Polymer microfluidic systems for samplepreparation for bacterial detection

University dissertation from Stockholm : KTH Royal Institute of Technology

Abstract: Sepsis, caused by blood stream infection, is a very serious health condition thatrequires immediate treatment using antibiotics to increase the chances for patientsurvival. A high prevalence of antibiotic resistance among infected patients requiresstrong and toxic antibiotics to ensure effective treatment. A rapid diagnostic devicefor detection of antibiotic resistance genes in pathogens in patient blood would enablean early change to accurate and less toxic antibiotics. Although there is a pressingneed for such devices, rapid diagnostic tests for sepsis do not yet exist.In this thesis, novel advances in microfabrication and lab-on-a-chip devices arepresented. The overall goal is to develop microfluidics and lab-on-a-chip systems forrapid sepsis diagnostics. To approach this goal, novel manufacturing techniques formicrofluidics systems and novel lab-on-a-chip devices for sample preparation havebeen developed.Two key problems for analysis of blood stream infection samples are that lowconcentrations of bacteria are typically present in the blood, and that separation ofbacteria from blood cells is difficult. To ensure that a sufficient amount of bacteria isextracted, large sample volumes need to be processed, and bacteria need to be isolatedwith high efficiency. In this thesis, a particle filter based on inertial microfluidicsenabling high processing flow rates and integration with up- and downstream processesis presented.Another important function for diagnostic lab-on-a-chip devices is DNA amplificationusing polymerase chain reaction (PCR). A common source of failure for PCRon-chip is the formation of bubbles during the analysis. In this thesis, a PCR-on-chipsystem with active degassing enabling fast bubble removal through a semipermeablemembrane is presented.Several novel microfabrication methods were developed. Novel fabrication techniquesusing the polymer PDMS that enable manufacturing of complex lab-on-a-chipdevices containing 3D fluidic networks and fragile structures are presented. Also,a mechanism leading to increased accuracy in photopatterning in thiol-enes, whichenables rapid prototyping of microfluidic devices, is described. Finally, a novel flexibleand gas-tight polymer formulation for microfabrication is presented: rubbery OSTE+.Together, the described achievements lead to improved manufacturing methodsand performances of lab-on-a-chip devices, and may facilitate future development ofdiagnostic devices.