A novel electrochemical aptasensor for ultrasensitive detection of kanamycin based on MWCNTs-HMIMPF6 and nanoporous PtTi alloy

A simple self-assembly aptasensor for ultrasensitive detection of kanamycin based on carbon dots and Ti3C2 MXene nanocomposite

Antibiotics play an excellent role in preventing and treating animal diseases, but their improper use poses a potential threat to public health. Designing a sensing platform to detect trace amounts of antibiotic residues in actual samples is a significant challenge. To achieve this objective, a self-assembly aptasensor based on a two-round signal amplification strategy for kanamycin (KANA) trace detection was demonstrated by employing carbon dot (CD) decorated Ti3C2 MXene as electrode modification material and the complex of double-stranded DNA (dsDNA) and methylene blue (MB) as probes, where dsDNA was composed of complementary DNA (cDNA) and aptamers. The CDs can effectively suppress the self-stacking of Ti3C2 MXene to promote electron transfer and provide plenty of exposed active sites for the aptamer to capture KANA precisely. The MB inserted into dsDNA would be liberated upon interaction with KANA due to a competitive process that occurs among cDNA and KANA, reducing electrical signal. Under the optimal conditions, the constructed aptasensor exhibited a good linear relationship between the output signal and the logarithm of KANA concentration in the range of 1 fM-1 mM, and the limit of detection is 0.892 fM. The satisfactory selectivity, stability, and reproducibility suggested that the prepared aptasensor can be a universal platform to detect other antibiotic residues by anchoring corresponding aptamers. Furthermore, it has been successfully applied to determine KANA in milk samples (recovery rates ranged from 101.01% to 107.21%, and the RSD was below 5%), demonstrating potential application prospects in the food-safety analysis field.

Recent Advances in Electrochemical Aptasensors for Detection of Clinical and Veterinary Drugs

Nowadays, aptamer-based biosensors and electrochemical measurements represent one of the efficient tools for the detection of drugs in both medical and veterinary. Precise trace values analysis of chemicals, especially drugs, plays a crucial role in food and therapeutic safety evaluations that are often time-consuming and costly. Ultimately, accurate determination of therapeutic medications like antibiotics in food, environmental resources, and biological matrices is very important for protecting public health and drug monitoring (TDM) for effective treatment. This review highlights recent advancements in electrochemical aptasensors as an innovative approach offering high sensitivity, specificity, and rapid detection of clinical and veterinary drugs at lower costs. We provide a comprehensive overview of the advancements and discuss the challenges and prospects of electrochemical aptasensing in drug residue detection across various samples.

Sensitive detection of Escherichia coli in diverse foodstuffs by electrochemical aptasensor based on 2D porphyrin-based COF

The two-dimensional porphyrin-based covalent organic framework (denoted by Tph-TDC-COF) was used as the sensitive layerto build an aptamer-based electrochemical sensor for the detection of Escherichia coli (E.coli). Tph-TDC-COF produced with 5,10,15,20-tetrakis(4-aminophenyl)-21H, 23H-porphine (Tph) and [2,2'-bithiophene]-2,5'-dicarbaldehyde (TDC) as building blocks exhibited a highly conjugated structure, outstanding conductivity, large specific surface area, and strong bioaffinity towards aptamers. The adoption of Tph-TDC-COF-modified electrode resulted in improved sensing performance and increased anchoring affinity toward the E.coli-targeted aptamer. Under optimal conditions, the Tph-TDC-COF-based electrochemical aptasensor demonstrated an extremely low detection limit of 0.17 CFU mL-1 for E.coli detection within a linear range of 10 to 1 × 108 CFU mL-1, accompanied by good stability, excellent reproducibility and regeneration ability, and wide practical applications. The current electrochemical aptasensing technique has the potential to be extended to detect different foodborne bacteria using specific aptamer, therefore widening the application of COFs in biosensing and food safety fields.

An inner filter effect-based fluorescent aptasensor for sensitive detection of kanamycin in complex samples using gold nanoparticles and graphene oxide quantum dots

In this work, a label-free fluorescent aptasensor based on the inner filter effect (IFE) between gold nanoparticles (AuNPs) and graphene oxide quantum dots (GOQDs) was developed for the detection of kanamycin in complex samples. AuNPs are capable of functioning as the fluorescence absorber of GOQDs because of the complementary overlap between their absorption spectra and the emission spectra of GOQDs. AuNPs can effectively quench the fluorescence of GOQDs via the IFE and modulate it with their aggregation state. In the presence of kanamycin, the aptamer is released from the surface of AuNPs, leading to their salt-induced aggregation and the fluorescence recovery of GOQDs. Under the optimum conditions, the fluorescence intensity of GOQDs was linearly proportional to the concentration of kanamycin over the range from 5 to 600 nM, with a detection limit of 3.6 nM. Moreover, the fluorescent aptasensor was successfully applied for kanamycin detection in complex samples (milk, honey and serum), which might hold great promise for kanamycin detection in food safety control and clinical research.

Porous Carbon Nanospheres and Gold Nanocomposite-Based Electrochemical Aptasensor for the Detection of Streptomycin

A novel electrochemical aptasensor modified with the nanocomposite of porous carbon nanospheres and Au urchins as the signal amplification and immobility platforms for aptamer was successfully constructed for ultrasensitive and selective determination of streptomycin. The streptomycin aptamer was fixed on the surface of the nanocomposite via the strong Au–S bond between Au urchins and aptamer. The target binding-induced conformational change of aptamer resulted in signal attenuation, which was expressed as “ΔI = IBSA − Istreptomycin.” Based on the synergic signal amplification platform, the as-prepared aptamer-based sensor showed a wider linearity to streptomycin from 0.01 to 350 ng/mL with a low detection limit of 5.0 pg/mL under the optimized condition. Finally, the aptasensor was operated in milk and honey to detect streptomycin. This study has provided a facile way to develop highly sensitive, effective and efficient aptamer-based electrochemical sensors for the detection of antibiotics at very low concentration.

An Aptasensor Based on a Flexible Screen-Printed Silver Electrode for the Rapid Detection of Chlorpyrifos

In this work, we propose a novel disposable flexible and screen-printed electrochemical aptamer-based sensor (aptasensor) for the rapid detection of chlorpyrifos (CPF). To optimize the process, various characterization procedures were employed, including Fourier transform infrared spectroscopy (FT-IR), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Initially, the aptasensor was optimized in terms of electrolyte pH, aptamer concentration, and incubation time for chlorpyrifos. Under optimal conditions, the aptasensor showed a wide linear range from 1 to 105 ng/mL with a calculated limit of detection as low as 0.097 ng/mL and sensitivity of 600.9 µA/ng. Additionally, the selectivity of the aptasensor was assessed by identifying any interference from other pesticides, which were found to be negligible (with a maximum standard deviation of 0.31 mA). Further, the stability of the sample was assessed over time, where the reported device showed high stability over a period of two weeks at 4 °C. As the last step, the ability of the aptasensor to detect chlorpyrifos in actual samples was evaluated by testing it on banana and grape extracts. As a result, the device demonstrated sufficient recovery rates, which indicate that it can find application in the food industry.

PCN-222@g-C3N4 cathodic materials for "signal-off" photoelectrochemical sensing of kanamycin sulfate

A novel cathodic photoelectrochemical (PEC) sensor was developed for the ultrasensitive detection of kanamycin sulfate (KAM) based on the g-C3N4 coupled zirconium-based porphyrinic metal-organic framework (PCN-222). Photocathodes made by double n-type semiconductors, which was attributed to the transfer of electrons and holes from g-C3N4 broad band to PCN-222 with narrow band gap. The photocurrent decreased when KAM was added, which was conducive to the construction of the PEC sensor. Then, the PCN-222@g-C3N4 was used as a photosensitive platform to construct a label-free strategy and ultrasensitive detection of KAM with wide linear range from 1 to 1000 nM and a low detection limit of 0.127 nM. Moreover, this sensing platform shows good selectivity, favourable reproducibility and brilliant stability. The reported sensors provided great potential for the detection of KAM in actual samples.

DNAzyme-powered DNA walking machine for ultrasensitive fluorescence aptasensing of kanamycin

A DNAzyme-powered DNA walking machine was constructed to develop the fluorescence aptasensing for sensitive detection of kanamycin. The aptamer for kanamycin is partially hybridized with complementary DNA (cDNA) modified on magnetic beads (MBs). The specific interaction of target and aptamer triggered the cDNA to be free tentatively, which captured walker DNA. Then the autonomous motion of DNA walker on MBs surface was propelled via DNAzyme digestion of recognition sites. The signal probe was separated, and the amplified fluorescence signal was achieved by the accumulation of the signal probe. Kanamycin was used as a model analyte, and the developed assay achieves a detection limit of 0.00039 ng·mL^-1 (S/N = 3) within a linear detection range from 0.001 to 2000 ng·mL^-1. This aptasensing strategy can be extended for detection of other antibiotics by adapting corresponding target recognition aptamer sequence. Graphical abstract The fluorescence aptasensing for sensitive detection of kanamycin based on DNAzyme-powered DNA walking machine was constructed.

A novel electrochemical aptasensor for the sensitive detection of kanamycin based on UiO-66-NH2/MCA/MWCNT@rGONR nanocomposites

In this work, we designed and synthesized a nanocomposite comprising an amine-functionalized metal organic framework (UiO-66-NH₂), a multiwalled carbon nanotube@reduced graphene oxide nanoribbon (MWCNT@rGONR) and a covalent organic framework (COF) synthesized using melamine and cyanuric acidmonomers via polycondensation (represented by MCA). The UiO-66-NH₂/MCA/MWCNT@rGONR nanocomposite was used as a sensitive platform for an electrochemical aptasensor to detect kanamycin (kana). Owing to the rich chemical functionality, amino-rich structure and excellent electrochemical activity, the cDNA strands with terminal amino groups can not only anchor over the UiO-66-NH₂/MCA/MWCNT@rGONR surface but also penetrate into the interior of porous UiO-66-NH₂/MCA/MWCNT@rGONR networks. The characterization of the UiO-66-NH₂/MCA/MWCNT@rGONR nanocomposite was performed by scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD). Furthermore, cyclic voltammetry (CV) and square wave voltammetry (SWV) were employed for the electrochemical performance study of this biosensor. The results indicated that the UiO-66-NH₂/MCA/MWCNT@rGONR nanocomposite exhibited high bioaffinity toward the aptamer and the lowest limit of detection at 13 nM (S/N = 3) within a linearity of the kana concentration of 25-900 nM. In addition, it possessed great repeatability, stability and selectivity and obtained satisfactory recovery results in the real analysis of fish meat and milk, indicating the great potential for analytical measurements in food safety.

Impedimetric Determination of Kanamycin in Milk with Aptasensor Based on Carbon Black-Oligolactide Composite

The determination of antibiotics in food is important due to their negative effect on human health related to antimicrobial resistance problem, renal toxicity, and allergic effects. We propose an impedimetric aptasensor for the determination of kanamycin A (KANA), which was assembled on the glassy carbon electrode by the deposition of carbon black in a chitosan matrix followed by carbodiimide binding of aminated aptamer mixed with oligolactide derivative of thiacalix[4]arene in a cone configuration. The assembling was monitored by cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. In the presence of the KANA, the charge transfer resistance of the inner interface surprisingly decreased with the analyte concentration within 0.7 and 50 nM (limit of detection 0.3 nM). This was attributed to the partial shielding of the negative charge of the aptamer and of its support, a highly porous 3D structure of the surface layer caused by a macrocyclic core of the carrier. The use of electrostatic assembling in the presence of cationic polyelectrolyte decreased tenfold the detectable concentration of KANA. The aptasensor was successfully tested in the determination of KANA in spiked milk and yogurt with recoveries within 95% and 115%.

Visual detection of kanamycin with DNA-functionalized gold nanoparticles probe in aptamer-based strip biosensor

Kanamycin has been widely used to treat human and animal diseases. The excessive use of kanamycin causes its accumulation in animal-derived foods, and eventually threats human health. In the present study, we develop a lateral flow strip biosensor for fast and sensitive detection of kanamycin. The strip biosensor combines the easy separation of magnetic microspheres (MMS) with target-mediated chain displacement of single-stranded DNA and the capture of the visible DNA-functionalized gold nanoparticles (AuNPs) probe. The presence of kanamycin can competitively bind to the aptamer and release cDNA to the supernatant. The concentration of free cDNA, which is the direct target of the strip, is proportional to the concentration of kanamycin. The capture of DNA-functionalized AuNPs on the test zone of the strip through cDNA-induced hybridization provides a visual detection signal. The assay can be completed within 20 min. The visual detection limit by naked eyes of the strip is 50 nM. A linear detection range of 5-500 nM is derived for quantitative determination, with the detection limit of 4.96 nM (S/N = 3). This lateral flow strip biosensor can quickly and sensitively detect kanamycin in different food samples, which holds great application potential in medicine and daily life.

Development of a Label-Free Electrochemical Aptasensor for the Detection of Tau381 and its Preliminary Application in AD and Non-AD Patients' Sera

The electrochemical aptamer sensor has been designed for detecting tau381, a critical biomarker of Alzheimer's disease in human serum. The aptasensor is obtained by immobilizing the aptamer on a carboxyl graphene/thionin/gold nanoparticle modified glassy-carbon electrode. As a probe and bridge molecule, thionin connected carboxyl graphene and gold nanoparticles, and gave the electrical signal. Under optimal conditions, the increment of differential pulse voltammetry signal increased linearly with the logarithm of tau381 concentration in the range from 1.0 pM to 100 pM, and limit of detection was 0.70 pM. The aptasensor reliability was evaluated by determining its selectivity, reproducibility, stability, detection limit, and recovery. Performance analysis of the tau381 aptasensor in 10 patients' serum samples showed that the aptasensor could screen patients with and without Alzheimer's disease. The proposed aptasensor has potential for use in clinically diagnosing Alzheimer's disease in the early stage.

Two kanamycin electrochemical aptamer-based sensors using different signal transduction mechanisms: A comparison of electrochemical behavior and sensing performance

Two typical kanamycin-A (KAN-A) electrochemical aptamer-based sensors employing different signal transduction mechanisms were deliberately designed and constructed with a similar structure. One sensor (sensor-1) was based on the classical probe conformation changing mode (PCCM) with a methylene blue (MB) label used as an electrochemical tag; the other sensor (sensor-2) used the target-induced signal probe shifting (TISPS) method with a free MB label in the assay solution. The difference in signal transduction mechanisms resulted in big differences in basic electrochemical behavior and comprehensive sensing performance. The results show that both sensor types exhibit different electrochemical behavior in square wave voltammetry, cyclic voltammetry, and in sensitivity, with detection limits of 3.0 nM for sensor-1 and 60.0 pM for sensor-2 in buffer. When validated for practical and quantitative detection of tap water and milk samples, both sensing methods performed well with detection limits of <260 nM and measurement times of <40 min. In addition, accuracy was good with mean recoveries of 72.3-92.6% and precision was acceptable with a relative standard deviation (RSD) of ≤14.2%. The basis for the similarities and differences in performance is also presented.

Voltammetric kanamycin aptasensor based on the use of thionine incorporated into Au@Pt core-shell nanoparticles

A signal-on aptasensor is described for the voltammetric determination of kanamycin (KANA). Au@Pt core-shell nanoparticles with large surface and good electrical conductivity were synthetized and act as both a conductive material and as the carrier for complementary strands (CS2) and thionine (TH). In the presence of KANA, the electrochemical response of TH changes due to hybridization between CS1 immobilized on the electrode and the Au@Pt-CS2/TH system. The peak current increases linearly with the logarithm of the KANA concentration in the range from 1 pM to 1 μM, and the limit of detection is 0.16 pM. The sensor was characterized in terms of selectivity, reproducibility and stability, and satisfactory results were obtained. It was also utilized for the determination of KANA in (spiked) chicken samples. The recoveries (95.8-103.2%) demonstrate the potential of the method for KANA detection in real samples. Graphical abstract A signal-on aptasensor for kanamycin (KANA) was developed by using Au@Pt core-shell nanoparticles as nanocarrier for probe aptamer and as a sensing probe.

Electrochemical aptamer-based sensors for food and water analysis: A review

Global food and water safety issues have prompted the development of highly sensitive, specific, and fast analytical techniques for food and water analysis. The electrochemical aptamer-based detection platform (E-aptasensor) is one of the more promising detection techniques because of its unique combination of advantages that renders these sensors ideal for detection of a wide range of target analytes. Recent research results have further demonstrated that this technique has potential for real world analysis of food and water contaminants. This review summaries the recently developed E-aptasensors for detection of analytes related to food and water safety, including bacteria, mycotoxins, algal toxins, viruses, drugs, pesticides, and metal ions. Ten different electroanalytical techniques and one opto-electroanalytical technique commonly employed with these sensors are also described. In addition to highlighting several novel sensor designs, this review also describes the strengths, limitations, and current challenges this technology faces, and future development trend.

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.

Flexible freestanding graphene paper-based potentiometric enzymatic aptasensor for ultrasensitive wireless detection of kanamycin

Flexible sensing devices have drawn tremendous attention in the past decades due to their potential applications in future hand-held, potable consumer, and wearable electronics. Here, we firstly developed an ultrasensitive wireless potentiometric aptasensor based on flexible freestanding graphene paper for kanamycin detection. Flexible graphene paper made from a simple vacuum filtration method was used as a biocompatible platform for effective immobilization of aptamer. A nuclease-assisted amplification strategy was introduced into this potentiometric biosensing system in order to significantly improve the detection sensitivity through a classic catalytic recycling reaction of target induced by the nuclease (DNase I). As expected, an ultra-low detection limit of 30.0 fg/mL for kanamycin was achieved. Furthermore, the developed potentiometric enzymatic aptasensor exhibits high selectivity, favorable flexibility, excellent stability and reproducibility, which holds great promising for its routine sensing application.

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.

Enzyme- and label-free electrochemical aptasensor for kanamycin detection based on double stir bar-assisted toehold-mediated strand displacement reaction for dual-signal amplification

It is critically important to detect antibiotic residues for monitoring food safety. In this study, an enzyme- and label-free electrochemical aptasensor for antibiotics, with kanamycin (Kana) as a typical analyte, was developed based on a double stir bar-assisted toehold-mediated strand displacement reaction (dSB-TMSDR) for dual-signal amplification. First, we modified two gold electrodes (E-1 and E-2) with different DNA probes (S1/S2 hybrid probe in E-1 and DNA fuel strand S3 in E-2). In the presence of Kana, an S1/S2 probe can be disassembled from E-1 to form an S2/Kana complex in supernatant. The S2/Kana could react with S3 on E-2 to form S2/S3 hybrid and release Kana through TMSDR. After then, the target recycling was triggered. Subsequently, the formed S2/S3 hybrid can also trigger a hybridization chain reaction (HCR). Consequently, the dual-signal amplification strategy was established, which resulted in many long dsDNA chains on E-2. The chains can associate with methylene blue (MB) as redox probes to produce a current response for the quantification of Kana. The assay exhibited high sensitivity and specificity with a detection limit at 16 fM Kana due to the dual-signal amplification. The double stir bars system can both increase phase separation and prevent leakage of DNA fuel to reduce background interference. Moreover, it allows flexible sequence design of the TMSDR probes. The assay was successfully employed to detect Kana residues in food and showed potential application value in food safety detection.

Homogeneous electrochemical aptasensor based on a dual amplification strategy for sensitive detection of profenofos residues

A homogeneous type of electrochemical aptasensor was designed based upon the principle of target-induced and tool enzyme-assisted signal amplification, which was employed for the detection of profenofos residues.

A kanamycin sensor based on an electrosynthesized molecularly imprinted poly-o-phenylenediamine film on a single-walled carbon nanohorn modified glassy carbon electrode

A single-walled carbon nanohorn (SWCNH) has been used to construct a molecularly imprinted electrochemical sensor for the first time. Kanamycin, a widely used aminoglycoside antibiotic, is used as a representative analyte to test the detection strategy. The kanamycin sensor was constructed by the electropolymerization of a molecularly imprinted poly-o-phenylenediamine film on a SWCNH modified glassy carbon electrode. The sensor was investigated in the presence or absence of kanamycin by cyclic voltammetry to verify the changes in the redox peak currents of K₃Fe(CN)₆. The sensor exhibits a linear range of 0.1-50 μM with a detection limit of 0.1 μM. It also shows high recognition ability, indicating that the SWCNH-based molecularly imprinted sensor is promising.

Evanescent wave aptasensor for continuous and online aminoglycoside antibiotics detection based on target binding facilitated fluorescence quenching

The biosensors capable for on-site continuous and online monitoring of pollutants in environment are highly desired due to their practical importance and convenience. The group specific detection of pollutants is especially attractive due to the diversity of environmental pollutants. Here we devise an evanescent wave aptasensor based on target binding facilitated fluorescence quenching (FQ-EWA) for the online continuous and group-specific detection of aminoglycoside antibiotics (AMGAs). In FQ-EWA, a fluorophore labeled DNA aptamer selected against kanamycin was used for both the target recognition in solution and signal transduction on optical fiber of EWA. The aptamers form multiple-strand complex (M-Apt) in the absence of AMGAs. The binding between AMGA and the aptamer disrupts M-Apt and leads to the formation of AMGA -aptamer complex (AMGA-Apt). The photo-induced electron transfer between the fluorophore and AMGA partially quenches the fluorescence of AMGA-Apt. The structure-selective absorption of AMGA-Apt over M-Apt on the graphene oxide further quenches the fluorescence of AMGA-Apt. Meanwhile, the unbound aptamers in solution assemble with the unlabeled aptamers immobilized on the fiber to form M-Apt. The amount of M-Apt on the fiber is inversely proportional to the concentration of AMGAs, enabling the signal-off detection of AMGAs from 200nM to 200μM with a detection limit of 26nM. The whole detection process is carried out in an online mode without any offline operation, providing a great benefit for system automation and miniaturization. FQ-EWA also shows great surface regeneration capability and enables the continuous detection more than 60 times.

An Overview on Recent Progress in Electrochemical Biosensors for Antimicrobial Drug Residues in Animal-Derived Food

Anti-microbial drugs are widely employed for the treatment and cure of diseases in animals, promotion of animal growth, and feed efficiency. However, the scientific literature has indicated the possible presence of antimicrobial drug residues in animal-derived food, making it one of the key public concerns for food safety. Therefore, it is highly desirable to design fast and accurate methodologies to monitor antimicrobial drug residues in animal-derived food. Legislation is in place in many countries to ensure antimicrobial drug residue quantities are less than the maximum residue limits (MRL) defined on the basis of food safety. In this context, the recent years have witnessed a special interest in the field of electrochemical biosensors for food safety, based on their unique analytical features. This review article is focused on the recent progress in the domain of electrochemical biosensors to monitor antimicrobial drug residues in animal-derived food.

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.

Ultra-sensitive detection of kanamycin for food safety using a reduced graphene oxide-based fluorescent aptasensor

Overuse of antibiotics has caused serious problems, such as appearance of super bacteria, whose accumulation in the human body through the food chain is a concern. Kanamycin is a common antibiotic used to treat diverse infections; however, residual kanamycin can cause many side effects in humans. Thus, development of an ultra-sensitive, precise, and simple detection system for residual kanamycin in food products is urgently needed for food safety. In this study, we identified kanamycin-binding aptamers via a new screening method, and truncated variants were analyzed for optimization of the minimal sequence required for target binding. We found various aptamers with high binding affinity from 34.7 to 669 nanomolar K_d^app values with good specificity against kanamycin. Furthermore, we developed a reduced graphene oxide (RGO)-based fluorescent aptasensor for kanamycin detection. In this system, kanamycin was detected at a concentration as low as 1 pM (582.6 fg/mL). In addition, this method could detect kanamycin accurately in kanamycin-spiked blood serum and milk samples. Consequently, this simple, rapid, and sensitive kanamycin detection system with newly structural and functional analysis aptamer exhibits outstanding detection compared to previous methods and provides a new possibility for point of care testing and food safety.

Highly sensitive aptasensor based on synergetic catalysis activity of MoS2-Au-HE composite using cDNA-Au-GOD for signal amplification

Single or few-layer nanosheets of MoS₂ (MoS₂ nanosheets) and a composite composed of MoS₂ nanosheets, Au nanoparticles (AuNPs) and hemin (HE) (denoted as MoS₂-Au-HE) were prepared. The composites possessed high synergetic catalysis activity towards the electroreduction of hydrogen peroxide. Furthermore, glucose oxidase (GOD) and AuNPs were used as marker of the complementary DNA (cDNA) strand of kanamycin aptamer to prepare a conjugate (reffered as cDNA-Au-GOD) that was designed as the signal probe. Both cDNA-Au-GOD and MoS₂-Au-HE were applied to fabricate aptasensor for kanamycin. MoS₂-Au-HE acted as solid platform for kanamycin aptamer and signal transmitters. AuNPs were employed as the supporter of cDNA and GOD which catalyze dissolved oxygen to produce hydrogen peroxide in the presence of glucose. Then cathodic peak current of H₂O₂ was recorded by differential pulse voltammetry (DPV). The electrochemical reduction of H₂O₂ was catalyzed by MoS₂-Au-HE that was modified onto the surface of a glassy carbon electrode (GCE). The cathodic peak current of H₂O₂ was highly linearly decreased with an increase of kanamycin concentrations from 1.0ng/L to 1.0×10⁵ng/L, with a detection limit of 0.8ng/L. This aptasensor can be used to detect kanamycin in milk with high specificity, sensitivity and selectivity.

A versatile fluorescent biosensor based on target-responsive graphene oxide hydrogel for antibiotic detection

A fluorescent sensing platform based on graphene oxide (GO) hydrogel was developed through a fast and facile gelation, immersion and fluorescence determination process, in which the adenosine and aptamer worked as the co-crosslinkers to connect the GO sheets and then form the three-dimensional (3D) macrostructures. The as-prepared hydrogel showed high mechanical strength and thermal stability. The optimal hydrogel had a linear response for oxytetracycline (OTC) of 25-1000μg/L and a limit of quantitation (LOQ) of 25μg/L. Moreover, together with the high affinity of the aptamer for its target, this assay exhibited excellent sensitivity and selectivity. According to its design principle, the as-designed hydrogel was also tested to possess the generic detection function for other molecules by simply replacing its recognition element, which is expected to lay a foundation to realize the assembly of functionalized hierarchical graphene-based materials for practical applications in analytical field.

Fluorescent aptasensor for chloramphenicol detection using DIL-encapsulated liposome as nanotracer

A novel fluorescence aptasensor was successfully developed to respond to chloramphenicol (CAP) in food based on magnetic aptamer-liposome vesicle probe. In order to fabricate it, aptamer labeled on functionalized magnetic beads (MB) was firstly employed as capture adsorbent (MB-Apt), then SSB (single-stranded DNA binding protein) and DIL (1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanineperchlorate) coimmobilized liposomes (SSB/DIL-Lip) was employed as vesicle signal tracer. The composite vesicle probe is formed between SSB/DIL-Lip and MB-Apt based on SSB's specific recognition towards aptamer on vesicle signal tracer. Upon the vesicle probe solution reacted with CAP, the aptamer on the magnetic beads preferentially bounded with CAP, and then released SSB/DIL-Lip vesicle signal tracer in the supernatant after magnetic separation. The released tracer can emit fluorescence which was correspondence with the concentration of the analyte. At the optimum conditions, the aptasensor exhibited a good linear response for CAP detection in the range of 0.003-10nM with a detection limit of 1pM. Importantly, the methodology was further validated for analyzing CAP in fish samples with consistent results obtained by ELISA kit, thus providing a promising approach for quantitative monitoring of CAP and significant anti-interference ability in food safety.

Signal-on electrochemical detection of antibiotics at zeptomole level based on target-aptamer binding triggered multiple recycling amplification

In the work, a signal-on electrochemical DNA sensor based on multiple amplification for ultrasensitive detection of antibiotics has been reported. In the presence of target, the ingeniously designed hairpin probe (HP1) is opened and the polymerase-assisted target recycling amplification is triggered, resulting in autonomous generation of secondary target. It is worth noting that the produced secondary target could not only hybridize with other HP1, but also displace the Helper from the electrode. Consequently, methylene blue labeled HP2 forms a "close" probe structure, and the increase of signal is monitored. The increasing current provides an ultrasensitive electrochemical detection for antibiotics down to 1.3 fM. To our best knowledge, such work is the first report about multiple recycling amplification combing with signal-on sensing strategy, which has been utilized for quantitative determination of antibiotics. It would be further used as a general strategy associated with more analytical techniques toward the detection of a wide spectrum of analytes. Thus, it holds great potential for the development of ultrasensitive biosensing platform for the applications in bioanalysis, disease diagnostics, and clinical biomedicine.

Signal-on electrochemical detection of antibiotics based on exonuclease III-assisted autocatalytic DNA biosensing platform

In this work, a novel electrochemical DNA sensor based on exonuclease III (Exo III)-assisted autocatalytic DNA biosensing platform for ultrasensitive detection of antibiotics has been reported.

A regular “signal attenuation” electrochemical aptasensor for highly sensitive detection of streptomycin

A novel aptasensor based on PCNRs and MWCNTs–CuO–AuNPs as the nanomatrix was constructed for the highly sensitive detection of streptomycin.

A novel signal amplification strategy of an electrochemical aptasensor for kanamycin, based on thionine functionalized graphene and hierarchical nanoporous PtCu

An ultrasensitive electrochemical aptasensor for the quantitative detection of kanamycin antibiotic was fabricated based on a novel signal amplification strategy. This aptasensor was developed using thionine functionalized graphene (GR-TH) and hierarchical nanoporous (HNP) PtCu alloy as biosensing substrates for the first time. HNP-PtCu alloy with controllable bimodal ligament/pore distributions was successfully prepared by two-step dealloying of a well-designed PtCuAl precursor alloy combined with an annealing operation. GR-TH composite was synthesized by one-step reduction of graphene oxide (GO) in TH solution. Greatly amplified sensitivity was achieved by using GR-TH/HNP-PtCu composite owing to its large specific surface and good electron-transfer ability. Under the optimized conditions, the proposed aptasensor exhibited a high sensitivity and a wider linearity to kanamycin in the range 5 × 10(-7)-5 × 10(-2) μgmL(-1) with a low detection limit of 0.42 pgmL(-1). This aptasensor also displayed a satisfying electrochemical performance with good stability, selectivity and reproducibility. The as-prepared aptasensor was successfully used for the determination of kanamycin in animal derived food.