Browsing by Author "Bhatt, Geeta"

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2022 Index IEEE Transactions on NanoBioscience Vol. 21
(IEEE, 2022-10) Bhatt, Geeta
This index covers all technical items—papers, correspondence, reviews, etc.—that appeared in this periodical during 2022, and items from previous years that were commented upon or corrected in 2022. Departments and other items may also be covered if they have been judged to have archival value. The Author Index contains the primary entry for each item, listed under the first author’s name. The primary entry includes the coauthors’ names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and inclusive pagination. The Subject Index contains entries describing the item under all appropriate subject headings, plus the first author’s name, the publication abbreviation, month, and year, and inclusive pages. Note that the item title is found only under the primary entry in the Author Index.
Advances in Polymer Materials and Composites for Additive Manufacturing
(AIP, 2022) Bhatt, Geeta
Analysis of graphene coated optical fiber for visible range refractive index sensing
(Elsevier, 2023-02) Bhatt, Geeta
In this work, graphene coated optical fiber structure has been exploited theoretically for refractive index sensing within visible operating region. A high refractive index polymer layer is also considered as a matching layer between graphene and the fiber core to generate lossy mode resonances in the desired spectrum. It is observed that multilayer graphene coating supports much sharper and narrower resonances than the graphene monolayer. Sensing characteristics with variation in number of graphene layers and polymer layer thickness are investigated with different polarizations of light. Calibration curves indicating change in resonant wavelength corresponding to the refractive index variation of sensing medium are also presented. It is observed that polymer layer act as the catalyst in enabling the structure to support resonances and shifting the operating region in visible spectrum. A maximum sensitivity of 300 nm/RIU for RI range of 1.33–1.40 is reported for p-polarization of light. It is believed that visible range operation of the proposed structure will make it cost effective and highly suitable for the development of bio-chemical sensors.
Anisotropic Motion of Aqueous Drops on Lubricated Chemically Heterogenous Slippery Surfaces
(Wiley, 2020-12) Bhatt, Geeta
Conventional slippery surfaces show isotropic drop mobility in all directions, whereas anisotropic drop motion may often be required to guide drops in a particular direction. In most cases, topographically structured substrates are employed to provide anisotropic drop motion, but this technique is neither efficient nor cost-effective. Current findings elucidate a novel approach to control the drop motion by virtue of designing lubricated chemically heterogenous (LCHet) surfaces. Upon depositing aqueous drops on such surfaces, the underneath lubricating film dewets only from the hydrophilic regions but remains intact on the hydrophobic ones. This results in the formation of lubricated microchannels, which subsequently provides sticky and slippery regions for the drops. Fabricated surfaces show remarkable anisotropic drop sliding behavior, from uniform motion along parallel to stripes to stick–slip motion along perpendicular to them. Drop motion on such LCHet surfaces can be easily controlled and tuned in the desired direction by tuning the area fraction of hydrophobic region. Furthermore, a phase diagram is presented to summarize different dynamic situations exhibited by drops; sticking or moving in one or both directions. This approach can be easily adapted to different systems to produce multiranging applications from liquid micropatterning to anisotropic drop mobility.
Anisotropic Stick-Slip Behavior of Aqueous Drops on Lubricated Chemically Heterogeneous Slippery Surfaces
(ARXIV, 2020-08) Bhatt, Geeta
Conventional slippery surfaces show isotropic drop mobility in all directions, but many applications require directional drop motion along a particular path only. In previous studies, researchers used topographic substrates, together with different external stimuli, to demonstrate anisotropic drop motion, which is not very efficient and cost-effective. Herein, we report a novel approach to smartly control drop motion on lubricating fluid-coated chemically heterogeneous surfaces composed of alternating hydrophobic and hydrophilic stripes. Upon depositing an aqueous drop on such a surface, the underneath lubricating fluid dewets from the hydrophilic regions but remains intact on the hydrophobic ones, providing sticky and slippery areas for the drop. This results in remarkable anisotropic drop sliding behavior, from uniform motion along parallel to stripes to stick-slip motion along the perpendicular to them. Furthermore, we also demonstrate a phase diagram summarizing different dynamic situations exhibited by drops, sticking, or moving in one or both directions.
Application of Polymers in Biomems Biomedical Devices and Related Challenges
(AIP, 2021) Bhatt, Geeta
Application of Various Detection Platforms for Sensitive Detection of Biological Entities
(AIP, 2021) Bhatt, Geeta
Basic principles of impedance spectroscopy
(CRC Press, 2023) Bhatt, Geeta
Impedance spectroscopy of biomolecules is a growing domain that deals with the study and analysis of various analyte molecules to express high-utility applications. The analytes can be directly extracted from the environment or are derived from nature through some biological/biochemical processes. The common biological analytes are drugs, DNA/RNA, cells, pathogenic bacteria, enzymes, ions, and gases. Impedance analysis measures the impedance characteristics of an analyte over a long-range frequency sweep and interprets its behavior for various frequency domains. This detection method can be utilized for analysis in an independent or integrated format with various discrete analysis/supporting techniques. Along with extensive application in the biomedical field, this technique is also used in several other applications like the analysis of electroactive polymer thin films, colloids, lubricants, paints, and batteries/fuel cells. This chapter explains the utility of impedance analysis through a detailed explanation of fundamental principles, its several components, equivalent circuit diagrams, and their common applications.
Biosensors on chip: A critical review from an aspect of micro/nanoscales
(Sage, 2019-06) Bhatt, Geeta
Biosensors are a very well cherished research topic and have found an inseparable status from clinical diagnostics in specific and society at large. As the name suggests, biosensors or biological sensors are devices which detect the presence of biological entities or their constituents and derivatives. The field started decades ago and has matured quite well since its inception. The most important performance factors that are associated with biosensors are sensitivity, specificity, and limit of detection. The remaining efforts of the biosensor research domain focus on miniaturization aspects of the sensors. The growing advancements in this field have evolved the technology of biosensors to cater to full-scale diagnosis on microchips, bedside diagnostics, reduced cost, and increased speed of diagnostics. Biosensors are characterized through many different aspects; for example, one way is to classify them on the basis of the type of bio-recognition step that they would utilize or another way can be based on the type of detection scheme that they may integrate, etc. Depending on the bio-recognition layer’s properties, biosensors can be cell based, nucleic acid probe based, antibody/antigen based, or aptamer based, while depending on the type of detection scheme, biosensors can be viewed as colorimetric sensors, optical sensors, electrochemical sensors, mechanical sensors, etc. There are some other parallel areas of research like microfluidics and microelectromechanical systems where one of the main applications lies in the biosensor domain. This review article discusses the various aspects of biosensors, from their design, realization, to testing, along with various detection strategies. The assembly includes fabrication strategies particularly for microchip technology-based biosensing solutions, microchannels, integration to microfluidics, etc., while categorization deals with various kinds and applications of different biosensors.
Corrosion Monitoring and Control in Aircraft: A Review
(Springer, 2018-11) Bhatt, Geeta
There has been increasing trend for health monitoring of an aircraft to deal its life issues and to minimize the operational cost. The corrosion is one of the important factors which limits the life of an aircraft due to material loss and fatigue cracking. The development of corrosion monitoring systems and models can provide the solution for health monitoring and prediction for remaining life of an aircraft. This chapter provides a comprehensive review on different types of corrosion, corrosion monitoring, and corrosion control. The latest studies on aircraft corrosion have been discussed in chapter. The different techniques based on nondestructive testing methods such as ultrasonic, electromagnetic, radiographic, thermographic have been detailed out in the chapter. Further for corrosion control, different schemes of corrosion control and coating removal techniques have been discussed in detail.
Dielectrophoresis assisted impedance spectroscopy for detection of gold-conjugated amplified DNA samples
(Elsevier, 2019-06) Bhatt, Geeta; Bhatt, Geeta
Molecular diagnostics have always been at the forefront of disease identification and control. Various approaches exist for carrying out molecular diagnostics through identification of genes or proteins and are largely deployed in the laboratories for testing; although there exist a wide possibility of refinement in these existing processes. In this respect, impedance-based detection methods have emerged as one of the most deployable methods primarily due to their robust and easy nature of measurement and easy integrability with microelectronic systems. Impedance assisted technique is very commonly used for detection of DNA and DNA amplification through PCR process although it does not really make a very specific identification system parallel to some other optical techniques; like TaqMan PCR, qPCR or Molecular beacon assisted detection of DNA sequences. In the current article, we have developed a novel strategy through nanoparticle labeling and dielectrophoretic manipulation which enhances the specificity of the identification of tagged-amplified DNA samples coming out of a PCR process. Impedance characteristics with respect to a various number of PCR cycles with a product consisting of nanoparticle-labeled DNA samples are measured with respect to increasing concentration. A significant differentiation is observed between the non-labeled non-specifically amplified DNA and the labeled specifically amplified sequence through varied impedance signals. The impedance characterization is performed at the instance where the analyte is mostly near the electrodes and this is accomplished through dielectrophoresis scheme. The different dielectrophoretic capture frequencies have been observed for non-labeled and labeled DNA products. This sensor has achieved a limit of detection of the range of 25–30 DNA copies. The eventual goal here is to integrate this strategy with microchip PCR to evolve a paradigm shift in the PCR microchip technology.
DNA-Based Sensors
(Springer, 2017-12) Bhatt, Geeta
Sensing and detection for clinical diagnostic can be accomplished through various routes. Additionally what and how of sensing is critically optimized to meet individual needs. Diagnostics is carried out with various types of sensors out of which the electrochemical sensors are most used due to their unique ability to couple seamlessly with electronic circuitry. The DNA sensor is one of the most common types of sensors which is majorly deployed to perform expression monitoring, transcription profiling, etc., for example, the products developed by Affymetrix and Nanogen. This chapter is a consolidated review of the various aspects of DNA sensors, like the principle of detection, various ways of sensing and detection, applications of such DNA-based sensing. It looks at the various principles that are utilized for gene mapping like dielectrophoresis, polymerase chain reaction (PCR), real-time PCR or quantitative PCR (better known as q-PCR), hybridization, solid-phase PCR, droplet-based PCR, etc. It also reviews various sensing/detection strategies for sensing DNA like electrophoresis, impedance spectroscopy, colorimetric sensing, optical sensing and inertial sensing. The chapter provides a state-of-the-art review of basic techniques, sensing methodologies and applications for DNA-based diagnostics as carried out by industry.
Enhanced Fluorescence-Based Detection of Vibrio Cells Over Nanoporous Silica Substrate
(Springer, 2019-04) Bhatt, Geeta
The food and waterborne pathogens threaten the human health through porous borders that require immediate detection in real time. The present work reports the development of a nanoporous silica-based platform for the rapid detection of Vibrio cells. The nanoporous thin film has been developed over silicon substrate utilizing PMSSQ (polymethylsilsesquioxane, (CH3SiO1.5)n) and PPG (polypropylene glycol, CH((CH3)CH2O)n) combination in PGMEA (propylene glycol methyl ether acetate) solvent as provided earlier by Gangopadhyay et al. (Nanotechnology 20, 2009 [1]). The PPG acts as a porogen and evaporates on heat treatment giving a porous structure and assembles the PMSSQ nanoparticles. The films were characterized through FTIR, EDAX, and SEM microscopy, and it was found out that the functional groups like OH, CH3, Si–CH3, Si–O, and Si–O–Si were present abundantly in the porous structure, which can be further modified for its application in biology. An aliquot of 2.5 µl Vibrio cell solution was immobilized (over nanoporous silica film) to study its fluorescence intensity under an epifluorescence microscope. Vibrio (Vibrio harveyi (ATCC® 700106™)) cells possess self-fluorescing effects with bleaching characteristics. The fluorescence images (with the progression of time) are acquired and processed through Image J (courtesy NIH), and relative fluorescence of the cells are calculated as a function of time. A 1.7 times increase in the overall fluorescence intensity level is recorded in the presence of the porous silica layer as compared to uncoated silicon substrate showing immobilization capabilities of these films.
Enhanced He gas detection by V2O5-noble metal (Au, Ag, and Pd) nanocomposite with temperature dependent n- to p-type transition
(Springer, 2021-03) Bhatt, Geeta
In this study, nanocomposite of V2O5 nanowires with noble metal (Au, Ag, and Pd) nanoparticles were fabricated by solution mixing and hydrothermal synthesis. These nanomaterials were analysed for their sensing properties towards Helium gas. Experiments carried out at room temperature conditions showed that V-Ag composite yielded the highest percentage response (73% at 150 ppm) and fast response/recovery times (8s/13 s at 100 ppm). The highest electrical conductivity of Ag nanoparticle was attributed as the principle reason behind the ultra-high response of V-Ag composite. The temperature dependent n- to p-type transition of the semiconducting material was also observed at higher sensing temperatures which was validated through Hall Effect measurements. The majority charge carrier transition from n- to p-type was observed near 47 °C. The highest response of V-Ag nanocomposite was recorded (108% at 5 ppm) at 100 °C when the material behaved like a p-type semiconductor.
Evolution of 3d printing technology in fabrication of microfluidic devices and biological applications: a comprehensive review
(Sage, 2024-04) Bhatt, Geeta
Lab-on-a-chip or LOC is a term that is used to describe microfluidic devices that integrate multiple analyte detection, which are normally carried out in a laboratory, into one micro-chip unit and may have applications in diverse fields such as electronics, medicine and biomedical domains. Even though microfluidics has advanced greatly during the past decade due to increased needs for portability, reduced sample requirement and multiple analyte detection capabilities biological research has not adopted the technology at the required pace. This may be owing to the time-consuming and expensive process involved in the microfabrication of biochips, the requirement of specialised setup facilities and the extremely high cost associated with microfluidics as compared to conventional technologies. In recent years, three-dimensional (3D) printing has piqued curiosity in the scientific community. It has the potential to create complex, high-resolution structures and that too in a short timeframe depending upon device complexity. This could inspire progressive research in microfluidics, particularly finding applications in biomedical engineering and point-of-care diagnostics. This article gives an overview of how 3D printing aids in the manufacture of microfluidic devices for biological applications, as well as the existing 3D printing methods which are utilised for fabrication and the future perspective in the development of microfluidic devices.
Experimental Investigation of Magnetic Field Assisted Powder Mixed Electric Discharge Machining
(Taylor & Francis, 2015-06) Bhatt, Geeta
Electric discharge machining (EDM) is the most promising modern machining process amongst all the modern machining processes. This paper presents the application of metal powders that are mixed in dielectric medium during EDM to improve process performance like material removal, tool wear, surface finish, overcut, and microhardness. An external magnetic field is provided to further assist the machining process which affects differently for different output characteristics. Taguchi's design of experimentation and analysis of variance is used for analysis of results. Current, pulse on time, workpiece, and powders show significant effect on different responses Results showed that the material removal rate increases with the field strength at low values of current, while increase in overcut is observed with increase in field strength. Tool wear rate is observed to increase with the field strength at lower current values while microhardness is observed to enhance with increase in magnetic field strength. Surface finish is observed to improve at lower current with increase in field strength. Different optimal parameters are characterized for machining purpose in terms of current, powder, powder concentration, and tool for machining different workpiece materials. Results are further supported by selected microstructure and x-ray diffraction results.
Extraction, Fabrication, and Mechanical Aspects in Composites of Bamboo Fiber
(AIP, 2022) Bhatt, Geeta
High Efficiency Coupling of Optical Fibres with SU8 Micro-droplet Using Laser Welding Process
(Springer, 2016-04) Bhatt, Geeta
Apart from micro- structure fabrication, ablation, lithography etc., lasers find a lot of utility in various areas like precision joining, device fabrication, local heat delivery for surface texturing and local change of microstructure fabrication of standalone optical micro-devices (like microspheres, micro-prisms, micro-scale ring resonators, optical switches etc). There is a wide utility of such systems in chemical/ biochemical diagnostics and also communications where the standalone optical devices exist at a commercial scale but chip based devices with printed optics are necessary due to coupling issues between printed structures and external optics. This paper demonstrates a novel fabrication strategy used to join standalone optical fibres to microchip based printed optics using a simple SU8 drop. The fabrication process is deployed for fiber to fiber optical coupling and coupling between fiber and printed SU-8 waveguides. A CO2 laser is used to locally heat the coupling made up of SU8 material. Optimization of various dimensional parameters using design of experiments (DOE) on the bonded assembly has been performed as a function of laser power, speed, cycle control, spot size so on so forth. Exclusive optical [RF] modelling has been performed to estimate the transmissibility of the optical fibers bonded to each other on a surface with SU8. Our studies indicate the formation of a Whispering gallery mode (WGM) across the micro-droplet leading to high transmissibility of the signal. Through this work we have thus been able to develop a method of fabrication for optical coupling of standalone fibers or coupling of on-chip optics with off-chip illumination/detection.
A historical perspective on impedance spectroscopy and its application in biological detection
(CRC Press, 2023) Bhatt, Geeta
Electrical/electrochemical impedance spectroscopy (EIS) is a generalized term for the technique in which the impedance response of a system/analyte is generally measured over a particular range of frequencies to analyze its behavior. Sometimes, the measurement can also be taken over the time domain, and then Fourier-transformed to the frequency domain. The impedance measurements recorded in a particular medium interpret the behavior of the analyte, which is further adapted as per the user’s needs. The EIS measurements can be utilized for any kind of analyte, viz. biological/nonbiological and solid/liquid/gas, provided they show a noticeable impedance change. Hence, EIS has a large domain of applicability and with a view to enhance its capability, extensive research in this field is being done with various analytes. To offer the knowledge of this field’s most recent literature to researchers and experimentalists, this book primarily compiles the various studies available in the impedance spectroscopy domain. The chapters of this book have been organized to initially detail the fundamentals of the EIS process, its device fabrication aspects, various substrate/material requirements, the utility of microfluidic integration, its applications (mostly biological), various technological integrations, and, finally, the challenges in EIS implementation.
Impact of surface roughness on Dielectrophoretically assisted concentration of microorganisms over PCB based platforms
(Springer, 2017-04) Bhatt, Geeta
This article presents a PCB based microfluidic platform for performing a dielectrophoretic capture of live microorganisms over inter-digitated electrodes buried under layers of different surface roughness values. Although dielectrophoresis has been extensively studied earlier over silicon and polymer surfaces with printed electrodes the issue of surface roughness particularly in case of buried electrodes has been seldom investigated. We have addressed this issue through a layer of spin coated PDMS (of various surface roughness) that is used to cover the printed electrodes over a printed circuit board. The roughness in the PDMS layer is generally defined by the roughness of the FR4 base which houses the printed electrodes as well as other structures. Possibilities arising out of COMSOL simulations have been well validated experimentally in this work.