Anharmonic Acoustic Technique for Detection of Surface-bound Particles

This thesis is embargoed pending a patent application. Please contact the author on [email protected] if you have any enquiriesReceptor-based biological detection techniques often suffer from the problem of non-specific interactions. This is largely due to the presence of weak electrostatic and Van der Waals forces between the receptor and the non-target substances in the analyte that are not easily dissociated in practice. Most existing detection techniques are unable to probe the interaction between the bound entity and the surface and differentiate between specific and non-specific interactions in terms of bond strength or activation energy. The resulting false positive responses lead to various issues, such as misdiagnosis and mistreatment in clinical diagnostics and false alarms in biosecurity. The problem is even more significant with direct direction techniques, such as the resonant frequency shift based detection using quartz crystal microbalance (QCM) or micro-cantilevers, which involve minimal sample processing and washing steps. The work presented in this thesis investigates, through modeling and experiments, the mechanical interactions of a resonator with microparticles attached via biomolecular linkers and analyses the resulting nonlinear acoustic modulation of the resonator from the transduced electrical signal. Physisorbed and specific interactions both in air and liquid medium are studied using thickness shear mode quartz crystal resonators and streptavidin-coated polystyrene microbeads (SCPM) of various sizes. It is found that the modification in the transduced electrical signal measured at the third harmonic (3f), or three times the driving frequency f, is significant in presence of the attached particles and approximately proportional to the number of particles. A detection limit of approximately 2 SCPM of 5.6 µm diameter in air and 6700 SCPM of 0.39 µm diameter in liquid is demonstrated, which corresponds to a mass detection limit of ~200 pg. Most interestingly, the deviation in the magnitude of the 3f signal as a function of the resonator oscillation amplitude is found to hold a distinct relationship with the type of particle-surface interaction. This provides a basis for selectivity in detection over and above the efficacy of the receptor. The function is also found to correlate well with the event of SCPM diffusion on the surface. This detection technique, based on the measurement of deviation in magnitude of the transduced electrical signal measured at a higher odd harmonic of the drive frequency due to the presence of surface-bound particles on a resonator, is termed as the anharmonic detection technique (ADT). A feasibility study with Bacillus subtilis spores in phosphate buffer saline (PBS) is carried out successfully where the modeling and experimental results with SCPM are successfully reproduced. A detection limit of 430 spores is demonstrated, which corresponds to a mass detection limit of ~650 pg. Capability for differentiation of the specifically-captured spores from unwashed physisorbed SCPM of similar dimensions is demonstrated using the shape of the ADT signal. These results indicate that the spore immobilization step may be directly followed by the detection step, which are 9 mins and 2 mins respectively in these experiments. ADT thus potentially enables a rapid, sensitive, reliable and direct detection without the need for any sample processing. Moreover, being an entirely electronic technique, ADT suitably lends itself to multiplexing, large scale fabrication and implementation on a miniaturized low-cost point-of-care detection platform that is of immense need in clinical diagnostics, food and environmental monitoring and biosecurity. Furthermore, fitting the experimental results with modeling estimates enables ADT to determine the force-extension characteristics of the binding biomolecular linker. The force-extension characteristics and the estimated unbinding force for a streptavidin-biotin complex estimated using ADT agrees well with those computed using molecular dynamics (MD) simulation at similar loading rates. Thus ADT contributes a unique force-spectroscopic method, which unlike conventional techniques such as the atomic force microscopy (AFM) provides statistically averaged data for multiple biomolecules in a relatively quicker and simpler experimental format. A method for determination of activation energy of the interaction is also proposed using ADT. This potentially enables a method for rapid and large scale biomolecular screening and studying of interaction networks, which have important applications in drug discovery and individualized therapy

High security image encryption by 3stage process

As a result of the development of computer network technology, communication of in- formation through personal computer is becoming more convenient. Meanwhile, it also gives hackers opportunities to attack the network. Therefore the security is now an important issue for multimedia communications. Image compression and image encryption are pivotal to proper storage and transmission of images. Simultaneous image compression and encryption aims at achieving enhanced bandwidth utilization and security at the same time. The concepts used here are : Chinese Reminder Theorem, Chaotic map, Bit plane mix- ing. The use of chaotic mixing increases the security of the proposed method and provides the additional feature of imperceptible encryption of the image owner logo in the host image. The image coding results, calculated from actual image size and encoded im- age le, are comparable to the results obtained through much more sophisticated and computationally complex methods. In addition, the algorithm has been applied to the scenario of image multiplexing in order to obtain enhanced level of security along with compression. Here one layer of encryption involves bit plane mixing. Encrypted and compressed image is applied to hiding algorithms. The idea behind our proposed method is, the cover image will be altered based upon the secret image. The secret image will be split into number of blocks and these blocks will be shued intellectually and then it will be merged with the cover image to generate the Segno image. Our proposed method, originally designed for dealing with color images, but also be extended to for grayscale images. Experimental results show that our proposed method improves the security and makes the information hacking hard

POLITICS OF THE DOMICILE IN THIONG’O’S MATIGARI

My paper offers a reading of Ngugi Wa Thiong’o’s Matigari (1989) and investigates the use of the home space as a site of protest. It is the home space that Matigari struggles to retrieve in the novel. The journeys undertaken by Matigari are metaphorically interwoven with his journeys within-the journeys in the realm of memory. In Matigari (1989), Matigari’s search for a home space in the aftermath of the independence of an anonymous nation (identified as Kenya) culminates in the grim discovery of the neocolonial oppression that marks the collapse of the nationalist dreams. Hence, my main aim in this paper is to analyse the journeys undertaken by the characters in the novel, and in doing so, I will also try to explain the spatial politics that define these journeys

Minimum Magnetizability Principle

A new electronic structure principle, viz. the minimum magnetizability principle (MMP) has been proposed and also has been verified through ab initio calculations, to extend the domain of applicability of the conceptual density functional theory (DFT) in explaining the magnetic interactions and magnetochemistry. This principle may be stated as, "A stable configuration/conformation of a molecule or a favorable chemical process is associated with a minimum value of the magnetizability". It has also been shown that a soft molecule is easily polarizable and magnetizable than a hard one.Comment: 2 Pages, 3 Figure