Optical biosensors have exhibited worthwhile performance in detecting biological systems and promoting significant advances in clinical diagnostics, drug discovery, food process control, and environmental monitoring. Without complexity in their pretreatment and probable influence on the nature of target molecules, these biosensors have additional advantages such as high sensitivity, robustness, reliability, and potential to be integrated on a single chip. In this review, the state of the art optical biosensor technologies, including those based on surface plasmon resonance (SPR), optical waveguides, optical resonators, photonic crystals, and optical fibers, are presented. The principles for each type of biosensor are concisely introduced and particular emphasis has been placed on recent achievements. The strengths and weaknesses of each type of biosensor have been outlined as well. Concluding remarks regarding the perspectives of future developments are discussed.

Optical biosensors: an exhaustive and comprehensive review.

Recently, nanosilver pastes have emerged as one of the most promising high temperature bonding materials for high frequency and high power applications, which provide an effective lead-free electronic packaging solution instead of high-lead and gold-based solders Although nanosilver pastes can be sintered at lower temperature compared to bulk silver, applications of nanosilver pastes are limited by long-term sintering time (20⁻30 min), relative high sintering temperature (>250 °C), and applied external pressure, which may damage chips and electronic components Therefore, low temperature rapid sintering processes that can obtain excellent nanosilver joints are anticipated In this regard, we present a review of recent progress in the rapid sintering of nanosilver pastes Preparation of nanosilver particles and pastes, mechanisms of nanopastes sintering, and different rapid sintering processes are discussed Emphasis is placed on the properties of sintered joints obtained by different sintering processes such as electric current assisted sintering, spark plasma sintering, and laser sintering, etc Although the research on rapid sintering processes for nanosilver pastes has made a great breakthrough over the past few decades, investigations on mechanisms of rapid sintering, and the performance of joints fabricated by pastes with different compositions and morphologies are still far from enough

Recent Progress in Rapid Sintering of Nanosilver for Electronics Applications

There is a keen interest in the exploration of new generation emitters and detectors due to advancements in innovation of new materials and device processing technologies which have opened up new frontiers in the Terahertz (THz) spectrum. Therefore, it is necessary to review the developments in THz technology for healthcare applications, their impact, implications and prospects for ongoing research and development. This paper provides a broad overview of the current status and prospects of application of THz imaging and sensing for the healthcare domain. We present current knowledge, identify existing challenges for wide scale clinical adoption of THz systems and prospective opinions to facilitate research and development towards optimized and miniaturized THz systems and biosensors that provide real operational convenience through emerging trends. Firstly, we provide an overview of the THz imaging and sensing techniques that exploit properties of THz generation and detection with emphasis on terahertz time domain spectroscopy (THz-TDS) and THz Metamaterials. The mechanisms of tissue image contrast and the application of THz imaging and sensing for biomedical applications in particular, the cancer detection application is reported. Secondly, an outlook toward the advancements in THz technology in the interface of healthcare 4.0 and its enabling technologies is explored for next generation smart and connected healthcare systems. Third, we identify the merits and existing challenges in THz cancer imaging and sensing and suggest prospective opinions to pave way to ongoing and future research. Further, we discuss the recent advances in THz imaging development and the contribution of near-field techniques based on plasmonic, and resonance based metasurfaces, waveguides etc. for breaking the diffraction limit towards development of THz systems that are convenient for point of care. We bring researchers a roadmap for future research scope. 

/pdf/terahertz-imaging-and-sensing-for-healthcare-current-status-2fy98k07.pdf

Terahertz Imaging and Sensing for Healthcare: Current Status and Future Perspectives

In-depth assessments of cutting-edge solar cell technologies, emerging materials, loss mechanisms, and performance enhancement techniques are presented in this article. The study covers silicon (Si) and group III–V materials, lead halide perovskites, sustainable chalcogenides, organic photovoltaics, and dye-sensitized solar cells. In this regard, promising architectural advancements with graphene and metamaterials are highlighted. The study also encompasses various types of losses, including intrinsic and extrinsic losses in single-junction solar cells. Additionally, it evaluates efficiency improvement techniques such as light management and spectral utilization. While the efficiency of Si-based solar cells has plateaued around 25%, the efficiency of III–V compound semiconductor-based multi-junction solar cells is increasing. However, the high material cost of III–V compound semiconductors is a drawback. Furthermore, CIGS and CdTe solar cell technologies compete with crystalline solar cells, owing to recent advances in cell performance, however environmental concerns and CdTe solar cells' low open-circuit voltage remain challenges. On the other hand, Perovskite solar cells are extremely efficient in both single and multijunction arrangements. Device deterioration, hysteresis, and film quality are among issues that must be addressed when industrialising perovskite solar cells. 

A comprehensive evaluation of solar cell technologies, associated loss mechanisms, and efficiency enhancement strategies for photovoltaic cells

Temperature-sensitive materials are known as phase change materials (PCMs) which has transition between two different states. Dynamically tunable devices can be designed utilizing these materials. Vanadium dioxide (VO2) considered as a PCM material which transits from the insulator state to the metal one by increasing the temperature. VO2 has recently been utilized to design tunable absorbers. In this article, we presented a dual-band absorber structure design which consist of double arrays of VO2 ring-based placed on top of a dielectric buffer/spacer terminated with a conducting layer acting as a back reflector. Each ring acts as a resonator producing a surface plasmon resonance (SPR). Having a proper unit cell design with an appropriate dimension, a dual-band absorber with an absorption amplitude above 95% (ON state) can be achieved at terahertz (THz) frequency range in the metallic state; whereas the absorption value is 0.6% (OFF state) in the insulator state of VO2. Therefore, the proposed structure design has the possibility to switch between these two ON/OFF states by changing the material’s temperature. The interference theory and the equivalent circuit model are investigated to verify the achieved result using high-frequency structure simulator (HFSS) software which works based on finite element method (FEM). This structure has the potential optoelectronic applications such as refractive index (RI) optical sensing and biomedical detection, photonics detectors, and optical storage applications. 

Dynamically Switchable Sub-THz Absorber Using VO2 Metamaterial Suitable in Optoelectronic Applications

Metamaterials (MM) are artificially designed materials that possess unique properties due to their geometrical design. They also display some peculiar properties, such as negative refractive index, Snell’s law reversal, Doppler effect reverse, and left-handed behavior. MMs are used in a myriad of applications, including invisibility cloaking, perfect lensing, perfect absorption, and sensing. In this review article, the property of electromagnetic absorption by structures known as metamaterial absorbers (MMAs) is discussed. An MMA is a composite made up of many layers of metallic patterns separated by dielectric. This novel device helps in achieving near-unity absorption by various mechanisms, which are investigated in this article. The MMAs are classified based on their absorption characteristics, such as polarization tunability, broadband operation, and multiband absorption, in different frequency regimes.

/pdf/a-review-on-metamaterial-absorbers-microwave-to-optical-3vibs52s.pdf

A Review on Metamaterial Absorbers: Microwave to Optical

A terahertz metamaterial absorber, capable of detecting cancerous cells, is proposed in this letter. The proposed design consists of several merged circular ring resonators over a gallium arsenide substrate. It achieves an absorption of 99% at 3.71 THz and a high quality factor (Q-factor) of 92.75. The resonance frequency shifts with alterations in the refractive index of the encompassing medium, which is used to detect cancerous cells. The refractive index has varied in the range of 1.3–1.40, and its sensitivity is 1447 GHz/RIU. The equivalent circuit is proposed, and the resonance mechanism is studied. The structure behaves as an epsilon negative metamaterial, and the resonance is plasmonic. The sensor's high Q factor and a figure of merit of 36.175 have several biomedical sensing applications.

A Biomedical Sensor for Detection of Cancer Cells Based on Terahertz Metamaterial Absorber

Effect of Silver nanoparticles (AgNPs) morphology on their fluorescence behavior is reported. AgNPs sol stabilized by Ethylene Diamine Tetra Acetic-Acid (EDTA) was prepared by chemical reduction method. Morphology of the AgNPs was tuned through changing the Ag+ ion concentration and PH of reaction mixture. Additional peaks observed in surface Plasmon resonance spectra suggest the an-isotropic nature of AgNPs. Actual morphology was judged by Transmission Electron Microscopy. Emission spectra recorded using Spectrofluoremeter suggest the fluorescent nature of AgNPs, which also influenced by morphology of AgNPs and attributed to the variation in surface structure of an-isotropic AgNPs.

Morphological effect on fluorescence behavior of silver nanoparticles

Surface optimization of metal halide perovskite solar cells using ZnS nanorods

Reduction of extrinsic defects in ZnSe:perovskite composites based solar devices

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