Paper-based Devices Research Articles

High-performance flexible and broadband photodetectors on paper substrates using FeSnS bimetallic sulfide nanosheets

Advancements in technology have made it easier to construct flexible broadband photodetectors for wearable devices, improving light harvesting and detecting capabilities. This work described a new study that used bimetallic sulfide nanosheets (FeSnS) to produce flexible and broadband photodetectors on paper substrates using hand-print method. A simple, economical, one-step hydrothermal technique was employed to synthesise FeSnS materials, which were characterised using XRD, UV–Vis Spectroscopy, FESEM, EDS, XPS, and UPS. Photodetection tests found that 2-FeSnS (Fe at 2 wt%) outperformed similar work on paper-based devices, with a responsivity of 32.4 mA/W under a 470 nm incident wavelength, high specific detectivity, and a response time of 1.16 s. Durability and flexibility testing validated the robustness of the device. The use of a simple hydrothermal synthesis and hand-print fabrication method to create high-performance, eco-friendly, and flexible photodetectors is novel, expanding their potential applications in wearable electronics, environmental monitoring, and low-cost disposable sensing platforms.

Utilization of functionalized paper-based microfluidic devices for the detection and characterization of starch in milk

We pronounce a quick cost-effective, and one-of-a-kind single-step approach for fabricating paper-based devices by using correction pens instead of expensive materials. The highlighted areas were filled with Deposits from the correction pen and the surroundings were coated with wax, showing that will have a wide range of aqueous resistances. In the transverse direction, favorable natural convection occurs during the process along the axial direction of the fabricated paper channel. Due to its cost-effectiveness, the platform is believed to be ideally suited for chemical sensing and point-of-care applications, as well as diagnostics in resource-limited settings. We show that a lab-on-a-chip method based on paper can be used for colorimetric analysis to identify both qualitative and quantitative changes in milk caused by the presence of starch impurities. The challenges of sample storage, handling, and transport to the laboratory are circumvented by combining detection technology with smartphone imagery that permits on-site data collection. Diagnostic and sensing applications in low-resource settings, such as those seen in developing nations, can now use this technology.

A Trianalyte µPAD for Simultaneous Determination of Iron, Zinc, and Manganese Ions.

In this work, a microfluidic paper-based analytical device (µPAD) for simultaneous detection of Fe, Zn, and Mn ions using immobilized chromogenic reagents Ferene S, xylenol orange, and 1-(2-pyridylazo)-2-naphthol, respectively, is presented. As the effective recognition of analytes via respective chromogens takes place under extremely different pH conditions, experiments reported in this publication are focused on optimization of the µPAD architecture allowing for the elimination of potential cross effects. The paper-based microfluidic device was fabricated using low-cost and well-reproducible wax-printing technology. For optical detection of color changes, an ordinary office scanner and self-made RGB-data processing program were applied. Optimized and stable over time, µPADs allow fast, selective, and reproducible multianalyte determinations at submillimolar levels of respective heavy metal ions, which was confirmed by results of the analysis of solutions mimicking real samples of wastewater. The presented concept of simultaneous determination of different analytes that required extremely different conditions for detection can be useful for the development of other multianalyte microfluidic paper-based devices in the µPAD format.

Microfluidic paper-based colorimetric chemo-sensing of formaldehyde using tetramethylbenzidine-conjugated gold nanoflowers: A point-on-demand approach for efficient chemosensing of volatile organic compounds

The presence of formaldehyde, a common environmental aldehyde and a recognized carcinogen, poses a significant health risk to humans. Monitoring its levels in environmental samples and human biofluids is crucial for both pollution control and advancements in health science. This study introduces an effective colorimetric method utilizing UV–Vis spectroscopy to identify formaldehyde in real samples. Various types of gold nanoparticles (AuNPs) with diverse sizes and structures were employed to develop a photochemical chemosensing device. The method exhibited high sensitivity in detecting formaldehyde, particularly through the use of gold nanoflowers (AuNFs) at a pH of 6.15, with a low quantification limit of 0.1 µM and a linear range of 0.6 µM to 1 M. Furthermore, the method was successfully utilized to assess formaldehyde in human biofluids. Additionally, a paper-based microfluidic colorimetric opto-device was incorporated for on-site and on-demand formaldehyde screening. This study showcases the application of AuNPs for the precise and sensitive detection of formaldehyde in human biofluids, offering potential for advanced analytical methods targeted at formaldehyde and other volatile organic compounds (VOCs). The practicality, affordability, and portability of the microfluidic paper-based colorimetric device (µPCDs) make it a promising choice for point-of-care VOC testing. This represents the first demonstration of µPCDs for the selective photochemical sensing of toxic substances, and its one-step process that does not rely on novel sorbents, membranes, or external stimuli, making it easily scalable. The potential for µPCDs to be broadly applicable to the selective monitoring of formaldehyde from complex bio-matrices is evident. This method demonstrated robust performance in terms of accuracy, sensitivity, reproducibility, and selectivity.

Laser‐scribed graphene toward scalable fabrication of electrochemical paper-based devices for lidocaine detection in forensic and pharmaceutical samples

Lidocaine (LID), a tertiary amine drug, is widely used as a local anesthetic for topical anesthesia and also presents antiarrhythmic and analgesic properties. Given its use can induce a temporary loss of sensory, motor, and autonomic function, it has been associated with criminal instances of drug-facilitated sexual assault. Herein, we manufactured an electrochemical paper-based analytical device (ePAD) using the laser-scribed graphene (LSG) technique for LID detection in pharmaceutical and forensic applications. The paper-based devices were characterized by scanning electron microscopy (SEM) and Raman spectroscopy, confirming the porosity and graphene-derived nature of the LSG material. In addition, to enhance the electrocatalytic properties, the LSG electrode was modified with a nanocomposite based on the mixture of multi-walled carbon nanotubes (MWCNT) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). Electrochemical characterizations of the non-modified and MWCNT/PEDOT:PSS-modified electrodes by impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV), revealed the enhancement of the electrochemical properties of the modified electrode, providing higher detectability for LID detection. An analytical curve was built using DPV technique and exhibited a linear response in the concentration range of 31 to 248 µmol L−1 LID. The limits of detection (LOD) and quantification (LOQ) of the method were 0.72 µmol L−1 and 2.39 µmol L−1, respectively. The manufacturing reproducibility of the method was assessed by testing 8 sensors from different batches and provided a relative standard deviation (RSD) of 4.92 % (n = 8). The developed sensor was applied to LID determination in a commercial anesthetic sample and, as proof of the applicability of potential use in crime scenes of drug-facilitating crimes, we analyzed spiked LID in alcoholic drinks (vodka and tequila samples). The recovery percentages ranged from 79 % to 109 %, highlighting the practical use of our portable method for in-field analysis. In addition, four seized cocaine samples containing LID were successfully analyzed to demonstrate the potential use as a LID screening tool in street drug samples.

A selective dual-signal electrochemical paper-based device using imprinted sensors for voltammetric and impedance analysis of 4-NQO and carcinoembryonic antigen (CEA)

BackgroundCarcinoembryonic Antigen (CEA) and 4-nitroquinoline-N-oxide (4-NQO) are cancer markers that play a crucial role in tumor risk assessment and early cancer diagnosis. Therefore, it is in demand to develop a fast, accurate, simple, and cost-effective method to detect these cancer markers for quick and early stage-cancer diagnosis and treatment. ResultsHerein, we report a dual signaling approach for direct and indirect signal transduction of cancer biomarker binding on molecularly imprinted-electrodes integrated on an ePAD, enabling sensitive and selective quantitative analysis of 4-NQO and CEA. Multiple test zones on a single device based on artificial recognition sites using core-shell Cu-MOF@MIP were developed to create a selective “Dual-signal-ePAD”. An effective and facile imprinting method on a Cu-MOF surface based on the synthesized of 4-VPBA/MAA/TRIM polymer. It resulted in a novel MIP useable as a high-performance sensing tool for the ultrasensitive and specific quantification of the target cancer biomarkers. Multiple tests consisted of voltammetric analysis of 4-NQO via oxidation of the analyte on a WE1, and impedance analysis of CEA via the molecular interaction with the imprinted WE2. SignificanceThe proposed device provides enhanced electrochemical signal amplification due to its high conductivity, electrocatalytic activity, and the target-specific recognition sites for accurate determination of 4-NQO and CEA targets. The Dual-signal-ePAD exhibits good voltammetric and EIS response, oxidation currents of 4-NQO at −0.06 V and RCT of CEA, resulting in high selectivity and sensitivity with a linear response range covering the concentration range of clinical interest for both analytes. Dual-signal ePAD is a good candidate for clinical screening and POCT.

Paper-Based Microfluidic Device for Extracellular Lactate Detection.

Lactate is a critical regulatory factor secreted by tumors, influencing tumor development, metastasis, and clinical prognosis. Precise analysis of tumor-cell-secreted lactate is pivotal for early cancer diagnosis. This study describes a paper-based microfluidic chip to enable the detection of lactate levels secreted externally by living cells. Under optimized conditions, the lactate biosensor can complete the assay in less than 30 min. In addition, the platform can be used to distinguish lactate secretion levels in different cell lines and can be applied to the screening of antitumor drugs. Through enzymatic chemical conversion, this platform generates fluorescent signals, enabling qualitative assessment under a handheld UV lamp and quantitative analysis via grayscale intensity measurements using ImageJ (Ver. 1.50i) software. The paper-based platform presented in this study is rapid and highly sensitive and does not necessitate other costly and intricate instruments, thus making it applicable in resource-constrained areas and serving as a valuable tool for investigating cell lactate secretion and screening various anti-cancer drugs.

Electrocatalytic efficiency of carbon nitride supported gold nanoparticle based sensor for iodide and cysteine detection

Extensive investigations are being conducted on gold nanoparticles focusing on their applications in biosensors, laser phototherapy, targeted drug delivery and bioimaging utilizing advanced detection techniques. In this work, an electrochemical sensor was developed based on graphite carbon nitride supported gold nanoparticles. Carbon nitride supported gold nanoparticles (Au–CN) was synthesized by applying a deposition-precipitation route followed by a chemical reduction technique. The composite system was characterized by X-ray diffraction and X-ray photo electron spectroscopy methods. Electron microscopy analysis confirmed the formation of gold nanoparticles within the size range of 5–15 nm on the carbon nitride support. Carbon nitride supported gold based sensor was employed for the electrochemical detection of iodide ion and l-cysteine. The limit of detection and sensitivity of the sensor was attained 8.9 μM and 0.96 μAμM⁻1cm⁻2, respectively, for iodide ion, while 0.48 μM and 5.8 μAμM⁻1cm⁻2, respectively, was achieved for the recognition of cysteine. Furthermore, a paper-based electrochemical device was developed using the Au–CN hybrid system that exhibited promising results in detecting iodide ions, highlighting its potential for economic and portable device applications.

Wearable electrochemical device based on butterfly-like paper-based microfluidics for pH and Na+ monitoring in sweat

A wearable potentiometric device is reported based on an innovative butterfly-like paper-based microfluidic system, allowing for continuous monitoring of pH and Na+ levels in sweat during physical activity. Specifically, the use of the butterfly-like configuration avoids evaporation phenomena and memory effects, enabling precise and timely biomarker determination in sweat. Two ad hoc modified screen-printed electrodes were embedded in the butterfly-like paper-based microfluidics, and the sensing device was further integrated with a portable and miniaturized potentiostat, leveraging Bluetooth technology for efficient data transmission. First, the paper-based microfluidic configuration was tested for optimal fluidic management to obtain optimized performance of the device. Subsequently, the two electrodes were individually tested to detect the two biomarkers, namely pH and Na+. The results demonstrated highly promising near-Nernstian (0.056 ± 0.002 V/dec) and super-Nernstian (− 0.080 ± 0.003 V/pH) responses, for Na+ and pH detection, respectively. Additionally, several important parameters such as storage stability, interferents, and memory effect by hysteresis study were also investigated. Finally, the butterfly-like paper-based microfluidic wearable device was tested for Na+ and pH monitoring during the physical activity of three volunteers engaged in different exercises, obtaining a good correlation between Na+ increase and dehydration phenomena. Furthermore, one volunteer was tested through a cardiopulmonary test, demonstrating a correlation between sodium Na+ increase and the energetic effort by the volunteer. Our wearable device highlights the high potential to enable early evaluation of dehydration and open up new opportunities in sports activity monitoring.Graphical abstract

Comprehensive numerical prototyping of paper-based microfluidic devices using open-source tools

Paper-based microfluidics has emerged as a promising field with diverse applications ranging from medical diagnostics to environmental monitoring. Despite significant progress in research and development, the translation of paper-based prototypes into practical end-user devices remains limited. This limitation stems from challenges related to devices not being sufficiently portable and autonomous, which paper-based microfluidics is expected to overcome. Yet for this purpose, we note the lack of comprehensive numerical modeling tools capable of simulating the intricate physicochemical phenomena involved in order to optimize the development process; hence, in this study, we introduce porousMicroTransport, a novel simulation package integrated with the open-source platform OpenFOAM®, designed to address these challenges. porousMicroTransport offers efficient solvers for fluid flow and transport phenomena in microfluidic porous media, including capillarity models and (bio)chemical reactions. Moreover, under horizontal flow conditions, porousMicroTransport application field can be extended to any porous media. We demonstrate the software’s effectiveness in two example cases, showcasing its ability to accurately reproduce complex phenomena involved in paper-based devices. By virtue of being an easy-to-use and computationally efficient tool, porousMicroTransport facilitates the design and optimization of devices, potentially enabling more devices to meet the WHO’s REASSURED criteria for point-of-care testing. We anticipate that this tool will accelerate the development and deployment of robust and portable diagnostic devices, bridging the gap between research and practical applications.

Decentralized food safety and authentication on cellulose paper-based analytical platform: A review.

Food safety and authenticity analysis play a pivotal role in guaranteeing food quality, safeguarding public health, and upholding consumer trust. In recent years, significant social progress has presented fresh challenges in the realm of food analysis, underscoring the imperative requirement to devise innovative and expedient approaches for conducting on-site assessments. Consequently, cellulose paper-based devices (PADs) have come into the spotlight due to their characteristics of microchannels and inherent capillary action. This review summarizes the recent advances in cellulose PADs in various food products, comprising various fabrication strategies, detection methods such as mass spectrometry and multi-mode detection, sampling and processing considerations, as well as applications in screening food safety factors and assessing food authenticity developed in the past 3 years. According to the above studies, cellulose PADs face challenges such as limited sample processing, inadequate multiplexing capabilities, and the requirement for workflow integration, while emerging innovations, comprising the use of simplified sample pretreatment techniques, the integration of advanced nanomaterials, and advanced instruments such as portable mass spectrometer and the innovation of multimodal detection methods, offer potential solutions and are highlighted as promising directions. This review underscores the significant potential of cellulose PADs in facilitating decentralized, cost-effective, and simplified testing methodologies to maintain food safety standards. With the progression of interdisciplinary research, cellulose PADs are expected to become essential platforms for on-site food safety and authentication analysis, thereby significantly enhancing global food safety for consumers.

Unveiling the potential of the capillary-driven microfluidic paper-based device integrated with smartphone-based for simultaneously colorimetric salivary ethanol and △9-tetrahydrocannabinol analysis

Monitoring various biomarkers in saliva samples emerges as a dynamic and non-invasive method. However, the high viscosity of saliva presents a distinct challenge when integrating paper-based platforms for on-site analysis. In addressing this challenge, we introduced the capillary-driven microfluidic paper-based analytical devices (μCD-PAD) designed for user-friendly and simultaneous detection of ethanol and tetrahydrocannabinol (THC) in saliva without a sample preparation step. Employing a colorimetric approach, we quantified both analytes. Synthetic salivas of varying viscosity flowed seamlessly to the detection zone without needing a sample preparation step, and no impact on colorimetric detection due to viscosity was observed (RSD <5 %). Within 10 min after the solution reached the detection zone, the device produced a homogeneous color signal, easily analyzed by a smartphone camera. To extend the application for determination to cover a legal limit concentration of ethanol and concentration of salivary THC even 24 h after marijuana consumption, the detection time of 30 min was optimized. Moreover, a saliva sample containing both analytes was used to demonstrate the capability of the developed device to detect ethanol and THC simultaneously. No cross-talk between ethanol and THC occurred and showed recovery in the 98–102 % for ethanol and 95–105 % for THC with acceptable accuracy. This developed device exhibits excellent potential for forensic applications, providing a user-friendly, cost-effective, and real-time screening tool for detecting ethanol and THC in saliva.

Quantification of Ions in Human Urine-A Review for Clinical Laboratories.

Urine is an organic fluid produced by the kidney, and its analysis is one of the most requested laboratory tests by clinicians. The ionic composition of urine has been shown to be a good health indicator: it is useful for the diagnosis of several diseases, as well as monitoring therapeutics. This review considers laboratorial techniques that have been used throughout time for the quantification of ions in urine, and also considers some methodologies that can potentially be used in clinical laboratories for this kind of analysis. Those methods include gravimetry, titration, flame emission spectrophotometry (flame photometry), fluorimetry, potentiometry (ion selective electrodes), ion chromatography, electrophoresis, kinetic colorimetric tests, enzymatic colorimetric tests, flow cytometry, atomic absorption, plasma atomic emission spectrometry, and paper-based devices. Sodium, potassium, chloride, calcium, and magnesium are among the most important physiological ions, and their determination is frequently requested in hospitals. There have been many advances regarding the analysis of these ions in 24 h urine. However, there is still some way to go concerning the importance of intracellular ions in this type of sample as well as the use of occasional urine for monitoring these parameters.

Determination of hydroquinone in beverages using colorimetric and electrochemical sensors on paper-based device.

Hydroquinone (HQ) is aphenolic compound used in industry processes. We aim to demonstrate a rapid and simple procedure forthe determination ofHQ. This work has developed two techniques, including colorimetric and electrochemical sensors on paper-based devices. Firstly, we havedevelopedthe colorimetric detection for the rapid screening test of HQ using 1.5% 4-(dimethylamino) benzaldehyde with alkaline condition (5M NaOH). Under suitable conditions, the calibration curve between the intensity and HQ concentration wasin the range of50-500mg L-1. Then, we developed a multi-walled carbon nanotube/graphene oxide/copper/palladium/platinum (MWCNT/GO/Cu/Pd/Pt) onto a screen-printed carbon electrode (SPCE). The optimalamount ofMWCNT/GO/Cu/Pd/Pt nanomaterial is 2mg for HQ detection.The linear concentration range was foundin the range 1 to 20mg L-1anda detection limit was foundto be 0.40mg L-1 (3.6µM) for HQ. Moreover, the proposed device can be applied to determine HQ inrealsamples and is inexpensivetechnique, portable, and low consumer time.

Adjusting Paper Device Properties for Bioelectrochemical Analysis and 3D Cell Culture

Context- Paper is an innovative material for cell culture due to its biocompatibility, its inert chemical properties and its low-cost. Paper is already used in many biomedical applications such as immunoassays and, more recently, as affordable electrochemical sensors. In this context, tuning the properties of paper devices can achieve better, more efficient and user-friendly assays for biomedical applications. Here, and by modifying the electrochemical properties of paper electrochemical devices, it is possible to create electrodes that can detect neurotransmitters, a critical type of biomolecules involved in neuronal communication. Dopamine is a neurotransmitter involved in reward and addiction and a molecule of considerable scientific interest. Dopamine is secreted in the brain by dopaminergic neurons. However, the fine chemical mechanisms of neuron networks are still obscure. Being able to spatially measure dopamine secretion, in response to activation of precise neuronal regions in a unique system, can lead to a better understanding of neuronal dynamics, as well as their response to drug alterations. Proposing a research model describing neuronal chemical function in a network will therefore help shining light on their mechanisms and testing new neuropharmacological solutions. Developing new tools for the analytical electrochemistry of the brain will make quantitative neuro-analysis more accessible, thus paving the way for a better understanding of the chemical mechanisms of the brain. Tuning paper electrode for neurochemical analysis- Conductive inks, i.e. conductive polymer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) and carbon nanotubes (CNT) suspensions, were used to improve the detection of dopamine at paper-based electrodes. The physical and chemical properties of different preparations and mixtures of inks were considered. Solvent secondary doping, a common technique for PEDOT-PSS based electrode, was used to improve the electrical properties of the electrodes. Ferrocyanide electroanalysis was used to benchmark 10 different electrode preparations, revealing that combining CNT and PEDOT-PSS improves the electroactivity of the surface of the sensor. Interestingly, it was found that CNT has a doping effect on PEDOT-PSS, leading to improved electrochemical properties. Finally, these electrodes were tested for dopamine detection. It was found that combining PEDOT-PSS and CNT in the surface layer of ink deposited on the paper electrode allows for lower capacitance, higher anodic current as well as better fouling resistance. Figure 1 presents a CV voltammogram for Dopamine obtained with a paper electrode. Overall, this strategy improves the sensitivity of the assay. Growing neurons on paper- Paper-based devices can also be used for cell culture. Cell on paper constructs are 3D cell culture models that are more suitable to study cell in a biomimetic 3D environment, thus better recapitulating their functions and biology. By carefully modifying the surface of the paper devices, it is possible to adjust their biocompatible properties to ameliorate the survival rate of cell culture on paper. This opens the possibility to achieve neuronal cell culture on paper. We will present different paper preparations compatible with murine dopaminergic maintenance. The neurons were maintained alive for several days of culture. We were able to effectively observe and study neurons in a 3D paper environment and quantify the growth of their processes. Figure 1 : Electrochemical detection of Dopamine for 20 cycles. Working electrode is a paper electrode with PEDOT:PSS and CNT conductive inks, shown on the right, scale is 1 cm. The reference electrode is an Ag/AgCl electrode, and the counter electrode is a platinum electrode. Scan rate is 0.02 Vs-1. Figure 1

Microfluidic devices to monitor water pollution

Microfluidic devices offer a promising future for monitoring water pollution caused by heavy metals, especially as the world continues to develop and the dangers of pollutants increases. This highlights the importance of developing these devices. These devices operate within the dynamics of fluids and quantify pollutants with numerous advantages, such as high sensitivity and specificity. They can also be integrated with mini sensors alongside analytical techniques. This study provides a brief overview of the types of microfluidic devices, such as polydimethylsiloxane (PDMS) and microfluidic paper-based (µPADs), and their application in pollutant detection. Microfluidic devices are associated with analytical methods such as spectrometric, colorimetric, and electrochemical techniques. Their importance lies in their simple manufacturing, rapid detection capabilities, and portability. Additionally, these devices can be updated to meet current needs in water pollution detection by integrating various analytical methods and enhancing these methods with programs that provide on-site results. There for microfluidics are currently of great importance due to their ease of manufacturing and applicability to various analytical methods, particularly for detecting pollutants in water. Many studies highlight the extraordinary potential of paper-based devices, which are the easiest to manufacture among all microfluidic devices and are not subject to stringent engineering and physical constraints. Most importantly, they can utilize colorimetric detection methods, providing instant results visible to the naked eye. This study demonstrates these advantages and suggests the potential for expanding their applications in medical, environmental, and biological fields.

Intermittent lysis on a single paper-based device to extract exosomal nucleic acid biomarkers from biological samples for downstream analysis.

As the role of exosomes in physiological and pathological processes has been properly perceived, harvesting them and their internal components is critical for subsequent applications. This study is a debut of intermittent lysis, which has been integrated into a simple and easy-to-operate procedure on a single paper-based device to extract exosomal nucleic acid biomarkers for downstream analysis. Exosomes from biological samples were captured by anti-CD63-modified papers before being intermittently lysed by high-temperature, short-time treatment with double-distilled water to release their internal components. Exosomal nucleic acids were finally adsorbed by sol-gel silica for downstream analysis. Empirical trials not only revealed that sporadically dropping 95°C ddH2O onto the anti-CD63-modified papers every 5min for 6 times optimized the exosomal nucleic acids extracted by the anti-CD63 paper but also verified that the whole deployed procedure is applicable for point-of-care testing (POCT) in low-resource areas and for both in vitro (culture media) and in vivo (plasma and chronic lesion) samples. Importantly, downstream analysis of exosomal miR-21 extracted by the paper-based procedure integrated with this novel technique discovered that the content of exosomal miR-21 in chronic lesions related to their stages and the levels of exosomal carcinoembryonic antigen originated from colorectal cancer cells correlated to their exosomal miR-21.

Streamlined integrated protein isoelectric focusing using microfluidic paper-based device

An innovative integrated paper-based microdevice was developed for protein separation by isoelectric focusing (IEF), allowing for robust design thanks to a 3D-printed holder integrating separation channel, reservoirs, and electrodes. To reach robustness and precision, the optimization focused on the holder geometry, the paper nature, the reservoir design, the IEF medium, and various focusing parameters. A well-established and stable pH gradient was obtained on a glass-fiber paper substrate with simple sponge reservoirs, and the integration of the electrodes in the holder led to a straightforward system. The separation medium composed of water/glycerol (85/15, v/v) allowed for reducing medium evaporation while being an efficient medium for most hydrophobic and hydrophilic proteins, compatible with mass spectrometry detection for further proteomics developments. To our knowledge, this is the first report of the use of glycerol solutions as a separation medium in a paper-based microdevice. Analytical performances regarding pH gradient generation, pI determination, separation efficiency, and resolution were estimated while varying the IEF experimental parameters. The overall process led to an efficient separation within 25 min. Then, this methodology was applied to a sample composed of saliva doped with proteins. A minimal matrix effect was evidenced, underscoring the practical viability of our platform. This low-cost, versatile and robust paper-based IEF microdevice opens the way to various applications, ranging from sample pre-treatment to integration in an overall proteomic-on-a-chip device.

In Vivo Detection of Abscisic Acid in Tomato Leaves Based on a Disposable Stainless Steel Electrochemical Immunosensor.

Abscisic acid (ABA) plays an important regulatory role in plants. It is very critical to obtain the dynamic changes of ABA in situ for botanical research. Herein, coupled with paper-based analysis devices, electrochemical immunoelectrodes based on disposable stainless steels sheet were developed for ABA detection in plants in situ. The stainless steel sheets were modified with carbon cement, ferrocene-graphene oxide-multi walled carbon nanotubes nanocomposites, and ABA antibodies. The system can detect the ABA in the range of 1 nM to 100 μM, with a limit of detection of 100 pM. The ABA content in tomato leaves under high salinity was detected in situ. The trend of ABA changes was similar to the expression of SlNCED1 and SlNCED2. Overall, this study offers an approach for in situ detection of ABA in plants, which will help to study the regulation mechanism of ABA in plants and to promote the development of precision agriculture.

Host-Guest Interaction Mediated Perovskite@Metal-Organic Framework Z-Scheme Heterojunction Enabled Paper-Based Photoelectrochemical Sensing.

Exploring the high-performance photoelectronic properties of perovskite quantum dots (QDs) is desirable for paper-based photoelectrochemical (PEC) sensing;however, challenges remain in improving their stability and fundamental performance. Herein, a novel Z-scheme heterostructure with host-guest interaction by the confinement of CH3NH3PbBr3 QDs within Cu3(BTC)2 metal-organic framework (MOF) crystal (MAPbBr3@Cu3(BTC)2) is successfully constructed on the paper-based PEC device for ultrasensitive detection of Ochratoxin A (OTA), with the assistance of the exciton-plasmon interaction (EPI) effect. The host-guest interaction is estabilished by encapsulating MAPbBr3 QDs as guests within Cu3(BTC)2 MOF as a host, which prevents MAPbBr3 QDs from being damaged in the polar system, offering access to long-term stability with high-performance PEC properties. Benefiting from the precise alignment of energy levels, the photogenerated charge carriers can migrate according to the Z-scheme charge-transfer pathway under the driving force of the internal electric field, achieving a high photoelectric conversion efficiency. Upon OTA recognition, the EPI effect is activated to modulate the exciton response in MAPbBr3 QDs by accelerating radiative decay, finally achieving sensitive OTA sensing with a detection limit of 0.017 pg mL-1. We believe this work renders new insight into designing host-guest Z-scheme heterojunctions in constructing the paper-based PEC sensing platforms for environmental monitoring.