# Infrared Spectroscopy-Quo Vadis?
## 4 Infrared Spectroscopy: The Future
In addition, active structures that are fabricated and utilized similar to electronics in integrated circuits are on the horizon for applications in IR spectroscopy (Figure 7). Multiplexing analyte-dedicated recognition structures into highly integrated circuits is a mayor advantage and will lead to the elevated exploitation of IR tools in the future. Here, the development of the so-called 'light or photonic computer concepts' potentially operating with infrared radiation is a potential key technology that would reduce the cost of IR technology potentially to the level where electrochemical sensors are already at now. Accessing low target analyte quantities or concentrations in the infrared can be challenging. There are different approaches to elevate signal interaction with the probing photons. First, the probe amount can be increased. Hence, specific concepts for pre-concentration via adsorption, absorption into membranes, porous films [123] or fishing molecules via recognition motives out of a bulk volume are possible for, e.g., virus detection [124; 125; 126; 127]. Second, analytes can be converted into species that provide stronger interaction with infrared radiation, like converting H\({}_{2}\)S into SO\({}_{2}\)[128; 129]. Alternatively, sample interactions can be designed so that multiple interactions are achieved. Common approaches via multi-pass cells are accompanied with an increasing number of integrated microscopic structures. Here, structures can be designed to locally elevate electric fields instead of increasing the signal response via multiplied interaction. Standing wave resonators, via, micro-tori [130] and whispering gallery modes [131] are one example of such resonant structures. Surface enhancement in the infrared (SEIRAS; surface enhanced infrared spectroscopy) can be exploited as in Raman spectroscopy (SERS; surface enhanced Raman spectroscopy). To achieve signal enhancement factors ranging from about 10 to 100, plasmonic nanostructures can be deposited on surfaces to locally elevate electric field strength. Normally, noble metal nanoparticles are used for that purpose [132]. The most common shape of spherical nanoparticles has been extended by cubes, rods, and stars [133; 134; 135] that provide sharp tips as nano-antennas [136]. In addition, alternative materials such as less expensive silver, copper or iron oxide nano particles have been implemented for signal enhancement [137; 138]. With the introduction of graphene-based signal enhancement [139; 140; 141] and quantum dots made from dielectrics and metallic alloys, a wide field of potential materials has been opened. With such materials, the precise tuning of the enhancement as well as the surface decoration thereof will lead to exquisite signal enhancing tools that are potentially non-toxic for applications in biological and medical scenarios. Figure 7: Conceptual design of infrared spectroscopy/sensor devices with a high level/on chip integration providing all necessary components hybridized or monolithically integrated onto a single chip-sized die derived from CMOS/IC technology. Such chip-scale devices can be realized, for example, via on-chip laser sources and detectors. Analyte interaction may be realized via various approaches including but not limited to evanescent field interaction via straight strip dielectric waveguides (**a**), more sophisticated waveguide structures such as slot, bimodal or MZI waveguides (**b**), plasmonic waveguides (**c**), or by using resonant cavities with the possible addition of analyte scavenging/enriching motifs (**d**). Defined sample-photon interaction may be realized via microfluidic channels or hollow structures accommodating gas/vapor, liquid or solid sample matrices, respectively. Quantum dots have been recently developed for realizing bright light panels in television screens at optical frequencies, namely red, green and blue (RGB). As the emission wavelength of such quantum dots can be precisely tuned by their size, their increased diameters lead to the emission of infrared light.