Electrodeposition of gold nanoparticles on indium/tin oxide electrode for fabrication of a disposable hydrogen peroxide biosensor

A novel disposable third-generation hydrogen peroxide (H₂O₂) biosensor based on horseradish peroxidase (HRP) immobilized on the gold nanoparticles (AuNPs) electrodeposited indium tin oxide (ITO) electrode is investigated. The AuNPs deposited on ITO electrode were characterized by UV-vis, SEM, and electrochemical methods. The AuNPs attached on the ITO electrode surface with quasi-spherical shape and the average size of diameters was about 25 nm with a quite symmetric distribution. The direct electron chemistry of HRP was realized, and the biosensor exhibited excellent performances for the reduction of H₂O₂. The amperometric response to H₂O₂ shows a linear relation in the range from 8.0 μmol L⁻¹ to 3.0 mmol L⁻¹ and a detection limit of 2 μmol L⁻¹ (S/N = 3). The value of HRP immobilized on the electrode surface was found to be 0.4 mmol L⁻¹. The biosensor indicates excellent reproducibility, high selectivity and long-term stability.     

Amperometric hydrogen peroxide biosensor based on the immobilization of heme proteins on gold nanoparticles-bacteria cellulose nanofibers nanocomposite

A novel matrix, gold nanoparticles-bacterial cellulose nanofibers (Au-BC) nanocomposite was developed for enzyme immobilization and biosensor fabrication due to its unique properties such as satisfying biocompatibility, good conductivity and extensive surface area, which were inherited from both gold nanoparticles (AuNPs) and bacterial cellulose nanofibers (BC). Heme proteins such as horseradish peroxidase (HRP), hemoglobin (Hb) and myoglobin (Mb) were successfully immobilized on the surface of Au-BC nanocomposite modified glassy carbon electrode (GCE). The immobilized heme proteins showed electrocatalytic activities to the reduction of H₂O₂ in the presence of the mediator hydroquinone (HQ), which might be due to the fact that heme proteins retained the near-native secondary structures in the Au-BC nanocomposite which was proved by UV-vis and IR spectra. The response of the developed biosensor to H₂O₂ was related to the amount of AuNPs in Au-BC nanocomposite, indicating that the AuNPs in BC network played an important role in the biosensor performance. Under the optimum conditions, the biosensor based on HRP exhibited a fast amperometric response (within 1 s) to H₂O₂, a good linear response over a wide range of concentration from 0.3 μM to 1.00 mM, and a low detection limit of 0.1 μM based on S/N = 3. The high performance of the biosensor made Au-BC nanocomposite superior to other materials as immobilization matrix.     

Hydrogen peroxide biosensor based on hemoglobin modified zirconia nanoparticles-grafted collagen matrix

A novel method for the immobilization of hemoglobin (Hb) and preparation of reagentless biosensor was proposed using a biocompatible non-toxic zirconia enhanced grafted collagen tri-helix scaffold. The formed membrane was characterized with UV-vis and FT-IR spectroscopy, scanning electron microscope and electrochemical methods. The Hb immobilized in the matrix showed excellent direct electrochemistry with an electron transfer rate constant of 6.46 s⁻¹ and electrocatalytic activity to the reduction of hydrogen peroxide. The apparent Michaelis-Menten constant for H₂O₂ was 0.026 mM, showing good affinity. Based on the direct electrochemistry, a new biosensor for H₂O₂ ranging from 0.8 to 132 μM was constructed. Owing to the porous structure and high enzyme loading of the matrix the biosensor exhibited low limit of detection of 0.12 μM at 3σ, fast response less than 5 s and high sensitivity of 45.6 mA M⁻¹ cm⁻². The biosensor exhibited acceptable stability and reproducibility. ZrO₂-grafted collagen provided a good matrix for protein immobilization and biosensing preparation. This method was useful for monitoring H₂O₂ in practical samples with the satisfactory results.     

Direct electrocatalytic oxidation of nitric oxide and reduction of hydrogen peroxide based on α-Fe2O3 nanoparticles-chitosan composite

α-Fe₂O₃ nanoparticles prepared using a simple solution-combusting method have been dispersed in chitosan (CH) solution to fabricate nanocomposite film on glass carbon electrode (GCE). The as-prepared α-Fe₂O₃ nanoparticles were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM). The nanocomposite film exhibits high electrocatalytic oxidation for nitric oxide (NO) and reduction for hydrogen peroxide (H₂O₂). The electrocatalytic oxidation peak is observed at +0.82 V (vs. Ag/AgCl) and controlled by diffusion process. The electrocatalytic reduction peak is observed at −0.45 V (vs. Ag/AgCl) and controlled by diffusion process. This α-Fe₂O₃-CH/GCE nanocomposite bioelectrode has response time of 5 s, linearity as 5.0 × 10⁻⁷ to 15.0 × 10⁻⁶ M of NO with a detection limit of 8.0 × 10⁻⁸ M and a sensitivity of −283.6 μA/mM. This α-Fe₂O₃-CH/GCE nanocomposite bioelectrode was further utilized in detection of H₂O₂ with a detection limit of 4.0 × 10⁻⁷ M, linearity as 1.0 × 10⁻⁶ to 44.0 × 10⁻⁶ M and with a sensitivity of 21.62 μA/mM. The shelf life of this bioelectrode is about 6 weeks under room temperature conditions.     

Development of hydrogen peroxide biosensor based on in situ covalent immobilization of horseradish peroxidase by one-pot polysaccharide-incorporated sol-gel process

A simple and reliable one-pot approach was established for the development of a novel hydrogen peroxide (H₂O₂) biosensor based on in situ covalent immobilization of horseradish peroxidase (HRP) into biocompatible material through polysaccharide-incorporated sol-gel process. Siloxane with epoxide ring and trimethoxy anchor groups was applied as the bifunctional cross-linker and the inorganic resource for organic-inorganic hybridization. The reactivity between amine groups and epoxy groups allowed the covalent incorporation of HRP and the functional biopolymer, chitosan (CS) into the inorganic polysiloxane network. Some experimental variables, such as mass ratio of siloxane to CS, pH of measuring solution and applied potential for detection were optimized. HRP covalently immobilized in the hybrid matrix possessed high electrocatalytic activity to H₂O₂ and provided a fast amperometric response. The linear response of the as-prepared biosensor for the determination of H₂O₂ ranged from 2.0 × 10⁻⁷ to 4.6 × 10⁻⁵ mol l⁻¹ with a detection limit of 8.1 × 10⁻⁸ mol l⁻¹. The apparent Michaelis-Menten constant was determined to be 45.18 μmol l⁻¹. Performance of the biosensor was also evaluated with respect to possible interferences. The fabricated biosensor exhibited high reproducibility and storage stability. The ease of the one-pot covalent immobilization and the biocompatible hybrid matrix serve as a versatile platform for enzyme immobilization and biosensor fabricating.     

Prussian Blue electrodeposited on MWNTs-PANI hybrid composites for H2O2 detection

A Prussian Blue (PB)/polyaniline (PANI)/multi-walled carbon nanotubes (MWNTs) composite film was fabricated by step-by-step electrodeposition on glassy carbon electrode (GCE). The electrode prepared exhibits enhanced electrocatalytic behavior and good stability for detection of H₂O₂ at an applied potential of 0.0 V. The effects of MWNTs thickness, electrodeposition time of PANI and rotating rate on the current response of the composite modified electrode toward H₂O₂ were optimized to obtain the maximal sensitivity. A linear range from 8 × 10⁻⁹ to 5 × 10⁻⁶ M for H₂O₂ detection has been observed at the PB/PANI/MWNTs modified GCE with a correlation coefficient of 0.997. The detection limit is 5 × 10⁻⁹ M on signal-to-noise ratio of 3. To the best of our knowledge, this is the lowest detection limit for H₂O₂ detection. The electrode also shows high sensitivity (526.43 μA μM⁻¹ cm⁻²) for H₂O₂ detection which is more than three orders of magnitude higher than the reported.     

Dendrimer-rhodium nanoparticle modified glassy carbon electrode for amperometric detection of hydrogen peroxide

Metallic nanoparticles of rhodium were prepared by using the newly synthesized N,N-bis-succinamide-based dendrimer as stabilizers. The Rh nanoparticles were spherical shaped with a particle size of ∼2 nm. The dendrimer Rh-encapsulated nanoparticles (Rh-DENs) were immobilized on glassy carbon electrode (GCE) and their electrocatalytic activity towards hydrogen peroxide reduction was investigated using cyclic voltammetry and chronoamperometry. The Rh-DENs modified GCE showed excellent electrocatalytic activity for hydrogen peroxide reduction reactions. The steady-state cathodic current response of the modified electrode at −0.3 V (vs SCE) in phosphate buffer (pH 7.0) showed a linear response to hydrogen peroxide concentration ranging from 8 to 30 μM with a detection limit and sensitivity of 5 μM and 0.03103 × 10⁻⁶ A μM⁻¹, respectively.     

Amperometric biosensor for hydrogen peroxide based on coimmobilized horseradish peroxidase and methylene green in ormosils matrix with multiwalled carbon nanotubes

A novel amperometric biosensor for the analytical determination of hydrogen peroxide was developed. The fabrication of the biosensor was based on the coimmobilization of horseradish peroxidase (HRP), methylene green (MG) and multiwalled carbon nanotubes within ormosils; 3-aminopropyltrimethoxysilane (APTMOS), 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (ETMOS) and phenyltrimethoxysilane (PHTMOS). APTMOS determined the hydrophilicity/hydrophobicity of the ormosils and PHTMOS and ETMOS increased the physical and mechanical strength of the ormosil matrix. The ormosil modified electrodes were characterized with SEM, UV-vis spectroscopy and electrochemical methods. Cyclic voltammetry and amperometric measurements demonstrated the MG coimmobilized with HRP in this way, displayed good stability and could efficiently shuttle electrons between immobilized enzyme and electrode, and MWCNTs facilitated the electrocatalytic reduction of H₂O₂ at reduced over potential. The Micheaelis constant of the immobilized HRP was 1.8 mM, indicating a high affinity of the HRP to H₂O₂ without loss of enzymatic activity in ormosil matrix. The prepared biosensor had a fast response of H₂O₂, less than 10 s, and excellent linear range of concentration from 5 × 10⁻⁷ to 2 × 10⁻⁵ M with the detection limit of 0.5 μM (S/N = 3) under the optimum conditions. At the same time, the influence of solution pH, effect of enzyme amount, steady-state applied potential and temperature on the biosensor were investigated. The enzyme electrode retained about 90% of its initial activity after 30 days of storage in a dry state at 4 °C. The preparation of the developed biosensor was convenient and showed high sensitivity with good stability.     

Preparation and characterization of Prussian blue nanowire array and bioapplication for glucose biosensing

Prussian blue nanowire array (PBNWA) was prepared via electrochemical deposition with polycarbonate membrane template for effective modification of glassy carbon electrode. The PBNWA electrode thus obtained was demonstrated to have high-catalytic activity for the electrochemical reduction of hydrogen peroxide in neutral media. This enabled the PBNWA electrode to show rapid response to H₂O₂ at a low potential of −0.1 V over a wide range of concentrations from 1 × 10⁻⁷ M to 5 × 10⁻² M with a high sensitivity of 183 μA mM⁻¹ cm⁻². Such a low-working potential also substantially improved the selectivity of the PBNWA electrode against most electroactive species such as ascorbic acid and uric acid in physiological media. A detection limit of 5 × 10⁻⁸ M was obtained using the PBNWA electrode for H₂O₂, which compared favorably with most electroanalysis procedures for H₂O₂. A biosensor toward glucose was then constructed with the PBNWA electrode as the basic electrode by crosslinking glucose oxidase (GOx). The glucose biosensor allowed rapid, selective and sensitive determination of glucose at −0.1 V. The amperometric response exhibited a linear correlation to glucose concentration through an expanded range from 2 × 10⁻⁶ M to 1 × 10⁻² M, and the response time and detection limit were determined to be 3 s and 1 μM, respectively.     

Composite film of carbon nanotubes and chitosan for preparation of amperometric hydrogen peroxide biosensor

A new amperometric biosensor for hydrogen peroxide was developed based on cross-linking horseradish peroxidase (HRP) by glutaraldehyde with multiwall carbon nanotubes/chitosan (MWNTs/chitosan) composite film coated on a glassy carbon electrode. MWNTs were firstly dissolved in a chitosan solution. Then the morphology of MWNTs/chitosan composite film was characterized by field-emission scanning electron microscopy. The results showed that MWNTs were well soluble in chitosan and robust films could be formed on the surface. HRP was cross-linked by glutaraldehyde with MWNTs/chitosan film to prepare a hydrogen peroxide biosensor. The enzyme electrode exhibited excellent electrocatalytic activity and rapid response for H₂O₂ in the absence of a mediator. The linear range of detection towards H₂O₂ (applied potential: −0.2 V) was from 1.67 × 10⁻⁵ to 7.40 × 10⁻⁴ M with correction coefficient of 0.998. The biosensor had good repeatability and stability for the determination of H₂O₂. There were no interferences from ascorbic acid, glucose, citrate acid and lactic acid.     

Direct electrochemistry and electrocatalysis of myoglobin based on silica-coated gold nanorods/room temperature ionic liquid/silica sol-gel composite film

A novel biosensor based on the silica-coated gold nanorods (GNRs@SiO₂) and hydrophilic room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tetrafluroborate ([bmim][BF₄]) was fabricated for the determination of hydrogen peroxide (H₂O₂) and nitrite. GNRs@SiO₂ can not only act as a binder to hinder [bmim][BF₄] (RTIL) leaking from the electrode surface, but also provide a favorable microenvironment for direct electrochemistry of myoglobin (Mb). A pair of well-defined and quasi-reversible redox peaks of Mb was obtained at the GNRs@SiO₂-Mb/RTIL-sol-gel composite film modified GCE (GNRs@SiO₂-Mb/RTIL-sol-gel/GCE) through direct electron transfer between Mb and the underlying electrode. This biosensor showed an excellent electrocatalytic activity towards hydrogen peroxide and nitrite. The linear range for the determination of H₂O₂ was from 0.2 to 180 μM with a detection limit of 0.12 μM based on the signal-to-noise ratio of 3. In addition, the biosensor also exhibited high selectivity, good reproducibility, and long-term stability. Therefore, this kind of composite film can provide an ideal matrix for protein immobilization and biosensor fabrication.     

Prussian blue modified glassy carbon electrodes-study on operational stability and its application as a sucrose biosensor

Stabilisation of electrochemically deposited Prussian blue (PB) films on glassy carbon (GC) electrodes has been investigated and an enhancement in the stability of the PB films is reported if the electrodes are treated with tetrabutylammonium toluene-4-sulfonate (TTS) in the electrochemical activation step following the electrodeposition. A multi-enzyme PB based biosensor for sucrose detection was made in order to demonstrate that PB films can be coupled with an oxidase system. A tri-enzyme system, comprising glucose oxidase, mutarotase and invertase, was crosslinked with glutaraldehyde and bovine albumin serum on the PB modified glassy carbon electrode. The deposited PB operated as an electrocatalyst for electrochemical reduction of hydrogen peroxide, the final product of the enzyme reaction sequence. The electrochemical response was studied using flow injection analysis for the determination of sucrose, glucose and H₂O₂. The optimal concentrations of the immobilisation mixture was standardised as 8 U of glucose oxidase, 8 U of mutarotase, 16 U of invertase, 0.5% glutaraldehyde (0.025 μl) and 0.5% BSA (0.025 mg) in a final volume of 5 μl applied at the electrode surface (0.066 cm²). The biosensor exhibited a linear response for sucrose (4-800 μM), glucose (2-800 μM) and H₂O₂ (1-800 μM) and the detection limit was 4.5, 1.5 and 0.5 μM for sucrose, glucose and H₂O₂, respectively. The sample throughput was ca. 60 samples h⁻¹. An increase in the operational and storage stability of the sucrose biosensor was also noted when the PB modified electrodes were conditioned in phosphate buffer containing 0.05 M TTS during the preparation of the PB films.     

A colloidal suspension of nanostructured poly(N-butyl benzimidazole)-graphene sheets with high oxidase yield for analytical glucose and choline detections

A colloidal suspension of nanostructured poly(N-butyl benzimidazole)-graphene sheets (PBBIns-Gs) was used to modify a gold electrode to form a three-dimensional PBBIns-Gs/Au electrode that was sensitive to hydrogen peroxide (H₂O₂) in the presence of acetic acid (AcOH). The positively charged nanostructured poly(N-butyl benzimidazole) (PBBIns) separated the graphene sheets (Gs) and kept them suspended in an aqueous solution. Additionally, graphene sheets (Gs) formed “diaphragms” that intercalated Gs, which separated PBBIns to prevent tight packing and enhanced the surface area. The PBBIns-Gs/Au electrode exhibited superior sensitivity toward H₂O₂ relative to the PBBIns-modified Au (PBBIns/Au) electrode. Furthermore, a high yield of glucose oxidase (GOD) on the PBBIns-Gs of 52.3 mg GOD per 1 mg PBBIns-Gs was obtained from the electrostatic attraction between the positively charged PBBIns-Gs and negatively charged GOD. The non-destructive immobilization of GOD on the surface of the PBBIns-Gs (GOD-PBBIns-Gs) retained 91.5% and 39.2% of bioactivity, respectively, relative to free GOD for the colloidal suspension of the GOD-PBBIns-Gs and its modified Au (GOD-PBBIns-Gs/Au) electrode. Based on advantages including a negative working potential, high sensitivity toward H₂O₂, and non-destructive immobilization, the proposed glucose biosensor based on an GOD-PBBIns-Gs/Au electrode exhibited a fast response time (5.6 s), broad detection range (10 μM to 10 mM), high sensitivity (143.5 μA mM⁻¹ cm⁻²) and selectivity, and excellent stability. Finally, a choline biosensor was developed by dipping a PBBIns-Gs/Au electrode into a choline oxidase (ChOx) solution for enzyme loading. The choline biosensor had a linear range of 0.1 μM to 0.83 mM, sensitivity of 494.9 μA mM⁻¹ cm⁻², and detection limit of 0.02 μM. The results of glucose and choline measurement indicate that the PBBIns-Gs/Au electrode provides a useful platform for the development of oxidase-based biosensors.     

Electrochemistry and scanning electron microscopy of polyaniline/peroxidase-based biosensor

An amperometric biosensor was prepared by in situ deposition of horseradish peroxidase (HRP) enzyme on a polyaniline (PANI)-doped platinum disk electrode. The PANI film was electrochemically deposited on the electrode at 100 mV s⁻¹/Ag-AgCl. Cyclic voltammetric characterization of the PANI film in 1 M HCl showed two distinct redox peaks, which prove that the PANI film was electroactive and exhibited fast reversible electrochemistry. The surface concentration and film thickness of the adsorbed electroactive species was estimated to be 1.85×10⁻⁷ mol cm⁻² and approximately 16 nm, respectively. HRP was electrostatically immobilized onto the surface of the PANI film, and voltammetry was used to monitor the electrocatalytic reduction of hydrogen peroxide under diffusion-controlled conditions. Linear responses over the concentration range 2.5×10⁻⁴ to 5×10⁻³ M were observed. Spectroelectrochemistry was used to monitor the changes in UV-vis properties of HRP, before and after the catalysis of H₂O₂. The biosensor surface morphology was characterized by scanning electron microscopy (SEM) using PANI-doped screen-printed carbon electrodes (SPCEs) in the presence and absence of (i) peroxidase and (ii) peroxide. The SEM images showed clear modifications of the conducting film surface structure when doped with HRP, as well as the effect of hydrogen peroxide on the morphology of biosensor.     

Amperometric biosensor for hydrogen peroxide based on hemoglobin entrapped in titania sol-gel film

Hemoglobin (Hb) was entrapped in a titania sol-gel matrix and used as a mimetic peroxidase to construct a novel amperometric biosensor for hydrogen peroxide. The Hb entrapped titania sol-gel film was obtained with a vapor deposition method, which simplified the traditional sol-gel process for protein immobilization. The morphologies of both titania sol-gel and the Hb films were characterized using scanning electron microscopy (SEM) and proved to be chemically clean, porous, homogeneous. This matrix provided a biocompatible microenvironment for retaining the native structure and activity of the entrapped Hb and a very low mass transport barrier to the substrates. H₂O₂ could be reduced by the catalysis of the entrapped hemoglobin at −300 mV without any mediator. The reagentless H₂O₂ sensor exhibited a fast response (less than 5 s) and sensitivity as high as 1.29 mA mM⁻¹ cm⁻². The linear range for H₂O₂ determination was from 5.0×10⁻⁷ to 5.4×10⁻⁵ M with a detection limit of 1.2×10⁻⁷ M. The apparent Michaelis-Menten constant of the encapsulated hemoglobin was calculated to be 0.18±0.02 mM. The stability of the biosensor was also evaluated.     

A novel polybenzimidazole-modified gold electrode for the analytical determination of hydrogen peroxide

The imine of polybenzimidazole (PBI) is chemically oxidized by hydrogen peroxide (H₂O₂) in the presence of acetic acid (AcOH). Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopies (XPS) showed that when the AcOH concentration remained constant, the degree of oxidation increased with increasing H₂O₂ levels. Moreover, the imine also exhibited electrochemical redox behavior. Based on these properties, a PBI-modified Au (PBI/Au) electrode was developed as an enzyme-free H₂O₂ sensor. At an applied potential of −0.5 V vs. Ag/AgCl, the current response of the PBI/Au electrode was linear with H₂O₂ concentration over a range from 0.075 to 1.5 mM, with a sensitivity of 55.0 μA mM⁻¹ cm⁻². The probe had excellent stability, with <5% variation from its initial response current after storage at 50 °C for 10 days. Potentially interfering species such as ascorbic or uric acid had no effect on sensitivity. Sensitivity improved dramatically when multiwalled carbon nanotubes (MWCNT) were incorporated in the probe. Under optimal conditions, the detection of H₂O₂ using a MWCNT-PBI/Au electrode was linear from 1.56 μM to 2.5 mM, with a sensitivity of 928.6 μA mM⁻¹ cm⁻². Analysis of H₂O₂ concentrations in urine samples using a MWCNT-PBI/Au electrode produced accurate real-time results comparable to those of traditional HPLC methods.     

A novel nonenzymatic sensor based on LaNi0.6Co0.4O3 modified electrode for hydrogen peroxide and glucose

In this paper, LaNi_0.6Co_0.4O₃ (LNC) nanoparticles were synthesized by the sol–gel method, and the structure and morphology of LNC nanoparticles were characterized by X-ray diffraction spectrum, scanning electron microscopy and transmitting electron microscopy. And then, LNC was used to modify carbon paste electrode (CPE) without any adhesive to fabricate hydrogen peroxide and glucose sensor, and the results demonstrated that LNC exhibited strong electrocatalytical activity by cyclic voltammetry and amperometry. In H₂O₂ determination, linear response was obtained in the concentration range of 10 nM–100 μM with a detection limit of 1.0 nM. In glucose determination, there was the linear region of 0.05–200 μM with a detection limit of 8.0 nM. Compared with other reports, the proposed sensor also displayed high sensitivity toward H₂O₂ (1812.84 μA mM⁻¹ cm⁻²) and glucose (643.0 μA mM⁻¹ cm⁻²). Moreover, this prepared sensor was applied to detect glucose in blood serum and hydrogen peroxide in toothpaste samples with satisfied results, indicating its possibility in practical application.     

Application of Fenton reaction for nanomolar determination of hydrogen peroxide in seawater

A simple and sensitive method for the determination of nanomolar levels of hydrogen peroxide (H₂O₂) in seawater has been developed and validated. This method is based on the reduction of H₂O₂ by ferrous iron in acid solution to yield hydroxyl radical (OH) which reacts with benzene to produce phenol. Phenol is separated from the reaction mixture by reversed phase high performance liquid chromatography and its fluorescence intensity signals were measured at excitation and emission of 270 and 298 nm, respectively. Under optimum conditions, the calibration curve exhibited linearity in the range of (0-50) × 10³ nmol L⁻¹ H₂O₂. The relative standard deviations for five replicate measurements of 500 and 50 nmol L⁻¹ H₂O₂ are 1.9 and 2.4%, respectively. The detection limit for H₂O₂, defined as three times the standard deviation of the lowest standard solution (5 nmol L⁻¹ H₂O₂) in seawater is 4 nmol L⁻¹. Interference of nitrite ion (NO₂⁻) on the fluorescence intensity of phenol was also investigated. The result indicated that the addition of 10 μmol L⁻¹ NO₂⁻ to seawater samples showed no significant interference, although, the addition of 50 μmol L⁻¹ NO₂⁻ to the seawater samples decreases the fluorescence intensity signals of phenol by almost 40%. Intercomparison of this method with well-accepted (p-hydroxyphenyl) acetic acid (POHPAA)-FIA method shows excellent agreement. The proposed method has been applied on-board analysis of H₂O₂ in Seto Inland seawater samples.     

Polyethyleneimine-capped silver nanoclusters as a fluorescence probe for sensitive detection of hydrogen peroxide and glucose

In this work, we utilized polyethyleneimine-capped silver nanoclusters (PEI-Ag nanoclusters) to develop a new fluorometric method for the determination of hydrogen peroxide and glucose with high sensitivity. The PEI-Ag nanoclusters have an average size of 2 nm and show a blue emission at 455 nm. The photostable properties of the PEI-Ag nanoclusters were examined. The fluorescence of the PEI-Ag nanoclusters could be particularly quenched by H₂O₂. The oxidization of glucose by glucose oxidase coupled with the fluorescence quenching of PEI-Ag nanoclusters by H₂O₂ can be used to detect glucose. Under optimum conditions, the fluorescence intensity quenched linearly in the range of 500 nM–100 μM with high sensitivity. The detection limit for H₂O₂ was 400 nM. And a linear correlation was established between fluorescence intensity (F₀ − F) and concentration of glucose in the range of 1.0 × 10⁻⁶ to 1.0 × 10⁻⁵ M and 1.0 × 10⁻⁵ to 1.0 × 10⁻³ M with a detection limit of 8.0 × 10⁻⁷ M. The method was used for the detection of glucose in human serum samples with satisfactory results. Furthermore, the mechanism of sensitive fluorescence quenching response of Ag nanoclusters to glucose and H₂O₂ has been discussed.     

A portable and low cost equipment for flow injection chemiluminescence measurements

A compact, reliable and low cost flow injection chemiluminescence system is described. The flow system consists of a set of solenoid micro-pumps that can dispense reproductive micro-volumes of solutions. The luminometer was based on a coiled cell constructed from polyethylene tubing that was sandwiched between two large area photodiodes. The whole equipment costs about US$ 750 and weights ca. 3 kg. Equipment performance was evaluated by measuring low concentrations of hydrogen peroxide by oxidation of luminol and for the determination of ammonium, based on its inhibition of the luminescence provided by the reaction of luminol and sodium hypochlorite. Linear responses were achieved within 1.0-80 μmol L⁻¹ H₂O₂ and 0.6-60 μmol L⁻¹ NH₄⁺ with detection limits estimated as 400 nmol L⁻¹ H₂O₂ and 60 nmol L⁻¹ NH₄⁺ at the 99.7% confidence level. Coefficients of variation were 1.0 and 1.8%, estimated for 20 μmol L⁻¹ H₂O₂ and 15 μmol L⁻¹ NH₄⁺ (n = 20), respectively. Reagent consumption of 55 μg luminol, effluent volume of 950 μL per determination and sampling rate of 120 samples per hour were also achieved.