Nanomaterials-modified cellulose paper as a platform for biosensing applications

Skin-Attachable Ink-Dispenser-Printed Paper Fluidic Sensor Patch for Colorimetric Sweat Analysis

In situ analysis of sweat biomarkers potentially provides noninvasive lifestyle monitoring and early diagnosis. Quantitative detection of sweat rate is crucial for thermoregulation and preventing heat injuries. Here, a skin-attachable paper fluidic patch is reported for in situ colorimetric sensing of multiple sweat markers (pH, glucose, lactate, and uric acid) with concurrent sweat rate tracking. Two sets of fluidic patterns-multiplexed detection zones and a longitudinal sweat rate channel-are directly printed by an automated ink dispenser from a specially developed ceramic-based ink. The ceramic ink thermal-cures into an impervious barrier, confining sweat within the channels. The ceramic-ink-printed boundary achieves higher pattern resolution, prevents fluid leakage, attains pattern thermal stability, and resistant to organic solvents. The cellulose matrix of the detection zones is modified with nanoparticles to improve the color homogeneity and sweat sensor sensitivity. The sweat rate channel is made moisture sensitive by incorporating a metal-salt-based dye. The change in saturation/color of the detection zones and/or channels upon sweat addition can be visually detected or quantified by a smartphone camera. A cost-effective way is provided to fabricate paper fluidic sensor patches, successfully demonstrating on-body multiplexed evaluation of sweat analytes. Such skin wearables offer on-site analysis, meaningful to an increasingly health-conscious population.

Development of a colorimetric sensor based on nanofiber cellulose film modified with ninhydrin to measure the formalin index of fruit juice

In this research, a color sensor based on nanofiber cellulose film modified with ninhydrin was designed to measure amino acids and formalin index in fruit juice. For this purpose, three types of cellulose films with porosity of 5, 30 and 125 μm were used. These films were treated with standard solution of ninhydrin. The characteristics of modified films were investigated using Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and X-ray Diffraction (XRD) tests. The color factors of the sensors (a and b) changed in the presence of amino acids and juice with different levels of formalin index. Therefore, the modified films with ninhydrin as a colorimetric sensor were calibrated using 7 types of amino acids and based on the formalin index of 4 types of juice. Then the sensors were used to measure the formalin index in 4 types of juice. The results showed that the sensors have relative selectivity towards methionine amino acid. The formalin index values calculated in the juices by the sensor were compared with the titration method as a reference method. All three types of sensors were able to detect formalin index. The results of the sensor performance verification showed that the sensors can measure formalin index in different juices with 95-98 % accuracy. These sensors showed fast sensitivity and selectivity to the amino acids in juice, also these sensors are safe and the measurement method is fast and simple.

Ultra-Sensitive Portable Visual Paper-Based Viral Molecularly Imprinted Sensor without Autofluorescence Interference

Detection of the virus is the primary factor to discover and block the occurrence and development of the virus epidemic. Here, an ultrasensitive paper-based virus molecular imprinting sensor is developed to detect two viruses simultaneously in which the detection limit of the influenza virus (H5N1) is 16.0 aM (9.63 × 103 particles/mL) while that of the Hepatitis B Virus (HBV) is 129 fM (7.77 × 107 particles/mL). This paper-based sensor is low cost and is easy to cut, store, and carry. In addition, the visual semiquantitative detection of two viruses is achieved by using two aptamer-functionalized persistent luminescent nanoparticles as signal probes. These probes and the imprinted cavities on the paper-based material formed sandwich-type double recognition of the target viruses. This sensor has extremely high sensitivity to the H5N1 virus, which is of great value to solve the influenza epidemic with the most outbreaks in history, and also opens up a new way for the prevention and control of other virus epidemics. This cheap and portable visual sensor provides the possibility for self-service detection and can greatly reduce the pressure on medical staff and reduce the risk of virus infection caused by the concentration of people to be tested.

μPADs on Centrifugal Microfluidic Discs for Rapid Sample-to-Answer Salivary Diagnostics

A fully integrated device for salivary detection with a sample-in-answer-out fashion is critical for noninvasive point-of-care testing (POCT), especially for the screening of contagious disease infection. Microfluidic paper-based analytical devices (μPADs) have demonstrated their huge potential in POCT due to their low cost and easy adaptation with other components. This study developed a generic POCT platform by integrating a centrifugal microfluidic disc with μPADs to realize sample-to-answer salivary diagnostics. Specifically, a custom centrifugal microfluidic disc integrated with μPADs is fabricated, which demonstrated a high efficiency in saliva treatment. To demonstrate the capability of the integrated device for salivary analysis, the SARS-CoV-2 Nucleocapsid (N) protein, a reliable biomarker for SARS-CoV-2 acute infection, is used as the model analyte. By the chemical treatment of the μPAD surface, and by optimizing the protein immobilization conditions, the on-disc μPADs were able to detect the SARS-CoV-2 N protein down to 10 pg mL-1 with a dynamic range of 10-1000 pg mL-1 and an assay time of 8 min. The integrated device was successfully used for the quantification of the N protein of pseudovirus in saliva with high specificity and demonstrated a comparable performance to the commercial paper lateral flow assay test strips.

Clarity improvement of the discoloration boundary and detection of Hg2+ ions by using a polystyrene nanoparticle-modified paper-based microdevice

Distance-based microfluidic paper-based analytical devices (μPADs) can be used to calculate the analyte content by reading the length of the discolored area in the channel. A blurred discoloration boundary is difficult to distinguish, resulting in reading errors. In this study, we constructed a μPAD modified with carboxyl-containing polystyrene nanoparticles (PS-μPAD) to improve the discoloration-boundary clarity. The filling of the pores of the fibers with the deposited polystyrene nanoparticles (PS NPs) caused a decrease in the paper porosity, resulting in a flow delay. Meanwhile, the carboxyl groups carried by PS NPs were able to form hydrogen bonds with hydroxyl-containing compounds FLPI, a Hg²⁺ probe, and the two factors acted synergistically to fix the FLPI to react in situ, raising the discoloration-boundary clarity. Compared with the unmodified μPAD, the detection of Hg²⁺ ions using the PS-μPAD still had a good linear relationship. Importantly, the color-depth difference inside and outside the discoloration boundary improved by about four times and showed excellent reproducibility in different populations. The method was simple and easy to expand, thereby providing an idea for more widespread application of distance-based μPADs.

Organized mineralized cellulose nanostructures for biomedical applications

Cellulose is the most abundant naturally-occurring polymer, and possesses a one-dimensional (1D) anisotropic crystalline nanostructure with outstanding mechanical robustness, biocompatibility, renewability and rich surface chemistry in the form of nanocellulose in nature. Such features make cellulose an ideal bio-template for directing the bio-inspired mineralization of inorganic components into hierarchical nanostructures that are promising in biomedical applications. In this review, we will summarize the chemistry and nanostructure characteristics of cellulose and discuss how these favorable characteristics regulate the bio-inspired mineralization process for manufacturing the desired nanostructured bio-composites. We will focus on uncovering the design and manipulation principles of local chemical compositions/constituents and structural arrangement, distribution, dimensions, nanoconfinement and alignment of bio-inspired mineralization over multiple length-scales. In the end, we will underline how these cellulose biomineralized composites benefit biomedical applications. It is expected that this deep understanding of design and fabrication principles will enable construction of outstanding structural and functional cellulose/inorganic composites for more challenging biomedical applications.

Progression of Paper-Based Point-of-Care Testing toward Being an Indispensable Diagnostic Tool in Future Healthcare

Point-of-care (POC) diagnostics in particular focuses on the timely identification of harmful conditions close to the patients' needs. For future healthcare these diagnostics could be an invaluable tool especially in a digitalized or telemedicine-based system. However, while paper-based POC tests, with the most prominent example being the lateral flow assay (LFA), have been especially successful due to their simplicity and timely response, the COVID-19 pandemic highlighted their limitations, such as low sensitivity and ambiguous responses. This perspective discusses strategies that are currently being pursued to evolve such paper-based POC tests toward a superior diagnostic tool that provides high sensitivities, objective result interpretation, and multiplexing options. Here, we pinpoint the challenges with respect to (i) measurability and (ii) public applicability, exemplified with select cases. Furthermore, we highlight promising endeavors focused on (iii) increasing the sensitivity, (iv) multiplexing capability, and (v) objective evaluation to also ready the technology for integration with machine learning into digital diagnostics and telemedicine. The status quo in academic research and industry is outlined, and the likely highly relevant role of paper-based POC tests in future healthcare is suggested.

An up-conversion test paper based on "switch-off" of fluorescence is constructed to sensitively and selectively detect cancer-causing dye Sudan III in lipstick

Cancer-causing dye Sudan III is banned adding to cosmetics, so a method for detecting trace Sudan III in cosmetics is established. A single dispersed up-conversion molecularly imprinted fluorescent nanoprobe is constructed and coated on the filter paper. The mechanism for detecting Sudan III by this composite fluorescent nanoprobes-paper is systematically analyzed. The fluorescent response (max emission peak is at 541 nm) is linearly related to 10-1000 nM Sudan III, and Sudan III can be selectively recognized (imprinting factor increased to 4.1). The limit of detection and quantitation are further reduced to 2.89 nM and 9.63 nM, respectively. The recoveries of Sudan III in lipstick samples are between 93.18 and 108.3%, and relative standard deviation is less than or equal to 4.6%. Trace Sudan III in cosmetics are detected accurately and sensitively by this method due to up-conversion nanoparticles with little interference of background fluorescence and molecularly imprinted polymers with selective enrichment.

In situ growth of WO3/BiVO4 nanoflowers onto cellulose fibers to construct photoelectrochemical/colorimetric lab-on-paper devices for the ultrasensitive detection of AFP

In this work, novel dual-mode lab-on-paper devices based on in situ grown WO₃/BiVO₄ heterojunctions onto cellulose fibers, as signal amplification probes, were successfully fabricated by the integration of photoelectrochemical (PEC)/colorimetric analysis technologies into a paper sensing platform for the ultrasensitive detection of alpha-fetoprotein (AFP). Specifically, to achieve an impressive PEC performance of the lab-on-paper device, the WO₃/BiVO₄ heterojunction was in situ grown onto the surface of cellulose fibers assisted with Au nanoparticle (Au NP) functionalization for enhancing the conductivity of the working zone of the device. With the target concentration increased, more immune conjugates could be captured by the proposed paper photoelectrode, which could lead to a quantitative decrease in the photocurrent intensity, eventually realizing the accurate PEC signal readout. To meet the requirement of end-user application, a colorimetric signal readout system was designed for the lab-on-paper device based on the color reaction of 3,3'5,5'-tetramethylbenzidine (TMB) oxidized by WO₃/BiVO₄ nanoflowers in the presence of H₂O₂. Noticeably, it is the first time that the WO₃/BiVO₄ heterojunction is in situ grown onto cellulose fibers, which enhances the sensitivity in view of both their PEC activity and catalytic ability. By controlling the conversion process of hydrophobicity and hydrophilicity on the lab-on-paper device combined with diverse origami methods, the dual-mode PEC/colorimetric signal output for the ultrasensitive AFP detection was realized. Under optimal conditions, the proposed dual-mode lab-on-paper device could enable the sensitive PEC/colorimetric diagnosis of AFP in the linear range of 0.09-100 ng mL^-1 and 5-100 ng mL^-1 with the limit of detection of 0.03 and 1.47 ng mL^-1, respectively.

Cellulose Structures as a Support or Template for Inorganic Nanostructures and Their Assemblies

Cellulose is the most abundant natural polymer and deserves the special attention of the scientific community because it represents a sustainable source of carbon and plays an important role as a sustainable energent for replacing crude oil, coal, and natural gas in the future. Intense research and studies over the past few decades on cellulose structures have mainly focused on cellulose as a biomass for exploitation as an alternative energent or as a reinforcing material in polymer matrices. However, studies on cellulose structures have revealed more diverse potential applications by exploiting the functionalities of cellulose such as biomedical materials, biomimetic optical materials, bio-inspired mechanically adaptive materials, selective nanostructured membranes, and as a growth template for inorganic nanostructures. This article comprehensively reviews the potential of cellulose structures as a support, biotemplate, and growing vector in the formation of various complex hybrid hierarchical inorganic nanostructures with a wide scope of applications. We focus on the preparation of inorganic nanostructures by exploiting the unique properties and performances of cellulose structures. The advantages, physicochemical properties, and chemical modifications of the cellulose structures are comparatively discussed from the aspect of materials development and processing. Finally, the perspective and potential applications of cellulose-based bioinspired hierarchical functional nanomaterials in the future are outlined.

Biopolymer-based nanocarriers for sustained release of agrochemicals: A review on materials and social science perspectives for a sustainable future of agri- and horticulture

Devastating plant diseases and soil depletion rationalize an extensive use of agrochemicals to secure the food production worldwide. The sustained release of fertilizers and pesticides in agriculture is a promising solution to the eco-toxicological impacts and it might reduce the amount and increase the effectiveness of agrochemicals administration in the field. This review article focusses on carriers with diameters below 1 μm, such as capsules, spheres, tubes and micelles that promote the sustained release of actives. Biopolymer nanocarriers represent a potentially environmentally friendly alternative due to their renewable origin and biodegradability, which prevents the formation of microplastics. The social aspects, economic potential, and success of commercialization of biopolymer based nanocarriers are influenced by the controversial nature of nanotechnology and depend on the use case. Nanotechnology's enormous innovative power is only able to unfold its potential to limit the effects of climate change and to counteract current environmental developments if the perceived risks are understood and mitigated.

Highly sensitive SERS substrates with multi-hot spots for on-site detection of pesticide residues

Pesticide residues will be a huge threat to food security and ecological environment; therefore, there is an urgent need to achieve rapid and on-site detection of pesticide residues. Herein, a plasmonic substrate with multiple "hot spots" was fabricated by transferring three-dimensional (3D) Au nanoparticles (NPs) onto the polydimethylsiloxane (PDMS) membrane for highly sensitive surface-enhanced Raman scattering (SERS) detection of pesticide residues. In combination with 3D-FDTD simulations, high SERS enhancement (EF = 1.2 × 10⁸) and high detection sensitivity (LOD = 6.3 × 10^-10 M) were achieved, mainly due to the enhanced electromagnetic fields around the "hot spots". Additionally, the PDMS-based SERS substrate held good transparency and flexibility, enabling conformal contact with non-planar surfaces and allowing the laser to penetrate the back of the analytes. Combined with a portable Raman spectrometer, the substrates holds great potential for rapid, high-sensitive, and on-site detection of contaminants in food, especially for the analyte on the nonplanar surfaces.

Enhancement of the Detection Performance of Paper-Based Analytical Devices by Nanomaterials

Paper-based analytical devices (PADs), including lateral flow assays (LFAs), dipstick assays and microfluidic PADs (μPADs), have a great impact on the healthcare realm and environmental monitoring. This is especially evident in developing countries because PADs-based point-of-care testing (POCT) enables to rapidly determine various (bio)chemical analytes in a miniaturized, cost-effective and user-friendly manner. Low sensitivity and poor specificity are the main bottlenecks associated with PADs, which limit the entry of PADs into the real-life applications. The application of nanomaterials in PADs is showing great improvement in their detection performance in terms of sensitivity, selectivity and accuracy since the nanomaterials have unique physicochemical properties. In this review, the research progress on the nanomaterial-based PADs is summarized by highlighting representative recent publications. We mainly focus on the detection principles, the sensing mechanisms of how they work and applications in disease diagnosis, environmental monitoring and food safety management. In addition, the limitations and challenges associated with the development of nanomaterial-based PADs are discussed, and further directions in this research field are proposed.

Sensory materials for microfluidic paper based analytical devices - A review

The microfluidic paper-based analytical devices (μPADs) have grown-up swiftly over the decade due to its low cost, simple fabrication procedure, resource-limitedness, non-toxicity and their environmentally benign nature. The μPADs, also identified as point-of-care devices or health care devices have successfully applied in several fields such as diagnostics, biological, food safety, environmental, electrochemical and most importantly colorimetric/fluorimetric sensors, owing to the attractive passive motions of analyte without any external forces. In recent years, a large number of colorimetric and fluorimetric probes have been reported that can selectively recognize the analytes in μPADs. However, there is no organized review on its structure-activity relationship. In this review, we have focused to summarize the colorimetric and fluorimetric probes utilized in μPADs. This review discuss about the relationships between the structure and functions of various probes as signaling units of the efficient μPADs. The probes including nanomaterials, nanozymes, polymers and organic molecules, their structural activity with regard to sensing performances along with their limit of detection are also discussed. This review is expected to assist readers for better understanding of the sensing mechanisms of various chemo and bio-probes utilized in μPADs, as well as promote their advancement in the field. On the other hand, this review also helps the researchers for enhancement of μPADs and paves way for synergistic application of existing molecular probes as an effective diagnostic tool for the worldwide pandemic novel corona virus COVID-19.

Paper-based field-effect transistor sensors

The present scenario in the world largely demands affordable, fast, recyclable, and flexible electronic devices for bio sensing. Varieties of paper-based devices such as microfluidics paper electrodes, paper diodes, and paper-based transistors etc. have been developed and validated. Most of the fabrication techniques published so far have focused on economic, environment-friendly straightforward methods to develop paper-based field-effect transistors (PFET) sensors, additionally, explored their applications. The synthetic-free, mechanically flexible, biocompatible, and signal amplification capability render PFET based sensors for wearable device makers. Modified organic/inorganic PFETs identify target analytes based on the electrical signal and endow them as perfect transducers. In the field of PFET bio sensing technology, numerous challenges are needed to be discussed to proceed forward in biomedical and other analytical applications. Realizing biologically or chemically modified PFET having an exceptional signal to noise ratio, specificity, with rapid detection ability is challenging. This review recapitulates the fabrication techniques, performances of various PFET sensors, and summarizes the report by concluding remarks including the limitations of the existing PFET based sensors and the future holds in regards to the sustainable nature of PFET.

Low-cost potentiometric paper-based analytical device based on newly synthesized macrocyclic pyrido-pentapeptide derivatives as novel ionophores for point-of-care copper(ii) determination

A simple, cost-effective, portable and disposable paper-based analytical device is designed and fabricated for copper(ii) determination. All solid-state ion-selective electrodes (ISEs) for copper and a Ag/AgCl reference electrode were constructed and optimized on the paper substrate. The copper electrodes were built using carbon nano-tube ink as a conductive substrate and an ion-to electron transducer. A suitable polymeric membrane is drop-cast on the surface of the conductive carbon ink window. The copper-sensing membrane is based on newly synthesized macrocyclic pyrido-pentapeptide derivatives as novel ionophores for copper detection. Under the optimized conditions, the presented all-solid-state paper-based Cu²⁺-ISEs showed a Nernstian response toward Cu²⁺ ions in 30 mM MES buffer, pH 7.0 over the linear range of 5.0 × 10⁻⁷–1.0 × 10⁻³ M with a limit of detection of 8.0 × 10⁻⁸ M. The copper-based sensors exhibited rapid detection of Cu²⁺ ions with a short response time (<10 s). The selectivity pattern of these new ionophores towards Cu²⁺ ions over many common mono-, di- and trivalent cations was evaluated using the modified separate solution method (MSSM). The presented paper-based analytical device exhibited good intra-day and inter day precision. The presented tool was successfully applied for trace Cu²⁺ detection in real samples of serum and whole blood collected from different children with autism spectrum disorder. The data obtained by the proposed potentiometric method were compared with those obtained by the inductively-coupled plasma (ICP) as a reference method. The presented copper paper-based analytical-device can be considered as an attractive tool for point-of-care copper determination because of its affordability, vast availability, and self-pumping ability, particularly when combined with potentiometric detection.

A simple, cost-effective, portable and disposable paper-based analytical device is designed and fabricated for copper(ii) determination.

Recent advances of environmental pollutants detection via paper-based sensing strategy

Paper has become one of the most promising substrates for building low-cost and powerful sensing platforms due to its self-pumping ability and compatibility with multiple patterning methods. Paper-based sensors have been greatly developed in the field of environmental monitoring. In this review, we introduced the research and application of paper-based sensors in environmental monitoring, focusing on the deposition and patterning methods of building paper-based sensors, and summarized the applications of detecting environmental pollutants, including metal ions, anions, explosives, neurotoxins, volatile organic compounds, and small molecules. In addition, the development prospects and challenges of promoting paper-based sensors are also discussed. The current review will provide references for the construction of portable paper-based sensors, and has implications for the field of on-site real-time detection of the environment.

Molecularly imprinted polymer grafted on paper and flat sheet for selective sensing and diagnosis: a review

Molecularly imprinted polymers are efficient and selective adsorbents which act as artificial receptors for desired compounds with the ability to recognize the size, shape, and functional groups of the compounds simultaneously. A molecularly imprinted polymer is prepared by the polymerization of functional monomers around a template (analyte) molecule. Afterward, the removal of the template from the polymer matrix leaves a selective cavity behind. The fabrication and development of molecularly imprinted polymers grew rapidly, due to their low cost, simple preparation, selectivity, sensitivity, and stable physicochemical properties. Traditionally, molecularly imprinted polymers can be synthesized using two main methods, namely bulk and surface imprinting. For more efficient use of the latter method, researchers have developed molecularly imprinted polymers grafted on the solid-phase matrix (substrate). This grafting technique would be particularly useful for surface imprinting of macromolecules, such as proteins. Cellulose fibers of papers with unique properties such as being abundant, retaining a porous structure, having good adsorption properties, and possessing hydroxyl groups naturally have gained much attention as substrate. The goal of this review is to introduce molecularly imprinted polymer-grafted or molecularly imprinted polymer-coated paper, as an interesting, simple, and efficient method in the detection and separation of small and large molecules. Therefore, in the present paper, several recent preparation techniques and applications of molecularly imprinted polymer-grafted paper are reviewed and discussed in detail. Green, cost-effective, selective, and sensitive paper-based sensor prepared via grafting molecularly imprinted polymer on paper surface with the potential use for online detection trace of analytes in the point-of-care testing.

Functionalization of Cellulose-Based Hydrogels with Bi-Functional Fusion Proteins Containing Carbohydrate-Binding Modules

Materials with novel and enhanced functionalities can be obtained by modifying cellulose with a range of biomolecules. This functionalization can deliver tailored cellulose-based materials with enhanced physical and chemical properties and control of biological interactions that match specific applications. One of the foundations for the success of such biomaterials is to efficiently control the capacity to combine relevant biomolecules into cellulose materials in such a way that the desired functionality is attained. In this context, our main goal was to develop bi-functional biomolecular constructs for the precise modification of cellulose hydrogels with bioactive molecules of interest. The main idea was to use biomolecular engineering techniques to generate and purify different recombinant fusions of carbohydrate binding modules (CBMs) with significant biological entities. Specifically, CBM-based fusions were designed to enable the bridging of proteins or oligonucleotides with cellulose hydrogels. The work focused on constructs that combine a family 3 CBM derived from the cellulosomal-scaffolding protein A from Clostridium thermocellum (CBM3) with the following: (i) an N-terminal green fluorescent protein (GFP) domain (GFP-CBM3); (ii) a double Z domain that recognizes IgG antibodies; and (iii) a C-terminal cysteine (CBM3C). The ability of the CBM fusions to bind and/or anchor their counterparts onto the surface of cellulose hydrogels was evaluated with pull-down assays. Capture of GFP-CBM3 by cellulose was first demonstrated qualitatively by fluorescence microscopy. The binding of the fusion proteins, the capture of antibodies (by ZZ-CBM3), and the grafting of an oligonucleotide (to CBM3C) were successfully demonstrated. The bioactive cellulose platform described here enables the precise anchoring of different biomolecules onto cellulose hydrogels and could contribute significatively to the development of advanced medical diagnostic sensors or specialized biomaterials, among others.

Quantum dots functionalised artificial peptides bioinspired to the D1 protein from the Photosystem II of Chlamydomonas reinhardtii for endocrine disruptor optosensing

Herein we describe the design and synthesis of novel artificial peptides mimicking the plastoquinone binding niche of the D1 protein from the green photosynthetic alga Chlamydomonas reinhardtii, also able to bind herbicides. In particular, molecular dynamics (MD) simulations were performed to model in silico the behaviour of three peptides, D1Pep70-H, D1Pep70-S264K and D1Pep70-S268C, as genetic variants with different affinity towards the photosynthetic herbicide atrazine. Then the photosynthetic peptides were functionalised with quantum dots for the development of a hybrid optosensor for the detection of atrazine, one of the most employed herbicides for weed control in agriculture as well as considered as a putative endocrine disruptor case study. The excellent agreement between computational and experimental results self consistently shows resistance or super-sensitivity toward the atrazine target, with detection limits in the μg/L concentration range, meeting the requirements of E.U. legislation.

Well-Dispersed Silver Nanoparticles on Cellulose Filter Paper for Bacterial Removal

In this study, a polydopamine (PDA) and polyethyleneimine (PEI)-assisted approach was developed to generate well-distributed PDA/PEI/silver (PDA/PEI/Ag) nanocomplexes on the surfaces of commercial cellulose filter papers to achieve substantial bacterial reduction under gravity-driven filtration. PDA can bind to cellulose paper and act as a reducer to produce silver nanoparticles (AgNPs), while PEI can react with oxidative dopamine and act as a dispersant to avoid the aggregation of AgNPs. The successful immobilization of PDA/PEI/Ag nanocomplexes was confirmed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) were used as pathogen models to test the efficacy of the PDA/PEI/Ag nanocomplex-incorporated filter papers. The PDA/PEI/Ag nanocomplex-incorporated filter papers provided a substantial bacterial removal of up to 99% by simple gravity filtration. This work may be useful to develop a feasible industrial production process for the integration of biocidal AgNPs into cellulose filter paper and is recommended as a local-condition water-treatment technology to treat microbial-contaminated drinking water.

Electrospun fibers based on botanical, seaweed, microbial, and animal sourced biomacromolecules and their multidimensional applications

This review summarizes and broadly classifies all of the major sustainable natural carbohydrate bio-macromolecular manifestations in nature - from botanical (cellulose, starch, and pectin), seaweed (alginate, carrageenan, and agar), microbial (bacterial cellulose, dextran, and pullulan), and animal (hyaluronan, heparin, chitin, and chitosan) sources - that have been contrived into electrospun fibers. Furthermore, a relative study of these biomaterials for the fabrication of nanofibers by electrospinning and their characteristics viz. solution behavior, blending nature, as well as rheological and fiber attributes are discussed. The potential multidimensional applications of nanofibers (filtration, antimicrobial, biosensor, gas sensor, energy storage, catalytic, and tissue engineering) originating from these polysaccharides and their major impacts on the properties, functionalities, and uses of these electrospun fibers are compared and critically examined.

Ion Transfer Voltammetry with an Electrochemical Pen

We present a new electrochemical system that combines paper-based sensing and ion-transfer voltammetry, bringing the latter a step closer toward point-of-care applications. Studies at the interface between two immiscible electrolyte solutions (ITIES) are often performed to detect redox-inactive species; unfortunately, due to the inherent instability of the interface, it is rather poorly explored outside specialized laboratories. Here, we address this limitation by combining a pen-like device containing the gelled organic phase with a paper-supported aqueous phase. This combination makes the system more user-friendly, potentially low-cost, and easy to assemble. We show the applicability of the new cell to analyze both simple and ionophore-facilitated transfer of ions and proteins, preconcentration of species, and analysis of mixtures through combination with paper chromatography. The native ion content of the paper also enabled measurements without added electrolytes. Those studies could broaden the scope for the application of the label-free electrochemical detection of nonredox-active species at points-of-need.

A vinyl sulfone clicked carbon dot-engineered microfluidic paper-based analytical device for fluorometric determination of biothiols

A microfluidic paper-based analytical device integrating carbon dot (CDs) is fabricated and used for a fluorometric off-on assay of biothiols. Vinyl sulfone (VS) click immobilization of carbon dots (CDs) on paper was accomplished by a one-pot simplified protocol that uses divinyl sulfone (DVS) as a homobifunctional reagent. This reagent mediated both the click oxa-Michael addition to the hydroxyl groups of cellulose and ulterior covalent grafting of the resulting VS paper to NH₂-functionalized CDs by means of click aza-Michael addition. The resulting cellulose nanocomposite was used to engineer an inexpensive and robust microfluidic paper-based analytical device (μPAD) that is used for a reaction-based off-on fluorometric assay of biothiols (GSH, Cys, and Hcy). The intrinsic blue fluorescence of CDs (with excitation/emission maxima at 365/450 nm) is turned off via the heavy atom effect of an introduced iodo group. Fluorescence is turned on again due to the displacement of iodine by reaction with a biothiol. The increase in fluorescence is related to the concentration over a wide range (1 to 200 μM for GSH and 5-200 μM for Cys and Hcy, respectively), and the assay exhibits a low detection limit (0.3 μM for GSH and Cys and 0.4 μM for Hcy). The method allows for rapid screening and can also be used in combination with a digital camera readout. Graphical abstract Schematic representation of a μPAD based on click immobilized carbon dots and used for a reaction-based fluorometric off-on assay of biothiols. The intrinsic blue fluorescence of carbon dots is turned off via the heavy atom effect of an introduced iodo group and turned on by the displacement of this atom by reaction with a biothiol.

Advances in Paper-Based Analytical Devices

Microfluidic paper-based analytical devices (μPADs) are the newest generation of lab-on-a-chip devices and have made significant strides in both our understanding of fundamental behavior and performance characteristics and expansion of their applications. μPADs have become useful analytical techniques for environmental analysis in addition to their more common application as medical point-of-care devices. Although the most common method for device fabrication is wax printing, numerous other techniques exist and have helped address factors ranging from solvent compatibility to improved device function. This review highlights recent reports of fabrication and design, modes of detection, and broad applications of μPADs. Such advances have enabled μPADs to be used in field and laboratory studies to address critical needs in fast, cheaper measurement technologies.

Designed antifouling peptides planted in conducting polymers through controlled partial doping for electrochemical detection of biomarkers in human serum

An antifouling electrochemical biosensing platform was constructed based on conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) planted with designed peptides. The designed peptides containing doping and antifouling sequences were anchored to an electrode surface, followed by the electrochemical polymerization of PEDOT. The negatively charged doping sequence of the peptide was gradually doped into the PEDOT during the polymerization process, and by controlling the polymerization time, it was able to exactly dope the whole doping sequence into the PEDOT film, leaving the antifouling sequence of the peptide stretched out of the PEDOT surface. Therefore, an excellent conducting and antifouling platform was constructed just like planting a peptide tree in the PEDOT soil. With antibodies immobilized on the peptide, an antifouling electrochemical biosensor for the detection of a typical biomarker CA15-3 was developed. Owing to the unique properties of the conducting polymer PEDOT and the antifouling peptide, the electrochemical biosensor exhibited high sensitivity and long-term stability, and it was capable of detecting CA15-3 in serum of breast cancer patients without suffering from biofouling. The strategy of planting designed antifouling peptides in conducting polymers offered an effective way to develop electrochemical sensors for practical biomarkers assaying in complex biological samples.

Coaxial Spinning of All-Cellulose Systems for Enhanced Toughness: Filaments of Oxidized Nanofibrils Sheathed in Cellulose II Regenerated from a Protic Ionic Liquid

Hydrogels of TEMPO-oxidized nanocellulose were stabilized for dry-jet wet spinning using a shell of cellulose dissolved in 1,5-diazabicyclo[4.3.0]non-5-enium propionate ([DBNH][CO₂Et]), a protic ionic liquid (PIL). Coagulation in an acidic water bath resulted in continuous core-shell filaments (CSFs) that were tough and flexible with an average dry (and wet) toughness of ∼11 (2) MJ·m^-3 and elongation of ∼9 (14) %. The CSF morphology, chemical composition, thermal stability, crystallinity, and bacterial activity were assessed using scanning electron microscopy with energy-dispersive X-ray spectroscopy, liquid-state nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermogravimetric analysis, pyrolysis gas chromatography-mass spectrometry, wide-angle X-ray scattering, and bacterial cell culturing, respectively. The coaxial wet spinning yields PIL-free systems carrying on the surface the cellulose II polymorph, which not only enhances the toughness of the filaments but facilities their functionalization.

A novel trimodal system on a paper-based microfluidic device for on-site detection of the date rape drug "ketamine"

Paper-based microfluidic device was designed with wax-printing to combine potentiometric, fluorimetric and colorimetric detection zones. This newly developed trimodal paper chip has been used for on-site determination of ketamine hydrochloride (KET) as a date rape drug in beverages. The device employed polyaniline nano-dispersion as conducting polymer in ion sensing paper electrodes designed to fit USB plug connector. Carbon dots-gold nanoparticles and cobalt thiocyanate were used in fluorescence and color detection zones, respectively. Cellular phone's camera facilitated the on-site fluorimetric and color detection. The implemented trimodal detection system exhibited specificity for KET detection in the presence of several other beverage interferences i.e., biogenic amines. This innovative sensor brings together analytical figures of merit for effective KET detection in single aliquot of spiked beverages. The proposed paper-based chip also fulfils WHO criteria for point-of-care devices posing the proposed trimodal paper device as an active part for rapid, on-site drug diagnostics and to be applied further for other similar drugs.

Enhanced functional DNA biosensor for distance-based read-by-eye quantification of various analytes based on starch-hydrolysis-adjusted wettability change in paper devices

Low-cost, equipment-free and quantitative detection of a wide range of analytes of interest at home and in the field holds the potential to revolutionize disease diagnosis, environmental pollution monitoring, and food safety analysis. Herein, we describe a functional DNA biosensor for the first time that integrates analyte-directed assembly of enzyme-coated microbead probes for robust yet efficient signal amplification with a simple quantitative detection motif of distance measurement on portable paper devices based on starch-hydrolysis-adjusted wettability change of paper. Its utility is well demonstrated with highly sensitive and specific detection of model analytes ranging from adenosine (an important small biomolecule; 1.6 μM detection limit) to interferon-γ (a protein marker; 0.3 nM detection limit) and Pb²⁺ (a highly toxic metal ion; 0.5 nM detection limit) by simply using an inexpensive, ubiquitous ruler. The developed general method with the distance-measuring readout should be easily tailored for the portable, read-by-eye, quantitative detection of many other types of analytical targets by taking advantage of their specific functional DNA partners like aptamers and DNAzymes.

A functional DNA sensor was initially developed for the distance-measuring quantification of various analytes based on the starch-hydrolysis-adjusted wettability change of paper.

Au-Luminol-decorated porous carbon nanospheres for the electrochemiluminescence biosensing of MUC1

Electrochemiluminescence (ECL) nanomaterials are usually deposited compactly on the surface of electrodes, which may cause poor mass transfer of reactants, thereby resulting in low ECL efficiency. In this work, we developed a novel kind of luminescent material denoted as C-Au-luminol nanospheres (C-Au-Lum NSs) by high dispersion of luminophores on porous carbon nanospheres (PCNSs). C-Au-Lum NSs were facilely prepared by the in situ reduction of chloroauric acid with the luminescent reagent luminol (Lum) on the nano-pores of PCNSs. Plenty of luminescent Au-Lum NPs were dispersedly concentrated inside the numerous pores and hollow interiors of PCNSs, effectively increasing the mass transfer of reagents and accelerating the electron transport inside the porous nanospheres. This greatly improved the availability of luminophores and endowed C-Au-Lum NSs with excellent ECL emission. After further integrating with enzymatic circulation and strand displacement, an ultrasensitive ECL biosensor was achieved for the ultrasensitive detection of an important tumor biomarker, mucin1. The logarithmically linear range from 0.1 pg mL-1 to 1 ng mL-1 with the detection limit of 47.6 fg mL-1 (S/N = 3) was achieved, demonstrating the superior performance of C-Au-Lum NSs. This work would provide new ideas for the construction of high-performance ECL sensing platforms for diverse applications.

Fast Strategy to Functional Paper Surfaces

Paper, with advantages of low-cost, easy fabrication and disposal, flexibility and renewability, is a suitable substrate material for various applications. Functionalization and patterning on paper substrates are commonly required in many applications. Although many methods have been developed to achieve this, they typically suffer from some drawbacks such as time-consuming process, specific device dependence, lack of flexibility, low patterning resolution, and so forth. Herein, we present a general and fast method to functionalize paper sheets and create patterns. The whole modification process can be completed in 10 min and can be applied on various types of paper substrates and other natural materials such as natural fabrics. By our method, many commonly used functional groups can be covalently attached and patterned on paper substrates, while the characteristic features of the original paper substrates, for example, color, transparency, and conductivity, can be perfectly retained after modification to allow these properties to be incorporated into the resultant materials. High-resolution patterns can be created on paper by applying a photomask during the modification or controlling the time of modification to precisely control the functionality at any area on the obtained paper substrates. We also show the potential applications of our method in the fabrication of superhydrophobic coatings and biomaterials.

Advanced methods for microRNA biosensing: a problem-solving perspective

MicroRNAs (miRNAs) present several features that make them more difficult to analyze than DNA and RNA. For this reason, efforts have been made in recent years to develop innovative platforms for the efficient detection of microRNAs. The aim of this review is to provide an overview of the sensing strategies able to deal with drawbacks and pitfalls related to microRNA detection. With a critical perspective of the field, we identify the main challenges to be overcome in microRNA sensing, and describe the areas where several innovative approaches are likely to come for managing those issues that put limits on improvement to the performances of the current methods. Then, in the following sections, we critically discuss the contribution of the most promising approaches based on the peculiar properties of nanomaterials or nanostructures and other hybrid strategies which are envisaged to support the adoption of these new methods useful for the detection of miRNA as biomarkers of practical clinical utility. Graphical abstract ᅟ.

Phosphorylated micro- vs. nano-cellulose: a comparative study on their surface functionalisation, growth of titanium-oxo-phosphate clusters and removal of chemical pollutants

Phosphorylation imparts cellulose (amorphous or crystalline) with original surface reactivity to bridge metal oxide clusters and to scavenge for chemicals.

Flexible Electronics Based on Micro/Nanostructured Paper

Over the past several years, a new surge of interest in paper electronics has arisen due to the numerous merits of simple micro/nanostructured substrates. Herein, the latest advances and principal issues in the design and fabrication of paper-based flexible electronics are highlighted. Following an introduction of the fascinating properties of paper matrixes, the construction of paper substrates from diverse functional materials for flexible electronics and their underlying principles are described. Then, notable progress related to the development of versatile electronic devices is discussed. Finally, future opportunities and the remaining challenges are examined. It is envisioned that more design concepts, working principles, and advanced papermaking techniques will be developed in the near future for the advanced functionalization of paper, paving the way for the mass production and commercial applications of flexible paper-based electronic devices.

Direct laser writing of barriers with controllable permeability in porous glass

Barriers were produced in porous glass through its local bulk density modification by direct femtosecond writing accompanied by СО₂-laser surface thermal densification, to make functional microfluidic elements separated by such physical barriers with different controlled permeability. The separation of multi-component solutions into individual components with different molecule sizes (molecular separation) was performed in this first integrated microfluidic device fabricated in porous glass. Its application in the environmental gas-phase analysis was demonstrated.

Multiplexed Instrument-Free Bar-Chart SpinChip Integrated with Nanoparticle-Mediated Magnetic Aptasensors for Visual Quantitative Detection of Multiple Pathogens

A portable multiplexed bar-chart SpinChip (MB-SpinChip) integrated with nanoparticle-mediated magnetic aptasensors was developed for visual quantitative instrument-free detection of multiple pathogens. This versatile multiplexed SpinChip combines aptamer-specific recognition and nanoparticle-catalyzed pressure amplification to achieve a sample-to-answer output for sensitive point-of-care testing (POCT). This is the first report of pathogen detection using a volumetric bar-chart chip, and it is also the first bar-chart chip using a "spinning" mechanism to achieve multiplexed bar-chart detection. Additionally, the introduction of the spin unit not only enabled convenient sample introduction from one inlet to multiple separate channels in the multiplexed detection, but also elegantly solved the pressure cross-interference problem in the multiplexed volumetric bar-chart chip. This user-friendly MB-SpinChip allows visual quantitative detection of multiple pathogens simultaneously with high sensitivity but without utilizing any specialized instruments. Using this MB-SpinChip, three major foodborne pathogens including Salmonella enterica, Escherichia coli, and Listeria monocytogenes were specifically quantified in apple juice with limits of detection of about 10 CFU/mL. This MB-SpinChip with a bar-chart-based visual quantitative readout has great potential for the rapid simultaneous detection of various pathogens at the point of care and wide applications in food safety, environmental surveillance, and infectious disease diagnosis.

Ag/Au Nanoparticle-Loaded Paper-Based Versatile Surface-Enhanced Raman Spectroscopy Substrates for Multiple Explosives Detection

We present a systematic study on the fabrication, characterization of versatile, and low-cost filter paper-based surface-enhanced Raman spectroscopy (SERS) substrates loaded with salt-induced aggregated Ag/Au nanoparticles (NPs). These were demonstrated as efficient SERS substrates for the detection of multiple explosive molecules such as picric acid (5 μM), 2,4-dinitrotoluene (1 μM), and 3-nitro-1,2,4-triazol-5-one (10 μM) along with a common dye molecule (methylene blue, 5 nM). The concentrations of the dye and explosive molecules in terms of mass represent 31.98 pg, 11.45 ng, 1.82 ng, and 13.06 ng, respectively. Silver (Ag) and gold (Au) colloidal NPs were prepared by femtosecond laser (∼50 fs, 800 nm, 1 kHz) ablation of Ag/Au-target immersed in distilled water. Subsequently, the aggregated nanoparticles were achieved by mixing the pure Ag and Au NPs with different concentrations of NaCl. These aggregated NPs were characterized by UV-visible absorption and high-resolution transmission electron microscopy techniques. The SERS substrates were prepared by soaking the filter paper in aggregated NPs. The morphologies of the paper substrates were investigated using field-emission scanning electron microscopy technique. We have achieved superior enhancements with high reproducibility and sensitivity for filter paper substrates loaded with Ag/Au NPs mixed for an optimum concentration of 50 mM NaCl.