Erdoğan Özgür

Quartz crystal microbalance based nanosensor for lysozyme detection with lysozyme imprinted nanoparticles

The aim of this study is to prepare quartz crystal microbalance (QCM) nanosensor for the real-time detection of lysozyme. In the first part, the lysozyme imprinted (MIP) nanoparticles were prepared by mini-emulsion polymerization. The MIP nanoparticles were characterized by TEM, zeta-sizer and FTIR-ATR measurements. Particle size was found around 50 nm. The MIP nanoparticles were attached by dropping of nanoparticle solution to gold surface and then, dried at 37°C for 6h. QCM nanosensor was characterized with AFM and ellipsometer. The observations indicated that the nanoparticle film was almost monolayer. The detection limit was found as 1.2 ng/mL. The specificity of the QCM nanosensor was shown by using albumin as a competitor molecule. The results show that the QCM nanosensor has high selectivity and sensitivity with a wide range of lysozyme concentrations in both aqueous solutions (0.2-1500 μg/mL) and natural sources (egg white) (460-1500 ng/mL).

Molecular Imprinting of Macromolecules for Sensor Applications

Molecular recognition has an important role in numerous living systems. One of the most important molecular recognition methods is molecular imprinting, which allows host compounds to recognize and detect several molecules rapidly, sensitively and selectively. Compared to natural systems, molecular imprinting methods have some important features such as low cost, robustness, high recognition ability and long term durability which allows molecularly imprinted polymers to be used in various biotechnological applications, such as chromatography, drug delivery, nanotechnology, and sensor technology. Sensors are important tools because of their ability to figure out a potentially large number of analytical difficulties in various areas with different macromolecular targets. Proteins, enzymes, nucleic acids, antibodies, viruses and cells are defined as macromolecules that have wide range of functions are very important. Thus, macromolecules detection has gained great attention in concerning the improvement in most of the studies. The applications of macromolecule imprinted sensors will have a spacious exploration according to the low cost, high specificity and stability. In this review, macromolecules for molecularly imprinted sensor applications are structured according to the definition of molecular imprinting methods, developments in macromolecular imprinting methods, macromolecular imprinted sensors, and conclusions and future perspectives. This chapter follows the latter strategies and focuses on the applications of macromolecular imprinted sensors. This allows discussion on how sensor strategy is brought to solve the macromolecules imprinting.

Plastic antibody based surface plasmon resonance nanosensors for selective atrazine detection

This study reports a surface plasmon resonance (SPR) based affinity sensor system with the use of molecular imprinted nanoparticles (plastic antibodies) to enhance the pesticide detection. Molecular imprinting based affinity sensor is prepared by the attachment of atrazine (chosen as model pesticide) imprinted nanoparticles onto the gold surface of SPR chip. Recognition element of the affinity sensor is polymerizable form of aspartic acid. The imprinted nanoparticles were characterized via FTIR and zeta-sizer measurements. SPR sensors are characterized with atomic force microscopy (AFM), scanning electron microscopy (SEM), Fourier transform infrared spectrophotometry (FTIR) and contact angle measurements. The imprinted nanoparticles showed more sensitivity to atrazine than the non-imprinted ones. Different concentrations of atrazine solutions are applied to SPR system to determine the adsorption kinetics. Langmuir adsorption model is found as the most suitable model for this affinity nanosensor system. In order to show the selectivity of the atrazine-imprinted nanoparticles, competitive adsorption of atrazine, simazine and amitrole is investigated. The results showed that the imprinted nanosensor has high selectivity and sensitivity for atrazine.

Microcontact imprinted quartz crystal microbalance nanosensor for protein C recognition.

Detection of protein C (PC) in human serum was performed by quartz crystal microbalance (QCM) based on molecular imprinting technique (MIP). The high-resolution and mass-sensitive QCM based sensor was integrated with high sensitivity and selectivity of the MIP technique. The PC microcontact imprinted (PC-μCIP) nanofilm was prepared on the glass surface. Then, the PC-μCIP/QCM sensor was prepared with 2-hydroxyethyl methacrylate (HEMA), ethylene glycol dimethacrylate (EGDMA) and N-methacryloyl l-histidine methylester (MAH) as the functional monomer with copper(II) ions. The polymerization was performed under UV light (100W and 365nm) for 20-25min under nitrogen atmosphere. The characterization studies of QCM sensor were done by observation using atomic force microscopy (AFM), contact angle measurements, ellipsometry and fourier transform infrared spectroscopy (FTIR). Detection of PC was investigated in a concentration range of 0.1-30μg/mL. Selectivity of PC-μCIP and PC non-imprinted/QCM (PC-non-μCIP) sensors for PC determination was investigated by using proteins namely hemoglobin (Hb), human serum albumin (HSA) and fibrinogen solutions. QCM sensor was also used for detection of PC molecules in aqueous solutions and human plasma. The detection limit was determined as 0.01μg/mL for PC analysis. The PC-μCIP/QCM sensor was used for five consecutive adsorption-desorption cycles. According to the results, the PC-μCIP/QCM sensor had obtained high selectivity and sensitivity for detection of PC molecules.

Surface Plasmon Resonance Sensors for Medical Diagnosis

Surface plasmon resonance (SPR) sensors have fascinated impressive attention to detect clinically related analytes in recent years. SPR sensors have also multiple advantages over existing conventional diagnostic tools such as easy preparation, no requirement of labeling, and high specificity and sensitivity with low cost, and they provide real-time detection capability. There are some articles and reviews in literature focusing on the applications of SPR-based sensors for the diagnosis of medically important entities such as proteins, cells, viruses, disease biomarkers, etc. These articles generally give information on the determination of such structures merely, whereas this presented manuscript combines recent literature for most of the medically important structures together including proteins, hormones, nucleic acids, whole cells, and drugs that especially the latest applications of SPR sensors for medical diagnosis to follow up new strategies and discuss how SPR strategy is brought to solve the medical problems.

Printable graphene ink produced by liquid-phaseshear exfoliation of graphite

Electrical interconnections are one of the main challenges in the printed electronics, to connect different functional units of anelectronic device. With the progressive advancement of large area and low cost printed electronic devices, the requirement forreliable interconnections with lower power consumption fabricated at low temperature is necessary. The conventional copperbased interconnections suffer severe problems in terms of cost efficiency when they are processed with photolithographytechnique. Therefore, there is being a copious amount of re-search to find alternative interconnect materials to overcome suchproblems. Recently, carbon nanotubes (Kordas et al. 2006), silver nanowires (Liu et al. 2011) and graphene (Huang et al. 2011)are being developed as the alter-native interconnection materials. Among them, graphene has high potential for suchapplication due to its remarkable inherent properties: high electrical conductivity, high transparency, mechanical flexibility,higher tensile strength, higher thermal conductivity, extremely high surface area and higher electron mobility. In spite of thoseexcellent properties, graphene has some shortcomings which are needed to be solved. Stacking of graphene sheets issues largeinterface resistance, which is responsible for poor electrical performance. Printing of graphene proved to be a promisingapproach since it combines the attractive features of graphene and the cost effective printing methods (ink-jet printing, nozzleprinting, spray printing) which enable additive patterning, direct writing, scalability to large area manufacturing. In order tofacilitate the printing process, the graphene solution needs to be highly stable, uniform and should contain smaller sheet sizes (~1μm). In this work we have proposed a cost-effective approach for large-scale production of printable stable graphene solutionto be used for the printing of inter-connects. The liquid-phase shear exfoliation (Paton, et al. 2014) of graphite allowed us toprepare large-scale production of solution with exfoliated graphene sheets. The process is scalable and requires shorterprocessing time compared to the other existing exfoliation methods. We have exfoliated graphene sheets from graphite flakesusing environmental-friendly solvent, ethanol, and a stabilizing polymer, ethyl cellulose (EC). The ethyl cellulose was used inorder to encapsulate graphene sheets in the solution and to avoid any reversible process (Secor, et al. 2013). The graphenebased solution prepared after several optimizations of the shear-mixing process leads to a stable solution for more than threemonths without any sedimentation. The microscopic studies of the films prepared from the spin-coating of the solution showedgraphene sheets without any agglomeration and with sheet sizes < 1μm. The process allowed us to prepare a cost-effectivegraphene solution which can be used for producing electrical interconnections by various printing methods.