Force Measurement for the Interaction between Cucurbit[7]uril and Mica and Self-Assembled Monolayer in the Presence of Zn2+ Studied with Atomic Force Microscopy

Electrochemical sensor based on the synergy between Cucurbit[8]uril and 2D-MoS2 for enhanced melatonin quantification

We present the development of an electrochemical sensor towards melatonin determination based on the synergistic effect between MoS₂ nanosheets and cucurbit[8]uril. For the sensor construction cucurbit[8]uril suspensions were prepared in water, and MoS₂ nanosheets were obtained by liquid exfoliation in ethanol:water. The sensing platform was topographically characterized by Atomic Force Microscopy. Electrochemical Impedance Spectroscopy experiments allowed us to study the charge transfer process during melatonin oxidation. Moreover, stoichiometry of the resulting complex has also been determined. After the optimization of the sensor construction and the experimental variables involved in the Differential Pulse Voltammetric response of melatonin, detection limit of 3.80 × 10^-7 M, relative errors minor than 3.8% and relative standard deviation lower than 4.4% were obtained. The proposed sensor has been successfully applied to melatonin determination in pharmaceutical and biological samples as human urine and serum, with very good recoveries ranging from 90 to 102%.

Direct Measurements of the Cobalt-thiolate Bonds Strength in Rubredoxin by Single-Molecule Force Spectroscopy

Cobalt is a trace transition metal. Although it is not abundant on earth, tens of cobalt-containing proteins exist in life. Moreover, the characteristic spectrum of Co(II) ion makes it a powerful probe for the characterization of metal-binding proteins through the formation of cobalt-ligand bonds. Since most of these natural and artificial cobalt-containing proteins are stable, we believe that these cobalt-ligand bonds in the protein system are also mechanically stable. To prove this, we used atomic force microscopy-based single-molecule force spectroscopy (AFM-SMFS) to directly measure the rupture force of Co(II)-thiolate bond in Co-substituted rubredoxin (CoRD). By combining the chemical denature/renature method for building metalloprotein and cysteine coupling-based polyprotein construction strategy, we successfully prepared the polyprotein sample (CoRD) n suitable for single-molecule study. Thus, we quantified the strength of Co(II)-thiolate bonds in  rubredoxin with a rupture force of ~140 pN, revealing that the bond is a stable chemical bond. In addition, the Co-S bond is more labile than the Zn-S bond in proteins, similar to the result from the metal-competing titration experiment.

Supramolecular Chemotherapy: Noncovalent Bond Synergy of Cucurbit[7]uril against Human Colorectal Tumor Cells

Supramolecular chemotherapy has drawn increasing interest due to its ability to improve the efficiency of antitumor drugs and fewer associated toxic side effects. In this study, the smart supramolecular cargo, the doxorubicin-ZnO-cucurbit[7]uril (CDZ) nanocomplex, was constructed through ion-dipole interactions between cucurbit[7]uril {CB[7]} and doxorubicin-ZnO (dox-ZnO). The binding affinity of CB[7] and dox-ZnO was determined to be 10⁴ M^-1 by isothermal titration calorimetry. Importantly, spermine had a stronger binding affinity (10⁶ M^-1) with CB[7] than dox-ZnO through host-guest interactions. In the tumor microenvironment, spermine disassembled the CDZ nanocomplex, and dox was released from the nanocomplex by XRD, UV-visible spectra, and contact angle analysis. Compared to the single drug dox, the CDZ nanocomplex was demonstrated to possess higher activity of killing colorectal tumor cells by confocal laser scanning microscopy and cytotoxicity, which could be attributed to spermine concentration, spermine synthase, free radical damage, and G₁ cell cycle arrest. Overall, the supramolecular delivery of dox can enhance the inhibition of human colorectal tumor cell proliferation and reduce cytotoxicity in human myocardial cells through the noncovalent bond synergy of {CB[7]}.

Recent advances in techniques for fabrication and characterization of nanogap biosensors: A review

Nanogap biosensors have fascinated researchers due to their excellent electrical properties. Nanogap biosensors comprise three arrays of electrodes that form nanometer-size gaps. The sensing gaps have become the major building blocks of several sensing applications, including bio- and chemosensors. One of the advantages of nanogap biosensors is that they can be fabricated in nanoscale size for various downstream applications. Several studies have been conducted on nanogap biosensors, and nanogap biosensors exhibit potential material properties. The possibilities of combining these unique properties with a nanoscale-gapped device and electrical detection systems allow excellent and potential prospects in biomolecular detection. However, their fabrication is challenging as the gap is becoming smaller. It includes high-cost, low-yield, and surface phenomena to move a step closer to the routine fabrications. This review summarizes different feasible techniques in the fabrication of nanogap electrodes, such as preparation by self-assembly with both conventional and nonconventional approaches. This review also presents a comprehensive analysis of the fabrication, potential applications, history, and the current status of nanogap biosensors with a special focus on nanogap-mediated bio- and chemical sonsors.