A novel amperometric immunosensor for human serum carbohydrate antigen 19-9 (CA19-9) based on its antibody (anti CA19-9) coated Fe3O4(core)/Au(shell) gold-magnetic nanocomposites(GMP) modified electrode is investigated.Firstly,chitosan(CS) was adsorbed on the surface of Au electrode (Au|CS),then Fe (CN) 3-6(FeCN) was connected to-NH+3 on the surface of chitosan film to form Au|CS-FeCN electrode by electrostatic attraction in acidic pH.FeCN can be employed as an electron transfer mediator.Furthermore anti CA19-9 coated GMP(GMP-anti CA19-9) was immobilized on the surface of Au|CS-FeCN by outside magnetic field adsorption to form one CA19-9 amperometric immunosensor (Au│CS-FeCN/GMP-anti CA19-9).The surface of the modified electrode was characterized by scanning electron microscopy (SEM),X-ray fluorescence (XFS) and X-ray photoelectron spectrometry(XPS).Its electrochemical characters were studied by cyclic voltammetry (CV),differential pulse voltammetry (DPV) and AC impedance (EIS).In pH 6.5 PBS,after the immunosensor is incubated with CA19-9solution at 35℃ for 25min,the electron transfer access of FeCN is partly inhibited,which leads to a linear decrease of current.Under optium conditions,the linear range of CA19-9 by the immunosensor is from 0.1 U/mL to 10 U/mL and 10 U/mL to 50 U/mL with a detection limit of 0.056 U/mL estimated at 3 times noise.The immunosensor was employed to determine CA19-9 in human serums and the results were consistent with ELISA method.Moreover,its surface can renew after magnetic field was removed.The immunosensor combines many functions as separation,enrichment and determination in one,with high sensitivity and good stability.This method would be valuable for clinical immunoassay for CA19-9 in human serum.
A novel amperometric immunosensor for carcinoembryonic antigen(CEA)in human serum was established based on [Cu(bpy)2(ONO)]NO3(CuL)and CEA antibody coated with gold nanoparticles(AuNPs)composite film.The glassy carbon electrode(GCE)was firstly oxided and carboxyel group was formed on its surface,and then ethylene diamine was bonded to it.The ammoniated electrode was soaked in CuL and electroless gold plating solution.Then CuL can be absorbed on GCE surface by π-π stacking interaction and AuNPs film of 30~50 nm were formed by electroless gold plating to form GCE-CuL-AuNPs.Furthermore CEA antibody(anti CEA)was absorbed on the surface of AuNPs film with HRP employed as blocking reagent to form one CEA immunosensor(GCE-CuL-AuNPs /anti CEA-HRP).CuL can be employed as an electron transfer mediator of catalytic activity detection of carbamide peroxide(CP),and HRP could enhance the sensitivity of immunosensor.After the immunosensor was incubated with CEA solution at 37 ℃ for 30 min,the electron transfer access of CuL to CP was partly inhibited,which lead to a linear decrease of the catalytic efficiency to CP in pH 6.5 phosphate buffer solution(PBS),the decrease percentage of current had a linear relationship with the concentration of CEA between 0.1 and 80 ng/mL.Under optimal conditions,the detection limit for CEA is 0.052 ng/mL(3σ).This method simplifies the detection system.It has a high sensitivity and wide detection range for clinical immunoassay of CEA in patients' serums.
A novel reagentless H_2O_2 sensor,based on the coimmobilization of horseradish peroxide(HRP) and the redox dye safranine T(ST) by their cross-linking with glutaradehyde on the surface of a glassy carbon electrode,was fabricated.The resulting modified electrode exhibited good electrochemical activity in aqueous solution,and the electron transfer rate constant between the derivative safranine T and glassy carbon electrode was about 0.066s~(1)(calculated from laviron's method).The apparent surface coverage of ST was about 9.22×10~(-11) mol/cm~2.It was found ST could mediate the electron transfer of HRP with the electrode substrate.Performance and characteristics of the biosensor were evaluated with respect to response time,detection limit,applied potential,pH and temperature.The results indicated that this biosensor is of high sensitivity to hydrogen peroxide with a low detection limit down to 1.0×10~(-7) mol/L.Moreover,dopamine,ascorbic acid and uric acid did not interfere with the determination of H_2O_2.Meanwhile,this enzyme electrode also showed good stability and reproducibility for long-term use.
One monolayer containing thiol-tailed groups was formed through the covalent binding of Cu ion with acetyl cysteamine modified gold electrode by using the self-assembly technique.The electrode shows one pairofredoxpeaks(V paⅠ =246mV,V pcⅠ =101mV)in pH3.0NaAc-HAc buffer.Its surface has been characˉterized by SEM,XRFS,XPS and cyclic voltammetry(CV).The electron transfer constant(α)of the electrode was0.52,rate constant(K s)is0.04s-1.The average surface coverage of CuACYS was1.2×10-10 mol/cm 2 which shows it's monolayer modified.The modified gold electrode shows an excellent electrocatalytic acˉtivity for reduction of NO in NaAc buffer between pH2.0to5.0.In pH3.0the NO's reductive potential was V paⅡ =-672mVwith an overpotential ca.600mVlower than that at a bare electrode.The peak currents of differential pulse voltammograms(DPV)is linear with NO concentration in the range of3.1×10-9-4.7×10-8 mol/L.The hetero electron transfer rate constant was3.12×10-3 cm/s.
In this study, fluorescent red-carbon quantum dots (R-CQDs) with an ultrahigh fluorescence quantum yield of 45% were rapidly and easily synthesized by thermal pyrolysis of 2,5-diaminotoluene sulfate and 4-hydroxyethylpiperazineethanesulfonic acid using a one-step microwave-assisted hydrothermal approach. R-CQDs possessed the excitation-independent fluorescence property with the optimal emission peak at 607 nm under the excitation wavelength of 585 nm. R-CQDs exhibited excellent fluorescence stability under extremely harsh conditions in a pH range of 2-11, high ionic strength (1.8 M of NaCl), and long UV light irradiation time (160 min). The fluorescence quantum yield of these R-CQDs was as high as 45%, implying their preferable application in chemosensors and biological analysis. Because Fe3+ ion bound with R-CQDs and statically quenched the fluorescence of R-CQDs, the fluorescence intensity of R-CQDs was recovered after the addition of ascorbic acid (AA) via its redox reaction with Fe3+ ion. R-CQDs were developed as highly sensitive fluorescent on-off-on probes for sequentially sensing Fe3+ ions and AA. Under the optimal experimental conditions, the linear range for Fe3+ ion detection was 1-70 μM with a detection limit of 0.28 μM, and the linear range for AA detection was 1-50 μM with a detection limit of 0.42 μM. The successful detection of Fe3+ ions in authentic water samples and the successful sensing of AA in human body fluids and vitamin C tablets further proved the practical application prospects of this efficient strategy in the environmental protection and disease diagnosis fields.
One monolayer containing thiol-tailed groups was formed via the covalent binding of Ru(Ⅱ) phthlocyanine(RuPc) on a dimercaptosuccinic amine-modified gold electrode by self-assembly,which was characterized by IR and XPS.The modified gold electrode showed an excellent electrocatalytic activity for the oxidation of homocysteine(Hcy) in a phosphate buffer solution(pH=5.5).The electrocatalytic mechanism and effect of pH of the buffer solution were also investigated.The steady-state current of chronoamperometry increased linearly with Hcy concentration in the range of 5.0×10-7~5.4×10-5 mol/L with a detection limit of 0.18 μmol/L(S/N=3).The sensor also showed excellent reproducibility that makes it an ideal amperometric detector for Hcy in human serum.
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