食品安全监管食品安全 (12).pdf

Biosensors Searching for fast,simple,ease-to-use,inexpensive,rugged analytical methods The most common analytical techniques employed in food safety management are chromatography-based:TLC,HPLC,GC,IC,etc.They are sensitive,selective,and capable of multiple-analyte detection.But these methods are generally complicated,time-consuming,and costly.pH meter is a fast,simple,ease-to-use,inexpensive,rugged device for determination of pH values,i.e.,logH+.pH electrode An electrochemical sensors the concentrations of targeted ions or chemicals are converted into electrical signal,i.e.,voltage.A gold standard for potable analytical devices,including biosensor.A combined pH electrode A glass electrode An electrochemical cell a device that generates electrical voltage and current.Any oxidation-reduction reaction can be converted to an electrochemical cell.Nernst equation Ion-selective electrodes(ISEs)are classified into three types:Solid-state ISEs,containing a crystalline membrane Example of ions F,Ag+,Cl,Br,SCN,and S2.Liquid membrane ISEs,e.g.,vallinomycin-absorbed polyvinyl chloride(PVC)for NO3,Cu2+,Cl,BF4,ClO4,and K+.Glass membrane ISEs,mainly glass electrodes,i.e.,pH electrodes.A chemical sensor a device,which responds to a particular analyte in a selective way by means of a reversible chemical interaction and can be used for the quantitative or qualitative determination of the analyte.The two main features of a sensor the transducer,which converts chemical information into an electrical signal,and the interface,a sensing or recognition element,which allows selectivity and/or sensitivity to the chemical detection process.The biosensors a subclass of chemical sensors.simple analytical devices that combine the high sensitivity and specificity of a biological molecule with the versatility of a range of different physical transducers to convert a biological response or biorecognition event into a readable digital electronic signal.A typical biosensor consists of three parts:(1)a biological,biologically derived,or biomimetic sensing element;(2)a physical transducer;and(3)a detector.Sensing/Biorecognition Elements Commonly Used in Sensor Systems 1.Antibodies and antibody derivatives e.g.,complete,biospecific,fragmented,or genetically engineered antibodies(Fab fragment,scFv,or diabody).2.Enzymes e.g.,an enzyme specific for particular analyte(glucose oxidase,specific for glucose)3.Receptor E.g.,a component from the antennae of an insect or a cell membrane receptor.Sensing/Biorecognition Elements Commonly Used in Sensor Systems(continued)4.A living cell that reacts to a particular stimulus or that registers the presence of a toxic material.5.Nucleic acid-based probe e.g.,DNA or RNA,or derivatives such as a peptide nucleic acids and aptamers.6.Plastibody or chemically generated recognition surface e.g.,“antibody-like”molecularly imprinted polymer The main categories of transducers 1.Electrochemical:such as ion-selective electrodes(ISE),ion-selective field affects transistors(ISFET),solid electrolyte gas sensors,semiconductor-based gas sensors,and conducting polymer sensors,mostly based on potentiometry,voltammetry,or amperometry.2.Piezoelectric:such as surface acoustic wave(SAW)sensors.A mechanical deformation gives rise to polarization of a dielectric material,which,in turn,generates an electric potential difference across the material.Piezoelectric materials tend to be sensitive to changes in mass,density,or viscosity,and it is because of these features that frequency can be used as a sensitive transduction parameter.The most widely used piezoelectric material is quartz.3.Optical:examples including fiber optics and devices making use of the principles of absorbance,reflectance,luminescence,and surface plasmon resonance(SPR).With fiber optics,evanescent wave technology is of prime importance.4.Thermal systems:the heat of a chemical reaction involves the analyte and,is monitored with a transducer.The example can be a thermistor,which is a type of resistor whose resistance varies significantly with temperature.Blood Glucose Sensor The most successful commercial biosensor.The highly specific enzyme glucose oxidase(GOx)is employed as a bioreceptor.Glucose reacts with this enzyme and generates a redox-acitive species,which can be measured electrochemically.An amperometric glucose biosensor given to the electrode reduced form Glucose dehydrogenase(GDH)oxygen is not required glucose oxidase In optical glucose sensing,the by-product H2O2 is the molecule being detected.This color change(colorless to blue)can be read visually using glucose test strips.