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Cationic cellulose, despite its long history, has yet to find a place in the paper industry. However, recent research is evaluating the potential of its nanoscale forms. Likewise, the processes of Western manufacturers are optimized for wood pulps, relegating non-wood crops to specific products that, as also proposed by current research, could include nanocellulose. We combined these trends with the existing knowledge of the strong adsorption of poly(diallyldimethylammonium chloride) (polyDADMAC) on cellulosic fibers, which can be deemed a non-covalent kind of cationization. For that, polyDADMAC was first anchored to refined hemp pulps, under conditions that allowed the deprotonation of the primary hydroxyl groups of cellulose. The fiber surface remained positively-charged even after thoroughly washing the samples, owing not only to the small proportions of acidic hemicelluloses and lignin, but also to stable ion-dipole interactions. This non-covalent cationization was found to follow pseudo-second order kinetics, indicating that diffusion through the fiber was the rate-controlling step. PolyDADMAC-containing fibers were then fibrillated by high-pressure homogenization. The surface charge of cationic nanocellulose was greater than that of the starting fibers, as the specific surface area increased. Nonetheless, polyDADMAC caused agglomeration of fibrils to a certain extent. As a drawback, when applied in papermaking, cationic nanocellulose lowered air permeability to a lesser extent than non-cationized nanofibers. As an advantage, the tensile index increased by up to 57% in the absence of any retention agent Authors wish to acknowledge the financial support of the Spanish Ministry of Science and Innovation to the Project CON-FUTURO-ES (PID2020-113850RB-C22). Marc Delgado-Aguilar and Quim Tarrés are Serra Húnter Fellows Open Access funding provided thanks to the CRUE-CSIC agreement with Elsevier

This chapter mainly focuses on the recent developments made in rapid detection of cancer cells using novel paper-based analytical devices (PADs). Due to their simplicity, portability and biocompatibility, PADs have gained great attention in recent years for rapid detection of biomarkers. Since cancer has become an increasing worldwide concern, there stands an imminent requirement for minimally invasive detection and monitoring techniques. The progress made in paper-based detection of cancer biomarkers has proven to hold great potential for the development of point-of-care (POC) diagnostic devices for early detection of tumor cells. In this chapter, after an introduction on paper diagnosis, we will provide a brief explanation on the fabrication methods used for PADs. Then recently developed sensors based on colorimetric, fluorescence, chemiluminescence (CL), electrochemical, electrochemiluminescence (ECL) and surface-enhanced Raman scattering (SERS) techniques will be elaborated. In the end, current limitations and problems hindering the commercialization of paper-based sensors will be pointed out.

[EN] Nowadays, miniaturization and portability are crucial characteristics that need to be considered for the development of water monitoring systems. In particular, the use of handheld technology, including microfluidics, is exponentially expanding due to its versatility, reduction of reagents and minimization of waste, fast analysis times and portability. Here, a hybrid handheld miniaturized polymer platform with a paper-based microfluidic device was developed for the simultaneous detection of nitrite and nitrate in real samples from both, fresh and seawaters. The platform contains an ionogel-based colorimetric sensor for nitrite detection and a paper-based microfluidic device for the in situ conversion of nitrate to nitrite. The platform was fully characterized in terms of its viability as a portable, cheap and quick pollutant detector at the point of need. The calibration was carried out by multivariate analysis of the color of the sensing areas obtained from a taken picture of the device. The limits of detection and quantification, for nitrite were 0.47 and 0.68mgL-1, while for nitrate were 2.3 and 3.4mgL-1, found to be within the limits allowed by the environmental authorities, for these two pollutants. Finally, the platform was validated with real water samples, demonstrating its potential to monitor nitrite and nitrate concentrations on-site as a first surveillance step before performing extensive analysis. This project has received funding from the European Union Seventh Framework Programme (FP7) for Research, Technological Development and Demonstration under grant agreement no. 604241. The funding support from Gobierno de España, Ministerio de Ciencia y Educación de España” under grant PID2020-120313 GB-I00/AIE/10.13039/501100011033, and Gobierno Vasco Dpto. Educación for the consolidation of the research groups (IT1271-19) are also acknowledged. RC-C acknowledges funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 778001. Special thanks to (SGIker) of the University of the Basque Country (UPV/EHU). FB-L and LB-D acknowledge the “Red de Microfluídica Española” RED2018-102829-T.

Electrochemical paper-based analytical devices (ePADs) are receiving increasing attention in recent years, overcoming the publication number of colorimetric paper-based analytical devices in the literature. This chapter covers recent advances in the manufacturing of ePADs for chemical analysis. Initially, an introduction about its beginning in the literature and mainly practical theoretical principles are discussed. The following sections present how the devices are being fabricated and used in the literature, exploring their advantages and limitations and describing electrochemical sensing detection and future outlooks.

This chapter presents and discusses the most usual methodologies for colorimetric detection on paper-based analytical devices (PADs). State of the art associated with pioneering, popularity, physical aspect, surface modifications, instrumental and instrumental-free colorimetric measurements are carefully presented. Moreover, a side-by-side comparison among the most usual colorimetric detection modes on PADs was performed using a well-known complexometric reaction model. The pros and cons were discussed to show their advantages for chemical analysis.