Browsing by Author "Wu, Kai (TTU)"
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Item Advancements and Perspectives in Optical Biosensors(2024) Mostufa, Shahriar (TTU); Rezaei, Bahareh (TTU); Ciannella, Stefano (TTU); Yari, Parsa (TTU); Gómez-Pastora, Jenifer (TTU); He, Rui (TTU); Wu, Kai (TTU)Optical biosensors exhibit immense potential, offering extraordinary possibilities for biosensing due to their high sensitivity, reusability, and ultrafast sensing capabilities. This review provides a concise overview of optical biosensors, encompassing various platforms, operational mechanisms, and underlying physics, and it summarizes recent advancements in the field. Special attention is given to plasmonic biosensors and metasurface-based biosensors, emphasizing their significant performance in bioassays and, thus, their increasing attraction in biosensing research, positioning them as excellent candidates for lab-on-chip and point-of-care devices. For plasmonic biosensors, we emphasize surface plasmon resonance (SPR) and its subcategories, along with localized surface plasmon resonance (LSPR) devices and surface enhance Raman spectroscopy (SERS), highlighting their ability to perform diverse bioassays. Additionally, we discuss recently emerged metasurface-based biosensors. Toward the conclusion of this review, we address current challenges, opportunities, and prospects in optical biosensing. Considering the advancements and advantages presented by optical biosensors, it is foreseeable that they will become a robust and widespread platform for early disease diagnostics.Item Flexible Magnetic Field Nanosensors for Wearable Electronics: A Review(2023) Mostufa, Shahriar (TTU); Yari, Parsa (TTU); Rezaei, Bahareh (TTU); Xu, Kanglin (TTU); Wu, Kai (TTU)Flexible magnetic field nanosensors hold immense potential for wearable electronics, offering a range of advantages such as comfort, real-time health monitoring, motion sensing, durability, and seamless integration with other sensors. They are expected to revolutionize wearable technologies and drive innovation in various domains, enhancing the overall user experience. In this review, we provide an overview of recent advances in flexible magnetic field nanosensors, including flexible Hall sensors, flexible magnetoresistive (MR) sensors such as giant magnetoresistance (GMR), magnetic tunnel junction (MTJ), and anisotropic magnetoresistance (AMR) sensors, flexible fluxgate sensors, and flexible giant magnetoimpedance (GMI) sensors. We discuss different fabrication methods and real-life applications for each type of sensor as well as the technical challenges faced by these sensors. The use of these flexible nanosensors opens more possibilities for human–computer interaction and presents exciting opportunities for wearable technology in diverse fields. The robustness of these sensors along with the trend to reduce energy consumption will continue to be important research areas. Future trends in flexible magnetic field nanosensors include energy harvesting from the body, miniaturization and lower power consumption, improved durability and reliability, and reduced cost. These advancements have the potential to drive the widespread adoption of flexible magnetic field nanosensors in wearable devices, enabling innovative applications and enhancing the overall user experience.Item Giant Magnetoresistance Based Biosensors for Cancer Screening and Detection(2023) Mostufa, Shahriar (TTU); Rezaei, Bahareh (TTU); Yari, Parsa (TTU); Xu, Kanglin (TTU); Gómez-Pastora, Jenifer (TTU); Sun, Jiajia; Shi, Zongqian; Wu, Kai (TTU)Early-stage screening of cancer is critical in preventing its development and therefore can improve the prognosis of the disease. One accurate and effective method of cancer screening is using high sensitivity biosensors to detect optically, chemically, or magnetically labeled cancer biomarkers. Among a wide range of biosensors, giant magnetoresistance (GMR) based devices offer high sensitivity, low background noise, robustness, and low cost. With state-of-the-art micro- and nanofabrication techniques, tens to hundreds of independently working GMR biosensors can be integrated into fingernail-sized chips for the simultaneous detection of multiple cancer biomarkers (i.e., multiplexed assay). Meanwhile, the miniaturization of GMR chips makes them able to be integrated into point-of-care (POC) devices. In this review, we first introduce three types of GMR biosensors in terms of their structures and physics, followed by a discussion on fabrication techniques for those sensors. In order to achieve target cancer biomarker detection, the GMR biosensor surface needs to be subjected to biological decoration. Thus, commonly used methods for surface functionalization are also reviewed. The robustness of GMR-based biosensors in cancer detection has been demonstrated by multiple research groups worldwide and we review some representative examples. At the end of this review, the challenges and future development prospects of GMR biosensor platforms are commented on. With all their benefits and opportunities, it can be foreseen that GMR biosensor platforms will transition from a promising candidate to a robust product for cancer screening in the near future.Item Giant Magnetoresistance Biosensors for Food Safety Applications(2022) Liang, Shuang; Sutham, Phanatchakorn; Wu, Kai (TTU); Mallikarjunan, Kumar; Wang, Jian-PingNowadays, the increasing number of foodborne disease outbreaks around the globe has aroused the wide attention of the food industry and regulators. During food production, processing, storage, and transportation, microorganisms may grow and secrete toxins as well as other harmful substances. These kinds of food contamination from microbiological and chemical sources can seriously endanger human health. The traditional detection methods such as cell culture and colony counting cannot meet the requirements of rapid detection due to some intrinsic shortcomings, such as being time-consuming, laborious, and requiring expensive instrumentation or a central laboratory. In the past decade, efforts have been made to develop rapid, sensitive, and easy-to-use detection platforms for on-site food safety regulation. Herein, we review one type of promising biosensing platform that may revolutionize the current food surveillance approaches, the giant magnetoresistance (GMR) biosensors. Benefiting from the advances of nanotechnology, hundreds to thousands of GMR biosensors can be integrated into a fingernail-sized area, allowing the higher throughput screening of food samples at a lower cost. In addition, combined with on-chip microfluidic channels and filtration function, this type of GMR biosensing system can be fully automatic, and less operator training is required. Furthermore, the compact-sized GMR biosensor platforms could be further extended to related food contamination and the field screening of other pathogen targets.Item Magnetic field detection using spin-torque nano-oscillator combined with magnetic flux concentrator(2023) Tonini, Denis; Wu, Kai (TTU); Saha, Renata; Wang, Jian PingSpin-torque nano-oscillators (STNO) are studied in terms of the Landau-Lifshitz-Gilbert (LLG) equation. The effect on the limit of detectivity of an STNO concerning externally applied magnetic fields is studied with micromagnetic models by placing adjacent magnetic flux concentrators (MFCs) at different distances from the nanopillar to analyze the effect on the induced auto-oscillations and magnetization dynamics. Perpendicular STNO structures allow for different detectivities with respect to externally applied magnetic fields depending on the distance from the MFCs to the nanopillar. The optimal design of an STNO combined with MFCs is proposed to improve the limit of detectivity, where the STNO consists of two out-of-plane (OP) ferromagnetic (FM) layers separated by a MgO insulating nonmagnetic (NM) thin film, and the MFCs positioned in the vicinity of the STNO are made of permalloy. The time evolution of the free-layer magnetization is governed by the Landau-Lifshitz-Gilbert (LLG) equation. The auto-oscillations induced within the free-layer averaged magnetization are provoked by externally applied magnetic fields. In addition, the DC current-driven auto-oscillations in the STNO structure are studied as a function of the externally applied magnetic field strength, with and without MFCs. The suppression of the DC current-driven auto-oscillations is observed due to the damping effect generated by the MFCs positioned at varying distances with respect to the STNO. By placing MFCs adjacent to the STNO, the lowest detectable magnetic field strength is enhanced from 10 (μT) to 10 (nT). Therefore, it is concluded that MFCs improve the sensitivity of STNO to externally applied magnetic fields thanks to the damped magnetization dynamics. The results presented in this work could inspire the optimal design of STNO and MFC-based ultra-low magnetic field sensors based on nanoscale oscillators and spintronic diodes.Item Magnetic Particle Spectroscopy for Point-of-Care: A Review on Recent Advances(2023) Yari, Parsa (TTU); Rezaei, Bahareh (TTU); Dey, Clifton (TTU); Chugh, Vinit Kumar; Veerla, Naga Venkata Ravi Kumar (TTU); Wang, Jian Ping; Wu, Kai (TTU)Since its first report in 2006, magnetic particle spectroscopy (MPS)-based biosensors have flourished over the past decade. Currently, MPS are used for a wide range of applications, such as disease diagnosis, foodborne pathogen detection, etc. In this work, different MPS platforms, such as dual-frequency and mono-frequency driving field designs, were reviewed. MPS combined with multi-functional magnetic nanoparticles (MNPs) have been extensively reported as a versatile platform for the detection of a long list of biomarkers. The surface-functionalized MNPs serve as nanoprobes that specifically bind and label target analytes from liquid samples. Herein, an analysis of the theories and mechanisms that underlie different MPS platforms, which enable the implementation of bioassays based on either volume or surface, was carried out. Furthermore, this review draws attention to some significant MPS platform applications in the biomedical and biological fields. In recent years, different kinds of MPS point-of-care (POC) devices have been reported independently by several groups in the world. Due to the high detection sensitivity, simple assay procedures and low cost per run, the MPS POC devices are expected to become more widespread in the future. In addition, the growth of telemedicine and remote monitoring has created a greater demand for POC devices, as patients are able to receive health assessments and obtain results from the comfort of their own homes. At the end of this review, we comment on the opportunities and challenges for POC devices as well as MPS devices regarding the intensely growing demand for rapid, affordable, high-sensitivity and user-friendly devices.Item Metamaterial as perfect absorber for high sensitivity refractive index based biosensing applications at infrared frequencies(2023) Mostufa, Shahriar (TTU); Yari, Parsa (TTU); Rezaei, Bahareh (TTU); Xu, Kanglin (TTU); Sun, Jiajia; Shi, Zongqian; Wu, Kai (TTU)In this paper, we introduce a novel design of a metamaterial unit cell absorber, which is based on a metal/insulator/metal sandwich structure. The design is subjected to comprehensive finite element method computational analysis to ensure accurate and reliable results. The proposed metamaterial sandwich structure demonstrates exceptional absorption performance, achieving a nearly perfect absorption rate of 99.996% at the resonance infrared frequency of 39.8 THz. To provide a detailed theoretical explanation of nearly perfect absorption, we employ the effective medium theory, impedance matching, and field distribution analysis. Additionally, we have optimized the structural parameters of the sensor to maximize its absorption peak. This includes optimizing the thickness of the gold (Au) layer (from 0.03 to 0.28 μm), the distance between the L shape corners (from 0.60 to 0.90 μm), and the thickness of SiC dielectric spacer (from 0.20 to 0.45 μm). Furthermore, we showcase the remarkable sensitivity of the proposed metamaterial unit cell in detecting subtle changes in the refractive index through the implementation of a sensing medium setup in our model. Remarkably, we achieve a frequency shift sensitivity of 3.74 THz/RIU, along with a quality factor of 10.33, for a wide range of refractive indices (1.0–2.0). Moreover, for cancer detection, we attain a sensitivity of 3.5 THz/RIU. These findings highlight the exceptional performance of our approach in accurately detecting changes in refractive index, making it a promising candidate for various sensing applications. The novelty of our work lies in the design of a metamaterial unit cell structure. This configuration exhibits several noteworthy features, including wide incident angle ($\theta $) coverage up to 60°, polarization insensitivity, exceptional frequency shift sensitivity, high absorption peaks across a wide range of refractive indices, and the ability to distinguish cancer cells from healthy ones.Item Nanomaterial-Based Biosensors for SARS-CoV-2 and Future Epidemics(2023) Yari, Parsa (TTU); Liang, Shuang; Chugh, Vinit Kumar; Razaei, Bahareh (TTU); Mostufa, Shahriar (TTU); Krishna, Venkatramana Divana; Saha, Renata; Cheeran, Maxim C. J. (TTU); Wang, Jian-Ping (TTU); Gómez-Pastora, Jenifer (TTU); Wu, Kai (TTU)The outbreak of the coronavirus disease 2019 (COVID-19) pandemic has put enormous pressure on global healthcare and economic systems. The cause of this pandemic, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a positive-sense single-stranded RNA (+ssRNA) virus belonging to the beta family of coronaviruses. This highly contagious virus mainly spread through droplet transmission and contact transmission. People who are infected can release droplets and aerosol particles that contain the SARS-CoV-2 virus in the air when they exhale, cough, or sneeze. The droplets or aerosol particles of different sizes (from visible to microscopic) will continue to spread in the air or land on subjects. Healthy people may catch the virus via inhalation of aerosol particles from the air, or through the contact with contaminated surfaces before touching their nose, eyes, or mouth. Besides the direct droplet and contact transmissions, other viral transmission routes are also reported, such as spatter (e.g., blood spatter, spatter during intubation, etc.), fecal-eye transmission, nasal-eye transmission, mouth-eye transmission (through contaminated hands or objects) and the transmission of eye secretions and tears. In addition to its strong transmission power, SARS-CoV-2 can cause acute respiratory distress syndrome (ARDS), septic shock, coagulation dysfunction, intestinal dysfunction, and other clinical symptoms post-infection. Many people infected with COVID-19 display light symptoms like the common cold and influenza, and in some cases they are asymptomatic. Nevertheless, these asymptomatic carriers can still transmit SARS-CoV- 2, making the prevention of COVID-19 infection a major challenge in the world. In view of this, implementing fast, low-cost, accurate, easy-to-access, and integrated diagnostic devices available at the point of care (POC) is paramount to contain not only COVID-19, but also to cope with future epidemics.Item Static and dynamic magnetization models of magnetic nanoparticles: an appraisal(2023) Yari, Parsa (TTU); Chugh, Vinit Kumar; Saha, Renata; Tonini, Denis; Rezaei, Bahareh (TTU); Mostufa, Shahriar (TTU); Xu, Kanglin (TTU); Wang, Jian-Ping; Wu, Kai (TTU)Nowadays, magnetic nanoparticles (MNPs) have been extensively used in biomedical fields such as labels for magnetic biosensors, contrast agents in magnetic imaging, carriers for drug/gene delivery, and heating sources for hyperthermia, among others. They are also utilized in various industries, including data and energy storage and heterogeneous catalysis. Each application exploits one or more physicochemical properties of MNPs, including magnetic moments, magnetophoretic forces, nonlinear dynamic magnetic responses, magnetic hysteresis loops, and others. It is generally accepted that the static and dynamic magnetizations of MNPs can vary due to factors such as material composition, crystal structure, defects, size, shape of the MNP, as well as external conditions like the applied magnetic fields, temperature, carrier fluid, and inter-particle interactions (i.e., MNP concentrations). A subtle change in any of these factors leads to different magnetization responses. In order to optimize the MNP design and external conditions for the best performance in different applications, researchers have been striving to model the macroscopic properties of individual MNPs and MNP ensembles. In this review, we summarize several popular mathematical models that have been used to describe, explain, and predict the static and dynamic magnetization responses of MNPs. These models encompass both individual MNPs and MNP ensembles and include the Stoner-Wohlfarth model, Langevin model, zero/non-zero field Brownian and Néel relaxation models, Debye model, empirical Brownian and Néel relaxation models under AC fields, the Landau–Lifshitz–Gilbert (LLG) equation, and the stochastic Langevin equation for coupled Brownian and Néel relaxations, as well as the Fokker–Planck equations for coupled/decoupled Brownian and Néel relaxations. In addition, we provide our peers with the advantages, disadvantages, as well as suitable conditions for each model introduced in this review. The shrinking size of magnetic materials brings about a significant surface spin canting effect, resulting in higher anisotropy and lower magnetization in MNPs compared to bulk materials. Accurate prediction of static and dynamic magnetizations in MNPs Requires both precise data on their magnetic properties and an accurate mathematical model. Hence, we introduced the spin canting effect and models to estimate anisotropy and saturation magnetization in MNPs.Item Static and Dynamic Magnetization Responses of Self-Assembled Magnetic Nanoparticle Chains(2023) Chugh, Vinit Kumar; Liang, Shuang; Tonini, Denis; Saha, Renata; Liu, Jinming; Yari, Parsa (TTU); Krishna, Venkatramana D.; Cheeran, Maxim C-J; Wu, Kai (TTU); Wang, Jian-PingThe dynamic magnetization responses of magnetic nanoparticles (MNPs) subjected to alternating magnetic fields have been exploited for many biomedical applications, such as hyperthermia therapy, magnetic biosensing, and imaging. This dynamic process is governed by the combined Brownian and Néel relaxations via various energy terms. Both extrinsic factors, such as external alternating fields, dipolar fields, and the properties of the MNP medium, and intrinsic factors, such as the shape, size, and the magnetic properties of the MNPs, can affect their dynamic magnetization responses. However, due to the complex energy terms and interparticle interactions involved, it can be challenging to characterize how each factor influences the dynamic magnetization responses. In this study, we systematically examined the static and dynamic magnetization responses of an ensemble of MNPs. By solidifying the MNP suspension under a fixation field, the immobilized MNPs form long chains, and their easy axes are artificially tuned. In this simplified model, factors such as relative orientations of MNPs’ easy axes to the external field and the dipolar interactions of MNPs are studied. Using a magnetic particle spectroscopy (MPS) platform, the time domain dynamic magnetization responses, dynamic hysteresis loops, high harmonics (which are of interest for MPS and magnetic particle imaging applications), and phase lag of MNPs’ magnetizations to external fields were recorded. A strong correlation between the phase lag of MNPs and the nonlinearity in AC magnetization loops was established.Item Theoretical Investigation on the Metamaterials Based on the Magnetic Template-Assisted Self-Assembly of Magnetic–Plasmonic Nanoparticles for Adjustable Photonic Responses(2023) Sun, Jiajia; Shi, Zongqian; Liu, Xiaofeng; Ma, Yuxin; Li, Ruohan; Chen, Shuang; Xin, Shumin; Wang, Nan; Jia, Shenli; Wu, Kai (TTU)The assembly of artificial nano- or microstructured materials with tunable functionalities and structures, mimicking nature’s complexity, holds great potential for numerous novel applications. Despite remarkable progress in synthesizing colloidal molecules with diverse functionalities, most current methods, such as the capillarity-assisted particle assembly method, the ionic assembly method based on ionic interactions, or the field-directed assembly strategy based on dipole–dipole interactions, are confined to focusing on achieving symmetrical molecules. But there have been few examples of fabricating asymmetrical colloidal molecules that could exhibit unprecedented optical properties. Here, we introduce a microfluidic and magnetic template-assisted self-assembly protocol that relies mainly on the magnetic dipole–dipole interactions between magnetized magnetic–plasmonic nanoparticles and the mechanical constraints resulting from the specially designed traps. This novel strategy not only requires no specific chemistry but also enables magnetophoretic control of magnetic–plasmonic nanoparticles during the assembly process. Moreover, the assembled asymmetrical colloidal molecules also exhibit interesting hybridized plasmon modes and produce exotic optical properties due to the strong coupling of the individual nanoparticle. The ability to fabricate asymmetrical colloidal molecules based on the bottom-up method opens up a new direction for the fabrication of novel microscale structures for biosensing, patterning, and delivery applications.