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.

A high-frequency QCM biosensing platform for label-free detection of the SARS-CoV-2 spike receptor-binding domain: an aptasensor and an immunosensor.

Herein, high-frequency quartz crystal microbalance biosensing platforms were constructed using an aptamer and antibody as bioreceptors for fast and label-free detection of the SARS-CoV-2 RBD.

An electrochemical aptasensor for amyloid-ß oligomer based on double-stranded DNA as "conductive spring".

In order to overcome the antibody-based sensor's shortcomings, an electrochemical aptamer (Apt)-based sensor was developed for amyloid-ß40 oligomer (Aß40-O). The aptasensor was constructed by locating Apt and ferrocence (Fc) on streptavidin-modified gold (SA-gold) nanoparticles. The obtained AptFc@SA-gold nanoparticles were linked onto the Au electrode via the connection of double-stranded DNA (dsDNA) as a "conductive spring." The determination of Aß40-O was performed with square-wave voltammetry (SWV). Upon bio-recognition between Apt and Aß40-O, the conformation of Apt changed and the formed Apt/Aß40-O complex separated from the SA-gold surface. As a result, the surface charge of SA-gold positively shifted, weakening the electrostatic attraction between the SA-gold and the positively charged Au electrode surface (at potential range of 0.1~0.5 V, corresponding to the Fc redox transformation), and stretching the dsDNA chain. Based on the exponential decay of dsDNA's electron transfer efficiency on its chain stretching, the oxidation current density from Fc decreased and displayed linear correlation to the concentration of Aß40-O. A wide linear range of 0.100 nM to 1.00 µM with a low detection limit of 93.0 pM was obtained. The aptasensor displayed excellent selectivity toward Aß40-O in contrast to other possible interfering analogs (Aß40 monomer, Aß42 monomer, and oligomer) at × 100 higher concentrations. The recoveries for Aß40-O-spiked artificial cerebrospinal fluid and healthy human serum were 94.0~104% and 92.8~95.4%, respectively. The electrochemical aptasensor meets the demands of clinic determination of Aß40-O, which is significant for the early diagnosis of AD. Graphical abstract Schematic representation of the electrochemical aptasensor for amyloid-ß oligomer based on the surface charge change induced by target binding.

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.

A novel detection of MicroRNA based on homogeneous electrochemical sensor with enzyme-assisted signal amplification.

Rapid and sensitive detection of microRNAs is of great importance in biological researches and cancer diagnosis. Herein, we proposed a novel homogeneous electrochemical sensor to detect microRNA-21 (miRNA-21) using functionalized magnetic nanoparticles combined with enzyme-assisted signal amplification. The biotinylated capture probe (CP) labeled magnetic nanoparticles can capture miRNA-21 and introduce streptavidin-conjugated hydroxyapatite (HAP) nanoparticles. In the presence of miRNA-21, hybridization between RNA and DNA results in the formation of RNA/DNA duplexes, and then duplex-specific nuclease (DSN) cleave the duplexes to digest the capture chain and release the miRNA-21 in a loop. Meanwhile, the HAP nanoparticles strip from the magnetic nanoparticles and electrochemical signal by the reaction of HAP with molybdate is changed. The current variation before and after incubation with miRNA-21 is linearly correlated with the miRNA-21 concentration between 1 aM and 1 pM with a low detection limit (LOD) of 0.27 aM. Remarkably, the expression of miRNA-21 in human serum and different cell lysate was successfully performed, which fully demonstrates the great practical potentials in biomedical diagnostics and clinical therapeutics.

In-situ induced ethanol-water phase separation extraction of phthalate esters in alcoholic liquid sample using potassium triphosphate and analysis by gas chromatography-mass spectrometry.

A novel and efficient analytical method consisting of in-situ potassium triphosphate induced ethanol-water phase separation extraction and followed by gas chromatography-mass spectrometry (GC-MS) detection was developed for determination of eighteen phthalate esters (PAEs) in alcoholic liquid samples. Experimental parameters affecting the extraction efficiency were studied and optimized by univariate analysis. The effects of salt type and concentration, concentration of ethanol, redissolve solvent, vortex and standing time, solution pH on extraction efficiency were investigated. The developed method exhibited good linearity at a concentration range of 5-2500 µg·L-1 for diisononyl phthalate and 1-500 µg·L-1 for other PAEs. In addition, the coefficients of determination (R2) for all PAEs ranged from 0.9979 to 0.9999, the detection limits (LODs) and the limits of quantification (LOQs) were in the range of 0.014-0.530 µg·L-1 and 0.047-1.767 µg·L-1, respectively, the spiked recoveries were in the range of 92.2%-110.2% with the relative standard deviation (RSD) less than 8.6%. As ethanol within alcoholic liquid samples was used to separate PAEs with none solvent added at extraction processing, the proposed method could be considered simple and environmentally friendly.

Wide-field determination of aqueous mercury(II) based on tail-extensible DNA fluorescent probe with tunable dynamic range.

Mercury (Hg) is one of the most hazardous pollutants, widely distributed in water, atmosphere, and soil, while the Hg contents from different sources are greatly different. Until now, numerous reported methods are only suitable for a kind of sample because they cannot reconcile sensitivity and linear range. In this work, a tail-extensible DNA fluorescent probe for "turn on" detection of Hg2+ with tunable dynamic range and high sensitivity was developed, which was based on segmental hybridization between silver nanoclusters (AgNCs)-covered DNA and different guanine-rich DNAs. By adding adenine-guanine-cytosine (AGC) base repeats as a tail of the guanine-rich DNA, the formation constant of T-Hg2+-T complex was effectively modulated within two orders of magnitude. Based on it, a tunable dynamic range from 0.035 to 0.2 pM to 8.0-120.0 pM was achieved by combining four fluorescent probes with different tail lengths. The Hg2+contents from different sources were successfully measured. This evidenced the proposed sensor's application toward wide-field detection, which is useful for the direct and objective comparison of results from different sources, and therefore providing a way for solving the shortcomings of reported methods for Hg2+ detection. Additionally,this present method is simple, cost-effective and time-saving, ultrasensitive and highly selective, which is favorable for expanding its applications and subsequent mercury pollution control.

Label-free and near-zero-background-noise photoelectrochemical assay of methyltransferase activity based on a Bi2S3/Ti3C2 Schottky junction.

Herein, a novel label-free photoelectrochemical (PEC) sensing platform with near-zero background noise was developed for M.SssI CpG methyltransferase (M.SssI MTase) activity assay based on a new Schottky junction of Bi2S3/Ti3C2 nanosheets. The proposed PEC sensor exhibited a low detection limit and a high signal-to-noise ratio for M.SssI MTase assay.

A simple aptasensor for Aß40 oligomers based on tunable mismatched base pairs of dsDNA and graphene oxide.

ß-amyloid 1-40 oligomers (Aß40O) is considered to be one of the important biomarkers for the diagnosis and treatment of Alzheimer's disease (AD). To explore a method with excellent performance is favorable for measuring the low concentration of Aß40O in AD patients. Here, we developed a simple and fast method with a double stranded DNA (dsDNA)/graphene oxide (GO) based sensor, which was a fluorescent probe for a highly sensitive detection of Aß40O down to 0.1 nM with a linear detectable range from 0.1 nM to 40 nM. The proposed sensor effectively reduced non-specific adsorption and improved the specificity of detection because of the covalent conjugation of a binding DNA (bDNA) containing Aß40O-targeting aptamer (AptAß) onto GO surface, as well as the optimization of the number of mismatch base pairs of dsDNA. Moreover, AD patients and healthy persons were distinguished by this present method. All advantages of this method are exactly what the clinical detection of AD biomarkers need. This novel aptasensor might pave a way towards the early diagnosis of AD.

Refractory petrochemical wastewater treatment by K2S2O8 assisted photocatalysis.

The K2S2O8 assisted photocatalytic system was applied for treating refractory petrochemical wastewater. Co-TiO2/zeolite catalyst synthesized by sol-gel method was demonstrated to possess a good activity towards mineralization of the refractory petrochemical wastewater in the K2S2O8 assisted photocatalytic system. Orthogonal design was employed to optimize the reaction parameters, according to the results, K2S2O8 dosage was the most prominent impact factor. More experiments were conducted to further enhance the COD removal efficiency. In consideration of both efficiency and costs, the petrochemical wastewater was treated in the K2S2O8 assisted photocatalytic system at pH 4, K2S2O8 dosage 2.03 g/L, catalyst amount 250 g/L with irradiation by 1 lamp and aeration. The COD removal efficiency reached up to 93.4% with a rate constant of 1.14 × 10-2 per min, and Co-TiO2/zeolite showed a good stability towards the K2S2O8 assisted photocatalytic degradation of petrochemical wastewater.

Magnetic single-enzyme nanoparticles with high activity and stability.

Magnetic single-enzyme nanoparticles (SENs) encapsulated within a composite inorganic/organic polymer network were fabricated via the surface modification and in situ aqueous polymerization of separate enzyme molecule. The resultant nanoparticles were characterized by transmission electron microscope (TEM), Fourier transform infrared (FTIR) spectrometer and X-ray diffraction (XRD). These particles are almost spherical in shape and have a unique size of about 50 nm in diameter. Electrical and magnetic measurements reveal that the magnetic SENs have a conductivity of 2.7 x 10(-3)Scm(-1), and are superparamagnetic with a saturation magnetization of 14.5e microg(-1) and a coercive force of 60Oe. Compared with free enzyme, encapsulated enzyme exhibits a strong tolerance to the variation of solution pH, high temperature, organic solvent and long-term storage, thus showing significantly enhanced enzyme performance and stability.

Mechanism and kinetics of apatite formation on nanocrystalline TiO2 coatings: a quartz crystal microbalance study.

Apatite (Ca5(PO4)3OH) has long been considered as an excellent biomaterial to promote bone repairs and implant. Apatite formation induced by negatively charged nanocrystalline TiO2 coatings soaked in simulated body fluid (SBF) was investigated using in situ quartz crystal microbalance (QCM), scanning electron microscopy (SEM), Fourier-transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) techniques, and factors affecting its formation such as pH, size of TiO2 particles and thickness of TiO2 coatings, were discussed in detail. Two different stages were clearly observed in the process of apatite precipitation, indicating two different kinetic processes. At the first stage, the calcium ions in SBF were initially attracted to the negatively charged TiO2 surface, and then the calcium titanate formed at the interface combined with phosphate ions, consequently forming apatite nuclei. After the nucleation, the calcium ions, phosphate ions and other minor ions (i.e. CO3(2-) and Mg2+) in supersaturated SBF deposited spontaneously on the original apatite coatings to form apatite precipitates. In terms of the in situ frequency shifts, the growth-rate constants of apatite (K1 and K2) were estimated, respectively, at two different stages, and the results were (1.96+/-0.14)x10(-3)s(-1) and (1.28+/-0.10)x10(-4)s(-1), respectively, in 1.5 SBF solution. It was found that the reaction rate at the first stage is obviously higher than that at the second stage.

Removal of vanadium from vanadium-containing wastewater by amino modified municipal sludge derived ceramic.

In this work, an amino modified porous ceramic derived from municipal sludge was synthesized for the adsorption of vanadium (V) from wastewater. In this approach, a maximum vanadium (V) removal of 99.8% can be achieved by using 800 g adsorbent with a height of 800 mm when the initial concentration of vanadium (V) was 50 mg/L, pH was 4, flow rate was 5 L/h.

Piezoelectric urea biosensor based on immobilization of urease onto nanoporous alumina membranes.

The urease was immobilized onto nanoporous alumina membranes prepared by the two-step anodization method, and a novel piezoelectric urea sensing system with separated porous alumina/urease electrode has been developed through measuring the conductivity change of immobilized urease/urea reaction. The process of urease immobilization was optimized and the performance of the developed urea biosensor was evaluated. The obtained urea biosensor presented high-selectivity monitoring of urea, better reproducibility (S.D.=0.02, n=6), shorter response time (30s), wider linear range (0.5 microM to 3mM), lower detection limit (0.2 microM) and good long-term storage stability (with about 76% of the enzymatic activity retained after 30 days). The clinical analysis of the urea biosensor confirmed the feasibility of urea detection in urine samples.

Quartz crystal microbalance studies on bilirubin adsorption on self-assembled phospholipid bilayers.

Bilirubin adsorption on self-assembled phospholipid bilayers was studied using quartz crystal microbalance, and factors influencing its adsorption such as pH, temperature, and solution ionic strength were discussed in detail. The results show the amount of adsorbed bilirubin on self-assembled phospholipid bilayers is small at higher temperature and large at higher pH and solution ionic strength, and the adsorption kinetic parameter estimated from the in situ frequency measurement is (1.8+/-0.27)x10(6) M(-1) (mean +/- S.D.). With the present method, the desorption of adsorbed bilirubin caused by human serum albumin and the photoinduced decomposition of adsorbed bilirubin under light illumination were also examined. QCM measurement provides a useful method for monitoring the adsorption/desorption process of bilirubin on self-assembled phospholipid bilayers.

A highly selective photoelectrochemical biosensor for uric acid based on core-shell Fe3O4@C nanoparticle and molecularly imprinted TiO2.

Combining the surface modification and molecular imprinting technique, a novel photoelectrochemical sensing platform with excellent photochemical catalysis and molecular recognition capabilities was established for the detection of uric acid based on the magnetic immobilization of Fe3O4@C nanoparticles onto magnetic glassy carbon electrode (MGCE) and modification of molecularly imprinted TiO2 film on Fe3O4@C. The developed biosensor was highly sensitive to uric acid in solutions, with a linear range from 0.3 to 34µM and a limit of detection of 0.02µM. Furthermore, the biosensor exhibited outstanding selectivity while used in coexisting systems containing various interferents with high concentration. The practical application of the biosensor was also realized for the selective detection of uric acid in spiked samples. The study made a successful attempt in the development of highly selective and sensitive photoelectrochemical biosensor for urine monitoring.

Study of adsorption behavior of bilirubin on human-albumin monolayer using a quartz crystal microbalance.

The quartz crystal microbalance was employed to study the adsorption behavior of bilirubin on human-albumin layer, which was chemically bound to the self-assembled monolayer of 4-aminothiophenol on the surface of a gold electrode of the crystal via glutaraldehyde. A long-time adsorption process of bilirubin that took place on a human-albumin-modified surface was observed, and the adsorption kinetic parameters were estimated from the in situ frequency measurements. The amount of adsorbed bilirubin increased with increasing of both hydrogen ions and bilirubin concentration and was larger than that estimated based on the conclusion that there are two affinity sites for bilirubin per albumin molecule. With the present method, the displacement of bilirubin from an albumin layer caused by aspirin was also examined. QCM measurement provides a facile method for in situ monitoring of the adsorption/desorption of bilirubin on proteins layers.

A fluorescent nanoprobe based on graphene oxide fluorescence resonance energy transfer for the rapid determination of oncoprotein vascular endothelial growth factor (VEGF).

Oncoprotein vascular endothelial growth factor (VEGF) is one of the most critical growth factors that regulates tumor growth and division. The vascular endothelial growth factor (VEGF) is also an important biomarker for different diseases and clinical disorders. Herein, we propose a graphene oxide (GO) fluorescence resonance energy transfer (FRET)-based aptasensor for rapid, sensitive, and selective detection of VEGF in homogeneous solution. The fluorescent dye-labeled anti-VEGF aptamer is adsorbed on the surface of GO via π-π interaction between the flat planar GO sheets and the ring structures in the nucleobases, which results in the fluorescence quenching of the dye due to the highly effective FRET from the dye to GO. Upon recognition and binding with the target VEGF, it specifically forms a VEGF/aptamer complex and then release from the GO surface, leading to the restoration of fluorescence signal of the dye. This GO-based sensing platform exhibits high sensitivity and specificity toward VEGF versus other proteins, with the detection limits corresponding to 2.5×10(-10) M. The sensitivity of this new type of aptamer-based assay is at least one order of magnitude higher than that of conventional homogeneous optical assays. Moreover, the application of this nanosensor for human serum sample analysis is also demonstrated. The GO/aptamer-based assay approach holds great promise as a general platform for detection of a variety of target molecules.

Electrochemical oxidation of purine and pyrimidine bases based on the boron-doped nanotubes modified electrode.

Based on the excellent physicochemical properties of boron-doped carbon nanotubes (BCNTs), the electrochemical analysis of four free DNA bases at the BCNTs modified glassy carbon (GC) electrode was investigated. Herein, the BCNTs/GC electrode exhibited remarkable electrocatalytic activity towards the oxidation of purine bases (guanine (G), adenine (A)). More significantly, the direct oxidation of pyrimidine bases (thymine (T), cytosine (C)) was realized. It may be due to that BCNTs have the advantages of high electron transfer kinetics, large surface area, prominent antifouling ability and electrode activity. On basis of this, a novel and simple strategy for the determination of G, A, T and C was proposed. The BCNTs/GC electrode showed high sensitivity, wide linear range and capability of detection for the electrochemical determination of G, A, T, and C. On the other hand, the electrochemical oxidation of quaternary mixture of G, A, T, and C at the BCNTs/GC electrode was investigated. It was obtained that the peak separation between G and A, A and T, T and C were large enough for their potential recognition in mixture without any separation or pretreatment. The BCNTs/GC electrode also displayed good stability, reproducibility and excellent anti-interferent ability. Therefore, it can be believed that the BCNTs/GC electrode would provide a potential application for the electrochemical detection of DNA in the field of genetic-disease diagnosis.

Simple and sensitive aptasensor based on quantum dot-coated silica nanospheres and the gold screen-printed electrode.

A novel electrochemical aptasensor involving quantum dots-coated silica nanospheres (QDs/Si) and the screen-printed gold electrodes (SPGE) was developed for the detection of thrombin. The screen-printed electrodes with several advantages, including low cost, versatility, miniaturization, and mechanical regeneration after each measurement cycle, were employed. On the other hand, the gold nanoparticles (AuNPs) were electrodeposited on the surface of SPGE to obtain AuNPs/SPGE. And this sandwich format (Apt/thrombin/Apt-QDs/Si) was fixed on the AuNPs/SPGE to fabricate the electrochemical aptasensor. The bound CdTe QDs were dissolved in an acid-dissolution step and were detected by electrochemical stripping analysis. The proposed aptasensor has excellent performance such as high sensitivity, good selectivity and analytical application in real samples. The combination of nanoparticles with the screen-printed electrode is favorable for amplifying electrochemical signals, and useful for large-scale fabrication of the electrochemical aptasensors, which would lay a potential foundation for the development of the electrochemical aptasensor.