​Abstract:  Biosensors monitor physiological activities for diagnosis and treatment of disease. Molecularly imprinted polymers (MIPs) are a viable synthetic approach for molecular recognition in biosensing. For biosensing purposes, the most important properties in MIP optimization are sensitivity and selectivity towards a desired analyte. This study aims to optimize MIP sensitivity and selectivity by varying the amount and type of cross-linker used in the synthesis of cortisol and melatonin. The four cross-linkers tested were trimethylpropane trimethacrylate (TRIM), ethyleneglycodimethacrylate (EGDMA), divinylbenzene (DVB), and pentaerythritol triacrylate (PETRA). Based on literature, the following ratios were used for the template molecule to functional monomer to cross-linker in MIP synthesis: for EGDMA cross-linked polymers, 1:6:30; for TRIM and PETRA cross-linked polymers, 1:8:8, 1:6:3, and 1:8:35; for DVB cross-linked polymers, 1:6:30, 1:4:16, and 4:1:60. The polymers were ground and washed, then suspended in a polyvinyl matrix which was spin-coated onto an organic electrochemical transducer (OECT). The device performance was evaluated using electrochemical impedance spectroscopy. For each device, the impedance was measured in electrolyte solutions containing target molecules in concentrations ranging from 1 pM to 100 uM. The impedance was plotted against the analyte concentration to give the sensing slope, which is a measurement for the binding affinity of the polymer. For a device to be considered sensitive, its sensing slope should be greater than its non-imprinted counterpart by a factor above the error margin (+/- 1.79). Of the devices tested, CM1835T (highly cross-linked with TRIM) showed sensitivity towards cortisol, but lacks selectivity towards cortisol over its structural analog, estradiol. Of the melatonin selective polymers, MM163T (low cross-linking with TRIM), MM1630D, and MM4160D (both highly cross-linked with DVB) all showed promising results in sensitivity to melatonin. Overall, the results indicate that high degrees of cross-linking in MIPs improve sensitivity for large, rigid, non-aromatic molecules such as cortisol; however there is no correlation between selectivity and the degree of cross-linking. Meanwhile, divinylbenzene as a cross-linker improves sensitivity and selectivity towards aromatic analytes such as melatonin and estradiol. This study could be improved upon by further characterization of imprinted and non-imprinted polymers, investigation of molecular dynamics, and optimization of devices.

MORE INFORMATION

• CONTACTLinda J. Sapolu
• EMAILLinda.Sapolu@kaust.edu.sa

​Abstract:  "Polystyrene homopolymer and copolymer were synthesized via atom transfer radical emulsion polymerization (ATRP). Water soluble initiator was synthesized by reacting diethanolamine and α-bromoisobutyrate bromide. Polystyrene homopolymer was made by using the synthesized water soluble initiator with varied initiator concentration. The synthesis of diblock copolymer of Poly (ethylene glycol)-b-poly (styrene) was carried out with different non-ionic surfactants. The synthesized water soluble initiator and homopolymer as well as diblock polymers were characterized by nuclear magnetic resonance (NMR), Gel permeation chromatography (GPC), and Dynamic light scattering (DLS)".

MORE INFORMATION

• CONTACTLinda J. Sapolu
• EMAILLinda.Sapolu@kaust.edu.sa

​ABSTRACT: Gaseous pollution has become a global issue and its presence above certain limits is hazardous to human health and environment. Detection of such gases is an immediate need and researchers around the world are trying to solve this problem. Metal oxides are being used as sensing materials for a long time, but a high operating temperature limits applications in many areas. On the other hand, two-dimensional materials with high surface-to-volume ratio and chemical stability are promising candidates in the field of gas sensing. This includes monolayer transition metal dichalcogenides, such as MoS2 and WS2, which are direct band gap materials. While few layer transition metal dichalcogenides are indirect band gap materials, they are easier to synthesize than monolayers. Therefore, it is important to understand whether few layer transition metal dichalcogenides possess the same sensing behavior as the corresponding monolayers. For this reason the first part of this dissertation compares the sensing behavior of monolayer and few layer MoS2 and WS2. Two dimensional hexagonal boron nitride is a highly stable structural analogue of graphene. However, its insulating behavior with large band gap is not suitable for sensing. Recently, monolayer Si2BN has been proposed to exist. As the presence of Si makes this material reactive, the second part of this dissertation addresses its application as sensing material. 

In the final part of this dissertation, in search of a metal free, non-toxic, and earth abundant sensor material, further structural analogues of graphene are considered, namely monolayer C3N, monolayer C3Si, and monolayer C6BN. In particular, different theoretical approaches for studying the sensing performance of materials are compared to each other.

MORE INFORMATION

• CONTACTMazen E. Mero

MORE INFORMATION

• CONTACTProf. Shuyu Sun

​Abstract: Ion transport is ubiquitous in aqueous environments in biological, geological, chemical and environmental systems. Electrokinetics plays a very important and key role in some special cases where pore size is comparable to the screening length of electrical double layer. The applications include tight oil/gas exploration and development, radiative waste disposal, high-quality water purification, and even ion channels in cells. This talk will present (1) electrokinetic and interface theories for ion transport in micro/nanoporous media; (2) a mesoscopic numerical framework for predictions and the validations by comparisons with theories and experimental data; (3) multiscale analysis in both spacial and temporal scales for special applications.

MORE INFORMATION

• CONTACTProf. Shuyu Sun

MORE INFORMATION

• CONTACTDr. Thomas Finkbeiner