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

Zeta potential (A) and sample size of <i>Botryococcus sp</i>. FACGB-762, <i>Chlorella sp</i>. XJ-445 <i>and D</i>. <i>bijugatus</i> XJ-231 under different growth phases.

<p>The <i>d50</i> (particle size at 50% cumulative undersize) termed sample size was reported.</p

Results of Pearson’s correlation between lipid content and the surface properties.

<p>Results of Pearson’s correlation between lipid content and the surface properties.</p

Sample size expressed as <i>d50</i>, contact angles and surface physicochemical properties determined for <i>Botryococcus sp</i>. FACGB-762, <i>Chlorella sp</i>. XJ-445 and <i>D</i>. <i>bijugatus</i> XJ-231.

<p>Sample size expressed as <i>d50</i>, contact angles and surface physicochemical properties determined for <i>Botryococcus sp</i>. FACGB-762, <i>Chlorella sp</i>. XJ-445 and <i>D</i>. <i>bijugatus</i> XJ-231.</p

Sample size distribution of <i>Botryococcus sp</i>. FACGB-762, <i>Chlorella sp</i>. XJ-445 <i>and D</i>. <i>bijugatus</i> XJ-231 at different growth phase.

<p>Sample size distribution of <i>Botryococcus sp</i>. FACGB-762, <i>Chlorella sp</i>. XJ-445 <i>and D</i>. <i>bijugatus</i> XJ-231 at different growth phase.</p

Changes in dry weight during 20-day cultivation of <i>Botryococcus</i> sp. FACGB-762, <i>Chlorella sp</i>. XJ-445 and <i>D</i>. <i>bijugatus</i> XJ-231.

<p>Changes in dry weight during 20-day cultivation of <i>Botryococcus</i> sp. FACGB-762, <i>Chlorella sp</i>. XJ-445 and <i>D</i>. <i>bijugatus</i> XJ-231.</p

Lipid contents of <i>f Botryococcus sp</i>. FACGB-762, <i>Chlorella sp</i>. XJ-445 <i>and D</i>. <i>bijugatus</i> XJ-231 under different growth phases.

<p>Lipid contents of <i>f Botryococcus sp</i>. FACGB-762, <i>Chlorella sp</i>. XJ-445 <i>and D</i>. <i>bijugatus</i> XJ-231 under different growth phases.</p

Potentiometric titration modeling results for <i>Botryococcus sp</i>. FACGB-762, <i>Chlorella sp</i>. XJ-445 <i>and D</i>. <i>bijugatus</i> XJ-231 under different growth phases.

<p>Potentiometric titration modeling results for <i>Botryococcus sp</i>. FACGB-762, <i>Chlorella sp</i>. XJ-445 <i>and D</i>. <i>bijugatus</i> XJ-231 under different growth phases.</p

On-Chip Pressure Generation for Driving Liquid Phase Separations in Nanochannels

In this Article, we describe the generation of pressure gradients on-chip for driving liquid phase separations in submicrometer deep channels. The reported pressure-generation capability was realized by applying an electrical voltage across the interface of two glass channel segments with different depths. A mismatch in the electroosmotic flow rate at this junction led to the generation of pressure-driven flow in our device, a fraction of which was then directed to an analysis channel to carry out the desired separation. Experiments showed the reported strategy to be particularly conducive for miniaturization of pressure-driven separations yielding flow velocities in the separation channel that were nearly unaffected upon scaling down the depth of the entire fluidic network. Moreover, the small dead volume in our system allowed for high dynamic control over this pressure gradient, which otherwise was challenging to accomplish during the sample injection process using external pumps. Pressure-driven velocities up to 3.1 mm/s were realized in separation ducts as shallow as 300 nm using our current design for a maximum applied voltage of 3 kV. The functionality of this integrated device was demonstrated by implementing a pressure-driven ion chromatographic analysis that relied on analyte interaction with the nanochannel surface charges to yield a nonuniform solute concentration across the channel depth. Upon coupling such analyte distribution to the parabolic pressure-driven flow profile in the separation duct, a mixture of amino acids could be resolved. The reported assay yielded a higher separation resolution compared to its electrically driven counterpart in which sample migration was realized using electroosmosis/electrophoresis

Liquid-Phase Cyclic Chemiluminescence for the Identification of Cobalt Speciation

Accurate discrimination of metal species is a significant analytical challenge. Herein, we propose a novel methodology based on liquid-phase cyclic chemiluminescence (CCL) for the identification of cobalt speciation. The CCL multistage signals (In) of the luminol–H2O2 reaction catalyzed by different cobalt species have different decay coefficients k. Thereby, we can facilely identify various cobalt species according to the distinguishable k values, including the complicated and structurally similar cobalt complexes, such as analogues of [Co­(NH3)5X]n+ (X = Cl–, H2O, and NH3), Co­(II) porphyrins, and bis­(2,4-pentanedione) cobalt­(II) derivatives. Especially, the number of substituent atoms also influences the k value greatly, which allows excellent discrimination between complexes that only have a subtle difference in the substituent group. In addition, linear discriminant analysis based on In provides a complementary solution to improve the differentiating ability. We performed density functional theory calculations to investigate the interaction mode of H2O2 over cobalt species. A close negative correlation between the adsorption energy and the k value is observed. Moreover, the calculation of energy evolutions of H2O2 decomposition into a double hydroxide radical shows that a high level of consistency exists between the activation energy barrier and the k value. The results further demonstrate that the decay coefficient of the CCL multistage signal is associated with the catalytic reactivity of the cobalt species. Our work not only broadens the application of chemiluminescence but also provides a complementary technology for speciation analysis