Facile synthesis of ultrafine Co3O4 nanocrystals embedded carbon matrices with specific skeletal structures as efficient non-enzymatic glucose sensors

A facile, effective, and environmentally friendly method has been adopted for the first time to prepare tiny Co₃O₄ nanocrystals embedded carbon matrices without using surfactants, harmful organic reagents or extreme conditions. Structural characterizations reveal that the size-controlled Co₃O₄ nanocrystals are uniformly dispersed on carbon matrices. Electrochemical measurements reveal that Co₃O₄-ordered mesoporous carbon (OMC) can more efficiently catalyze glucose oxidation and acquire better detection parameters compared with those for the Co₃O₄-macroporous carbon, Co₃O₄-reduced graphene oxide, and free Co₃O₄ nanoparticles (NPs) (such as: the large sensitivity (2597.5 μA cm⁻² mM⁻¹ between 0 and 0.8 mM and 955.9 μA cm⁻² mM⁻¹ between 0.9 and 7.0 mM), fast response time, wide linear range, good stability, and surpassingly selective capability to electroactive molecules or Cl⁻). Such excellent performances are attributed to the synergistic effect of the following three factors: (1) the high catalytic sites provided by the uniformly dispersed and size-controlled Co₃O₄ nanocrystals embedded on OMC; (2) the excellent reactant transport efficiency caused by the abundant mesoporous structures of OMC matrix: (3) the improved electron transport in high electron transfer rate (confinement of the Co₃O₄ NPs in nanoscale spaces ensured intimate contact between Co₃O₄ nanocrystals and the conducting OMC matrix). The superior catalytic activity and selectivity make Co₃O₄-OMC very promising for application in direct detection of glucose.     

CuNiO nanoparticles assembled on graphene as an effective platform for enzyme-free glucose sensing

We utilized CuNiO nanoparticles modified graphene sheets (CuNiO–graphene) to the application of enzymeless glucose sensing. The hydrothermal synthesized CuNiO nanoparticles were successfully assembled on graphene sheets. Distinct from general method, the high quality pristine graphene was produced by chemical vapor deposition (CVD) and bubbling transferred on the electrode. Incorporating the excellent electronic transport of graphene and high electrocatalytic activity of CuNiO nanoparticles, the CuNiO–graphene nanocomposite modified electrode possessed strong electrocatalytic ability toward glucose in alkaline media. The proposed nonenzymatic glucose sensor exhibited wide linear range up to 16 mM (two parts, from 0.05 to 6.9 mM and 6.9–16 mM) and high sensitivity (225.75 μA mM⁻¹ cm⁻² and 32.44 μA mM⁻¹ cm⁻², respectively). Excellent selectivity and acceptable stability were also achieved. Such an electrode would be attractive to sensor construction for its good properties, simple operation and low expense.     

Direct electron transfer of glucose oxidase and dual hydrogen peroxide and glucose detection based on water-dispersible carbon nanotubes derivative

A water-dispersible multi-walled carbon nanotubes (MWCNTs) derivative, MWCNTs-1-one-dihydroxypyridine (MWCNTs-Py) was synthesis via Friedel–Crafts chemical acylation. Raman spectra demonstrated the conjugated level of MWCNTs-Py was retained after this chemical modification. MWCNTs-Py showed dual hydrogen peroxide (H₂O₂) and glucose detections without mutual interference by adjusting pH value. It was sensitive to H₂O₂ in acidic solution and displayed the high performances of sensitivity, linear range, response time and stability; meanwhile it did not respond to H₂O₂ in neutral solution. In addition, this positively charged MWCNTs-Py could adsorb glucose oxidase (GOD) by electrostatic attraction. MWCNTs-Py-GOD/GC electrode showed the direct electron transfer (DET) of GOD with a pair of well-defined redox peaks, attesting the bioactivity of GOD was retained due to the non-destroyed immobilization. The high surface coverage of active GOD (3.5 × 10⁻⁹ mol cm⁻²) resulted in exhibiting a good electrocatalytic activity toward glucose. This glucose sensor showed high sensitivity (68.1 μA mM⁻¹ cm⁻²) in a linear range from 3 μM to 7 mM in neutral buffer solution. The proposed sensor could distinguish H₂O₂ and glucose, thus owning high selectivity and reliability.     

Electrocatalytic H2O2 amperometric detection using gold nanotube electrode ensembles

Arrays of nanoscopic gold tubes were prepared by electroless plating of the metal within the pores of nanoporous polycarbonate track-etched membranes. A procedure for fabricating an ensemble of enzyme-modified nanoelectrodes has been developed based on the efficient immobilization of horseradish peroxidase (HRP) to the gold nanotubes array using self-assembled monolayers (mercaptoethylamine or mercaptopropionic acid) as anchoring layers. Hydrogen peroxide (H₂O₂) was determined electrochemically by using gold nanoelectrode ensembles (NEE) functionalized or not in phosphate buffer solution (PB) with or without a mediator (hydroquinone, H₂Q). Bare NEE displays a remarkable sensitivity (14 μA mM⁻¹ in H₂Q at −0.1 V versus Ag/AgCl) compared to a classical gold macroelectrode (0.41 μA mM⁻¹). The gold nanoparticles that form the tubular structure act as excellent catalytic surfaces towards the oxidation and the reduction of H₂O₂. The HRP modified NEE presents a slightly lower sensitivity (9.5 μA mM⁻¹) than bare NEE. However, this system presents an enhanced limit of detection (up to 4 × 10⁻⁶ M) and a higher selectivity towards the detection of H₂O₂ over a wide range of potentials. The lifetime, fabrication reproducibility and measurement repeatability of the HRP enzyme electrode were evaluated with satisfactory results.     

Layer by layer assembly of catalase and amine-terminated ionic liquid onto titanium nitride nanoparticles modified glassy carbon electrode: Study of direct voltammetry and bioelectrocatalytic activity

A novel, simple and facile layer by layer (LBL) approach is used for modification of glassy carbon (GC) electrode with multilayer of catalase and nanocomposite containing 1-(3-Aminopropyl)-3-methylimidazolium bromide (amine terminated ionic liquid (NH₂-IL)) and titanium nitride nanoparticles (TiNnp). First a thin layer of NH₂-IL is covalently attached to GC/TiNnp electrode using electro-oxidation method. Then, with alternative self assemble positively charged NH₂-IL and negatively charged catalase a sensitive H₂O₂ biosensor is constructed, whose response is directly correlated to the number of bilayers. The surface coverage of active catalase per bilayer, heterogeneous electron transfer rate constant (k_s) and Michaelis–Menten constant (K_M) of immobilized catalase were 3.32 × 10⁻¹² mol cm⁻², 5.28 s⁻¹ and 1.1 mM, respectively. The biosensor shows good stability, high reproducibility, long life-time, and fast amperometric response with the high sensitivity of 380 μA mM⁻¹ cm⁻² and low detection limit of 100 nM at concentration range up to 2.1 mM.     

Highly accessible Pt nanodots homogeneously decorated on Au nanorods surface for sensing

Some nanostructures are reported to possess enzyme-mimetic activities similar to those of natural enzymes. Herein, highly-dispersed Pt nanodots on Au nanorods (HD- PtNDs@AuNRs) with mimetic peroxidase activity were designed as an active electrode modifier for fabrication of a hydrogen peroxide (H₂O₂) electrochemical sensor. The HD-PtNDs@AuNRs were synthesized by a seed-mediated growth approach and confirmed by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and UV–vis spectroscopy. The electrochemical and catalytical performances of HD-PtNDs@AuNRs towards H₂O₂ reduction were investigated in detail by cyclic voltammetry and amperometry. The HD-PtNDs@AuNRs modified electrode displayed a high catalytic activity to H₂O₂ at −0.10 V (versus SCE), a rapid response within 5 s, a wide linear range of 2.0–3800.0 μM, a detection limit of 1.2 μM (S/N = 3), and a high sensitivity of 181 μA mM⁻¹ cm⁻². These results suggested a promising potential of fabricating H₂O₂ electrochemical sensor using HD- PtNDs@AuNRs.     

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.     

High loading MnO2 nanowires on graphene paper: Facile electrochemical synthesis and use as flexible electrode for tracking hydrogen peroxide secretion in live cells

Recent progress in flexible and lightweight electrochemical sensor systems requires the development of paper-like electrode materials. Here, we report a facile and green synthesis of a new type of MnO₂ nanowires–graphene nanohybrid paper by one-step electrochemical method. This strategy demonstrates a collection of unique features including the effective electrochemical reduction of graphene oxide (GO) paper and the high loading of MnO₂ nanowires on electrochemical reduced GO (ERGO) paper. When used as flexible electrode for nonenzymatic detection of hydrogen peroxide (H₂O₂), MnO₂–ERGO paper exhibits high electrocatalytic activity toward the redox of H₂O₂ as well as excellent stability, selectivity and reproducibility. The amperometric responses are linearly proportional to H₂O₂ concentration in the range 0.1–45.4 mM, with a detection limit of 10 μM (S/N = 3) and detection sensitivity of 59.0 μA cm⁻² mM⁻¹. These outstanding sensing performances enable the practical application of MnO₂–ERGO paper electrode for the real-time tracking H₂O₂ secretion by live cells macrophages. Therefore, the proposed graphene-based nanohybrid paper electrode with intrinsic flexibility, tailorable shapes and adjustable properties can contribute to the full realization of high-performance flexible electrode material used in point-of-care testing devices and portable instruments for in-vivo clinical diagnostics and on-site environmental monitoring.     

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.     

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.     

Amperometric biosensor based on a nanoporous ZrO2 matrix

A biosensor was investigated based on the use of ZrO₂ sol-gel matrix for enzyme immobilization in the mild condition. This bioceramic zirconia alcogel has been prepared by the novel alcohothermal route with a cheap inorganic salt Zr(NO₃)₄·5H₂O with several desirable features including a large surface area (about 460 m² g⁻¹) as well as pore volume and a well-developed textural mesoporosity, and horseradish peroxidase was selected as a model enzyme. The results of transmission electron microscopy (TEM) and BET measurement of the substrate showed that the as-prepared zirconia matrix has an advantageous microenvironment and large surface area available for high enzyme loading. The parameters affecting both the entrapment of enzyme and the biosensor response were optimized. The resulting biosensor exhibited high sensitivity of 111 μA mM⁻¹ for hydrogen peroxide over a wide range of concentrations from 2.5×10⁻⁷ to 1.5×10⁻⁴ mol l⁻¹, quick response of less than 10 s and good stability over 3 months.     

Reusable and robust high sensitive non-enzymatic glucose sensor based on Ni(OH)2 nanoparticles

Nickel hydroxide nanoparticles were successfully electrodeposited on graphite electrode (Gr/NiONP) and employed as a robust non-enzymatic glucose sensor. The results of cyclic voltammetry (CV) and chronoamperometry demonstrated that the Gr/NiONP electrode displayed high electrocatalytic activity toward glucose. The oxidation current is directly related to the glucose concentration from 1 μM to 15 mM. Besides, the glucose sensor displayed high sensitivity (2400 μA mM⁻¹ cm⁻²) with a detection limit of 0.53 μM (S/N = 3) in basic solution. Moreover, the sensor showed excellent selectivity, reproducibility and stability properties. The relative standard deviation is 1.2% for 10 successive measurements in 16 μM glucose. Interestingly, the signal for glucose was maintained at 95% of its initial value even after 6 months of storage under ambient conditions. Gr/NiONP electrode has also been tested to detect glucose in human serum with satisfactory results.     

Immobilization of [Cu(bpy)2]Br2 complex onto a glassy carbon electrode modified with α-SiMo12O40 and single walled carbon nanotubes: Application to nanomolar detection of hydrogen peroxide and bromate

A simple procedure has been used for preparation of modified glassy carbon electrode with carbon nanotubes and copper complex. Copper complex [Cu(bpy)₂]Br₂ was immobilized onto glassy carbon (GC) electrode modified with silicomolybdate, α-SiMo₁₂O₄₀⁴⁻ and single walled carbon nanotubes (SWCNTs)_. Copper complex and silicomolybdate irreversibly and strongly adsorbed onto GC electrode modified with CNTs. Electrostatic interactions between polyoxometalates (POMs) anions and Cu-complex, cations mentioned as an effective method for fabrication of three-dimensional structures. The modified electrode shows three reversible redox couples for polyoxometalate and one redox couple for Cu-complex at wide range of pH values. The electrochemical behavior, stability and electron transfer kinetics of the adsorbed redox couples were investigated using cyclic voltammetry. Due to electrostatic interaction, copper complex immobilized onto GC/CNTs/α-SiMo₁₂O₄₀⁴⁻ electrode shows more stable voltammetric response compared to GC/CNTs/Cu-complex modified electrode. In comparison to GC/CNTs/Cu-complex the GC/CNTs/α-SiMo₁₂O₄₀⁴⁻ modified electrodes shows excellent electrocatalytic activity toward reduction H₂O₂ and BrO₃⁻ at more reduced overpotential. The catalytic rate constants for catalytic reduction hydrogen peroxide and bromate were 4.5(±0.2) × 10³ M⁻¹ s⁻¹ and 3.0(±0.10) × 10³ M⁻¹ s⁻¹, respectively. The hydrodynamic amperommetry technique at 0.08 V was used for detection of nanomolar concentration of hydrogen peroxide and bromate. Detection limit, sensitivity and linear concentration range proposed sensor for bromate and hydrogen peroxide detection were 1.1 nM and 6.7 nA nM⁻¹, 10 nM-20 μM, 1 nM, 5.5 nA nM⁻¹ and 10 nM-18 μM, respectively.     

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.     

In-tube magnetic solid phase microextraction of some fluoroquinolones based on the use of sodium dodecyl sulfate coated Fe3O4 nanoparticles packed tube

In-tube magnetic solid phase microextraction (in-tube MSPME) of fluoroquinolones from water and urine samples based on the use of sodium dodecyl sulfate (SDS) coated Fe₃O₄ nanoparticles packed tube has been reported. After the preparation of Fe₃O₄ nanoparticles (NPs) by a batch synthesis, these NPs were introduced into a stainless steel tube by a syringe and then a strong magnet was placed around the tube, so that the Fe₃O₄ NPs were remained in the tube and the tube was used in the in-tube SPME-HPLC/UV for the analysis of fluoroquinolones in water and urine samples. Plackett–Burman design was employed for screening the variables significantly affecting the extraction efficiency. Then, the significant factors were more investigated by Box–Behnken design. Calibration curves were linear (R² > 0.990) in the range of 0.1–1000 μg L⁻¹ for ciprofloxacin (CIP) and 0.5–500 μg L⁻¹ for enrofloxacin (ENR) and ofloxacin (OFL), respectively. LODs for all studied fluoroquinolones ranged from 0.01 to 0.05 μg L⁻¹. The main advantages of this method were rapid and easy automation and analysis, short extraction time, high sensitivity, possibility of fully sorbent collection after analysis, wide linear range and no need to organic solvents in extraction.     

β−cyclodextrins-based inclusion complexes of CoFe2O4 magnetic nanoparticles as catalyst for the luminol chemiluminescence system and their applications in hydrogen peroxide detection

β−cyclodextrins (β−CD)-based inclusion complexes of CoFe₂O₄ magnetic nanoparticles (MNPs) were prepared and used as catalysts for chemiluminescence (CL) system using the luminol-hydrogen peroxide CL reaction as a model. The as-prepared inclusion complexes were characterized by XRD (X-ray diffraction), TGA (thermal gravimetric analysis) and FT-IR. The oxidation reaction between luminol and hydrogen peroxide in basic media initiated CL. The effect of β−CD-based inclusion complexes of CoFe₂O₄ magnetic nanoparticles and naked CoFe₂O₄ magnetic nanoparticles on the luminol-hydrogen peroxide CL system was investigated. It was found that inclusion complexes between β−CD and CoFe₂O₄ magnetic nanoparticles could greatly enhance the CL of the luminol-hydrogen peroxide system. Investigation on the kinetic curves and the chemiluminescence spectra of the luminol-hydrogen peroxide system demonstrates that addition of CoFe₂O₄ MNPs or inclusion complexes between β−CD and CoFe₂O₄ MNPs does not produce a new luminophor of the chemiluminescent reaction. The luminophor for the CL system was still the excited-state 3-aminophthalate anions (3-APA*). The enhanced CL signals were thus ascribed to the possible catalysis from CoFe₂O₄ MNPs or inclusion complexes between β−CD and CoFe₂O₄ nanoparticles. The feasibility of employing the proposed system for hydrogen peroxide sensing was also investigated. Experimental results showed that the CL emission intensity was linear with hydrogen peroxide concentration in the range of 1.0 × 10⁻⁷ to 4.0 × 10⁻⁶ mol L⁻¹ with a detection limit of 2.0 × 10⁻⁸ mol L⁻¹ under optimized conditions. The proposed method has been used to determine hydrogen peroxide in water samples successfully.     

Enzyme-free amperometric sensing of hydrogen peroxide and glucose at a hierarchical Cu2O modified electrode

In this paper, an enzyme-free amperometric electrochemical sensor was fabricated by casting Nafion-impregnated Cu₂O particles onto a glassy carbon electrode. A dual dependence of peak current on sweeping rate, which can be attributed for the accumulation of reaction products, was observed on the sensor. Electrochemical analysis of the particulate Cu₂O for detecting H₂O₂ and glucose is described, showing remarkable sensitivity in both cases. The estimated detection limits and sensitivities for H₂O₂ (0.0039 μM, 52.3 mA mM⁻¹ cm⁻²) and glucose (47.2 μM, 0.19 mA mM⁻¹ cm⁻²) suggest that the response for H₂O₂ detection was much higher than for glucose detection. Electron microscopy observation suggested that the hierarchical structures of Cu₂O resulting from self-assembly of nanocrystals are responsible for the specific electrochemical properties.     

Polythiophene-coated Fe3O4 superparamagnetic nanocomposite: Synthesis and application as a new sorbent for solid-phase extraction

In the present work, a novel type of superparamagnetic nanosorbent, polythiophene-coated Fe₃O₄ nanoparticles (Fe₃O₄@PTh NPs), have been successfully synthesized. The synthesized NPs were characterized by scanning electron microscopy (SEM), Fourier transform-infrared (FT-IR) spectroscopy, and thermal gravimetric analysis (TGA). The synthesized Fe₃O₄@PTh NPs were applied as an efficient sorbent for extraction and preconcentration of several typical plasticizer compounds (di-n-butyl phthalate (DBP), di-(2-ethylhexyl) phthalate (DEHP), and dioctyl adipate (DOA)) from environmental water samples. Separation of Fe₃O₄@PTh NPs from the aqueous solution was simply achieved by applying external magnetic field. Separation and determination of the extracted plasticizers was performed by gas chromatography–flame ionization detection (GC–FID). Several variables affecting the extraction efficiency of the analytes i.e., amount of NPs sorbent, salt concentration, extraction time, and desorption conditions were investigated and optimized. The best working conditions were as follows: amount of sorbent, 100 mg; NaCl concentration, 30% (w/v); sample volume, 45 mL; extraction time, 10 min; and 100 μL of ethyl acetate for desorption of the analytes within 2 min. Under optimized conditions, preconcentration factors for DBP, DEHP, and DOA were obtained as 86, 194, and 213, respectively. The calibration curves were linear (R² > 0.998) in the concentration range of 0.4–100 μg L⁻¹ for both DEHP and DOA and 0.7–100 μg L⁻¹ for DBP. The limits of detection (LODs) were obtained in the range of 0.2–0.4 μg L⁻¹. The intra-day relative standard deviations (RSDs%) based on four replicates were obtained in the range of 4.0–12.3%. The proposed procedure was applied to analysis of water samples including river water, bottled mineral water, and boiling water exposed to polyethylene container (after cooling) and recoveries between 85 and 99% and RSDs lower than 12.8% were obtained.     

Quenched electrochemiluminescence of Ag nanoparticles functionalized g-C3N4 by ferrocene for highly sensitive immunosensing

In this paper, a novel sandwich electrochemiluminescence (ECL) immunosensor was constructed by ferrocene for quenching Ag nanoparticles functionalized g-C₃N₄ (Ag@g-C₃N₄) emission. The prepared Ag@g-C₃N₄ had strong and stable ECL signals compared to pure g-C₃N₄ and primary antibody (Ab₁) can be immobilized on Ag@g-C₃N₄ by adsorption of Ag nanoparticles. Ferrocene carboxylic acid (Fc-COOH) labeled secondary antibody was immobilized on Au doped mesoporous Al₂O₃ nanorods (Au@Al₂O₃–Fc-COOH@Ab₂) as labels through adsorption ability of Au toward proteins. After a sandwich-type immunoreaction, a remarkable decrease of ECL signal was observed due to the ECL quenching of Ag@g-C₃N₄ by Au@Al₂O₃–Fc-COOH@Ab₂. As a result, the change of ECL intensity has a direct relationship with the logarithm of CEA concentrations in the range of 1 pg mL⁻¹–100 ng mL⁻¹ with a detection limit of 0.35 pg mL⁻¹ (S/N = 3). Additionally, the proposed immunosensor shows high specificity, good reproducibility, and long-term stability.