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Alkaline phosphatase (ALP) is an essential enzyme in various tissues, which has been reported to be extensively involved in various physiological and pathological processes. Fluorescent probe assays carried out in vivo are desirable for monitoring the ALP activity. In this study, a novel red-light fluorescent DHP probe, which exhibited good selectivity and high sensitivity, for monitoring the ALP activity in real time was described. The DHP probe exhibited good water solubility, and the detection limit of ALP was determined as 0.031 U/L; this value is almost less than those of the other probes reported previously. The probe exhibited high selectivity, which will not interfere with various enzymes and amino acids. Moreover, the sensing and luminescence mechanisms of ALP to DHP was investigated by density functional theory (DFT) and time-dependent DFT. Furthermore, the DHP probe was applied for the detection of endogenous ALP in BEL-7402 cells, and the fluctuation of the ALP levels in BEL-7402 and HEK 293 T cells was successfully tracked by fluorescence microscopy. [ABSTRACT FROM AUTHOR]

Tyrosinase (TYR) plays vital roles in melanin biosynthesis and function as an important biomarker for melanoma cancer; and thus has made rapid and sensitive detections for its activity to be on urgent demands. In this study, a facile aqueous fluorescence probe based on dopamine-functionalized-Mn-doped ZnS quantum dots (Dopa-Mn:ZnS QDs) was developed to detect TYR activity. When dopamine moiety in Dopa-Mn:ZnS QDs was oxidized to dopaquinone derivative by TYR, an intra-particle phot o- induced electron transfer (PET) process between Dopa-Mn:ZnS QDs and dopaquinone moiety takes place, and as a result, the fluorescence is quenched. Quantitative evaluation of TYR activity was studied in terms of the relationship between fluorescence quenching efficiency and TYR activity. The probe could detect TYR in a broad linear range of up to 1620 U L −1 with a low detection limit of 1.82 U L −1 . It was then applied to detect TYR in chicken serum samples, in which, TYR could be recovered by 88.3–100.7%. Finally, the probe demonstrated low cytotoxicity as evaluated by MTT assay and successfully applied to intracellular imaging of A549 cells. This study has indicated potential applications of Dopa-Mn:ZnS QDs probe in monitoring TYR-associated diseases, clinical diagnostics, and drug discovery. [ABSTRACT FROM AUTHOR]

In this work, two novel fluorescence probes, named as RBQ1 and RBQ2, were designed and synthesized based on rhodamine B lactam. RBQ1 was employed for sensitive fluorometric sensing of H + in the pH range of 2–4. Since RBQ1 exhibits color responses toward Cu 2+ , it was also employed for sensitive detection of Cu 2+ by photoelectric colorimetry. By using RBQ1 as the fluorescence probe, the detection limit of Cu 2+ obtained was 0.0365 μmol L −1 . RBQ2, with a similar chemical structure to RBQ1, also shows obvious fluorescence responses to H + , but no response to any metal ions. By using H + and Cu 2+ ions as chemical inputs and fluorescence or absorbance as outputs, a novel dual-mode molecular logic gate was constructed with RBQ1. [ABSTRACT FROM AUTHOR]

• A MOF-based potentiometric Cu2+ sensor was proposed without ion selective membrane. • The Cu 3 (HHTP) 2 plays a bifunctional role of ion recognition and ion-to-electron transduction. • The sensor discloses features of fast response, organic solvent tolerance and short conditioning. The conductive metal organic framework (MOF) discloses efficient electron transfer ability and its specific framework structure could realize ion recognition. The state-of-the-art solid-contact ion-selective electrodes (SC-ISEs) rely on both solid contact (SC) and ion-selective membrane (ISM) for respective functions of ion-to-electron transduction and ion recognition. Herein, we report an ISM-free SC-ISE by using the conductive MOF of Cu 3 (HHTP) 2 (Cu as metallic nodes and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) as triphenylene-based organic linkers) as a bifunctional role of SC and ISM for Cu2+ sensing. The experimental results demonstrated a Nernstian and selective response to Cu2+ with a slope of 29.5 ± 0.3 mV dec−1. Compared with traditional Cu2+-ISM-based SC-ISEs, the potentiometric response time has been greatly reduced from ∼ 50 s to 10 s. Moreover, the ISM-free conductive MOF could offer normal potentiometric responses even under a short conditioning time in solution (minutes). In addition, organic solvent tolerance has also been proved for the ISM-free conductive MOF-based SC-ISE. This work demonstrates that the MOF could be feasible for constructing a type of ISM-free solid potentiometric ion sensors. [ABSTRACT FROM AUTHOR]

• Development of a novel red-emitting fluorescent probe (HSA) for the detection of Cys. • The probe can high sensitivity detect Cys with a low LOD. • Successfully verified the experimental results by the theoretical calculation study. • The probe can be used for exogenous Cys monitoring and endogenous Cys cell imaging experiments. Herein, we synthesized a red-emitting fluorescence turn-on probe (HSA) for specific detection of cysteine (Cys) over other biothiols (glutathione (GSH) and homocysteine (Hcy)). The acrylate group was chosen as the recognition site for specific discrimination of Cys. Absorption and emission spectra display a high selectivity towards Cys over GSH/Hcy, organic small-molecule interfering substances and anions, with a high sensitivity towards Cys (0.12 μM) in 1% ethanol-containing PBS buffer solution (25 mM, pH = 7.4). Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were conducted to clarify the luminescence mechanism of the probe. Furthermore, the probe was successfully applied to the determination of free Cys in human serum and the fluorescence imaging of endogenous Cys in living cells. [ABSTRACT FROM AUTHOR]

Herein we propose a fluorescence turn-on strategy for the sensitive and selective detection of trypsin based on fluorescence resonance energy transfer (FRET) between gold nanoparticles (AuNPs) and amino-functionalized carbon dots (C-dots). In this assay, C-dots were treated as fluorometric reporter, while AuNPs were treated as fluorescence quencher. A specially designed negatively charged short peptide chain with one functioned cysteine group as the substrate for trypsin. The sensor works as follows: the negatively charged part of the peptide can be hydrolyzed by trypsin, resulting in the releasing of shorter and positively charged peptides. These shorter peptides then induces AuNPs aggregation due to the strong electrostatic interaction between positively charged peptides and the negatively charged AuNPs, thus leading to the restoration of the FRET-quenched fluorescence emission of C-dots. Measuring the changes in the fluorescence of C-dots, the concentrations of trypsin can be determined. Under the optimized conditions, we achieved quantitative evaluation of trypsin in a range of 2.5–80 ng mL −1 with the detection limit of 0.84 ng mL −1 . Meanwhile, this sensing system also exhibited excellent selectivity and sensitivity for trypsin, and we successfully applied it for the detection of trypsin in human serum samples. Based on the above findings, we conclude that this new FRET based sensor might be significant in disease diagnosis in the future. [ABSTRACT FROM AUTHOR]

Herein we report a new carbazole-benzo[e]indolium dye (CEBI) as a ratiometric fluorescent and chromogenic probe for sulfite (SO 3 2− ) detection based on intramolecular charge transfer (ICT) mechanism. Upon treatment with SO 3 2− , the probe CEBI displayed a remarkable fluorescence ratiometric response (∼560-fold fluorescenc enhancement) together with a color change from red to weak red and a large shift (135 nm) in emission wavelength. The experimentally observed changes in the spectral features of the probe upon addition of SO 3 2− were systematically studied using high resolution electrospray ionization mass spectrometry (HR-ESI–MS), proton nuclear magnetic resonance ( 1 H NMR), and time-dependent density functional theory (TDDFT) calculations. We found a linear relationship between the ratio of fluorescence intensities at 465 nm and 600 nm ( F 465 /F 600 ) and SO 3 2− concentration over the range of 0–40 μM with a detection limit of 0.025 μM. Moreover, the novel probe demonstrated fluorescence imaging of SO 3 2− in living cells and zebrafish, suggesting its potential in clinical diagnostics. [ABSTRACT FROM AUTHOR]

Sweat pH monitoring is a routine indicator in wearable biotechnology. The state‐of‐the‐art wearable pH sensors mostly rely on organic materials but face the risk of biological toxicity. WO3 is a typical H+‐sensitive inorganic material with chemical stability, biocompatibility, and low cost but low sensitivity and slow response. Lattice H+ intercalation is herein proposed as an efficient approach that can greatly improve the sensitivity and selectivity of WO3‐based pH sensors. Specifically, lattice H+ intercalation can promote WO3 from the monoclinic phase to cubic phase, which enhances the ion exchange capacity between WO3 and H+. The resistance decreases more than two orders of magnitudes, which improves the interfacial charge transport. The occupancy of lattice H+ leads to ion exchange only with H+, thus increasing the H+ recognition. The intercalated HxWO3 exhibits much improved sensitivity, reversibility, and response time. Additionally, the HxWO3 is integrated with a solid reference electrode on a miniaturized chip for wearable sweat pH monitoring. The pH sensor exhibits good potential response even at curving over 270°. On‐body sweat pH measurments show high accuracy compared with ex situ analyses. This work emphasizes the concept of lattice proton intercalation to regulate the H+ recognition of solid contacts. [ABSTRACT FROM AUTHOR]

Abstract Typically, sialic acids (SA) with a nine-carbon backbone are found at the glycan chain termini on the cell membranes, which play crucial roles in various physiological and pathological processes. The expression level of SA in the blood serum has been reported to correlate with various disease states among cancer. In this study, a novel approach for preparing fluorescent boronic-acid-modified carbon dots (C-dots) for the detection of SA was developed. The functionalized C-dots were synthesized by a facile, one-step hydrothermal method using 3-pyridineboronic acid as the sole carbon source. The added SA selectively recognized the C-dots, leading to the fluorescence quenching of the C-dots in a linear range of 80–4000 μM with a detection limit of 54 μM. The as-developed boronic-acid nanoprobe was successfully applied for the detection of SA in human serum samples with satisfactory results. In addition, this method afforded results within 4 min. Compared to other methods, this new proposed approach was simpler and exhibited excellent sensitivity and selectivity, demonstrating immense potential as an alternative for SA detection. Graphical abstract fx1 Highlights • In this study, a simple, sensitive nonenzymatic strategy for SA detection with carbon dots. • The sensor exhibited high selectivity and sensitivity. • This method is applied to detect sialic acid in real samples with satisfactory recoveries. • This method does not require any complicated modifications and expensive instrumentation. [ABSTRACT FROM AUTHOR]

Abstract A novel fluorescence detection method based on competitive immunoassay and magnetic bioseparation technique was developed and applied to the determination of pig immunoglobulin G (IgG) in serum samples. Core-shell structured Fe 3 O 4 @SiO 2 nanoparticles were synthesized by chemical coprecipitation, followed by functionalization with amino groups and immobilization of pig IgG antibodies. The synthesized Fe 3 O 4 @SiO 2 -antibody nanoparticles were employed as the probe for the competitive immune recognition of the target antigens in samples and the antigens labeled with fluorescein isothiocyanate (FITC). After the magnetic separation of probes binding with these two types of antigens, fluorescence of the free FITC-labeled antigens was measured for the quantification of the target antigens, since the ratio of the FITC-labeled antigens in supernatant before and after the competitive immune recognition depends on the amount of the target antigens in sample, due to the competitive nature of the binding of the antibody for these two types of antigens. Under the optimal conditions, a linear relationship was obtained between the change of fluorescence intensity and the concentration of pig IgG in a range from 0.75 to 23.50 µg L−1, with a detection limit (LOD) of 0.031 µg L−1. With the facile-prepared probes, this fluorescence competitive method can provide a rapid, specific and highly sensitive immunoassay protocol for the determination of target proteins in complex matrix samples. Graphical abstract fx1 Highlights • The analysis was simplified through competitive immunoreactions and magnetic bioseparation. • Good sensitivity and selectivity were obtained by taking advantage of fluorescence immunoassay. • The results of analyzing serum samples indicate its promising potential in clinical diagnosis. [ABSTRACT FROM AUTHOR]

Herein, we report a novel Schiff base “turn-on” fluorescent and chromogenic probe N′-(3-(benzo[d]thiazol-2-yl)-2-hydroxybenzylidene)-4-(dimethylamino)-benzohydrazide (BHDB) for CN − detection under physiological pH, based on nucleophilic reaction of imine ( CH N ) and CN − , exhibiting almost 66-fold fluorescence increase and a remarkable color change from colorless to yellow. The experimentally observed changes in the spectral properties of the probe upon addition of CN − were systematically studied using high resolution electrospray ionization mass spectrometry (HR-ESI-MS), proton nuclear magnetic resonance ( 1 H-NMR), and time-dependent density functional theory (TDDFT) calculations. Using the fluorescence spectra changes, we found a detection limit for CN − of 0.15 μmol L −1 , far lower than the maximum permissive level of CN − (1.9 μmol L −1 ) in drinking water recommended by World Health Organization (WHO). Moreover, the novel probe demonstrated fluorescence imaging of CN − in living cells and zebrafish, suggesting its potential in clinical diagnostics. [ABSTRACT FROM AUTHOR]

Strongly blue fluorescent N-doped carbon dots (CDs) were synthesized by using citric acid (CA) as the carbon source and diethylenetriamine (DETA) as the nitrogen source using a one-step hydrothermal method. Several synthetic parameters, including the molar ratios of initial starting materials, the temperature and time of hydrothermal reaction, were investigated and optimized. The range and average value of the diameters of the resultant CDs were 1.2-4.0 nm and 2.3 nm, respectively. The synthesized CDs display fluorescence with excitation/emission maxima of 391/438 nm and a quantum yield of 58%. Fluorescence is quenched by Co(II) ions, and this effect was exploited to design a method for determination of Co(II) in water and to image it in living HeLa (cervical carcinoma) cells. The limit of detection and linear range of Co using the synthesized CDs as fluorescence probe are 0.4 μmol·L and 0-90 μmol·L, respectively. Due to the selective and sensitive response of Co, the CDs possess potential applications in biological labeling for the demands such as monitoring the distribution of vitamin B-12 or other cobalt-containing medicines in cells or organisms . [ABSTRACT FROM AUTHOR]

[Display omitted] • A new constant potential coulometric method based on ISM-free SC-ISE was proposed. • LiMn 2 O 4 was used as a combined ion-recognition and signal-transduction layer. • The sensor has exhibited excellent signal amplification for detecting small Li+ activity changes. A coulometric signal readout method, which was originally developed for solid-contact ion-selective electrodes, was investigated in this work using LiMn 2 O 4 (LMO) as a combined ion-recognition and signal-transduction layer. The redox process of LMO, which is associated with reversible intercalation/expulsion of Li+ ions, allowed coulometric sensing of Li+ ions in aqueous solutions. On increasing the active area (mass loading) of LMO, the coulometric signal increased for a given change in Li+ ion activity. The excellent redox reversibility of LMO and its relatively low resistance were instrumental in achieving a high signal amplification together with a relatively fast response. Coating the LMO layer with a conventional Li+-selective plasticized PVC membrane was found to dramatically lower the coulometric response. Hence, the application of LMO as a combined Li+-selective electrode material and ion-to-electron transducer was found to be highly compatible with the coulometric signal readout method, especially for detecting small Li+ activity changes at high Li+ concentrations. [ABSTRACT FROM AUTHOR]

[Display omitted] • A self-adhesive tannin–graphene supramolecular pH-sensitive material is proposed. • The material adheres well to various solid and soft substrates. • The sensor exhibits reversible, Nernstian and selective pH responses. • The material can be printed directly to fabricate a wearable sensor for sweat pH monitoring. The pH of sweat is the most common biochemical parameter monitored by integrated wearable devices. A crucial factor in sensing materials for wearable applications is strong contact both with the skin and with the electrode substrate. Currently, the deposition of many sensitive materials on a substrate relies on mixing a small amount of binder, which raises the issue of biocompatibility and the risk of detachment. Herein, we report self-adhesive tannin–graphene supramolecular aggregates for use in wearable potentiometric pH sensors. The abundant phenolic hydroxyl groups in tannin (TA) result in strong adhesion and are also the pH response sites. The graphene (reduced graphene oxide, RGO) induces the supramolecular formation of TA and promotes electron transfer based on the π-π conjugation interaction. The pH sensor has a reversible and Nernstian response, and is not affected by potentially interfering ions. Owing to the strong adhesion of TA–RGO, a wearable pH device was directly fabricated using a dispensing printing technique. The sensor has been shown to be successful in monitoring the pH of sweat in real time. This work emphasizes the importance of the adhesion of sensing materials for use in wearable electrochemical sensors. [ABSTRACT FROM AUTHOR]

Current solid potentiometric ion sensors mostly rely on polymeric-membrane-based, solid-contact, ion-selective electrodes (SC-ISEs). However, anion sensing has been a challenge with respect to cations due to the rareness of anion ionophores. Classic metal/metal insoluble salt electrodes (such as Ag/AgCl) without an ion-selective membrane (ISM) offer an alternative. In this work, we first compared the two types of SC-ISEs of Cl− with/without the ISM. It is found that the ISM-free Ag/AgCl electrode discloses a comparable selectivity regarding organic chloride ionophores. Additionally, the electrode exhibits better comprehensive performances (stability, reproducibility, and anti-interference ability) than the ISM-based SC-ISE. In addition to Cl−, other Ag/AgX electrodes also work toward single and multi-valent anions sensing. Finally, a flexible Cl− sensor was fabricated for on-body monitoring the concentration of sweat Cl− to illustrate a proof-of-concept application in wearable anion sensors. This work re-emphasizes the ISM-free SC-ISEs for solid anion sensing. [ABSTRACT FROM AUTHOR]

We designed and synthesized a water-soluble near-infrared (NIR) fluorescent probe with the recognition unit of the cyanine-like structure and acrylate group. Through an aromatic ring nucleophilic substitution reaction based on sulfhydryl moiety, an off-on fluorescence response toward cysteine (Cys) was realized. The probe exhibited excellent spectral performance with an emission wavelength of 720 nm and a detection limit of 0.20 μM. The spectral properties, selectivity and anti-interference performance of the probe were systematically investigated. Density functional theory (DFT) calculations were conducted to clarify the luminescence mechanism of the probe. Furthermore, the probe was successfully applied to the detection of free Cys in human serum and the NIR imaging of endogenous Cys in living cells. Thus, the probe has a promising application prospect in clinical diagnosis and fluorescence imaging. Image 1 • Development of a novel near-infrared fluorophore (MTR). • Design and application of fluorescent probe (MTR-C) for the detection of endogenous Cys. • Successfully verified the experimental results by the theoretical calculation study. • Successfully tracked the fluctuations of Cys levels in BEL-7402 cells. [ABSTRACT FROM AUTHOR]