Near-Infrared Silicon Photonic Crystals with High-Order Photonic Bandgaps for High-Sensitivity Chemical Analysis of Water-Ethanol Mixtures

Design and simulation of a high performance Ag3CuS2 jalpaite-based photodetector

This work provides a comprehensive investigation by using simulations and performance analysis of a high performance and narrowband Ag3CuS2 photodetector (PD) that operates in the near-infrared (NIR) region and is built using WS2 and BaSi2 semiconductors. Across its operational wavelength range, a comprehensive assessment of the device's electrical and optical properties such as photocurrent, open-circuit voltage, quantum efficiency, responsivity and detectivity is methodically carried out. Furthermore, a thorough investigation has been conducted into the impact of many parameters, including width, carrier density and defects of various layers. Also, the intricate interactions between WS2/Ag3CuS2 and Ag3CuS2/BaSi2 interface properties of the photodetector are explored. The Ag3CuS2-based PD remarkably produces the best outcomes with an open-circuit voltage of 0.74 V, current of 43.79 mA/cm2, responsivity of 0.79 AW-1 and detectivity of 4.73 × 1014 Jones and over 90 % QE in the NIR range for the Ag3CuS2 PD. The results showcase this jalpaite material as a promising one in the field of PD.

Voltage- and Metal-assisted Chemical Etching of Micro and Nano Structures in Silicon: A Comprehensive Review

Sculpting silicon at the micro and nano scales has been game-changing to mold bulk silicon properties and expand, in turn, applications of silicon beyond electronics, namely, in photonics, sensing, medicine, and mechanics, to cite a few. Voltage- and metal-assisted chemical etching (ECE and MaCE, respectively) of silicon in acidic electrolytes have emerged over other micro and nanostructuring technologies thanks to their unique etching features. ECE and MaCE have enabled the fabrication of novel structures and devices not achievable otherwise, complementing those feasible with the deep reactive ion etching (DRIE) technology, the gold standard in silicon machining. Here, a comprehensive review of ECE and MaCE for silicon micro and nano machining is provided. The chemistry and physics ruling the dissolution of silicon are dissected and similarities and differences between ECE and MaCE are discussed showing that they are the two sides of the same coin. The processes governing the anisotropic etching of designed silicon micro and nanostructures are analyzed, and the modulation of etching profile over depth is discussed. The preparation of micro- and nanostructures with tailored optical, mechanical, and thermo(electrical) properties is then addressed, and their applications in photonics, (bio)sensing, (nano)medicine, and micromechanical systems are surveyed. Eventually, ECE and MaCE are benchmarked against DRIE, and future perspectives are highlighted.

Design of an Artificial Opal/Photonic Crystal Interface for Alcohol Intoxication Assessment: Capillary Condensation in Pores and Photonic Materials Work Together

Alcohol intoxication has a dangerous effect on human health and is often associated with a risk of catastrophic injuries and alcohol-related crimes. A demand to address this problem adheres to the design of new sensor systems for the real-time monitoring of exhaled breath. We introduce a new sensor system based on a porous hydrophilic layer of submicron silica particles (SiO₂ SMPs) placed on a one-dimensional photonic crystal made of Ta₂O₅/SiO₂ dielectric layers whose operation relies on detecting changes in the position of surface wave resonance during capillary condensation in pores. To make the active layer of SiO₂ SMPs, we examine the influence of electrostatic interactions of media, particles, and the surface of the crystal influenced by buoyancy, gravity force, and Stokes drag force in the frame of the dip-coating preparation method. We evaluate the sensing performance toward biomarkers such as acetone, ammonia, ethanol, and isopropanol and test sensor system capabilities for alcohol intoxication assessment. We have found this sensor to respond to all tested analytes in a broad range of concentrations. By processing the sensor signals by principal component analysis, we selectively determined the analytes. We demonstrated the excellent performance of our device for alcohol intoxication assessment in real-time.

Real-time and high-sensitivity refractive index sensing with an arched optofluidic waveguide

Refractive index (RI) sensing plays an important role in analytical chemistry, medical diagnosis, and environmental monitoring. The optofluidic technique is considered to be an ideal tool for RI sensor configuration for its high integration, high sensitivity, and low cost. However, it remains challenging to achieve RI measurement in real time with high sensitivity and low detection limit (DL) simultaneously. In this work, we design and fabricate a RI sensor with an arched optofluidic waveguide by monitoring the power loss of the light passing through the waveguide, which is sandwiched by the air-cladding and the liquid-cladding under test, we achieve RI detection of the sample in real time and with high sensitivity. Furthermore, both numerical simulation and experimental investigation show that our RI sensor can be designed with different geometric parameters to cover multiple RI ranges with high sensitivities for different applications. Experimental results illustrate that our sensor is capable to achieve a superior sensitivity better than -19.2 mW/RIU and a detection limit of 5.21×10^-8 RIU in a wide linear dynamic range from 1.333 to 1.392, providing a promising solution for real-time and high-sensitivity RI sensing.

Plasmon mediated spectrally selective and sensitivity-enhanced uncooled near-infrared detector

Here, we present a high performance uncooled near-infrared (NIR) detector comprising of a giga hertz (GHz) solidly mounted resonator (SMR) and gold nanorods (GNRs) arrays. By coupling the localized surface plasmon resonances of GNRs, the resonator system exhibits optimized optical response to vis-NIR region. Both simulation and experiments demonstrate the hybrid GNRs-SMR exhibit significantly enhanced optical responsive sensitivity of NIR, the tunable aspect ratios (AR) of GNRs enable resonator respond sensitively to selected light. Specially, taking advantage of the acoustofluidic effect of SMR, the GNRs can be controllably and precisely modified on the microchip surface in an ultra-short time, which addresses one of the most fundamental challenges in the localized functionalization of micro/nano scale surface. The presented work opens new directions in development of novel miniaturized, tunable NIR detector.

Biosensing platforms based on silicon nanostructures: A critical review

Biosensors are revolutionizing the health-care systems worldwide, permitting to survey several diseases, even at their early stage, by using different biomolecules such as proteins, DNA, and other biomarkers. However, these sensing approaches are still scarcely diffused outside the specialized medical and research facilities. Silicon is the undiscussed leader of the whole microelectronics industry, and novel sensors based on this material may completely change the health-care scenario. In this review, we will show how novel sensing platforms based on Si nanostructures may have a disruptive impact on applications with a real commercial transfer. A critical study for the main Si-based biosensors is herein presented with a comparison of their advantages and drawbacks. The most appealing sensing devices are discussed, starting from electronic transducers, with Si nanowires field-effect transistor (FET) and porous Si, to their optical alternatives, such as effective optical thickness porous silicon, photonic crystals, luminescent Si quantum dots, and finally luminescent Si NWs. All these sensors are investigated in terms of working principle, sensitivity, and selectivity with a specific focus on the possibility of their industrial transfer, and which ones may be preferred for a medical device.

Nanopatterning with Photonic Nanojets: Review and Perspectives in Biomedical Research

Nanostructured surfaces and devices offer astounding possibilities for biomedical research, including cellular and molecular biology, diagnostics, and therapeutics. However, the wide implementation of these systems is currently limited by the lack of cost-effective and easy-to-use nanopatterning tools. A promising solution is to use optical methods based on photonic nanojets, namely, needle-like beams featuring a nanometric width. In this review, we survey the physics, engineering strategies, and recent implementations of photonic nanojets for high-throughput generation of arbitrary nanopatterns, along with applications in optics, electronics, mechanics, and biosensing. An outlook of the potential impact of nanopatterning technologies based on photonic nanojets in several relevant biomedical areas is also provided.

Demonstration of mid-infrared slow light one-dimensional photonic crystal ring resonator with high-order photonic bandgap

Integrated mid-infrared sensing offers opportunities for the compact, selective, label-free and non-invasive detection of the absorption fingerprints of many chemical compounds, which is of great scientific and technological importance. To achieve high sensitivity, the key is to boost the interaction between light and analytes. So far, approaches like leveraging the slow light effect, increasing optical path length and enhancing the electric field confinement (f) in the analyte are envisaged. Here, we experimentally investigate a slow light one-dimensional photonic crystal ring resonator operating at high-order photonic bandgap (PBG) in mid-infrared range, which features both strong field confinement in analyte and slow light effect. And the optical path length can also be improved by the resoantor compared with waveguide structure. The characteristics of the first- and second-order bandgap edges are studied by changing the number of patterned periodical holes while keeping other parameters unchanged to confine the bands in the measurement range of our setup between 3.64 and 4.0 µm. Temperature sensitivity of different modes is also experimentally studied, which helps to understand the field confinement. Compared to the fundamental PBG edge modes, the second PBG edge modes show a higher field confinement in the analyte and a comparable group index, leading to larger light-matter interaction. Our work could be used for the design of ultra-sensitive integrated mid-infrared sensors, which have widespread applications including environment monitoring, biosensing and chemical analysis.

Impact of Fabrication and Bioassay Surface Roughness on the Performance of Label-Free Resonant Biosensors Based On One-Dimensional Photonic Crystal Microcavities

Micro- and nanofabrication offer remarkable opportunities for the preparation of label-free biosensors exploiting optical resonances to improve sensitivity and reduce detection limit once specificity is imparted through surface biofunctionalization. Nonetheless, both surface roughness, peculiar of fabrication processes, and bioassay roughness, resulting from uneven molecular coverage of the sensing surfaces, produce light scattering and, in turn, deterioration of biosensing capabilities, especially in resonant cavities where light travels forth and back thousands to million times. Here, we present a quantitative theoretical analysis about the impact of fabrication and bioassay surface roughness on the performance of optical biosensors exploiting silicon-based, vertical one-dimensional (1D) photonic crystal resonant cavities, also taking noise sources into account. One-dimensional photonic crystal resonant cavities with different architectures and quality factors ranging from 10² to 10⁶ are considered. The analysis points out that whereas sensitivity and linearity of the biosensors are not affected by the roughness level, either due to fabrication or bioassay, the limit of detection can be significantly degraded by both of them, depending on the quality factor of the cavity and noise level of the measurement system. The paper provides important insights into performance versus design, fabrication, and readout of biosensors based on resonant 1D photonic crystal cavities for real-setting operation.

Near-infrared spectroscopic study of molecular interaction in ethanol-water mixtures

Given the importance of ethanol-water mixtures in many chemical and biological processes, the molecular interaction in ethanol-water binary system was studied using near-infrared (NIR) spectroscopy. Excess spectra (in form of excess absorption coefficient) and Gaussian fitting were applied to analyze low concentration ethanol-water mixtures, ranging from 0 to 10% (v/v). With the knowledge of aquaphotomics, six kinds of water species were identified for 0-10% ethanol-water system, and it was indicated that water can be a sensitive probe for analyzing the structural changes and the interactions in the solutions. The excess spectra and two-dimensional (2D) correlation spectroscopy were introduced for high concentration mixtures (10-100%) analysis and found that the intermolecular hydrogen bonding strength between ethanol and water reaches to the maximum at 40% ethanol concentration which may be related to some abnormal properties of alcoholic solutions reported previously. In 40-100% mixtures, ethanol molecules tend to initiate the self-association which leads to the weakening of the interaction between ethanol and water. This paper not only deepens the understanding of the structure and dynamics of alcoholic solution, but also opens a new perspective in molecular interaction analysis in aqueous system by understanding the roles of water.

Porous Silicon Optical Biosensors: Still a Promise or a Failure?

Even if the first published article on a porous silicon (PSi)-based biosensor dates back to more than twenty years ago, this technology still attracts great attention from many research groups around the world. In this brief review, the pros and cons of porous silicon-based optical biosensors will be highlighted on the basis of some recent results and published papers on this subject. The aim of the paper is to give a straightforward introduction to PhD students and young researchers on this subject, which is particularly full of educative content, since it is highly multidisciplinary. Fabrication of PSi-based optical biosensors requires competencies related to many different scientific topics ranging from material science, physics and optics to healthcare and environmental monitoring through surface chemistry and more.