Replacement-Free Electrodeless Quartz Crystal Microbalance Biosensor Using Nonspecific-Adsorption of Streptavidin on Quartz

High-Frequency Quartz Crystal Microbalance and Dual-Signaling Electrochemical Ratiometric Assays of PTP1B Activity Based on COF@Au@Fc Hybrids

The abnormal expression of protein tyrosine phosphatase 1B (PTP1B) is highly related to several serious human diseases. Therefore, an accurate PTP1B activity assay is beneficial to the diagnosis and treatment of these diseases. In this study, a dual-mode biosensing platform that enabled the sensitive and accurate assay of PTP1B activity was constructed based on the high-frequency (100 MHz) quartz crystal microbalance (QCM) and dual-signaling electrochemical (EC) ratiometric strategy. Covalent-organic framework@gold nanoparticles@ferrocene@single-strand DNA (COF@Au@Fc-S0) was introduced onto the QCM Au chip via the chelation between Zr4+ and phosphate groups (phosphate group of the phosphopeptide (P-peptide) on the QCM Au chip and the phosphate group of thiol-labeled single-stranded DNA (S0) on COF@Au@Fc-S0) and used as a signal reporter. When PTP1B was present, the dephosphorylation of the P-peptide led to the release of COF@Au@Fc-S0 from the QCM Au chip, resulting in an increase in the frequency of the QCM. Meanwhile, the released COF@Au@Fc-S0 hybridized with thiol/methylene blue (MB)-labeled hairpin DNA (S1-MB) on the Au NPs-modified indium-tin oxide (ITO) electrode. This caused MB to be far away from the electrode surface and Fc to be close to the electrode, leading to a decrease in the oxidation peak current of MB and an increase in the oxidation peak current of Fc. Thus, PTP1B-induced dephosphorylation of the P-peptide was monitored in real time by QCM, and PTP1B activity was detected sensitively and reliably using this innovative QCM-EC dual-mode sensing platform with an ultralow detection limit. This platform is anticipated to serve as a robust tool for the analysis of protein phosphatase activity and the discovery of drugs targeting protein phosphatase.

Ultrahigh-Frequency, Wireless MEMS QCM Biosensor for Direct, Label-Free Detection of Biomarkers in a Large Amount of Contaminants

Label-free biosensors, including conventional quartz-crystal-microbalance (QCM) biosensors, are seriously affected by nonspecific adsorption of contaminants involved in analyte solution, and it is exceptionally difficult to extract the sensor responses caused only by the targets. In this study, we reveal that this difficulty can be overcome with an ultrahigh-frequency, wireless QCM biosensor. The sensitivity of a QCM biosensor dramatically improves when the quartz resonator is thinned, which also makes the resonance frequency higher, causing high-speed surface movement. Contaminants weakly (nonspecifically) interact with the quartz surface, but they fail to follow the fast surface movement and cannot be detected as the loaded mass. The targets are, however, tightly captured by the receptor proteins immobilized on the surface, and they can move with the surface, contributing to the loaded mass and decreasing the resonant frequency. We have developed a MEMS QCM biosensor in which an AT-cut quartz resonator, 26 μm thick, is packaged without fixing, and we demonstrate this phenomenon by comparing the frequency changes of the fundamental (∼64 MHz) and ninth (∼576 MHz) modes. At ultrahigh-frequency operation with the ninth mode, the sensor response is independent of the amount of impurity proteins, and the binding affinity is unchanged. We then applied this method to the label-free and sandwich-free, direct detection of C-reactive protein (CRP) in serum and confirmed its applicability.

Microtubule severing by katanin p60 AAA+ ATPase requires the C-terminal acidic tails of both α- and β-tubulins and basic amino acid residues in the AAA+ ring pore

The microtubule (MT) network is highly dynamic and undergoes dramatic reorganizations during the cell cycle. Dimers of α- and β-tubulins rapidly polymerize to and depolymerize from the end of MT fibrils in an intrinsic GTP-dependent manner. MT severing by ATP-driven enzymes such as katanin and spastin contributes significantly to microtubule dynamics, and it has been shown that katanin p60, a AAA+ family protein, has ATPase and MT-severing activities. The mechanism of MT severing by katanin p60 is poorly understood, and the residues in katanin p60 and tubulins important for severing activity were therefore explored in this study. MT-severing activity, but not ATPase activity, was inhibited by mutations of the conserved aromatic residue and the flanking basic residues in the pore region of the katanin p60 hexameric ring. When the acidic residue-rich C-terminal unstructured segment of either α- or β-tubulin was removed, polymerized MTs were resistant to katanin p60 treatment. Interactions between katanin p60 and the mutant MTs, on the other hand, were unaffected. Taken together, these findings led us to propose that the interactions between the positively charged residues of katanin p60 and the acidic tails of both tubulins are essential for efficient severing of MTs.

Ultrafast propagation of β-amyloid fibrils in oligomeric cloud

Interaction between monomer peptides and seeds is essential for clarifying the fibrillation mechanism of amyloid β (Aβ) peptides. We monitored the deposition reaction of Aβ_1–40 peptides on immobilized seeds grown from Aβ_1–42, which caused formation of oligomers in the early stage. The deposition reaction and fibrillation procedure were monitored throughout by novel total-internal-reflection-fluorescence microscopy with a quartz-crystal microbalance (TIRFM-QCM) system. This system allows simultaneous evaluation of the amount of deposited peptides on the surface seeds by QCM and fibril nucleation and elongation by TIRFM. Most fibrils reached other nuclei, forming the fibril network across the nucleus hubs in a short time. We found a fibril-elongation rate two-orders-of-magnitude higher in an oligomeric cloud than reported values, indicating ultrafast transition of oligomers into fibrils.

Wireless-electrodeless quartz-crystal-microbalance biosensors for studying interactions among biomolecules: a review

The mass sensitivity of quartz-crystal microbalance (QCM) was drastically improved by removing electrodes and wires attached on the quartz surfaces. Instead of wire connections, intended vibrations of quartz oscillators were excited and detected by antennas through electromagnetic waves. This noncontacting measurement is the key for ultrahigh-sensitive detection of proteins in liquids as well as quantitative measurements. This review shows the principle of wireless QCMs, their applications to studying interactions among biomolecules and aggregation reactions of amyloid β peptides, and the next-generation MEMS QCM, the resonance acoustic microbalance with naked embedded quartz (RAMNE-Q).