Correction: Microfluidic ELISA employing an enzyme substrate and product species with similar detection properties.

Correction for 'Microfluidic ELISA employing an enzyme substrate and product species with similar detection properties' by Basant Giri et al., Analyst, 2018, 143, 989-998, https://doi.org/10.1039/C7AN01671A.

Microfluidic ELISA employing an enzyme substrate and product species with similar detection properties.

The requirement for an enzyme label to carry out a chemical reaction directly at the signaling region of the enzyme substrate in order to produce a large change in its detectability places a significant constraint on the scope of enzyme-linked immunosorbent assays (ELISAs). In particular, this requirement limits the kinds of enzyme label-substrate couples employable in ELISAs and prevents their independent optimization with respect to the enzyme reaction and the detectability of the enzyme reaction substrate/product. The detection limit and multiplexing capabilities of the assay are consequently restricted in addition to rendering the technique applicable to a narrow range of assay conditions/samples. Attempting to address some of these limitations, the current article describes a microfluidic ELISA method that does not require the enzyme label to act around the signaling region of the substrate molecule. A highly detectable rhodamine based substrate was synthesized to demonstrate the reported assay which upon cleavage by the enzyme label, alkaline phosphatase, transformed from a monoanionic to a monocationic species, both of which had nearly identical fluorescence properties. These species were later separated based on their charge difference using capillary zone electrophoresis in an integrated device yielding a quantitative measure for the analyte (human TNF-α) in our sample. Impressively, the noted approach not only enabled the use of a new kind of enzyme substrate for ELISAs but also allowed the detection of human TNF-α at concentrations over 54-fold lower than that possible on commercial microwell plates primarily due to the better detectability of the rhodamine dye.

Multiplex ELISA in a single microfluidic channel.

In this article, we demonstrate a novel approach to implementing multiplex enzyme-linked immunosorbent assay (ELISA) in a single microfluidic channel by exploiting the slow diffusion of the soluble enzyme reaction product across the different assay segments. The functionality of the reported device is realized by creating an array of ELISA regions within a straight conduit that are selectively patterned with chosen antibodies/antigens via a flow-based method. The different analytes are then captured in their respective assay segments by incubating a 5-µL aliquot of sample in the analysis channel for an hour under flow conditions. Once the ELISA surfaces have been prepared and the enzyme substrate introduced into the analysis channel, it is observed that the concentration of the soluble enzyme reaction product (resorufin) at the center of each assay region grows linearly with time. Further, the rate of resorufin generation at these locations is found to be proportional to the concentration of the analyte being assayed in that segment provided that the ELISA reaction time in the system (τ(R)) is kept much shorter than that required by the resorufin molecules to diffuse across an assay segment (τ(D)). Under the operating condition τ(R) << τ(D), the reported device has been shown to have a 35% lower limit of detection for the target analyte concentration compared with that on a commercial microtiter plate using only a twentieth of the sample volume.

Sodium silicate based sol-gel structures for generating pressure-driven flow in microfluidic channels.

In this article, we report the design of a microchip based hydraulic pump that employs a sodium silicate derived sol-gel structure for generating pressure-driven flow within a microfluidic network. The reported sol-gel structure was fabricated in a chosen location of our device by selectively retaining sodium silicate solution within a sub-micrometer deep segment via capillary forces, and then providing the precursor material appropriate thermal treatment. It was shown that while the molecular weight cut-off for these membranes is at least an order of magnitude smaller than their photo-polymerized counterparts, their electrical conductance is significant. Moreover, unlike their polymeric counterparts these structures were found to be capable of blocking electroosmotic flow, thereby generating a pressure-gradient around their interface with an open microchannel upon application of an electric field across the microchannel-membrane junction. In this work, a fraction of the resulting hydrodynamic flow was successfully guided to an electric field-free analysis channel to implement a pressure-driven assay. Our experiments show that the pressure-driven velocity produced in the analysis channel of our device varied linearly with the voltage applied across the sol-gel membrane and was nearly independent of the cross-sectional dimensions of the membrane and the microfluidic channels. With our current design pressure-driven velocities up to 1.7 mm/s were generated for an applied voltage of 2 kV, which easily covers the range of flow speeds that can minimize the plate height in most microfluidic separations. Finally, the functionality of our device was demonstrated by implementing a reverse phase chromatographic separation in the analysis channel of our device using the pressure-driven flow generated on-chip.

SERS detection of indirect viral DNA capture using colloidal gold and methylene blue as a Raman label.

An indirect capture model assay using colloidal Au nanoparticles is demonstrated for surface enhanced Raman scattering (SERS) spectroscopy detection of DNA. The sequence targeted for capture was derived from the West Nile Virus (WNV) RNA genome and selected on the basis of exhibiting minimal secondary structure formation. Upon incubation with colloidal Au, hybridization complexes containing the WNV target sequence, a complementary capture oligonucleotide conjugated to a strong tethering group and a complementary reporter oligonucleotide conjugated to methylene blue (MB), a Raman label, anchors the resultant ternary complex to Au nanoparticles and positions MB within the required sensing distance for SERS enhancement. The subsequent elicitation of surface enhanced plasmon resonance by laser excitation provides a spectral peak signature profile that is capture-specific and characteristic of the Raman spectrum for MB. Detection sensitivity is in the submicromolar range and was shown to be highest for thiol, and less so for amino, modifications at the 5' terminus of the capture oligonucleotide. Finally, using Quartz Crystal Microbalance-Dissipation as a tool for modeling ternary complex binding to Au surfaces, quantitative measurements of surface mass coverage on Au plated sensor crystals established a positive correlation between levels of ternary complex adsorption and their correspondent levels of SERS signal intensification. Adapted to a compact Raman spectrometer, which is designed for analyte detection in capillary tubes, this assay provides a rapid, mobile and cost effective alternative to expensive spectroscopic instrumentation, which is often restricted to analytical laboratories.

Unusual, bifurcated photoreactivity of a rhenium(I) carbonyl complex of triethynylphosphine.

Preparations of the first metal complexes of triethynylphosphine (TEP) are described. They are of the type fac-Re(bpy)(CO)(3)(TEP)(+) (1) and cis,trans-[Re(bpy)(CO)(2)(TEP)L](n)(+) (CH(3)CN, n = 1, complex 2; Cl, n = 0, complex 3), where bpy is 2,2'-bipyridine. Complex 1 displays unusual photochemical behavior compared to analogous fac-[Re(bpy)(CO)(3)(PR(3))](+) complexes in that it emits from a state that has pi-pi* character but undergoes competitive photosubstitution of both TEP and CO. Density functional theory (DFT)/time-dependent DFT calculations predict that the lowest emitting state should, in fact, have pi-pi* character.

Phosphonate lipid tubules II.

We describe a new chiral tubule-forming lipid in which the C-O-P phosphoryl linkage of the archetypal tubule-forming molecule, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine, "DC(8,9)PC", is replaced by a C-P linkage. Tubule formation with this phosphonate analogue proceeds under the same mild conditions as with DC(8,9)PC and produces similar yields, but synchrotron small-angle X-ray scattering, atomic force microscopy, and optical microscopy show the new tubules to have diameters 1.94 times as great, to be significantly shorter, and to be thinner-walled. A significant portion of the enantiomerically pure chiral phosphonate precipitate is in the form of stable open helices, and these helices are divided almost evenly between left- and right-handed members.