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The excessive formation of peroxynitrite (ONOO−) in mitochondria has been implicated in various pathophysiological processes and diseases. However, owing to short emission wavelengths and small Stokes shifts, previously reported fluorescent probes pose significant challenges for mitochondrial ONOO− imaging in biological systems. In this study, a near-infrared (NIR) fluorescent probe, denoted as DCO-POT, is designed for the visual monitoring of mitochondrial ONOO−, displaying a remarkable Stokes shift of 170 nm. The NIR fluorophore of DCO-CHO is released by DCO-POT upon the addition of ONOO−, resulting in off–on NIR fluorescence at 670 nm. This phenomenon facilitates the high-resolution confocal laser scanning imaging of ONOO− generated in biological systems. The practical applications of DCO-POT as an efficient fluorescence imaging tool are verified in this study. DCO-POT enables the fluorometric visualization of ONOO− in organelles, cells, and organisms. In particular, ONOO− generation is analyzed during cellular and organism-level (zebrafish) inflammation during ferroptosis and in an Alzheimer's disease mouse model. The excellent visual monitoring performance of DCO-POT in vivo makes it a promising tool for exploring the pathophysiological effects of ONOO−. [ABSTRACT FROM AUTHOR]

In this work, a ratiometric fluorescent nanoplatform for the detection of ascorbic acid (AA) was constructed based on the Ag2S quantum dots (QDs) and multifunctional hydroxyl cobalt oxide nanoflakes (CoOOH NFs). Ag2S QDs can be assembled on the surface of CoOOH NFs by electrostatic adsorption, resulting in the quenching of the NIR fluorescence emission of Ag2S QDs at 680 nm effectively through the inner filter effect (IFE). o-Phenylenediamine (OPD), a common substrate of oxidase-like (OXD) mimic, is rapidly oxidized into the fluorescent product of 2,3-diaminophenazine (DAP) with the appearance of an emission peak at 575 nm under the catalysis of CoOOH NFs. After AA was added, the fluorescence emission of DAP declined because of the decline in the OXD-like activity of CoOOH NFs due to the transformation of Co2+. Simultaneously, Ag2S QDs were released, accompanied by the recovery of red fluorescence. These two fluorescent signals can be excited at the same excitation wavelength, simplifying the detection procedure. Using F575/F680 as the readout, the quantification of AA can be realized with the linear range and detection limit of 0.2 μM–20 mM and 0.014 μM, respectively. The ratiometric fluorescence sensor can be effectively used to determine the content of AA in real samples such as juice and serum. This work integrates the in-situ formation of the fluorescent species via the catalysis of the nanozyme and the redox reaction to destroy the CoOOH NFs nanozyme as well as the two dimensional nanoflake induced turn-off-on strategy for Ag2S QDs, which provides a specific strategy for the selective detection of AA and may offer a reliable approach for the construction of other biosensing platforms. [ABSTRACT FROM AUTHOR]

Electrochemically active oxides play important roles in the fabrication of electrochemical sensing platforms, in which they can be utilized as electrochemical probes or catalysts in electrochemical reactions. Herein, a novel ratiometric electrochemical sensor for uric acid (UA) was developed based on the newly synthesized Cu2O nanocubes with good electrochemical activity combined with boron carbide (B4C) with excellent conductivity. The oxidation peak of Cu2O remained unchanged, which could be used as a reference, while the oxidation peak of UA catalyzed by the modified electrode increased with the concentration of UA. The two signals displayed a large peak-to-peak potential and thus a ratiometric electrochemical sensor for UA was established, which could further reduce the effects of unrelated factors, such as the environment influence. The sensor exhibited good linear ranges of 0.1–100 μM and 100–1000 μM, and showed good sensitivity, selectivity, repeatability, and stability. The sensor was successfully applied in the detection of UA in complex human serum and urine samples. [ABSTRACT FROM AUTHOR]

A novel pyrene-pyridyl conjugated oligomer (OPP-OMe) was conveniently prepared by one-pot Sonogashira coupling. Intriguingly, it was found that introducing only one methoxy moiety at the 4-pyridyl position can be sufficient for creating an oligomer-based ultrafine reactive fluorescent nanoprobe, i.e., OPP-OMe NPs (ca. 2.5 nm in diameter). Spectral analyses and elucidation of the intermediate structure revealed that the methoxy triggered-oxidation, together with nanoaggregation of OPP-OMe NPs, results in rapid, specific and supersensitive sensing of hypochlorite (LOD, 0.3 nM, S/N = 3). [ABSTRACT FROM AUTHOR]

A new fluorene–pyridine oligoelectrolyte (OFP) is rationally proposed and readily synthesized via a simple one-pot Sonogashira approach. Hence, an unexpectedly small cationic oligomer nanosensor (i.e. OFPNPs, ∼ 1.2 nm in diameter) was conveniently fabricated owing to the enhanced flexibility endowed by the meta-substituted pyridyl unit. Inspiringly, this facile nanoplatform with low cytotoxicity favors the ultrasensitive fluorescence assay for heparin and protamine with a detection limit (LOD, S/N = 3) as low as 1.2 ng mL−1 and 0.5 ng mL−1, respectively, involving heparin-induced aggregation of OFPNPs through electrostatic interaction or competitive rebinding of protamine to heparin. [ABSTRACT FROM AUTHOR]

Alkaline phosphatase (ALP) is an essential hydrolase and widely distributed in living organisms. It plays important roles in various physiological and pathological processes. Herein, a turn-on near-infrared (NIR) fluorescent probe (DXMP) was developed for sensitive detection of ALP activity both in vitro and in vivo based on the intramolecular charge transfer (ICT) mechanism. Upon incubation with ALP, DXMP exhibited a strong fluorescence increment at 640 nm, which was attributed to the fact that ALP-catalyzed cleavage of the phosphate group in DXMP induced the transformation of DXMP into DXM-OH. The probe exhibited prominent features including outstanding selectivity, high sensitivity, and excellent biocompatibility. More importantly, it has been successfully used to detect and image endogenous ALP in living cells and zebrafish. [ABSTRACT FROM AUTHOR]

Group IV nanodots (NDs) mainly including carbon (C), silicon (Si), germanium (Ge) have aroused much attention as one type of important nanomaterials that are widely studied in optoelectronics, semiconductors, sensors and biomedicine-related fields owing to the low cost of synthesis, good stability, excellent biocompatibility, and some attractive newly emerged properties. In this review, the synthesis, surface engineering and application in bioimaging and biotherapy of group IV NDs are summarized and discussed. The recent progress in the rational synthesis and functionalization, specific therapy-related properties, together with in vivo and in vitro bioimaging are highlighted. Their new applications in biotherapy such as photothermal therapy (PTT) and photodynamic therapy (PDT) are illustrated with respect to C, Si and Ge NDs. The current challenges and future applications of these emerging materials in bioimaging and biotherapy are presented. This review provides readers with a distinct perspective of the group IV NDs nanomaterials for synthesis and surface engineering, and newly emerging properties related to applications in biomedicine. [ABSTRACT FROM AUTHOR]

Conjugated polymers (CPs) can be fabricated into conjugated polymer nanoparticles of various shapes, thus tuning the hydrophobicity and sensing performances of the parent polymers. Herein, two new hydrophobic oligomeric CPs containing pyrene–pyridyl moieties, P1 and P2, were directly prepared and conveniently converted into hydrophilic nanorods, i.e. P1NRs and P2NRs (about 4–21 and 6–20 nm in diameter), by a modified microemulsion method. Notably, separated P1NRs exhibit excellent stability while P2NRs tend to stack on each other perhaps due to their different rigidity of π-delocalized backbones, which may have a profound effect on their fluorescence properties. In addition, Pd2+ can coordinate with the pyridyl N atoms, thereby causing ultrasensitive fluorescence quenching of P1NRs and P2NRs owing to the aggregation of oligomeric CP nanorods. These two simple nanosensors can help to determine Pd2+ with detection limits as low as 1 and 70 nM, respectively. It is worth noting that biocompatible P1NRs with bright blue fluorescence can be employed for efficient imaging of trace level Pd2+ ions in live cells. [ABSTRACT FROM AUTHOR]

Titanium carbides (Ti3C2), a new family of two-dimensional (2D) nanomaterials, have attracted extensive attention due to their unique structure and desirable physiochemical properties. Herein, we developed an effective and selective fluorescent turn-on nanosensor for glucose detection based on Ti3C2 nanosheets combined with red-emitting carbon dots (RCDs). The fluorescence intensity of RCDs could be effectively quenched (>96%) by Ti3C2 nanosheets through the inner-filter effect (IFE). In the presence of H2O2, the quenched fluorescence of the RCDs can remarkably recover due to the Ti3C2 nanosheets which were oxidized into Ti(OH)4 by H2O2. Based on H2O2 generated from oxidation of glucose catalyzed by glucose oxidase, the nanosensor can also be exploited for monitoring glucose. Under optimal conditions, a linear relationship between the increased fluorescence intensity of RCDs and the concentration of glucose was established in the range from 0.1 to 20 mM. The detection limit was 50 μM (S/N = 3). The proposed nanosensor also represented excellent selectivity for glucose analysis in biological fluid samples, providing a valuable platform for glucose sensing in clinical diagnostics. [ABSTRACT FROM AUTHOR]

The high-temperature and high-pressure Haber–Bosch process for industrial NH3 production is rather energy-intensive with heavy CO2 emission. Electrochemical N2 reduction in aqueous media offers an eco-friendly and sustainable alternative to ambient NH3 synthesis with the aid of efficient electrocatalysts for the N2 reduction reaction (NRR), but they suffer from limited current efficiency for NH3 formation due to the unavoidable competing hydrogen evolution reaction (HER). Here, we report that LaF3 nanoplates act as a superb NRR electrocatalyst for ambient N2-to-NH3 fixation with excellent selectivity due to their effective inhibition of the HER and activation of the N≡N triple bond. In 0.5 M LiClO4, they achieve a high faradaic efficiency of 16.0% and a large NH3 yield of 55.9 μg h−1 mgcat.−1 at −0.45 V vs. the reversible hydrogen electrode, much higher than those of La2O3 (1.4%; 12.5 μg h−1 mgcat.−1) and most reported aqueous-based NRR catalysts. This catalyst also shows high long-term electrochemical and structural stability. The detailed NRR mechanism is also discussed. [ABSTRACT FROM AUTHOR]

Currently, industrial-scale NH3 production mainly relies on the energy-intensive and CO2-emitting Haber–Bosch process from atmospheric N2 and fossil fuels. Electrochemical N2 fixation offers an eco-friendly and sustainable alternative to ambient NH3 synthesis with the aid of efficient electrocatalysts for the N2 reduction reaction (NRR). Here, a perylene-3,4,9,10-tetracarboxylic acid nanorod-reduced graphene oxide (PTCA–rGO) nanohybrid is proposed as a metal-free electrocatalyst to synergistically enhance N2 reduction under ambient reaction conditions. In 0.1 M HCl, the PTCA–rGO hybrid provides a large NH3 yield of 24.7 μg h−1 mgcat.−1 and a high faradaic efficiency of 6.9% at −0.50 V vs. the reversible hydrogen electrode, which are much superior to those of PTCA and rGO counterparts. This catalyst also shows a high electrochemical and structural stability. Density functional theory calculations suggest that the NRR over the hybrid catalyst takes place via both distal associative and partially alternative routes. [ABSTRACT FROM AUTHOR]

The simple and highly sensitive detection of organophosphorus pesticides (OPs) is urgently required. Here, we have developed a sensing method for OPs based on the trypsin digestion of the template of bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs), thus leading to BSA-AuNC aggregation and quenching of their fluorescence. While the activity of trypsin was irreversibly inhibited in the presence of OPs, the fluorescence quenching efficiency of BSA-AuNCs decreased. Under the optimal conditions, the logarithm of OPs concentration was proportional to inhibition efficiency in the range of 0.1 ng mL−1 to 5 μg mL−1. The detection limit of OPs reached 0.037 ng mL−1. What's more, the sensing method was successfully utilized in the detection of OPs in real food samples. These results indicated that the OPs sensor has potential applications in the safety and monitoring of agricultural samples. [ABSTRACT FROM AUTHOR]

Electrocatalytic N2 reduction as an alternative approach to the energy-intensive and large CO2-producing Haber–Bosch process for NH3 synthesis under mild conditions has attracted extensive attention. Current research efforts on N2 reduction have mainly focused on metal-based catalysts, but metal-free alternatives can avoid the issue of metal ion release. In this work, oxygen-doped hollow carbon microtubes (O-KFCNTs) derived from natural kapok fibers are reported as a metal-free NRR electrocatalyst for N2-to-NH3 conversion with excellent selectivity. In 0.1 M HCl, the O-KFCNTs achieve a high faradaic efficiency of 9.1% at −0.80 V vs. a reversible hydrogen electrode (RHE) and a NH3 yield rate of 25.12 μg h−1 mgcat.−1 at −0.85 V vs. RHE under ambient conditions. Notably, this catalyst also demonstrates high stability. [ABSTRACT FROM AUTHOR]

In this study, a highly selective and eco-friendly fluorescent sensor consisting of upconversion (UCNPs) and gold nanoparticles (AuNPs) was developed for the detection of iodide (I−). The negatively charged AuNPs were able to electrostatically adsorb on the positively charged UCNPs, leading to the fluorescence quenching of the UCNPs. In the presence of l-cysteine, AuNPs were released from the surface of the UCNPs and aggregated due to the Au–S interactions that occurred between the AuNPs and l-cysteine, which resulted in the fluorescence recovery of the UCNPs. Upon the addition of I−, the fluorescence of the UCNPs was gradually quenched meaning that I− catalyzes the oxidation of l-cysteine, preventing the aggregation of AuNPs and forming a fluorescence resonance energy transfer system. The I−-catalyzed oxidation reaction provides a method for the l-cysteine-triggered sensor to detect I−, using l-cysteine to modulate the fluorescence signal in an eco-friendly manner. Based on the above special detection strategies, this sensor has excellent selectivity for I− even in a complex matrix such as urine, which is much better than most assays for I−. Under the optimal conditions, the sensor allows the quantitative analysis of I− with a detection limit of 55 nM. The high selectivity, sensitivity and environmental friendliness of the sensor proves that it has the potential for the detection of I− in actual samples. Most importantly, the excellent results of the sensor for the detection of I− in urine prove that the probe can be used as an ideal tool in clinic diagnoses. [ABSTRACT FROM AUTHOR]

In this work, a colorimetric and ratiometric fluorescent probe, 2,3-bis(((E)-4-(diethylamino)-2-hydroxybenzylidene)amino)maleonitrile (DHM), was developed based on N2H4-induced bond cleavage. Two cyanide groups of DHM were applied to sense hydrazine (N2H4) for the first time, which was demonstrated using 1H NMR and HRMS spectra. The specific ‘C-CN’ bond cleavage induced by N2H4 showed an excellent fluorescence ratiometric behavior and a visible colorimetric change from purple to yellow. Meanwhile, it showed a low detection limit of 58.1 nM (1.65 ppb), which is far below the safety level (10 ppb) set by the U.S. EPA. Moreover, the probe was successfully employed for the quantitative detection toward N2H4 in real water samples. [ABSTRACT FROM AUTHOR]

In this study, a facile and environment-friendly method for the preparation of bovine serum albumin (BSA) capped fluorescent Cu nanoclusters (BSA-CuNCs) was adopted. The as-prepared BSA-CuNCs were characterized by ultraviolet-visible spectroscopy (UV-Vis), fluorescent spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM). The fluorescence excitation and emission wavelength of BSA-CuNCs appeared at 325 and 406 nm, respectively. The as-synthesized BSA-CuNCs can be utilized as a bi-functional nanomaterial for pH sensing and dopamine (DA) detection with good performance. The fluorescence intensity decreased linearly with decrease in pH from 12 to 5 and increased linearly with increase in DA concentration from 0.5 to 50 μM. TEM measurements proved that the decrease in the pH value resulted in the aggregation of BSA-CuNCs, leading to color change and the quenching of fluorescence. The FT-IR spectra, fluorescent spectra, UV-Vis spectra and zeta potential measurements demonstrated that DA can be combined with Cu2+ and the Cu2+ would be removed from the surface of BSA-CuNCs. As a result, the fluorescence was recovered owing to the formation of the highly stable compound CuH2(DA)2. The pH value of five water samples was determined by the proposed method with relative errors of less than 0.91%. Furthermore, DA in human urine samples was also analyzed by BSA-CuNCs with good recoveries ranging from 90.4% to 104.7% using the standard addition method. It is believed that the bi-functional BSA-CuNCs will show great potential in bio-systems. [ABSTRACT FROM AUTHOR]

Synthesis of graphene oxide quantum dots (GO-dots) often requires strong concentrated acid, and takes a long time. Herein, we used black carbon as a precursor and H2O2 as a facile oxidant and developed a simple and facile one-pot hydrothermal method for synthesis of GO-dots without the need to use strong concentrated acid and the entire synthetic process only took 90 min. Furthermore, any other post-processing steps are avoided. [ABSTRACT FROM AUTHOR]

An enhanced understanding of the interactions between charged nanoparticles (CNPs) and a curved vesicle membrane may have important implications for the design of nanocarrier agents and drug delivery systems. In this work, coarse-grained molecular dynamics (CGMD) simulations of the CNPs with vesicles were performed to evaluate the effects of hydrophobicity, surface charge density and distribution on the curved vesicle membrane. The simulations reveal that there exist four distinct modes (insertion, repulsion, adhesion, and penetration) in the CNP–vesicle interaction. In contrast to previous studies on a planar membrane, the interactions of CNPs and a curved vesicle membrane show some novel properties. CNPs with low surface charge density (or neutral ones) can penetrate into the interior of the vesicle membrane more easily because of the increased membrane tension. The asymmetry between two leaflets of the membrane induces different interaction strengths of the negatively CNPs with the outer and inner leaflets. After penetration, the negatively CNPs prefer to stay close to the inner leaflet inside the vesicle where CNPs have stronger interactions with their surroundings. In the present work, we analyze the detailed mechanism of CNP's spontaneous penetration into vesicles, which is rarely mentioned in previous simulations. Moreover, we found that the negatively CNPs with the same surface charge density but different distribution result in different modes: the homogeneous mode is more likely to adsorb on the vesicle surface while the inhomogeneous mode tends to be more penetrable. In addition, the flip-flop phenomenon of the lipid membrane and the exchanging of water in or out of the vesicle were observed during penetration. Our results demonstrate that the electrostatic effect plays an essential role in the interaction between CNPs and vesicles. These findings suggest a way of controlling the CNP–vesicle interaction by coupling the hydrophobic properties, surface charge density and distribution of CNPs to enhance the probability of CNP's penetration into vesicles. [ABSTRACT FROM AUTHOR]

We have found that hydroxyl-rich carbon dots (C-dots) have the ability to reduce Au3+ to form gold nanoparticles (AuNPs). Thiocyanate (SCN−) can be absorbed on the surface of the AuNPs due to its high affinity toward the AuNPs, which inhibits the growth of the AuNPs. Meanwhile, SCN− has the ability to etch the as-synthesized big AuNPs to small AuNPs, which can also cause the absorption peak of the AuNPs to decrease. Therefore, an optical sensor is developed for the detection of SCN− based on measuring the plasmon resonance absorption peak change of the AuNPs. Under optimal conditions, this method yields excellent sensitivity (the limit of detection is 0.16 μM) and selectivity toward SCN−. This method can detect SCN− in raw milk with satisfactory results. This work gives new insight into monitoring the quality of milk. [ABSTRACT FROM AUTHOR]

Hydroxyl-rich C-dots were used as both the reducing and stabilizing agent in the preparation of noble metal nanoparticles (AuNPs, AgNPs and Au@AgNPs) for the detection of glucose. [ABSTRACT FROM AUTHOR]

A novel ratiometric fluorescent Hg2+ detecting system was rationally developed based on the typical excited state intramolecular proton transfer (ESIPT) characteristic of the latent fluorophore, 2-(1-(p-tolyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenol (Pol) and the Hg2+-mediated cleavage of the vinyl group. The probe responds selectively to Hg2+ over various other metal ions with a larger bathochromic shift (∼100 nm). The sensing mechanism was investigated in detail by fluorescence spectroscopy, NMR spectra and mass spectrometry. Taking advantage of the enhancement effect of dichloromethane on the ESIPT efficiency, a facile dichloromethane extraction was introduced in the process of detection of Hg2+, which affords a high sensitivity for the probe with a detection limit of 7.8 × 10−9 M for Hg2+. By using the new strategy, the novel probe can be used for the detection of Hg2+ in practical water samples with good recovery. Moreover, the probe was successfully applied to the fluorescence image of Hg2+ in living cells. These results indicated that the probe and the proposed method have promising applications for Hg2+ sensing in biological and environmental sciences. [ABSTRACT FROM AUTHOR]

In this study, we synthesized a new fluorescence probe which was used to detect melamine by coupling with gold nanoparticles (AuNPs). The new fluorescence probe has good optical stability and high fluorescence intensity, which can greatly improve the detection sensitivity. Compared to the traditional fluorophore, it is less dependent on the pH value. It has a very strong fluorescence emission peak at 550 nm, which has larger overlap with the absorption peak of AuNPs. When the probe incubates with the AuNPs, the fluorescence of the probe can be effectively quenched by AuNPs. Adding melamine into a probe–AuNPs mixture caused aggregation of AuNPs and released the adsorbed probe; the fluorescence intensity of the probe was recovered. By measuring the changes of the fluorescence intensity of the probe, the detection of melamine can be realized. Under optimized conditions, the linear response to melamine is in the range of 1.0 × 10−8–4.0 × 10−6 mol L−1 and lowers the detection limit down to 3.0 nmol L−1 with the sensor. This method can detect melamine in milk and milk-based productions. [ABSTRACT FROM AUTHOR]

High quality carbon dots (C-dots) with down- and up-conversion fluorescence have been synthesized through low-temperature carbonization using sweet pepper as the carbon source. The C-dots with a quantum yield (QY) of 19.3% exhibit superior photophysical properties, for example, narrow and symmetric emission spectra, large stock shifts, resistance to photobleaching, and excitation-dependent fluorescence behavior. The excellent C-dots serve as useful fluorescent probes for hypochlorite (ClO−) detection by both down- and up-conversion fluorescence. Two consecutive linear ranges allow a wide determination of ClO− concentrations with a low detection limit of 0.05 μmol L−1 and 0.06 μmol L−1 (S/N = 3) for down- and up-conversion fluorescence measurements, respectively. The proposed detection method is advantageous because it is simple, sensitive, dual-signalling model and low-cost and has potential extensive applications in environmental and biological assays. [ABSTRACT FROM AUTHOR]

A label-free fluorescent sensor for the detection of Cu2+ was constructed based on internal DNA cleavage and DNA intercalator SYBR Green I. The DNAzyme complex formed by the hybridization of the enzyme strand and substrate strand has two base-pairing regions including a DNA duplex and a DNA triplex. The copper ion-induced catalytic reaction makes the substrate strand irreversibly break at the cleavage site, which disturbs the formation of DNA strands. The weakly fluorescent dye SYBR Green I served as a fluorescence indicator that intercalated into the base-pairing regions of DNAzyme, resulting in a strong fluorescence emission. In the presence of Cu2+ in the test system, the complementary regions were reduced due to the fracture of the DNA strand. The fluorescence intensity was decreased because SYBR Green I was released from the cleaved regions. Other metal ions had no notable “on-off” phenomenon even at 50 times Cu2+ concentration. Under the optimal conditions, a linear response with Cu2+ concentration ranging from 4 × 10−8 to 120 × 10−8 M was obtained. The detection limit reached as low as 10 nM. Moreover, the cost-effective sensor was successfully applied to the determination of Cu2+ in drinking water. [ABSTRACT FROM AUTHOR]

Based on guanine (G)-quenching, a simple and sensitive fluorescent aptasensor for the detection of adenosine was constructed. G located on the end of a DNA strand was selected as a fluorescence quencher of a FAM fluorophore. The FAM-labeled adenosine aptamer (FAM-DNA) was partly complementary to the DNA sequence containing five G on the end. In the absence of adenosine, the hybridization between FAM-DNA and complementary strand cause G to approach FAM, hence, the fluorescence of FAM was effectively quenched by the photoinduced electron transfer (PET) between FAM and G. In the presence of adenosine, FAM-DNA reacts with adenosine and starts structural switching, resulting in the release of the complementary strand and the recovery of the fluorescence of FAM. The linear detection range of adenosine with present proposed sensor is 20–200 μM, and the detection limit down to 6.7 μM (S/N = 3). Most importantly, no organic dye molecules-labeled DNA or extra nanomaterials were used as quenchers in this proposed adenosine detection strategy. The method is simple, sensitive and inexpensive and has potential for application in clinical diagnostic assays. [ABSTRACT FROM AUTHOR]

Apoferritin is a uniform spherical nano-size biomaterial with excellent bio-compatibility. In this work, we report the use of apoferritin as a novel biocompatible carrier for stabilizing enzymes and enhancing their activities. We used glucose oxidase (GOx) as a model enzyme in this study. GOx was immobilized on the surface of the apoferritin through a green synthetic approach, taking advantage of bioaffinity binding between streptavidin and biotin. As a result, a glucose oxidase–biotin/streptavidin/biotin–apoferritin conjugate (Apo–GOx) was prepared using streptavidin as the bridge. The synthesized Apo–GOx was characterized by transmission electron microscopy, ultraviolet and fluorescence spectroscopy. The activity and stability of GOx on the surface of the apoferritin were investigated and challenged by different environmental factors, such as the temperature, chemicals and pH, in comparison with the biotinylated GOx (B-GOx). The results demonstrate that the activity of Apo-GOx is significantly enhanced while the thermal and chemical stabilities of Apo-GOx are also greatly improved compared to free B-GOx. For instance, the activity of the Apo-GOx only lost 30% after 2 h incubation at 50 oC in comparison to a 70% loss of free B-GOx. The activity of Apo-GOx remains intact after 30 min incubation in 5 M urea solution while B-GOx lost 80% activity after the same treatment. Furthermore, glucose detection was used as a model application for the enzyme immobilization method developed in this work. The GOx immobilized apoferritin nanoparticles exhibited high sensitivity for glucose detection with a detection limit of 3 nM glucose. This work offers a novel approach for immobilizing enzymes with enhanced stability and activity, thus holds the promising advantage for a number of applications, such as in enzyme catalysis, DNA assays and immunoassays. [ABSTRACT FROM AUTHOR]

Ultrathin graphitic carbon nitride nanosheets (g-C3N4) with a thickness of about 2 nm were synthesized by a one-step electrochemical method for the first time. The possible mechanism of the electrochemical synthesis was discussed. This as-synthesized g-C3N4 showed intrinsic peroxidase-like activity and was successfully applied for the detection of uric acid. [ABSTRACT FROM AUTHOR]

A fluorescent probe (N-(4-methyl-2-oxo-2H-chromen-7-yl)-2,4-dinitrobenzenesulfonamide), which exhibits high selectivity to glutathione and cysteine among amino acids including sulphur-containing methionine and metal ions, was synthesized. The experiments demonstrate that the fluorescent probe is a reliable and specific probe for glutathione and cysteine in living cells. [ABSTRACT FROM AUTHOR]