141 research outputs found

    Nanogap capacitive biosensor for label-free aptamer-based protein detection

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    Recent advances in nanotechnology offer a new platform for the label free detection of biomolecules at ultra-low concentrations. Nano biosensors are emerging as a powerful method of improving device performance whilst minimizing device size, cost and fabrication times. Nanogap capacitive biosensors are an excellent approach for detecting biomolecular interactions due to the ease of measurement, low cost equipment needed and compatibility with multiplex formats.This thesis describes research into the fabrication of a nanogap capacitive biosensor and its detection results in label-free aptamer-based protein detection for proof of concept. Over the last four decades many research groups have worked on fabrication and applications of these type of biosensors, with different approaches, but there is much scope for the improvement of sensitivity and reliability. Additionally, the potential of these sensors for use in commercial markets and in everyday life has yet to be realized.Initial work in the field was limited to high frequency (>100 kHz) measurements only, since at low frequency there is significant electronic thermal noise (=4kBTR) from the electrical double layer (EDL). This was a significant drawback since this noise masked most of the important information from biomolecular interactions of interest. A novel approach to remove this parasitic noise is to minimize the EDL impedance by reducing the capacitor electrode separation to less than the EDL thickness. In the case of aptamer functionalized electrodes, this is particularly advantageous since device sensitivity is increased as the dielectric volume is better matched to the size of the biomolecules and their binding to the electrode surface. This work has demonstrated experimentally the concepts postulated theoretically.In this work we have fabricated a large area (100 x 5 μm x 5 μm) vertically oriented capacitive nanogap biosensor with a 40 nm electrode separation between two gold electrodes. A silicon dioxide support layer separates the two electrodes and this is partially etched (approximately 800 nm from both sides of each 5 μm x 5 μm capacitor), leaving an area of the gold electrodes available for thiol-aptamer functionalization.AC impedance spectroscopy measurements were performed with the biosensor in the presence of air, D.I. water, various ionic strength buffer solutions and aptamer/protein pairs inside the nanogap. Applied frequencies were from 1Hz to 500 kHz at 20 mV AC voltage with 0 DC. We obtained relative permittivity results as a function of frequency for air (ɛ=1) and DI water (ɛ~80) which compares very favorably with previous works done by different research groups.The sensitivity and response of the sensors to buffer solution (SSC buffer) with various ionic strengths (0.1x SSC, 0.2x SSC, 0.5x SSC and 1x SSC) was studied in detail. It was found that in the low frequency region (<1 kHz) the relative permittivity (capacitance) was broadly constant, that means it is independent from the applied frequency in this range. With increasing buffer concentration, the relative permittivity starts to increase (from ɛ=170 for 0.1x SSC to ɛ=260 for 1x SSC).The sensor performance was further investigated for aptamer-based protein detection, human alpha thrombin aptamers and human alpha thrombin protein pairs were selected for proof of concept. Aptamers were functionalized into the gold electrode surface with the Self-Assembly-Monolayer (SAM) method and measurements were performed in the presence of 0.5x SSC buffer solution (ɛ=180). Then the hybridization step was carried out with 1 μM of human alpha thrombin protein followed by measurements in the presence of the same buffer (ɛ=130). The response of the sensors with different solutions inside the nanogap was studied at room temperature (5 working devices were tested for each step). The replacement of the buffer solution (ɛ=250) with lower relative permittivity biomolecules (aptamer ɛ=180) and further binding proteins to immobilized aptamer (ɛ=130) was studied. To validate these results, a control experiment was carried out using different aptamers, in this case which are not able to bind to human alpha thrombin protein. It was found that the relative permittivity did not change after the hybridization step compared to the aptamer functionalization step, which indicates that the sensors performance is highly sensitive and reliable.This work serves as a proof of concept for a novel nanogap based biosensor with the potential to be used for many applications in environmental, food industry and medical industry. The fabrication method has been shown to be reliable and consistent with the possibility of being easily commercialized for mass production for use in laboratories for the analysis of a wide range of samples

    Nanoscale Electrodes for Bionanosensing

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    Cancer is globally the second most common cause of death. Cancer burden rises to about 10 million deaths and more than 18 million new cases in 2018. Cancers are often diagnosed at a later stage preventing curative treatment. This underscores the need for an early stage diagnosis of cancer. Consequently, screening methods that can test patients’ samples taken by less invasive methods capable of early stage diagnosis are highly sought for. Based on this motivation, here we developed lab-on-a-chip diagnostic systems that can be used for early detection of cancer. Three different types of nanoscale electrodes were fabricated: (i) nanogap electrodes (ii) nano interdigitated electrodes and (iii) nanodisc electrodes and the possibility of using them for sensing and signal transduction were investigated. Chapter 2 describes the fabrication of nanogap device using conventional optical lithography and DNA detection across it using the electrical method. Chapter 3 details the fabrication of nano interdigitated electrodes (nIDEs) and their electrochemical validation. Chapter 4 describes the biosensing application of nIDEs using nanoparticle sandwich assay for the detection of DNA molecules. Chapter 5 describes the capturing of tdEVs on nIDEs, and its quantification using a sandwich immunosorbent assay on nIDEs. Chapter 6 proposes a new type of nanoscale electrodes which are termed as nanodisc electrodes. Chapter 7 explores the possibility of developing the nanodisc technology to a business idea. In short, the whole thesis tries to explore the different possibilities in developing a sensor that can be useful for cancer diagnosis

    Nanoscale Electrochemical Sensing and Processing in Microreactors

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    In this review, we summarize recent advances in nanoscale electrochemistry, including the use of nanoparticles, carbon nanomaterials, and nanowires. Exciting developments are reported for nanoscale redox cycling devices, which can chemically amplify signal readout. We also discuss promising high-frequency techniques such as nanocapacitive CMOS sensor arrays or heterodyning. In addition, we review electrochemical microreactors for use in (drug) synthesis, biocatalysis, water treatment, or to electrochemically degrade urea for use in a portable artificial kidney. Electrochemical microreactors are also used in combination with mass spectrometry, e.g., to study the mimicry of drug metabolism or to allow electrochemical protein digestion. The review concludes with an outlook on future perspectives in both nanoscale electrochemical sensing and electrochemical microreactors. For sensors, we see a future in wearables and the Internet of Things. In microreactors, a future goal is to monitor the electrochemical conversions more precisely or ultimately in situ by combining other spectroscopic techniques

    Biosensors for Biomolecular Computing: a Review and Future Perspectives

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    Biomolecular computing is the field of engineering where computation, storage, communication, and coding are obtained by exploiting interactions between biomolecules, especially DNA, RNA, and enzymes. They are a promising solution in a long-term vision, bringing huge parallelism and negligible power consumption. Despite significant efforts in taking advantage of the massive computational power of biomolecules, many issues are still open along the way for considering biomolecular circuits as an alternative or a complement to competing with complementary metal–oxide–semiconductor (CMOS) architectures. According to the Von Neumann architecture, computing systems are composed of a central processing unit, a storage unit, and input and output (I/O). I/O operations are crucial to drive and read the computing core and to interface it to other devices. In emerging technologies, the complexity overhead and the bottleneck of I/O systems are usually limiting factors. While computing units and memories based on biomolecular systems have been successfully presented in literature, the published I/O operations are still based on laboratory equipment without a real development of integrated I/O. Biosensors are suitable devices for transducing biomolecular interactions by converting them into electrical signals. In this work, we explore the latest advancements in biomolecular computing, as well as in biosensors, with focus on technology suitable to provide the required and still missing I/O devices. Therefore, our goal is to picture out the present and future perspectives about DNA, RNA, and enzymatic-based computing according to the progression in its I/O technologies, and to understand how the field of biosensors contributes to the research beyond CMOS

    Novel nanoarchitectures for electrochemical biosensing

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    Thesis advisor: Thomas C. ChilesSensitive, real-time detection of biomarkers is of critical importance for rapid and accurate diagnosis of disease for point-of-care (POC) technologies. Current methods, while sensitive, do not adequately allow for POC applications due to several limitations, including complex instrumentation, high reagent consumption, and cost. We have investigated two novel nanoarchitectures, the nanocoax and the nanodendrite, as electrochemical biosensors towards the POC detection of infectious disease biomarkers to overcome these limitations. The nanocoax architecture is composed of vertically-oriented, nanoscale coaxial electrodes, with coax cores and shields serving as integrated working and counter electrodes, respectively. The dendritic structure consists of metallic nanocrystals extending from the working electrode, increasing sensor surface area. Nanocoaxial- and nanodendritic-based electrochemical sensors were fabricated and developed for the detection of bacterial toxins using an electrochemical enzyme-linked immunosorbent assay (ELISA) and differential pulse voltammetry (DPV). Proof-of-concept was demonstrated for the detection of cholera toxin (CT). Both nanoarchitectures exhibited levels of sensitivity that are comparable to the standard optical ELISA used widely in clinical applications. In addition to matching the detection profile of the standard ELISA, these electrochemical nanosensors provide a simple electrochemical readout and a miniaturized platform with multiplexing capabilities toward POC implementation. Further development as suggested in this thesis may lead to increases in sensitivity, enhancing the attractiveness of the architectures for future POC devices.Thesis (PhD) — Boston College, 2016.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Biology

    Towards novel lab-on-a-chip electrochemical detection of infectious disease biomarkers

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    Thesis advisor: Thomas C. ChilesRapid diagnosis of infectious disease at the site of the patient is critical for preventing the escalation of an outbreak into an epidemic. This is particularly true for cholera, a disease known to spread swiftly within resource-limited populations. A device suited to point-of- care (POC) diagnosis of cholera must not only demonstrate laboratory levels of sensitivity and specificity, but it must do so in a highly portable, low-cost manner, with a simplistic readout. Here, we report novel proof-of-concept lab-on-a-chip (LOC) electrochemical immunosensors for the detection of cholera toxin subunit B (CTX), based on two nanostructured architectures: the gold dendritic array, and the extended core coax (ECC). The dendritic array has an ~18x greater surface area than a planar gold counterpart, per electrochemical measurements, allowing for a higher level of diagnostic sensitivity. An electrochemical enzyme-linked immunosorbant assay (ELISA) for CTX performed via differential pulse voltammetry (DPV) on the dendritic sensor demonstrated a limit-of detection of 1 ng/mL, per a signal-to-noise ratio of 2.6, which was more sensitive than a simple planar gold electrode (100 ng/mL). This sensitivity also matches a currently available diagnostic standard, the optical ELISA, but on a miniaturized platform with simple electrical readout. The ECC was optimized and explored, undergoing several changes in design to facilitate sensitive LOC electrochemical detection. The ECC matched the off-chip sensitivity towards CTX demonstrated by a previous non-extended core coaxial iteration, which was comparable to a standard optical ELISA. In contrast to the previous coaxial architecture, the ECC is amenable to functionalization of the gold core, allowing for LOC detection. ECCs were functionalized using a thiolated protein G, and CTX was detected via an electrochemical ELISA. While this work is ongoing, the ECC shows promise as a platform for LOC electrochemical ELISA. The ability to potentially meet POC demands makes biofunctionalized gold dendrites and ECCs promising architectures for further development as LOC sensors for the detection of infectious disease biomarkers.Thesis (PhD) — Boston College, 2018.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Biology

    Surface-enhanced Raman Spectroscopy for Single Molecule Analysis and Biological Application

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    Surface-enhanced Raman spectroscopy (SERS) is a surface analytical technique, which enhances the Raman signal based on the localized surface plasmon resonance (LSPR) phenomenon. It has been successfully used for single molecule (SM) detection and has extended SERS to numerous applications in biomolecular detection. However, SM detection by SERS is still challenging especially with traditional SERS substrates and detection methods. In addition, the fundamental understanding of the SERS enhancement mechanism is still elusive. Furthermore, the application of SERS in biological field is still in the early stage. To address these challenges, there are two main aspects of SERS studied in my dissertation: (a) fundamental aspects through systematic experimental studies combined with simulations, which focus on SM detection, Raman enhancement mechanisms, and (b) the development and optimization of the SERS-based nanoprobe for biomarkers detection from fluidic devices to a single cell. In my dissertation, the following studies have been investigated. First, the sensitivity of a home-made SERS instrument was tested. SM detection was realized by utilizing a highly curved nanoelectrode (NE) to limit the number of attached nanoparticle (NP), which will allow us to have even a single NP on NE (NPoNE) junction in the SERS detection area. The molecule number in a single NPoNE junction which contributes to SERS can be hundreds or even SM. In this first study, we also conducted a correlation study between electrochemical current and SERS to monitor the dynamic formation of the plasmonic junctions. Second, we investigate electromagnetic and chemical enhancement factor tuning by the electrode potential with the assistant of Au@Ag core-shell NPs. The electrode potential induced electromagnetic enhancement (EME) tuning in the Au@Ag NPoNE structure has been confirmed by 3D Finite-difference time-domain (FDTD) simulations. Last is the design of a SERS-based nanoprobe for biomarkers detection and the effort towards single cell analysis. Finally, several SERS-active substrates were examined for biomarkers (H+, glucose, and H2O2) detection, including gold NPs (AuNPs) colloid and AuNPs decorated glass nanopipette. In summary, my dissertation presents the fabrication and development of gold tip nanoelectrode for chemical detection, which can achieve SM sensitivity. SM SERS can be used to improve the fundamental understanding and provide more in-depth insight into mechanisms of SERS and the chemical behaviors of SM on surfaces and in plasmonic cavities. Second, the fabrication and optimization of SERS-active, flexible nanopipette for biological applications. The flexible nanopipette probe provides a platform for reliable detection and quantitative analysis of biomarkers at a single cell level, which is critical and vital for detecting diseases earlier and understanding the fundamental biological process better

    DESIGN OF GRAPHENE-BASED SENSORS FOR NUCLEIC ACIDS DETECTION AND ANALYSIS

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    DNA (Deoxyribonucleic Acid) is the blueprint of life as it encodes all genetic information. In genetic disorder such as gene fusion, Copy Number Variation (CNV), and single nucleotide polymorphism, Nucleic acids such as DNA bases detection and analysis is used as the gold standard for successful diagnosis. Researchers have been conducting rigorous studies to achieve genome sequences at low cost while maintaining high accuracy and high throughput. A quick, accurate, and low-cost DNA detection approach would revolutionize medicine. Genome sequence helps to enhance people’s perception of inheritance, disease, and individuality. This research aims to improve DNA bases detection accuracy, and efficiency, and reduce the production cost, thus novel based sensors were developed to detect and identify the DNA bases. This work aims at first to develop specialized field effect transistors which will acquire real-time detection for different concentrations of DNA. The sensor was developed with a channel of graphite oxide between gold electrodes on a substrate of a silicon wafer using Quantumwise Atomistix Toolkit (ATK) and its graphical user interfaces Virtual Nanolab (VNL). The channel was decorated with trimetallic nanoclusters that include gold, silver, and platinum which have high affinity to DNA. The developed sensor was investigated by both simulation and experiment. The second aim of this research was to analyze the tissue transcriptome through DNA bases detection, thus novel graphene-based sensors with a nanopore were designed and developed to detect the different DNA nucleobases (Adenine (A), Cytosine (C), Guanine (G), Thymine (T)). This research focuses on the simulation of charge transport properties for the developed sensors. This work includes experimental fabrication and software simulation studies of the electronic properties and structural characteristics of the developed sensors. Novel sensors were modeled using Quantumwise Atomistix Toolkit (ATK) and its graphical user Interface Virtual Nanolab (VNL) where several electronic properties were studied including transmission spectrum and electrical current of DNA bases inside the sensor’s nanopore. The simulation study resulted in a unique current for each of the DNA bases within the nanopore. This work suggests that the developed sensors could achieve DNA sequencing with high accuracy. The practical implementation of this work represents the ability to predict and cure diseases from the genetic makeup perspective

    Micro- and nanogap based biosensors

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