Studies On Carbon-based Anodes In Microbial Fuel Cells And Fluorescent/amperometric Biosensing Of Staphylococcus Aureus

Microbial fuel cells(MFCs),as a special kind of fuel cells,can convert chemical energy in organic matters to electricity by means of the catalytic activity of electrogenic microorganisms on anodes.MFCs are not only a potential green power source but also a new wastewater treatment technology,which have drawn much attention in recent years.However,the relatively low power densities of MFCs still hinder the widespread practical applications.As the carrier of biocatalysts,the MFC anodes are currently considered as the major limiting factor to achieve high power output.The bacterial loading capacity and the extracellular electron transfer at the anode play important roles in the performance of the anode.In this dissertation,to increase the bacterial loading and improve the mediated extracellular electron transfer,novel three-dimensional(3D)macroporous graphene electrode and ionic liquid polymer(ILP)modified carbon-based electrode were fabricated and used for constructing high-performance MFCs.As an important cause of foodborne disease,foodborne pathogenic bacteria have aroused wide public concern.So developing fast,sensitive and reliable detection method will contribute to the prevention and timely treatment of foodborne disease,which will better ensure the safety of people’s life and property.In recent years,with the development of science and technology,various biosensors have shown great advantages in food safety,disease diagnosis and environmental detection.In particular,electrochemical and fluorescence biosensors with high sensitivity,good selectivity,and robustness at low cost,have been playing the more and more important role in the food safety field.Currently,the detection limits of most biosensors are ca.102～105 CFU mL-1,but the detection limits for pratical application should reach ten even single-digit,so the sensitivities of biosensor need to be further improved.In this dissertation,several novel fluorescent/electrochemical labels were developed for constructing fluorescence/electrochemical biosensors with improved sensitivites.On the basis of briefly reviewing the fields of MFCs and pathogen detection,this dissertation contains the following contents.1.Facile fabrication of graphene-containing foam as a high performance anode for microbial fuel cellsFacile fabrication of novel three-dimensional anode materials to increase the bacterial loading capacity and improve substrate transport in MFCs is of great interest and importance.Herein,a novel graphene-containing foam(GCF)was fabricated simply by freeze-drying and pyrolysis of a graphene oxide-agarose gel.Owing to the involvement of graphene and stainless steel mesh in the GCF,the GCF shows high electrical conductivity,enabling the GCF to be a conductive electrode for MFC applications.With the aid of agarose,the GCF electrode possesses a supermacroporous structure with pore sizes ranging from 100 to 200μm and a high surface area,which greatly increases the bacterial loading capacity.Cell viability measurements indicate that the GCF possesses excellent biocompatibility.The MFC equipped with a 0.4 mm-thick GCF anode,shows a maximum area power density of 786 mW m-2,which is 4.1 times that of a MFC equipped with a commercial carbon cloth anode.2.Boosting current generation in microbial fuel cells by an order of magnitude by coating an ionic liquid polymer on carbon anodesMFCs have attracted great attentions due to their great application potentials,but the relatively low power densities of MFCs still hinder their widespread practical applications.Herein,we report that the current generation in MFCs can be boosted by an order of magnitude,simply by coating a hydrophilic and positively charged ionic liquid polymer(ILP)on carbon cloth(CC)or carbon felt(CF).The ILP coating not only can increase the bacterial loading capacity due to the electrostatic interactions between ILP and bacterial cells,but also can improve the mediated extracellular electron transfer between the electrode and the cytochrome proteins on the outer membrane of Shewanella putrefaciens cells.As a result,the maximum power density of a MFC equipped with the CF-ILP bioanode is as high as 4400 士 170 mW m-2,which is amongst the highest values reported to date.This work demonstrates a new strategy for greatly boosting the current generation in MFCs.3.Fluorescent immunoassay of pathogenic bacteria at the single-cell level using carbon dots-encapsulated breakable organosilica nanocapsule as labelsHerein,carbon dots(CDs)-encapsulated breakable organosilica nanocapsules(BONs)were facilely prepared and used as advanced fluorescent labels for ultrasensitive detection of Staphylococcus aureus.The CDs were entrapped in organosilica shells by cohydrolyzation of tetraethyl orthosilicate and bis[3-(triethoxysilyl)propyl]disulfide to form core-shell CDs@BONs,where hundreds of CDs were encapsulated in each nanocapsule.Immunofluorescent nanocapsules,i.e.,anti-S.aureus antibody-conjugated CDs@BONs,were prepared to specifically recognize S.aureus.Before the fluorescent detection,CDs were released from the BONs by simple NaBH4 reduction.The fluorescent signals were amplified by 2 orders of magnitude because of hundreds of CDs encapsulated in each nanocapsule,compared with a conventional immunoassay using CDs as fluorescent labels.A linear range was obtained at the S.aureus concentration from 1 to 200 CFU mL-1.CDs@BONs are also expected to expand to other systems and allow the detection of other analytes at ultralow concentrations.4.Fluorescent/electrochemical dual-signal detection of Staphylococcus aureus using gold-silver nanoclusters-encapsulated chitoan nanocapsules as biolabelsFluorescent/electrochemical dual-signal detection of Staphylococcus aureus was achieved by using gold-silver nanoclusters(Au-AgNCs)-encapsulated chitoan nanocapsules(CNs)as labels.Au-AgNCs@CNs were facilely prepared by pH-triggered self-aggregation of chitoan in the presence of Au-AgNCs,where a large number of Au-AgNCs were embedded in each nanocapsule.Expeimetally,immunonanocapsules and immunomagnetic nanoparticles specifically captured and recognized S.aureus simultaneously.After magnetic separation,bacterial cells bound to immunonanocapsules and immunomagnetic nanoparticles were used for fluorescent/electrochemical detetion.A linear range was obtained from 10 to 5000 CFU mL-1 for fluorescent and electrochemical detection.This method was successfully used to detect S.aureus in milk samples.