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A method is described to achieve accurate quantitative detection of atrazine (ATZ) in maize by using lateral flow strips based on gold nanoparticles (GNPs) and a handheld scanning reader. GNPs of 15 nm in diameter were applied as label, and a lateral flow immune assay strip was prepared. The linear range was 5.01-95.86 ng mL

We have established an assay that relies on aptamer and isothermal amplification for the tetrodotoxin (TTX)detection. The method uses triple cycle amplification (strand displacement amplification combined with catalytic hairpin assembly) and fluorescent reporter as an output signal. Free TTX and cDNA compete for binding to aptamer-modified magnetic beads. The cDNA collected by magnetic separation then used as a primer to trigger triple cycle amplification to obtain more ssDNA. The ssDNA combined with the reporter probe, and the original quenched fluorescence can be recovered. In addition, a linear relationship between fluorescence spectrum and different target concentrations is revealed. This method allows TTX to be detected by fluorometry with a detection limit as low as 0.265 pg mL−1. It was applied to clams and shellfish, achieving recoveries ranging from 100% to 107.33% and 99.67%–116.67%, respectively. The results were consistent with the commercial TTX ELISA kit. This assay is highly sensitive, reliable and has a good specificity. Therefore, it provides a better alternative to the standard method for quantitative detection of TTX.

Environmental endocrine disruptors in the environment and food, especially 17 β-estradiol (E2), are important factors affecting the growth and development of organisms. In this research, we constructed a fluorescence strategy for two-step amplification that combined two currently popular methods, exponential amplification reaction (EXPAR) and hybridization chain reaction (HCR). E2 competed with the complementary DNA (cDNA) to bind the aptamer modified on the magnetic beads. The free complementary strand in the supernatant was used as a trigger sequence to activate EXPAR, producing a large amount of short single-stranded DNA (ssDNA). The amplified ssDNA can trigger the second HCR amplification, producing many long double-stranded DNA (dsDNA) analogues. According to the principle of fluorescence resonance energy transfer, the carboxyfluorescein (FAM) signals in H1 and H2 hairpins were quenched by black hole quencher (BHQ-1). After the addition of E2 and initiation of amplification, the initially quenched fluorescent signal would be restored. This strategy with a detection limit of 0.37 pg mL−1 (S/N = 3) showed a good linear relationship in the range of 0.4–800 pg mL−1. In addition, the recovery rates of the method for milk and water samples were 98.55%–116.95% and 92.32%–107.00%, respectively. This is the first report of the combined detection of EXPAR and HCR, providing a reference for rapid and highly sensitive detection using multiple isothermal amplification methods.

Escherichia coli O157:H7 has been reported as an important pathogenic bacteria causing serious infection and economic loss. However, detection of Escherichia coli O157:H7 needs improvement, given its current complexity and sensitivity. Herein, we attempt to build a fluorescence sensing method to detect Escherichia coli O157:H7 with easy operation and high efficiency. The target virulence gene sequences are recognized and cleaved by the CRISPR-Cas9 system, and trigger strand displacement amplification and rolling circle amplification. After amplification reactions, massive products can hybridize with the probes, the fluorescence of which are quenched based on a metal-organic framework platform, leading to the fluorescence recovery at typical excitation/emission wavelengths of 480/518 nm. This method exhibits high sensitivity with the detection limit at 4.0 × 101 CFU mL-1 and a wide range from 1.3 × 102 CFU mL-1 to 6.5 × 104 CFU mL-1. Meanwhile, this assay also shows significant specificity and applies to practical samples with high accuracy. Therefore, our method would have great potential application in bacterial detection, food safety monitoring, or clinical diagnostics.

Introduction: Anemia and Ascaris infection are important indicators to reflect the health status of students. In this study, by investigating the current situation of low hemoglobin and positive rate of Ascaris eggs of primary and secondary school students in Hohhot, the health status of local primary and secondary school students is actually reflected. Objectives: To understand the prevalence of Low Hemoglobin and Ascaris infection among primary and secondary school students in Hohhot in 2015 and to give some suggestions on the health status of primary and secondary school students in Hohhot. Study Design: This project uses a cross-sectional study to investigate the distribution of disease and health status of primary and middle school students in Hohhot at a specific time, and to provide a clue to the cause of the hypothesis test. Methods: A stratified cluster random sampling method was used to select 4 districts, 4 counties and 1 flag in Hohhot, a total of 36 primary and secondary schools for sample survey. Cyanine HiCN and smear method is to detect hemoglobin and ascaris eggs positive. Results: In 2015, the positive rate of low hemoglobin in primary and secondary school students was 21.45% in urban and rural areas, 33.17% in urban and rural areas, 43.69% in rural areas, 13.59% in ascaris eggs, 10.69% in urban and rural areas, 7.81% in rural areas. There are geographical differences and gender differences between cities, urban-rural junctions and rural areas (p < 0.05). Conclusion: The prevalence of low hemoglobin in primary and secondary school students in Hohhot is high in rural areas. The detection rate of ascaris egg positive rate in the city is high. Monitoring, publicity and education should continue to be strengthened.

The overuse of antibiotics has aroused widespread concern in recent decades. Their residues in food and environment may pose potential risks to human health. Therefore, highly sensitive and rapid detection methods of antibiotics are urgently needed. Inspired by allosteric transcription factors (aTFs), we proposed a novel strategy for small molecules detection based on antibody controlled isothermal chain displacement amplification (ACISDA). A combination of nicking endonuclease, Klenow Fragment polymerase, specific antibody and a pair of antigen-labeled DNA regulate the synthesis of a G-quadruplex by isothermal chain displacement amplification. The presence of a target induces the antibody dissociation from the antigen-labeled DNA, which induces the synthesis of a G-quadruplex, and a fluorescent signal is produced by thioflavine T (ThT) binding to G-quadruplex. To test this notion, norfloxacin-conjugated DNA (named Primer-NOR) was prepared and ACISDA system was established combining with anti-norfloxacin antibody. This system could detect norfloxacin in a linear range of 0.1 ∼ 500 ng/mL with detection limit of 0.04 ng/mL, and this system could be applied to the detection of norfloxacin in real samples with good performance. Meanwhile, this system could also realize washing-free, immobilization-free and "ready-to-use", and could be used for other small molecules quickly by replacing the antigen-labeled DNA and specific antibody.

Staphylococcal enterotoxin B (SEB) is one of the most common serotypes in staphylococcal food-poisoning cases. A rapid, sensitive, and simple method for SEB detection is crucial for public health. A photonic crystal (PC) sensing material for label-free detection of ultra-trace SEB was proposed in this study. Gold nanoparticle-doped silica microspheres were stacked to form an opal PC through self-assembly, and SEB aptamers, as the recognition element, were modified onto the PC. When the target protein of SEB came in contact with the PC sensing material, the reflection peak intensity of PCs decreased accordingly. The detection range was 1 × 10

Sensitive and accurate detection of nucleic acid biomarkers is critical for early cancer diagnosis, disease monitoring, and clinical treatment. In this study, we developed a switch fluorescence biosensor for simple and high-efficient detection of nucleic acid biomarkers using 6-carboxyfluorescein (FAM)-modified single-stranded DNA (ssDNA) probes (FAM-P1/P2), and zirconium porphyrin metal-organic framework nanoparticles (ZrMOF) acted as fluorescence quencher. FAM-P1/P2 probes were adsorbed on ZrMOF surface because of π-π stacking, hydrogen bonding, and electrostatic interactions. Fluorescence quenching event occurred by fluorescence resonance energy transfer (FRET) and photo-induced electron transfer (PET) processes, thereby achieving the “off” fluorescence status. Once the specific binding was formed between the fluorescence probes and the targets, the rigid double-stranded DNA (dsDNA) structures were released from ZrMOF surface, resulting in the recovery of fluorescence and the “on” status. Because of the superior adsorption ability of ZrMOF toward ssDNA than dsDNA, the switch of fluorescence signals from “off” to “on” allowed rapid and ultrasensitive detection of ssDNA (T1) and microRNA-21 (miR-21) within 30 min. The limit of detection (signal-to-noise ratio = 3) for T1 and miR-21 were 2 fM and 11 aM, respectively. Moreover, the proposed strategy was very simple as it worked by the facile adsorption-quenching-recovery mechanism without difficult and complicated immobilization processes. Also, this biosensor showed an excellent analytical performance in the detection of miR-21 in human serum samples. Therefore, this biosensor might be considered a potential tool for the detection of DNA and miRNA biomarkers in clinical samples.

Metal-organic frameworks (MOFs) have captured substantial attention of an increasing number of scientists working in sensing analysis fields, due to their large surface area, high porosity, and tunable structure. Recently, MOFs as attractive fluorescence quenchers have been extensively investigated. Given their high quenching efficiency toward the fluorescence intensity of dyes-labeled specific biological recognition molecules, such as nucleic acids, MOFs have been widely developed to switch fluorescence biosensors with low background fluorescence signal. These strategies not only lead to specificity, simplicity, and low cost of biosensors, but also possess advantages such as ultrasensitive, rapid, and multiple detection of switch fluorescence methods. At present, researches of the analysis of switch fluorescence biosensors based on MOFs and nucleic acids mainly focus on sensing of different types of in vitro and intracellular analytes, indicating their increasing potential. In this review, we briefly introduce the principle of switch fluorescence biosensor and the mechanism of fluorescence quenching of MOFs, and mainly discuss and summarize the state-of-the-art advances of MOFs and nucleic acids-based switch fluorescence biosensors over the years 2013 to 2020. Most of them have been proposed to the in vitro detection of different types of analytes, showing their wide scope and applicability, such as deoxyribonucleic acid (DNAs), ribonucleic acid (RNAs), proteins, enzymes, antibiotics, and heavy metal ions. Besides, some of them have also been applied to the bioimaging of intracellular analytes, emerging their potential for biomedical applications, for example, cellular adenosine triphosphate (ATP) and subcellular glutathione (GSH). Finally, the remaining challenges in this sensing field and prospects for future research trends are addressed. Graphical abstract.

Polydiacetylene (PDA) is very suited for sensitively detecting large biomolecules, and its unique chromatic properties enable visual read-out. However, application to the selective detection of small molecules remains challenging. Here, bifunctional ligands are studied to amplify the color change of PDA for biorecognition of small molecules for the smartphone-based detection of diethylstilbestrol (DES). PDA is decorated with streptavidin (PDA-SA, blue), and biotin-modified DES (bio-DES) is prepared as a bifunctional ligand to couple with PDA-SA and DES antibody. Since multiple bio-DES can bind to a single SA, then multiple SAs on PDA lead to an increased surface coverage of the vesicle. In samples without DES, PDA-SA-bio-DES-DES antibody complexes will form, leading to a color transition (blue to red); this color transition is greatly amplified by antibody-induced aggregation of the complexes. When DES is present, aggregation is inhibited due to competition for the antibody and PDA-SA-bio-DES retains its blue color. A linear relationship (0.4–1250 ng mL−1) is found between the colorimetric response and the logarithmic DES concentration, with adequate selectivity, accuracy (82.24–118.64%), and precision (below 8.24%). Finally, a paper-based DES PDA biosensor is developed with visual and smartphone-based detection limits of 10 ng mL−1 and 0.85 ng mL−1 in water, respectively.

Raman spectroscopy combined with artificial intelligence algorithms have been widely explored and focused on in recent years for food safety testing. It is still a challenge to overcome the cumbersome culture process of bacteria and the need for a large number of samples, which hinder qualitative analysis, to obtain a high classification accuracy. In this paper, we propose a method based on Raman spectroscopy combined with generative adversarial network and multiclass support vector machine to classify foodborne pathogenic bacteria. 30,000 iterations of generative adversarial network are trained for three strains of bacteria, generative model G generates data similar to the actual samples, discriminant model D verifies the accuracy of the generated data, and 19 feature variables are obtained by selecting the feature bands according to the Raman spectroscopy pattern. Better classification results are obtained by optimising the parameters of the multi-class support vector machine, etc. Our detection and classification method not only solves the problem of needing a large number of samples as training set, but also improves the accuracy of the classification model. Therefore, this GAN-SVM classification model provides a new idea for the detection of bacteria based on Raman spectroscopy technology combined with artificial intelligence algorithms.

With the development of society, physical activity has come to be an effective means by which people pursue good health to improve the quality of life. However, with the increase of intensity and the passage of time, exercise injury has become a hazard that can no longer be ignored. It is imperative to find effective ways to inhibit or reduce the negative effects of exercise. Mitochondria are important organelles involved in exercise and play an important role in exercise injury and prevention. Studies have found that exercise preconditioning and increased mitochondrial nutrition can effectively decrease mitochondrial damage after exercise. Against this background, some of the newest developments in this important field are reviewed here. The results discussed indicate that exercise preconditioning and supplement mitochondrial nutrition need to be increased to prevent exercise-related injuries.

Sensitive and reliable analytical methods for monitoring of microcystin-LR (MC-LR) are urgently necessary due to its great harm to human health and aquatic organisms. In this work, a novel Cu/Au/Pt trimetallic nanoparticles (Cu/Au/Pt TNs)-encapsulated DNA hydrogel was prepared for colorimetric detection of MC-LR. The Cu/Au/Pt TNs were captured and released with precise control by the target-responsive 3D DNA hydrogels, which combined dual advantages of the target responsive DNA hydrogel and Cu/Au/Pt TNs of enhanced peroxidase-like activity. The DNA hydrogel network was constructed by hybridizing MC-LR aptamer with two complementary DNA strands on linear polyacrylamide chains. As long as MC-LR presented, the aptamer competitively binds with the MC-LR, causing the hydrogel to dissolve and release the preloaded Cu/Au/Pt TNs which could catalyze the reaction between H2O2 and TMB to produce color changes. In view of this sensitive strategy, this Cu/Au/Pt TNs-encapsulated DNA hydrogel-based colorimetric biosensor can achieve quantitative determination of MC-LR. The results showed that as-proposed colorimetric biosensor could sensitively detect MC-LR with a linear range of 4.0–10000 ng L−1 and a detection limit of 3.0 ng L−1. This work proved that the sensor had great potential to be applied in MC-LR detection and also provided the opportunity to develop colorimetric biosensor for other targets using this target-responsive and signal-amplification strategy.

In this study, an anticalin that could specifically bind paraquat (PQ), a quaternary nitrogen herbicide, as a new set of engineered receptor protein with antibody-like properties was generated to detect PQ concentration. To this end, a native and random library was constructed and engineered to allow in vitro transcription and translation using an Escherichia coli lysate system. Meanwhile, a PQ derivative that carries an active aliphatic carboxylate group at the end of an aliphatic spacer arm was synthesized. Then, this compound was coupled covalently to the carrier protein bovine serum albumin/ovalbumin and amino-functionalized paramagnetic beads. Alternating selection in solution and immobilization in microtiter wells were used to pan mRNA-ribosome-antibody complexes. After several rounds of ribosome display, three variants were selected from a random library of the bilin-binding protein. The variants that could bind complex PQ with high affinity and exhibit IC50 values as low as 14.039 ± 0.970 ng/mL were identified. Moreover, the limits of detection reached 0.083 ± 0.011 ng/mL. Our data suggest that the generation of anticalins may provide a promising alternative to recombinant antibody fragments to create a stable receptor protein against hapten with bioanalytical relevance.

A low-field nuclear magnetic resonance (LF-NMR) DNA-hydrogel (LNDH) nanoprobe was designed for bisphenol A (BPA) determination. It consists of Fe3O4 superparamagnetic iron oxide nanoparticles (SPIONs) and a DNA-hydrogel technology. Fe3O4 SPIONs were encapsulated in the DNA-hydrogel to form an aggregated state. After adding BPA, the gel system transformed into a sol gel due to the target-aptamer specific binding. The coated gathered particles dispersed and thus, the relaxation time T2 declined. The LNDH nanoprobe was developed to realize a simple, sensitive, and effective BPA determination method without repeated magnetic separation steps. Under the optimal experimental conditions, the determination range of the LNDH biosensor was 10−2~102 ng mL−1 and the limit of determination was 0.07 ng mL−1. The LNDH nanoprobe was applied to two kinds of water samples (tap water and bottled water). The recovery ranged from 87.85 to approximately 97.87%. This strategy offered a new method to detect BPA by LF-NMR. It is also expected to be applicable in related fields of food safety determination, environmental monitoring, and clinical diagnosis.

A novel sensitive assay was established by using strand displacement amplification (SDA) and DNA G-quadruplex with aggregation-induced emission (AIE) for the detection of patulin (PAT) toxin. The complementary DNA (cDNA) of the aptamer and PAT competed for binding to aptamer-modified magnetic beads. The cDNA was obtained by magnetic separation and used as a primer in SDA to produce a large amount of G-base single-stranded DNA (ssDNA). They can form the G-quadruplex to be combined with the AIE of TTAPE dye, which features a special combination of G-quadruplex that amplify the fluorescent signals. This work can reach a lower detection limit of 0.042 pg mL−1 with a wide linear range of 0.001–100 ng mL−1 for PAT detection than other methods. The results also showed good recoveries of 97.8%–104% and 101.7%–105.3% in spiked apple and grape juices, respectively. The assay used for the detection of PAT exhibits high sensitivity and good specificity. It also provides a stable and reliable platform for detecting other small-molecule toxins.

An enzyme-free fluorometric assay is described for the determination of zearalenone (ZEN). The method combines (a) catalyzed hairpin assembly (CHA), (b) ultrahigh fluorescent light-up G-rich DNA sequences in proximity to silver nanoclusters (Ag NCs), and (c) the use of aptamers (Apt). In the presence of ZEN, the inhibit sequence (Inh) is released from the aptamer-trigger sequence (Apt-T) via the binding of ZEN and the aptamer of Apt-T. The free Apt-T acts as a switch that opens the hairpins H1 and H2 to generate H1-H2 complex. The released Apt-T is available to trigger the next round of CHA between H1 and H2. Finally, the hybridization between H1 and the Ag NCs probe (P) causes the G-rich sequence to be in close proximity to the dark Ag NCs encapsulated by P. This leads to highly efficient lighting up of the Ag NCs and the production of amplified fluorescence with excitation/emission peaks at 575/628 nm. Under the optimized conditions, a linear correlation was observed with concentrations ranging from 1.3 pg mL

A novel upconversion fluorescent aptasensor based on hybridization chain reaction and nicking endonuclease has been developed for detection of polychlorinated biphenyls (PCBs). It combined the dual advantages of UCNPs and HCR. Two harpins (H1 and H2) were first designed according to the partial complementary sequence (cDNA) of the PCB72/106. Since the aptamer specifically recognized the target, the cDNA was detached from the magnetic microspheres (MMPs). The cDNA could initiate hybridization chain reaction (HCR) and open the stems of H1 and H2. After the addition of nicking endonuclease, UCNPs were further away from the quenchers (BHQ-1). Hence, the fluorescence intensity of upconversion nanoparticals (UCNPs) could be restored via fluorescence resonance energy transfer (FRET). Therefore, the fluorescence of UCNPs was directly proportional to concentration of PCB72/106, which was the basis for the quantification of PCB72/106. PCB72/106 could be analyzed within the ranges of 0.004 to 800 ng/mL with a detection limit of 0.0035 ng/mL ( S/ N = 3). The aptasensor was also used for the detection of water and soil samples, and the average recoveries ranged from 93.4% to 109.7% and 83.2% to 118.5%, respectively. The relative standard deviations (RSDs) were all below 3.2%. The signal was first amplified through HCR and further amplified with the help of nicking endonuclease. This work also provided the opportunity to develop fluorescent aptasensors for other targets using this dual-amplification strategy.

A sensing system based on AuNP-AuNP-UCNP triple structure for efficient detection of dual targets bisphenol A and estradiol was constructed. In the preparation of triple structure, the gold nanoparticles (AuNPs) and upconversion nanoparticles (NaYF4: Yb, Er, Gd, UCNPs) were synthesized and surface modified. Then, the two nanoparticles and their aptamers were connected to form two kinds of optical fluorescent probes. A nucleic acid sequence that matches with two aptamers was designed, rendering the probes to get close based on the principle of complementary base pairing. On the basis of this, a sensing system with triple structure was prepared, and its connecting effect was characterized by TEM. With this system, dual targets of bisphenol A and estradiol were detected efficiently and conveniently through quantitatively determination by fluorescence and UV spectrophotometer. At the reaction temperature 30 °C and pH 7.8, this method exhibited good linear range for determination of bisphenol A and estradiol from 2 ng mL–1 to 200 ng mL–1 and from 10 ng mL–1 to 150 ng mL–1, with the limits of detection of 0.2 ng mL–1 and 0.5 ng mL–1, respectively. This sensing system with triple structure owned better specificity to structural and functional analogues, showed good repeatability and stability. What's more, this sensing system could be applied to actual water detection, with the recoveries of 86.1%–107.4%, and the relative standard deviation below 6.8%. This method shows promising applications in other environmental estrogens in water sample.

A rapid, simple, and sensitive method has been developed to detect staphylococcal enterotoxin B (SEB). To establish the hybridization chain reaction-based aptasensor, we described the new probes of two hairpins (H1 and H2), which were first designed based on the partial complementary sequence of the SEB aptamer (cDNA). The H1 labeled with a fluorophore and a quencher can act as a molecular fluorescence “switch”. Hence, in the presence of SEB, the aptamer binds SEB, while the unbound cDNA triggers HCR to carry out the cyclic hybridization of H1 and H2 so as to turn “ON” the fluorescence through forming long nicked DNA. By using this new strategy, SEB can be sensitively detected within the range of 3.13 ng mL−1 to 100 ng mL−1 with a detection limit of 0.33 ng mL−1 (S/N = 3). Furthermore, the developed method could facilitate the detection of SEB effectively in milk samples.

Owing to the limitation of DNA-specific recognition, improving the sensitivity of bacteria detection without additional culture poses a considerable challenge. Herein, a sensitive, novel, and high-specificity fluorescence detection method was developed using transcription activator-like effectors (TALEs) as the specifically recognized element. Based on the property of TALEs for recognizing double-stranded DNA, the detection method was first proposed. Its sensitivity was further improved by isothermal amplification of RPA. The "humanoid" molecular beacon (H-MB) was designed to achieve signal output. The steric hindrance of the protein opens the stem, enhancing the fluorescence intensity of an attached FAM/BHQ-1 pair. This method can be used to detect Escherichia coli O157:H7 with single-base mismatch specificity and high sensitivity (detection limit of 3 cfu mL-1) and can be applied in actual sample detection by boiling the sample for 10 min. TALEs can be assembled according to the target, so the method can be used to detect other foodborne pathogens and viruses in the food safety and clinical fields.

An enhanced surface plasmon resonance (SPR) biosensor system using magnetic nanoparticles as amplifying element was developed for the real-time determination of estradiol (E 2 ) based on indirect competition method. The anti-estradiol monoclonal antibody (E 2 -mAb) was conjugated with the magnetic nanoparticles (MNPs) via protein A for signal amplification to improve the detection sensitivity. The chitosan, spin-coated on the sensor chip surface, was used to immobilize the antigen (E 2 -BSA) by glutaraldehyde. The chitosan could significantly improve the performance and stability of the immobilized E 2 -BSA. During the detection, E 2 -BSA competed with E 2 in samples for binding with the E 2 -mAb-MNPs conjugates. Then the SPR response decreased in the presence of E 2 because E 2 prevented the combination of E 2 -mAb-MNPs conjugates and E 2 -BSA. In other words, the response of SPR sensor was inversely proportional to E 2 concentration. Assay parameters, such as the amount of antibody and MNPs, the amount of immobilized E 2 -BSA and E 2 -mAb-MNPs concentration, were optimized in detail and E 2 -spiked milk samples were detected. A good linear relationship was obtained between inhibition and lgC(E 2 ) ranging from 1.95 to 2000 ng/mL and the limit of detection (LOD) was 0.81 ng/mL. The result implied that the detection sensitivity was improved compared with the traditionnal sensor without magnetic nanoparticles. Meanwhile, an ELISA method was conducted to detect E 2 in milk as comparation with the enhanced SPR method, and the results indicated that these two methods had good consistency. The present study demonstrated a presumable general way and the enhanced sensors possessed a promising application for detection of various kinds of small molecules.

A dual-readout immunoassay based on QDs-FM@ALP-SA and click chemistry was developed for quick and sensitive detection of norfloxacin (NOR), which is an important fluoroquinolone antibiotic. In the system, the NOR-biotin conjugate (NOR-Biotin) was synthesized by click chemistry for signal transformation, and alkaline phosphatase–labeled streptavidin (ALP-SA) was attached to quantum dot fluorescence microspheres (QDs-FM) by an activated ester method to form QDs-FM@ALP-SA for signal amplification. Here, QDs-FM was a dual-functional carrier: it was used not only as a chemiluminescence signal amplification carrier but also as a fluorescent signal due to its fluorescence character. The NOR antibody was coated on a 96-well chemiluminescence microtiter plate, and NOR-Biotin was bound to the antibody specifically. Then, QDs-FM@ALP-SA was combined with NOR-Biotin to develop a direct competition chemiluminescence/fluorescence immunoassay (dc-CLIA/FIA). The IC50 values were 0.345 and 1.206 ng/mL for dc-CLIA/FIA, respectively. The linear range was 0.013–12.48 ng/mL and 0.042–39.86 ng/mL, respectively. The recovery from the standard fortified blank milk samples was in the range of 86.44%–101.3%. Therefore, this method could be a useful tool for routine screening of NOR residues in milk.

Abuse of antibiotics results in a large number of antibiotics residues in the environment and even causes the problem of "super bacteria". Therefore, it is crucial to develop a powerful analytic method to monitor antibiotics quickly and simply. Photonic crystal (PC), as a sensing material, has promising application prospects. Herein, we try to use PC to realize pretreatment-free and label-free detection of Ciprofloxacin (CF) through Michael addition reaction. The recognition process is carried out by the Michael addition reaction between the piperazine group of CF and the o-benzoquinone group on the PC. The monodisperse microspheres with o-benzoquinone groups are prepared by polymerization and oxidation and then stacked to form PC. During the detection, the peak intensity of the PC decreases with the increasing CF concentration, and the linear range is from 2 to 512 μg/L. The limit of detection (LOD) is 0.76 μg/L. Furthermore, the PC retains 97% of the initial response after storage in a Petri dish at room temperature for 1 month, which shows that it has good stability. Moreover, CF in fish farming water can be detected directly without any pretreatment and label, and the results are in good accordance with the LC-MS-MS results. This Michael-addition-mediated PC is accurate, easily prepared, cost-efficient, and long-term stable. In addition, it is environmentally friendly, because little organic solvent is needed during both the preparation and the detection.

DNA glycosylase is an indispensable DNA damage repair enzyme which can recognize and excise the damaged bases in the DNA base excision-repair pathway. The dysregulation of DNA glycosylase activity will give rise to the dysfunction of base excision-repair and lead to abnormalities and diseases. The simultaneous detection of multiple DNA glycosylases can help to fully understand the normal physiological functions of cells, and determine whether the cells are abnormal in pre-disease. Regrettably, the synchronous detection of functionally similar DNA glycosylases is a great challenge. Herein, we developed a multifunctional dsDNA probe mediated exponential rolling circle amplification (E-RCA) method for the simultaneously sensitive detection of human alkyladenine DNA glycosylase (hAAG) and uracil-DNA glycosylase (UDG). The multifunctional dsDNA probe contains the hypoxanthine sites and the uracil sites which can be recognized by hAAG and UDG respectively to generate apyrimidinic (AP) sites in the dsDNA probe. Then the AP sites will be recognized and cut by endonuclease Ⅳ (Endo IV) to release corresponding single-stranded primer probes. Subsequently, two padlock DNA templates are added to initiate E-RCA to generate multitudinous G-quadruplexes and/or double-stranded dumbbell lock structures, which can combine N-methyl mesoporphyrin IX (NMM) and SYBR Green Ⅰ (SGI) for the generation of respective fluorescent signals. The detection limits are obtained as low as 0.0002 U mL−1 and 0.00001 U mL−1 for hAAG and UDG, respectively. Notably, this method can realize the simultaneous detection of two DNA glycosylases without the use of specially labeled probes. Finally, this method is successfully applied to detect hAAG and UDG activities in the lysates of HeLa cells and Endo1617 cells at single-cell level, and to detect the inhibitors of DNA glycosylases.

Diazepam (DZP) has increasingly appeared in the nonmedical field, posing an ever-growing threat to public-health safety. Methods that accelerate and simplify the on-site detection of DZP are urgently needed. In this study, we investigated the feasibility of applying a flow-injection analysis (FIA)-based thermometric enzyme-linked immunosorbent assay (TELISA) biosensing strategy to rapidly detect DZP in real samples. The scheme involved three key steps: 1) FIA-TELISA was modified to optimize performance in DZP detection; 2) the selected samples that were spiked with a predetermined amount of DZP were respectively determined; and 3) detection results were validated by high-performance liquid chromatography. After calibrations, a linear range of 45.37–726.71 ng mL −1 was obtained, with a corresponding detection limit of 33.71 ng mL −1 . During the continuous detection, each sample required 15 min to generate an entire heat signal, and the cycle time including regeneration and retrimming was

A new opal photonic crystal (PC) sensing material, allowing label-free detection of transferrin (TRF), is proposed in the current study. This photonic crystal was prepared via a vertical convective self-assembly method with monodisperse microspheres polymerized by methyl methacrylate (MMA) and 3-acrylamidophenylboronic acid (AAPBA). FTIR, TG, and DLS were used to characterize the components and particle size of the monodisperse microspheres. SEM was used to observe the morphology of the PC. The diffraction peak intensity decreases as the TRF concentration increase. This was due to the combination of TRF to the boronic acid group of the photonic crystal. After condition optimization, a standard curve was obtained and the linear range of TRF concentration was from 2 × 10–3 ng/mL to 200 ng/mL. Measurement of TRF concentration in simulated urine sample was also investigated using the sensing material. The results indicated that the PC provided a cheap, label-free, and easy-to-use alternative for TRF determina...

An ultrasensitive electrochemical sensor for determination of diethylstilbestrol (DES) was successfully constructed in this paper. Gold nanoparticles (AuNPs) and multi-walled carbon nanotubes-chitosan composite (MWCNTs-CS) were stepwise modified on glassy carbon electrode (GCE). And these two nanomaterials were used to increase the electrode surface area to enhance the electron transfer rate, and finally amplify the sensor signal. Moreover, sol-gel molecularly imprinted polymer was then electrodeposited on the electrode surface. The modified electrode was characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The important parameters controlling the performance of the modified electrode were also optimized. Electrochemical measurements were performed via differential pulse voltammetry (DPV). And under optimal conditions, the sensor showed a detection range of 1.0 × 10−10–1.0 × 10−6 mg/mL with a detection limit of 24.3 fg/mL. At three concentration levels, the recovery rates for the detected DES in milk samples were 91.5%–106.7%. The sensor also had good reproducibility, stability and selectivity for DES detection.

Herein, we report a novel fluorescent sensor based on molecularly imprinted polymer-coated upconversion nanoparticles (MIP-coated UCNPs) for the recognition and detection of diethylstilbestrol (DES). We used one-step process to modify the surface of the UCNPs with alkenyl groups, which was not only a simple process, but also greatly saved the preparation time. Then, a molecularly imprinted polymer was synthesized on the UCNPs by the surface-graft molecular imprinting method. MIP-coated UCNPs combine the advantages of UCNPs and molecularly imprinted polymers such as strong fluorescence properties, excellent stability, reusability, good adsorption capacity, and high specificity. After the removal of the template molecules, the UCNPs were able to selectively recognize DES, and the fluorescence intensity decreased as the concentration of DES increased. A good linear relationship was obtained in the concentration range of 50–1000 ng mL−1 with the correlation coefficient of 0.9989, and the detection limit was 12.8 ng mL−1 (S/N = 3). MIP-coated UCNPs could be applied for the detection of DES in real milk samples, and the average recoveries for five different concentrations ranged from 90.3% to 107.8%, with the relative standard deviations (RSD) below 2.7%. This fluorescence sensor provides a more convenient, simple and highly specific method for the on-field detection of DES and is promising for a wide range of applications in the future.

In this study, sandwich chemiluminescent immunoassay (CLIA) for the detection of Staphylococcal enterotoxin B (SEB) was developed using nanobody–alkaline phosphatase (Nb–ALP) fusion protein. The SEB-binding nanobodies were obtained from a naive phage-display library and the Nb–ALP fusion protein was constructed and obtained as a thermally stable and potentially effective substance for detecting antibodies in CLIA. The working range of the sandwich CLIA based on anti-SEB monoclonal antibodies (mAbs) and our fusion protein, Nb37–ALP, was 3.12–50.0 ng mL−1 with SC50 = 8.59 ± 0.37 ng mL−1. The limit of detection was 1.44 ng mL−1 according to the blank value plus 3 standard deviations. In order to understand the interaction of SEB and Nb37 in depth, the 3D structure of the SEB–Nb37 complex was constructed and verified by molecular modeling and the docking method. The results showed that the complementary-determining region 3 (CDR3) of Nb37 embedded itself in the opening generated by the major histocompatibility complex (MHC) and T-cell receptor- (TcR) binding sites of SEB, indicating that Nb37 may affect the recognition of SEB by MHC class Ⅱ molecules and the TcR. The arginine residue (Arg) 101, Arg102 and phenylalanine residue (Phe)103 of CDR3 in Nb37 may have contributed to specific binding to form six salt-bridges between these and SEB. In conclusion, in terms of their specificity and sensitivity, the obtained anti-SEB Nb–ALP appears to have the potential to replace chemically labeled probes for the detection of SEB.

Microplastics are abundant in oceans, lakes, soils and even air, and can pose potential threats to human health through food or respiratory intake. Moreover, microplastics have synergistic toxicity to the body after absorbing organic pollutants. In this study, laser scanning confocal microscope and flow cytometry were used to observe the intake of colonic cancer Caco-2 cells to polystyrene plastic with five different particlesizes (300 nm, 500 nm, 1 μm, 3 μm, 6 μm). The uptake rates of microplastics with different particle sizes were 73%, 71%, 49%, 43%, and 30%, respectively. Then, High Performance Liquid Chromatography (HPLC) was used to analyze the adsorption differences of polystyrene plastic with different particle sizes to bisphenol A (BPA). Finally, the proliferation toxicity of polystyrene microplastics with different particle sizeson Caco-2 cells before and after adsorption of BPA was compared. MTT experiments confirmed that microplastics caused an increase in cytotoxicity. This result may be related to increased cellular oxidative stress and mitochondrial depolarization. This hypothesis has been confirmed in reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) assays because nanoscale microplastics cause a large amount of ROS on Caco-2 cells after microplastic exposure, and micron-scale microplastics cause a significant decrease in MMP. At the same time, nanoscale microplastics can cause further depolarization of mitochondria due to their large specific surface area adsorption of BPA, which leads to enhanced cytotoxicity of microplastics after BPA adsorption. The results of this study are of great significance in the evaluation of the safety of microplastics in the human body.

Multiplex DNA methylation and glycosylation are ubiquitous in the human body to ensure the normal function and stability of the genome. The methyltransferases and glycosylases rely on varied enzymes with different action mechanism, which still remain challenges for multiple detection. Herein, we developed a tri-functional dsDNA probe mediated exponential amplification strategy for sensitive detection of human DNA (cytosine-5) methyltransferase 1 (Dnmt1) and uracil-DNA glycosylase (UDG) activities. The tri-functional dsDNA probe was rationally designed with M-DNA and U-DNA. M-DNA contains the 5′-GCmGCGC-3′ site for Dnmt1 recognition. U-DNA possesses one uracil as the substrate of UDG and a primer sequence for initiating the amplification reaction. M-DNA was complementary to partial sequence of U-DNA. In the presence of Dnmt1 and UDG, BssHⅡ and Endo Ⅳ were used to nick the 5′-GCGCGC-3′ and AP sites respectively, resulting in the release of single-stranded DNA sequence (primer sequence), respectively. After magnetic separation, the released primer sequence hybridizes with padlock DNA (P-DNA), initiating exponential rolling circle amplification to produce numerous G-quadruplexes for recordable signals. The strategy exhibited the limit of detection as low as 0.009 U mL−1 and 0.003 U mL−1 for Dnmt1 and UDG, respectively. Meanwhile, this strategy was successfully applied to detect Dnmt1 and UDG activities in living cell samples at single-cell level and assay the inhibitors of Dnmt1 and UDG. Therefore, the strategy provided a potential method to detect Dnmt1 and UDG activities in biological samples for early clinic diagnosis and therapeutics.

Herein, a highly sensitive ochratoxin A (OTA) detection strategy was developed based on a bio-barcode immunoassay with catalytic hairpin assembly (CHA). Two nanoprobes were designed for the assay: one was a gold nanoparticle (AuNP) harbouring numerous bio-barcode DNA and antibodies, and the other was an antigen-functionalized magnetic nanoparticle (MNP). In the presence of target OTA, the antigens of the MNPs competed with OTA for binding to the antibodies on the AuNPs. After magnetic separation, the unbound AuNPs and target OTA were washed away. Dithiothreitol (DTT) was then added to the MNP-bound AuNPs to elute the bio-barcode DNAs of AuNPs, which triggered the CHA reaction. Under optimal conditions, the proposed method could sensitively detect target OTA ranging from 0.001 to 10000 ng/mL. The limit of detection (LOD, 3 N/S) and limit of quantification (LOQ, 10 N/S) for OTA were 0.54 pg/mL and 1.80 pg/mL, respectively. The bio-barcode immunoassay was used to analyse food samples (corn, wheat, and peanut), and the recovery and relative standard deviations (RSD) ranged from 93.30% to 108.80% and from 3.2% to 6.9%, respectively. The total assay time was 6 h. Therefore, the proposed strategy will provide a new approach for the detection of mycotoxins and other small molecule analytes and can be applied for quality control to ensure food safety.

Bisphenol A (BPA), as one of the environmental endocrine disruptors, is extensively existing and threatening to human health. To evaluate the environmental exposure level and protect human from the hazard of BPA, a precise and sensitive method is established. In this work, Graphene@ Fe3O4 (G@Fe3O4) is prepared by chemical coprecipitation method as magnetic dispersion solid phase extraction (MDSPE) material. The rapid and specific detection method of BPA is carried out by high-performance liquid chromatography (HPLC). Properties of G@Fe3O4 are identified by the fourier infrared spectrum and scanning electron microscopy. Conditions of solid phase extraction are optimized. Under the optimal extraction conditions, G@Fe3O4 has perfect enrichment effect on BPA. There is a good linear relationship in the range of 5.0~1000.0 μg/L with the correlation coefficient of 0.9997. The detection limit is 0.1 μg/L. This method is applied to water samples successfully, and recoveries of BPA are between 88.19% and 99.56% (RSDs

Abrin is one of the most toxic phytotoxins to date, and is a potential biological warfare agent. A bio–barcode triggered isothermal amplification for fluorometric determination of abrin is described. Free abrin competes with abrin–coated magnetic microparticles (MMP) probes to bind to gold nanoparticle (AuNP) probes modified with abrin antibody and bio–barcoded DNA. Abundant barcodes are released from the MMP–AuNP complex via dithiothreitol treatment. This triggers an exponential amplification reaction (EXPAR) that is monitored by real–time fluorometry, at typical excitation/emission wavelengths of 495/520 nm. The EXPAR assay is easily operated, highly sensitive and specific. It was used to quantify abrin in spiked commercial samples. The detection limit (at S/N = 3; for n = 6) is 5.6 pg·mL−1 which is considerably lower than previous reports. This assay provides a universal sensing platform and has great potential for determination of various analytes, including small molecules, proteins, DNA, and cells.

The authors describe an aptamer based assay for the mycotoxin T-2. The method is making use of exponential isothermal amplification reaction (EXPAR) and fluorescent silver nanoclusters (AgNCs). Free T-2 and cDNA (which is a DNA that is partially complementary to the aptamer) compete for binding to aptamer-modified magnetic beads. The cDNA collected by magnetic separation can be used as a primer to trigger EXPAR to obtain ssDNA. The C-base-rich ssDNA binds and reduces Ag(I) ion to form fluorescent AgNCs. Fluorescence is measured at excitation/emission wavelengths of 480/525 nm. T-2 can be detected by fluorometry with a detection limit as low as 30 fg·mL−1. The method was applied to analyse spiked oat and corn, and the average recoveries ranged from 97.3 to 102.3% and from 95.9 to 107.5%, respectively. The results were in good agreement with data of the commercial ELISA kit. The assay is highly sensitive, has a wide analytical range, good specificity and reliable operation. It provides a promising alternative for the standard method for quantitative detection of T-2.

This study describes an upconversion fluorescent aptasensor based on black phosphorus nanohybrids and self-assembled DNA tetrahedrons dual-amplification strategy for rapid detection of the environmental estrogens bisphenol A (BPA) and 17β-estradiol (E2). Tetrahedron complementary DNAs (T-cDNAs) were self-assembled in an oriented fashion on a 2D nanohybrid composed of black phosphorus (BP) and gold to give a materials of architecture BP-Au@T-cDNAs. In parallel, core-shell upconversion nanoparticles were modified with aptamers (UCNPs@apts) and used as capture probes. On complementary pairing, the BP-Au@T-cDNA quench the fluorescence of UCNPs@apts (measured at an excitation wavelength 808 nm and at main emission peaks at 545 nm and 805 nm.) Compared with single-stranded probes based on black phosphorus and gold, the dual-amplification strategy increases quenching efficiency by nearly 25%–30% and reduces capture time to 10 min. This is due to the higher optical absorption of 2D nanohybrid and the reduction of steric hindrance by T-cDNAs. Exposure to BPA or E2 cause the release of UCNPs@apts from the BP-Au@T-cDNAs due to stronger binding between aptamer and analyte. Hence, fluorescence recovers at 545 nm for BPA and 805 nm for E2. Based on these findings, a dually amplified aptamer assay was constructed that covers the 0.01 to 100 ng mL−1 BPA concentration range, and the 0.1 to 100 ng mL−1 E2 concentration range. The detection limits are 7.8 pg mL−1 and 92 pg mL−1, respectively. This method was applied to the simultaneous determination of BPA and E2 in spiked samples of water, food, serum and urine.

Optical fibers made of polymeric materials possess high flexibility that can potentially integrate with flexible electronic devices to realize complex functions in biology and neurology. Here, a multichannel flexible device based on four individually addressable optical fibers transfer-printed with flexible electronic components and controlled by a wireless circuit is developed. The resulting device offers excellent mechanics that is compatible with soft and curvilinear tissues, and excellent diversity through switching different light sources. The combined configuration of optical fibers and flexible electronics allows optical stimulation in selective wavelengths guided by the optical fibers, while conducting distributed, high-throughput biopotential sensing using the flexible microelectrode arrays. The device has been demonstrated in vivo with rats through optical stimulation and simultaneously monitoring of spontaneous/evoked spike signals and local field potentials using 32 microelectrodes in four brain regions. Biocompatibility of the device has been characterized by behavior and immunohistochemistry studies, demonstrating potential applications of the device in long-term animal studies. The techniques to integrate flexible electronics with optical fibers may inspire the development of more flexible optoelectronic devices for sophisticated applications in biomedicine and biology.

An Au nanoparticle-(Au NP)-doped molecularly imprinted photonic crystal (Au-MIPC) is successfully prepared for naked-eye analysis. The resultant crystal displays a periodically ordered inverse opal structure. The proposed photonic crystal (PC) overtly reveals a 69 nm red shift accompanied by a naked-eye distinguishable structural color change from blue to green when detecting bisphenol A from 1 ng ml−1 to 1 mg ml−1. By comparing the detection results of the MIPC without Au NPs with those of non-molecularly imprinted PCs (NIPCs) with and without Au NPs, we note that the introduction of Au NPs can effectively amplify the response signal but it does not interfere with the response signals of NIPCs. The naked-eye distinguishable color change and amplification effect are also observed in monocrotophos- and ractopamine-imprinted Au-MIPCs. All of these Au-MIPCs possess high selectivity for target molecules. Thus, Au-MIPCs can potentially be applied to the equipment-free detection of various molecules in-field to facilitate significant naked-eye detection as pH paper. We expect to form new functional photonic materials or sensors for molecular analysis.

The demand for advanced, sensitive, and low-cost sensor platforms is growing. However, sensors containing biological recognition elements sometimes present restrictions, which limit their use. This work focused on the development of surface plasmon resonance (SPR) based on a molecularly imprinted polymer (MIP) film, which builds a foundation for biomimetic sensors. The MIP films in the sensor chip were prepared by spin-coating method. The MIP film was found to be readily incorporated into the sensor for detection of histamine in aqueous media. The effect of pH conditions was also investigated. The sensing technique allows for the detection of histamine in a wide range of concentration from 25 μg L−1 to 1000 μg L−1. By using structural analogs, the sensor platform was demonstrated to be specific for the detection of histamine.

The sensitive and accurate detection of cancer biomarkers is critically important to early clinical diagnosis, disease monitoring, and successful cancer treatment. Here, we first demonstrate an aptamer-based frequency shift Raman approach via sensing of graphene. This biosensor allows the rapid, sensitive, and label-free detection of the acknowledged protein cancer biomarker, prostate-specific antigen (PSA). Monolayer graphene is employed as the Raman substrate, which is highly sensitive to its electronic structure and interface properties. The PSA aptamer can be adsorbed strongly on the surface of substrates through π-π stacking interactions. The vibrational frequency of the G peak of graphene shifted upon the specific binding between the PSA and its aptamer. The corresponding frequency shifts of the G peak are directly correlated with PSA concentrations. The limit of detection is as low as 0.01 ng/mL, with a wide linear range from 0.05 ng/mL to 25 ng/mL. The analytic samples can be detected directly without any extensive preparation and label process. The whole detection is completed in only 30 min. Furthermore, excellent recoveries are acquired to validate the feasibility of this assay in human serum samples. The proposed technology could provide a selective, versatile, and user-friendly strategy for the early detection of cancer biomarkers.

The responsive photonic crystals (PC) are promising sensing materials owning to their response signal self-expression, but how to attach the recognition element efficiently and how to improve the sensitivity are still challenging. Au nanoparticles (Au NPs), which possess high reactive activity and localized surface plasmon resonance (LSPR) effect, provide a strategy. So, Au NPs are introduced to opal PC, in order to not only amplify the optical signal but also facilitate the fixation of recognition element onto PC. Furthermore, the signal enhancement mechanism is investigated and a universal PC sensing material is developed. This PC is easy-prepared and can reach ultrasensitive detection without label. Coupled with the enhancement of Au NPs, the PC can respond to the trace target with the concentration down to 10−12 g/mL. Simultaneously, the detection of hazardous chemicals can be achieved by replacing the recognition element. This design extensively broadens the PC application in clinical assays, food safety, environmental monitoring, etc.