Synchronous fluorescence determination of ciprofloxacin in the pharmaceutical formulation and human serum based on the perturbed luminescence of rare-earth ions

A simple, rapid and sensitive synchronous fluorescence method was developed for the determination of ciprofloxacin (CPFX) in the pharmaceutical formulation and human serum. The results show that when Y³⁺ is added into the CPFX solution, the characteristic fluorescence of Y³⁺ is not emitted whereas the fluorescence intensity of CPFX is significantly enhanced. The synchronous fluorescence technology is employed in this method to directly determine trace amount of CPFX in human serum. A linear relationship between the fluorescence intensity and the CPFX concentration is obtained in the range of 1.0×10⁻⁹ ∼5.0×10⁻⁶ mol L⁻¹. The limit of detection (LOD) of this method attains as low as 2.0×10⁻¹⁰ mol L⁻¹ (S/N=3). The selectivity of this method is also very good. Common metal ions, rare-earth ions and some pharmaceuticals, which are usually used together with CPFX in the clinic, do not interfere with the determination of CPFX under general conditions.     

Sensitive determination of enoxacin by its enhancement effect on the fluorescence of terbium(III)-sodium dodecylbenzene sulfonate and its luminescence mechanism

The fluorescence system of enoxacin-Tb³⁺-sodium dodecylbenzene sulfonate (SDBS) was investigated in this paper. The experiments indicated that the fluorescence intensity of Tb³⁺-SDBS was greatly enhanced by enoxacin. Accordingly, a sensitive fluorimetric method for determining enoxacin was established. The fluorescence intensity was measured by a 1-cm quartz cell with an excitation wavelength of 290 nm and an emission wavelength of 545 nm. The enhanced fluorescence intensity of the system (ΔF) showed a good linear relationship with the concentration of enoxacin in the range of 5.0×10⁻⁹ to 2.0×10⁻⁶ mol L⁻¹, its correlation coefficient was 0.9992 and the detection limit (S/N=3) was 2.8×10⁻⁹ mol L⁻¹. The presented method was used to determine enoxacin in real pharmaceutical samples. The luminescence mechanism was also discussed in detail. In the fluorescence system of enoxacin-Tb³⁺-SDBS, SDBS not only acted as the surfactant but also acted as the energy donor.     

Spectrofluorimetric study on the inclusion behavior of p-sulfonated calix arene with cetyltrimethylammonium bromide and analytical application

The characteristics of host-guest complexation between p-sulfonated calix [G. Arena, S. Gentile, F. G. Gulino, D. Sciotto, C. Sgarlata, Tetrahedron Lett. 45 (2004) 7091] arene (SC6A) and cationic surfactant cetyltrimethylammonium bromide (CTAB) were studied by fluorescence spectrometry. A 1:1 stoichiometry for the complexation was established and the complex constant was also calculated by a deduced equation. It was found the fluorescence of the complex could be remarkably quenched by an appropriate amount of ceftriaxone sodium (CTRX). Based on the results, a novel spectrofluorimetric method for determination of CTRX was developed with a linear range of 9.2×10⁻⁷-8.5×10⁻⁵ mol L⁻¹ and a detection of 3.5×10⁻⁷ mol L⁻¹. The proposed method was used to determine CTRX in their commercial preparations with satisfactory results. Moreover, the probable interaction mechanisms of the systems were also discussed.     

Static quenching of bovine serum albumin conjugated with small size CdS nanocrystalline quantum dots

The author reports on a strong fluorescence quenching of a model transport protein, bovine serum albumin BSA, when bioconjugated with CdS quantum dots QDs. The 4.4 nm size CdS QDs were synthesized using wet chemistry method and were characterized using UV-vis spectroscopy, scanning electron microscopy SEM and X-ray diffraction XRD techniques. It was found that the BSA fluorescence quenching increases linearly with increasing the CdS QDs concentrations in the range of 3×10⁻⁷-2.0×10⁻⁶ mol L⁻¹. This quenching is explained in terms of Stern-Volmer equation and is ascribed to static quenching with quenching constant 1.321×10⁴ L mol⁻¹ at 300 K.     

Spectrofluorimetric determination of trace amount of coenzyme II using ciprofloxacin-terbium complex as a fluorescent probe

A new spectrofluorimetric method was developed for the determination of trace amount of nicotinamide adenine dinucleotide phosphate (NADP). Using terbium ion (Tb³⁺)-ciprofloxacin (CIP) complex as a fluorescent probe, in the buffer solution of pH=9.00, NADP can remarkably enhance the fluorescence intensity of the Tb³⁺-CIP complex at and the enhanced fluorescence intensity of Tb³⁺ ion is in proportion to the concentration of NADP. Optimum conditions for the determination of NADP were also investigated. The dynamic range for the determination of NADP is 4.9×10⁻⁷−3.7×10⁻⁶ mol L⁻¹ with detection limit of 1.3×10⁻⁷ mol L⁻¹. This method is simple, practical and relatively free interference from coexisting substances and can be successfully applied to determination of NADP in synthetic water samples. Moreover, the enhancement mechanisms of the fluorescence intensity in the Tb³⁺-CIP system and the Tb³⁺-CIP-NADP system have been also discussed.     

The co-luminescence effect of a europium (III)-lanthanum (III)-gatifloxacin-sodium dodecylbenzene sulfonate system and its application for the determination of trace amount of europium (III)

A novel co-luminescence system based on the formation of a complex between europium (III) (Eu³⁺) and gatifloxacin (GFLX) in sodium dodecylbenzene sulfonate (SDBS) micelle solution containing lanthanum (III) (La³⁺) has been developed for the determination of Eu³⁺. The experimental results show that the complex formed by Eu³⁺ and GFLX here can emit the characteristic luminescence of Eu³⁺. With the addition of La³⁺, the luminescence intensity of the system was enhanced about 7-fold compared with that without La³⁺. Under the optimal conditions, the luminescence intensity exhibits an excellent linear relationship with Eu³⁺ concentration in the range of 1.0×10⁻¹⁰-5.0×10⁻⁸ mol L⁻¹. The correlation coefficient (r) is 0.9998, and the detection limit (3σ) is 7.0×10⁻¹⁴ mol L⁻¹. A test method with satisfactory accuracy based on this system was applied to determine trace amounts of Eu³⁺ in rare earth samples. In addition, the detailed luminescence mechanism of this system was investigated by analyzing the ultraviolet absorption spectra, surface tension, fluorescence polarization, quantum yield, and the number of water molecules in the first coordination sphere of the Eu³⁺ complex.     

Dye-sensitized phototransformation of chlorophenols and their subsequent chemiluminescence reactions

A novel chemiluminescence (CL) reaction of chlorophenols (CPs), including 2-chlorophenol (2-CP), 4-CP, 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP) was reported, which was based on the oxidation of the phototransformed CPs by N-bromosuccinimide (NBS). It was found that the dye-sensitized phototransformation is a prerequisite for the subsequent CL reaction, and the presence of 1.9×10^-2 mol L⁻¹ Triton X-100 or 3.7×10^-3 mol L⁻¹ CTAB can greatly enhance the CL intensity. A neutral sample solution with the presence of 2×10^-5 mol L⁻¹ fluorescein (FL) was found to be optimum for the phototransformation of 2-CP, 4-CP, 2,4-DCP and PCP, but a lower pH of 5.3 was more suitable for 2,4,6-TCP. Based on the CL reaction, detection limits of 8.6×10⁻⁸, 1.1×10⁻⁷, 1.5×10^-7, 4.6×10^-8 and 3.0×10⁻⁵ mol L⁻¹ were achieved, respectively, for 2-CP, 4-CP, 2,4-DCP, 2,4,6-TCP and PCP with the optimized conditions in the flow system. The mechanism of the phototransformation and the subsequent CL reaction were preliminarily studied and it was suggested that the singlet oxygen formed in the dye-sensitization process was responsible for the conversion of CPs into light-emitting precursors. These intermediate products were suggested to be peroxide compounds after testing by a luminal-based post-column CL detection experiment.     

Luminescence enhancement effect for the determination of balofloxacin with balofloxacin-europium (III)-sodium dodecylbenzene sulfonate system

A novel method of luminescence enhancement effect for the determination of balofloxacin (BLFX) was proposed. A new system of the BLFX-Eu³⁺-SDBS (sodium dodecylbenzene sulfonate) was investigated. It was found that SDBS significantly enhanced the luminescence intensity of the BLFX-Eu³⁺ complex (about 20-fold). Under the optimized experimental conditions, the system exhibits an excellent linear relationship between the enhanced luminescence intensity and the concentration of BLFX over the range of 1.0×10⁻⁸-8.0×10⁻⁷ mol L⁻¹ with a correlation coefficient (R) of 0.9994, and the detection limit (3σ) of the method was determined as 2.0×10⁻⁹ mol L⁻¹. This method has been successfully applied for the determination of BLFX in pharmaceuticals and human urine/serum samples. Compared with most of the other methods reported, the rapid and simple procedure proposed in the text offers higher sensitivity, wider linear range, and better stability.     

Hydrogen peroxide biosensor based on gold nanoparticles/thionine/gold nanoparticles/multi-walled carbon nanotubes-chitosans composite film-modified electrode

In this paper, an amperometric electrochemical biosensor for the detection of hydrogen peroxide (H₂O₂), based on gold nanoparticles (GNPs)/thionine (Thi)/GNPs/multi-walled carbon nanotubes (MWCNTs)-chitosans (Chits) composite film was developed. MWCNTs-Chits homogeneous composite was first dispersed in acetic acid solution and then the GNPs were in situ synthesized at the composite. The mixture was dripped on the glassy carbon electrode (GCE) and then the Thi was deposited by electropolymerization by Au-S or Au-N covalent bond effect and electrostatic adsorption effect as an electron transfer mediator. Finally, the mixture of GNPs and horseradish peroxidase (HRP) was assembled onto the modified electrode by covalent bond. The electrochemical behavior of the modified electrode was investigated by scanning electron microscope, cyclic voltammetry and chronoamperometry. This study introduces the in situ-synthesized GNPs on the other surface of the modified materials in H₂O₂ detection. The linear response range of the biosensor to H₂O₂ concentration was from 5 × 10⁻⁷ mol L⁻¹ to 1.5 × 10⁻³ mol L⁻¹ with a detection limit of 3.75 × 10⁻⁸ mol L⁻¹ (based on S/N = 3).     

CdSe quantum dots decorated by mercaptosuccinic acid as fluorescence probe for Cu

Water-soluble CdSe quantum dots (QDs) were synthesized using mercaptosuccinic acid (MSA) as a stabilizer. The growth process and characterization of CdSe quantum dots were determined by transmission electron microscopy (TEM), X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, Ultraviolet-visible (UV-vis) spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy. Results demonstrated the MSA-capped CdSe QDs were highly crystalline and possessed good optical properties. Further, the resulting products could be used as fluorescent probes to detect Cu²⁺ ions in physiological buffer solution. The response was linearly proportional to the concentration of Cu²⁺ ion in the range 2×10⁻⁸- 3.5×10⁻⁷ mol L⁻¹ with a detection limit of 3.4 nmol L⁻¹.     

Microgravimetric and voltammetric study of Zn underpotential deposition on platinum in alkaline medium

The microgravimetric and voltammetric responses of a polycrystalline Pt electrode in 0.1 mol L⁻¹ NaOH solution in the presence and the absence of 1.6 × 10⁻⁴ Zn²⁺, at 0.1 V s⁻¹ were analyzed. During the positive potential sweep, the water molecules are progressively substituted by OH⁻ ions, prior to PtO formation. The voltammetric charges obtained under the Zn_ads dissolution peaks suggest that 0.7 monolayers are deposited, with each Zn ad-atom occupying one active site and transferring two electrons. The total loss of mass due to the dissolution of the Zn ad-layer was 136.6 ng cm⁻² and the mass increase due to PtO formation was found to be only 12 ng cm⁻² less than the theoretical ones, 157.5 and 37.4 ng cm⁻², respectively, indicating that both processes are overlapped. In this way it is proposed that an adsorbed by-layer of Zn and OH⁻ ions is formed.     

Interaction between titanium dioxide nanoparticles and human serum albumin revealed by fluorescence spectroscopy in the absence of photoactivation

Titanium dioxide (TiO₂) nanoparticles (NPs) are widely used as an important kind of biomaterials. The interaction between TiO₂ (P25) at 20 nm in diameter and human serum albumin (HSA) was studied by fluorescence spectroscopy in this work. Under the simulative physiological conditions, fluorescence data revealed the presence of a single class of binding site on HSA and its binding constants (K_a) were 2.18±0.04×10⁴, 0.87±0.05×10⁴, 0.68±0.06×10⁴ M⁻¹ at 298, 304 and 310 K, respectively. In addition, according to the Van’t Hoff equation, the thermodynamic functions standard enthalpy (ΔH⁰) and standard entropy (ΔS⁰) for the reaction were calculated to be −75.18±0.15 kJ mol⁻¹ and −170.11±0.38 J mol⁻¹ K⁻¹. These results indicated that TiO₂ NPs bond to HSA mainly by van der Waals force and hydrogen bonding formation in low dielectric media, and the electrostatic interactions cannot be excluded. Furthermore, the effects of common ions on the binding constant of TiO₂ NPs-HSA complex were discussed.     

Destabilization of artificial biomembrane induced by the penetration of tryptophan

The effect of tryptophan on the membrane stability was studied by using three artificial biological membranes including liposome, Langmuir monolayer and solid supported bilayer lipid membrane (s-BLM) as models. All the results indicate that the penetration of tryptophan can destabilize different artificial biological membranes. The diameter of liposome and the leakage of calcein from liposome increased with the increase of tryptophan concentration because the penetration of tryptophan was beneficial for dehydrating the polar head groups of lipids and the formation of fusion intermediates. π-A isotherms of lecithin on the subphase of tryptophan solution further confirm that tryptophan can penetrate into lipid monolayer and reduce the stability of lipid monolayer. When the concentration of tryptophan increased from 0 to 2 × 10⁻³ mol L⁻¹, the limiting molecular area of lecithin increased from 110.5 to 138.5 Å², but the collapse pressure of the monolayer decreased from 47.6 to 42.3 mN m⁻¹, indicating the destabilization of lipid monolayer caused by the penetration of tryptophan. The resistance spectra of s-BLM demonstrate that the existence of tryptophan leads to the formation of some defects in s-BLM and the destabilization of s-BLM. The values of electron-transfer resistance and double layer capacitance respectively decreased from 5.765 × 10⁶ Ω and 3.573 × 10⁻⁸ F to 1.391 × 10⁶ Ω and 3.340 × 10⁻⁸ F when the concentration of tryptophan increased from 0 to 2 × 10⁻³ mol L⁻¹. Correspondingly, the breakdown voltage of s-BLM decreased from 2.51 to 1.72 V.     

Dual fluorescence and laser emissions from fluorescein-Na and eosin-B

Dual laser emissions were observed from fluorescein-Na and eosin-B in ethanolic solutions individually in the concentration range from 10⁻² to 10⁻³ mol dm⁻³ under N₂ laser excitation. The first compound was found to lase at two distinct regions with wavelength maxima around 540, 550 nm, while the second one around 558, 574 nm. Steady-state absorption, fluorescence excitation, fluorescence polarization, fluorescence emission and decays of the dyes in various solvents under varying conditions of excitation and detection systems were carried out to identify the nature of the emitting species responsible for laser emissions in two distinct regions. Both the dyes exhibited concentration and excitation wavelength dependence of fluorescence and the effects were found to be more pronounced in binary solution. The fluorescence decays of dyes were monoexponential in ethanol, while in some other solvents used, the decays showed biexponential behavior. The absorption and excitation studies using thin layers of solutions revealed the formation of dimers with the dye concentration around 1×10⁻³ mol dm⁻³. Fluorescence polarization and decay studies confirmed the presence of dimers. The two laser bands observed in the shorter and longer wavelengths were respectively ascribed to monomeric and dimeric species.     

Determination of albumins by its quenching effect on the fluorescence of Tb-oxolinic acid complex in presence of sodium dodecyl sulphate

It is found that the fluorescence intensity of Tb³⁺-oxolinic acid (OA) complex can be greatly quenched by albumins in sodium dodecyl sulphate (SLS). Under optimum conditions, the quenched fluorescence intensity is in proportion to the concentration of proteins in the range of 5.0×10⁻⁸-1.0×10⁻⁵ g ml⁻¹ for bovine serum albumin (BSA), 1.0×10⁻⁷-1.0×10⁻⁵ g ml⁻¹ for human serum albumin (HSA) and 4.0×10⁻⁷-1.0×10⁻⁵ g ml⁻¹ for egg albumin (EA). Their detection limits (S/N=3) are 2.1×10⁻⁸, 2.5×10⁻⁸ and 5.0×10⁻⁸ g ml⁻¹, respectively. In addition, the interaction mechanism is also investigated.     

Determination of norfloxacin using gold nanoparticles catalyzed cerium(IV)-sodium sulfite chemiluminescence

A rapid flow-injection chemiluminescence (CL) method is proposed for the determination of norfloxacin (NFLX). The method is based on the fact that the weak CL from the redox reaction of Ce(IV)-Na₂SO₃ can be greatly strengthened by gold nanoparticles (NPs). UV-visible spectra, fluorescence spectra and transmission electron microscopy (TEM) studies are carried out before and after the CL reactions to investigate the CL reinforcing mechanism. The mechanism is supposed to originate from the reinforcer of gold NPs, which facilitates the radical generations and electron-transfer processes taking place on the surface of the gold NPs. Under the selected experimental conditions, a linear relationship was obtained between the CL intensity and the concentrations of NFLX in the range 7.9×10⁻⁷ to 1.9×10⁻⁵ M and the detection limit was 8.2×10⁻⁸ M. This method is successfully applied to the determination of NFLX in human urine.     

Fluorometric determination of proteins using the yttrium(III)-sodium lauryl sulfate-rutin-protein system

It is found that rutin can react with yttrium(III) (Y³⁺), and emits fluorescence of rutin. The intensity is greatly enhanced by proteins in the presence of sodium lauryl sulfate (SLS). Based on this, a new fluorimetric method of determination of proteins is developed. Under optimum conditions, the enhanced intensity of fluorescence is in proportion to the concentration of proteins in the range of 5.0×10⁻⁹-1.0×10⁻⁵ g/mL for bovine serum albumin (BSA), 3.0×10⁻⁸-1.0×10⁻⁵ g/mL for human serum albumin (HSA) and 1.0×10⁻⁷-2.0×10⁻⁵ g/mL for egg albumin (EA). Their detection limits (S/N=3) are 1.6×10⁻⁹, 9.8×10⁻⁹ and 2.1×10⁻⁸ g/mL, respectively. The interaction mechanism is also studied.     

Removal of chloridazon by natural and ammonium kerolite samples

The adsorption of chloridazon (5-amino-4-chloro-2-phenylpyridazin-3(2H)-one) on natural and ammonium kerolite samples from aqueous solution at 10, 25 and 40 °C has been studied by using batch experiments. The experimental data points were fitted to the Langmuir equation in order to calculate the adsorption capacities (X_m) of the samples; two straight lines were obtained, which indicates that the adsorption process takes place in two different stages. Values for X_m1 (first stage) ranged from 1.1 × 10⁻² mol kg⁻¹ for natural kerolite at 40 °C up to 5.1 × 10⁻² mol kg⁻¹ for ammonium kerolite at 10 °C and the values for X_m2 (second stage) ranged from 9.1 × 10⁻² mol kg⁻¹ for natural kerolite at 40 °C up to 14 × 10⁻² mol kg⁻¹ for natural kerolite at 10 °C. The adsorption experiments showed on the one hand, that the ammonium kerolite is more effective than natural kerolite to adsorb chloridazon in the range of temperature studied and on the other hand, that the lower temperature, the more effective the adsorption of chloridazon on the adsorbents studied.     

Complex and new modification techniques of thiocholine detection electrodes with carbon nanotubes

A new and complex modification technique of glassy carbon electrode (GCE) with multi-walled carbon nanotubes (MWNTs) was developed. Firstly, MWNTs were electro-deposited on GCE at 1.70 V for 2 h. Secondly, by layer-by-layer (LBL) self-assembly technique, a functional membrane of {PDDA/MWNTs}_n were fabricated by alternative immersion in 1% PDDA solution and 1 mg L⁻¹ MWNTs dispersion either. As a result, the modified membrane with five {PDDA/MWNTs} bilayers have good sensitivity, stability, anti-fouling ability and catalytic activity for thiocholine (TCh) detection, the oxidation potential on the modified GCE was decreased almost by 50% while the peak current was increased almost by 100% compared with that on bare GCE. Meanwhile, it showed a low detection limit of less than 7.500 × 10⁻⁷ mol L⁻¹ TCh.     

Fluorometric determination of proteins using the terbium (III)-2-thenoyltrifluoroacetone-sodium dodecyl benzene sulfonate-protein system

It is found that in hexamethylene tetramine (HMTA)-HCl buffer of pH=8.00, proteins can enhance the fluorescence of terbium (III) (Tb³⁺)-2-thenoyltrifluoroacetone (TTA)-sodium dodecyl benzene sulfonate (SDBS) system. Based on this, a sensitive method for the determination of proteins is proposed. The experiments indicate that under the optimum conditions, the enhanced fluorescence intensity is in proportion to the concentration of proteins in the range of 4.0×10⁻⁹-7.5×10⁻⁶ g/mL for bovine serum albumin (BSA), 5.0×10⁻⁹-1.5×10⁻⁵ g/mL for human serum albumin (HSA), 1.0×10⁻⁸-7.5×10⁻⁶ g/mL for egg albumin (EA). Their detection limits (S/N=3) are 0.5, 0.8 and 2.0 ng/mL, respectively. The interaction mechanism is also studied.