Real-time monitoring of dephosphorylation process of phosphopeptide and rapid assay of PTP1B activity based on a 100 MHz QCM biosensing platform

The misregulation of protein phosphatases is a key factor in the development of many human diseases, notably cancers. Here, based on a 100 MHz quartz crystal microbalance (QCM) biosensing platform, the dephosphorylation process of phosphopeptide (P-peptide) caused by protein tyrosine phosphatase 1B (PTP1B) was monitored in real time for the first time and PTP1B activity was assayed rapidly and sensitively. The QCM chip, coated with a gold (Au) film, was used to immobilized thiol-labeled single-stranded 5'-phosphate-DNAs (P-DNA) through Au-S bond. The P-peptide, specific to PTP1B, was then connected to the P-DNA via chelation between Zr4+ and phosphate groups. When PTP1B was injected into the QCM flow cell where the P-peptide/Zr4+/MCH/P-DNA/Au chip was placed, the P-peptide was dephosphorylated and released from the Au chip surface, resulting in an increase in the frequency of the QCM Au chip. This allowed the real-time monitoring of the P-peptide dephosphorylation process and sensitive detection of PTP1B activity within 6 min with a linear detection range of 0.01-100 pM and a detection limit of 0.008 pM. In addition, the maximum inhibitory ratios of inhibitors were evaluated using this proposed 100 MHz QCM biosensor. The developed 100 MHz QCM biosensing platform shows immense potential for early diagnosis of diseases related to protein phosphatases and the development of drugs targeting protein phosphatases.

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.

Bifunctional Magnetic Fe3O4@Cu2O@TiO2 Nanosphere-Mediated Dual-Mode Assay of PTP1B Activity Based on Photocurrent Polarity Switching and Nanozyme-Engineered Biocatalytic Precipitation Strategies

Dysregulation of protein phosphatases is associated with the progression of various human diseases and cancers. Herein, a photoelectrochemical (PEC)-quartz crystal microbalance (QCM) dual-mode sensing platform was developed for protein tyrosine phosphatase 1B (PTP1B) activity assay based on bifunctional magnetic Fe₃O₄@Cu₂O@TiO₂ nanosphere-mediated PEC photocurrent polarity switching and QCM signal amplification strategies. The PTP1B-specific phosphopeptide (P-peptide) with a cysteine end was designed and immobilized onto the QCM Au chip via the Au-S bond. Subsequently, the Fe₃O₄@Cu₂O@TiO₂ nanosphere was connected to the P-peptide via the specific interaction between the phosphate group on the P-peptide and TiO₂. After incubation with PTP1B, the dephosphorylation of the P-peptide occurred, causing some Fe₃O₄@Cu₂O@TiO₂ nanospheres to be released from the chip surface. The released magnetic Fe₃O₄@Cu₂O@TiO₂ nanospheres (labeled as R-Fe₃O₄@Cu₂O@TiO₂) were quickly separated via magnetic separation technology and attached to the Bi₂S₃-decorated magnetic indium-tin oxide (Bi₂S₃/MITO) electrode by magnetic force, inducing the switch of the photocurrent polarity of the electrode from anodic current (the Bi₂S₃/MITO electrode) to cathodic current (the R-Fe₃O₄@Cu₂O@TiO₂/Bi₂S₃/MITO electrode). Also, the nondephosphorylated P-peptide linked Fe₃O₄@Cu₂O@TiO₂ nanospheres as nanozymes with horseradish peroxidase activity to catalyze the formation of precipitation on the surface of the Au chip, leading to a frequency change of the QCM. Thus, the proposed PEC-QCM dual-mode sensing platform achieved accurate and reliable assay of PTP1B activity because of the different mechanisms and independent signal transductions. In addition, this dual-mode sensing platform can be easily extended for other protein phosphatase activity analysis and shows great potential in the early diagnosis of the protein phosphatase-related diseases and the protein phosphatase-targeted drug discovery.

Zinc-Air Battery-Assisted Self-Powered PEC Sensors for Sensitive Assay of PTP1B Activity Based on Perovskite Quantum Dots Encapsulated in Vinyl-Functionalized Covalent Organic Frameworks

The self-powered sensors have attracted widespread attention in the analysis field due to a huge demand of point-of-care testing (POCT) in the early diagnosis of diseases. However, the output voltage of the reported self-powered sensors is always small, resulting in a narrow linear detection range and low assay sensitivity. Herein, a self-powered photoelectrochemical (PEC) sensor with zinc-air batteries as a power source was developed for activity assay of protein tyrosine phosphatase 1B (PTP1B) based on perovskite quantum dots encapsulated in the vinyl-functionalized covalent organic framework (COF-V). CsPbBr₃ nanocrystals were stabilized by the confinement effect of the COF-V cage without aggregation, and the resulting CsPbBr₃@COF-V composite was used as the cathodic photoelectric material to construct the zinc-air battery with a large open-circuit voltage (OCV, 1.556 V). Before PTP1B activity assay, an auxiliary peptide-polyamidoamine-phosphopeptide (P2-PAMAM-P1) hybrid was introduced into the photocathode via thiol-ene click reaction between the thiol group on the P1 and the vinyl group on the COF-V. The steric hindrance effect of the P1-PAMAM-P2 hybrid inhibited the PEC performance of the photocathode, resulting in a small OCV of the zinc-air battery. When the PTP1B existed, PTP1B-catalyzed dephosphorylation of tyrosine on P1 facilitated the cleavage process of P1 by chymotrypsin, leading to the removal of the P2-PAMAM-P1 hybrid from the photocathode and consequently the enhancement of the OCV. Therefore, the activity of PTP1B was sensitively detected. The developed self-powered PEC sensor showed superior performance for PTP1B activity assay (broad linear response range, 0.1 pM to 10 nM and low detection limit, 0.032 pM) due to the large output voltage of the constructed zinc-air battery and has great potential in POCT of protein phosphatase-related diseases and the discovery of protein phosphatase-targeted drugs.

Syntheses and crystal structures of guanidine hydrochlorides with two Schiff base functions as efficient colorimetric and selective sensors for fluoride

A series of guanidinium chloride derivatives have been synthesized by condensation of 1,3-diaminoguanidine monohydrochloride with heteroaromatic formaldehydes in good yields. All compounds were characterized by nuclear magnetic resonances and infrared spectroscopies, and the molecular structures of four compounds were determined by single crystal X-ray diffraction. The optical properties of these guanidinium chloride derivatives with fluoride anions were investigated, showing selective color changes from colorless to yellow or orange, red-shifted in the ultraviolet/visible absorption spectra.