Designing and Fabrication of Microfluidic Device for Therapeutic Drug Monitoring

Abstract

Cardiovascular diseases are one of the leading causes of mortality in Pakistan with prevalence rate of 19 %. Digoxin, a cardiac glycoside with positive inotropic effect is most commonly prescribed to cardiac patients; involving therapeutic monitoring of drug in serum/plasma through lengthy immunoassay procedures in practice. Also, the detection facility is restricted to private labs in major cities of Pakistan. Nanotechnology with the help of nanomaterials as compared to conventional lengthy procedures offers robust, patient centered on chip methodologies for detection of therapeutically important drugs in serum/plasma. The aim of the current study was fabrication of microfluidic device offering on chip QDs based detection of clinical range of digoxin (0.8-2.0 ng per ml) in custom-made optical setup. To achieve the said objectives, sequence of experiments were conducted. It was imperative to delineate the effect of pH of media on the fluorescence of zinc sulphide (ZnS). ZnS nanowires were conjugated with different log dilutions of mercaptoacetic acid (MAA) and digoxin antibody (Ab). To observe the effect of each dilution on fluorescence of NWs, pH of the media was monitored before conjugation. This study highlights the enhancement in PL of ZnS NWs when pH of the media is almost equal to the pKa of carboxyl group of MAA (pH ~ pKa). While, quenching in fluorescence was observed when pKa < pH> pKa. Thus, proving our hypothesis of use of ZnS as a fluorescent tag for biological applications. The effect of pH, ions in media and time of incubation on the PL of MAA coated QDs was studied by incubating dots in three different phosphate buffers. The pH of media for each buffer was adjusted as acidic (pH <7.2), neutral (7.2 - 8.0) and basic (pH> 14.0). The PL response from dots in buffer 1 was more profound as compared to other two buffers. The current study demonstrated maximum fluorescence from dots in buffer 1 within pH range of 7.0 – 10.0, which increases with increasing time of incubation.Electrochemical analysis was performed to study the mechanism of electron transfer from QDs to linker (MAA) and then to Ab using electrochemical analysis. Electrochemical analysis shows resistance in electron transfer when electrode was modified with QDs and Ab conjugated QDs (QD-MAA-Ab) as compared to when modified with MAA only. The number of electrons calculated during the oxidation or anodic cycle were: 2, 1,3 and 4 for GCE, QD, QD-MAA and QD-Ab, respectively. During the reduction or cathodic cycle, the electrons found were 2, 1,4 and 6 for GCE, QD, QD-MAA and QD-Ab. Finally, detection of different log dilutions of digoxin inclusive of the therapeutic range (0.8-2.0 ng/ml) spiked in PBS buffer (1ml) using emission (quantum dots (QD)) and plasmon based (gold nanoparticles (SERS)) methods. Limit of detection (LOD) achievable through emission-based methodology was 0.5 ng/ml while 0.4 ng/ml through plasmon resonance of gold nanoparticles. Then the emission-based detection was performed in fabricated microfluidic device using homemade optical detection setup. The fabricated device is of ((H x W x D) 2.7’’ x 0.98” x 0.005)) as compared to conventional digoxin detection machine (Architect i2000SR: (H x W x D) 48’’ x 61” x 49”). The current study envisages replacement of conventional methodologies with microfluidic device or chip using quantum dots and SERs based tags as compared to conventional enzyme-based labels. The said device would be cost effective, portable and can easily be carried to remote areas of country.