The consumption of contaminated food may cause serious illnesses,and traditional methods to detect Escherichia coli are still associated with long waiting times and high costs given the necessity to transport samples to specialized laboratories.There is a need to develop new technologies that allow cheap,fast,and direct monitoring at the site of interest.Thus,in this work,we developed optical immunosensors for the selective detection of E.coli,based on liquid crystal technology,whose molecules can align in different manners depending on the boundary conditions (such as substrates) as well as the environment that they experience.Each glass substrate was functionalized with anti-E.coli antibody using cysteamine as an intermediate,and a vertical alignment was imposed on the liquid crystal molecules by using DMOAP during functionalization.The presence of bacteria disrupts the alignment of the liquid crystal molecules,changing the intensity of light emerging between cross polarizers,measured using a polarized optical microscope and a monochromator.It was possible to detect E.coli in suspensions in the concentration range from 2.8 cells/mL to 2.8×10^(9) cells∕mL.Selectivity was also evaluated,and the sensors were used to analyze contaminated water samples.A prototype was developed to allow faster,in-situ,and easier analysis avoiding bulky instruments.
CoSe_(2) nanosheet materials with a wrinkled sheet structure and large surface area were synthesized via a simple hydrothermal method.Then polyethyleneimine(PEI)was used to functionalize wrinkled CoSe_(2)(w-CoSe_(2))to make gold nanocubes(AuNCs)uniformly anchored onto the surface of PEI-w-CoSe_(2) via Au-N bonds.And its application in electrochemical immunosensors for the detection of dipropyl phthalate(DPrP)was studied.The obtained material was characterized by the Fourier transform infrared spectroscopy(FTIR),transmission electron microscope(TEM),energydispersive spectroscopy(EDS),X-ray diffraction(XRD)and Raman spectroscopy.The effective surface area and conductivity of the electrode were enhanced by the introduction of AuNCs/PEI-w-CoSe_(2) nanocomposite.Cyclic voltammetry(CV),differential pulse voltammetry(DPV)and electrochemical impedance spectroscopy(EIS)were used to characterize the performance of immunosensor.After DPrP binds to antibodies via the antigen-antibody interaction,[Fe(CN)6]3-/4-was used as a signal probe to monitor the change of oxidation current of different DPrP concentrations.Under optimal conditions,the electrochemical responses of the prepared immunosensor were linear when the DPrP concentrations ranged from 1×10^(-11) to 1×10^(-5) mol·L-1,with a detection limit of 1.39×10^(-12) mol·L^(-1).The coefficient of determination(R2)is 0.995,indicating that the degree of fitting is good.Besides,the constructed immunosensor exhibited acceptable reproducibility,selectivity,and stability.Therefore,it may be found that the composite material has good application prospects in the electrochemical sensors field.
In this study, we have for the first time preformed the facile substrate-enhanced electroless deposition(SEED) of metal nanoparticles onto monolithic graphene@Ni foams for construction of disposable three-dimensional(3 D) electrochemical immunosensors. Specifically, we firstly used the SEED method to deposit gold nanoparticles(AuNPs) onto the graphene@Ni foam for immobilization of antibody(Ab1). This is followed by a second step SEED deposition to produce silver nanoparticles(AgNPs) for electrochemical stripping detection. Using a-fetoprotein antigen(AFP) as a module analyte, the newly-developed sensor showed a wide linear response, ranging from 5.0 pg/mL to 5.0 ng/mL and a low detection limit down to 2.3 pg/mL. The newly-developed 3 D-immunosensor is sensitive, reliable,and easy to be fabricated, showing great potential for clinic applications.
