A catalyst-free co-reaction system of long-lasting and intensive chemiluminescence applied to the detection of alkaline phosphatase

Bimetallic Ag/Fe-MOG derived flake-like Ag2O/Fe2O3 p-n heterojunction for efficient photodegradation organic pollutants within a wide pH range

In this paper, we reported a facile and clean strategy to prepare the flake-like Ag2O/Fe2O3 bimetallic p-n heterojunction composites for photodegradation organic pollutants. The surface morphology, crystal structure, chemical composition and optical properties of Ag2O/Fe2O3 were characterized by SEM, high-resolution TEM images with EDX spectra, XRD, XPS, FT-IR and UV-vis DRS spectra respectively. The formation of Ag2O/Fe2O3 p-n heterojunction facilitated the interfacial transfer of electrons as well as the separation of charge carries. Hence, the as-synthesized Ag2O/Fe2O3-3 composites exhibited ultra-high photocatalytic activity. Under the experimental conditions of catalyst dosage of 0.4 mg mL-1 and irradiation time of 60 min, the degradation conversion rate of rhodamine B reached 96.1 %, which was 5.0 and 2.8 times of pure phase Ag2O and Fe2O3, respectively. Meanwhile, the degradation performance of Ag2O/Fe2O3-3 was not limited by pH, and it can achieve high degradation efficiency under 3-11. In addition, Ag2O/Fe2O3-3 also showed superb degradation ability for other common anionic dyes, cationic dyes and antibiotics. XPS and FT-IR spectra showed that Ag2O/Fe2O3-3 retained a carbon skeleton that facilitated electron transport and light absorption conversion. And the analyses of quenching experiment and EPR demonstrated •O2-, •OH and h+ were crucial reactive oxidant species contributing to the rapid organic pollutant degradation. This work provides new insights into obtaining p-n photocatalysts heterojunction with excellent catalytic activity for removing organic pollutants from wastewater.

Hydrogen peroxide enhanced glow-type chemiluminescence of hydrazine hydrate modified carbon quantum dots-potassium persulfate system

Most known chemiluminescence (CL) systems are flash-type that generate weak luminescence and decline quickly after dozens of seconds, while the glow-type CL systems have stable emission for an extended period to achieve accurate quantitation. In this work, a long-term CL system based on hydrazine-hydrate (N2H4·H2O) modified carbon quantum dots (N-CQDs) as a luminescent probe, with K2S2O8 and H2O2 as co-reactants, was proposed. The CL emission enhanced by H2O2 increased 18-fold more than that of N-CQDs and K2S2O8 direct reaction, and decayed by 5% of the maximum intensity over 700 s. In the reaction system, K2S2O8 and H2O2 co-reactants can promote each other to continuously generate corresponding radicals (•OH, O2•-, 1O2), which in turn trigger the CL emission of N-CQDs. This phenomenon was identified as the primary cause for the production of persistent CL. In addition, a stable and selective CL sensor based on the N-CQDs-K2S2O8-H2O2 CL enhancing system was developed for ascorbic acid quantitation in the linear range from 0.1 to 10.0 mM with a detection limit of 0.036 mM. The method has been applied to the analysis of tablet samples and holds potential in pharmaceutical analysis field.

MnO2-based dual channel surface plasmon resonance fiber sensor for trace glutathione and refractive index detection

Glutathione (GSH) plays vital role in human biological systems, so its rapid and sensitive detection is necessary for health condition monitoring. In this work, a simple structure for dual channel GSH and refractive index (RI) detection is proposed. By introducing Au-MnO2 thin film coating on the fiber surface for the first time, GSH solution would lead to the dissolution of MnO2, the change in GSH levels could be monitored over a short period in channel 2. For channel 1, ITO-Ag thin film is applied for RI change detection. After optimization, the GSH detection sensitivity reached about -2.361 nm/mM in the range of 0.005-50 mM, and the RI sensitivity reached 1704.252 nm/RIU in the range of 1.331-1.3895 RIU. Channel 1 could also put into GSH detection in the high concentration scale to enlarge the sensor's range and 0.095 nm/mM of sensitivity is acquired within the range of 50-600 mM. With the presence of MnO2 film, the detection sensitivity increased 25.663 times. Neither channel interferes with the operation of the other. Proposed sensor provides stability, high selectivity and elevation in GSH detection sensitivity, which shows great potential for environmental and biological detection field and their applications.

Quantification strategy of absolute chemiluminescence efficiency for systems of luminol with hydrogen peroxide

An important feature to be determined in mechanistic studies on chemiluminescence (CL) is its quantum efficiency, which can give significant chemical reaction information on the influence of the reactant structures and reaction conditions. However, most of the previous quantitative measurements of luminescence and quantum efficiencies are complex and incomplete. To overcome the inconvenience and underestimated quantum efficiency in each measurement, we report a simple and highly effective strategy to determine the absolute CL quantum efficiencies for three systems of luminol with hydrogen peroxide by means of a spectrometer along with an integrating sphere. The integrating sphere facilitated collection of all the emitted light and then transferred it to the spectrometer via an optical fiber proportionally. The CL quantum efficiency was determined by taking the ratio of total photons generated in the reaction system to the number of the limiting reactant molecules consumed. Absolute CL efficiencies of three luminol-H2O2 reaction systems with varied reactant concentrations or coreactants were found to be 37 %, 7.0 % and 6.6 % in a time course, which are much higher than those previously reported values of 1.0-1.3 %. Due to our complete photon collection design, a higher absolute CL efficiency can be realized. Furthermore, spooling CL spectra also provided a powerful visualization tool to observe the real-time CL evolution and devolution, allowing the study on kinetics of CL reaction systems. The above investigations are anticipated to promote further development of CL methodologies and their applications.

Carbon dot/Co-MOF nanocoral mediated fluorescence-scattering ratiometric sensor for highly sensitive detection of alkaline phosphatase

Abnormal expression of alkaline phosphatase (ALP) in serum has received considerable attention in health monitoring and disease diagnosis. However, conventional optical analysis based on a single signal must compromise background interference and limited sensitivity in trace analysis. As an alternative candidate, the ratiometric approach depends on the self-calibration of two independent signals in a single test to minimize interferences from the background for accurate identification. Here, a carbon dot/cobalt-metal organic framework nanocoral (CD/Co-MOF NC) mediated fluorescence-scattering ratiometric sensor has been developed for simple, stable, and highly sensitive detection of ALP. ALP-responsive phosphate production was used to coordinate cobalt ion and collapse the CD/Co-MOF NC, resulting in the recovery of fluorescence signal from dissociative CDs and the decrease of second-order scattering (SOS) signal from the cracked CD/Co-MOF NC. The ligand-substituted reaction and the optical ratiometric signal transduction provide a rapid and reliable chemical sensing mechanism. The ratiometric sensor effectively converted ALP into a ratio signal of fluorescence-scattering dual emission throughout a wide linear concentration range of six orders of magnitude with a detection limit of 0.6 mU/L. In addition, self-calibration of fluorescence-scattering ratiometric method can reduce background interference and improve sensitivity in serum, approaching recoveries of ALP from 98.4% to 101.8%. Due to the above advantages, the CD/Co-MOF NC mediated fluorescence-scattering ratiometric sensor readily provides rapid and stable quantitative detection of ALP as a promising in vitro analytical method for clinical diagnostics.

Synergistic effect-triggered fluorescence quenching enables rapid and sensitive detection of alkaline phosphatase

The development of biosensors mediated by synergistic quenching effect is of great significance for rapid and accurate clinical diagnosis. Hence, we prepared a cyan-emitting fluorescent Si dots for alkaline phosphatase (ALP) detection through the synergistic quenching effect of inner filter effect (IFE) and photo-induced electron transfer (PET). Si dots were prepared by microwave-assisted method, which displayed high quantum yield (28.7%), as well as good physiochemical properties, such as photo-stability, pH stability, and chemical stability. As the hydrolysate of 4-nitrophenyl phosphate disodium salt hexahydrate catalyzed by ALP, both IFE and PET of 4-nitrophenyl to Si dots were used for the turn-off mode detection of ALP. The linear relationships were established between the change of fluorescence intensity and ALP concentration in the range of 0.05 U L^-1 to 5.0 U L-1, and 5.0 U L^-1 to 80.0 U L^-1, respectively. The detection limit was 0.01 U L^-1. The synergistic quenching effect caused the turn-off mode detection to be more sensitive, and it can also be used for the accurate detection of ALP in human serum, thereby showing great anti-interference ability in complex environments.

A turn-on chemiluminescent assay for alkaline phosphatase using two-dimensional Fe-centered metal-organic frameworks as the signaling probe

Alkaline phosphatase (ALP) is an essential enzyme involved in cell phosphorus metabolism. Developing sensitive and accurate ALP quantitative assays is significant. In this study, a turn-on chemiluminescence (CL) analysis platform for the detection of ALP activity in human serum was established based on two-dimensional (2D) Fe-centered metal-organic frameworks with 1,3,5-benzene tricarboxylic acid as ligands (denoted as 2D Fe-BTC). The 2D Fe-BTC as the signaling probe reacts with ascorbic acid forming reduced Fe-BTC which catalyzes the luminol CL reaction producing a strong CL signal. The 2D Fe-BTC-based luminol CL reaction exhibited good CL responses when the concentration of ascorbic acid was in the range of 5-500 nM. By employing magnesium ascorbyl phosphate (MAP) as the substrate which can be hydrolyzed by ALP to generate ascorbic acid, a turn-on CL assay for the detection of ALP was established. Under optimal conditions, as low as 0.00046 U L-1 of ALP could be sensitively detected with a linear range of 0.001-0.1 U L-1. ALP in human serum can be detected after a simple dilution process without any other pretreatment.

A novel luminol-coordinated silver(I) organic gel with self-enhanced chemiluminescence applied for uric acid detection

A novel silver(I)-based metal-organic gel (AgMOG) consisting of luminol as the ligand was synthesized by a facile strategy, which was found to exhibit self-enhancing chemiluminescence (CL) property. Based on this, a new AgMOG-K₂S₂O₈ CL system without additional catalyst was established. According to the results of CL spectra, electron spin resonance (ESR) spectra as well as the influence of radical scavengers to AgMOG-K₂S₂O₈ system, the possible CL mechanism of this system was discussed. In this CL system, AgMOG exhibited the dual properties of catalysis and luminescence. On the one hand, AgMOG can catalyze K₂S₂O₈ to produce SO₄^•-. The generated SO₄^•- can be converted to hydroxyl radical (OH^•) under alkaline condition, and further converted to other radical oxygen species (ROS, such as ¹O₂ and O₂^•-). Furthermore, the reaction between the K₂S₂O₈ and H₂O can form H₂O₂, which also can be catalyzed by AgMOG to produce ROS. On the other hand, the AgMOG can be oxidized by ROS to emit strong CL signal. Then, based on the quenching effect of uric acid (UA) to this CL system, a method for UA detection was established with a good linearity over the range from 0.08 to 10 µmol·L^-1. In this work, a new CL luminant with catalytic property was synthesized by a simple method, and a self-enhancing AgMOG-K₂S₂O₈ CL system was developed for the first time, providing a novel direction for the application of MOG in the CL field.