Paper-based electronics have emerged as a sustainable, low-cost, and flexible alternative to traditional substrates for electronics, particularly for disposable and wearable applications. This review outlines recent developments in paper-based devices, focusing on sensors and paper-based field-effect transistors (PFETs). Key fabrication techniques such as laser-induced graphene, inkjet printing, and screen printing have enabled the creation of highly sensitive and selective devices on various paper substrates. Material innovations, especially the integration of graphene, carbon-based materials, conductive polymers, and other novel micro- and nano-enabled materials, have significantly enhanced device performance. This review discusses modern applications of paper-based electronics, with a particular emphasis on biosensors, electrochemical and physical sensors, and PFETs designed for flexibility, low power, and high sensitivity. Advances in PFET architectures have further enabled the development of logic gates and memory systems on paper, highlighting the potential for fully integrated circuits. Despite challenges in durability and performance consistency, the field is rapidly evolving, driven by the demand for green electronics and the need for decentralized, point-of-care diagnostic tools. This paper also identifies detection strategies used in paper-based sensors, reviews limitations in the current fabrication methods, and outlines opportunities for the scalable production of multifunctional paper-based systems. This review addresses a critical gap in the literature by linking device-level innovation with real-world sensor applications on paper substrates.

Aim: After the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic and the realization of mass vaccination against the virus, the availability of a reliable, rapid, and easy-to-use system for registering the individual anti-S1 antibody titer could facilitate the personalized assessment of the need for booster vaccine doses and the reduction of social distancing and other measures. Methods: The biosensor system is based on immobilized engineered SK-N-SH neuroblastoma cells, bearing the S1 protein, and it can detect immunoglobulin G (IgG) antibodies against the SARS-CoV-2 S1 spike antigen. A disposable electrode strip bearing the engineered mammalian cells is connected to a customized read-out potentiometric device with real-time data transmission to a wireless fidelity (WiFi)-connected smartphone. Blood samples from past-infected individuals and individuals vaccinated against SARS-CoV-2 were used for validation. Results: In the present study, a smartphone application (app), capable of analyzing data regarding the levels of anti-S1 antibodies in blood is introduced. The app works in conjunction with a portable, ultra-rapid, and sensitive biosensor transmitting real-time measurements to the smartphone. Both historical and current individual data can be encoded by using the app, resulting in a widely accepted quick response (QR) code, which can then be constantly updated to match a person’s status. Conclusions: This novel system could be utilized for the eventual development of a coronavirus disease 2019 (COVID-19) electronic passport, which could be further employed to improve the population-wide, cross-country surveillance of vaccination efficiency, as well as facilitate the implementation of cross-border digital health services in a user-friendly and secure way.

Reduced graphene oxide (rGO) is a derivative of graphene, which has been widely used as the conductive pigment of many water-based inks and is recognized as one of the most promising graphene-based materials for large-scale and low-cost production processes. In this work, we evaluate a custom functionalised reduced graphene oxide ink (f–rGO) via inkjet-printing technology. Test line structures were designed and fabricated by the inkjet printing process using the f–rGO ink on a pretreated polyimide substrate. For the electrical characterisation of these devices, two-point (2P) and four-point (4P) probe measurements were implemented. The results showed a major effect of the number of printed passes on the resulting resistance for all ink concentrations in both 2P and 4P cases. Interesting results can be extracted by comparing the obtained multipass resistance values that results to similar effective concentration with less passes. These measurements can provide the ground to grasp the variation in resistance values due to the different ink concentrations, and printing passes and can provide a useful guide in achieving specific resistance values with adequate precision. Accompanying topography measurements have been conducted with white-light interferometry. Furthermore, thermal characterisation was carried out to evaluate the operation of the devices as temperature sensors and heaters. It has been found that ink concentration and printing passes directly influence the performance of both the temperature sensors and heaters.

In recent years, there has been a growing interest in the development of flexible thermal flow sensing devices due to their wide-ranging applications. In this study, we present the fabrication of a screen-printed flow sensor with optical readout on a 125 μm polyethylene terephthalate substrate in a three-layer configuration. The device comprises electrodes made from a commercial silver (Ag) ink, a heating area using a commercial carbon ink, and a thermochromic (TC) layer employing a commercial ink with a standard activation temperature of 31 °C. We designed a specialized experimental setup to evaluate the performance of the optical flow sensor under static and dynamic conditions. To analyze the device’s thermal response and performance across various flow conditions, we utilized a combination of electrical measurements and infrared (IR)-optical imaging techniques. The all-printed device operates on the basis of a thermodynamic cycle frequency, which activates the TC ink, causing it to blink at a frequency related to the flow passing over the sensor. The results of our preliminary testing are highly promising, as the sensor successfully demonstrated a clear relationship between flow and optical duty cycle. This innovative device offers a contactless, low-cost, easy-to-use flow detection method and holds significant potential for various practical applications.

Printed paper-based electronics offer a sustainable alternative to conventional substrates, but their development is limited by the poor dispersibility of conductive pigments and the thermal properties of paper. We report the formulation of eco-friendly water-based inks using a hybrid of carbon black (CB) and functionalized reduced graphene oxide ( f -rGO) for devices that operate as both temperature sensors and microheaters. The inks ( f -rGO and CB ₇₀ - f -rGO ₃₀ ) were prepared using commercial resins without addition of surfactants or other additives and exhibited film uniformity on low-cost reference paper. Drawdown devices exhibited linear behaviour in the 25 °C–60 °C range, with a temperature coefficient of resistance (TCR) of −3.94 × 10 ⁻³ °C ⁻¹ for CB ₇₀ - f -rGO ₃₀ and −7.37 × 10 ⁻³ °C ⁻¹ for f -rGO. In heater mode, CB ₇₀ - f -rGO ₃₀ devices achieved surface temperatures up to 82.8 °C at only 1.3 W, with rise/fall times of ∼16 s. Long-term cycling (∼340 on–off cycles) confirmed stable operation with <5% resistance drift. Compared to pure f -rGO films, the hybrid formulation delivered comparable low resistance, smoother surface morphology, and improved electrothermal conversion efficiency. These results demonstrate that cost-effective CB ₇₀ - f -rGO ₃₀ hybrids enable scalable, disposable paper-based electronics with combined sensing and heating functionality, offering a promising route toward sustainable thermal management and low-power sensor applications.