This review covers the recent progress made in the photonic crystal-based sensing technology for gas sensing applications. Photonic crystal-based sensing has tremendous potential because of its obvious advantages in sensitivity, stability, miniaturisation, portability, online use, remote monitoring etc. Several 1D and 2D photonic crystal structures including photonic crystal waveguides and cavities for gas sensing applications have been discussed in this review. For each kind of photonic crystal structure, the novelty, measurement principle and their respective gas sensing properties are presented. The reported works and the corresponding results predict the possibility to realize a commercially viable miniaturized and highly sensitive photonic crystal-based optical gas sensor having flexibility in the structure of ultra-compact size with excellent sensing properties.

In this manuscript, a highly sensitive Bloch surface wave (BSW)-based sensor is proposed for refractive index sensing analysis. The structure is designed using an one-dimensional photonic crystal (1D-PhC) structure. A top defective layer of transition metal dichalcogenides (TMDC) material with atomic layer thickness is introduced to confine a Bloch mode analogues to surface plasmon-like mode at the top interface. The detailed analysis is carried out to investigate the impact of number of TMDC monolayers on sensing performance. The wavelength (angular) interrogation provides the significant higher sensitivity of around 9650 nm/RIU (or 231°/RIU). Besides the sensitivity, the rigorous analysis of full-width-half-maximum (FWHM) and figure-of-merit (FOM) is also carried out and a FOM of around 48,250/RIU (38,500/RIU) has been reported. The proposed design possesses the advantage in terms of easy fabrication and integration capability to develop handheld senor systems, especially for biological and chemical sensing.

Cooling represents a significant sector of energy consumption.¹ It is the most significant driver of peak electricity demand as well as considerable end use of energy globally.² The global energy consumption can be reduced by adopting a cooling strategy that can cool without any electrical input, which is also known as passive cooling technique. The cooling can be achieved if one is able to reach and maintain a temperature below ambient temperature. Radiative cooling, as a passive radiative cooling scheme, does not require any external active devices, such as fans, air conditioners, or thermoelectric.^{3 – 5} It works on the principle that the atmosphere is almost transparent between 8 and $13\mu \mathrm{m}$ (also known as ‘‘sky window”). Thus, utilizing outer space as a heat sink by allowing the emission of thermal radiation from surface to the universe.^6,7

This review manuscript presents Thin-Film Transistors (TFTs) for various highly sensitive biosensing applications. A low-cost, highly sensitive, early-stage diagnostic bio-sensing devices are vital for different biomedical and biological applications. Nanotechnology-based biosensor devices such as bioFET, thin-film transistor (TFT), etc. are used to overcome the problems of conventional health diagnostic approaches. Among them, TFT based biosensors have gained a lot of attention owing to high sensitivity, high-scalability, low power consumption, rapid electrical detection, low-cost mass production, and direct electrical readouts. Further to improve the sensitivity of TFT bases biosensor, transparent materials are frequently used in current biosensing research fields and it is found that indium tin oxide (ITO) is most favorable for biosensing applications. Thus, the amalgamation of ITO on TFT paves the way with the existing CMOS technology for early-stage diagnostic of protein-related diseases such as coronary artery disease, ovarian cancer, and Alzheimer’s diseases.

In this paper, the thermal stability of a Bloch Surface Wave (BSW) assisted bio-photonic sensor is investigated. The structural analysis is carried out using the transfer matrix method (TMM). The design comprises a truncated one-dimensional photonic crystal (1D-PhC) structure along with a defective top layer. The structural parameters are optimized to excite a BSW at the top interface for an operating wavelength of 632.8 nm. The mode confinement is confirmed by using wavelength interrogation, angular interrogation and surface electric field profile. Further, the effect of thermal variation on BSW excitation angle and sensitivity is carried out. The analysis shows the average variations in excitation angle and sensitivity of about −0.00096 degree/$°\mathrm{C}$ and 0.01046 (degree/RIU)/$°\mathrm{C}$, respectively. Additionally, the analysis is also extended towards different lower wavelengths of 400 nm and 550 nm, which provides average variations in the excitation angles of about −0.0027 degree/$°\mathrm{C}$, and 0.0016 degree/$°\mathrm{C}$. This shows that the structural sensitivity response is more thermally stable at the lower wavelength range. Thus, showing its potential applications in designing thermally stable bio-photonic sensors.