Microfluidic Magnetic Spatial Confinement Strategy for the Enrichment and Ultrasensitive Detection of MCF‑7 and Escherichia coli O157:H7

A microfluidic magnetic spatial confinement strategy was developed and employed to realize an ultrasensitive cell immunoassay. The straight confined channels in poly(dimethylsiloxane)-glass hybrid microchips were used as the enrichment and detection chambers for the proposed microfluidic magnetic cell immunoassays (μMCI). To accomplish the μMCI, prepared magnetic cell immunocomplexes were introduced into microchannels and preconcentrated in the detection zone under a permanent magnet. The magnetic cell immunocomplexes were constructed from aptamer-/antibody-coated magnetic beads and antibody-linked horseradish peroxidase-labeled target cells to guarantee the specificity and enhance the detection signal generated from the enzyme reaction. The sensitivity enhancement of μMCI was confirmed in a one-dimensional space confined microchamber, especially in the analysis of cells having more enzyme conjugating sites on their surface. This spatial confinement strategy based μMCI was then applied for model cell detection in the microchannel, the limits of detection (LODs) were 2 cells/mL for MCF-7 and 34 colony-forming unit/mL for Escherichia coli O157:H7 (E. coli O157:H7), which corresponded to up to 1202-fold LOD sensitivity improvement compared to the results of the similar immunoassays in microwell plates. The satisfactory selectivity and reproducibility of the strategy were also obtained. Moreover, it enabled rare MCF-7 detection in whole blood and E. coli O157:H7 detection in milk after time-shortened incubation. Constructing an appropriate confined space, this strategy can be extended to detect various cells with higher sensitivity, which provides a valuable approach for rare cell detection in practical applications

Hybrid Field-Assisted Solid–Liquid–Solid Dispersive Extraction for the Determination of Organochlorine Pesticides in Tobacco with Gas Chromatography

A novel one-step sample preparation technique termed hybrid field-assisted solid–liquid–solid dispersive extraction (HF-SLSDE) was developed in this study. A simple glass system equipped with a condenser was designed as an extraction vessel. The HF-SLSDE technique was a three-phase dispersive extraction approach. Target analytes were extracted from the sample into the extraction solvent enhanced by the hybrid field. Meanwhile, the interfering components were adsorbed by dispersing sorbent. No cleanup step preceded chromatographic analysis. The efficiency of the HF-SLSDE approach was demonstrated in the determination of organochlorine pesticide (OCP) residues in tobacco with a gas chromatography-electron capture detector (GC-ECD). Various operation conditions were studied systematically. Low detection limits (0.3–1.6 μg/kg) and low quantification limits (1.0–4.5 μg/kg) were achieved under the optimized conditions. The recoveries of OCPs ranged from 70.2% to 118.2%, with relative standard deviations of <9.6%, except for the lowest fortification level. Because of the effect of the hybrid field, HF-SLSDE showed significant predominance compared with other extraction techniques. The dispersing sorbent with good cleanup ability used in this study was also found to be a microwave absorption medium, which could heat the nonpolar extraction solvent under microwave irradiation. Different microstructures of tobacco samples before and after extractions demonstrated the mechanism of HF-SLSDE was based on an explosion at the cell level. According to the results, HF-SLSDE was proved to be a simple and effective sample preparation method for the analysis of pesticide residues in solid samples and could potentially be extended to other nonpolar target analytes in a complex matrix

Simple and Excellent Selective Chemiluminescence-Based CS₂ On-Line Detection System for Rapid Analysis of Sulfur-Containing Compounds in Complex Samples

To study the interesting chemical reaction phenomenon can greatly contribute to the development of an innovative analytical method. In this paper, a simple CL reaction cell was constructed to study the chemiluminescence (CL) emission from the thermal oxidation of carbon disulfide (CS₂). We found that the CL detection of CS₂ exhibits unique characteristics of excellent selectivity and rapid response capacity. Experimental investigations together with theoretical calculation were performed to study the mechanism behind the CL reaction. The results revealed that the main luminous intermediates generated during the thermal degradation of CS₂ are SO₂* and CO₂*. Significantly, this CL emission phenomenon has a wide application due to many sulfur-containing compounds that can convert to CS₂ under special conditions. On the basis of this scheme, a CS₂-generating and detection system was developed for rapid measurement of CS₂ or other compounds that can convert to CS₂. The usefulness of the system was demonstrated by measuring dithiocarbamate (DTC) pesticides (selected mancozeb as a representative analyte) based on the evolution of CS₂ in spiked agricultural products. Results showed that the system allows online and large volume detection of CS₂ under nonequilibrium condition, which greatly reduces the analytical time. The concentrations of mancozeb in the spiked samples were well-quantified with satisfied recoveries of 76.9–97.3%. The system not only addresses the urgent need for rapid in-field screening of DTC residues in foodstuffs but also opens a new opportunity for the fast, convenient, and cost-effective detection of CS₂ and some other sulfur-containing compounds in complex samples

Aptamer Recognition Induced Target-Bridged Strategy for Proteins Detection Based on Magnetic Chitosan and Silver/Chitosan Nanoparticles Using Surface-Enhanced Raman Spectroscopy

Poor selectivity and biocompability remain problems in applying surface-enhanced Raman spectroscopy (SERS) for direct detection of proteins due to similar spectra of most proteins and overlapping Raman bands in complex mixtures. To solve these problems, an aptamer recognition induced target-bridged strategy based on magnetic chitosan (MCS) and silver/chitosan nanoparticles (Ag@CS NPs) using SERS was developed for detection of protein benefiting from specific affinity of aptamers and biocompatibility of chitosan (CS). In this process, one aptamer (or antibody) modified MCS worked as capture probes through the affinity binding site of protein. The other aptamer modified Raman report molecules encapsulated Ag@CS NPs were used as SERS sensing probes based on the other binding site of protein. The sandwich complexes of aptamer (antibody)/protein/aptamer were separated easily with a magnet from biological samples, and the concentration of protein was indirectly reflected by the intensity variation of SERS signal of Raman report molecules. To explore the universality of the strategy, three different kinds of proteins including thrombin, platelet derived growth factor BB (PDGF BB) and immunoglobulin E (lgE) were investigated. The major advantages of this aptamer recognition induced target-bridged strategy are convenient operation with a magnet, stable signal expressing resulting from preventing loss of report molecules with the help of CS shell, and the avoidance of slow diffusion-limited kinetics problems occurring on a solid substrate. To demonstrate the feasibility of the proposed strategy, the method was applied to detection of PDGF BB in clinical samples. The limit of detection (LOD) of PDGF BB was estimated to be 3.2 pg/mL. The results obtained from human serum of healthy persons and cancer patients using the proposed strategy showed good agreement with that of the ELISA method but with wider linear range, more convenient operation, and lower cost. The proposed strategy holds great potential in highly sensitive and selective analysis of target proteins in complex biological samples

Development of a Cyclic System for Chemiluminescence Detection

In this paper, we described a new concept of cyclic chemiluminescence (CCL) detection, and a homemade system was designed to realize such detection. The direction of the carrier in the CCL system is in a state of periodical change that can trigger a succession of chemiluminescence (CL) reactions in a single sample injection. Therefore, in contrast to the traditional CL detection, which only records a single signal, CCL allows us to obtain multistage signals. To evaluate the new method, the cataluminescence (CTL) reaction of the volatile organic compounds (VOCs) on a nanosized catalyst was selected as the analytical model. We found that each CCL reaction has a unique exponential decay equation (EDE) to describe the change law of its multistage signals. Further study showed that the initial amount (<i>A</i>) of the EDE is linear with the analyte concentration, while the decay coefficient (<i>k</i>) is a characteristic constant for a given reaction. The formation mechanism of the exponential function and the determinants of the decay coefficient were discussed in detail. As a distinct application, CCL is capable of rapidly discriminating various analytes and even structural isomers

Miniaturized Thermal-Assisted Purge-and-Trap Technique Coupling with Surface-Enhanced Raman Scattering for Trace Analysis of Complex Samples

It still remains a great challenge for quantification of trace analytes in complex samples by surface-enhanced Raman scattering (SERS) technique due to potential matrix influence or weak SERS responses of analytes. In this work, a miniaturized thermal-assisted purge-and-trap (MTAPT) device was designed and developed to eliminate matrix influence coupled with derivatization method before SERS analysis. The design of MTAPT chamber was optimized based on quantitative calculation of its dead volume by computational fluid dynamics simulation. The small straight chamber was selected as an optimized design with a recovery of 96.1% for formaldehyde. The practical feasibility of MTAPT was validated based on four real analytical applications including phenthiol in industrial water, formaldehyde in flour, sulfion in wastewater, and methanol in industrial alcohol. The results showed that SERS responses of all analytes dramatically increased by eliminating sample matrices after MTAPT process. Phenthiol, formaldehyde, sulfion, and methanol in real samples could be accurately quantified with recoveries of 80.9–110.0%, and the analytical results were validated by corresponding standard methods. The time consumption of MTAPT-SERS for real sample analysis including sample preparation and determination was within 16 min. It is highly expected that the combination of MTAPT technique with portable SERS instrument can greatly expand the range of SERS analysis. The proposed MTAPT-SERS method has high potential for on-site analysis of complex samples

Conjugated Microporous Polymers with Built-In Magnetic Nanoparticles for Excellent Enrichment of Trace Hydroxylated Polycyclic Aromatic Hydrocarbons in Human Urine

Conjugated microporous polymers (CMPs), linked by a covalent bond to form an extension of the aromatic ring skeleton, are microporous materials characterized by a highly conjugated structure and high stability. The present study reported on a novel strategy for the synthesis of CMPs with built-in magnetic nanoparticles for excellent enrichment of trace hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) in human urine. We modified Fe₃O₄ nanoparticles with boronic acid groups and then reacted the nanoparticles with reactive monomers of polyphenylene conjugated microporous polymer (PP-CMP) to anchor the magnetic components in the PP-CMP framework. Chemical bonding between Fe₃O₄ nanoparticles and PP-CMP networks, together with equally firm covalent linkage and rigidity of the PP-CMP network, endows the magnetic PP-CMP with remarkable chemical stability and durability, even in harsh conditions. Magnetic PP-CMP has the characteristics of high conjugation ability, highly porous structure, and magnetism, which makes it an ideal magnetic adsorbent for trace analytes with aromatic conjugation structure. The adsorption mechanism of OH-PAHs on magnetic PP-CMP was investigated and demonstrated that hydrophobic interaction was important for the contribution of interaction between adsorbents and target analytes, together with the assistance of π–π stacking interaction. For the application, the magnetic PP-CMP was used for the enrichment of trace OH-PAHs in human urine of both smokers and nonsmokers in combination with high-performance liquid chromatography with fluorescence detection (HPLC-FLD). It showed good selectivity and excellent sensitivity to these OH-PAHs. Their detection limits were low and in the range of 0.01–0.08 μg·L^–1. The OH-PAHs were detected with different amounts from 0.054 to 0.802 μg·L^–1 in urine samples from smokers and nonsmokers. The recoveries were found to be 76.0%–107.8%. The results indicate that the magnetic PP-CMP offers an efficient enrichment method for trace OH-PAHs in human urine

Organic Building Block Based Microporous Network SNW‑1 Coating Fabricated by Multilayer Interbridging Strategy for Efficient Enrichment of Trace Volatiles

Microporous organic polymers (MOPs) are an emerging class of functional porous materials for diverse potential applications. Typically, tailored microporous structures of MOPs are generated by linkages of organic polymerizable monomer building blocks, providing high permanent porosity and excellent stability. Herein, we reported the first example of the application of organic building block based MOPs (OBB-MOPs) as efficient enrichment media for sample preparation. A novel multilayer interbridging strategy was proposed to fabricate OBB-MOP coatings, and hereby SNW-1 (a kind of OBB-MOPs) was coated on silica substrate with well-controlled thickness. Strong covalent bonds throughout the network and interlayer bridging improved the durability of the coating significantly. Outstanding chemical stability was observed in diverse solvents as well as solutions with a wide range of pH or high ionic strength and even under extremely harsh conditions like boiling water. The SNW-1 coating possessed a microporous network structure constructed of conjugated and nitrogen-rich building blocks. Thus, the coating exhibited a superior enrichment performance of polycyclic aromatic hydrocarbons and volatile fatty acids (VFAs) over commercial coatings based on interactions including π–π affinity and acid–base interaction. For further application, this coating was combined with gas chromatography/mass spectrometry for the noninvasive analysis of VFAs from tea leaf and tobacco shred samples. The low detection limits of 0.014–0.026 μg/L were achieved with the relative standard deviations (RSDs) between 4.3 and 9.0%. Consequently, trace original VFAs from the samples were detected. Good recoveries were obtained in the range of 90–129% and 77–118% with the corresponding RSDs (<i>n</i> = 3) of 2.6–9.3% and 1.9–10%, respectively

Amino Nitrogen Quantum Dots-Based Nanoprobe for Fluorescence Detection and Imaging of Cysteine in Biological Samples

Fluorescent amino nitrogen quantum dots (aN-dots) were synthesized by microwave-assisted method using 2-azidoimidazole and aqueous ammonia. The aN-dots have a nitrogen component up to 40%, which exhibit high fluorescence quantum yield, good photostability, and excellent biocompatibility. We further explored the use of the aN-dots combined with AuNPs as a nanoprobe for detecting fluorescently and imaging of cysteine (Cys) in complex biological samples. In this sensing system, the fluorescence of aN-dots was quenched significantly by gold nanoparticles (AuNPs), while the addition of Cys can lead to the fluorescence signal recovery. Furthermore, we have demonstrated that this strategy can offer a rapid and selective detection of Cys with a good linear relationship in the range of 0.3–3.0 μmol/L. As expected, this assay was successfully applied to the detection of Cys in human serum and plasma samples with recoveries ranging from 90.0% to 106.7%. Especially, the nanoprobe exhibits good cell membrane permeability and excellent biocompatibility by CCK-8 assay, which is favorable for bioimaging applications. Therefore, this fluorescent probe ensemble was further used for imaging of Cys in living cells, which suggests our proposed method has strong potential for clinical diagnosis. As a novel member of the quantum-dot family, the aN-dots hold great promise to broaden applications in biological systems

Fabrication of Gold Nanoparticle-Embedded Metal–Organic Framework for Highly Sensitive Surface-Enhanced Raman Scattering Detection

Surface-enhanced Raman scattering (SERS) signals strongly rely on the interactions and distance between analyte molecules and metallic nanostructures. In this work, the use of a gold nanoparticle (AuNP)-embedded metal–organic framework was introduced for the highly sensitive SERS detection. The AuNPs were in situ grown and encapsulated within the host matrix of MIL-101 by a solution impregnation strategy. The as-synthesized AuNPs/MIL-101 nanocomposites combined the localized surface plasmon resonance properties of the gold nanoparticles and the high adsorption capability of metal–organic framework, making them highly sensitive SERS substrates by effectively preconcentrating analytes in close proximity to the electromagnetic fields at the SERS-active metal surface. We discussed the fabrication, physical characterization, and SERS activity of our novel substrates by measuring the Raman signals of a variety of model analytes. The SERS substrate was found to be highly sensitive, robust, and amiable to several different target analytes. A SERS detection limit of 41.75 and 0.54 fmol for Rhodamine 6G and benzadine, respectively, was demonstrated. The substrate also showed high stability and reproducibility, as well as molecular sieving effect thanks to the protective shell of the metal–organic framework. Subsequently, the potential practical application of the novel SERS substrate was evaluated by quantitative analysis of organic pollutant <i>p</i>-phenylenediamine in environmental water and tumor marker alpha-fetoprotein in human serum. The method showed good linearity between 1.0 and 100.0 ng/mL for <i>p</i>-phenylenediamine and 1.0–130.0 ng/mL for alpha-fetoprotein with the correlation coefficients of 0.9950 and −0.9938, respectively. The recoveries ranged from 80.5% to 114.7% for <i>p</i>-phenylenediamine in environmental water and 79.3% to 107.3% for alpha-fetoprotein in human serum. These results foresee promising application of the novel metal–organic framework based composites as sensitive SERS-active substrates in both environmental and clinical samples