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The existence of contaminants in food poses a serious threat to human health. In recent years, aptamer sensors (aptasensors) have been developed rapidly for the detection of food contaminants because of their high specificity, design flexibility, and high efficiency. However, the development of high-throughput, highly sensitive, on-site, and cost-effective methods for simultaneous detection of food contaminants is still restricted due to multiple signal overlap or mutual interference and cross-reaction between different analytes with similar molecular structures. To overcome these problems, this Review summarizes some effective strategies from the articles published in recent years about multiplexed aptasensors for the simultaneous detection of food contaminants. This work focuses on the application of multiplexed aptasensors to simultaneously detect antibiotics, pathogens, and mycotoxins in food. These aptasensors mainly contain fluorescent aptasensors, electrochemical aptasensors, surface-enhanced Raman scattering-based aptasensors, microfluidic chip aptasensors, and paper-based multiplexed aptasensors. In addition, this Review also covers the application of nucleic acid cycle amplification and nanomaterial amplification strategies to improve the detection sensitivity. Finally, the limitations and challenges in the design of multiplexed aptasensor are also taken into account.

The development of multiplex assays to simultaneously monitor multiclass chemical contaminants that commonly coexist in foods, such as heavy metal ions, antibiotics, and estrogen residues, is gaining attention. Here, a microfluidic chip (MC)-based multianalysis method coupled with magnetic encoded aptamer probes was used for simultaneous detection of kanamycin, 17β-estradiol, and lead ion (Pb2+). Using this innovative strategy, the magnetic bead (MB)-based encoded probes labeled with aptamer hybrid chains were first used to selectively capture multiple targets, followed by generating single-stranded primers. The primers triggered a multibranched hybridization chain reaction (mHCR). Finally, three kinds of complementary strands (C-DNAs) with different lengths were hybridized with the arms of the mHCR products to form three types of multibranched DNA nanostructures. The decrement signals of C-DNAs were employed for qualification of targets. As the signal tags corresponded to different targets, the DNA nanostructures realized "one target for the decrease of massive C-DNAs" to improve sensitivity. The use of MB-based encoded probes could achieve magnetic separation to eliminate interference in the complex. The detection limits of this method were 1.76 × 10-4 nM (kanamycin), 1.18 × 10-4 nM (17β-estradiol), and 1.29 × 10-4 nM (lead ion). Furthermore, the MC platform is reusable and can be used for more than 4000 samples. The assay combining the MC with MB-based encoded probes with multibranched DNA signal tags offers a universal, reusable, and high-throughput detection platform for screening multiclass chemical contaminants in food samples with complex matrices.

It's important to eliminate matrix interference for accurate detecting antibiotic residues in complex food samples. In this study, we designed a zero-backgrounded fluorescence aptasensor to achieve on-site detection of antibiotic residues, with chloramphenicol (CAP) as representative analyte. Moreover, a three stir-bars assisted target recycling system (TSBTR) was designed to achieve triple signal amplification and increase the sensitivity. The bars included one magnetic stir-bar modified with two kinds of long DNA chains, and two gold stir-bars modified with Y shape-duplex DNA probes respectively. In the presence of CAP, the target could recurrently react with the probes on the bars and replace a large amount of long DNA chains into supernatant. After then, the bars were taken out and SYBR green dye was added to the solution. The dye can specifically intercalate into the duplex structures of DNA chains to emit fluorescence while not emitting a signal in its free state. Under the optimized experimental conditions, a wide linear response range of 5 orders of magnitude from 0.001 ng mL−1 to 10 ng mL−1 was achieved with a detection limit of 0.033 pg mL−1 CAP. The assay was successfully employed to detect CAP in food samples (milk & fish) with consistent results with ELISA's. High selectivity and sensitivity were attributed to the zero background signal and triple signal-amplification strategy. Moreover, the detection time can be shortened to 40 min due to that three signal amplified process can occur simultaneously. The fluorescent aptasensor was also label- and enzyme-free. All these ensure the platform to be rapid, cost-effective, easily-used, and is especially appropriate for detection antibiotics in food safety.

To detect trace level of tumor markers (TMs) plays a crucial role in the early diagnosis of cancer. However, the fabrication of assays to simultaneously detect trace levels of TMs was still challengeable. The study was aimed to develop a novel microchip electrophoresis (MC) and antibody-aptamer based hybrid detection strategy for simultaneous determination of prostate specific antigen (PSA), carcino-embryonic antigen (CEA) and carbohydrate antigen 125 (CA125) in human serum. The assay comprises the generation of magnetic aptamer capture probes and anti-TMs labeled encoded signal tags, then employment of nicking enzyme for signal amplification. Firstly, the aptamers of TMs were co-immobilized on surface of Fe3O4@AuNPs (AuMPs) as capture probes. Simultaneously, the antibodies of TMs labeled with different double stranded DNA (dsDNA) as nicked fragment-induced strand was prepared as encoded signal tags. Secondly, the TMs, capture probes and encoded signal tags were simultaneously incubated to form sandwich complex. After magnetic separation, the complex was collected by adding the nicking enzyme. As a result, the dsDNA on the complex can initiate nicking enzyme cleavage reaction to produce many single stranded DNA (ssDNA) products with different length corresponding to different targets. Finally, the ssDNA products were injected into MC for separation and determination of TMs, respectively. Under optimized conditions, the assay can simultaneously detect three TMs with detection limits of 0.1, 0.15, 0.12 pg mL−1 for PSA, CEA and CA125, respectively (S/N = 3). Moreover, the magnetic aptamer probes exhibited good stability and can be reused for 20 times with the recovery above 80% after heat treatments. The multianalysis method exhibits distinct advantages such as high-throughput, -sensitivity, easy-to-operate and offers a powerful tool for early diagnosis of cancers.

Solid phase microextraction (SPME) Arrows with enlarged sorption phases and Arrow-shaped tips are good alternatives to classic SPME fibers. Developing SPME Arrows with functionalized coatings has become a growing area of SPME research. In this study, a zirconium metal organic framework/molybdenum disulfide (UiO-66/MoS2) composite coating modified SPME Arrow was developed and coupled with gas chromatography-mass spectrometry for the headspace extraction and detection of 16 polycyclic aromatic hydrocarbons (PAHs). The coating preparation can be easily manipulated by the assembly strategy using silicone gels to adhere UiO-66/MoS2 powder onto the surface of the Arrows. The prepared UiO-66/MoS2 coated SPME Arrows exhibited clearly enhanced adsorption capacity (2.1–4.5 folds) and an improved degree of affinity to PAHs species when compared to commercial PDMS/CARS/DVB SPME Arrows or fibers. The improved mechanism may be due to the high specific area, hierarchical micropores and mesopores, and the largely increased and immobilized amount of UiO-66/MoS2 coating on the stainless-steel Arrow. Under optimized conditions, the SPME Arrow-based assay was successfully applied to determine PAH levels in fish samples with satisfactory recoveries of 80.2–101% and relative standard deviations (RSDs) of less than 6%. The detection limits of PAHs were between 0.11–1.40 ng kg−1. The coating showed satisfied reproducibility and repeatability (RSD

Biological fluorescence imaging technologies have attracted a lot of attention and have been widely used in biomedical fields. Compared with other technologies, fluorescence imaging has a lower cost, higher sensitivity, and easier operation. However, due to the disadvantages of one-photon (OP) fluorescence imaging, such as low spatial and poor temporal resolution and poor tissue permeability depth, the application of OP fluorescence imaging has some limitations. Though two-photon (TP) fluorescence imaging can well overcome these shortcomings of OP, the single-mode imaging remains deficient. Therefore, dual-mode imaging combined with TP imaging and magnetic resonance imaging (MRI) can make up for the deficiency well, which make dual-mode imaging for the early diagnosis of diseases more accurate. Hence, a dual-mode nanoprobe TP-CQDs@MnO2 was designed for probing the fluorescence/MR dual-mode imaging strategy of intracellular H+ by using TP-CQDs (two photon-carbon quantum dots) and MnO2 nanosheets. The MnO2 nanosheets treated as fluorescence quenching agents of TP-CQDs exhibited a supersensitive response to H+, which made the fluorescence signals turn "off" to "on" for TP fluorescence imaging, in the meantime, large amounts of Mn2+ were generated for MRI. A dual-mode nanoprobe TP-CQDs@MnO2 can monitor intracellular wide pH (4.0-8.0), and the fluorescence intensity of TP-CQDs@MnO2 has recovered up to more than six times and the corresponding results of MRI were satisfactory. TP fluorescence imaging of cells and tissues showed higher detection sensitivity and deeper tissue penetration (240.0 μm) than OP. The dual-mode imaging platform hold great promise for pH-related early diagnosis and treatment, which has great potential to improve clinical efficacy.

A pair of composite probes based on aptamer modified polyhedral oligomeric silsesquioxane-perovskite quantum dots (POSS-PQDs-Apt) as signal probe and titanium carbide (Ti3C2) MXenes as quencher were prepared for the first time. They were employed to fabricate one turn-on–type aptasensor relying on fluorescence resonance energy transfer (FRET) for Vibrio parahaemolyticus (VP) determination. The POSS-PQDs-Apt can be adsorbed on the MXenes nanosheets, and its fluorescence was quenched due to the FRET. After the composite probes were incubated with VP for 50 min, the POSS-PQDs-Apt binding with VP can be released from the surface of MXenes, and the signal recovered due to its higher affinity to the VP than MXenes. The fluorescence intensity from 519 nm emission of the system was measured at 480 nm excitation. Under In optimized conditions, the assay can determine VP in the concentration range 102 - 106 cfu/mL, and the detection limit (LOD) was 30 cfu/mL using fluorescence detection. The LOD is still 100 cfu/mL by naked eye detection which is proper for on-line monitoring VP in aquaculture water. This method was also used to detect VP in actual samples of seawater, the recovery of spiked samples was between 93% and 106%, and relative standard deviation (RSD) was between 2.7% and 6.7%. The result is consistent with the plate count. Therefore, this assay could provide a candidate platform for screening VP in aquaculture industry.

It was critically important to develop some sensitive, convenient and on-site methods for simultaneous assay of different pathogenic bacteria in foods. In this work, a dual-mode aptasensor was established for fulfilling above aims combing colorimetry with microfluidic chip. This as-prepared dual-mode aptasensor not only realized rapid screening by naked eye on-site, but also the simultaneous quantification of multiple bacteria. Namely, the presence of pathogenic bacteria was firstly judged by naked eyes with Salmonella typhimurium (S.T) and Vibrio parahaemolyticus (V.P) as models. And then, S.T and V.P in positive samples were simultaneously quantified by microfluidic chip. In order to obtain the multiple signals, a series of magnetic DNA encoded-probes (MDEs) was fabricated containing rolling cycle amplified long DNA chain (RCA-DNA) rich in G-quadruplex sequences. They can combine with hemin as DNAzyme to catalyze 3,3′-5,5′-Tetramethyl benzidine (TMB)-H2O2 system for color development and be cleaved by EcoRV endonuclease to produce DNA fragments with different lengths. The microfluidic chip was employed to separate and quantify the fragments for quantifying S.T and V.P simultaneously. For this protocol, 100 CFU·mL−1 of V.P or S.T could be observed by the naked eye and as low as 32 S.T and 30 CFU·mL−1 V.P could be detected by the chip within 3 min. The dual-mode aptasensor could quickly screen positive samples, and simultaneously perform quantitative detection of the bacteria in positive samples. Our protocol demonstrated its potential in on-site qualification & simultaneous quantification of foodborne bacteria in foods.

With a quartz crystal resonator as the core element, the quartz crystal microbalance (QCM) has been an important sensor for various samples including chemical, biomedical, gas, and liquid with broad applications. The sensing mechanism of QCM is based on the gravimetric effect of samples on vibration frequency of the quartz crystal blank. For accuracy and sensitivity, it is important to have a better estimation of the vibration frequency with the consideration of quartz crystal material, configuration, electrodes, mounting, absorption layer, among other factors. As a result, a thorough study of vibrations of the quartz crystal plate is vital for a good design of the QCM and fabrication processing.

Sensitive and rapid detection of pathogenic bacteria remains important and challenging for food safety and preventing outbreaks of foodborne disease. The major limitations of standard analytical methods for detecting vibrio parahaemolyticus (V.P) lie in their bulky equipment and tedious and long-time operation. This study presents an electrochemical aptasensor for the rapid on-site quantification of V.P in seafood. Magnetic nanoscale metal-organic frameworks (Fe3O4@NMOF) labeled with an aptamer against V.P served as capture probes, while gold nanoparticles combined with phenylboronic acid and ferrocene acted as the nanolabels. When detecting V.P, the sandwich-type complex of capture probe–V.P–nanolabel was formed and magnetically attached to a screen-printed electrode (SPE) for signal measurement. Under optimal conditions, the increase in the ferrocene electrochemical signals could assess the V.P amount; the quantified concentration range was 10–109 cfu/mL. Then, the developed signal-on sensor successfully detected V.P in real seafood samples, exhibiting many advantages. It could not only specifically enrich and rapidly separate the V.P in complex samples but also largely amplify the signal. Moreover, using compact SPE with a detection time of maximum 20 min as the measurement platform allows rapid on-site assays. Thus, the proposed method is a feasible strategy for screening V.P in seafood.

Ion-selective electrodes (ISE) can rapidly, sensitively detect their corresponding ions and are suitable for field testing. However, most ISE methods cannot detect other targets directly which limits their practice application. Herein, we established an aptamer-sensing platform to detect organic small molecule using a portable fluoride-selective electrode (FSE). To achieve the purpose, novel signal tags were fabricated based on nano metal-organic frameworks (NMOF) encapsulating Fˉ and labeling aptamers. They were then immobilized on one stir-bar. Subsequently, a double stir-bars (bar-a and b) assisted target recycling strategy was designed to convert organic small molecular target to Fˉ for signal development and amplification. The movement of tags from bar-a to b can be triggered by the analytes. After reaction, the transferred signal tags in bar-b were washed and released Fˉ which can be measured by FSE for qualification of the target. The assay was evaluated to detect kanamycin or chloramphenicol which was employed as the representatives of organic small molecular with a low detection limit of 0.35 nmol L−1 or 0.46 nmol L−1, respectively. Satisfactory performance was observed in complex sample analysis of kanamycin (milk, fish, urine and serum) with a recovery of 91–108% and an RSD (n = 6)

It is crucial to detect multiple tumor markers (TMs) for cancer diagnosis. In the study, an endonuclease-linked multiplex immunoassay for TMs detection, with alpha-fetoprotein (AFP), carcino-embryonic antigen (CEA), carbohydrate antigen 199 (CA199) as models, was developed using microfluidic chip electrophoresis (MCE) for DNA analysis as platform. Firstly, three endonuclease (EDOs) labels were prepared by labeling secondary antibodies of TMs with EDOs (BamHI, PstI, EcoRI), respectively. Then, the primary antibodies of TMs were co-immobilized on the bottoms of 96-pore plate. Finally, the TMs and labels were simultaneously incubated in the pore to form various sandwich immunocomplexes. The EDOs on them can cut their corresponding DNA substrate strands into half fragments which can be separated and detected by MCE. The signal ratio (Ih/Is) of half fragments (Ih) and substrate (Is) was proportional to logarithm of TMs concentrations from 1 pg mL−1 to 10 ng mL−1 (U mL−1 for CA199) with detection limits of 0.35, 0.3 pg mL−1 for AFP, CEA and 0.36 U mL−1 for CA199. The multiplex immunoassay was successfully employed in human serums. More importantly, based on the signal conversion mode, MCE for DNA analysis can be easily extended to detect many diagnosis markers and has applicable value in clinics.

An ultrasensitive colorimetric aptasensor was developed for antibiotics detection, with chloramphenicol (CAP) as model target, using DNAzyme labeled Fe-MIL-88-Pt as novel peroxidase mimic signal tags and target-triggered circular strand-displacement polymerization (CSDP) for signal amplification. The system consists of two components which can partially hybridize with each other: one is capture probe which was formed through immobilizing hairpin DNA containing aptamer sequence on magnetic beads (MB-cDNA), another is signal tag which was constructed through labeling single strand DNAzyme (G-quadruplex/Hemin) which can partially hybrid with cDNA on platinum nanoparticles functionalized Fe-MIL-88 (MIL-88-Pt-DNAzyme). All components of MIL-88, Pt and DNAzyme in the tag can act as peroxidase mimic to triply catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 into a blue-colored oxidized TMB (oxTMB) for the colorimetric readout. Thus distinctive signal can be observed by naked eye even in presence of 0.02 nM tags. In the presence of target and primer, cDNA loop can open to form cDNA/CAP intermediates, enabling primer to hybridize with the exposed sequences of the cDNA, which initiated target assisted CSDP recycles. Then numerous signal tags were released into supernatant to catalyze TMB for color development. There was a liner relationship between the absorbance and the concentration of CAP in the range of 0.1 pM (0.0323 pg/mL) to 1000 pM (323 pg/mL) with the detection limit of 0.03 pM (0.0097 pg/mL). The ultra-high sensitivity was ascribed to the multiplex catalytic activities from the tags and CSDP based signal amplification. Furthermore, this method can produce signals being observed by naked eye to facilitate in-situ detection and be further extended to detect other antibiotics in food just by simply replacing cDNA on the sensing system.

In the study, a novel two dimensional metal–organic framework (Cu-TCPP nanosheets) based fluorescence resonance energy transfer (FRET) aptasensing platform was developed for detecting antibiotics. Cu-TCPP nanosheets were employed for quenching the background fluorescence and circular strand-replacement DNA polymerization (CSRP) for signal amplification. To fulfill the purpose, we designed an aptamer hairpin probe (HP) whose stem can be opened while specifically binding to target. Then the opened HP would bind with the primer. Under the action of polymerase, extension reaction was induced to generate double-stranded DNA (dsDNA), and then the target was released for the next cycle. Finally, SYBR Green I (SG) can bind with dsDNA to produce strong fluorescence response for quantification of target. It's worth mentioning that the fluorescence of HP/SG complex and free SG could be completely quenched by Cu-TCPP nanosheets while that of dsDNA/SG complex wouldn't be affected. Thus, the sensor produced negligible background signals. It can produce 7.5-fold improved S/N compared to a graphene oxide (GO)-based FRET aptasensor. Chloramphenicol (CAP) was chosen as the model analyte to demonstrate the feasibility of the sensor system. The detection range is broad from 0.001 to 10 ng mL−1 with a detection limit down to 0.3 pg mL−1. The proposed assay was label free and can be used in homogenous detection which greatly simplifies the complexity of operations. The strategy opens a new way to develop sensitive, in-situ and simple assay for antibiotics in foods.

A microchip electrophoresis (MCE) array-based aptasensor for multiplex detection of antibiotics was developed using multi-capture DNA functionalized magnetic beads (AuMPs@captureDNA@assistantDNA) and polymerase chain reaction (PCR) for signal amplification. In this study, kanamycin (KANA) and chloramphenicol (CAP) were employed as model analytes. In the presence of a target, specific binding between the target and corresponding capture DNA (C-DNA) would induce the unwinding of double-strand structures, leading to the release of assistant DNA (A-DNA) into the supernatant after magnetic separation. The released A-DNA was co-amplified by PCR with an internal standard strand (I-DNA). After 20 cycles of PCR, the ratio (IA-DNA/II-DNA) between the above PCR products was proportional to the concentrations of the target with a detection limit of 0.0025 nM and 0.006 nM for KANA and CAP, respectively. Under optimal conditions, the method exhibited high sensitivity and selectivity for the targets, and the average detection time was about 1 min. Moreover, this assay was successfully employed to detect KANA and CAP in milk and fish samples with consistent results to that of enzyme-linked immunosorbent assay, suggesting that it is a promising platform for detecting small molecules in food by changing the corresponding aptamer.

Antibiotic tetracycline (TC) is a sort of main contaminates in water, and of adverse effect on ecosystems and human health. The development of simple and efficient methods for both detection and removal of TC in water is highly desirable but remains challenging. Herein, a dual-functional platform for detection and removal of antibiotic tetracycline (TC) is developed by a highly stable luminescent zirconium-based MOF (PCN-128Y). The detection is based on the efficient luminescence quenching of the PCN-128Y toward TC. Theoretical/experimental studies reveal that the luminescence quenching can be attributed to a combined effect of the strong absorption of TC at the excitation wavelength and the photo-induced electron transfer process from the ligand of PCN-128Y to TC. The strong cheating metal-ligand bonding between Zr6 nodes and TC through solvent-assisted ligand incorporation is suggested to mainly account for the high adsorption capability of PCN-128Y toward TC in water. The preconcentration of TC within the pores of PCN-128Y induced by the adsorption process makes TC contact with the framework more sufficient, thus significantly enhances the efficiency of TC sensing. This work is the first example demonstrating that MOF materials can integrate the functions of detection and removal of antibiotic TC in water, which highlights the opportunity of luminescent MOFs in the application of wastewater treatment.

An ultrasensitive electrochemical aptasensor for multiplex antibiotics detection based on endonuclease and exonuclease assisted dual recycling amplification strategy was proposed. Kanamycin and chloramphenicol were selected as candidates. Firstly, aptamers of the antibiotics were immobilized on bar A and then binding with their endonuclease labeled complementary DNA strands to construct enzyme-cleavage probes. Secondly, The nano zirconium-metal organic framework (NMOF) particles with 1,4-benzene-dicarboxylate (BDC) as linker was defined as UiO-66. And its updated version, hierarchically porous UiO-66 (HP-UIO-66) decorated with different electroactive materials as signal tags were synthesized. Then they were immobilized on bar B linked by two duplex DNA strands which can be specifically cleaved by corresponding enzyme-cleavage probes in bar A. Once targets were introduced into system, aptamers can capture them and then release enzyme-cleavage probes. In the presence of exonuclease-I, exonuclease assisted target recycling amplification was triggered and more enzyme-cleavage probes were released into solution. The probes can trigger endonuclease assisted recycles and repeatedly cleave their corresponding duplex DNA strands on bar B then released numerous signal tags into supernatant. Thus two recycling amplification was performed in the system. Finally, MB and Fc in the signal tags were detected by square wave voltammetry after removing bar A/B and the current intensities were correspondent with the concentration of KANA and CAP respectively. Under the optimum condition, the limits of detection for the KANA and CAP were 35 fM and 21 fM respectively with a wide linear range from 1 × 10−4 to 50 nM. This dual recycling amplification detection system exhibited high sensitivities and specificity. It can be easily extended to detect other targets if changing the corresponding aptamers and has potential application values for screening of multiplex antibiotics residues in food safety.

Recently, it has been crucial to be able to detect and quantify small molecular targets simultaneously in biological samples. Herein, a simple and conventional double-T type microchip electrophoresis (MCE) based platform for the multiplex detection of quality indicator molecule targets in urine, using ampicillin (AMPI), adenosine triphosphate (ATP) and estradiol (E2) as models, was developed. Several programmable hairpin probes (PHPs) were designed for detecting different targets and triggering isothermal polymerase-catalyzed target recycling (IPCTR) for signal amplification. Based on the target-responsive aptamer structure of PHP (Domain I), target recognition can induce PHP conformational transition and produce extension duplex DNA (dsDNA), assisted by primers & Bst polymerase. Afterwards, the target can be displaced to react with another PHP and initiate the next cycle. After several rounds of reaction, the dsDNA can be produced in large amounts by IPCTR. Three targets can be simultaneously converted to dsDNA fragments with different lengths, which can be separated and detected using MCE. Thus, a simple double-T type MCE based platform was successfully built for the homogeneous detection of multiplex targets in one channel. Under optimal conditions, the assay exhibited high throughput (48 samples per hour at most, not including reaction time) and sensitivity to three targets in urine with a detection limit of 1 nM (ATP), 0.05 nM (AMPI) and 0.1 nM (E2) respectively. The multiplex assay was successfully employed for the above three targets in several urine samples and combined the advantages of the high specificity of programmable hairpin probes, the excellent signal amplification of IPCTR, and the high through-put of MCE which can be employed for screening in biochemical analysis.

Dipicolinic acid (DPA) can serve as a convenient biomarker for Bacillus anthracis, which is an extremely hazardous pathogen and can be used as a biological weapon. Herein, we demonstrate a ratiometric luminescent sensor of DPA based on a dual-emissive MOF hybrid, which is developed by encapsulation of Tb3+ cations into an anionic MOF through a cation exchange process. The Tb3+@MOF hybrid well inherits the intrinsic ligand emission of the host framework and the Tb3+ emission. The parent framework can function as a host matrix to sensitize and protect the emission of incorporated Tb3+. The Tb3+ emission within the MOF hybrid is significantly enhanced in the presence of DPA molecules owing to the occurrence of antenna sensitization upon the formation of the Tb–DPA complex, while the ligand emission is insensitive to DPA. This unique ratiometric luminescence response of the Tb3+@MOF hybrid towards DPA can be exploited for sensitive self-calibrated detection of DPA. The Tb3+@MOF sensor shows a fast response rate, high sensitivity and selectivity with a limit of detection of 3.6 nM. Besides, the feasibility of this sensor operating in real samples is demonstrated by the good recovery of DPA in human serum. The present study provides a promising luminescent platform for routine analysis of an anthrax biomarker.

In this work, we demonstrate a double stirring bars-based signal-amplified strategy for the simultaneous electrochemical detection of Vibrio parahaemolyticus (V.P) and Salmonella typhimurium (S.T). Methylene blue (MB) or ferrocene (Fc) labeled functionalized branched-chain DNA hybrid structure (FBCHS) was immobilized on magnetic microspheres and used as encoded signal tags. The encoded signal tags were hybridized with the aptamer-embedded tetrahedral DNA nanostructures (TDNs), which acted as capture probes, on one gold stirring bar (bar-A). The magnetic signal tags on bar-A could capture V.P and S.T, and their complex was later released into the solution. The composites were then digested by exonuclease I that was modified on another gold stirring bar (bar-B). The released free bacteria participated in the next cycle, from bar-A to bar-B, and generated more magnetic tags for signal amplification. After the reaction, the tags were magnetically enriched on a screen-printed carbon electrode (SPCE), generating two distinct voltametric peaks derived from MB and Fc. Their current intensities could reflect the concentration of V.P and S.T in the samples. Under optimal conditions, the double stirring bars-based signal amplification strategy was able to increase the detection sensitivity with a lower detection limit of 4 and 7 CFU/mL for V.P and S.T, respectively, within a detection range of 10–108 CFU/mL. Importantly, the exonuclease I on the stirring bar (bar-B) for signal amplification was able to be reused up to 50 times and avoided its loss if being directly added in solution, which produced cost savings in terms of used enzymes.

A point of care testing (POCT) colorimetric aptasensor was developed to detect streptomycin (STR) using porous SiO 2 micro beads (pore size of 200 nm) −enzyme linked polymer (PowerVision™, PV) probes and exonuclease-assisted target recycling for signal amplification. The probe was fabricated by single- stranded DNA binding protein labelled SiO 2 micro particles (P-SiO 2 -SSB) as capture probes and Au NPs & aptamer (Apt) co-immobilized on PV (Apt-Au-PV) as nanotracer. In the presence of STR and exonuclease I (Exo I), the nanotracer would combine with STR to form the complex (STR/Apt-Au-PV). Hereafter, Exo I further digest the aptamer on STR/Apt-Au-PV, then STR was released again to participate new cycling, the approach lead to generate more nanotracers into supernatant to improve the sensitivity. Moreover, the dendrimer PV which contains large quantities of HRPs can efficiently catalyzed H 2 O 2 -TMB (3,3′,5,5′- tetramethylbenzidine) system for color development and the results can observed by the naked eye. Due to the excellent multiple signal amplification effects for porous SiO 2 micro particles to label more nanotracer, PV and exonuclease-assisted target recycling, the aptasensor exhibit a low detection limit with 1 pg mL −1 (S/N = 3). In addition, the developed method might provide a prospect assay for food tests at point of care.

A mimicking-enzyme-based colorimetric aptasensor was developed for the detection of kanamycin (KANA) in milk using magnetic loop-DNA-NMOF-Pt (m-L-DNA) probes and catalytic hairpin assembly (CHA)-assisted target recycling for signal amplification. The m-L-DNA probes were constructed via hybridization of hairpin DNA H1 (containing aptamer sequence) immobilized magnetic beads (m-H1) and signal DNA (sDNA, partial hybridization with H1) labeled nano Fe-MIL-88NH2-Pt (NMOF-Pt-sDNA). In the presence of KANA and complementary hairpin DNA H2, the m-L-DNA probes decomposed and formed an m-H1/KANA intermediate, which triggered the CHA reaction to form a stable duplex strand (m-H1-H2) while releasing KANA again for recycling. Consequently, numerous NMOF-Pt-sDNA as mimicking enzymes can synergistically catalyze 3,3',5,5'-tetramethylbenzidine (TMB) for color development. The aptasensor exhibited high selectivity and sensitivity for KANA in milk with a detection limit of 0.2 pg mL-1 within 30 min. The assay can be conveniently extended for on-site screening of other antibiotics in foods by simply changing the base sequence of the probes.

The authors describe an ultrasonic-assisted headspace method for solid phase micro-extraction (UA-HS-SPME) of 7 polychlorinated biphenyls (PCBs) with codes PCB28, PCB52, PCB101, PCB118, PCB138, PCB153 and PCB180. The coating is based on a poly-dopamine metal-organic framework [PDA-MIL-53(Fe)] on a stainless steel wire. The coating can be prepared and evenly deposited on the stainless fiber by dipping the PDA fiber into a solution of MIL-53(Fe). The assay is also environmentally friendly because water is used as the solvent. The effects of extraction time, addition of salts, pH value and power of ultrasonic power were optimized. The coating is found to possess a high selectivity and adsorption capacity for PCBs compared to commercial SPME fibers such as the divinylbenzene/carboxen/polydimethylsiloxane fibers. Following desorption, the PCBs were quantified by GC-MS. The detection limits are between 50 and 90 pg⋅g−1 of PCBs in soil. The fibers can be easily prepared, and the batch-to-batch reproducibility (RDS) is

Some harmful aliphatic diamines, e.g., putrescine (Put) and cadaverine (Cad), play important roles in food safety evaluation. In this study, we proposed on-fiber derivatization solid-phase microextraction analysis of non-volatile aliphatic diamines in fish using zeolitic imidazolate framework 8 (ZIF-8) as a solid-phase microextraction (SPME) coating. It was employed to encapsulate isobutyl chloroformate (IBCF, 40 °C, 15 min) for aqueous extraction of Put and Cad. After that, the derivatized aliphatic amines were thermally desorbed in the GC injection port and analyzed by GC-MS. The porous and hydrophobic ZIF-8 with high surface area can increase the IBCF loading amount and prevent it from decomposing, thus increasing the amine extraction effectiveness and sensitivity. In SIM mode and using the molecular ion for quantification, the limits of detection for Put and Cad were 27.1 and 33.2 μg L−1, respectively under the optimal conditions. The fiber-to-fiber reproducibility values (RSDs) for three ZIF-8 coated fibers were less than 11.4% for both Put and Cad. The extraction with the new fiber was reproducible for at least 30 cycles without a noticeable decrease of performance (RSD

The authors describe a microfluidic chip-based aptasensor platform combined with magnetic tripartite DNA structure-functionalized nanocomposites to achieve simultaneous determination of kanamycin (KANA), aflatoxin M1 (AFM1), and 17β-estradiol (E2) in milk. The two-duplex tripartite DNA nanostructure was first assembled on the surface of magnetic beads. When the aptamer on the probes recognized the specific target, the aptamer-target would be released into the supernatant. The pre-primer@circular DNA template structure initiates rolling circle amplification (RCA) by phi29 polymerase. After magnetic separation, the magnetic nanocomposites were added into a solution containing three different lengths of complementary strands to the RCA products. The number of complementary strands significantly decrease, and this can be quantitated by the microfluidic chip. Further, the employment of magnetic nanocomposites and microfluidic chip not only resolve the complex matrix interference, but also dramatically enhances the determination selectivity and sensitivity. This aptasensor allows for determination of KANA, AFM1, and E2 with limits of detection as low as 0.32 pg mL−1, 0.95 pg mL−1, and 6.8 pg mL−1, respectively. This novel method exhibits the advantages of excellent stability and fast response time (

Multicolor fluorescence probes can show fluorescence of different colors when detecting different targets, and the excellent feature can create a highly differentiated multicolor sensing platform. However, most of the previously reported multicolor luminescent materials usually suffer from high toxicity and photobleaching, complex preparation procedures, and poor water solubility, which may not be conducive to bioanalytical applications. Two-dimensional metal organic frameworks (2D MOFs), which have large specific surface areas with long-range fluorescence quenching coupled with biomolecular recognition events, have encouraged innovation in biomolecular probing. Here, we propose a 2D-MOF-based multicolor fluorescent aptamer nanoprobe using a double stirring bar assisted target replacement system for enzyme-free signal amplification. It utilizes the interaction between 2D MOFs and DNA molecules to detect multiple antibiotics quickly, sensitively, and selectively. Since 2D MOFs have excellent quenching efficiency for luminescence of fluorescent-dye-labeled single-strand DNA (ssDNA), the background fluorescence can be largely reduced and the signal-to-noise ratio can be improved. When the adsorbed ssDNA formed double helix double-stranded DNA with its complementary ssDNA, its fluorescence can be almost fully recovered. The assay was tested by detecting chloramphenicol (CAP), oxytocin (OTC), and kanamycin (KANA) in biological samples. The developed aptasensor was sufficiently sensitive to detect the antibiotic residues as low as 1.5 pM CAP, 2.4 pM OTC, and 1 pM KANA (S/N = 3). It has been preliminarily used for multicolor imaging of three different antibiotics in fish tissue slices with satisfactory results.

It is challenging to greatly increase of the extraction selectivity and efficiency by stir bar sorptive extraction of ultra-trace polychlorinated biphenyls (PCBs) in complex environmental matrix, e.g., soils. To fulfill this purpose, one of the critical works is to prepare some coatings with high selectivity, adsorptive capacity and reusability. It is also important to develop some green, simple methods for preperation the coatings. In this work, a kind of highly efficient and bioactive coating based on hyperbranched aptamer (HB-Apt) was constructed via hybridization chain reaction (HCR). Then, the HB-Apt was coated on a magnetic stir bar and applied to headspace extraction of PCB72 and PCB106 in soils. The core-shell gold magnetic particles (Fe3O4@AuNPs, AuMNPs for short) was employed as the substrate to immobilize the HB-Apt. The extracted PCBs on the stir bar could be easily eluted in ethanol by stirring, and then sampled in gas chromatography-mass spectrometry (GC-MS) for qualification. The ultra-low detection limit (0.003–0.005 ng•g−1), good linearity (0.01–500 ng•g−1, R2≥0.994) and reproducibility (RSD: 4.58–6.53%) were obtained. Compared with the common aptamer coating, the HB-Apt coating exhibited good selectivity and higher extraction capacity. The results might be related to the fact that there are more aptamer fragments grated on the HB-Apt coating than those of the common aptamer coating. The magnetic stir bar can not only be employed for easy headspace extraction, but also facilitate separation and elution. Moreover, the coating could be recycled for at least 60 times before recoveries of the PCB72 and PCB106 in the spiked samples drop below 90%. All these indicated that the assay is simple, robust, environment friendly and promising for detection of trace PCBs in complex environmental samples.

An aptamer based assay is presented that is making use of a catalytic hybrid assembly and a microfluidic chip electrophoresis format. It enables simultaneous determination of the biomarkers (BMs) α-fetoprotein (AFP), carbohydrate antigen 125 (CA125), and carcinoembryonic antigen (CEA). The respective aptamers were covalently bound to Fe3O4@AuNPs (AuMPs) magnetic beads and then used to capture the biomarkers on their surface. Different single-stranded DNA primers were then labeled with various antibodies as encoding and signaling tags. The signal tags reacted with AuMPs-BMs to form different antibody-BM-aptamer complexes. After magnetic separation, three pairs of hairpins as substrates were introduced to trigger catalytic hybrid assembly by the primers in the complex. This will form many duplex DNA products of different length in the supernatant. The products can be magnetically separated by microfluidic chip electrophoresis and determined by fluorometry at excitation/emission wavelengths of 495/525 nm. Several experimental conditions including the hairpin concentration, reaction time and temperature were systemically optimized. The method can simultaneously quantify AFP, CEA and CA125, respectively, with detection limits of 0.1, 0.2, 0.15 pg mL−1 (at S/N = 3). The aptamer functionalized magnetic beads can be reused for at least 20 times with a recovery of up to 80% after heat treatment. The method was employed to simultaneously detect the three BMs in serum samples.

An antibody free and signal-on type electrochemiluminescence(ECL) sensor was developed for diethylstilbestrol (DES) detection using magnetic surface magnetic molecular imprinting polymers (MMIPs) - aptamer labeled CdS quantum dots (CdS QDs) conjugated probes. Firstly, the MMIPs were synthesized through employing 4″-hydroxypropiophenone as mimicking template to form imprint sites on the poly-dopamine coating covering core-shell Fe3O4@SiO2 (MMIPs). Secondly, the aptamer which epitope is phenol group of 17β-estradiol (E2), was chosen to label on CdS QDs to form CdS-Apt signal tag and recognize phenol group of DES. When the target, MMIPs and CdS-Apt was incubated together, a sandwich MMIPs-DES-CdS-Apt composite was constructed. It was then adsorbed on the interface of a screen printed carbon electrode (SPCE) by external magnetic field, then emit electrochemical luminescence signal at potential − 1.1 V. The signal intensity was in proportion to the logarithm of DES' concentration from 0.3 to 1.0 × 105 pg ml− 1, with the detection limit (LOD) of 0.1 pg ml− 1 (S/N = 3). Several fish samples were tested by the sensor which showed high selectivity and good recoveries between 80% and 120% with consistent results as that of conventional ELISA. Since there have been no reports of aptamer for DES, we use E2 aptamer to recognize phenol epitope of DES, then MMIPs towards another epitope to form a sandwich complex. Thus a signal-on and sandwich sensor was fabricated. Moreover, no expensive antibody was employed for fabricating the sensor. Its selectivity and sensitivity were higher than the same type of sensor based on sole aptamer or MIPs probe. The assay can be explored to detect other analytes while changing the corresponding aptamer and imprinting template.

This study aimed to simultaneously determine three β2-agonists (clenbuterol, salbutamol, and ractopamine) in pork samples using novel stir bar array sorptive extraction coupled with gas chromatography–mass spectrometry. Pencil refill was employed as the substrate of stir, which was covered with carboxyl graphene sheets and polyluminol coating. The coating was simply prepared by electrochemical deposition of luminol at a voltage of 0–0.6 V. Then, an automatic device with the stir bar array for extraction was used. The conditions for the extraction were optimized. Under the optimum extraction conditions, with toluene as the extraction solvent, the extraction and desorption times were 20 min. A good linearity of three β2-agonists was obtained in the range of 0.5–100 ng g−1 by gas chromatography–mass spectrometry detection. The recovery of clenbuterol, salbutamol, and ractopamine in spiked pork samples ranged from 88.7 to 93.2%, 85.5–94.2%, and 85.7–93.9%, respectively, with the relative standard deviations less than 10%. The detection limits were in the range of 0.022–0.091 ng g−1 for pork samples. The extraction coating with high extraction capacity was simply fabricated by the electrochemical method, which could simplify the pretreatment procedures. Moreover, the array could extract several samples simultaneously and improve the pretreatment efficiency.

Herein, a promising colorimetric strategy for small molecule detection was developed based on one novel magnetic single-stranded DNA binding protein (SSB)-linked composite probe. Firstly, a magnetic probe was synthesized by labeling SSB on gold magnetic particles (Au MNPs-SSB) and detection probe by co-immobilizing aptamer (Apt) and horseradish peroxidase (HRP) on the core-shell SiO 2 @Au nanoparticles (Apt-SiO 2 @Au-HRP); furthermore, Au MNPs-SSB was bound with Apt-SiO 2 @Au-HRP to construct a composite probe relied on the specific affinity between SSB and free aptamer. When the target, with chloramphenicol (CAP) as model, was introduced into the reaction system, the formation of the target-Apt-SiO 2 @Au-HRP complex can release from its parent probe to supernatant after magnetic separation because SSB can’t bind target-aptamer complex. The target-Apt-SiO 2 @Au-HRP complex in supernatant could efficiently catalyze 3,3′,5,5′-tetramethylbenzidine(TMB)-H 2 O 2 system for the color development. Under the optimized reaction conditions, the linear range was from 0.05 to100 ng mL −1 with a low detection limit of 0.02 ng mL −1 for CAP. Moreover, the aptamer assay was employed to detect CAP in milk and the results were consistence with those from ELISA. In addition, the assay can be easily extended to other small molecules detection when changing the corresponding aptamer on the detection probe.

A novel fluorescent “signal-on” switch aptasensor based on a single stranded DNA binding protein (SSB) labeled quantum and exonuclease-assisted target recycling was designed for detecting antibiotics in homogeneous media. In this assay, streptomycin (STR) was employed as a model and the fluorescent probe was synthesized by labeling SSB on quantum dots (QDs–SSB). The SSB can specifically bind an aptamer. When an aptamer serving as a bridging ligand is added, it can hybrid with SSB. Meanwhile, the quantum dots dispersed in the solution were aggregated, which resulted in self-quenching of the QDs' fluorescence and its intensity decreased sharply and switched from “on” to “off”. When the fluorescent probe coexisted with STR and Exo I, the aptamer preferentially bound with a target, and the aptamer-target was digested into mononucleotides by Exo I. Then the liberated target could be further involved in the reaction cycling to produce a strong fluorescence signal. Consequently, the distance of QDs increased and the fluorescence intensity was recovered. Thus, the switch changed from the “off” state to “on”. Under optimized conditions, the assay indicates good linear relationship in a range from 0.1 to 100 ng mL−1 and the detection limit of STR was 0.03 ng mL−1 (S/N = 3). And after 8 times of detecting streptomycin, the fluorescence intensity of the system was still able to reach the initial 90.19% efficiency. In addition, this type of switch fluorescent probe provides a simple and specific approach for antibiotics detection especially suitable for a homogeneous system.

In this study, a novel three dimensional (3D) M × N type aptamer-functionalized solid-phase micro extraction (SPME) fibers array (M represents the number of targets; N represents the number of samples) was developed for selective enrichment of multiplex antibiotic residues from milk samples, with three chloramphenicols (CAPs) as models. First, gold nanoparticles (AuNPs) were electrodeposited on a gold wire (Φ = 0.2 mm), which was wound around a conductive indium tin oxide (ITO) glassy fiber. Then, the fiber was immersed into thiol-functionalized aptamer solution, which could specifically recognize three CAPs, including chloramphenicol (CAP), thiamphenicol (TAP) and florfenicol (FF). The aptamer can be covalently immobilized on AuNPs through Au–S bonds. Thus, a 3D aptamer-functionalized fiber interface (3D-Apt@AuNPs@Au wire–ITO) was built and employed for specifically sorptive extraction of CAPs from the milk samples with a matrix complex based on the high affinity of the aptamer for the targets. The extraction capacities for CAP, TAP and FF were 887, 840 and 801 ng per fiber, respectively. The enrichment folds were more than 500 times, which is 3.1 folds higher than that of the 2D-Apt@AuNPs–ITO fiber and 6.6 folds higher than that of the 1D-Apt@Au wire–ITO fiber. Afterwards, several similar fibers were assembled together into an array for simultaneous enrichment of three CAPs from 12 samples in one run. Finally, the adsorbed targets were washed away using a pH 8.5 0.1 M Tris–HCl buffer and then detected by high performance liquid chromatography (HPLC)-Diode Array Detector (DAD). The parameters, including extraction temperature, shuttle rates, extraction and desorption pH, and extraction and desorption time, were investigated and discussed. Under the optimized conditions, the limits of detection (LOD) and quantitation (LOQ) were determined as 0.262–0.293 and 0.864–0.967 ng mL−1, respectively, for several CAPs. The fibers array can be applied in replicate batch-extraction for at least 60 extraction cycles with a recovery of over 80%. The SPME fibers assay coupled with HPLC detection possessed advantages of high-throughput, high selectivity and adsorption capacity in one run. Furthermore, the process is environmentally friendly without using organic solutions during the entire extraction process. Thus, the method is a universal platform that can be extended to the selective extraction of other organic pollutant residues if the modified aptamers are changed.

Immunoaffinity procedure was developed for isolation of low density lipoprotein (LDL) from biological samples by using silica-derived immunoaffinity sorbent. Sorbent was prepared by immobilization of monoclonal anti-apoB-100 antibody onto macroporous silica particles, using carefully optimized binding chemistry. Binding capacity of the sorbent towards LDL was determined by batch extraction experiments with solutions of isolated LDL in phosphate-buffered saline, and found to be 8 mg LDL/g. The bound LDL fraction was readily released from the sorbent by elution with ammonia at pH 11.2. The total time needed for isolation procedure was less than 1 h, with LDL recoveries being essentially quantitative for samples containing less than 0.3 mg LDL/mL. With higher concentrations, recoveries were less favorable, most probably due to irreversible adsorption caused by LDL aggreggation. However, reusability studies with isolated LDL at concentration 0.2 mg/mL indicate that the developed immunoaffinity material may be used for multiple binding-release cycles, with minor losses in binding capacity. Finally, the sorbent was successfully applied to isolation of LDL from diluted plasma. Apart from its practical implications for LDL isolation, this study provides crucial insights into issues associated with LDL-sorbent interactions, and may be useful in future efforts directed to development of lipoprotein isolation approaches.

An ultrasensitive electrochemical aptasensor for simultaneous detection of oxytetracycline (OTC) and kanamycin (KAN) has been developed based on metal ions doped metal organic frame materials (MOFs) as signal tracers and RecJf exonuclease-catalyzed targets recycling amplification. The aptasensor consists of capture beads (the anti-single-stranded DNA Antibody, as anti-ssDNA Ab, labeled on Dynabeads) and nanoscale MOF (NMOF) based signal tracers (simplified as Apts-MNM, the NMOF labeled with metal ions and the aptamers). Particularly, the MOF (UiO-66-NH2), with large internal surface areas, ultrahigh porosity and abundant amine groups in the pores, was employed as substrates to carry plenty of metal ions (Pb2+ or Cd2+) and label aptamers of OTC or KAN. Thus, the aptasensor is formed by the specific recognition between anti-ssDNA Ab and aptamers. In the presence of targets (OTC and KAN), aptamers prefer to form targets-Apts-MNM complexes in lieu of anti-ssDNA Ab-aptamer complexes, which results in the dissociation of Apts-MNM from capture beads. With the employment of RecJf exonuclease, targets-Apts-MNM in supernatant was digested into mononucleotides and liberated the target, which can further participate in the next reaction cycling to produce more signal tracers. After magnetic separation, the enhanced square wave voltammetry (SWV) signals were produced from signal tracers. The aptasensor exhibited a linear correlation in the range from 0.5 pM to 50 nM, with detection limits of 0.18 pM and 0.15 pM (S/N=3) toward OTC and KAN respectively. This strategy provides specificity and sensitive approach for multiplex antibiotics detection and has promising applications in food analysis.

In this work, a facile and environmentally friendly solid-phase microextraction assay based on on-fiber derivatization coupled with gas chromatography and mass spectrometry was developed for determining four nonvolatile index biogenic amines (putrescine, cadaverine, histamine and tyramine) in fish samples. In the assay, the fiber was firstly dipped into a solution with isobutyl chloroformate as derivatization reagent and isooctane as extraction solvent. Thus, a thin organic liquid membrane coating was developed. Then the modified fiber was immersed into sample solution to extract four important bio-amines. Afterwards, the fiber was directly inserted into gas chromatography injection port for thermal desorption. 1,7-Diaminoheptane was employed as internal standard reagent for quantification of the targets. The limits of detection of the method were 2.98–45.3 μg kg−1. The proposed method was successfully applied to the detection of bio-amines in several fish samples with recoveries ranging 78.9–110%. The organic reagent used for extraction was as few as micro liter which can greatly reduce the harm to manipulator and environment. Moreover the extraction procedures were very simple without concentration and elution procedures which can greatly simplify the pretreatment process. The assay can be extended to the in situ screening of other pollutant in food safety by changing the derivatization reagent. This article is protected by copyright. All rights reserved

A quick and specific pretreatment method based on a series of extraction clean-up disks, consisting of molecularly imprinted polymer monoliths and C18 adsorbent, was developed for the specific enrichment of salbutamol and clenbuterol residues in food. The molecularly imprinted monolithic polymer disk was synthesized using salbutamol as a template through a one-step synthesis process. It can simultaneously and specifically recognize salbutamol and clenbuterol. The monolithic polymer disk and series of C18 disks were assembled with a syringe to form a set of tailor-made devices for the extraction of target molecules. In a single run, salbutamol and clenbuterol can be specifically extracted, cleaned, and eluted by methanol/acetic acid/H2 O. The target molecules, after a silylation derivatization reaction were detected by gas chromatography-mass spectrometry. The parameters including solvent desorption, sample pH, and the cycles of reloading were investigated and discussed. Under the optimized extraction and clean-up conditions, the limits of detection and quantitation were determined as 0.018-0.022 and 0.042-0.049 ng/g for salbutamol and clenbuterol, respectively. The assay described was convenient, rapid, and specific; thereby potentially efficient in the high-throughput analysis of β2 -agonists residues in real food samples.

This work has firstly constructed purely Lewis acidic sites on MCM-41 successfully, for which Zr-MCM-41 catalysts with different Zr contents are prepared through the hydrolysis of ZrOCl 2 on MCM-41, followed by calcination. Thus-prepared materials possess typical hexagonal mesostructures, irregular morphologies, large surface areas, and large pore sizes, as revealed by XRD, SEM, TEM, N 2 adsorption, and DRIFT FTIR. UV–vis, Raman and XPS spectra prove the formation of isolated species in high dispersion on the surface of MCM-41. NH 3 -TPD analysis shows that the acid intensity of the catalysts is proportional to the content of Zr, and the acidity of Zr-MCM-41 with the Zr content of

In this work, a novel homogeneous and signal “off–on” aptamer based fluorescence assay was successfully developed to detect chloramphenicol (CAP) residues in food based on the fluorescence resonance energy transfer (FRET). The vesicle nanotracer was prepared through labeling single stranded DNA binding protein (SSB) on limposome-CdSe/ZnS quantum dot (SSB/L-QD) complexes. It was worth mentioning that the signal tracer (SSB/L-QD) with vesicle shape, which was fabricated being encapsulated with a number of quantum dots and SSB. The nanotracer has excellent signal amplification effects. The vesicle composite probe was formed by combining aptamer labeled nano-gold (Au-Apt) and SSB/L-QD. Which based on SSB's specific affinity towards aptamer. This probe can't emit fluoresce which is in “off” state because the signal from SSB/L-QD as donor can be quenched by the Au-aptas acceptor. When CAP was added in the composite probe solution, the aptamer on the Au-Apt can be preferentially bounded with CAP then release from the composite probe, which can turn the “off” signal of SSB/L-QD tracer into “on” state. The assay indicates excellent linear response to CAP from 0.001 nM to 10 nM and detection limit down to 0.3 pM. The vesicle probes with size of 88 nm have strong signal amplification. Because a larger number of QDs can be labeled inside the double phosphorus lipid membrane. Besides, it was employed to detect CAP residues in the milk samples with results being agreed well with those from ELISA, verifying its accuracy and reliability.

A novel ratiometric electrochemiluminescent (R-ECL) aptasensor array was fabricated on a homemade screen-printed carbon electrode (SPCE) for antibiotic chloramphenicol (CAP) based on the ratio of working signal to internal reference signal. The SPCE substrate consists of a common Ag/AgCl reference electrode, carbon counter electrode and two spatial-resolved carbon working electrodes (WE1 and WE2). In the system, luminol-gold nanoparticles (L-Au NPs) as working signal tags were modified on WE1, and CdS quantum dots (QDs) were modified on WE2 as internal reference to provide a correction for avoiding the environmental effects. The L-Au NPs at WE1 were functionalized with a CAP aptamer′s DNA complementary (DNA1) and then CAP aptamer (DNA2) that was tagged with chlorogenic acid (CA) as quenchers of L-Au NPs. Upon CAP adding to WE1, the DNA2-CAP complexes were formed due to the highly affinity of CAP towards DNA2. Meanwhile, it could release the CA, which recovered the ECL of L-Au NPs. This ratio of ECL signals for quantification between target probes (at WE1) to internal standard probes (at WE2) could reduce the matrix environmental interference to a certain degree. Moreover, the two probes immobilized on two working electrodes while not one electrode, could also reduce cross-talk interference between each other. Such R-ECL approach offers a selective and sensitive platform and shows a great utility for detection of CAP in the food analysis.

It was extremely urgent to develop some simultaneous and sensitive biosensors for detecting multiplex serum tumor markers (TMs) for early screening of cancers. Herein, a multiplex assay was developed based on the DNA-LaMnO3 (DNA-LMO) perovskite encoded probes and targets mediated competitive replacement strategy. Alpha fetoprotein (AFP), carcinoembryonic antigen (CEA) and prostate specific antigen (PSA) markers were employed as representative target TMs. Aptasensor is prepared by a series of DNA-LMO-M encode probes which were prepared by three hyperbranched DNA firstly immobilized on LMO encapsulating Pb, Cd or Cu ions. Then, three TMs aptamers were labeled on the stirring-rod and hybridized with the probes. After the developed encoded probes was incubated the TMs, the encoded probes corresponding to different TMs can be released into the supernatant through the competitive replacement. The inner metal ion can be simultaneously detected by square wave voltammetry corresponding to various TMs. Since the stirring rod can enrich many encoded probes containing a lot of metal ions, multiplex signal amplification can be realized. Due to the enrichment and easy separation of the stirring rod, the signal-to-noise ratio was also obviously improved and thus to results in good sensitivity and accuracy. Moreover, it took only 20 min to detect three targets which much faster than many same types of aptasensor. Under the optimal conditions, the low detection limit for CEA (3.6 × 10-4 ng/mL), AFP (3.4 × 10-4 ng/mL) and PSA (2.8 × 10-4 ng/mL) were obtained. Therefore, this method is likely to be used for early and sensitive screening of tumors.

The feature of external shape in tea is a vital quality index that determines the rank quality of tea. The potential of a lab-made computer vision system (CVS) coupled with morphological features and chemometric tools is investigated for evaluating Congou black tea quality. First, Raw images of 700 tea samples from seven different quality grades are acquired using the CVS. The original images collected are processed by graying, binarization, and median de-noising. Then, six morphological parameters (viz. width, length, area, perimeter, length-width ratio, and rectangularity) from the samples are extracted by the shape segmentation of each tea leaf image, and the corresponding feature histogram is obtained. Finally, support vector machine (SVM) and least squares-support vector machine (LS-SVM) are utilized to build identification models based on the histogram distribution characteristic vectors. Three kernel methods (linear kernel, polynomial kernel, and radial basis function kernel) are compared for monitoring tea quality. The results show that the optimal LS-SVM model has a 12% higher correct discrimination rate (CDR) than the SVM model. The polynomial kernel LS-SVM model yields satisfactory classification results with the CDR of 100% based on selected six shape features in the calibration and prediction sets. This work demonstrates that it is feasible to discriminate Congou black tea quality using CVS technology along with morphological features and nonlinear chemometric methods. A new perspective on the sizes of morphological characteristics is proposed as an identifier of Congou black tea quality.

Robust, rapid, and specific assays for point-of-care testing of plasma low-density lipoprotein (LDL) are needed for the early diagnosis of cardiovascular diseases (CVD). While immuno-sensors have been widely used for this purpose, they suffer from high costs and difficult sample preparation. Here, we designed a magnetically controllable sandwich-type aptasensor to detect LDL based on disposable screen-printed electrodes (SPE). First, Fe3O4@SiO2 was employed to rapidly capture and separate LDL in plasma. An aptamer (Apt) and ferrocene (Fc) co-immobilized UiO-66 metal–organic framework was used as a signal tag (MOF-Fc@Apt) and was conjugated with the LDL on Fe3O4@SiO2. The sandwich complex can be magnetically adsorbed on SPE for signal generation. At optimum conditions, the material could detect LDL in plasma with a linear range of 1.0 ng·mL−1–100 μg·mL−1 and low detection (LOD) limit of 0.3 ng·mL−1 (S/N = 3). The system exhibited many distinctive advantages: First, Fe3O4@SiO2 replaced expensive immunosorbent to capture and isolate LDL from complex plasma samples with acceptable selectivity. The MOF-based signal tags could encapsulate a large amount of Fc and Apt to increase the detection selectivity and sensitivity. Second, the LDL sandwich complex conjugated with the composite probes could be easily adsorbed on the SPE for signal development by the magnet and washed away after removing the magnet. Thus, the measurement platform is reusable. Third, the entire detection process was as quick as 20 min, and the sample volume was only 0.1 mL. These features made the assay a good candidate for point-of-care testing of LDL for early diagnosis of CVD.

Aiming at obtaining new copper complexes with good cytotoxicity against cancer cells, triphenylphosphine (TPP) was introduced to obtain insight into the influence of the co-ligands. In this paper, two copper complexes, Cu(2-pbmq)(CH3OH)Br2 (1) and [Cu(2-pbmq)(TPP)Br]2 (2) were designed, synthesized, and characterized by X-ray crystallography, 2-((2-(pyrazin-2-yl)-1H-benzo[d]imidazol-1-yl)methyl))quinolone (2-pbmq), to investigate the influence of the TPP group on the anticancer activity of the metal complex. Although the presence of the TPP group diminished the intensity of the interaction properties of the complex with DNA, the in vitro anticancer activity and cellular uptake of the TPP-containing complex were markedly superior to those of its TPP-lacking counterpart. Detailed studies on the more potently cytotoxic complex 2 revealed that it accumulated in nucleus, arrested the cell cycle at the G0-G1 phase, causing mitochondrial dysfunction, involving the potential simultaneous mitochondrial membrane collapse, cellular ATP level depletion, and Ca2+ leakage, eventually inducing cell apoptosis. In summary, the introduction of a TPP group enhances the biological activity and cytotoxicity of the complex.

Zwitterionic super-hydrophilic polymers showed fascinating prospects because of their excellent biocompatibility, and antifouling characteristics. However, their commercial development and the application in different fields were limited by their tedious preparation process, unsatisfactory reproducibility and performance. In this study, a rapid fabrication approach based on a sole-monomer system (2-(methacryloyloxy)ethyl-[N-(2-methacryloyloxy)ethyl]phosphorylcholine (MMPC) was simultaneously employed as monomer and crosslinker) was proposed for preparing the cell membrane biomimetic polymers within only 1 h, which is significantly faster than the conventional multi-monomers based approach (~12 h). Furthermore, the proposed strategy turns out to be very simple, time saving and reproducible. The super-hydrophilicity, excellent separation efficiency, biocompatibility and antifouling ability were also achieved on the resulting biomimetic polymers. It is worth noting that the versatile biomimetic polymers exhibited excellent enrichment capacity for N-glycopeptides or C-reactive protein (CRP) from complex biological matrices as well as great separation performance for small bioactive molecules although the PC analogous moiety is located in the middle of the MMPC molecule. In particular, a quite similar binding mode exists between the MMPC dimer and the natural PC ligands to CRP. Therefore, the sole-monomer system can not only simplify the preparation process and improve the reproducibility of the zwitterionic materials, but also combine the advantages of the biomimetic cell membrane surface and the zwitterionic super-hydrophilic polymers for the separation of biomolecules in complex biological fluids.

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.

The development of simple, rapid-response sensors for water detection in organic solvents is highly desirable in the chemical industry. Here we demonstrate a unique luminescence water sensor based on a dual-emitting europium-organic framework (Eu-MOF), which is assembled from a purposely selected 2-aminoterephthalic acid ligand with responsive fluorescence inherent in its intramolecular charge transfer (ICT) process. This ICT process can be rapidly switched-on in the presence of water owing to its ability to boost and stabilize the ICT state. In contrast, the Eu3+ emission within the framework is insensitive to water and can serve as a reference, thus enabling highly sensitive water detection in a turn-on and ratiometric way. In addition, the significant ratiometric luminescence response induced by water makes Eu-MOF undergo a distinct change of emitting color from red to blue, which is favorable for visual analysis with the naked eye. Sensitive determination of water content (0.05-10% v/v) in various organic solvents is achieved in multiple readouts including ratiometric emission intensity, emission color, or the Commission Internationale de l'Eclairage (CIE) chromaticity coordinate. The present Eu-MOF sensor featuring high sensitivity and reusability, self-calibration, simple fabrication and operation, and capability for real-time and in situ detection is expected to have practical applications in water analysis for industrial processes.

A simple and highly sensitive fluorometric method is described for the determination of the antibiotic kanamycin (Kana) in food. Dual signal amplification is accomplished by making use of double Y-shaped aptamer DNA probes acting as a capture probes and signal amplification probes. The DNA probes were immobilized on a gold bar and on a magnetic bar, respectively. On addition of Kana, the Y-shaped aptamer probe captures Kana and then is disassembled to release two single-stranded DNAs. These trigger target recycling and HCR between the two bars simultaneously. As a result, many long duplex DNA chains are formed in the supernatant. After pulling out the bars and adding the fluorescent intercalating probe SYBR Green I, strong fluorescence (with excitation/emission peaks at 497/525 nm) is induced. The use of such double Y-shaped DNA probes obviously overcomes the unspecific signal amplification by HCR which increases selectivity and sensitivity. This is due to the fact that the hairpin of HCR is separated in being present in different arms of the Y-shaped probe. Under the optimal conditions, the assay has a limit of 0.45 pg·mL−1 for Kana. It was applied to analyze spiked milk, fish and pork samples.

Microchip electrophoresis (MCE) was a good available method for high-throughput and rapid detecting chemical pollutants in food samples. However, many of the reported MCE assays involve complex design of microchip, laborious operation and poor universality which limited its promotion in multiple antibiotics’ detection. Herein, a multiplexed aptasensor was developed based on a universal double-T type microchip to one-step and simultaneously detect several antibiotics within 3 min using chloramphenicol (CAP) and kanamycin (Kana) as representatives. Besides, a novel stir-bar assisted DNA multi-arm junctions recycling (MAJR) strategy was designed for transducing and amplifying the signal. The brief detection mechanism was as following: the added CAP and Kana can specifically react with their aptamer probes on the stir-bar and produce different single-stranded DNA primer, respectively. Afterwards, the primers can trigger MAJR to form a lot of three- and four-arm DNA junctions corresponding to different targets. The DNA multi-arm junctions can be easily separated and detected by MCE for quantification. Moreover, the stir-bar can facilitate phase separation and obviously eliminate matrix interference in food. The assay was successfully applied in milk and fish samples, showing excellent selectivity and sensitivity with a detection limits of 0.52 pg mL−1 CAP and 0.41 pg mL−1 Kana (S/N = 3). Thus, the assay holds a great potential application for screening of antibiotics in food.

Selective capturing and purification of C-reactive protein (CRP) from complex biological fluids plays a pivotal role in studying biological activities of CRP in various diseases. However, obvious nonspecific adsorption of proteins was observed on current affinity sorbents, and thus additional purification steps are often required, which could compromise the recovery of the target protein and/or introduce new impurities. In this study, inspired by the highly specific interaction between CRP and the cell membrane, an excellent anti-biofouling compound 2-(methacryloyloxy)ethyl phosphorylcholine and a highly hydrophilic crosslinker N, N'-methylenebisacrylamide were employed to fabricate a novel cell membrane biomimetic polymer for selective capture of CRP in the presence of calcium ions. Based on the polymer described above, a facile enrichment approach was established after systematic optimization of the washing and elution conditions. With its favorable properties, such as good porosity, weak electrostatic interaction, high hydrophilicity, and biocompatibility, the novel biomimetic polymer exhibits good specificity, selectivity, recovery (near 100%), purity (95%), and a lower nonspecific protein adsorption for CRP in comparison with commercial immobilized p-aminophenyl phosphoryl choline gel and other purification materials. Furthermore, the structural integrity and functionality of CRP in the elution fraction were well preserved and confirmed by circular dichroism spectroscopy, fluorescence spectroscopy, and immunoturbidimetric assay. Finally, the biomimetic polymer was successfully applied to the selective enrichment of CRP from sera of patients with inflammation and rats. The proposed novel enrichment approach based on the versatile biomimetic polymer can be used for effective CRP purification, which will benefit the in-depth study of its biological roles.