Synthesis of carbon dot based Schiff bases and selective anticancer activity in glioma cells.

Schiff bases have remarkable anticancer activity and are used for glioma therapy. However, the poor water solubility/dispersibility limits their therapeutic potential in biological systems. To address this issue, carbon dots (CDs) have been utilized to enhance the dispersibility in water and biological efficacy of Schiff bases. The amino groups on the surface of CDs were conjugated effectively with the aldehyde group of terephthalaldehyde to form novel CD-based Schiff bases (CDSBs). The results of the MTT assays demonstrate that CDSBs have significant anticancer activity in glioma GL261 cells and U251 cells, with IC50 values of 17.9 µg mL-1 and 14.9 µg mL-1, respectively. CDSBs have also been found to have good biocompatibility with normal glial cells. The production of reactive oxygen species (ROS) in GL261 glioma cells showed that CDSBs, at a concentration of 44 µg mL-1, resulted in approximately 13 times higher intracellular ROS production than in the control group. These experiments offer evidence that CDSBs induce mitochondrial damage, leading to a reduction in mitochondrial membrane potential in GL261 cells. In particular, in this work, CDs serve not as carriers, but as an integral part of the anticancer drugs, which can expand the role of CDs in cancer treatment.

In or on, a study of the influence of the binding site for TiO2 and MIL-101(Cr).

In this work, TiO2 was formed in situ in the internal pores and on the surface of MIL-101(Cr). Density functional theory (DFT) calculations demonstrate that the difference in the binding sites of TiO2 can be attributed to the different solvents used. The two composites were used to photodegrade methyl orange (MO), and the photocatalytic efficiency of TiO2-in-MIL-101(Cr) (90.1% in 120 min) was much stronger than that of TiO2-on-MIL-101(Cr) (14% in 120 min). This is the first work to study the influence of the binding site of TiO2 and MIL-101(Cr). The results show that MIL-101(Cr) modification with TiO2 can promote electron-hole separation, and TiO2-in-MIL-101(Cr) has better performance. Interestingly, the two prepared composites have distinct electron transfer processes. For TiO2-on-MIL-101(Cr), radical trapping and electron paramagnetic resonance (EPR) studies show that O2˙- is the main reactive oxygen species. Based on its band structure, it can be concluded that the electron transfer process of TiO2-on-MIL-101(Cr) conforms to that of a type II heterojunction. However, for TiO2-in-MIL-101(Cr), the EPR and DFT results show that 1O2 is the active substance that is formed from O2 through energy transfer. Therefore, the influence of binding sites should be considered for the improvement of MOF materials.

TiO2-In-MIL-101(Cr) with Visible Light-Induced Peroxidase Activity for Colorimetric Detection of Blood Glucose.

In this work, metal-organic framework MIL-101(Cr) with regular morphology, stable structure, and good dispersion was prepared by the hydrothermal method. MIL-101(Cr) has two different sizes of pores, but after TiO2 nanoparticles (NPs) were in situ prepared, the two pores disappear. The result demonstrates that TiO2 NPs were located in the pores of MIL-101(Cr). TiO2-decorated MIL-101(Cr) forms an inside type II heterojunction and the band gap energy is narrowed, which can promote electron-hole separation and enhance the light absorption. Therefore, the heterojunction shows a high visible light-induced peroxidase-like activity. Kinetic studies exhibit that the K m value of TiO2-in-MIL-101(Cr) to TMB is 0.17 mM, and the affinity of TiO2-in-MIL-101(Cr) is higher than that of natural horseradish peroxidase (HRP). Then, a "turn-on" colorimetric assay based on TiO2-in-MIL-101(Cr) was constructed for the detection of blood glucose. The detection range is 1-100 µM (R 2 = 0.9950) with a limit of detection (LOD) of 1.17 µM. Compared with the clinical method, the constructed colorimetric method has accurate and reliable results for the clinical detection. The anti-interference experiment confirms that the method has high selectivity to glucose.

Electrochemical Detection of Alpha-Fetoprotein Based on Black Phosphorus Nanosheets Modification with Iron Ions.

Black phosphorus nanosheets (BPNSs) were synthesized with liquid exfoliation combined with the ultrasonic method and loaded with Fe3+ by simply mixing. The morphology, structure and electrochemical properties of the synthesized Fe3+/BPNSs were characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV), etc. The load of Fe3+ can improve the electrochemical performance of BPNSs and enhance the sensitivity of the detection. Additionally, Fe3+/BPNSs display good biocompatibility. In this study, immunosensors based on Fe3+/BPNSs were constructed to detect alpha-fetoprotein (AFP). The detection is due to the specific binding between the AFP antigen and antibody on the surface of the immunosensors, which can reduce the current response of Fe3+/BPNSs. The immunosensors have a good linear relationship in the range of 0.005 ng·mL-1 to 50 ng·mL-1, and the detection limit is 1.2 pg·mL-1. The results show that surface modification with metal ions is a simple and effective way to improve the electrochemical properties of BPNSs, which will broaden the prospects for the future application of BPNSs in the electrochemical field.

Dual-mode turn-on ratiometric fluorescence sensor based on carbon dots and CuInS2/ZnS quantum dots for detection of chlorotetracycline.

A new ratiometric fluorescence sensor is prepared for selective detection of chlorotetracycline (CTC) through dual-mode fluorescence method. The sensor is composed of carbon dots (CDs) with blue emission and carboxyl-modified CuInS2/ZnS quantum dots (QDs) with dark-red emission. Usually QDs are used as fluorescent probes or signal sources, but it is interesting in this strategy that CuInS2/ZnS QDs innovatively work as quenching agent to reduce the fluorescence of CDs, mainly due to the fluorescence resonance energy transfer (FRET). After the addition of CTC, the interaction between CDs and CuInS2/ZnS QDs is restrained, resulting in the fluorescence recovery of CDs, whilstthe QDs' fluorescence remains unaffected. In this work, CTC is detected in the range of 0-50 µM by conventional fluorescence and synchronous fluorescence methods under an excitation wavelength of 360 nm or Δλ = 90 nm, and the detection limits of the two methods are 0.46 µM and 0.36 µM, respectively. The designed sensor displays good selectivity compared with other tetracycline drugs with similar structure to CTC, different ions and various natural - amino acids. And the sensor can also be applied to determine CTC in tap water and milk.

Construction of Photoelectrochemical DNA Biosensors Based on TiO2@Carbon Dots@Black Phosphorous Quantum Dots.

In this work, carbon dots (CDs) and black phosphorus quantum dots (BPQDs) were used to decorate titanium dioxide to enhance the photoelectrochemical (PEC) properties of the nanocomposites (TiO2@CDs@BPQDs), and the modified nanocomposites were used to sensitively detect DNA. We used the hydrothermal method and citric acid as a raw material to prepare CDs with good dispersion and strong fluorescence properties. BPQDs with a uniform particle size were prepared from black phosphorus crystals. The nanocomposites were characterized by fluorescence spectroscopy, UV-Vis absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The preparation method of the working electrode was explored, the detection conditions were optimized, and the sensitive detection of target DNA was achieved. The results demonstrate that CDs and BPQDs with good optical properties were successfully prepared, and they were successfully combined with TiO2 to improve the PEC performance of TiO2@CDs@BPQDs. The TiO2-based PEC DNA detection method was constructed with a detection limit of 8.39 nM. The constructed detection method has many advantages, including good sensitivity, a wide detection range, and good specificity. This work provides a promising PEC strategy for the detection of other biomolecules.

Simple and sensitive determination of trace nitrite in water by zero-crossing first-derivative synchronous fluorescence spectrometry using 6-amino-1,3- naphthalenedisulfonic acid as a new fluorescent probe.

A new fluorescent probe, 6-amino-1,3-naphthalenedisulfonic acid (ANDSA), has been developed for the determination of trace nitrite in different waters. This probe is based on the selective reaction of nitrite with ANDSA in hydrochloric acid solution to form the corresponding diazonium acid in sodium hydroxide solution at room temperature. The diazonium acid produced has high fluorescence intensity at 488 nm (excitation at 367 nm), whereas ANDSA has high fluorescence intensity at 465 nm (excitation at 354 nm). The synchronous fluorescence (Δλ = 121 nm) spectrum and the first-derivative synchronous fluorescence spectrum of diazonium acid greatly overlapped with those of ANDSA. The zero-crossing method was used to measure the first-derivative value (dF/dλ) of the first-derivative spectra, in which physical separation of excess ANDSA was unnecessary. The zero-crossing point was located at 351.2 nm for ANDSA, at which dF/dλ of diazonium acid was proportional to the nitrite concentration. Therefore, dF/dλ at 351.2 nm was selected as the analytical signal. Under the optimized experimental conditions, the signal intensity was linear over a nitrite concentration range of 0.006-0.075 mg L-1, with a correlation coefficient better than 0.9994. The limit of detection was 2.1 µg L-1 for the determination of nitrite by the proposed method. The relative standard deviation of the method for the determination of nitrite in real water samples was below 2.45%, and the corresponding recoveries were between 95.7% and 104.1%. The validity of the proposed method was further confirmed by comparison with the reference method with use of the t test. Graphical abstract ANDSA reacts with nitrite to form diazonium acid with higher fluorescence intensity. For ANDSA, dF/dλ was zero at 351.2 nm, whereas dF/dλ of diazonium acid at 351.2 nm was close to the maximum value.

Fluorimetric method based on diazotization-coupling reaction for determination of clenbuterol.

A novel fluorimetric method based on diazotization-coupling reaction (DCR) for the determination of clenbuterol is described. In acidic solution, clenbuterol was first diazotized with sodium nitrite, followed by coupling with bisphenol A to produce an azo-compound in NH3- NH4Cl buffer. It has found the diazotized clenbuterol- bisphenol A- NH3- NH4Cl (DCBN) system has strong fluorescence efficiency compare with the bisphenol A solution. There is a linear relationship between the increased intensity of the fluorescence emission spectra (λex/λem = 276 nm/306 nm) and the concentration of clenbuterol. The effects of the amount of sodium nitrite, diazo reaction time, the amount of bisphenol A, coupling reaction time and coupling reaction temperature have been examined. Under the optional conditions, clenbuterol can be determined over the concentration range of 0.02 to 2.0 µg mL(-1) with a correlation coefficient of 0.9953. The detection limit is 0.01 µg mL(-1) at a signal-to-noise ratio of 3. The relative standard deviation (RSD) for 11 repetitive determinations of 0.9 µg mL(-1) clenbuterol is 0.22 %. The utility of this method was demonstrated by determining clenbuterol in meat samples.

Spectrophotometric and high performance liquid chromatographic methods for sensitive determination of bisphenol A.

A new spectrophotometric method for the determination of trace amounts of bisphenol A based on a diazotization-coupling reaction was developed. In acidic solution, clenbuterol was first diazotized with sodium nitrite, then coupled with bisphenol A to from an azo-compound [I] in NH3-NH4Cl buffer, which shows a maximum absorption at 410 nm. The effects of the amount of sodium nitrite, diazo reaction time, the amount of clenbuterol, coupling reaction time and coupling reaction temperature have been examined. Under the optional conditions, the determination of the linear range of bisphenol A is 0.24-8.4 µg/mL, correlation coefficient is 0.9905 and detection limit of this method is 0.15 µg/mL. The spectrophotometric method is simple, rapid, high sensitivity with better accuracy. High performance liquid chromatography (HPLC) technique combined with this new spectrophotometric method has been also developed for the measurement of bisphenol A. The analysis was achieved on a C18 column using water and methanol as a mobile phase and the detection was done spectrophotometrically at 410 nm. These reported methods were applied to the determination of bisphenol A in hot water in contact with commercially available table-water bottle samples.

Simple and sensitive synchronous- fluorescence method for the determination of trace bisphenol S based on its inhibitory effect on the fluorescence quenching reaction of rhodamine B.

An inhibitory kinetic fluorimetric method is reported for the determination of trace bisphenol S (BPS). The proposed method is based on the inhibitory effect of BPS on the fluorescence quenching of rhodamine B (RhB) caused by potassium bromate in a dilute phosphoric acid medium. Under the optimal conditions of the experiment, the detection limit for BPS was 0.021 mg/L, and the linear range of determination was from 0.035 mg/L to 0.750 mg/L. The relative standard deviations of 11 measurements for 0.20 mg/L and 0.40 mg/L BPS solutions were 2.74 % and 1.87 %, respectively. The method was successfully applied to the determination of bisphenol S derived from commercially available plastic film samples in hot water. A possible reaction mechanism of the inhibitory effect of BPS on the fluorescence quenching of RhB was proposed.

Sensitive fluorescence detection of etimicin based on derivatives of formaldehyde and acetylacetone.

A novel fluorescence method for the determination of etimicin is described. Etimicin reacts with acetylacetone and formaldehyde in pH 4.0 Britton-Robinson (B.R.) buffer solution to from a fluorescent substance [I]. Emission spectra of [I] and the reagent blank were overlapped, so the arithmetic emission spectra of the fluorescent substance were obtained by subtracted form the spectra of [I] to the spectra of the reagent blank using the Fluorescence Data Software. There is a linear relationship between the intensity of the arithmetic emission spectra and the concentration of etimicin. Effects of pH, amount of acetylacetone-formaldehyde, and heating time on the determination of etimicin have been examined. Etimicin can be determined over the concentration range of 1.0 to 10.0 µg mL(-1) with a correlation coefficient of 0.9991. The relative standard deviation (RSD) for 11 repetitive determinations of 5.0 µg mL(-1) etimicin is 0.22%. The utility of this method was demonstrated by determining etimicin in commercial samples.

Flow injection analysis of ketoprofen based on the order transform second chemiluminescence reaction.

This paper explores an order-transform-second-chemiluminescence (OTSCL) method combining the flow injection technique for the determination of ketoprofen. When ketoprofen solution was injected into the mixture after the end of the reaction of alkaline luminol and sodium periodate or sodium periodate solution was injected into the reaction mixture of ketoprofen and alkaline luminol, a new chemiluminescence (CL) reaction was initiated and strong CL signal was detected. A mechanism for the OTSCL has been proposed on the basis of the chemiluminescence kinetic characteristic, UV-visible absorption and chemiluminescent spectra. Under optimal experimental conditions, the CL response is proportional to the concentration of ketoprofen over the range of 2.0×10(-7) to 1.0×10(-5)mol/L with a correlation coefficient of 0.9950 and a detection limit of 8.0×10(-9)mol/L (3σ). The relative standard deviation for 11 repetitive determinations of 1.0×10(-6)mol/L ketoprofen is 2.9%. The utility of this method was demonstrated by determining ketoprofen in pharmaceutical formulations without interference from its potential impurities.

Flow-injection chemiluminescence method for the determination of chloramphenicol based on luminol-sodium periodate order-transform second-chemiluminescence reaction.

A new chemiluminescence (CL) reaction was observed when chloramphenicol solution was injected into the mixture after the end of the reaction of alkaline luminol and sodium periodate or sodium periodate was injected into the reaction mixture of chloramphenicol and alkaline luminol. This reaction is described as an order-transform second-chemiluminescence (OTSCL) reaction. The OTSCL method combined with a flow-injection technique was applied to the determination of chloramphenicol. The optimum conditions for the order-transform second-chemiluminescence emission were investigated. A mechanism for OTSCL has been proposed on the basis of the chemiluminescence kinetic characteristics, the UV-visible spectra and the chemiluminescent spectra. Under optimal experimental conditions, the CL response is proportional to the concentration of chloramphenicol over the range 5.0 × 10(-7)-5.0 × 10(-5) mol/L with a correlation coefficient of 0.9969 and a detection limit of 6.0 × 10(-8) mol/L (3σ). The relative standard deviation (RSD) for 11 repeated determinations of 5.0 × 10(-6) mol/L chloramphenicol is 1.7%. The method has been applied to the determination of chloramphenicol in pharmaceutical samples with satisfactory results.

Electrochemiluminescence of an electrocatalytic action of etimicin on Tris(2,2'-bipyridyl)ruthenium(II) immobilized in Nafion modified carbon paste electrode.

A sensitive electrochemiluminescence (ECL) detection of etimicin at Tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3) (2+)]-Nafion modified carbon paste electrodes was developed. The immobilized Ru(bpy)(3) (2+) shows good electrochemical and photochemical activities. Electrochemical and electrochemiluminescence characterizations of the modified carbon electrodes were made by means of cyclic voltammetry and electrochemical impendence spectroscopy. The modified electrode showed an electrocatalytic response to the oxidation of etimicin, producing a sensitized ECL signal. The ECL sensor showed a linear response to etimicin in the range of 8.0-160.0 ng mL(-1) with a detection limit of 6.7 ng mL(-1). This method for etimicin determination possessed good sensitivity and reproducibility with a coefficient of variation of 5.1% (n = 7) at 100 ng mL(-1). The ECL sensor showed good selectivity and long-term stability. Its surface could be renewed quickly and reproducibly by a simple polish step.

Phenylboronic acid immunoaffinity reactor coupled with flow injection chemiluminescence for determination of alpha-fetoprotein.

A reusable and sensitive immunoassay based on phenylboronic acid immunoaffinity reactor in combination with flow injection chemiluminescence (CL) for determination of glycoprotein was described. The reactor was fabricated by immobilizing 3-aminophenylboronic acid (APBA) on glass microbeads with gamma-glycidoxypropyltrimethoxysilane (GPMS) as linkage. The alpha-fetoprotein (AFP) could be easily immobilized on the APBA coated beads through sugar-boronic interaction. After an off-line incubation, the mixture of the analyte AFP with horseradish peroxidase-labeled AFP antibody (HRP-anti-AFP) was injected into the reactor. This led the trapping of free HRP-anti-AFP by the surface coated AFP on glass beads. The trapped HRP-anti-AFP was detected by chemiluminescence due to its sensitizing effect on the reaction of luminol and hydrogen peroxide. Under optimal conditions, the chemiluminescent signal was proportional to AFP concentration in the range of 10-10 0 ng m L(-1). The whole assay process including regeneration of the reactor could be completed within 31 min. The proposed system showed acceptable detection and fabrication reproducibility, and the results obtained with the present method were in acceptable agreement with those from parallel single-analyte test of practical clinical sera. The described method enabled a low-cost, time saving and was potential to detect the serum AFP level in clinical diagnosis.

Sensitive determination of ketoprofen using flow injection with chemiluminescence detection.

A rapid chemiluminescence method is described for the determination of ketoprofen by combining the flow injection technique and its sensitizing effect on the weak chemiluminescence reaction between sulfite and acidic permanganate. The optimum conditions for the chemiluminescence emission were intensity. A mechanism for the chemiluminescence reaction has been proposed on the basis of chemiluminescent spectra. Ketoprofen can be determined over the concentration range of 5.0x10(-8) to 3.0x10(-6) mol/L with a correlation coefficient of 0.9999 and a detection limit of 2.0x10(-8) mol/L (3sigma). The relative standard deviation (R.S.D.) for 15 repetitive determinations of 1.0x10(-6) mol/L ketoprofen is 0.8%. The utility of this method was demonstrated by determining ketoprofen in capsules and human urine sample.

Sensitive determination of heroin based on electrogenerated chemiluminescence of tris(2,2'-bipyridyl)ruthenium(II) immobilized in zeolite Y modified carbon paste electrode.

A novel method for rapid, inexpensive, sensitive and selective determination of heroin was proposed by flow injection electrogenerated chemiluminescence (ECL). Zeolite Y sieves were used for the preparation of a ECL sensor by immobilizing tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3(2+)) in their supercages, which was achieved through the ion exchange properties of the sieves. The electrochemical and ECL behaviors of Ru(bpy)3(2+) immobilized in zeolite Y modified carbon paste electrode was investigated. The immobilized Ru(bpy)3(2+) displayed a pair of surface-controlled redox peaks with an electron transfer rate constant of 1.2 +/- 0.1 s(-1) in 0.1 mol dm(-3) pH 6.3 phosphate buffer. The modified electrode showed an electrocatalytic response to the oxidation of heroin, producing a sensitized ECL signal. The ECL sensor showed a linear response to flow injection of heroin in the range of 2.0-80 micromol dm(-3) with a detection limit of 1.1 micromol dm(-3). This method for heroin determination possessed good sensitivity and reproducibility with a coefficient of variation of 1.99% (n = 15) at 50.0 micromol dm(-3). The ECL sensor showed good selectivity and long-term stability. Its surface could be renewed quickly and reproducibly by a simple polish step.

[Flow injection chemiluminescent detection of acemetacin in KMnO4 - Na2 SO3 system].

AIM: To study the sensitizing effect of acemetacin (ACE) on the weak chemiluminescent (CL) reaction of KMnO4 with sulfite and establish a fast and convenient method for CL detection of ACE. METHODS: Using the sensitizing effect of ACE on KMnO4-Na2SO3 system and flow injection technique to determine the concentration of ACE. RESULTS: Under optimal conditions, the CL intensity of 1.0 x 10(-2) mol x L(-1) H3PO4 - 5.0 x 10(-5) mol x L(-1) KMnO4 - 4.0 x 10(-4) mol x L(-1) Na2SO3 was proportional to the concentration of ACE ranging from 1.0 x 10(-7) to 1.0 x 10(-5) mol x L(-1). The detection limit of ACE was 6.9 x 10(-8) mol x L(-1) at 3sigma. Satisfactory results were obtained for determination of ACE at 2.5 x 10(-6) mol x L(-1). CONCLUSION: The present method showed good precision, high sensitivity and selectivity and could be used for fast and convenient detection of ACE. It would be of significance to the clinical and pharmacological study of acemetacin.

Flow injection determination of papaverine based on its sensitizing effect on the chemiluminescence reaction of permanganate-sulfite.

A novel chemiluminescence (CL) method for the determination of papaverine (PAP) has been developed by combining the flow injection technique and its sensitizing effect on the weak CL reaction between sulfite and acidic permanganate. A mechanism for the CL reaction has been proposed on the basis of fluorescent and chemiluminescence spectra. The CL response is proportional to the concentration of PAP over the range 0.2-10 micro mol L(-1). The detection limit of PAP is 0.10 micro mol L(-1) (3 s) with a relative standard deviation (RSD) of 2.0% for 10 repetitive determinations of 1.0 micro mol L(-1) PAP. Interferences from other alkaloids in the opium, such as morphine and codeine, are negligible except that of narcotine. The method has been satisfactorily used for the determination of PAP in injections and compound liquorice tablets.