A microchip electrophoresis-based assay for ratiometric detection of kanamycin by R-shape probe and exonuclease-assisted signal amplification

Dual-mode photoelectrochemical/electrochemical sensor based on Z-scheme AgBr/AgI-Ag-CNTs and aptamer structure switch for the determination of kanamycin

A "signal-on" dual-mode aptasensor based on photoelectrochemical (PEC) and electrochemical (EC) signals was established for kanamycin (Kana) assay by using a novel Z-scheme AgBr/AgI-Ag-CNTs composite as sensing platform, an aptamer structure switch, and K₃[Fe(CN)₆] as photoelectron acceptor and electrochemical signal indicator. The aptamer structure switch was designed to obtain a "signal-off" state, which included an extended Kana aptamer (APT), one immobilized probe (P1), and one blocking probe (P2) covalently linked with graphdiyne oxide (GDYO) nanosheets. P1, P2, and aptamer formed the double helix structure, which resulted in the inhibited photocurrent intensity because of the weak conductivity of double helix layer and serious electrostatic repulsion of GDYO towards K₃[Fe(CN)₆]. In the presence of Kana, APT specifically bound to the target and dissociated from P1 and P2, and thus, a "signal-on" state was initiated by releasing P2-GDYO from the platform. Based on the sensing platform and the aptamer structure switch, the dual-mode aptasensor realized the linear determination ranges of 1.0 pM-2.0 μM with a detection limit (LOD) of 0.4 pM (for PEC method) and 10 pM-5.0 μM with a LOD of 5 pM (for EC method). The aptasensor displayed good application potential for Kana test in real samples.

Development of label-free fluorescent biosensor for the detection of kanamycin based on aptamer capped metal-organic framework

The abuse of antibiotics has caused serious threat to human health, so it is of great significance to develop a simple and sensitive method for the detection of trace residues of antibiotics in the environment and food. Herein, a novel label-free fluorescent biosensing platform based on the fluorescence change of aptamers-capped zeolitic imidazolate framework-8 (ZIF-8) @ 2,2',2″,2‴-((ethene-1,1,2,2-tetrayltetrakis (benzene-4,1-diyl)) tetrakis (oxy)) tetraacetic acid (TPE) through ATP-assisted competitive coordination reaction was designed for such an end. ZIF-8@TPE/Aptamer (Apt) emits strong fluorescence at 425 nm in HEPES buffer due to the aggregation induced luminescence properties of TPE molecules in confined state. Once kanamycin was added, the conformation of aptamer capped on the surface of ZIF-8@TPE changes because of the specific recognition of kanamycin with aptamer, leading to the collapse of ZIF-8 and release of TPE, accompanied with a dramatic decrease of fluorescence intensity. Under the optimal conditions, a good correlation was obtained between the fluorescence intensity of ZIF-8@TPE/Apt and the concentration of kanamycin ranging from 10 to 10³ ng/mL with a detection limit of 7.3 ng/mL. The satisfactory analytical performance of the assay for kanamycin detection suggests good prospect for its application in food safety analysis.

Recent progress of microfluidic technology for pharmaceutical analysis

In recent years, the progress of microfluidic technology has provided new tools for pharmaceutical analysis and the proposal of pharm-lab-on-a-chip is appealing for its great potential to integrate pharmaceutical test and pharmacological test in a single chip system. Here, we summarize and highlight recent advances of chip-based principles, techniques and devices for pharmaceutical test and pharmacological/toxicological test focusing on the separation and analysis of drug molecules on a chip and the construction of pharmacological models on a chip as well as their demonstrative applications in quality control, drug screening and precision medicine. The trend and challenge of microfluidic technology for pharmaceutical analysis are also discussed and prospected. We hope this review would update the insight and development of pharm-lab-on-a-chip.

Multiply-amplified strategy for the ultrasensitive detection of kanamycin via aptamer-triggered three-dimensional G-quadruplex/Ni-Fe layered double oxide frame networks

In this work, a multiply-amplified peroxidase-like colorimetric strategy was proposed for the high-specific recognition and ultrasensitive detection of kanamycin (Kana). Based on two Kana-aptamer triggered sequential reactions, G-quadruplex (G4) and DNA (hairpins) modified Ni-Fe layered double oxides (LDOs) could be obtained simultaneously. Later, a three-dimensional G4/LDO frame networks, as a novel DNAzyme, with enhanced peroxidase-like catalytic activity was assembled through electrostatic interaction. This DNAzyme catalyzed 3,3',5,5'-tetramethylbenzidine oxidation for the colorimetric detection of Kana. The enhancement principle was discussed and the charge transfer process during the catalytic reaction was investigated. Under the optimal experiment conditions, the proposed method exhibited high sensitivity, where the linear range is from 10 fM to 10 nM (r² = 0.992), and the limit of detection is 3 fM (S/N = 3). The practicability of this assay was demonstrated by successfully application of residual Kana detection in genuine milk and urine samples.

Development of DNA Biosensors Based on DNAzymes and Nucleases

DNA biosensors play important roles in environmental, medical, industrial and agricultural analysis. Many DNA biosensors have been designed based on the enzyme catalytic reaction. Because of the importance of enzymes in biosensors, we present a review on this topic. In this review, the enzymes were divided into DNAzymes and nucleases according to their chemical nature. Firstly, we introduced the DNAzymes with different function inducing cleavage, metalation, peroxidase, ligation and allosterism. In this section, the G-quadruplex DNAzyme, as a hot topic in recent years, was described in detail. Then, the nucleases-assisted signal amplification method was also reviewed in three categories including exonucleases, endonucleases and other nucleases according to the digestion sites in DNA substrates. In exonucleases section, the Exo I and Exo III were selected as examples. Then, the DNase I, BamH I, nicking endonuclease, S1 nuclease, the duplex specific nuclease (DSN) and RNases were chosen to illustrate the application of endonucleases. In other nucleases section, DNA polymerases and DNA ligases were detailed. Last, the challenges and future perspectives in the field were discussed.

Photoelectrochemical Aptasensors Constructed with Photosensitive PbS Quantum Dots/TiO2 Nanoparticles for Detection of Kanamycin

Kanamycin (Kana) is widely used as a veterinary medicine and its abuse causes a serious threat to human health, raising the urgent demand for detection of residual Kana in animal-derived food with high specificity and sensitivity. Here, we developed a photoelectrochemical (PEC) biosensor for rapid quantification of Kana, with lead sulfide quantum dots/titanium dioxide nanoparticles (PbS QDs/TiO₂ NPs) as a photosensitive composite, a Kana-specific DNA aptamer as a functional sensor, and ruthenium(III) hexaammine (Ru(NH₃)₆³⁺) as a signal booster. To prepare the PEC aptasensor, TiO₂ NPs, PbS QDs, and polyethyleneimine (PEI) were respectively used to modify the indium tin oxide electrode, and then the amine-terminated aptamer probe was connected to the PEI via glutaraldehyde. Finally, Ru(NH₃)₆³⁺ was attached on the surface of the aptamer to increase the photocurrent intensity. When Kana binds competitively with Ru(NH₃)₆³⁺ to the aptamer immobilized on the surface of the aptasensor, Ru(NH₃)₆³⁺ will be released from the aptamer, resulting in a decrease of the photocurrent signal. This PEC aptasensor exhibits a good linear relationship between the photocurrent shift and the logarithm of Kana concentration within the range of 1.0-300.0 nmol L^-1, and the detection limit is 0.161 nmol L^-1. Importantly, the PEC aptasensor presented good detection selectivity owing to specific interaction with Kana and was successfully implemented to quantify Kana in honey and milk, suggesting that the PEC aptasensor has the potential of rapid detection of residual Kana in animal-derived foods.

Label-free exonuclease I-assisted signal amplification colorimetric sensor for highly sensitive detection of kanamycin

A label-free colorimetric method based on exonuclease I (Exo I)-assisted signal amplification with protamine as a medium was developed for analysis of kanamycin. In this study, a double-stranded DNA (dsDNA) probe was tailored by manipulating an aptamer and its complementary DNA (cDNA) ensuring detection of target with high selectivity and excellent sensitivity. Herein, protamine could not only combine with negatively charged gold nanoparticles but also interaction with polyanion DNA. Upon addition of target kanamycin, the target-aptamer complex was formed and the cDNA was released. Thus, both aptamer and cDNA could be digested by Exo I, and the captured kanamycin was liberated for triggering target recycling and signal amplification. Under optimized conditions, the proposed colorimetric method realized a low detection limit of 2.8 × 10^-14 M along with a wide linear range plus excellent selectivity. Our strategy exhibited enormous potentials for fabricate various kinds of biosensors based on target-induced aptamer configuration changes.

Highly sensitive electrochemiluminescence aptasensor based on dual-signal amplification strategy for kanamycin detection

In order to effectively monitor the residue of kanamycin (KAN), a dual-signal-amplified electrochemiluminescence (ECL) aptasensor based on multi-walled carbon nanotubes@titanium dioxide/thionine (MWCNTs@TiO₂/Thi) was proposed. MWCNTs@TiO₂ with large specific surface area and favorable biocompatibility could accelerate charge transfer and enable high loading of luminol to enhance ECL response. As a perfect electronic mediator, Thi could also accelerate electron conductivity to further enhance ECL intensity. The ECL intensity of MWCNTs@TiO₂/Thi was enhanced for 3.6-fold compared with that of individual Thi because Thi could strongly interact with MWCNTs through π-π stacking force to enhance the electronic transmission. With the outstanding electron transfer property of MWCNTs@TiO₂ and Thi, ECL intensity of the proposed aptasensor was obviously increased. Upon addition of KAN, the aptamer bound to its target, which caused that the ECL intensity decrease significantly. Therefore, KAN concentration could be monitored on the basis of signal intensity. Under optimal conditions, the constructed aptasensor exhibited a sensitive response towards KAN and a low detection limit of 0.049 ng mL^-1 was obtained. It also possessed the excellent specificity, favorable stability and good reproducibility. Importantly, the application of proposed ECL aptasensor provides an efficient approach for highly sensitive detection of various small molecular contaminants.

Aptamer biorecognition-triggered hairpin switch and nicking enzyme assisted signal amplification for ultrasensitive colorimetric bioassay of kanamycin in milk

A colorimetric aptasensing strategy for detection of kanamycin was designed based on aptamer biorecognition and signal amplification assisted by nicking enzyme. The aptamer of kanamycin was designed to be contained in the metastable state hairpin DNA. The target DNA as recycling DNA was located in the loop of hairpin DNA. The presence of kanamycin stimulates the continuous actions, including specific recognition of the aptamer to kanamycin, the hybridization between target DNA and signal probe, the cleavage function of nicking enzyme. The actions induced accumulation of numerous free short sequences modified by platinum nanoparticles (PtNPs), which can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB)-H₂O₂ to produce a colorimetric response. The aptasensor exhibited good selectivity and sensitivity for kanamycin in milk with a detection limit as low as 0.2 pg·mL^-1. In addition, the proposed assay is potentially to be extended for other antibiotics detection in foods by adapting the corresponding aptamer sequence.

Recent Advances and Applications of Microfluidic Capillary Electrophoresis: A Comprehensive Review (2017-Mid 2019)

Microfluidic capillary electrophoresis (MCE) is the novel technique resulted from the CE mininaturization as planar separation and analysis device. This review presents and discusses various application fields of this advanced technology published in the period 2017 till mid-2019 in eight different sections including clinical, biological, single cell analysis, environmental, pharmaceuticals, food analysis, forensic and ion analysis. The need for miniaturization of CE and the consequence advantages achieved are also discussed including high-throughput, miniaturized detection, effective separation, portability and the need for micro- or even nano-volume of samples. Comprehensive tables for the MCE applications in the different studied fields are provided. Also, figure comparing the number of the published papers applying MCE in the eight discussed fields within the studied period is included. The future investigation should put into consideration the possibility of replacing conventional CE with the MCE after proper validation. Suitable validation parameters with their suitable accepted ranges should be tailored for analysis methods utilizing such unique technique (MCE).

A microfluidic chip based ratiometric aptasensor for antibiotic detection in foods using stir bar assisted sorptive extraction and rolling circle amplification

A ratiometric and sensitive microfluidic chip based aptasensor was developed for antibiotic detection with kanamycin (Kana) as a model analyte. A novel stir bar assisted sorptive extraction and rolling circle amplification strategy was designed to largely amplify the signal and overcome complex matrix interference in food samples. The detection mechanism was as follows: firstly, many duplex DNA probes (a single-stranded DNA as a primer hybrid with an aptamer sequence) were modified on a stir bar. In the presence of Kana, the probes on the bar could specifically capture Kana and release the primer to trigger RCA in the presence of a circular DNA template (CDT). As the reaction proceeds, the amount of CDT decreased and the number of RCA products increased. It is worth mentioning that they can be efficiently separated and detected using a microfluidic chip. The signal ratio of RCA products and CDT (IR/IC) can be employed to qualify Kana in a wide linear range from 0.8 pg mL-1 to 10 ng mL-1 with a low detection limit of 0.3 pg mL-1. This method exhibited excellent sensitivity and selectivity and can obviously reduce the matrix interference through a ratiometric strategy combined with stir bar extraction. The aptasensor was successfully tested in milk and fish samples, confirming that it can be applied for on-site quantitation of antibiotic residues in foods.

Electrochemical aptasensor for sulfadimethoxine detection based on the triggered cleavage activity of nuclease P1 by aptamer-target complex

Herein, a simple and selective electrochemical method was developed for sulfadimethoxine detection based on the triggered cleavage activity of nuclease P1 by the formation of aptamer and sulfadimethoxine conjugate. After probe DNA was immobilized on gold electrode surface, aptamer DNA labeled with biotin at its 5'-terminal was then captured on electrode surface through the hybridization reaction between probe DNA and aptamer DNA. The formed double-stranded DNA (dsDNA) can block the digestion activity of Nuclease P1 towards the single-stranded probe DNA. Then, the anti-dsDNA antibody was further modified on electrode surface based on the specific interaction between dsDNA and antibody. Due to the electrostatic repulsion effect and steric-hindrance effect, a weak electrochemical signal was obtained at this electrode. However, in the presence of sulfadimethoxine, it can interact with aptamer DNA, and then the formation of dsDNA can be blocked. As a result, the probe DNA at its single-strand state can be digested by Nuclease P1, which leads to the failure of the immobilization of anti-dsDNA antibody. At this state, a strong electrochemical signal was obtained. Based on the change of the electrochemical signal, sulfadimethoxine can be detected with linear range of 0.1-500 nmol/L. The detection limit was 0.038 nmol/L. The developed method possesses high detection selectivity and sensitivity. The applicability of this method was also proved by detecting sulfadimethoxine in veterinary drug and milk with satisfactory results.

Luminescent carbon nanodots based aptasensors for rapid detection of kanamycin residue

Despite the success in long-term storage of food and dietary products using antibiotics as supplements, enormous levels of their residues have remained as a significant health concern, leading to severe toxicity issues on consumption. Herein, we report an ultrasensitive and highly selective aptasensor based on carbon nanoparticles (CNPs) through a fluorescence-based aptamer-linked immunosorbent assay (FALIA) for rapid detection of kanamycin (KAA) residue. The fabricated CNP-aptasensor exhibited superior selectivity with exceptional photoluminescence properties. Under the optimal conditions, the linear equation of standard KAA solution was Y = -0.2279LogX+1.3648 (R = -0.9893) ranged from 10^-4 to 10^-7 ppb with excellent relative standard deviations (RSD) between 3.12 and 5.59 % (n = 3). Moreover, the limit of detection (LOD) was lower than 5.0 × 10^-8 ppb. Together, the excellent recovery and significant efficacy in the rapid detection of antibiotics at a low level in milk indicate that this fabricated CNP-aptasensor has a great potential in the establishment of an efficient antibiotic detector system in food and other nutraceutical industries.

Exonuclease I-assisted fluorescent method for ochratoxin A detection using iron-doped porous carbon, nitrogen-doped graphene quantum dots, and double magnetic separation

In this paper, a fluorescent method was developed for ochratoxin A (OTA) detection that uses iron-doped porous carbon (MPC) and aptamer-functionalized nitrogen-doped graphene quantum dots (NGQDs-Apt) as probes. In this method, the adsorbance of the NGQDs-Apt on the MPC due to a π-π interaction between the aptamer and the MPC results in the quenching of the fluorescence of the NGQDs-Apt. However, since OTA interacts strongly with the aptamer, the presence of OTA leads to the detachment of the NGQDs-Apt from the MPC, resulting in the resumption of fluorescence from the NGQDs-Apt. When exonuclease I (Exo I) is also added to the solution, this exonuclease specifically digests the aptamer, leading to the release of the OTA back into the solution. This free OTA then interacts with another MPC-NGQDs-Apt system, inducing the release of more NGQDs into the solution, which enhances the fluorescent intensity compared to that of the system with no Exo I. Utilizing this behavior of OTA in the presence of NGQDs-Apt, it was possible to detect concentrations of OTA ranging from 10 to 5000 nM, with a limit of detection of 2.28 nM. Our method was tested by applying it to the detection of OTA in wheat and corn samples. This method has four advantages: (1) the magnetic porous carbon is easy to prepare, its porosity enhances its loading capacity for NGQDs, it highly efficiently quenches the fluorescence of the NGQDs, and its magnetic properties facilitate the separation of the MPC from other species in solution; (2) applying double magnetic separation decreases the background signal; (3) Exo I digests the free aptamer effectively, which allows the resulting free OTA to induce the release of more NGQDs-Apt, ultimately enhancing the fluorescent signal; and (4) the proposed method presented high sensitivity and a wide linear detection range. This method may prove helpful in food safety analysis and new biosensor development (achieved by using different aptamer sequences to that used in the present work). Graphical abstract Exonuclease I (Exo I)-assisted fluorescent method for ochratoxin A (OTA) detection using magnetic porous carbon (MPC), nitrogen-doped graphene quantum dots (NGQDs), and double magnetic separation.