The development of gas sensors has been marked by significant advancements. From the early days of simple gas detection methods to the current era of smart gas sensor systems, gas sensors have evolved into sophisticated devices that play a critical role in ensuring safety, environmental quality, and health in various industries and applications. Photovoltaics have come a long way since their inception, evolving from a niche technology to a mainstream energy source with significant global impact, highlighting innovation in harnessing the only abundant energy to create a sustainable future for generations to come. Desirable material and system customizations and downsizings led to the availability of various multi-scale systems for gas sensing and energy conversion, but based on separate components. The integration of the mentioned systems into multi functional and dual-use systems hardly exists. This chapter presents one such integration approach; a proof-of-concept within the energy autonomous nanosensors domain. Namely, for the case of humidity sensor, it is possible to evolve and tailor the sensing performance of photoactive semiconducting materials based on swelling by implementing the quantum confinement phenomena. A multilayer thin film composite was fabricated where the photoactive layer was prepared by infusion of CdSe quantum dots into cellulose II microfibrils. Only this specific layer was modified without adding new layers and by doing that, sensing principles were implemented into a photovoltaic device yielding a novel concept that has not been shown yet, a two-in-one: solar cell and humidity sensor. A customized synthetic pathway was devised to enhance comprehension of the interaction and functionality of the components involved. The primary objective was to achieve compatibility between ligands connecting quantum dots and cellulosic matrices. Diffraction analysis indicated the structural and mesostructural stability, uniformity and homogeneous distribution of joined constituents. Spectroscopic analysis demonstrated how the constituents organize, enabling qualitative differentiation between samples, and suggested sizes and distribution in the range of ten nanometres. Electron microscopy provided a statistical foundation for the aforementioned findings, and revealed a transition from a fibrous to a granular appearance on the sample surface, possibly explaining the increased surface conductivity. Energy dispersive X-ray spectroscopy mapping showed the homogenous distribution of the quantum dots within the cellulose matrix. Atomic force microscopy corroborated the findings from scanning electron microscopy. Solid-state impedance spectroscopy highlighted the presence of multiple charge transport mechanisms in the composite films. Notably, a significant temperature-dependent conductivity behavior was observed, linked to the presence of –OH groups in the film structure and the positive segmental motion of the cellulose polymer chains. The introduction of CdSe quantum dots positively impacted the transport properties, with the conductivity in air exceeding that in an inert atmosphere by more than five orders of magnitude, indicating an instantaneous relaxation process. The significance of developing an energy autonomous nanosensors lies in their wide-ranging applications, particularly in the realms of environmental monitoring, agriculture, biomedicine, and human enhancement research. In the context of human enhancement, potential applications span from health monitoring to the development of wearable technologies.