Exosomes are extracellular vesicles (50–100 nm) circulating in biofluids as intercellular signal transmitters. Although the potential of cancerous exosomes as tumor biomarkers is promising, sensitive and rapid detection of exosomes remains challenging. Herein, we combined the strengths of advanced aptamer technology, DNA-based nanostructure, and portable electrochemical devices to develop a nanotetrahedron (NTH)-assisted aptasensor for direct capture and detection of hepatocellular exosomes. The oriented immobilization of aptamers significantly improved the accessibility of an artificial nucleobase-containing aptamer to suspended exosomes, and the NTH-assisted aptasensor could detect exosomes with 100-fold higher sensitivity when compared to the single-stranded aptamer-functionalized aptasensor. The present study provides a proof-of-concept for sensitive and efficient quantification of tumor-derived exosomes. We thus expect the NTH-assisted electrochemical aptasensor to become a powerful tool for comprehensive exosome studies.Keywords: aptasensor; electrochemistry; exosomes; expanded nucleotide; nanotetrahedron;

Herein, an ultrasensitive and selective assay for antibiotic tetracycline (TC) was developed based on an aptamer and graphene oxide (GO). The assay was designed based on the protection effect of the aptamer on GO due to aggregation. When the GO-based aptasensor was incubated with TC, TC could capture the TC aptamer from GO, leading to the aggregation of GO in a high salt solution. The increase in size and decrease in zeta-potential can be detected by adding TC in the assay. A linear relationship between the optical response and the logarithm concentration of TC was observed after centrifugation. The detection range was 0.002 to 20 ng mL−1 and the detection limit was 0.001 ng mL−1 (S/N = 3). The recoveries of TC in honey samples (0.001 mg kg−1, 0.01 mg kg−1 and 0.1 mg kg−1) were from 82.5% to 117%.

Based on the study of intrinsic conformational structure-dependent molecular recognition between tetracycline (TC) and anti-TC aptamers, herein, we focus on the classic gold nanoparticle (AuNPs)-based colorimetric aptasensor. We adopt a 40 mer T-rich aptamer with considerations of stand length, primary sequence, and conformational structure. A computational analysis was applied to further decipher the molecular binding property among the AuNPs, aptamer, and TC. The short length of the aptamer assisted easy adsorption of the aptamer onto the surface of AuNPs. The rich T bases with less affinity onto the surface of AuNPs contributed to the sensitivity of the biosensor. The computational analysis revealed that the binding sites on the 40 mer aptamer distributed closely, and the aptamer had a flexible conformational structure to be adsorbed onto or desorbed from the surface of AuNPs. After detailed optimization, we developed a label-free colorimetric aptasensor which provided both visual and spectrographic quantitation for TC detection in a honey sample with high specificity and a limit of detection (LOD) of 12.4 ng mL−1. The present assay can be developed as a simple and efficient method for basic on-site screening for TC residue in honey products, both visually and quantitatively. Moreover, the present study proves the concept for TC aptasensor development with a successful prediction practice and may lay the foundation for the development of other aptasensors.

Different aptamers towards one target molecule can be selected by Systematic Evolution of Ligands by Exponential Enrichment (SELEX), however, not all aptamers have real world practicability. In this study, conformational structure-dependent molecular recognition of two aptamers towards tetracycline (TC), 76 mer and 40 mer, was studied both quantitatively and computationally. Two formats of competitive enzyme-linked aptamer assay (ELAA), a molecular docking module and Isothermal Titration Calorimeter (ITC) analysis were used to further investigate the two selected aptamers. With longer strand length, more G, C bases, and more recognition sites for TC, the 76 mer aptamer showed better performance than the 40 mer aptamer. Deciphering the relevance of aptamers with different molecular characteristics towards one target molecule can furnish as a referral guidance for aptamer selection and further practical application.

The direct analysis in real time (DART) ionization source coupled with quadrupole time-of-flight tandem mass spectrometry (Q-TOF MS/MS) system has the capability to desorb analytes directly from samples without sample cleanup or chromatographic separation. In this work, a method based on DART/Q-TOF MS/MS has been developed for rapid identification of dicyandiamide (DCD) present in powdered milk. Simple sample extraction procedure employing acetonitrile-water (80:20, v/v) mixture was followed by direct, high-throughput determination of sample extracts spread on a steel mesh of the transmission module by mass spectrometry under ambient conditions. The method has been evaluated for both qualitative and quantitative analysis of DCD in powdered milk. Variables including experimental apparatus, DART gas heater temperature, sample presentation speed, and vacuum pressure were investigated. The quantitative method was validated with respect to linearity, sensitivity, repeatability, precision, and accuracy by using external standards. After optimization of these parameters, a limit of detection (LOD) of 100 μg kg–1 was obtained for DCD with a linear working range from 100 to 10000 μg kg–1 and a satisfactory correlation coefficient (R2) of 0.9997. Good recovery (80.08%–106.47%) and repeatability (RSD = 3.0%–5.4%) were achieved for DCD. The DART/Q-TOF MS/MS-based method provides a rapid, efficient, and powerful scheme to analyze DCD in powdered milk with limited sample preparation, thus reducing time and complexity of quality control.

•First, we aimed at enabling a simultaneous gel permeation chromatography (GPC) method to analyze the content and molecular-weight distribution (MWD) of natural trans-1,4-polyisoprene (TPI) from Eucommia ulmoides Oliver.•Second, we investigated TPI from multiple plant issues of E. ulmoides, such as leaves, fruit coatings and bark, and explored the MWD relationship among them.•Results showed that because of higher yield and higher MW, fruit coating was more suitable for rubber industry use and turned out to be a promising source of natural TPI.Natural trans-1,4-polyisoprene (TPI) as a functional biomaterial has aroused great interest for rubber industrial product use. Here, we proposed a method that enables simultaneous analysis of the content and molecular-weight distribution (MWD) of natural TPI by gel permeation chromatography (GPC). The natural TPIs were collected from leaves, fruit coatings and bark of Eucommia ulmoides Oliver (E. ulmoides) through toluene extraction followed by ethanol purification. The results of TPI contents from leaves and fruit coatings were shown ca. 3.5% and 13.8%, respectively. Accordingly, limits of detection (LODs) of TPI were 0.58 mg/mL from leaves and 0.47 mg/mL from fruit coatings. The MWDs of TPI demonstrated a bimodal distribution from leaves, a unimodal distribution from bark, and a unimodal distribution with a tiny peak shoulder from fruit coatings. In real-life E. ulmoides analysis, the results from three independent methods (GPC, gravimetric method, and infrared spectroscopy) were obtained with good consistency.

•An aptasensor was developed to detect tetracycline in honey with high-throughput.•Detailed optimization was performed for assay conditions.•An improved operation procedure of dc-ELAA was carried out for the first time.•The aptasensor presented a good limit of detection and a wide linear range.•The ic-ELAA and dc-ELAA for TC detection in honey was compared preliminarily.Tetracycline (TC) is a common antibacterial agent used for prevention and control of animal diseases. The increasing concern about TC residue in food demands high-performing analytical techniques for food quality assessment. Biosensors represent a promising tool for food safety analysis as they can fulfill some demand that the conventional methods do not attain. In this study, a novel colorimetric aptasensor was developed for sensitive detection of TC in honey. The aptasensor was based on a modified direct competitive enzyme-linked aptamer assay (dc-ELAA) scheme utilizing a 76mer single-stranded DNA (ssDNA) aptamer selected by Systematic Evolution of Ligands by Exponential Enrichment (SELEX). The optimized aptasensor showed a good limit of detection (LOD of 0.0978 ng/mL), a wide linear range (0.1–1000 ng/mL) toward TC in honey, with good recoveries (92.09–109.7%) in TC-spiked honey, and was compared with an indirect competitive assay-based aptasensor and validated with a standard ELISA. The biosensor based on dc-ELAA with good limit of detection and simplicity can be applied for high-throughput detection of TC in food.

We present a novel method to analyze clenbuterol based on a competitive microfluidic immunoassay scheme with a micro-ELISA system, and obtain a limit of detection that is less than 0.1 ng ml−1 with a quantitative working range of 0.1 ng ml−1 to 27.0 ng ml−1. The approach was envisaged to be a promising method for efficient onsite clenbuterol control with good sensitivity and portability.

•An aptasensor was developed to detect tetracycline in honey with simplicity.•Detailed stepwise optimization for working conditions was carried out.•The biosensor presented superior sensitivity and a relatively wide linear range.•The biosensor might be utilized for high-throughput TC detection.Tetracycline (TC) is widely used for prevention and control of animal diseases for its broad spectrum antimicrobial activity and low cost, but its abuse can seriously affect human health and may result in trade loss. Thus there is an imperative need to develop high-performing analytical technique for TC detection. In this study, we developed a biosensor based on an indirect competitive enzyme-linked aptamer assay (ic-ELAA). A 76mer single-stranded DNA (ssDNA) aptamer, selected by Systematic Evolution of Ligands by Exponential Enrichment (SELEX), was applied for the recognition and detection of TC in honey. The limit of detection was 9.6×10−3 ng/mL with a linear working range from 0.01 to 100 ng/mL toward TC in honey, and a mean recovery rate of 93.23% in TC-spiked honey was obtained. This aptasensor can be applied to detect TC residue in food with high sensitivity and simplicity, and it is prospective to develop useful ELAA Kits for TC determination in food.

Access to security and safe food is a basic human necessity and essential for a sustainable world. To perform hi-end food safety analysis and risk assessment with state of the art technologies is of utmost importance thereof. With applications as exemplified by microfluidic immunoassay, aptasensor, direct analysis in real time, high resolution mass spectrometry, benchmark dose and chemical specific adjustment factor, this review presents frontier food safety analysis and risk assessment technologies, from which both food quality and public health will benefit undoubtedly in a foreseeable future.

•A rapid screening and quantification method for pesticides and adulterants in wine.•The first time to combine DART with QqQ-MS to detect pesticides and adulterants.•The simple modified QuEChERS preparation procedure to shorten the time of analysis.•No column used for separation.A rapid method to screen and quantify multi-class analytic targets in red wine has been developed by direct analysis in real time (DART) coupled with triple quadruple tandem mass spectrometry (QqQ-MS). A modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) procedure was used for increasing analytical speed and reducing matrix effect, and the multiple reaction monitoring (MRM) in DART-MS/MS ensured accurate analysis. One bottle of wine containing 50 pesticides and 12 adulterants, i.e., preservatives, antioxidant, sweeteners, and azo dyes, could be totally determined less than 12 min. This method exhibited proper linearity (R2 ≥ 0.99) in the range of 1–1000 ng/mL for pesticides and 10–5000 ng/mL for adulterants. The limits of detection (LODs) were obtained in a 0.5–50 ng/mL range for pesticides and 5–50 ng/mL range for adulterants, and the limits of quantification (LOQs) were in a 1–100 ng/mL range for pesticides and 10–250 ng/mL range for adulterants. Three spiked levels for each analyte in wine were evaluated, and the recoveries were in a scope of 75–120%. The results demonstrated DART-MS/MS was a rapid and simple method, and could be applied to rapid analyze residual pesticides and illegal adulterants in a large quantities of red wine.