembly of gold nanocube arrays, revealing that the accelerated electrocatalytic effect should be attributed to the confinement of the heterogeneous diffusion fields with tremendous electrochemically active surface area variations. AuNC drop-casting at ITO, GC, and Au led to various mechanisms of heterogeneous charge transfer; only in the case of GC did the decoration significantly increase the electrochemically active surface area (EASA) and ferrocyanide redox kinetics. For ITO and Au substrates, AuNC drop-casting decreases system dimensionality rather than increasing the EASA, where Au-Au self-diffusion was also observed. Interactions of the gold, ITO, and GC surfaces with themselves and with surfactant CTAB and ferrocyanide molecules were investigated using density functional theory.

A review on the recent achievements on coronaviruses recognition using electrochemical detection methods

Various coronaviruses, which cause a wide range of human and animal diseases, have emerged in the past 50 years. This may be due to their abilities to recombine, mutate, and infect multiple species and cell types. A novel coronavirus, which is a family of severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), has been termed COVID-19 by the World Health Organization (WHO). COVID-19 is the strain that has not been previously identified in humans. The early identification and diagnosis of the virus is crucial for effective pandemic prevention. In this study, we review shortly various diagnostic methods for virus assay and focus on recent advances in electrochemical biosensors for COVID-19 detection.

The Application of Nanomaterials for the Electrochemical Detection of Antibiotics: A Review

Antibiotics can accumulate through food metabolism in the human body which may have a significant effect on human safety and health. It is therefore highly beneficial to establish easy and sensitive approaches for rapid assessment of antibiotic amounts. In the development of next-generation biosensors, nanomaterials (NMs) with outstanding thermal, mechanical, optical, and electrical properties have been identified as one of the most hopeful materials for opening new gates. This study discusses the latest developments in the identification of antibiotics by nanomaterial-constructed biosensors. The construction of biosensors for electrochemical signal-transducing mechanisms has been utilized in various types of nanomaterials, including quantum dots (QDs), metal-organic frameworks (MOFs), magnetic nanoparticles (NPs), metal nanomaterials, and carbon nanomaterials. To provide an outline for future study directions, the existing problems and future opportunities in this area are also included. The current review, therefore, summarizes an in-depth assessment of the nanostructured electrochemical sensing method for residues of antibiotics in different systems.

A photoelectrochemical aptasensor for sensitively monitoring chloramphenicol using plasmon-driven AgNP/BiOCl composites

A photoelectrochemical (PEC) aptasensor based on silver nanoparticle/BiOCl (AgNP/BiOCl) composites was constructed for detecting chloramphenicol (CAP). The surface-plasmon resonance (SPR) effect of AgNPs can focus the incident light and promote the migration and separation of the photogenerated carriers of AgNP/BiOCl composites. As a result, the AgNP/BiOCl composites showed an enhanced PEC performance compared to that of pure BiOCl. A PEC CAP aptasensor was fabricated using AgNP/BiOCl composites as photoactive materials and a CAP aptamer as a recognition element. The PEC aptasensor exhibited a broad linear response range (0.2 pM-10 nM), a low limit of determination (0.08 pM), satisfactory selectivity, stability, and reproducibility to meet the practical analysis requirements. This work demonstrates that the PEC CAP aptasensor has a promising prospect in environmental assays.

Electrochemical determination of chloramphenicol and metronidazole by using a glassy carbon electrode modified with iron, nitrogen co-doped nanoporous carbon derived from a metal-organic framework (type Fe/ZIF-8)

In this study, an iron-doped metal-organic framework (MOF) Fe/ZIF-8 was synthesized from ZIF-8 at room temperature. Direct carbonization of Fe/ZIF-8 under a nitrogen atmosphere produced nanoporous nitrogen doped carbon nanoparticles decorated with Fe component (Fe/NC). The Fe/NC exhibited a large surface area (1221.185 m² g^-1) and narrow pore-size distribution (3-5 nm). The nanoporous Fe/NC components along with Nafion were used to modify a glassy carbon electrode for the electrochemical determination of chloramphenicol and metronidazole via linear sweep voltammetry. Under optimal conditions, the reduction peak currents (observed at -0.237 V and -0.071 V vs. Ag/AgCl) of these analytes increased linearly with increasing chloramphenicol and metronidazole concentrations in the range of 0.1-100 μM and 0.5-30 μM, with the detection limits estimated to be 31 nM and 165 nM, respectively. This result was attributed to the large surface area, porous structure, high nitrogen content, and as well as the electrocatalytic effect of Fe atoms embeded in the carbon support. The proposed sensor was used for chloramphenicol and metronidazole analysis in samples, providing satisfactory results.

Sensitive Electrochemical Detection of Tryptophan Using a Hemin/G-Quadruplex Aptasensor

In this study, we design an electrochemical aptasensor with an enzyme-free amplification method to detect tryptophan (Trp). For the amplified electrochemical signal, the screen-printed electrode was modified with dendritic gold nanostructures (DGNs)/magnetic double-charged diazoniabicyclo [2.2.2] octane dichloride silica hybrid (Fe3O4@SiO2/DABCO) to increase the surface area as well as electrical conductivity, and the hemin/G-quadruplex aptamer was immobilized. The presence of Trp improved the catalytic characteristic of hemin/G-quadruplex structure, which resulted in the efficient catalysis of the H2O2 reduction. As the concentration of Trp increased, the intensity of H2O2 reduction signal increased, and Trp was measured in the range of 0.007–200 nM with a detection limit of 0.002 nM. Compared with previous models, our sensor displayed higher detection sensitivity and specificity for Trp. Furthermore, we demonstrated that the proposed aptasensor successfully determined Trp in human serum samples, thereby proving its practical applicability.

Advances in Exosome Analysis Methods with an Emphasis on Electrochemistry

Exosomes, small extracellular vesicles, are released by various cell types. They are found in bodily fluids, including blood, urine, serum, and saliva, and play essential roles in intercellular communication. Exosomes contain various biomarkers, such as nucleic acids and proteins, that reflect the status of their parent cells. Since they influence tumorigenesis and metastasis in cancer patients, exosomes are excellent noninvasive potential indicators for early cancer detection. Aptamers with specific binding properties have distinct advantages over antibodies, making them effective versatile bioreceptors for the detection of exosome biomarkers. Here, we review various aptamer-based exosome detection approaches based on signaling methods, such as fluorescence, colorimetry, and chemiluminescence, focusing on electrochemical strategies that are easier, cost-effective, and more sensitive than others. Further, we discuss the clinical applications of electrochemical exosome analysis strategies as well as future research directions in this field.

Aptamer-based fluorometric determination of chloramphenicol by controlling the activity of hemin as a peroxidase mimetic

A method for the aptamer-based determination of chloramphenicol (CAP) was developed by exploiting the peroxidase mimicking activity of hemin. The method includes two hemin-modified DNA probes termed P1 and P2. P1, which was modified at its 5' end with one hemin monomer, contains the CAP-binding sequence. The hybridization between P1 and P2 brings the two hemin monomers in close proximity, resulting in the formation of a hemin dimer with low peroxidase mimicking activity. The duplex structure was dehybridized in the presence of CAP. The formed hemin monomer featured a strong peroxidase mimicking activity and catalyzed the conversion of non-fluorescent tyramine into fluorescent dityramine by hydrogen peroxide. Fluorescence (with an excitation/emission maxima at 320 and 410 nm, respectively) increased linearly in the 0.1 ng mL-1 to 10 ng mL-1 CAP concentration range. The detection limit based on the 3σ/k criterion reached 0.07 ng mL-1. The proposed assay was successfully employed for CAP detection in (spiked) honey samples with recoveries of 94.3-117.2%. Given its high sensitivity and good stability, this method shows potential in providing a platform for antibiotic detection.

Voltammetric Pathways for the Analysis of Ophthalmic Drugs

Background:

This review investigates the ophthalmic drugs that have been studied with voltammetry in the web of science database in the last 10 years.

Introduction:

Ophthalmic drugs are used in the diagnosis, evaluation and treatment of various ophthalmological diseases and conditions. A significant literature has emerged in recent years that investigates determination of these active compounds via electroanalytical methods, particularly voltammetry. Low cost, rapid determination, high availability, efficient sensitivity and simple application make voltammetry one of the most used methods for determining various kinds of drugs including ophthalmic ones.

Methods:

In this particular review, we searched the literature via the web of science database for ophthalmic drugs which are investigated with voltammetric techniques using the keywords of voltammetry, electrochemistry, determination and electroanalytical methods.

Results:

We found 33 types of pharmaceuticals in nearly 140 articles. We grouped them clinically into seven major groups as antibiotics, antivirals, non-steroidal anti-inflammatory drugs, anti-glaucomatous drugs, steroidal drugs, local anesthetics and miscellaneous. Voltammetric techniques, electrodes, optimum pHs, peak potentials, limit of detection values, limit of quantification values, linearity ranges, sample type and interference effects were compared.

Conclusion:

Ophthalmic drugs are widely used in the clinic and it is important to determine trace amounts of these species analytically. Voltammetry is a preferred method for its ease of use, high sensitivity, low cost, and high availability for the determination of ophthalmic drugs as well as many other medical drugs. The low limits of detection values indicate that voltammetry is quite sufficient for determining ophthalmic drugs in many media such as human serum, urine and ophthalmic eye drops.

Evaluation of single and combined toxicity of bisphenol A and its analogues using a highly-sensitive micro-biosensor

Bisphenol analogues have been developed as alternatives to bisphenol A (BPA), a common chemical with potential adverse effects on human health. It is imperative to perform a fast and sensitive evaluation for the toxicity of these bisphenol analogues. This study introduces a label-free electrochemical biosensor based on a screen-printed electrode modified with the carboxylated multi-walled carbon nanotube/rhodamine B/gold nanoparticle. Ctenopharyngodon idella kidney (CIK) cells were used as the biological recognition agent to detect changes in electrochemical signals and indicate the cell viability. Only 20 μL of sample was required for detection, which was much lower than that of other conventional electrochemical methods (≥ 1 mL). This biosensor was examined for the cytotoxicity of BPA, bisphenol AF (BPAF), bisphenol B (BPB), bisphenol F (BPF), and bisphenol S (BPS) to CIK cells. The half inhibition concentration (IC₅₀) values after 48 h of exposure indicated that the rank order of cytotoxicities was BPAF > BPB > BPA > BPF > BPS. The morphological changes in CIK cells after treatment with various bisphenols were investigated, and the combined toxicities of the binary bisphenol mixtures were determined. Potentially synergistic and additive effects were observed. These findings provide new insights into the cytotoxicity of bisphenol analogues.

Ultrasensitive and reusable electrochemical aptasensor for detection of tryptophan using of [Fe(bpy)3](p-CH3C6H4SO2)2 as an electroactive indicator

In this paper, we report the application of a reusable electrochemical aptasensor for detection of tryptophan by using [Fe(bpy)₃](p-CH₃C₆H₄SO₂)₂ as an electroactive indicator and based on the target-compelled aptamer displacement. The aptasensor fabricated by self-assembling the thiolated probe on the surface of graphite screen-printed electrode modified with gold nanoparticles/multiwalled carbon nanotubes and chitosan nanocomposite (AuNPs/MWCNTs-Chit/SPE). Afterward, Trp aptamer (Apt) immobilized on the modified electrode surface through hybridization. In the absence of Trp, a sharp peak of [Fe(bpy)₃](p-CH₃C₆H₄ SO₂)₂ can be observed in differential pulse voltammetry (DPV) study. The introduction of Trp led to the formation of aptamer-Trp complex and dissociation of the aptamer from the DNA-Apt duplex on the electrode surface into the solution and decreases the peak current intensity of electroactive indicator. This is because, [Fe(bpy)₃](p-CH₃C₆H₄SO₂)₂ tends to bind to the two strands DNA. Therefore, the peak current of [Fe(bpy)₃](p-CH₃C₆H₄ SO₂)₂ linearly decreased with increasing the concentration of Trp over a range of 3.0 nM- 100 μM. The detection limit (3 σ) was 1.0 nM. In addition, we examined the selectivity of the constructed biosensor for tyrosine, histidine, arginine, lysine, valine and methionine that belonged to the amino acid family. The obtained results showed that the fabricated sensor had a good selectivity for Trp against the other examined amino acids. Also, the potential applicability of the aptasensor was investigated by detecting the Trp in a complex media such as human blood plasma spiked with Trp.

Advances in aptasensors for the detection of food contaminants

Food safety is a global health objective, and foodborne diseases represent a major crisis in health. Techniques that are simple and suitable for fast screening to detect and identify pathogenic factors in the food chain are vital to ensure food safety. At present, a variety of analytical methods have been reported for the detection of pathogenic agents. Whereas the sensitivity of detection and quantification are still important challenges, we expect major advances from new assay formats and synthetic bio-recognition elements, such as aptamers. Owing to the specific folding capability of aptamers in the presence of an analyte, aptasensors have substantially and successfully been exploited for the detection of a wide range of small and large molecules (e.g., toxins, antibiotics, heavy metals, bacteria, viruses) at very low concentrations. Here, we review the use of aptasensors for the development of highly sensitive and affordable detection tools for food analysis.

Aptasensors as the future of antibiotics test kits-a case study of the aptamer application in the chloramphenicol detection

Antibiotics are a type of antimicrobial drug with the ubiquitous presence in foodstuff that effectively applied to treat the diseases and promote the animal growth worldwide. Chloramphenicol as one of the antibiotics with the broad action spectrum against Gram-positive and Gram-negative bacteria is widely applied for the effective treatment of infectious diseases in humans and animals. Unfortunately, the serious side effects of chloramphenicol, such as aplastic anemia, kidney damage, nausea, and diarrhea restrict its application in foodstuff and biomedical fields. Development of the sufficiently sensitive methods to detect chloramphenicol residues in food and clinical diagnosis seems to be an essential demand. Biosensors have been introduced as the promising tools to overcome the requirement. As one of the newest types of the biosensors, aptamer-based biosensors (aptasensors) are the efficient sensing platforms for the chloramphenicol monitoring. In the present review, we summarize the recent achievements of the accessible aptasensors for qualitative detection and quantitative determination of chloramphenicol as a candidate of the antibiotics. The present chloramphenicol aptasensors can be classified in two main optical and electrochemical categories. Also, the other formats of the aptasensing assays like the high performance liquid chromatography (HPLC) and microchip electrophoresis (MCE) have been reviewed. The enormous interest in utilizing the diverse nanomaterials is also highlighted in the fabrication of the chloramphenicol aptasensors. Finally, some results are presented based on the advantages and disadvantages of the studied aptasensors to achieve a promising perspective for designing the novel antibiotics test kits.

Synthesis and Characterization of Samarium-Substituted Molybdenum Diselenide and Its Graphene Oxide Nanohybrid for Enhancing the Selective Sensing of Chloramphenicol in a Milk Sample

The electronic conductivity and electrocatalytic activity of metal chalcogenides are normally enhanced by following the ideal strategies such as substitution/doping of heterogeneous atoms and hybridization of highly conductive carbon supportive materials. Here, a rare earth element (samarium) was substituted with MoSe₂ using the simple hydrothermal method. The lattice distortion due to the substitution of Sm³⁺ with MoSe₂ was clearly observed by using high-resolution transmission electron microscopy analysis. As a consequence, the prepared SmMoSe₂ nanorod was encapsulated with graphene oxide (GO) sheets by using ultrasonication process. Furthermore, the GO-encapsulated SmMoSe₂ nanocomposite modified glassy carbon electrode (GO@SmMoSe₂/GCE) was used for the sensing of chloramphenicol. The results showed that the GO@SmMoSe₂/GCE revealed the superior electrocatalytic activity with low detection (5 nM) and sensitivity (20.6 μA μM^-1 cm^-2) to electrochemical detection of proposed analyte. It indicates that the substitution of Sm³⁺ and encapsulation of GO significantly increased both the electrical conductivity and electrocatalytic activity of MoSe₂.

Aptamer-Based Biosensors for Antibiotic Detection: A Review

Antibiotic resistance and, accordingly, their pollution because of uncontrolled usage has emerged as a serious problem in recent years. Hence, there is an increased demand to develop robust, easy, and sensitive methods for rapid evaluation of antibiotics and their residues. Among different analytical methods, the aptamer-based biosensors (aptasensors) have attracted considerable attention because of good selectivity, specificity, and sensitivity. This review gives an overview about recently-developed aptasensors for antibiotic detection. The use of various aptamer assays to determine different groups of antibiotics, like β-lactams, aminoglycosides, anthracyclines, chloramphenicol, (fluoro)quinolones, lincosamide, tetracyclines, and sulfonamides are presented in this paper.

Development of a new paper based nano-biosensor using the co-catalytic effect of tyrosinase from banana peel tissue (Musa Cavendish) and functionalized silica nanoparticles for voltammetric determination of l-tyrosine

In this paper, a new and facile method for the electrochemical determination of l-tyrosine was designed. First, 3-mercaptopropyl trimethoxysilane-functionalized silica nanoparticles were added to a paper disc. Then, the banana peel tissue and the mediator potassium hexacyanoferrate were dropped onto the paper, respectively. The modified paper disc was placed on the top of the graphite screen printed electrode and electrochemical characterization of this biosensor was studied by cyclic voltammetry and electrochemical impedance spectroscopy methods. The effective parameters like pH, banana peel tissue percentage, and the amount of mediator loading were optimized. l-tyrosine measurements were done by differential pulse voltammetry with a little sample (3 μL) for analysis. The biosensor showed a linear response for l-tyrosine in the wide concentration range of 0.05-600 μM and a low detection limit about 0.02 μM because of the co-catalytic effect of enzyme and nanoparticles. The stability of the biosensor and its selectivity were evaluated. This biosensor was applied for the voltammetric determination of l-tyrosine in the blood plasma sample. The results of the practical application study were comparable with the standard method (HPLC). In conclusion, a simple, inexpensive, rapid, sensitive and selective technique was successfully applied to the l-tyrosine analysis of the little samples.

Construction of a highly sensitive signal-on aptasensor based on gold nanoparticles/functionalized silica nanoparticles for selective detection of tryptophan

In this work, a highly sensitive, low-cost, and label-free aptasensor based on signal-on mechanisms of response was developed by immobilizing the aptamer on gold nanoparticles (AuNPs)/amine-functionalized silica nanoparticle (FSN)/screen-printed electrode (SPE) surface for highly selective electrochemical detection of tryptophan (Trp). The hemin (Hem), which interacted with the guanine bases of the aptamer, worked as a redox indicator to generate a readable electrochemical signal. The changes in the charge transfer resistance have been monitored using the voltammetry and electrochemical impedance spectroscopic (EIS) techniques. The peak current of Hem linearly increased with increasing concentration of Trp, in differential pulse voltammetry, from 0.06 to 250 nM with a detection limit of 0.026 nM. Also, the results obtained from EIS studies showed that the Trp was detected sensitively with the fabricated aptasensor in the range of 0.06-250 nM. The detection limit is 0.01 nM, much lower than that obtained by most of the reported electrochemical methods. The usage of aptamer as a recognition layer led to a sensor with high affinity for Trp, compared with control amino acids of tyrosine, histidine, arginine, lysine, valine, and methionine. The usability of the aptasensor was successfully evaluated by the determination of Trp in a human blood serum sample. Thus, the sensor could provide a promising plan for the construction of aptasensors. Graphical abstract Schematic outline the principle for tryptophan aptasensing.

Electrochemical aptasensors for contaminants detection in food and environment: Recent advances

The growing number of contaminants requires the development of new analytical tools to meet the increasing demand for legislative actions on food safety and environmental pollution control. In this context, electrochemical aptamer-based sensors appear promising among all biosensors because they permit multiplexed analysis and provide fast response, sensitivity, specificity and low cost. The aim of this review is to give the readers an overview of recent important achievements in the development of electrochemical aptamer-based biosensors for contaminant detection over the last two years. Special emphasis is placed on aptasensors based on screen-printed electrodes which show a substantial improvement of analytical performances.

Design an aptasensor based on structure-switching aptamer on dendritic gold nanostructures/Fe3O4@SiO2/DABCO modified screen printed electrode for highly selective detection of epirubicin

The present work describes a label free electrochemical aptasensor for selective detection of epirubicin. In this project, 5'-thiole terminated aptamer was self-assembled on carbon screen printed electrode, which modified with electrodeposited gold nanoparticles on magnetic double-charged diazoniabicyclo [2.2.2] octane dichloride silica hybrid (Fe₃O₄@SiO₂/DABCO) by Au-S bond. The interactions of epirubicin with aptamer on the AuNPs/Fe₃O₄@SiO₂/DABCO/SPE have been studied by cyclic voltammetry, linear sweep voltammetry and electrochemical impedance spectroscopy. Under optimized conditions, the peak current of epirubicin increased linearly with increasing epirubicin concentration, due to the switching in the aptamer conformation and formation of aptamer- epirubicin complex instead of aptamer on the modified electrode surface. The Apt/AuNPs/Fe₃O₄@SiO₂/DABCO/SPE is sensitive, selective and has two linear range from 0.07µM to 1.0µM and 1.0µM to 21.0µM with a detection limit of 0.04µM. The applicability of the aptasensor was successfully assessed by determination of epirubicin in a human blood serum sample.

Ultrasensitive electrochemical aptasensor based on sandwich architecture for selective label-free detection of colorectal cancer (CT26) cells

Colorectal cancer is one of the most common cancers in the world and has no effective treatment. Therefore, development of new methods for early diagnosis is instantly required. Biological recognition probes such as synthetic receptor and aptamer is one of the candidate recognition layers to detect important biomolecules. In this work, an electrochemical aptasensor was developed by fabricating an aptamer-cell-aptamer sandwich architecture on an SBA-15-3-aminopropyltriethoxysilane (SBA-15-pr-NH₂) and Au nanoparticles (AuNPs) modified graphite screen printed electrode (GSPE) surface for the selective, label-free detection of CT26 cancer cells. Based on the incubation of the thiolated aptamer with CT26 cells, the electron-transfer resistance of Fe (CN)₆^3-/4- redox couple increased considerably on the aptasensor surface. The results obtained from cyclic voltammetry and electrochemical impedance spectroscopy studies showed that the fabricated aptasensor can specifically identify CT26 cells in the concentration ranges of 10-1.0×10⁵cells/mL and 1.0×10⁵-6.0×10⁶ cells/mL, respectively, with a detection limit of 2cells/mL. Applying the thiol terminated aptamer (5TR1) as a recognition layer led to a sensor with high affinity for CT26 cancer cells, compared to control cancer cells of AGS cells, VERO Cells, PC3 cells and SKOV-3 cells. Therefore a simple, rapid, label free, inexpensive, excellent, sensitive and selective electrochemical aptasensor based on sandwich architecture was developed for detection of CT26 Cells.

A bimetallic nanocomposite modified genosensor for recognition and determination of thalassemia gene

The main roles of DNA in the cells are to maintain and properly express genetic information. It is important to have analytical methods capable of fast and sensitive detection of DNA damage. DNA hybridization sensors are well suited for diagnostics and other purposes, including determination of bacteria and viruses. Beta thalassemias (βth) are due to mutations in the β-globin gene. In this study, an electrochemical biosensor which detects the sequences related to the β-globin gene issued from real samples amplified by polymerase chain reaction (PCR) is described for the first time. The biosensor relies on the immobilization of 20-mer single stranded oligonucleotide (probe) related to βth sequence on the carbon paste electrode (CPE) modified by 15% silver (Ag) and platinum (Pt) nanoparticles to prepare the bimetallic nanocomposite electrode and hybridization of this oligonucleotide with its complementary sequence (target). The extent of hybridization between the probe and target sequences was shown by using linear sweep voltammetry (LSV) with methylene blue (MB) as hybridization indicator. The selectivity of sensor was investigated using PCR samples containing non-complementary oligonucleotides. The detection limit of biosensor was calculated about 470.0pg/μL.

Label-free and sensitive aptasensor based on dendritic gold nanostructures on functionalized SBA-15 for determination of chloramphenicol

A highly sensitive and low-cost electrochemical aptasensor was developed for the determination of chloramphenicol (CAP). The system was based on a CAP-binding aptamer, a molecular recognition element, and 1,4-diazabicyclo[2.2.2]octane (DABCO)-supported mesoporous silica SBA-15 on the surface of a screen-printed graphite electrode for formation of dendritic gold nanostructures and improving the performance and conductivity of the biosensor. Hemin has been applied as an electrochemical indicator which interacted with the guanine bases of the aptamer. In the absence of CAP, hemin binds to the aptamer and produces a weak differential pulse voltammetric (DPV) signal. The presence of CAP led to stabilization of the folded aptamer, which generated an amplified DPV signal. The peak current of hemin increased linearly with the concentration of CAP. Under optimal conditions, two linear ranges were obtained from 0.03 to 0.15 μM and 0.15 to 7.0 μM, respectively, and the detection limit was 4.0 nM. The prepared biosensor has good selectivity against other non-target drugs. Thus, the sensor could provide a promising platform for the fabrication of aptasensors. The feasibility of using this aptasensor was demonstrated by determination of CAP in a human blood serum sample.

A novel colorimetric sandwich aptasensor based on an indirect competitive enzyme-free method for ultrasensitive detection of chloramphenicol

Analytical methods for detection and quantitation of chloramphenicol in blood serum and foodstuffs arse highly in demand. In this study, a colorimetric sandwich aptamer-based sensor (aptasensor) was fabricated for sensitive and selective detection of chloramphenicol, based on an indirect competitive enzyme-free assay using gold nanoparticles (AuNPs), biotin and streptavidin. The designed aptasensor acquires characteristics of AuNPs, including large surface area and unique optical properties, and strong interaction of biotin with streptavidin. In the absence of chloramphenicol, the sandwich structure of aptasensor forms, leading to the observation of sharp red color. In the presence of target, functionalized AuNPs could not bind to 96-well plates, resulting in a faint red color. The fabricated colorimetric aptasensor exhibited high selectivity toward chloramphenicol with a limit of detection as low as 451 pM. Moreover, the developed colorimetric aptasensor was successfully used to detect chloramphenicol in milk and serum with LODs of 697 and 601 pM, respectively.