Selective and sensitive fluorometric determinations of cobalt(II) and hydrogen peroxide with fluorescein-hydrazide

Synthesis and Applications of Prussian Blue and Its Analogues as Electrochemical Sensors

Prussian blue (PB) and its analogue (PBA) are a kind of representative cyanide-based coordination polymer. They have received enormous research interest and have shown promising applications in the electrochemical sensing field due to their excellent electrochemical activity and unique structural characteristics including open framework structure, high specific surface area, and adjustable metal active sites. In this review, we summarize the latest research progress of PB/PBA as an electrochemical sensor in detail from three aspects: fabrication strategy, synthesis method and electrochemical sensor application. For the fabrication strategy, we discussed different fabrication methods containing the combination of PBA and carbon materials, metal nanoparticles, polymers, etc., respectively, as well as their corresponding sensing mechanism for improving performance. We also presented the synthesis methods of PB/PBA materials in detail, such as: coprecipitation, hydrothermal and electrodeposition. In addition, the effects of different methods on the morphology, particle size and productivity of PB/PBA materials are also concluded. For the application of electrochemical sensors, the latest progress of such materials as electrochemical sensors for glucose, H2 O2 , toxic compounds, and biomolecules have been summarized. Finally, we conclude remaining challenges of PB/PBA-based materials as electrochemical sensors, and provide personal perspectives for future research in this field.

Efficiency improvement in non-enzymatic H2O2 detection induced by the simultaneous synthesis of Au and Ag nanoparticles in an RGO/Au/Fe3O4/Ag nanocomposite

Developing a quick and precise technique for hydrogen peroxide (H₂O₂) detection would open up a new class of technologies for biological, medical and chemical applications.

Ultra-Sensitive Nano Optical Sensor Samarium-Doxycycline Doped in Sol Gel Matrix for Assessment of Glucose Oxidase Activity in Diabetics Disease

A low cost and very sensitive method for the determination of the activity of glucose oxidase enzyme in different diabetics serum samples was developed. The method based on the assessment of the H₂O₂ concentration produced from the reaction of the glucose oxidase (GOx) enzyme with glucose as substrate in the serum of diabetics patients by nano optical sensor Sm-doxycycline doped in sol gel matrix. H₂O₂ enhances the luminescence intensity of all bands of the nano Sm-doxycycline complex [Sm-(DC)₂]⁺ doped in sol-gel matrix, especially the 645 nm band at λ_ex = 400 nm and pH 7.0 in water. The influence of the different analytical parameters that affect the luminescence intensity of the nano optical sensor, e.g. pH, H₂O₂ concentration and foreign ions concentrations were studied. The remarkable enhancement of the luminescence intensity of nano optical sensor [Sm-(DC)₂]⁺ complex in water at 645 nm by the addition of various concentrations of H₂O₂ was successfully used as an optical sensor for the assessment of the activity of the glucose oxidase enzyme in different diabetics serum samples. The calibration plot was achieved over the activity range 0.1-240 U/L with a correlation coefficient of 0.999 and a detection limit of 0.05 U/L.

Preparation of a Superhydrophobic and Peroxidase-like Activity Array Chip for H2O2 Sensing by Surface-Enhanced Raman Scattering

In this paper, we propose a novel and simple method for preparing a dual-biomimetic functional array possessing both superhydrophobic and peroxidase-like activity that can be used for hydrogen peroxide (H2O2) sensing. The proposed method is an integration innovation that combines the above two properties and surface-enhanced Raman scattering (SERS). We integrated a series of well-ordered arrays of Au points (d = 1 mm) onto a superhydrophobic copper (Cu)/silver (Ag) surface by replicating an arrayed molybdenum template. Instead of using photoresists and the traditional lithography method, we utilized a chemical etching method (a substitution reaction between Cu and HAuCl4) with a Cu/Ag superhydrophobic surface as the barrier layer, which has the benefit of water repellency. The as-prepared Au points were observed to possess peroxidase-like activity, allowing for catalytic oxidation of the chromogenic molecule o-phenylenediamine dihydrochloride (OPD). Oxidation was evidenced by a color change in the presence of H2O2, which allows the array chip to act as an H2O2 sensor. In this study, the water repellency of the superhydrophobic surface was used to fabricate the array chip and increase the local reactant concentration during the catalytic reaction. As a result, the catalytic reaction occurred when only 2 μL of an aqueous sample (OPD/H2O2) was placed onto the Au point, and the enzymatic product, 2,3-diaminophenazine, showed a SERS signal distinguishable from that of OPD after mixing with 2 μL of colloidal Au. Using the dual-biomimetic functional array chip, quantitative analysis of H2O2 was performed by observing the change in the SERS spectra, which showed a concentration-dependent behavior for H2O2. This method allows for the detection of H2O2 at concentrations as low as 3 pmol per 2 μL of sample, which is a considerable advantage in H2O2 analysis. The as-prepared substrate was convenient for H2O2 detection because only a small amount of sample was required in each analysis. Highly sensitive detection was realized using SERS. Therefore, this chip was shown to exhibit significant potential for applications in bioanalysis.

Poly (N-isopropylacrylamide)-co-(acrylic acid) microgel/Ag nanoparticle hybrids for the colorimetric sensing of H2O2

Poly (N-isopropylacrylamide)-co-(acrylic acid) (pNIPAm-co-AAc) microgels composed of Ag nanoparticles (Ag NPs) have been synthesized and employed for the colorimetric sensing of H2O2. Each pNIPAm-co-AAc microgel, which exhibited a diameter of ∼800 nm, contained multiple Ag NPs (diameter of ∼5 nm), and solutions of these hybrid materials showed a UV-vis absorption band at ∼400 nm. This is due to the excitation of the Ag NP surface plasmon. We go on to show that the intensity of this absorption band is dependent on the concentration of H2O2 in solution. Specifically, in the presence of H2O2 the magnitude of the absorption peak dramatically decreases in a linear fashion over the concentration range of 0.30 to 3.00 μM H2O2 (r(2) = 0.9918). We go on to show that the response is selective for H2O2 and can still function in complex mixtures, e.g., we showed that the response is still robust in milk samples. While Ag NPs themselves can exhibit similar responses, this system has many benefits including sample processing and long term stability - i.e., Ag NPs are destabilized in solutions of a certain pH, and aggregate readily. Our microgel/Ag NP hybrids have been shown to be extremely stable and are easily purified prior to use by simple centrifugation/washing protocols. This system is simple and straightforward to use, is low cost, and can be used in complex media, which makes it practical for analyzing complex biological and environmental samples.

Synthesis and anisotropic self-assembly of Ag nanoparticles immobilized by the Pluronic F127 triblock copolymer for colorimetric detection of H2O2

Facile and green synthesis of a Ag@DA@F127 system for the sensitive and quantitative detection of H₂O₂. Ag NPs in the network-like F127 micelles were well-dispersed and anisotropically self-assembled.

A ternary nanocomposite electrode of polyoxometalate/carbon nanotubes/gold nanoparticles for electrochemical detection of hydrogen peroxide

In this work, a nanocomposite film electrode containing polyoxometalate (POM) clusters K₆P₂W₁₈O₆₂ (P₂W₁₈), carbon nanotubes (CNTs) and Au nanoparticles (AuNPs) was fabricated by a layer-by-layer self-assembly technique.

A highly sensitive, selective ratiometric fluorescent probe for cobalt(ii) and its applications for biological imaging

A novel fluorescent probe, E3, was designed, synthesized and evaluated. It responded to Co²⁺ with high selectivity and sensitivity under physiological neutral conditions specifically. Furthermore, notably, probe E3 was demonstrated to detect Co²⁺ in living cells, indicative of its practical application potential.

Fluorescent, MRI, and colorimetric chemical sensors for the first-row d-block metal ions

Transition metals (d-blocks) are recognized as playing critical roles in biology, and they most often act as cofactors in diverse enzymes; however, improper regulation of transition metal stores is also connected to serious disorders. Therefore, the monitoring and imaging of transition metals are significant for biological research as well as clinical diagnosis. In this article, efforts have been made to review the chemical sensors that have been developed for the detection of the first-row d-block metals (except Cu and Zn): Cr, Mn, Fe, Co, and Ni. We focus on the development of fluorescent sensors (fall into three classes: "turn-off", "turn-on", and ratiometric), colorimetric sensors, and responsive MRI contrast agents for these transition metals (242 references). Future work will be likely to fill in the blanks: (1) sensors for Sc, Ti, and V; (2) MRI sensors for Cr, Mn, Co, Ni; (3) ratiometric fluorescent sensors for Cr(6+), Mn(2+), and Ni(2+), explore new ways of sensing Fe(3+) or Cr(3+) without the proton interference, as well as extend applications of MRI sensors to living systems.

DNA as sensors and imaging agents for metal ions

Increasing interest in detecting metal ions in many chemical and biomedical fields has created demands for developing sensors and imaging agents for metal ions with high sensitivity and selectivity. This review covers recent progress in DNA-based sensors and imaging agents for metal ions. Through both combinatorial selection and rational design, a number of metal-ion-dependent DNAzymes and metal-ion-binding DNA structures that can selectively recognize specific metal ions have been obtained. By attachment of these DNA molecules with signal reporters such as fluorophores, chromophores, electrochemical tags, and Raman tags, a number of DNA-based sensors for both diamagnetic and paramagnetic metal ions have been developed for fluorescent, colorimetric, electrochemical, and surface Raman detection. These sensors are highly sensitive (with a detection limit down to 11 ppt) and selective (with selectivity up to millions-fold) toward specific metal ions. In addition, through further development to simplify the operation, such as the use of "dipstick tests", portable fluorometers, computer-readable disks, and widely available glucose meters, these sensors have been applied for on-site and real-time environmental monitoring and point-of-care medical diagnostics. The use of these sensors for in situ cellular imaging has also been reported. The generality of the combinatorial selection to obtain DNAzymes for almost any metal ion in any oxidation state and the ease of modification of the DNA with different signal reporters make DNA an emerging and promising class of molecules for metal-ion sensing and imaging in many fields of applications.

A highly selective colorimetric chemosensor for cobalt(ii) ions based on a tripodal amide ligand

A highly selective colorimetric chemosensor for cobalt(ii) ions was synthesized and structurally characterized by single crystal X-ray diffraction. The ligand enabled the detection of cobalt(ii) ions at a concentration of 10⁻⁵ mol L⁻¹ by the “naked-eye”.

A new fluorescent chemosensor detecting Co2+ and K+ in DMF buffered solution

A new fluorescent chemosensor 2-(2-thiophene)imidazo [4,5,f]-1,10-phenanthroline (L) was prepared and characterized. By adding univalent or divalent metal ions such as Na(+), K(+), Mg(2+), Ba(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Ag(+), Zn(2+), Cd(2+) and Hg(2+) ions into the solution of L in DMF under buffered conditions with the working pH ranging from 7.0 to 8.0, we found that L could be used to detect K(+) ratiometricly and it could also be applied to sense Co(2+) with the phenomenon of fluorescence quenching of L. While the response behavior of L was not discernibly affected by other examined metal ions.

Fluorophotometric determination of hydrogen peroxide with fluorescin in the presence of cobalt (II) and reaction against other reactive oxygen species

A fluorophotometric method for the determination of hydrogen peroxide (H2O2) using fluorescin was developed. This method was based on the oxidative reaction of fluorescin, a colorless, non-fluorescent lactoid fluorescein, by H2O2 to give highly fluorescein fluorescence emission. In the determination of H2O2, the calibration curve exhibited linearity over the H2O2 concentration range of 1.5-310 ng mL(-1) at an emission wavelength of 525 nm with an excitation of 500 nm and with relative standard deviations (n = 6) of 2.51%, 2.48%, and 1.31% for 3.1 ng mL(-1), 30.8 ng mL(-1), and for 308 ng mL(-1) of H2O2, respectively. The detection limit for H2O2 was 1.9 ng mL(-1) six blank determinations was performed (rho = 6). This proposed method was applied to detection of other reactive oxygen species and nitrogen species (ROS/RNS) such as singlet oxygen (1O2), hydroxyl radical (*OH), peroxynitrite (ONOO-) etc., and it was possible to detect them with a high sensitivity. In addition, this proposed method was applied to the recovery tests of H2O2 in calf serum, human saliva, rain water, and wheat noodles; the results were satisfactory.

Fluorophotometric determination of hydrogen peroxide and other reactive oxygen species with fluorescein hydrazide (FH) and its crystal structure

Methods for the fluorophotometric determination of hydrogen peroxide (H(2)O(2)) and other reactive oxygen species (ROS) were proposed by using the fluorescence reaction between H(2)O(2) or other ROS and fluorescein hydrazide (FH). In the determination of H(2)O(2), the calibration curve exhibited linearity over the H(2)O(2) concentration range of 2.1-460 ng ml(-1) at an emission wavelength of 527 nm with an excitation of 460 nm and with the relative standard deviations (n=6) of 4.06%, 1.78%, and 2.21% for 3.1 ng ml(-1), 30.8 ng ml(-1), and for 308 ng ml(-1) of H(2)O(2), respectively. The detection limit for H(2)O(2) was 0.7 ng ml(-1) due to three blank determinations (rho=3). The calibration curves for ROS-related compounds were also constructed under the optimum conditions. This method was successfully applied in the assay of H(2)O(2) in human urine. In addition, we performed the characterization of FH, and interesting information was obtained with regard to the relationship between the chemical structure and fluorescence.

Synthesis of dipicolylamino substituted quinazoline as chemosensor for cobalt(II) recognition based on excited-state intramolecular proton transfer

A new fluorescent chemosensor for sensing Co(II) using di(2-picolyl)amino (DPA) as a recognition group and quinazoline as a reporting group has been synthesized and characterized. The quinazoline derivative contains an intramolecular hydrogen bond, which would undergo excited-state intramolecular proton transfer (ESIPT) at illumination. The fluorescence quenching is attributed to cation-induced inhibition of ESIPT, which constitutes the basis for the determination of Co(II) with the prepared chemosensor. The fluorophore forms 1:1 cobalt(II) complex with the logarithm of apparent dissociation constant log K(a)=6.8. The analytical performance characteristics of the proposed Co(II)-sensitive sensor were investigated. The chemosensor exhibits a linear response toward Co(II) in the concentration range 3.2 x 10(-8) to 1.4 x 10(-6) M, with a working pH range from 7.0 to 9.5 and high selectivity.

Sensitive Spectrofluorimetric Determination of Cytochrome c with Spirocyclic Rhodamine B Hydrazide in Micellar Medium

A new spectrofluorimetric method for the determination of cytochrome c using spirocyclic rhodamine B hydrazide (RBH) as fluorogenic reagent in the presence of sodium dodecylbenzene sulfonate (SDBS) surfactant micelles was developed. The method was based on the reaction of cytochrome c with RBH, a colorless, nonfluorescent spirolactam of rhodamine B in SDBS micelles to give highly fluorescent rhodamine B and hence led to a large increase in fluorescence intensity. The dynamic range and detection limit for the determination of cytochrome c are 4.0-120 ng ml(-1) and 0.87 ng ml(-1) (3sigma), respectively. The optimal conditions for the detection of cytochrome c were evaluated and the possible detection mechanism was also discussed.

A fluorescent chemosensor for cobalt ions based on a multi-substituted phenol-ruthenium(II) tris(bipyridine) complex

An amide-linked 2,6-bis{[(2-hydroxy-5-tert-butylbenzyl)(pyridyl-2-methyl)-amino]-methyl}-4-methylphenol-ruthenium(II) tris(bipyridine) 2PF6- complex, 1, was first used to recognize Co(II) in EtOH/H(2)O (1:1, v/v) solution, with the ruthenium(II) tris(bipyridine) moiety selected as a fluorophore and the multi-substituted phenol unit chosen as a receptor. The fluorescence quenching of 1 was attributed to the formation of an inclusion complex between multi-substituted phenol unit and Co(II) by 1:1 complex ratio (K=2.5 x 10(5)), which has been utilized as the basis of the fabrication of the Co(II)-sensitive fluorescent chemosensor. The analytical performance characteristics of the proposed Co(II)-sensitive chemosensor were investigated. The sensor can be applied to the quantification of Co(II) with a linear range covering from 1.0 x 10(-7) to 5.0 x 10(-5) M and a detection limit of 5 x 10(-8) M. The experiment results show that the response behavior of 1 to Co(II) is pH-independent in medium condition (pH 4.5-9.5) and show excellent selectivity for Co(II) over transition metal cations except Cu(II). The chemosensor has been used for determination of Co(II) in water samples.

A selective fluorescence-on reaction of spiro form fluorescein hydrazide with Cu(II)

The spiro form fluorescein hydrazide (1) bearing a cleavable active bond is characterized as a highly selective and sensitive fluorescence probe for Cu2+. In 0.01 M Tris-HCl buffer (pH 7.2), the probe displays a highly selective fluorescence-on response to Cu2+ only, instead of other common metal ions. The reaction mechanism has been explored and proposed as that the hydrazide group of 1 recognizes and binds Cu2+, and the subsequent complexation of Cu2+ promotes hydrolytic cleavage of the amide bond, causing the release of fluorophore (fluorescein) and thereby the retrievement of fluorescence. Conditions for fluorescence measurement were optimized, generating a calibration curve that is linear over the concentration range of 0.1-10 microM Cu2+. The detection limit for Cu2+ is 64 nM based on 11 blank determinations (k=3), also showing a highly sensitive feature. The fluorescence-on reaction described here has been used for the determination of trace Cu2+ in real biological fluids with satisfactory results.

Application of Crude Extract of Kohlrabi (Brassica oleracea gongylodes) as a Rich Source of Peroxidase in the Spectrofluorometric Determination of Hydrogen Peroxide in Honey Samples

Crude extract of kohlrabi (Brassica oleracea gongylodes) was prepared by a simple procedure and its enzymatic activity and total protein concentration were determined. It was found that this crude extract is a rich source of peroxidase (POx) and has high specific activity. Cross-linked polyvinylpyrrolidone was used as a stabilizer in the preparation of the crude extract. The POx activity of kohlrabi crude extract did not vary for at least 2 months when deoxygenated and stored at 4 degrees C. This extract was applied for the spectrofluorometric determination of hydrogen peroxide using homovanillic acid as a fluorogenic substrate. POx catalyzes the hydrogen peroxide oxidation of homovanillic acid to produce a dimer which shows strong fluorescence at 420 nm with excitation at 312 nm. In the optimum conditions, the calibration graph for hydrogen peroxide was linear up to 190 ng mL(-1), with a detection limit of 4.4 ng mL(-1). The relative standard deviation (RSD) was 1.48% for 50 ng mL(-1) hydrogen peroxide. The proposed method was successfully applied to the determination of hydrogen peroxide in honey. The concentration-time profile of H2O2 produced upon dilution of honey was studied and H2O2 contents of some different honeys from various areas of Iran were determined.

[Photometric analysis with reaction between metal ion (M) and organic reagent (R)]

Firstly, the syntheses of various organic reagents (R) containing such xanthene derivatives as O-hydroxyhydro-quinonephthalein (QnPh), and 3,4,5,6-tetrahydroxyfluoran (gallein, Gall) were studied. Secondarily, the coexisting effects of surfactant (cationic-, anionic-, amphoteric- and nonionic-surfactants alone or combination) on the coloring or fluorescence reactions between various (R) such as xanthene derivatives, aromatic amines and various metal ions (M) such as bismuth(III), tin(IV), iron(III), molybdenum(VI), uranium(VI), cobalt(II), aluminum(III), etc. were systematically investigated. Thirdly, numerous simple and sensitive photometric analyses (spectrophotometry and fluorophotometry) for various (M) and organic compounds(Org) such as biological samples, and pharmaceutical preparations by formation reactions of (R-M) binary or ((R-M)-Org) ternary complexes were established in the coexistence of surfactant alone or combination.