Lateral flow assay for carbohydrate antigen 19–9 in whole blood by using magnetized carbon nanotubes

The authors describe a rapid, low-cost and sensitive approach for the determination of carbohydrate antigen 19–9 (CA 19–9) in whole blood by using magnetized carbon nanotubes (MCNTs) and a lateral flow strip biosensor (LFSB). MCNTs were synthesized by depositing magnetite (Fe₃O₄) nanoparticles on multiwalled carbon nanotubes (CNTs) via co-precipitation of ferric and ferrous ions within a dispersion of shortened multiwalled CNTs. Antibody against CA 19–9 (Ab₁) was covalently immobilized on the MCNTs and were used to capture CA 19–9 in blood. After magnetic separation, the MCNT-Ab₁-CA 19–9 complexes are applied to the LFSB, in which a capture antibody (Ab₂) and a secondary antibody (Ab₃) are immobilized on the test zone and control zone of the LFSB, respectively. The captured MCNTs on the test zone and control zone are producing characteristic brown bands, and this enables CA 19–9 to be visually detected. Quantitation is accomplished by reading the intensities of the bands with a portable strip reader. Under optimized conditions, the assay has a detection limit as low as 30 U·mL^?1 of CA19–9 in blood. This is below the cutoff value (37 U mL^?1) of CA 19–9. The assay duration for blood samples is 35 min. In our perception, the assay represents a rapid and low-cost tool for rapid determination of CA19–9 in blood that holds promise for clinical applications, particularly in limited resource settings.

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Graphical abstract Schematic of a rapid, low-cost and sensitive approach to detect carbohydrate antigen 19–9 (CA 19–9) in whole blood by using magnetized carbon nanotubes (MCNT) and a lateral flow strip biosensor. The approach offers new opportunities for detecting protein markers in whole blood avoiding sample purification and pre-treatment. This may lead to a new tool for disease diagnosis and monitoring disease recurrence.

     

A homologous series of eunicellin-based diterpenes from Acalycigorgia sp. characterised by tandem mass spectrometry

The discovery and structure determination of a homologous series of eunicellin-based diterpenes from the gorgonian Acalycigorgia sp. is described. Extensive use was made of 1D and 2D NMR data to determine the structure of the diterpene skeleton. The relative stereochemistry was confirmed via the use of NOE data in conjunction with molecular modelling. A series of homologues were identified using a combination of product and precursor ion scanning modes in tandem mass spectrometry. This powerful technique afforded excellent clarification to aid the analysis of the complex mass spectral data.     

SAM‐II Riboswitch Samples at least Two Conformations in Solution in the Absence of Ligand: Implications for Recognition

Conformational equilibria are increasingly recognized as pivotal for biological function. Traditional structural analyses provide a static image of conformers in solution that sometimes present conflicting views. From ¹³C and ¹H chemical exchange saturation transfer experiments, in concert with ligation and selective labeling strategies, we show that in the absence of metabolite, a Mg²⁺ (0–0.5 mm )‐bound apo SAM‐II riboswitch RNA exists in a minor (≈10 %) partially closed state that rapidly exchanges with a predominantly (≈90 %) open form with a lifetime of ≈32 ms. The base and sugar (H6,C6, H1′,C1′) chemical shifts of C43 for the dominant conformer are similar to those of a free CMP, but those of the minor apo species are comparable to shifts of CMPs in helical RNA regions. Our results suggest that these transient, low populated states stabilized by Mg²⁺ will likely enhance rapid ligand recognition and, we anticipate, will play potentially ubiquitous roles in RNA signaling.     

Bistable perpendicular switching with in-plane spin polarization and without external fields

To-date, all experiments switching perpendicular magnetic anisotropy (PMA) materials with in-plane spin polarization require external B-fields. Here, in two approaches, it is shown that with Rashba-type in-plane spin polarization and PMA, bistable switching is achievable without external B  -fields, and at currents on the order of 10⁷ A/cm²${10}^7\text{A}/{\text{cm}}^2$, consistent with recent experiments. Utilization of PMA is primarily discussed, demonstrating the potential for two possibilities: (1) in-plane polarization as a ‘natural’ candidate for precessional switching and (2) bistable switching using a tilted anisotropy axis. Both are shown to lead to stable perpendicular switching without an external B-field, even though spin polarization is in-plane.     

Discovery of a Single Monooxygenase that Catalyzes Carbamate Formation and Ring Contraction in the Biosynthesis of the Legonmycins

Pyrrolizidine alkaloids (PAs) are a group of natural products with important biological activities. The discovery and characterization of the multifunctional FAD‐dependent enzyme LgnC is now described. The enzyme is shown to convert indolizidine intermediates into pyrrolizidines through an unusual ring expansion/contraction mechanism, and catalyze the biosynthesis of new bacterial PAs, the so‐called legonmycins. By genome‐driven analysis, heterologous expression, and gene inactivation, the legonmycins were also shown to originate from non‐ribosomal peptide synthetases (NRPSs). The biosynthetic origin of bacterial PAs has thus been disclosed for the first time.     

A Robust Method for Estimating Cross-Relaxation Rates from Simultaneous Fits to Build-Up and Decay Curves

This paper introduces a novel computational method for estimating relaxation rates among pairs of spin orders. This method simultaneously estimates all the auto- and cross-relaxation rates from the same measurements, and avoids the ill-conditioning problems associated with multiexponential fits. The method models the relaxation dynamics by a system of linear differential equations, and assumes that measurements of the spin orders have been made at an equally spaced sequence of time points. It computes a nonlinear least-squares fit of the exponential of the rate matrix at the shortest time point to these measurements. Preliminary estimates of the exponential matrix and initial spin orders from which to start the computations are obtained by solving simpler linear-least-squares problems. The performance of the method on simulated 2 × 2 test problems indicates that when measurements at eight or more equally spaced times spanning the maximum and inflection points of the build-up curves are available, the relative errors in the rates are usually less than the relative errors in the measurements. The method is further demonstrated by applying it to the problem of determining the cross correlation-induced cross-relaxation rates between the in-phase and antiphase coherence of the amide groups in the¹⁵N-labeled protein oxidized flavodoxin. Finally, the possibility of extending the method to other kinds of relaxation measurements and larger spin systems is discussed.     

Legonoxamines A-B,two new hydroxamate siderophores from the soil bacterium, Streptomyces sp. MA37

Two new siderophores belonging to the hydroxamate class, Legonoxamine A (1) and B (2) have been isolated from the soil bacterium, Streptomyces sp. MA37, together with one known compound, desferrioxamine B (3). Their structures were elucidated based on spectroscopic methods including 1D, 2D NMR, MS, as well as by comparison with the relevant literatures. To our knowledge, this is the first report describing a siderophore containing the N-hydroxyl phenylacetyl cadaverine (HPAC) moiety in the structure. Based on bioinformatics analysis and previous knowledge of the biosynthesis of the hydroxamate-type siderophore, the biosynthetic gene cluster (lgo) responsible for the production of 1–3 was identified in the annotated genome of the producing strain. The supplementation of phenylacetate and benzoate analogues with meta substitution into the cultures of Streptomyces sp. MA37 resulted in the production of new legonoxamine A derivatives as observed in LC-HR-ESIMS, suggesting that the legonoxamine biosynthetic pathway has a good degree of natural flexibility of accepting unnatural precursors with different functional groups.     

Aptamers with Tunable Affinity Enable Single-Molecule Tracking and Localization of Membrane Receptors on Living Cancer Cells

Tumor cell-surface markers are usually overexpressed or mutated protein receptors for which spatiotemporal regulation differs between and within cancers. Single-molecule fluorescence imaging can profile individual markers in different cellular contexts with molecular precision. However, standard single-molecule imaging methods based on overexpressed genetically encoded tags or cumbersome probes can significantly alter the native state of receptors. We introduce a live-cell points accumulation for imaging in nanoscale topography (PAINT) method that exploits aptamers as minimally invasive affinity probes. Localization and tracking of individual receptors are based on stochastic and transient binding between aptamers and their targets. We demonstrated single-molecule imaging of a model tumor marker (EGFR) on a panel of living cancer cells. Affinity to EGFR was finely tuned by rational engineering of aptamer sequences to define receptor motion and/or native receptor density.     

An explicit derivation of a relation between magnetization M and saturation magnetization Ms

An explicit relationship between a magnetization vector M and its saturation magnetization M_s is derived using the definition of M along with assumptions of the continuum exchange theory. The obtained expression is found to be an extension of the commonly used fixed-length constraint and represents the continuous analog of it for the elementary moment per unit volume. The derivation of this relation is carried out in detail and important potential implications relating to equations for M are also highlighted.