Development of nanomaterials and molecularly imprinted polymer based chemical sensors for selective and sensitive determination of biomarkers

This thesis focuses on the development of a new chemical sensor based on electrochemical measurements for the analysis of important biomarkers for medical diagnostic applications, which can be divided into 3 main parts. The first part focuses on the development of a three-dimensional electrochemical paper-based analytical device (3D-ePAD) with screen-printed graphite electrodes for the determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA) in pharmaceutical and urine samples. The device was fabricated by alkyl ketene dimer (AKD)-inkjet printing to form a circular hydrophobic zone on filter paper for the application of aqueous samples coupled with screen-printed electrodes on the paper. The electrochemical detection performed consists of three electrodes of graphite modified Fe3O4@Au-Cys/PANI nanocomposites. The three Fe3O4@Au-Cys/PANI/GFE electrodes screen-printed on the layout paper served as the working electrode, reference electrode, and counter electrode, respectively. Under optimum conditions, the fabricated device gave a linearity range of 20-700 μM for AA, and 20-1,000 μM for DA and UA. The detection limits were 3.20, 2.19, and 1.80 μM for AA, DA and UA, respectively. Additionally, the fabricated paper-based 3D electrochemical device has the following advantages: it is easy-to-use, inexpensive, and is a portable alternative for point of care monitoring. The second part focuses on the development of a novel amperometric flow-injection analysis (AMP-FIA) for determination of creatinine (Cre) based on a sensor consisting of copper oxide nanoparticles coated with a molecularly-imprinted polymer (CuO@MIP). The CuO@MIP was synthesized using CuO as the supporting core, Cre as the template, methacrylic acid (MAA) as functional monomer, N, N-(1,2-dihydroxyethylene)bis(acrylamide) (DHEBA) as cross-linker, and 2,2-azobis(2-methylpropionitrile) (AIBN) as initiates the polymerization process. CuO@MIP was then decorated on carbon-paste electrodes to obtain the CuO@MIP/CPE. The AMP-FIA system was used to quantitatively determine Cre at the CuO@MIP/CPE sensor, in a 0.1 M phosphate buffer (pH 8.0) carrier. The imprinted sensor exhibits excellent performance for Cre oxidation at an applied potential of +0.35V and a flow rate of 0.6 mL min-1. The sensor exhibits a linear dynamic range for Cre detection from 0.5 to 200 M (r2 = 0.995) with a limit of detection of 0.083 M (S/N = 3). The developed sensor was successfully applied for Cre determination in urine samples with accuracy and precision. The final part is the development of a novel dual-imprinted amperometric sensor for simultaneous determination of Cre and 8-hydroxy-2′-deoxyguanosine or 8-OHdG in human urine and serum. The determination used multiple-pulse amperometric detection coupled with flow injection analysis (MPA-FIA). For Cre sensing, CuO@MIP was applied. For 8-OHdG sensing, platinum nanoparticles embedded on reduced graphene oxide and then coated with guanosine poly-dopamine MIP to obtain PtNPs-rGO@MIP were applied. A dual MIP sensor (CuO@MIP and PtNPs-rGO@MIP/CPE) was then formed by CPE modified with both nanocomposites. A dual-potential waveform as a function of time, with Edet.1 at +0.4 V/150 ms to determine Cre selectively and Edet.2 at +0.6 V/250 ms for simultaneous analysis of both (Cre and 8-OHdG) compounds. Subtraction of a +0.6 V signal and +0.4 V signal using the respective correction factor, allows the developed sensor to perform quantitative analysis of 8-OHdG without Cre interference. The dual-imprinted sensor has a linear range of 0.5-150 μM for Cre and 0.005-50 μM for 8-OHdG, with limits of detection at the nano-molar level. The proposed method has been successfully applied in the accurate quantitative determination of Cre and 8-OHdG in urine and serum samples.