Rapid and quantitative determination of deoxynivalenol in cereal through the combination of magnetic solid-phase extraction and optical fiber-based homogeneous chemiluminescence immunosensor.

An integrated strategy for the rapid and sensitive detection of deoxynivalenol in cereals was developed by combining Fe3O4 magnetic nanoparticle-modified metal organic framework-5-based magnetic solid-phase extraction and the optical fiber-based homogeneous chemiluminescence immunosensor. The hybrid magnetic material was prepared and characterized, exhibiting good enrichment capacity up to 1.68 mg/g. The competitive immunoassay-based homogeneous chemiluminescence immunosensor enabled washing-free and high-sensitivity detection of deoxynivalenol. Under optimized conditions, this immunosensor could detect deoxynivalenol as low as 46.7 pg/mL with a quantitatively linear range of 0.1 to 1000 ng/mL. The recoveries of this integrated detection strategy in rice, corn, and wheat ranged from 80.0 % to 118.2 %, 91.1 % to 116.7 %, and 80.0 % to 91.5 %, respectively, with a relative standard deviation that did not exceed 9.11 %. More importantly, it shows great consistency with the high-performance liquid chromatography-mass spectrometry in blind sample analysis. This integrated detection strategy provides a convenient approach for mycotoxins screening in cereals.

Integrating magnetic metal-organic frameworks-based sample preparation with microchannel resistance biosensor for rapid and quantitative detection of aflatoxin B1.

Aflatoxin B1, a secondary metabolite produced by fungi, is one of the most toxic mycotoxins that poses a major food security and public health threat worldwide. Effective sample pretreatment and high sensitivity detection techniques are urgently needed due to its trace amount in complex samples. Herein, an integrated detection strategy was developed by combining Mg/Zn-metal organic framework-74 modified Fe3O4 magnetic nanoparticles (Mg/Zn-MOF-74 @Fe3O4 MNPs)-based sample preparation and microchannel resistance biosensor for rapid and highly sensitive detection of aflatoxin B1 in food samples. The synthesis and characterization of Mg/Zn-MOF-74 @Fe3O4 MNPs was reported, which exhibited efficient separation and enrichment capacity when exposed to complex grain samples. The competitive immunoassay-based microchannel resistance biosensor enabled specific and high-sensitive analysis of aflatoxin B1 by using current as a readout, which caused by the blocking effect between the functionalized-polystyrene microspheres and microchannel. Under optimized conditions, this biosensor was capable to quantitatively analysis aflatoxin B1 from 10 pg/mL to 20 ng/mL, and with a limit of detection of 4.75 pg/mL. This integrated detection strategy has been tested for the quantitative detection of aflatoxin B1 in grain samples that is a potential protocol for food safety control and environmental monitoring.

Low-Cost and Convenient Microchannel Resistance Biosensing Platform by Directly Translating Biorecognition into a Current Signal.

We report a low-cost and convenient microchannel resistance (MCR) biosensing platform that uses current signal to report biorecognition. The biorecognition behavior between targets and biometric molecules (antigens, antibodies, or oligonucleotides) immobilized on magnetic beads and polystyrene (PS) microspheres induces a quantitative change in the unreacted PS microspheres. After magnetic separation, the unreacted PS microsphere solution is passed through the microchannel, leading to an obvious blocking effect, resulting in an increase in resistance, which can in turn be measured by monitoring the electric current. Thus, the biorecognition is directly converted into a detectable current signal without any bulky instruments or additional chemical reactions. The MCR biosensing platform is cost-effective and user-friendly with high accuracy. It can be an appropriate analysis technique for point-of-care testing in resource-poor settings.

Chemiluminescent Optical Fiber Immunosensor Combining Surface Modification and Signal Amplification for Ultrasensitive Determination of Hepatitis B Antigen.

Optical fiber based immunosensors are very attractive for biomarker detection. In order to improve the sensor response, we propose a promising strategy which combines porous-layer modification of the fiber surface and streptavidin-biotin-peroxidase nano-complex signal amplification in chemiluminescent detection. Two hepatitis B antigens, hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg), are used as the targets for analysis using the proposed sensor. Comparing to immunoassays using normal optical fiber sensors, the response of the present sensor is enhanced by a factor of 4.8 and 6.7 for detection of HBsAg and HBeAg, respectively. The limit-of-quantitation of the proposed method is as low as 0.3 fg/mL (0.01 fg/mL) with a wide linear response range of 3 fg/mL-150 ng/mL (0.1 fg/mL-160 ng/mL) for sensing HBsAg (HBeAg). Quantitative determination of HBsAg and HBeAg in human serum samples is performed, showing the applicability of the proposed method for biomarker detection.

Immunoassays Using Optical-Fiber Sensor with All-Directional Chemiluminescent Collection.

While chemiluminescent optical-fiber sensors present essential advantages for immunoassays of biomarkers, an inherent limitation hampering their detection sensitivity is the low collection efficiency of chemiluminescent emission induced by samples, owing to the microspatial scale of an optical fiber for transmission of light via total internal reflection. Here we present a robust approach to overcome this limitation, based on a uniquely designed all-optical chemiluminescent collection vial (CC vial) by using a concave mirror and a coaxial tubular mirror as its bottom and wall, respectively. Using cardiac troponin I (cTnI), a highly specific but low abundance cardiac biomarker, as the test sample, we show that accurate assays can be achieved in a wide linear range of 1-80000 pg/mL. The limit of detection is as low as 0.31 pg/mL, which is about 2 orders of magnitude lower than that obtained by a normal chemiluminescent optical fiber sensor. The method is successfully applied for determination of cTnI in real human serum samples with good accuracy and repeatability. Our study shows that the method can perform an all-directional collection of the chemiluminescent emission, thus, greatly enhancing the collection efficiency and improving the sensitivity of the immunoassays. It is also worth mentioning that the proposed strategy requires neither complex equipment nor additional chemicals, making it a cost-effective and universal approach for ultrasensitive detection of trace biomarkers.

A portable pencil-like immunosensor for point-of-care testing of inflammatory biomarkers.

Portable devices for immunoassays are in high demand for point-of-care testing (POCT) of biomarkers. Here, we report a robust portable pencil-like immunosensor (PPS) platform for the determination of three inflammatory biomarkers including interleukin-6 (IL-6), procalcitonin (PCT), and C-reactive protein (CRP) in human serum samples. The PPS platform is composed of a unique pencil-like optical-fiber-based sensor, a reagent strip consisting of a series of pencil-cap-like wells, and a battery-powered photon counting detector for recording chemiluminescence. The PPS probe moves from well to well with a plug-into/out approach and goes through the immunoassay steps. Each fiber probe in the PPS platform can be sequentially used in up to 10 assays by simply propelling the intact probe out of the pencil body. The PPS platform is well-integrated into a portable suitcase-like device (32 cm × 23 cm × 11 cm) and is only 3 kg in weight. The sensor has good repeatability and can maintain 90% response after 14 days of storage at room temperature, showing its ability for assays in the field. The good linear relationship and efficient dynamic range with a limit-of-detection (LOD) of 1.05 pg/mL for IL-6, 10.64 pg/mL for PCT, and 29.40 ng/mL for CRP are obtained. The assay results are compared with clinical methods, and the findings confirm the high accuracy and precision of the proposed method. The proposed PPS platform is versatile and operable with minimal instruments and technical skills and simplifies the process of immune analysis, thus has great prospects for POCT of biomarkers. Graphical abstract.

Ultra-sensitive capillary immunosensor combining porous-layer surface modification and biotin-streptavidin nano-complex signal amplification: Application for sensing of procalcitonin in serum.

We propose a promising capillary immunosensor by combining porous-layer surface modification of an open-tubular capillary and streptavidin-biotin-peroxidase nano-complex signal amplification of chemiluminescence read-out. The immunosensor, namely Porous Layer Open Tubular-Signal Amplification (PLOT-SA) sensor, is successfully applied for ultra-sensitive sensing of procalcitonin (PCT) in human serum samples. The results show the PLOT-SA sensor exhibits essential features for PCT determination, including a wide linear detection range of 0.1 pg/mL-100 ng/mL, an extremely low limit-of-quantitation of 0.01 pg/mL, excellent intra-day and inter-day stability and reproducibility with RSDs less than 4.5%. Our study provides a reliable and robust approach for developing capillary sensors that can be used in analysis of complex biologic samples.

Optical Fiber-Mediated Immunosensor with a Tunable Detection Range for Multiplexed Analysis of Veterinary Drug Residues.

We describe herein a newly developed chemiluminescent optical fiber immunosensor (OFIS) with a tunable detection range for multiplexed analysis of veterinary drug residues with vastly different concentrations in milk samples. The optical fiber probe is used as a carrier of biorecognition element as well as a transducer, enabling a low-cost compact design, which makes this system suitable for cost-effective on-site detection of the target analytes. Importantly, the synergy between modulation of the length of the optical fiber sensing region and the number of fibers allows performing multiplexed immunoassays in an easily controllable manner over a tunable detection range from pg/mL to µg/mL analyte concentrations. By combining the optical fiber sensor with a nanocomplex signal amplification system, a highly sensitive chemiluminescent OFIS system is demonstrated for the multiplexed assaying of veterinary drug residues in milk samples with linear ranges of 10-(2 × 104) pg/mL for chloramphenicol, 0.5-500 ng/mL for sulfadiazine, and 0.1-300 µg/mL for neomycin. This controllable strategy, based on modulation of the fiber probe, provides a versatile platform for multiplexed quantitative detection of both low-abundance and high-abundance targets, which shows great potential for on-site testing in food safety.

Multiplex immunoassays using surface modification-mediated porous layer open tubular capillary.

We proposed an innovative surface modification-mediated porous layer open tubular (PLOT) capillary, which was modified via an in situ biphasic reaction. This capillary comprised three-dimensional homogeneous and porous structures, which could increase the surface-area-to-volume ratio for antibody immobilization. The PLOT capillary was shown as an ideal immunoreaction base to enhance the sensitivity of immunoassays and shorten analysis time. By connecting two separate PLOT capillaries using a suitable sleeve tube, we can perform multiplex targets detection in the same sample. We developed a sensitive, rapid, and multiplex PLOT capillary-mediated immunosensor for the simultaneous identification of alpha fetoprotein (AFP) and carcinoembryonic antigen (CEA) in clinical serum samples with good accuracy. The detection sensitivity of the PLOT immunosensor improved by 10-fold compared with that of bare-capillary sensor, and the whole analysis could be completed within 1 h. This work suggest that suitable surface modification strategy is an effective tool to improve the analytical performance of conventional immunoassay and our study provided a feasible, sensitive, and multi-target assay for the detection of cancer biomarkers, which would be of valuable application in clinical diagnosis.

Highly uniform porous silica layer open-tubular capillary columns produced via in-situ biphasic sol-Gel processing for open-tubular capillary electrochromatography.

We report a highly uniform porous layer open tubular (PLOT) column for capillary electrochromatography (CEC) analysis. The PLOT column is easily fabricated using a single-step in-situ biphasic reaction, producing homogeneous porous-layer modified surface with ∼240 nm thickness in a 50 µm-id capillary. CEC performance of the PLOT column has been investigated and optimized under various experimental parameters. Using a mixture of naphthalene and biphenyl as the test sample, we show that the PLOT column exhibits good separation efficiency with resolution >3.0 and theoretical plate numbers over 6 × 104, as well as good intra-/inter-day repeatability and column-to-column repeatability. The column has been successfully applied for CEC analysis of three different types of samples without any further modification of the columns, including complicated peptide products from tryptic-digestion of proteins (lysozyme and BSA), ß-blockers (basic samples) and polycyclic aromatic hydrocarbons (neutral samples). Efficient separation has been achieved, which could be attributed to the enhanced surface-to-volume ratio of the PLOT column that will increase the interaction between solid phase and mobile phase in CEC. In addition, base-line separation of neutral samples indicates the reversed phase chromatographic property of the PLOT column, which could be induced by the residue of hexadecyltrimethylammonium bromide used in the fabrication process. Our study show that the present PLOT column is a promising approach that can significantly enhance CEC separation efficiency and could be of potential value in analysis of various different samples.

Online enzyme discrimination and determination of substrate enantiomers based on electrophoretically mediated microanalysis.

We proposed the first application of an electrophoretically mediated microanalysis (EMMA) method for fast online discrimination and determination of substrate enantiomers, which was achieved by just one EMMA assay. Lactate dehydrogenase (LDH)-catalyzed reaction was studied to evaluate the feasibility and performance of the presented method. The L- and D-LDH chiral enzymatic reactions, which are highly stereoselective to the lactate enantiomers, were initiated successively in one capillary, and the corresponding products, nicotinamide adenine dinucleotide (NADH), were online discriminated and detected by UV absorption. Excellent linear dependence of the two NADH peak intensities on the concentration of the corresponding lactate enantiomers was obtained within a wide range of 0.1-10 mM. The limit of detection was 26 µM for D-lactate and 49 µM for L-lactate (S/N = 3). Good repeatability of online chiral discrimination was demonstrated with relative standard deviation (RSD) < 6.3% for NADH peak height and RSD < 1.5% for migration time (n = 5). K(m) values for L- and D-lactate were measured and were consistent with those of the off-line enzyme assays. The presented method was successfully applied to determine the L-/D-lactate in several yogurt and wine samples. Our study shows a new application of the EMMA method utilizing high stereoselectivity of enzymes for fast online chiral analysis.