The influence of surfactants on capillary driven flow in open hydrophobic microchannels towards chip-based fluorescent detection of HSV

Herpes Simplex Virus (HSV) is widespread among the human population. HSV infection can have subtle symptoms and often go undiagnosed. There are two types of HSV infections. HSV type 1 (HSV-1) is associated with orofacial blisters transmitted through saliva whereas HSV type 2 (HSV-2) causes genital ulcers, genital herpes and in severe cases meningitis. HSV-2 is transmitted through sexual contact. Current methods of detecting HSV infection are labour intensive and time consuming. Patients that attend a doctor's surgery often have to wait weeks to obtain a result due to transportation of the patient's sample to a laboratory with suitable facilities and personnel with expertise to diagnose HSV infection. Currently, there is a need to develop a rapid point-of-care (POC) device that is capable of detecting HSV infections from a patient's bedside, doctor's surgery or a remote location. Currently, there are capillary flow driven devices for the detection of HSV infections but the microdevice developed in this study for the fluorescent detection of HSV infection has a novel method of detection via capillary flow through open microchannels made of a cyclo-olefin polymer. In this thesis, a capillary driven microdevice was developed with the goal of fluorescent detection of HSV-1 and HSV-2 as a first step toward developing a POC microdevice. The first step in the development of this microdevice was to assess the influence of surfactants on the capillary flow through open hydrophobic microchannels and the hydrophilisation of the hydrophobic microchannels through the use of surfactant coatings which to the author’s knowledge has not been explored to date. An algorithm was developed which measured the meniscus position of the fluid in the microchannels by processing digitally captured high speed images of the fluid flow. It was found for the surfactant solutions flowing in hydrophobic open microchannels via capillary action did not follow conventional capillary flow theory possibly due the adsorption of surfactant molecules to the microchannel surfaces. To the author’s knowledge, the dynamic contact angles of fluids flowing in open microchannels have never been measured and in this thesis an algorithm was used to measure dynamic contact angles non-invasively by analysing digital images of the fluid flow. Surfactant coating of flat hydrophobic surfaces increased their wettabilty although surfactant coating of hydrophobic open microchannels promoted capillary flow of water but as the concentration of surfactant increased the flow through the microchannels decreased. The surfactant coating created a hydrophobic barrier that increased in strength with increasing surfactant concentration. Also, the meniscus shape started to deform from conventional capillary flow into a nonconventional shape which has not been documented before. This hydrophobic barrier and deformation of the meniscus shape may be due to the water adsorbing surfactant molecules from the surface of the microchannels. The second step was to assess the performance of the fluorescent detection of HSV infection using the microdevice based on a miniaturised ELISA technique. The detection method was based on the immobilisation of 100-1000μg/ml of capture antibodies specific for either HSV-1 or HSV-2 antigens. The concentration of HSV specific antigens and fluorescent detection antibodies used were 75-200 and 20μg/ml respectively. The concentration of HSV antigens used was 4-5 orders of magnitude higher than a POC device would use. An algorithm was developed that eliminated background noise allowing accurate qualitative and quantitative measurement of fluorescent detection. The microdevice failed in fluorescently detecting both HSV-1 and HSV-2. This technique requires substantial modifications to improve its performance.