All-in-One Luminescent Lanthanide Coordination Polymer Nanoprobe for Facile Detection of Protein Kinase Activity.

This study developed a novel luminescent assay for kinase activity using metal-organic coordination polymer nanoparticles (Tb/ATP-Zn) as the probe. Tb/ATP-Zn, self-assembled by adenosine triphosphate (ATP), Zn2+, and Tb3+, is non-luminescent. Protein kinase A (PKA) can catalyze the transformation of ATP within Tb/ATP-Zn nanoparticles to adenosine diphosphate (ADP), which in turn effectively sensitizes the luminescence of Tb3+. Based on this mechanism, Tb/ATP-Zn can realize the facile luminescent "turn-on" sensing of protein kinase activity without the use of external ATP and substrate peptide. Under optimized conditions, the fluorescence intensities of Tb/ATP-Zn at 550 nm are linear with the PKA activity within a range of 0.3-1.5 U·µL-1. The LOD (S/N = 3) of this method is down to 0.001 U·µL-1. The presented assay also features high selectivity, long-term stability, fast response, and convenient operation. Furthermore, Tb/ATP-Zn was successfully employed for monitoring PKA activity in cell lysis solutions. Probe Tb/ATP-Zn is thus expectable to be a powerful tool for the practical study of PKA in relevant biological events.

Dual-Response Ratiometric Electrochemical Microsensor for Effective Simultaneous Monitoring of Hypochlorous Acid and Ascorbic Acid in Human Body Fluids.

Redox homeostasis between hypochlorous acid (HClO/ClO-) and ascorbic acid (AA) significantly impacts many physiological and pathological processes. Herein, we report a new electrochemical sensor for the simultaneous determination of HClO and AA in body fluids. We first coated a carbon fiber microelectrode (CFME) with a three-dimensional nanocomposite consisting of graphene oxide (GO) and carbon nanotubes (CNTs) to fabricate the CFME/GO-CNT electrode. After the electrochemical reduction of GO (ERGO), we integrated a latent 1-(3,7-bis(dimethylamino)-10H-phenothiazin-10-yl)-2-methylpropan-1-one (MBS) electrochemical molecular recognition probe to monitor HClO and employed anthraquinone (AQ) as an internal reference. The compact CFME/ERGO-CNT/AQ + MBS sensor enabled the accurate and simultaneous measurement of HClO and AA with excellent selectivity and sensitivity. Measurements were highly reproducible, and the sensor was stable and exceptionally biocompatible. We successfully detected changes in the redox cycles of HClO and AA in human body fluids. This sensor is a significant advance for the investigation of reactions involved in cellular redox regulation. More importantly, we have devised a strategy for the design and construction of ratiometric electrochemical biosensors for the simultaneous determination of various bioactive species.

Potentiometric analysis of sialic acid with a flexible carbon cloth based on boronate affinity and molecularly imprinted polymers.

An electrochemical platform was proposed for highly sensitive and selective analysis of sialic acid based on molecularly imprinted polymers (MIPs), which were electropolymerized with the monomer molecules of 3-aminophenylboronic acid (ABA) on a carbon cloth (CC) electrode in the presence of template molecules. The fabricated sensor, named the PABA/CC-based MIP electrode, could be used for the detection of sialic acid because the reversible and covalent boronic acid-diol binding was sensitive to the electrochemical potential of the prepared sensor. The utilization of a CC film as the substrate could improve the sensitivity due to its good electrical conductivity and large surface area. Under the optimized conditions, a good relationship between the change in potential and the concentration of sialic acid was obtained in the range from 40 µM to 440 µM with a detection limit of 0.5 µM. The resulting MIP sensor also displayed good selectivity, reproducibility and stability. Moreover, this sensor was successfully applied for the evaluation of the sialic acid level in infant formulas.

Lanthanide Functionalized Metal-Organic Coordination Polymer: Toward Novel Turn-On Fluorescent Sensing of Amyloid ß-Peptide.

Metal-organic coordination polymers (MOCPs) have been emerging as very attractive nanomaterials due to their tunable nature and diverse applications. Herein, using Tb3+ as the luminescence center, 1,3,5-benzenetricarboxylate (BTC) as building block and Cu2+ as the signal modulator as well as a recognition unit, we propose a novel and effective lanthanide functionalized MOCP (LMOCP) fluorescent sensor (Cu-BTC/Tb) for amyloid ß-peptide (Aß) monomer, a biomarker for Alzheimer disease (AD). Specifically, Cu-BTC/Tb, created by postsynthesis modification strategy under room temperature, is almost nonemissive due to the quenching effect of Cu2+ in the MOCP, exhilaratingly, the presence of Aß1-40 triggered a significant emission enhancement of Cu-BTC/Tb assay due to the high binding affinity of Aß1-40 for Cu2+ and the subsequent suppression of the quenching effect. In the assay, this LMOCP sensor shows high sensitivity with detection limit of 0.3 nM. Due to its capability to eliminate autofluorescence, Cu-BTC/Tb was also applied to the time-gated detection of Aß1-40 in human plasma with promising results. This work presents a novel strategy for the construction of functional luminescent LMOCP for sensitively turn-on fluorescent sensing of Aß1-40. We believe the proposed strategy would inspire the development of various LMOCP-based fluorescent assays or medical imaging platforms for advanced biological implementations.

Controllable preparation of silver-doped hollow carbon spheres and its application as electrochemical probes for determination of glycated hemoglobin.

Silver-doped hollow carbon spheres (Ag@HCS) were firstly introduced as electrochemical probes for glycated hemoglobin (HbA1c) sensing at a molecularly imprinted polymer (MIP)-based carbon cloth (CC) electrode. Herein, Ag@HCS was prepared using one-pot polymerization of resorcinol and formaldehyde with AgNO3 on the SiO2 template, subsequent carbonization, and template removal. Furthermore, poly-aminophenylboronic acid (PABA) as the MIP film was used as a sensing platform for recognition of HbA1c, which captured the Ag@HCS probe by binding of HbA1c with aptamer modified on the probe surface. Due to regular geometry, large specific surface area, superior electrical conductivity, and highly-dispersed Ag, the prepared Ag@HCS probe provided an amplified electrochemical signal based on the Ag oxidation. By use of the sandwich-type electrochemical sensor, the ultrahigh sensitivity of 4.365 µA (µg mL-1)-1 cm-2 and a wide detection range of 0.8-78.4 µg mL-1 for HbA1c detection with a low detection limit of 0.35 µg mL-1 were obtained. Excellent selectivity was obtained due to the specific binding between HbA1c and PABA-based MIP film. The fabricated electrochemical sensing platform was also implemented successfully for the determination of HbA1c concentrations in the serum of healthy individuals.

Development of a novel ratiometric electrochemical sensor for monitoring ß-galactosidase in Parkinson's disease model mice.

Rapid, simple, accurate and highly sensitive detection of enzymes is essential for early screening and clinical diagnosis of many diseases. In this study, we report the fabrication of a turn-on ratiometric electrochemical sensor for the in situ determination of ß-Galactosidase (ß-Gal) based on surface engineering and the design of a molecular probe (Pygal) specific for ß-Gal recognition. First, Pygal probe was synthesized and characterized, and then co-assembled with the methylene blue (MB) internal reference probe on the surface of single-wall carbon nanotubes (SWCNT)-modified carbon fiber microelectrode (CFME). The resulting CFME/SWCNT/MB + Pygal sensor is activated in the presence of ß-Gal giving one peak at 0.33 V originating from the oxidation of the product of Pygal enzymatic hydrolysis (PyOH). Another oxidation peak attributed to MB appears simultaneously at -0.28 V allowing the construction of a ratiometric electrochemical sensor for ß-Gal detection with improved sensitivity and accuracy. The sensor showed a linear response to ß-Gal in a wide concentration range from 1.5 to 30 U L-1 and a low detection limit of 0.1 U L-1. Moreover, the sensor demonstrated excellent selectivity against several biologically relevant hydrolases and redox-active molecules. Finally, the combination of excellent electrochemical performance and favorable physicochemical properties of CFME allowed the determination of ß-Gal in the whole blood of Parkinson's Disease (PD) model mice. The workflow reported in this study provides a strategy for the design and development of sensors for the in vivo monitoring of other enzymes important for the early diagnosis of different health issues.

"Turn-on" ratiometric electrochemical detection of H2O2 in one drop of whole blood sample via a novel microelectrode sensor.

Oxidative stress plays an important role in the pathogenesis of many diseases, while the exact mechanism that hydrogen peroxide (H2O2) as one of the most abundant reactive oxygen species (ROS) exerts its influence on oxidative stress remains unclear. We developed a novel turn-on ratiometric electrochemical sensor for the detection of H2O2 in blood samples. The electrochemical probe 5-(1,2-dithiolan-3-yl)-N-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pent-anamide (BA) was designed and synthesized for the selective detection of H2O2 via a one-step amide reaction. Meanwhile, Nile Blue A (NB) was optimized as an internal reference molecule, thus enabling accurate quantification of H2O2 in a complex environment. BA and NB were then co-assembled onto a carbon fiber microelectrode (CFME) coated with Au cones. The oxidation peak current ratio between BA and NB demonstrated good linearity with the logarithm of the H2O2 concentration values ranging from 0.5 µM to 400 µM with a low detection limit of 0.02 µM. The developed sensor showed remarkable selectivity against potential interferences in whole blood samples, especially for ascorbic acid, uric acid, and dopamine. In combination with the unique characteristics of CFME, such as a small size and good biocompatibility, the microsensor was used for rapid analysis of one drop of whole blood sample. This sensor not only creates a new platform for the detection of H2O2 in whole blood samples, but also provides a new design strategy of other ROS analysis for early diagnosis of ROS-related diseases, drug discovery processes, and pathological mechanisms.

Lanthanide coordination polymer probe for time-gated luminescence sensing of pH in undiluted human serum.

Lanthanide coordination polymers (LCPs) have emerged as fascinating materials because of their specific structure and properties. In this work, utilizing hydrosoluble biomolecule of guanosine-5'-monophosphate (GMP) as bridging linker, lanthanide terbium ions (Tb3+) as metal nodes, and silver ions (Ag+) as sensitizers, we synthesized a pH responsive luminescent lanthanide CP probe of Tb/GMP/Ag. The probe possesses high luminescence due to the sensitization of Ag+; While in alkaline solutions, Ag+ in Tb/GMP/Ag immediately binds to OH-, forming Ag2O precipitation and resulting in a distinct fluorescence quenching of Tb/GMP/Ag. This probe displays high selectivity for OH- and a broader pH detection range of 7.5-13.0. In addition, based on the high anti-interference ability in serum, we applied Tb/GMP/Ag to measure pH in undiluted human serum samples, yielding satisfactory results.

Nafion-coated bismuth film and nafion-coated mercury film electrodes for anodic stripping voltammetry combined on-line with ICP-mass spectrometry.

Nafion-coated bismuth film electrodes (NCBFEs) and Nafion-coated mercury film electrodes (NCMFEs) were used to electrochemically preconcentrate metal analytes for subsequent analysis by inductively coupled plasma-mass spectrometry (ICP-MS). Either type of electrodes is part of a thin-layer electrochemical flow cell that is positioned upstream of a microconcentric nebulizer for the ICP-MS. Performances of these electrodes were compared in terms of the analytical "figures of merit" (e.g., dynamic ranges, reproducibility, hydrodynamic stability, and elimination of matrix effects detrimental to ICP-MS). The coupled technique (ASV-ICP-MS) is found to possess a wide dynamic range (at least 4 to 5 orders of magnitude) and to be reproducible. Both electrodes are much more stable than the thin mercury film electrode (TMFE) traditionally used for ASV-ICP-MS, with the lifetime of the NCBFE exceeding 8 h. Adopting these electrodes for ASV-ICP-MS overcomes the problems associated with a TMFE, the erosion of which decreases the sample throughput, affects the analysis precision, and contaminates conventional glass nebulizers and spray chambers of the spectrometer. The medium exchange procedure inherent in ASV is successfully implemented with a two-valve flow injection system for the accumulation of trace Cd2+ into the electrode from a certified seawater sample, followed by stripping Cd into a solution that is compatible to the ICP-MS operation.

Smart lanthanide coordination polymer fluorescence probe for mercury(II) determination.

Lanthanide coordination polymers (LCPs) have recently emerged as attractive biosensor materials due to their flexible components, high tailorable properties and unique luminescence features. In this work, we designed a smart LCP probe of Tb-CIP/AMP {(CIP, ciprofloxacin) (AMP, adenosine monophosphate)} for Hg(2+) detection by using lanthanide ions as metal nodes, CIP as ligand molecule, and AMP as bridging linker and recognition unit. Tb-CIP/AMP emits strong green luminescence due to the inclusion of AMP, which withdraws the coordinated water molecules and shields Tb(3+) from the quenching effect of O-H vibration in water molecules. The subsequent addition of Hg(2+) into Tb-CIP/AMP can strongly quench the fluorescence because of the specific coordination interaction between AMP and Hg(2+). As a kind of Hg(2+) nanosensor, the probe exhibited excellent selectivity for Hg(2+) and high sensitivity with detection limit of 0.16 nM. In addition, the probe has long fluorescence lifetime up to millisecond and has been applied to detect Hg(2+) in drinking water and human urine samples with satisfactory results. We envision that our strategy, in the future, could be extended to the designation of other LCP-based hypersensitive time-gated luminescence assays in biological media and biomedical imaging.

Effect of polyethylene glycols on the alkaline-induced molten globule intermediate of bovine serum albumin.

In the present study, the formation of one molten globule-like unfolding intermediate of bovine serum albumin (BSA) at pH 11.2 has been established with the help of circular dichroism (CD) spectra, fluorescence spectroscopy and 'phase diagram' approach. Additionally, we have shown the conformational changes occurring in the pH 11.2 intermediate of BSA when it was exposed to different molecular weight polyethylene glycols (PEGs) at varying concentrations. When the pH 11.2 intermediate of BSA was treated by PEG 400 there was induction of secondary and non-native tertiary contacts. In case of PEG 8000 and PEG 20,000, the loss in secondary as well as tertiary structure was observed. PEG 8000 and 20,000 altered the conformation of the pH 11.2 intermediate and resulted in its transition to another intermediate state in which the hydrophobic patches were inaccessible.

Electrochemical detection of dopamine in the presence of ascorbic acid using PVP/graphene modified electrodes.

Graphene (GR) was synthesized through electrochemical reduction of graphene oxide and characterized by spectroscopic and electrochemical techniques. Polyvinylpyrrolidone (PVP)/graphene modified glassy carbon electrode (PVP/GR/GCE) was prepared and applied for the fabrication of dopamine (DA) sensors without the interference of ascorbic acid (AA). Compared to bare GCE, an increase of current signal was observed, demonstrating that PVP/GR/GCE exhibited favorable electron transfer kinetics and electrocatalytic activity towards the oxidation of dopamine. Furthermore, PVP/GR/GCE exhibited good ability to suppress the background current from large excess ascorbic acid. Amperometric response results show that the PVP based sensor displayed a wide linear range of 5×10(-10) to 1.13×10(-3) mol/L DA with a correlation coefficient of 0.9990 and a detection limit of 0.2 nM (S/N=3). The determination of dopamine in urine and human serum samples were studied.