Codeposition Enhances the Performance of Electrochemical Aptamer-Based Sensors

Electrochemical aptamer-based (EAB) sensors, a minimally invasive means of performing high-frequency, real-time measurement of drugs and biomarkers in situ in the body, have traditionally been fabricated by depositing their target-recognizing aptamer onto an interrogating gold electrode using a “sequential” two-step method involving deposition of the thiol-modified oligonucleotide (typically for 1 h) followed by incubation in mercaptohexanol solution (typically overnight) to complete the formation of a stable, self-assembled monolayer. Here we use EAB sensors targeting vancomycin, tryptophan, and phenylalanine to show that “codeposition”, a less commonly employed EAB fabrication method in which the thiol-modified aptamer and the mercaptohexanol diluent are deposited on the electrode simultaneously and for as little as 1 h, improves the signal gain (relative change in signal upon the addition of high concentrations of the target) of the vancomycin and tryptophan sensors without significantly reducing their stability. In contrast, the gain of the phenylalanine sensor is effectively identical irrespective of the fabrication approach employed. This sensor, however, appears to employ binding-induced displacement of the redox reporter rather than binding-induced folding as its signal transduction mechanism, suggesting in turn a mechanism for the improvement observed for the other two sensors. Codeposition thus not only provides a more convenient means of fabricating EAB sensors but also can improve their performance

Addition of Sn–O^<i>i</i>Pr across a CC Bond: Unusual Insertion of an Alkene into a Main-Group-Metal–Alkoxide Bond

An example of unusual addition of a main-group-metal alkoxide across an alkene CC bond was demonstrated with a dimethylvinylsilyl-substituted Sn-POSS complex (POSS = incompletely condensed polyhedral oligomeric silsesquioxane). The structure of the pentacoordinated Sn chelate product was confirmed by ¹H, ¹³C, and ¹¹⁹Sn NMR and ESI-MS

Hierarchical-Coassembly-Enabled 3D-Printing of Homogeneous and Heterogeneous Covalent Organic Frameworks

Covalent organic frameworks (COFs) are crystalline polymers with permanent porosity. They are usually synthesized as micrometer-sized powders or two-dimensional thin films and membranes for applications in molecular storage, separation, and catalysis. In this work, we report a general method to integrate COFs with imine or β-ketoenamine linkages into three-dimensional (3D)-printing materials. A 3D-printing template, Pluronic F127, was introduced to coassemble with imine polymers in an aqueous environment. By limitation of the degree of imine polycondensation during COF formation, the amorphous imine polymer and F127 form coassembled 3D-printable hydrogels with suitable shear thinning and rapid self-healing properties. After the removal of F127 followed by an amorphous-to-crystalline transformation, three β-ketoenamine- and imine-based COFs were fabricated into 3D monoliths possessing high crystallinity, hierarchical pores with high surface areas, good structural integrity, and robust mechanical stability. Moreover, when multiple COF precursor inks were employed for 3D printing, heterogeneous dual-component COF monoliths were fabricated with high spatial precision. This method not only enables the development of COFs with sophisticated 3D macrostructure but also facilitates the heterogeneous integration of COFs into devices with interconnected interfaces at the molecular level

Rapid and annealing-free self-assembly of DNA building blocks for 3D hydrogel chaperoned by cationic comb-type copolymers

<p>The construction and self-assembly of DNA building blocks are the foundation of bottom-up development of three-dimensional DNA nanostructures or hydrogels. However, most self-assembly from DNA components is impeded by the mishybridized intermediates or the thermodynamic instability. To enable rapid production of complicated DNA objects with high yields no need for annealing process, herein different DNA building blocks (Y-shaped, L- and L′-shaped units) were assembled in presence of a cationic comb-type copolymer, poly (L-lysine)-<i>graft</i>-dextran (PLL-<i>g</i>-Dex), under physiological conditions. The results demonstrated that PLL-<i>g</i>-Dex not only significantly promoted the self-assembly of DNA blocks with high efficiency, but also stabilized the assembled multi-level structures especially for promoting the complicated 3D DNA hydrogel formation. This study develops a novel strategy for rapid and high-yield production of DNA hydrogel even derived from instable building blocks at relatively low DNA concentrations, which would endow DNA nanotechnology for more practical applications.</p> <p>This work illustrates a cationic comb-type copolymer to promote the self-assembly of different DNA building units especially of complicated 3D DNA hydrogel with highly efficiency and stability.</p

Highly Selective, Naked-Eye, and Trace Discrimination between Perfect-Match and Mismatch Sequences Using a Plasmonic Nanoplatform

A plasmonic nanoplatform to perform an enzyme-free, naked-eye, and trace discrimination of single-base mutation from fully matched sequence is reported. The nanoplatform showed great potential to enhance catalytic hairpin assembly (CHA) amplification efficiency and biocatalytic activity of hemin/G-quadruplex (DNAzyme). When human immunodeficiency virus (HIV) DNA biomarker was used as the model analyst, a naked-eye detection with high selectivity and high sensitivity down to 10^–17 M in whole serum was achieved by observing red-to-blue color change. Single-base mismatch and two-base mismatch were detected at the low concentrations of 10^–11 and 10^–8 M, respectively. The naked-eye detection based on the enzyme-free plasmonic nanoplatform is expected to have potential applications ranging from quick detection and early diagnostics to point-of-care research

High-Affinity Aptamers for <i>In Vitro</i> and <i>In Vivo</i> Cocaine Sensing

The ability to quantify cocaine in biological fluids is crucial for both the diagnosis of intoxication and overdose in the clinic as well as investigation of the drug’s pharmacological and toxicological effects in the laboratory. To this end, we have performed high-stringency in vitro selection to generate DNA aptamers that bind cocaine with nanomolar affinity and clinically relevant specificity, thus representing a dramatic improvement over the current-generation, micromolar-affinity, low-specificity cocaine aptamers. Using these novel aptamers, we then developed two sensors for cocaine detection. The first, an in vitro fluorescent sensor, successfully detects cocaine at clinically relevant levels in 50% human serum without responding significantly to other drugs of abuse, endogenous substances, or a diverse range of therapeutic agents. The second, an electrochemical aptamer-based sensor, supports the real-time, seconds-resolved measurement of cocaine concentrations in vivo in the circulation of live animals. We believe the aptamers and sensors developed here could prove valuable for both point-of-care and on-site clinical cocaine detection as well as fundamental studies of cocaine neuropharmacology

Supported Tetrahedral Oxo-Sn Catalyst: Single Site, Two Modes of Catalysis

Mild calcination in ozone of a (POSS)-Sn-(POSS) complex grafted on silica generated a heterogenized catalyst that mostly retained the tetrahedral coordination of its homogeneous precursor, as evidenced by spectroscopic characterizations using EXAFS, NMR, UV–vis, and DRIFT. The Sn centers are accessible and uniform and can be quantified by stoichiometric pyridine poisoning. This Sn-catalyst is active in hydride transfer reactions as a typical solid Lewis acid. However, the Sn centers can also create Brønsted acidity with alcohol by binding the alcohol strongly as alkoxide and transferring the hydroxyl H to the neighboring Sn–O–Si bond. The resulting acidic silanol is active in epoxide ring opening and acetalization reactions